THE ABSORPTION AND MODIFICATIOM OF RADXATIOH

BY SOME TELLURIUM DIOXIDE GLASSES

DISSERTATION Presented In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

CHARLES L. McKENNIS, B.S., M.S.

The Ohio State University

19$h

Approved by The University assumes no responsibility for the accuracy or the correctness of the statements or opinions advanced in this thesis. V.

To my wife, Margaret

iii ACKNO^L 35DGMEH T

The author would like to acknowledge the opportunity af­ forded him in working under Dr. H. H. Blau. His guidance and constructive criticism have been sincerely appreciated. The author would also like to express his appreciation to Drs. R» A. Oetjen and E. E. Bell of the Department of Physics, to Dr.

Rudolph Speiser of the Department of Metallurgy, and to Drs.

D. McConnell .and R. Foster of the Department of Mineralogy for their kindly help and suggestions. Appreciation is also due to Mr. W. L. Larsen of the Department of Metallurgy for his help in the X-ray diffraction work.

The work described herein was supported by a contract between the United States Bigineer Research and Development

Board, Fort Bel voir, Virginia, and The Ohio State University

Research Foundation.

iv TABLE OF CONTENTS

Page

I. INTRODUCTION...... 1

II. REVIEW OF LITERATURE ...... 3

III. MODE OF INVESTIGATION...... 20

IV. EQUIPMENT AND MATERIALS ...... 21

V. EXPERIMENTAL PROCEDURE...... 27

VI. RESULTS ...... 55 VII. DISCUSSION OF R E S U L T S ...... 95 VIII. SUMMARY AND CONCLUSIONS ...... 117

IX. BIBLIOGRAPHY...... 120

v I, INTRODUCTION

The problem of developing materials which are transparent to or \ihich selectively absorb infrared radiation has been given con­

siderable thought and effort by many investigators. These materials

find particular applications in the spectrographic, photographic,

and electronic fields, and more recently in certain optical devices used for military purposes. Advances in these fields have been lim­ ited, however, due to high costs, size and form limitations, as well as low flexibility of these envelopes or lenses. This has led to considerable emphasis being placed on the possibilities of developing infrared transmitting glasses, which tend to Incorporate improved physical and chemical stability together x*ith lower production costs when compared to single crystal components commonly used.

To formulate new glasses is ordinarily not a simple process. This is particularly true for glasses which will have the desired optical properties in unusual ranges of wavelength. Although a par­ ticular material in itself may be a good infrared transmitter, it may not be practicable to reduce It to a vitreous condition and have it still maintain the desired optical properties.

Two series of such infrared transmitting glasses have been de­ veloped in this laboratory, notably those consisting essentially of germanium dioxide and arsenic trisulfide, which have transmittances out to 6.0 and 12.0 microns, respectively.

1 This investigation is concerned with the development of another infrared transmitting glass series* that of tellurium dioxide* and more specifically with modifying this system to transmit definite ranges of radiation by the absorption and scattering of radiation as the result of additions of inorganic colorants to or developing dis*» perse phases in the glasses. These modifications were made to study the possibilities of glass radiation filters (i.e, a unit which manifests a change from opacity to transparency within a narrow spectral region), which ore opaque through the visible out into the near infrared, and become high­ ly transparent at longer wavelengths. II. REVIHrJ OF LITERATURE

In the search for better infrared transmitting glasses atten­ tion has been turned to those which are free of silica. This trend

results from a study of the infrared transmittance of known silicate glasses which reveals that these become opaque beyond 5.0 microns. In a study of silicate, phosphate, and borate glasses, Gerlovin (1) has found that the highest infrared transmittance is shown by the silicates, and among these by the lead silicates. Florence (2) has confirmed this observation. An investigation by Stair (3) has shown that silicate glasses covering a wide range of compositions have long vmvelength cutoffs at 3* 0 microns or below. Practically every glass discussed by the above mentioned investigators had specific absorption bands within the spectral region 2.7 to U.7 microns. Florence (b) has studied the origin of these various absorptions in silicate glasses and has compiled the following tabulation to Indicate their sources.

Wavelength (microns) Vibrating Group

2.70 CO 2 2.75 OH free 2.75 C02 2.90 OH associated 3.50 C03 3.65 NOcf 3.80 SI-0 h.OO c°3 U.15 K03~ U.25 co2 U-Ii5 Si-0 U .70 OH associated it Harrison (5) has attribxited the shift in absorption to longer wavelengths of the OH groups (with a distinction between free and associated OH), to an increase in hydrogen bonding between these hy­ droxyls and the structural units of the glass. The problem now be­ comes one of developing glasses which will be transparent beyond 5 -0 microns.

According to Daniels (6 ), the absorption of radiation in various portions of the spectrum by molecular units is the result of several different mechanisms. Within the ultraviolet and visible regions, 0.2 to 0.8 microns, the absorption of radiation is attributed to electronic shifts betx-jeen different energy levels within the molecule. Absorp­ tion in the near infrared, 0.8 to 25 microns, is brought about primar­ ily by oscillatory motions of the atoms or units of the absorbing medium, and this is called the fundamental vibration region. In the

far infrared, 25 to 500 microns, the absorption of radiation come about through a change in the energy of rotation of the molecxile. These different modes of absorption are interrelated so that the char­ acteristic absorption spectrum of a material may be the resxiLt of a combination of these mechanisms. These considerations may be gener­ ally applied to diatomic and polyatomic molecules, and it is assxuned that they also apply to glasses.

The absorption of near infrared radiation as given by glasses is the result primarily of oscillatory motions of the glassy netx^orlc rather than rotational motion or electronic shifts between different energy levels. The frequency of this vibration is determined by the ma3S of the structural units, their geometric arrangement, the forces acting between them, and their interaction with their surroundings. Heraberg (7) gives the folloxiing fundamental relation between the fre­

quency 7s , and the mass m of an oscillator having a force constant f,

Reststrahlen studies (8 ) have shown that strong reflection from di­

electric substances indicate regions of absorptions, and various work­

ers (9,1 0 ) have attempted to predict the structure of glass by this method.

The m o d e m concept of glass structure considers that the basic units of the glass network are either triangular or tetrahedral, these

exhibiting short range order, but long range disorder. As such there

are a variety of bond energies existing between these structural units. Into the "holes" of this network are situated complexes which tend to modify the glassy structure, these being free to migrate if the neces­

sary potential is applied. When radiation impinges upon the glass structure which has a frequency corresponding to the fundamental of this network, the vibrations set up are damped out and the energy absorbed. The difference in bond energies between structural units will cause

the glass to continuously absorb radiation at wavelengths longer than that attributed to the fundamental vibration of the network. The net­ work modifiers can contribute to the spectral location of this long 6 wavelength cutoff, depending upon their particular function within the network. Absorptions of this type cannot be eliminated, but their spectral position can be modified.

On the basis of the discussion just given, there are some basic considerations which may be established in order to predict which glass­ es will have infrared transmittanees extending to longer wavelengths.

It was previously shovm that the frequency of vibration of an oscillator is directly proportional to^the force constant of the oscillator and 6QURQE EOsf OP THI inversely proportional to theAmass of these units. In this oscillatory motion, the restoring force is proportional to the displacement, the proportionality constant being termed the force constant. Glasses x-fhose structures are made up of massive ions, haxing weak force constants be­ tween them should have high infrared transmittance. However, weak force constants are not common in a glass network, so the criterion must be based on the mass of the species x-rtiich make up the structure, i.e. high mass should lead to high infrared transmittance.

This theory on the extension of the limits of Infrared transmit­ tance of non-silicate glasses was predicted and verified by the investi­ gations of Chothia (ll) and Lorey (12), with the development of germanium dioxide glasses which had transmittance out to 6.0 microns. By apply­ ing this same hypothesis, Shonebarger (13) was able to produce arsenic trisulfide glasses which transmitted out to 12.0 microns.

In a recent investigation, Stanworth (1I4) x-jas led to the conclu­ sion that tellurium dioxide should function as a glass network former.

He based his considerations on the electronegativity of the types of 7 bonds contained in known oxide glasses, and observed that those elements whose oxides formed glasses had electronegativities which fell in the region 1.7 to 2.1. He further noticed that tellurium had an electro­ negativity of 2.1 and predicted that its oxide might function as a glass network former. This concept of the electronegativities of the elements which Stanworth (lJU) used in his investigation stems from the works of

Pauling (15), and is centered about his equation,

^ A-B “ 23.06'(X^ - Xg) where = ionic resonance energy between unlike atoms A and B

Xa , Xg - electronegativ­ ities of A and B

Pauling (15>) defines the ionic resonance energy between unlike atoms A and B as the additional ionic character of the bond, over and above that required for a normal covalent bond between these two unlike atoms.

The stable oxide of tellurium, the dioxide, can be melted without gain or loss of oxygen, and the (K -form of this oxide has a structure similar to that of tin dioxide. This consists of six oxygen atoms vrtiich surround the central metal atom, with two of the oxygens being closer to the central metal atom than the other four. This type of structure does not conform to Zachariasen1s (16) rules for glass formation. These state that the cations in a good glass network former should be sur­ rounded by three or four anions, the anions should be joined to no more than two of the cations, and that these structural polyhedra share only comers, never edges or faces. Furthermore, applying Goldschmidt*s (17) radius-ratio rule for glass formation (in which the ratio of the ionic f radii of anion to cation should fall within the limits of 0.2 to 0 .1*), it is found that tellurium dioxide has a value of 0 .5 7 , which would place it outside of the range for glass formation.

In spite of these unfavorable prognoses, Staiiworth (ill) was able to vindicate his original hypothesis and prepare glasses containing up to 80 percent tellurium dioxide, with additions of other glass network modifiers such as the oxides of lead, barium, and zinc. It was found that these tellurium dioxide glasses had a comparatively high refractive

Index, high density, and low softening point when compared with ordinary silicate glasses. It was also noted that these glasses were transparent to at least $,0 microns, which made them worthy of further investigation for their Infrared transmittances. That these glasses should have great­ er infrared transmittance than silicate glasses tends further to substan­ tiate the effect of the mass of the structural -unit when a comparison is made between the mass of silica and tellurium.

This discussion has considered the absorption of radiant energy by the oscillatory motions of the glass network, and shall now take up an­ other type of absorption of radiation, that produced by inorganic com­ plexes which are situated in the "holes" of the glass network or merely modify It. Into this category fall those compounds which are ordinarily classified as glass colorants. These colorants are for the most part oxides belonging to the transition groups of the periodic system, with most of them being found in the first group. These include vanadium, chromium, manganese, iron, cobalt, nickel, and copper. Of less import-

} ance are the oxides of the higher transition groups which include sil­ ver, uranium, and the rare earths.

The color which is produced by the transi tion group compounds is attributed to an incomplete sub-group of electrons in their atomic structure, these sub-shells not being entirely shielded by completed outer electronic shells. Transitions with the absorption of energy are then possible between lower and higher levels of the incomplete shell, and also between the transition metal atom and the atoms attached to it.

In the rare earths compounds on the other hand, the incomplete inner shell is shielded by completed outer shells, and this leads to transi­ tions only between the different levels of the incomplete subshell, giving rise to very narrow absorption bands.

Zsigmondy (l8 ) was the first to carry out a systematic study on the effect of coloring oxides in glass, and was able to show the effects of the usual coloring oxides in glass, and the manner in which glasses of different compositions could affect this color. Weyl (19) and his associates have contributed much to the understanding of the coloring ef­ fects produced in glass by grouping the coloring oxides into those in which the variation in color is due to differences in the ionic environ­ ment in the glass, and those in which it is due to differences in the states of oxidation of the coloring components.

A study of the specific absorption brought about by additions of 10 the inorganic colorants to silicate glasses (3 ? 1 8 , 19? 20, 21) reveals that the absorption bands so produced are located primarily in the vis-

; ible spectrum, with some of them extending down into the ultraviolet and out into the near infrared. Glasses which selectively absorb cer­ tain portions of the spectrum and transmit radiation in other regions have been produced by the additions of one or more of these inorganic colorants. A particular application of these selective radiation ab­ sorbing filters is one which is opaque to visible radiation, but trans­ mits strongly in the near infrared region of the spectrum. The position­ ing of the short wavelength cutoff of this type of radiation filter constitutes somewhat of a problem since it requires the combined absorp­ tions resulting from several inorganic colorants. If none of these colorants have absorption bands within the spectral region where the investigator desires to locate the short wavelength cutoff of the radia­ tion filter, there is not much that can be done about it. The position of these absorption bands can be shifted slightly by compositional changes in the base glass, and/or the conditions under vrtxlch the glass is melted. This is a very limited process, however. On the other hand, if a combination of colorants produces absorption of radiation within the desired spectral region, they may also impart to 'the filter strong absorptions at wavelengths where high transparency is desired.

In reviewing recently published data (3) on filters which are opaque to visible radiation, but have high transmittance in the near infrared, it appears that 0.85 micron is about the upper limit for the 11 region of opacity which can be expected by additions of inorganic col­ orants to glass systems. In order to move the short wavelength cutoffs of these selective radiation filters to longer wavelengths, use must be made of some mechanism other than the absorption of radiation. This then leads to the phenomenon of the scattering of radiation as a poss­ ible means of approaching this problem.

If radiation is passed through a transparent medium containing in suspension small particles, the refractive index of which differs from that of the surrounding medium, the particles become a source of secondary radiation, and are said to scatter the incident radiation.

Since the intensity of the scattered radiation is derived from the inci­ dent beam, the Intensity of the latter is reduced in the process. As 3uch, each particle in an otherwise homogeneous transparent medium contributes to the opacity of the system.

In 1871 the late Lord Rayleigh (22) formulated his successful mathematical theory of the scattering of radiation by small particles, in which he explained the blue color of the sky. Taking the case of a particle whose dimensions were small compared to the wavelength of radiation, Rayleigh considered that each particle acts as an oscillator undergoing forced vibrations of a certain amplitude in the direction of the impressed force. The particle therefore sends out waves which have components perpendicular to the direction of the incident radiation.

Rayleigh's equation for the. scattering of radiation is as follows: 12

9 ? !fc6^2 / nl - ni t (1 * Cos? 0) Is = 2 X A I nf -V 2uq

where N a number of inclusions per unit volume r a radius of inclusions A » amplitude of incident radiation x — distance from particle A = wavelength of radiation 0 = angle between direction of observation and incident radiation nl refractive index of particle nQ si refractive index of medium

It is seen that the scattered intensity varies inversely as the fourth

power of the wavelength of the radiation, and directly as the sixth

power of the radius of the particle. The only restrictions which

Rayleigh originally placed on this equation was that the particle be

a dielectric and have a much smaller diameter than the wavelength of

radiation. Mie (23) studied the effect of the scattering of radiation by spherical particles not restricted in size and was able to show that Rayleigh’s original equation held only in the limiting case of very small particles. Rayleigh (2l*) later revised his original equa­

tion so as to be applicable to any particle diameter, provided the

relative refractive index of the particle and suspending medium were approximately equal to unity. Although this initial work was based on

the scattering of radiation by an individual dielectric particle,

Schuster (25) approached the problem of the scattering of radiation by a large number of particles and resolved the scattered radiation

Into tiro diffuse fluxes of light traveling through the medium in opposite direction. 13 By the introduction of factors involving surface and boundary effects, Ryde and Cooper (26) have been able to apply the Rayleigh and Schuster relations directly to diffusing glasses. Ryde and Yates

(27) have further investigated the application of this scattering phenomenon in diffusing glasses by studying suspensions of shellac in water. They have shown that if a beam of light of intensity I0 is incident upon a sheet of diffusing glass of thickness x, some of the radiation wi.1l be scattered backward, some absorbed, and some scattered radiation will emerge together with Hie original parallel beam, and the intensity of this residual unscaltered beam can be given by an equation of the form,

®(Nq t u.)x I o IQe ' where q a the coefficient of scattering as cal­ culated from the Rayleigh equation

N q the number of part­ icles per unit volume a s the coefficient of absorption The relation of wavelength to the scattering coefficient q may be defined following Rayleigh’s equation as,

d = t V ”

Although Rayleigh (22) has shown that b msy have a limiting value of four, others (27) have indicated that it may vary as lot? as zero in some types of diffusing glasses.

The absorption coefficient ji is not entirely independent of the scattering coefficient q, but Bore primarily a function of the com­ ponents which make up the glass composition*, The absorption can be affected by the distance traversed by the light within the glass.

Various workers (28) have estimated that the light actually passes through the equivalent of five to eight times the actual thickness in some types of diffusing glasses.

The effect of the number of particles in the dispersed phase on the various light properties was investigated by Lax, Pirani, and

Schonbora (28), who studied suspensions of paraffin in water, and alumina in dilute acetic acid, and were able to derive the following empirical relations,

s intensity of directly transmitted light IQ s intensity of incident light 2) —i — l a 4 Kjj H s number of inclusions per unit volume s total transmitted light flux 3) log Fr a Ktj log N + K$ Fr 3 total reflected light flux K* s s constants

Ihe breakdown of an incident light flux FQ upon passing through a scattering, absorbing medium may be represented as consisting of a scattered flux FQ, an absorbed flux Fa, and a transmitted flux F^., in the following -type of equation, Although these mechanisms which diffuse or scatter radiation have been known for some time, Pfund (29) was probably the first to take advantage of the selectivity with reference to wavelength of scattering by small particles to effect a radiation filter of control­ lable transmission. He accomplished this by depositing finely divided particles onto a transparent ipeculura, for example, ainc Q3ri.de onto a rock salt plate. In order to produce a satisfactory filter, Pfund stipulated the following conditions, (a) the finely divided powder must be transparent in the spectral region to be studied, (b) the deposited particles must be uniform in size, (c) the substratum onto which the particles are deposited must be transparent, and (d) the film must be of uniform thickness.

In a later work, Pfund (30) found that a film of this type would give a sharp transmission peak just short of the reflection maximum for the solid crystalline material, if the powdered crystalline material had dimensions approximately equal to the wavelength of the radiation.

'Hiis effect was observed with two materials, quarts and caicite. In carrying on this work on radiation scattering filters, Pfund (3l) was able to show that under certain conditions, these powder film filters adhered to Rayleigh's inverse fourth power law. This adherence to

Rayleigh's law was exhibited by filters consisting of zinc oxide part­ icles suspended in crepe rubber, the particle dimensions being approxi­ mately one-third that of the shortest wavelength of radiation studied.

However, with the observed spectral region being maintained constant, an 16 increase in the particle diameters of the sine oxide resulted in a de- crease in selective scattering of radiation. Pfund attributed this to

a non-uniformity of particle dimensions. He concluded that these powder

film filters will selectively scatter radiation in accordance with

Rayleigh1s law only if all of the particle diameters of the film are

smaller than the shortest wavelength of the observed spectral region. Other investigators (32), utilising this same powder film process,

have obtained radiation filters which are opaque out to 60 microns and

transparent at longer wavelengths. This was accomplished by progres­ sively increasing the sise of the particles constituting the powder

film. Having established that selective radiation scattering filters can be effected by a thin powder film, the question now arises whether

a similar type of filter could not be produced in glass by a controlled

dispersed phase formation of one or more of the crystalline components of the glass composition. Opal glass has been used for some time in the production of light diffusing units for illumination, and consider­

able investigation has been carried era concerning the nature of light

diffusion, and on the development of crystalline particles in a glassy matrix. Blau (3 3 ) has published a thorough paper era the theory of dif­

fusing glasses and the underlying factors to be considered in the

controlled formation of dispersed phases in glasses to yield crystal­ lites of uniform and controlled sise. These considerations were based

on the molecular-kinetic conceptions of crystallisation as developed 17 by de Coppet C3U-) and Tansiann (35) ^ and it has been shoim that thqy may be adapted equally well to many types of diffusing glasses (3 6 ).

The determining factors in the controlled formation of these dispersed phase crystallites are the rates of nucleus formation, and the velocity of crystallization, and the relation among these and the viscosity of the glass are shorn in the accompanying figure, these being taken from the paper and patents of Blau (33)*

A = viscosity of the glass B s rate of nucleus formation (number of nuclei formed per unit mass of glass per minute)

C s crystallization velocity (vectorial rate of crystal­ line growth, microns per minute)

T* T3 Tn

Temperature (or time)

Since a relatively small section of a tine-temperature curve 18 for the cooling of glass approximates a straight line, the abscissa may be considered as either time or temperature if proper proportion­ ality constants are used. The actual curves for the several proper­ ties as a function of time differ so slightly frcoa those for tempera­

ture so as hardly to justify a second set of curves. Reference is now made to the set of curves just givenj consider a molten glass which is removed from the furnace at temperature TA. It cools from temperature to before nuclei begin to form, and is therefore below the ten- perature range conducive to crystalline growth. The number of crystallites may be determined by the time during which the glass is held within the range of curve B. Crystallites of definite and uni­

form dimensions may be obtained by reheating the glass to a temperature such as T*j9 and their dimensions are proportional to the area under curve C between and T^.

According to Blau, the controlling factors for the rate of nucleus formation and velocity of crystalline growth arei 1. The number of crystalline substituents per space lattice element. 2. The orientation of the crystalline substituents. 3» The kinetic energy of the crystallizing substituents. lie She viscosity of the glass. 5>. The concentration of the crystallizing substituents. 6. The magnitude of the energy changes involved (latent heats of crystallization or solution). 7. The thermal conductivity or rates of heat transfer to or from the region of crystallization. 8. The rate of diffusion to or from the region of crystallisation. 9* Interfacial concentrations (adsorption). 10. The influence of polar forces. 11. Variations in the fugacities of crystallites with their radii of curvature, etc. 19 Ryde and Yates (27) in their studies on diffusing glasses found that units which had inclusions whose observed diameters were of the order of O.li microns, completely scattered the visible radiation. These glasses became selectively more transmittant at longer wave­ lengths, however, being practically transparent at 2.0 microns.

On the basis of these observations, it appears that the con­ trolled formation of dispersed phases within a glassy matrix presents unique possibilities with regard to the development of a quite flexible selective radiation filter. Units of this type should have the desir­ able physical and chemical characteristics of glass, in addition to the ease of positioning of the short wavelength cutoff. They present a medium for working distinctly in three dimensions in contrast to the radiation scattering films or surfaces. III. MODE OF INVESTIGATION

This investigation was undertaken to study the possibilities of developing a selective radiation filter made of glass, which would be opaque through the visible spectrum and out to at least 1.5 microns, and transparent frcei this latter wavelength to at least U»0 microns.

The base glass selected for this investigation was one consist­ ing largely of tellurium dioxide, and which gave promise of being transparent out to 6.0 microns.

As a first approach to this problem, inorganic colorants were added to this tellurium dioxide base glass to study their specific absorption bands, particularly those which fell within the spectral region 1.5 microns.

The second phase of this investigation was concerned with the development of selective radiation scattering filters, produced by the controlled formation of a dispersed phase within the tellurium dioxide base glass.

20 IV. ERUIBIMT MID MATERIALS

A. Equipment

The equipment used during the course of this investigation is identified and described below.

1. Weighing of batches. All glass batches were weighed on a William Ainsworth & Sons, Incorporated chaincmatic type balance, having an accuracy of 0.0001 grams.

2. Mixing of batches. The glass batches were mixed in a small porcelain mortar and pestle, resulting in a quick and efficient method trith little chance of contamination.

3. Crucibles. All melts were made in commercially pure plat­ inum foil boats formed from squares of dimensions 3" x 3n 2 0 o002n. These melting containers were shaped around a rectangular plaster of pario form, and the finished boats had an approximate area of 2$ rcm x 2$ mm.

U. Furnaces a. Melting furnace. A Pereco ELectric laboratory Kiln,

Model LB-7U* was used for carrying out all of the melts. The kiln was Gio-bar fired, and had an operating temperature of 27$0°F. In order to control the atmospheric conditions during melting, this

21 lcixn was modified by centering into the heating chamber a McDaniel high temperature porcelain tube, of 3 inch inside diameter, and 2-1/2 feet in length. This tube had one closed end, and this end was placed inside of the furnace. The furnace opening around the tube was closed by cut and grooved Babcock and Wilcox K-30 insulating brick. The open end of the tube was sealed by a 3 inch rubber stop­ per, which had two small bore porcelain tubes passing through it, one of approximately 2-1/2 feet in length, the other of approximately 6 inches. The melting atmosphere was controlled by carrying the gas to the rear ofthe large tube, the closed end of the latter causing this gas tosweep out the large tube from front to back. The longer of the small bore porcelain tubes in the stoppering unit was used for the introduction of the gas for the controlled atmosphere, and the shorter was used as the exhaust.

b. Heat treating furnace. Scene of the heat treatments were made in a small Hoskins Klee trie Full Muffle Furnace, Model FB201*. Biis furnace was controlled by a Leeds and Northrup Mlcromax unit, a platinum-platinum 13 percent rhodium thermocouple being used. c. Heat treating furnace. This second heat treating furnace was constructed in order to check the results from the Hoskins furnace. It consisted of Norton grooved Alundum tube of 2-1/2 inch inside diameter, and 2 feet in length. The tube was heated over a 10 inch central section by external windings of Nichrome wire, these

Coated T3ith a layer of Norton Aiundum cement. This heating unit was centered into a large steel can which had openings at either end through which the tube protruded. The interior of this can was filled with powdered Sil-O-Cel insulation. A U inch plug of K-30 insulating brick was sealed into one end of the tube through which a platinua-platinus 13 percent rhodium thermocouple was inserted, the thermocouple being in the center of the heated zone. A removable li inch plug of K-30 brick plus a 2-1/2 inch rubber stopper constituted the fixtures for the open end of the tube. The container for heat treating the glass

samples was made from a U inch section of 2 inch diameter copper stock

into which was cut a well approximately nm by 12-1/2 mm by 6 mm

(with the long dimension parallel to the length, of the furnace), into

which the glass sample was placed. This unit was made secure by tap­

ping small pegs into the bottom half, onto which the lid half fitted. The holder was positioned in the furnace so that the thermocouple was directly over it, the removable K-30 plug placed in next, and the fur­

nace sealed by inserting the rubber stopper.

d. Annealing furnace. This furnace consisted of a 3

inch inside diameter, h feet long Alundum tube, having external wind­ ings of Hi chrome wire. The tube was completely contained inside of a large steel jacket (which was filled with Sil-0-Cei insulation), and had one end sealed with an 8 inch plug of K-30 brick. The open end

of this tube was sealed with another 8 inch plug of K-30 brick, which

had an attached plaque (also of K-30 brick), onto which the glass

specimen to b© annealed was placed. The glass specimen was positioned 2h into the hottest portion of the furnace, The temperature of this fur­ nace. The temperature of this furnace was determined with a Cferomel*®

Alumel thermocouple* this inserted into the open end of the tube. The input voltage of this furnace was adjusted by a type V-10 MT Variae.

After the desired annealing temperature had been attained* the thermo­ couple was removed, glass sample inserted, the furnace shut off and allowed to cool to room temperature, This provided a quite satis­ factory method of annealing the glass samples,

£0 Poiariscope, A conventional polar old poiariscopo was -used to detect the residual strain in specimens after annealing,

6- Grinding and polishing of specimens. All glass specimens were ground by hand using a flat glass plate and two grades of Corbor- undum abrasive, F for rough grinding, and FFF for fine grinding.

Polishing was accomplished by lapping by hand with cerium dioxide and a motor driven felt covered metal lap. It was found, with a little practice, that good optical quality could be attained with only a small degree of tJnon-parallelism11 between the two surfaces. This average

departure was approximately JO.03 iaa.

7. Spectrophotometers. Practically all of the infrared trans- mittances of transparent glasses were obtained from the Department

of Physics Beckman Infrared Spectrophotcmeter, Model IR-3, while meas­ urements in the infrared on radiation scattering glasses were obtained from the Physics Department Beckman Infrared Spectrophotometer, Model XR-2. Measurements in the visible spectrum were obtained from the

Chemistry Department Beckman Quarts Spectrophotometer, Model DU.

8. Microscope. An American Optical Company petrographie micro­

scope was used to observe the crystalline species present in the

dispersed phase glasses. This microscope had a maximum magnification of XUS0.

9. X-ray apparatus. The X-ray equipment used during the course of this investigation is jointly owned by the Departments of Metallurgy and Ceramic Engineering, and consists of a Norelco X-ray Diffraction

Unit, with attached High-Angle Geiger Counter X-ray Spectrometer.

Also used was a Philips powder diffraction camera. The source of

X-rays was a cobalt tube filtered with iron, and operated at 30 lev and 9 na. The exposure time for all powder diffraction patterns was

16 hours.

10. Infrared polarizer. This unit was obtained from the De­ partment of Physics and had been built and tested by one of the grad­ uate students (37)« It consisted of 8 silver chloride plates of approximate dimensions 3ts 3C 3”, these plates being separated by a distance of l/l6tJ and oriented so that they made an angle of 63§°

(Brewster*s angle for silver chloride) with the direction of the in­ cident beam. These plates were contained in a unit which could be rotated in a circular orbit perpendicular to the incident beam so as 26 to plane polarise the light either vertically or horisontally. At a wavelength 6f U*0 microns, this eight plate unit would give a polar­

isation of 99 percent (3?).

Bo Materials

All materials used in this investigation were either of an­

alytical or reagent quality, with the exception of the tellurium

dioxide. This compound was supplied by the R. T. Vanderbilt Compary, New York, Hew York, and had the following analysis:

tellurium 98.80 minimum selenium 0.80 maximum antimony 0.06 copper 0.02 lead 0.10 iron 0.03 sine 0.20 bismuth 0.03 100. Oli V, EKPERIMEHTAL PROCI33URE

A. Development of Tellurium Dioxide Base Glass

The development of the tellurium dioxide glass compositions designated as 207-GT and 207®HXg although not the primary investiga­ tion of this dissertation, will be briefly discussed at this time*

(This development work was jointly carried on by the author and Kr,

C. M. Phillippi, formerly of this laboratory,) The numbering system used to designate the different glass systems is as follows: the first three digits, for example 207 > indicate a family of glass cc3i= positions, in which the 207 indicates that tellurium dioxide is the primary constituent! the letters following these three digits indicate a sequence of composition modifications falling within the glass fam­ ily! the numbers in the suffix represent the number of a repeated melt! and the letters following the suffix indicate two specimens taken from the same melt. The work on tellurium dioxide glasses was instigated by the recent publication of Stanvorth (lh). Such glasses are not entirely new since they were reported by Berzelius in I83I4. (38)* with con­ firmation of such workers as Lenher and Wolensensky (39) in 1913. lit­ tle was known of the properties of these glasses, but such factors as

■the high ionic mass and the electronegativity value of tellurium rec­ ommended its consideration despite the fact that the tellurium-oxygen

27 28 ionic radius ratio falls outside of the Zachariasen (16) and Gold­ schmidt (17) radius ratio range for glass formation. The fact that crystalline tellurium dioxide has a refractive index of 2.1 recom­ mended it as a possible basis for infrared transmitting glasses in line with previous consistent correlation in this laboratory between high refractive index and longer wavelength transmittance (11,12).

The initial melts in this investigation were in the binary system tellurium dioxide-lead oxide. It was found that glasses con­ taining up to 80 percent tellurium dioxide could be produced although these melts had a high tendency to devitrify. By utilising platinum as the melting container it was possible to eliminate the uncertainty of Stanworth's (lU) work, since there was a possibility that his melts might have bean contaminated by the absorption of glass formers from the refractory containers used. It was found that glasses of this binary system could be stabilised by the addition of aluminum oxide. VJhen the infrared transmittances of these glasses were measured, it was apparent that the earlier predictions were confirmed, for these glasses were transparent out to approximately 6.0 microns. There were present, however, strong absorption bands located at approximately

3.25 and U.8 microns. The absorption at 3.25 microns was a broad

asymmetric band, and the one at U.8 microns was apparently a super­ position of two bands, one occurring at Lu 6 microns and the other at

U.9 microns. All of these absorption bands were attributed to the presence of hydroxyls in the glass, this view being based on the 29 previously given data of Florence (U). This Has farther confirmed by melting a glass in an atmosphere of steam, producing absorptions so

strong that the glass became completely opaque from 3.0 to 3-5 microns.

The transmittance from this latter wavelength to the cutoff at 6.0

microns did not go above 10 percent, with indications of the absorp­

tion sands at I4.6 and U-9 microns. By re-melting this glass in an

atmosphere of oxygen it was possible to reduce the intensities of all

of these bands. The ordinary drying techniques, which had proved so successful

in dehydration studies on germanium dioxide and silicate glasses (11,1 2 ),

were generally ineffective in greatly reducing the harmful absorptions

in these tellurium dioxide glasses. These consisted of atmospheres of nitrogen or oxygen, dried by passing them through columns of phos­

phorus anhydride, Drier!te, magnesium perchlorate, sulfuric acid, liquid

nitrogen traps, or combinations of these. It was therefore concluded that the retention of water in these tellurium dioxide glasses was more been tenacious or complex than had ^encountered in the previous glass systems,

and that the diminution of these absorption bands constituted a more

difficult problem. In the course of these dehydration studies it was found that

glasses which were melted in an atmosphere of nitrogen had very low

transmittfance in both the visible and near infrared. This low trans­ mittance was caused not by the presence of nitrogen, but by the absence

of oxygen, for transparent glasses could be produced by melting in an 30 atmosphere of air. The lew transmittance of these glasses melted in nitrogen could be increased by re-melting them in an atmosphere of air.

The ternary system tellurium dioxide-lead ocjcI do - aluminum oxide was investigated with no significant reduction of these strong absorp­ tion bands. Attention was then turned to the substitution of fluorides for lead oxide in the ternary system, since fluorides tend to exert more of a polar!cable effect than does lead oxide; their incorporation into the melt might extend the fields of glass formation tilth exten­ ded possibilities for reducing these strong absorption bands. Var­ ious fluorides were added as replacements for lead oxide in the ter­ nary system; these included lead, barium, magnesium, and strontium fluoride*

It was found that barium fluoride was most satisfactory in that it apparently functioned as a vitrifying influence (in opposition to its common classification as a mineralizer), with glasses containing up to 56 percent barium fluoride being produced. The replacement of lead oxide by barium fluoride was further beneficial in that it re­ duced the intensities of these absorption bands. A thorough study of the ternary system tellurium dioxide-barium fluoride-aluminum ox­ ide was made which resulted in composition 207-GT, containing 36 per­ cent tellurium dioxide, 56 percent barium fluoride, and 8 percent aluminum oxide* The transmittance of this glass from O.lj, microns out to the long wavelength cutoff at approximately 6.0 microns is 31 given in Figure 10. This glass was produced by raelting a 20 gram batch In a platinum container for 1 hour at 2000°F, in an atmosphere of air dried by passing through a sulfuric acid trap and two columns of composite Drierite-phosphorus anhydride. The melt was allowed to cool in a phosphorus anhydride desiccator, the platinum foil stripped off, and the specimen annealed from 800°F. It was ground and pol­ ished to approximately 3.0 mm using techniques previously described. This 207-GT composition, although having the best infrared transmittance of all glasses produced up to this time, still was unsatisfactory in that the intensities of the absorption bands fluc­ tuated from melt to melt, although no deliberate variations were made in the procedure. It was thought that the relative humidity at the

time of melting might possibly be an influence. This was recorded

for each melt over a period of four weeks, with no apparent correla­ tion between it and the intensities of the absorption bands being found. It was then thought that the aluminum oxide in this 207-GT com­ position, which was added as the hydroxide, might be the cause of hydroxyls getting into tha glass structure, and melts were made In which the source of this component was calcined alumina. This was not successful in that the calcined alumina was more difficult to get into solution, and the intensities of these absorption bands still

fluctuated. Attention was then turned to the partial replacement of the aluminum oxide by lanthanum oxide, since it had been shown in a previous investigation that this oxide can also exhibit a stabilising 32 influence on glass melts (11,12). This uas only moderately success­ ful, and resulted in the addition of other components such as arsenic pentoxide to this composition. These compositional studies finally gave a quite acceptable infrared transmitting glass, 207-HX2, whose transmittance is shown in Figure 11. It had the composition 32.8 per­ cent tellurium dioxide, 01.2 percent barium fluoride, 8.6 percent aluminum oxide, 0.0 percent arsenic pentoxide, and 1.9 percent lan­ thanum oxide. The actual function of the lanthanum oxide-arsenic oxide combination was not known, but their effects consistently sup­ pressed these absorption bands to within acceptable limits. Glasses of this 207-HX composition were melted under the same conditions as were those of the 207-GT composition, with the exception of the cool­ ing process. It was found that glasses of this 207-HX composition could be cooled in air without affecting their infrared transmittances.

B. Radiation Absorption Studies

At the time the 207-GT composition was developed, it was de­ cided to study the spectral effects produced by the addition of the various oxide colorants to this tellurium dioxide base glass. Of particular interest were those absorption bands which might be used in the development of the desired radiation filter. It was thought that these colorants might exhibit different spectra in this tellur­ ium dioxide glass than those which they impart to ordinary silicate glasses. As was previously indicated, the absorption bands produced by coloring oxides can be affected by the composition of the base glass. 33 Accordingly, the oxides of the transition elements were added to this 207-GT composition, these additions being made initially on the basis of one quarter of a part of colorant per 100 parts of base glass. These colored glasses were melted and cooled under the same conditions as described for the 207-GT composition. Their transmit- tances from O.U to 1.0 microns were measured on the Beckman Quartz

Spectrophotometer, Model HJ, and from 1.0 to 2.0 microns on the Beck­ man Infrared Spectrophotometer, Model IR-2. With these colored glass­ es, there was little deviation in the readings obtained for a com­ parable wavelength on the BO and on the IR-2 spectrophotometers. Of all of these colorant additions, copper oxide was the only one which exhibited a reasonably sharp absorption edge which extended into the near infrared region, and this is shown in Figure 7. Increas­ ing the concentration of this colorant shifted the edge of the near infrared absorption band to longer wavelengths, with 1 part of color­ ant per 100 parts base glass being the apparent saturation limit of copper oxide. As is seen in Figure 8, this concentration of copper oxide renders the glass almost completely opaque in the visible region, with only a small transmission band centering at approximately 0.5 microns. This glass becomes transmittant again in the near infrared, starting at 1.0 micron and increasing up to 80 percent transmittance at 2.0 micronsj this is shown in Figure 8. At this point in the investigation the composition 207-HX had been developed, and the spectral effects of copper oxide in this new 3k base glass were studied. As with the 207-GT base glass, it t*as found that 1.0 parts of copper oxide per 100 parts of 207-HX composition was the apparent saturation limit for this colorant, and its spectral effects are given in Figure 9. A comparison between Figures 8 and 9 revealed that the absorptions produced by copper oxide in a 207-HX base glass were practically the same as those given to a 207-GT composition.

It was obvious that the addition of this colorant to a tellurium diox­ ide base glass was not the complete solution to the development of the desired radiation filter.

C, Radiation Scattering Studies

Since it was apparent that a radiation filter *ihieh was opaque through the visible spectrum and out to 1.5 microns could not be pro­ duced by the absorption of radiation, attention was then turned to the development of a disperse phase in this 207-HX glass. By controlling the formation of the disperse phase, it was hoped that these glasses would approach the inverse fourth power wavelength scattering of radia­ tion as given by the Rayleigh equation. As a starting point in a disperse phase study of glasses, opaci­ fication temperature limits may be determined by running specimens or a fiber of the glass in a temperature gradient furnace. Unfortunately a workable gradient furnace was not available, and therefore a cut and try method of heat treatment was adopted. This was tedious, but yield­ ed satisfactory results. 35 The size of the specimens used in these heat treating studies was approximately 25 mm x 12| ran x 5 nun, two of these being obtained

from a melted slab of glass.

These first samples were heat treated in the Hoskins Electric

Furnace, which has been described in the section on Equipment. The

samples were inserted in a block of K-30 insulating brick which had a shallow well cut into it, this holder having been preheated at the specified temperature before the introduction of the glass specimen.

After heat treatment, the holder with glass sample, was removed from the furnace and allowed to cool to room temperature. The transmit­

tance was measured on the IR-2 spectrophotometer over the spectral

region, 1.0 to 2.3 microns. Attempts were made to develop a disperse phase in the 207-HX

composition by heat treatment, and these were not entirely unsuccess­

ful. The opacification produced was, however, quite inhomogeneous.

Temperatures ranging from 800° to 1000°F were tried, with a wide

variety of heat treating times.

Since these efforts did not yield the desired results, atten­

tion was turned to the addition of calcium fluoride to the 207-HX

composition. The reason for its trial was that this fluoride readily forms a disperse phase with heat treatment in many silicate glasses.

Additions were made to the 207-HX composition, starting with 1 part

of fluoride per 100 parts base glass, and increasing with 2, 1*, 6, etc. parts, until a composition was reached which would just remain vitreous 36 when cooled from the molten state,. This resulting composition, 207-JF, contained 10 parts of calcium fluoride per 100 parts of 207-HX base glass* The melting procedure of the 207-JF composition was the same as for the 207-HX glass, with the exception of the cooling procedure.

The addition of calcium fluoride to the 207-HX composition increased the interfacial tension between the glass and the platinum container to such an extent that -the resulting glass could not be cooled to room temperature in the container without breaking. The procedure adopted, therefore, was to cool the glass from the molten state until set, and then while still hot, the glass and platinum container were placed into

the annealing furnace operating at 750°F# and the furnace shut off. It is to be noted that a slightly lower annealing temperature was needed for this composition as compared with 800°F for the 207-HX composition.

This was necessary in order to prevent spontaneous opacification as the glass was annealed. This method proved satisfactory in that the result­ ing annealed glass could be removed from the platinum container without breaking, and its residual stress was low enough to allow It to be cut into two 25 mm x 12^ ram x 5 ram segments for heat treatment.

A wide range of heat treating temperatures were tried on this

composition until 800°F was established as the apparent optimum for this glass. It was found that heat treatment at this temperature yielded what appeared to be a homogeneous disperse phase, and the sam­ ples could be subjected to prolonged heat treating times without de­ forming appreciably. 37 Having eliminated temperature as one variable in these heat treating studies on the 207-JF composition, the variation of time of heat treatment was next considered. The initial results appeared to be quite satisfactory with moderately effective radiation filters be­ ing produced, their region of selective scattering moving to longer wavelengths with increased heat treating time, indicative of larger particle diameters of the disperse phase. These are indicated in

Figures 13, 1h, and 15, for glasses 207-JF9A, 7A, and 7B which were heated at 8C0°F for l-3/h> 2, and 2-| hours respectively. Since it appeared that a good degree of selective scattering of radiation was being obtained from these 207-JF composition glasses, these resulting transmittance curves were checked for conformance to the inverse fourth power of wavelength scattering as predicted by the Rayleigh equation. As previously stated, the reduction of the intensity of light passing through a diffusing glass can be defined by an equation of the form (27),

1 2 2 e where x 2 the thickness of the glass ly a the initial intensity of radiation entering the glass 12 2 the intensity of radiation after passing through a thickness, x 1c = a constant dependent upon the coefficients of ab­ sorption and scattering. 38 This equation is valid only for the reduction of the intensity within the glass itself, and does not consider reflection losses with reduc­ tion of intensity when the impinging beam encounters the air-medium interface upon entering the glass, and the medium-air interface upon leaving the glass. This loss by reflectance for normal incidence upon a glass surface can be calculated by means of Fresnel's equation,

R a f*L — A where n is the refractive index of \n ^ 1 1 the glass

Consider now the following diagram:

I, X, D

ki 'K o|

As the initial beam IQ impinges upon the diffusing glass, its intensity is reduced by a reflectance R, and the following relation holds,

a) It — I_ — I R, or I- 3 ID(1 « R) where I- is the intensity of the radiation entering the glass In passing through .the, glass of thickness x, the intensity is reduced to give I 2 , following the previously given exponential law, or

b) Ig q where 1c is a function of the coefficients of absorption and scattering 39 At the emerging surface* another reflectance R takes place* yielding*

d) 1^ s Ig *» IgR 5 or 1^ = Xg(l - R) where 1+ is the trans­ mitted emerging intensity of radiation Substitution of (b) into (c) gives*

d) It = (1 - R)! ^ o°tor

And, substitution of (a) into (d) yields*

e) I t s (1 » R)2 I 0 e”lac

This relation then gives the intensity of emerging radiation*

I^l, resulting from an incident beam of intensity* I0, impinging upon and passing through a diffusing glass of thickness, re.

The factor involving reflectance can be eliminated, and the

coefficient k evaluated by measuring the transmitted intensities, Ia

and Ib , at a particular wavelength for two different thicknesses of

diffusing glass, xa and ro^. By taking the ratios of these two rela­

tions and rearranging* the following is obtained,

f) i - Q-k(xa - xb )

*b " By taking logarithms of both sides of this equation and once

more rearranging, an evaluation of k may be found from,

g) k = -ln(Vlb)

As was previously stated, k is a function of both the scatter­ ing and absorption coefficients. However, in the spectral region 1.0 to 2.3 microns, the absorption of the base glass is approximately a constant as is seen in Figure 12, which gives the transmittance for 207-JF9B, a sample not heat treated. It was therefore assumed that any sharp reduction in intensity exhibited by these dispersed phase glasses within the spectral region 1.0 to 2.3 microns would be the re­ sult of scattering alone, as a first approximation. Rayleigh's law states that the scattering coefficient is pro­ portional to inverse of the fourth power of the wavelength, or,

qAjor, q q

In this equation, the assumption is made that the other variables in the Rayleigh scattering relation are constant, namely the influences of the diameters of the scattering particles, and the difference be­ tween the refractive Indices of the particle and of the medium.

If the logarithm of both sides of the above equation are taken, the following results:

In q = In A - In %

A plot of In q as the ordinate and In % as the abscissa should yield a straight line whose slope is four, with In A being the intercept on the q-axis. By the use of this mathematical evaluation, it was believed that the wavelength exponent of the radiation scattering exhibited by

these disperse phase glasses could be evaluated. Glasses 207-JF9A,

7A, and 7B were ground and polished to thinner sections, their trans­ mit tances taken, k calculated as a function of wavelength, and a plot of In k vs IrAmade. It is to be noted that the term k was used In­ stead of q (the true scattering coefficient), since this evaluation

of It involves both the scattering coefficient q and the absorption coefficient p , but has been assumed constant. The change in trans­ mittance with thinner sections of these three glass is shown in Fig­ ures 13, lU, end 15, and the plots of their calculated data are given in Figure 17, together with a plot for for comparative purposes.

It was apparent that the scattering of radiation as given by these dispersed phase glasses was approximately equivalent to that predicted by the Rayleigh equation for shorter wavelengths, and the scattering apparently exceeded this inverse fourth power factor for longer wavelengths. Ihis departure was more pronounced for glasses which had been subjected to shorter heat treating times, and judging from their respective transmittances, for glasses In which the re­ gion of selective scattering was displaced toward shorter wavelengths. In an attempt to better understand tills departure from Ray­ leigh' s law, it was decided to heat treat a sample for a shorter time than had been given 207-JF*?A (l-3/U hours at 800°F). It was found, however, that -this particular method of heat treatment was not repro­ ducible, and this resulted in the construction of the copper block U2 heat treating furnace which has been described in the section on Equip­ ment. The definite following procedure was established for heat treating the specimens in this special furnace. The copper block unit was pre-heated for at least one hour at 800°F. The furnace was then unsealed, copper block removed, sample inserted, block replaced into the furnace, and the furnace resealed. This entire procedure took less than one minute, therefore the copper had little opportunity to cool down. After heat treatment, the glass specimens were cooled by allowing them to drop into a 1*00 ml beaker filled with powdered Sil-O-Cel insulation. This powder had been pre­ heated for y hour on a small electric hot plate, attaining a tempera­ ture not in excess of 5>00°P. After the sample had been first cooled, the beaker was removed from the hot plate and allowed to cool to room temperature. By this method of cooling, it was possible to arrest satisfactorily the heat treatment without breaking the glass specimens, and also to give the samples enough of an anneal to allow them to be ground and polished* All glass samples were slightly beveled on all edges prior to heat treatment to reduce the possibility of breaking when subjected to the thermal shock of being placed into the heated copper block. Using this new furnace and techniques, sample 207-JF11A was given a heat treating time of 1 hour at 800°F. When the transmittance was taken for a thickness of it was noted that this specimen exhibited a region of selective scattering at shorter wavelengths than that of 207“*Jli'9A$ it could therefore be used to check the trend of this apparent departure from Rayleigh1 s law. Sample 207-JF11A was then ground and polished to two thinner sections of 3.13 and 2.1*1* mm, and the transmittances measured for each thickness. Having the trans­ mittance data from three thicknesses of this specimen, a double check on the evaluation of k for sample 207-JFX1A was possible. However, when the optical measurements for the 2.1*1* 12m section were taken, it was unexpectedly noted that this transmittance increased markedly over that obtained from the previous two thicknesses. In view of this, the sample was ground to a thickness of 1.9& nso, and the transmittance taken once more. The transmittances of these four thicknesses of

207-JF11A are given in Figure 16. It appeared that this sample "opened upt? transmittance-wise upon grinding to thinner sections.

The calculation of k from the transmittances of the 3.85 nm and

3.13 mm sections of 207-JF11A resulted in a slope of something less than four. This calculation for 2.1*1* ram and 1.96 mm sections gave a slope which over its entire length was greater than four (see Figure

17). It was thought that these marked differences in transmittances with decreasing thickness could have resulted frcm inhomogeneities at or near the surface of the glass, these being removed as the sample was ground to thinner sections. Up to this time the process of grinding was done by removing equal amounts from both surfaces of the sample, with no particular attention given to which surface was being ground. Sample 207-JF11B, which was heat treated for hours at 8Q0°F, was ground according to a definite procedure. One surface was ground just enough to make it flat, and defined as the "constant" surface. This surface was given good beveled edges so that it could be identi­ fied. The opposite surface was ground at least 0.5 ram to give a resulting thickness of 3*67 ram and defined as the "variable" surface.

This sample was mounted into the IR-2 Spectrophotometer so that the incident beam impinged normally upon the "constant" surface, and the transmittance taken. The sample was then re-oriented so that the in­ cident beam this time impinged upon the "variable" surface, and the transmittance taken once more. This process was repeated for thick­ nesses of 3*22 eou, 2.56 mm, and 2.20 mm, ail, grinding being done on the "variable" surface (see Figures 18 and 19). Although there was a definite transmittance difference with surface orientation for a speci­ fied thickness, the change in transmittance with decreasing thickness for each surface orientation did not conform with what would normally be expected. Ordinarily the transmittance of a given spectral region increases with decreasing thickness of specimen. Other specimens were ground and their transmittances measured in an analogous manner as 207-JF11B. These gave similar but unpre­ dictable transmittance data.

Since it appeared that these differences in transmittance might result from the structure of -the opacified glass, thin sections of these heat treated specimens were examined under a microscope. Although this work was tried numerous times, it was found that the

glassy matrix would break up into many minute fissures with grinding, thus making microscopic observations impossible.

Scrapings from each surface of a heat treated specimen before it had been ground and polished were examined by immersing these pow­ ders in oils of known refractive index under the microscope. This specimen, 207-JF16A, had been heat treated for 3 hours at 800°F with a definite orientation in the copper heating block. The top surface of the sample (the one exposed to the atmosphere during melting), was placed up in the copper block during the heat treatment; the opposite surface (the one in contact iriLth the platinum container during melting), was in contact with the copper block during the heat treatment. After heat treatment, fragments from each surface were obtained by scratch­ ing with a tungsten-carbide tipped tool; these were immersed in an oil of refractive index of 1.7U* and observed under the microscope at a magnification of Xh5>0. Glass fragments thin enough for observation appeared to be completely filled with tiny sppriodal particles, although these particles were just resolvable under the microscope. Under mag­ nification, this dispersed phase presented a "pebbled” or "honeycomb" structure. No appreciable difference could be detected in the dispersed phase of the fragments taken from either surface.

This specimen was then ground and polished the same as 207-JFUB; the surface which had been placed upln the copper block was ground just enough to make it flat, its four edges beveled for identification, and U6 this called the "constant" surface. The opposite or "variable” sur­

face was ground at least 0.5 mm.

Since no direct correlation could he obtained between the transmittance and the surface of the sample onto which the incident beam impinged, the question of the orientation of each individual surface arose. In order to eliminate this variable, one of the 12% nan edges of 207-JF16A was given a very heavy bevel. This specimen was then placed into the IE-2 Spectrophotometer so that the colli­ mated incident beam impinged normally upon the "constant*1 surface, the heavy bevel being in an "up" position, and the transmittance measured from 1.0 to 6.0 microns. The transmittance was again meas­ ured after inverting the sample, the incident beam still impinging upon the "constant" surface, but the heavy bevel in a "down" position. This procedure was repeated for the "variable" surface. The previous relations or findings were confirmed since there was a definite trans­ mittance difference for each surface and each orientation of surface, as shown in Figures 20 and 21.

In attempting to trace the origin of this difference in trans­ mittance with orientation, the possibility of the glass specimens being wedge-shaped was considered. Upon checking the thickness of

207-JFI6A, it was found that its thickness did not vary more than

2 per cent.

The possibility of physical or chemical inhomogeneity of the specimen being responsible for these transmittance differences was next considered. All previous specimens for heat treatment were ob­ tained by cutting the large slab of glass into half, giving two

samples of dimensions 25 mm x 12-^- mm x 5 nnrn In this instance, 207-JF17 was cut so as to yield three sections, the center section of dimensions 25 mm x 12^- m x 5 mm to b© used for heat treatment, with the other two sections of dimensions 25 nan x mm x 5 mm being selvage, and as such were discarded. This specimen was heat treated for 2i hours at 0OO°F, and Its orientation in the copper block was identical with that of 207-JF16A. It was ground and polished accord­ ing to the procedure established for the "constant" and "variable" surfaces, and the transmittance3 measured for the four types of orien­ tations previously given for 207-JF16A. *111636 results are depicted in Figure3 22 and 23, which show less marked variations than in 207- JFl6A (see Figures 20 and 21)*

Sample 207-JF18A was obtained by the ordinary procedure of cutting the large glass slab Into half. It was heat treated for 3s hours at 800°F, and ground and polished in the same manner as samples

207-JFX6A and 17* Its transmittance was measured in an analogous man­ ner to the previous two specimens, and these results are shown in Figures 2U and 25*

In all of the measurements taken up to this time on the IR-2 spectrophotometer, the distance from the source to monochromator was approximately 6.0 cm, giving a distance of about 3.0 cm from the speci­ men to monochromator. The design of the sample holder was such that U8

the specimen could be rotated only in increments of l8 0 ° in a direct tion perpendicular to the incident beam. / In an attempt to minimise scattered or non-colliraated radia­ tion as possible sources of error, the IR-2 was disassembled and re­

oriented so that the distance between the source and monochromator

was 1|0 era. Sample 207-JFX8A was positioned at a point midway between

these two components, and mounted over a 6 mm diameter aperture which was cut in a thin metal mask, thus allowing for greater freedom of rotation of the specimen. The mask, which was marked in increments

of U5°, was aligned so that the collimated radiation from the source

impinged normally upon the surface of the sample. A wavelength of

lt.0 microns was selected for these studies, this being removed from the

region of selective scattering for this specimen (see Figures 21* and

25) s a slit width of 2.0 ram was used in the monochromator. With the distance from the sample to monochromator being 20 era, it was assumed that all of the radiation detected by the monochromator would be col­ limated.

The orientation with the incident beam impinging upon the ”con-

stant” surface and the bevel in an "up** position was defined as con­

stant Surface first, © s 0°. Transraittances were taken, with the

sample being rotated 360° in increments of 1i$°, 0 being measured in

a counterclockwise direction as viewed from the source. The difference in transmittance varied much more than had been previously indicated. U9 (see Figure 26). The points on this curve were the average of four individual measurements taken for each orientation; such measurements did not vary more than h percent. With each reading for a particular orientation, the specimen was re-aligned so that a different portion of the sample covered the aperture. This method of talcing readings was used for all succeeding measurements. This same process of rota­ tion was repeated, this time with the incident beam impinging upon the "variable” surface of 207-JF18A (see Figure 28).

The possibilities that this rotational transmittance might be the result of some type of polarisation were investigated. An in­ frared polarizer was positioned between the source and the specimen, and rotational transmittances taken for both the "constant" and "variable" surfaces, with the incident light polarized first vertically and then horizontally. The polarizer was later placed between the sample and the monochromator so as to analyze the transmitted light, and measurements taken for the "constant" and "variable" surfaces; the transmitted light was analyzed first vertically and then horizon­ tally (see Figures 26, 27, 28, and 29)*

In view of the unusual transmittance data obtained from 207-

JFL8A, a similar type of experiment was tried on sample 207-JF16A, using the same optical set-up and procedures as defined for the prev­ ious specimen. In this instance, measurements were taken on the uson- stant" surface only, with no polarization, and with the incident light 50 polarised (see Figure 30).

In an attempt to determine the cause of this transmittance ef­ fect, 207-JF19 was sectioned across the diagonal of the large glass

slab. This specimen was heat treated for 3 hours at 800°F, and ground

and polished as in the other specimens. Its rotational transmittance was obtained in a manner analogous to 207-JF16A, and is shown in Fig­

ure 31. The effects produced by crossing two of the specimens which exhibit this rotational transmittance were studied. The samples se­ lected were 207-JF16A and l8A, and their orientation within the prev­

iously described optical system v/as as follows x 207-JF16A was aligned on the monochromator side of the aperture with the bevel in an ‘’up1’

position, so that the incident beam impinged normally upon the "con­ stant” surface; the IR-2 spectrophotometer was standardized against this specimen. Sample 207-JF18A was then placed on the source side

of the aperture so that the incident beam impinged upon its "constant" surface, with the bevel in an "up" position, giving 0 = 0°. Transmit*®

tances were measured with rotation of 207-JF18A through 3.80°, in in­

crements of U5°, with the results shown in Figure 32. It was found

that the orientation of these two crossed samples which gave a maximum

of transmitted intensity, yielded aivtransmittance of greater than 100 percent. Considering the possibility that this particular orientation

of the two specimens might be focusing more of the transmitted radia­ tion toward the monochromator than was experienced with only one 51 sample, the distance from the aperture to the monochromator was

changed to' 10 cm and 30 cm. The effect on the rotational transmit­ tance s obtained by crossing these two specimens at these distances

from aperture to monochromator is seen in Figure 32. The inconsis­ tencies of these results must be frankly admitted.

In view of these results, the rotational transraittances of

each of the two samples taken individually with similar distances

from aperture to monochromator were measured (see Figures 33 and 3U). X-ray diffraction was used to try to determine the structure

of these dispersed phase glasses. A small segment obtained from 207-JF16A was crushed to a very fine powder in a diamond tipped steel

pestle and mortar. This powder was mixed with Ducc cement, and then

extruded through a small aperture die, yielding a fine fiber. This was mounted and aligned Into a Philips X-ray diffraction camera and

given a 16 hour exposure, using iron filtered, cobalt radiation. A

diffraction pattern characteristic of a crystalline material was ob­ tained. The 11 d" values and relative intensities of each of these diffraction lines were determined, and are given in Table 3* This set of "d” values were checked through the ASTM X-Ray Diffraction

Data Cards with no success. The "d" values of the six primary com­ ponents which made up the 207-JF composition were tabulated, but none could be correlated with the results obtained. The possibility of the re-combination of the six primary components which made up this com­ position was considered, but yielded no clues. 52 By increasing the heat treatment of a sample it was thought I possible to aid in identifying credible crystalline components. Ac­ cordingly, 207“JF18B was given a heat treatment of 6 hours at 800°F.

A small segment of this sample was cut off, crushed, and prepared in the same manner for X-ray diffraction as 207-JF16A. The pattern of this specimen was obtained tinder the same conditions as given for the previous sample, but no appreciable difference could be found in the

!'dn values, or in the relative intensities.

The remainder of 207-JF18B was ground so as to yield the two surfaces previously described, and its rotational transmittance ob® tained on the '’constant*1 surface only (see Figure 35)* The sample to monochromator distance was 20 cm in this case. To make certain that these differences in transmittances with rotation were the result of the heat treatment, and not inherent in the glass itself, sample 207-JF16B (which had not been heat treated) was ground and polished according to the established procedure, and its rotational transmittances were measured with the same optical ar­ rangement as used for previous samples. No difference in transmit­ tance was found to result with direction or orientation of the specimen. The possibility that the X-ray diffraction patterns of 207-JF16A and l8B might have resulted from the glass matrix and not from the heat treatment was considered. An X-ray diffraction pattern of 207-JF16B

(not heat treated) was taken under identical conditions as those of 53 207”JF16A and 18B, and resulted in the broad diffuse bands character­ istic of glass structures*

A second infrared polarizer was constructed, making possible both a polarizer and an analyzer in these studies on the rotational transmittances of the dispersed phase glasses* Both the polarizer and the analyzer in this case had only four silver chloride plates per unit as compared trith the previously used eight plate unit* This was necessary, since the intensity of transmitted light through a single eight plate unit was quite reduced by the absorption of the silver chloride itself, disregarding any reduction in intensity as the result of polarization. Had crossed polarizers been used, each consisting of eight plates, it is quite probable that absorption alone would have accounted for no transmittance. The four plate unit gives approximately 88 percent polarization at 2**0 microns (37). One of these four plate units was placed between the source and the sample, and oriented so as to polarize the incident radiation horizontally; the other was placed between the sample and the monochromator and or­ iented so as to analyze the transmitted radiation vertically. The source to monochromator distance was 1*0 cm, and the sample to mono­ chromator distance was 20 era. The effects of these polarizing units on the rotational transmittance of 207-JF18A for the "constant” and

"variable” surfaces are seen in Figures 26 and 28, or 27 and 29*

In order to check whether these rotational transmittance pat­ terns were the result of the particular method of grinding previously 5U adopted, to yield a "constant” and a "variable” surface, 207-JF16A was ground to thinner sections of 2.06 and l.J?9 ram respectively, and the rotational transmittance measured for each thickness* A H grinding this time was done on the upper surface previously held constant* The results are given in Figure 36.

To check the possibility of combining not only the scattering of radiation as given by these dispersed phase glasses, but also an absorption of radiation, 1.0 parts of copper oxide was added to 100 parts of 207“JF base glass. This composition was melted, cooled, and annealed under the same conditions as the 207-JF composition. All of the copper oxide apparently went into solution during melting. This glass was cut into tiro sections, and o n e segment heat treated for 2§- hours at 800°F. It was found, however, that the specimen produced was too inhomogeneous to warrant study. VI. RESULTS

The following are the results obtained during the course of

this investigation. Included in this section are compilations of the glass compositions used (Table l), of the heat treateents accorded

glasses of 207-JF composition (Table 2), and of the X-ray diffrac­

tion data of sample 207-JF16A. (Table 3)* The data of the absorption spectra of the transition element oxides in silicate glasses as given in Figures 1 through 7 were obtained from the publications of Bachman (20) for Figures 1 and 2, U to 7, and from Frits-Schmidt, Gehloff, and Thomas (21) for Figure 3. There was an error in the labeling of the ordinate of Figures

10 to 12, and 20 to 25>. This should have read Transmittance'9 in­

stead of n% Transmission.99 It is to be noted that the scale on the

p'o 1 fir coordinates of Figures 26 to 31 > 33s 3h, and 36 goes from

US percent to 80 percent. In Figure 32 this scale goes from 0 to 120 percent, while in Figure 35 the scale is from 35 percent to 75 percent. TABLE 1

OXIDE SYNTHESES OF GLASS COMPOSITIONS

Oxide Compon­ 207-GT 207-GT 207-GT 207-GT 207-GT 207-GT 207-GT 207-GT 207-HX ent 207-GT 207-HX 207-JF C2 C9 Cll C12 Cll; Cl$ C17 C21 Cl

Te02 36.00? 32.80? 29.60? 35.91? 35.91? 35.91? 35.91? 35.91? 35.91? 35.91? 35.61;? 32.!;8? BaF2 $6.00 $1.20 U6.U0 55.86 $$.86 55.86 55.86 $$.86 $$.86 $$.86 5$.li$ 50.69 AI2O3 8.00 8.60 7.8 0 7.98 7.98 7.98 7.98 7.98 7.98 7.98 7.92 G.$l AS2O5 5.50 $ .0 0 5*U5 La203 1 .9 0 1 .7 0 1 .8 8 CaF2 9.$0 C0 3 OU 0.25 CuO 0.25 0099 0.99 Mn02 0.2? Fe203 0.2$ V2O5 0 .2$ Cr203 0.2$ Ni203 0.2$

100.00? 100.00? 100.00? 100.00? 100.00? IOOoOO? 100.00? 100.00? 100.00? 100.00? 100.00? 100.00?

All glasses obtained from 20 gram batches, melted in platinum containers for 1 hour at 2000°F, in an atmosphere of air, dried by being passed through a sulfuric acid trap and two columns of composite Drierite-phosphorus anhydride. All glasses annealed from 800°F, with the exception of 207-JF. Glasses of 207-JF composition annealed from 7$0°F.

VJl On TABLE 2

DATA ON GLASSES OF 207-JF COMPOSITION

Glass Heating Heating Orientation Grinding and Number Sectioning* Furnace Temperature Time in Furnace Polishing

207-JF7A half Hoskins 800°F 2 hours varied varied 207-JF7B half Hoskins 800° 2i varied varied 207-JF9A half Hoskins 800° 1-3/U varied varied 207-JF9B half -—-not heattreated—— varied

207-JF11A half copper 8000 1 varied varied block 207-JF11B half copper 800° varied constant and var®, block iable surfaces^ copper top-up® constant and var­ 207-JF16A half 800° 1 block constant** iable surfaces

207-JF163 half =>— -not heat treated®-— constant and var­ iable surfaces central copper 207-JF17 800° 2i top-up- constant and var­ half block constant iable surfaces copper top-up- constant and var­ 207-JF18A half 800° 3t block constant iable surfaces 207-JF18B half copper 800° 6 top-up- constant and var­ block constant iable surfaces

207-JF19 diagonal copper 800° 3 top-up- constant and var­ half block constant iable surfaces * All samples cut from glass slab 2J? mm x 25 mm x £ urn to give specimen 2$ mu x 12-| mu x 5 Ea Top melted surface placed up in copper bloclq this designated as constant surface '*** Constant surface ground just enough to make it flatj other grinding done on opposite or variable sur­ face 58

TABLE 3

X-RAY DIFFRACTION DATA FOR 207-JF16B

d value Intensity d value Intensity

a . 0780 1 1.7766 8

3.5U3? 3 1.7031 2

3.3219 10 1.6711 1

3.2510 a 1.6180 62

1 3.177U 10 1 .600a s X 2.9$h9 7 1.5087 2 1 2.8307 7 1.5027 £

X 2.63U1 3 1.U210 2 2.2939 2 1.3728

X 2.0907 8 1.3217 2 2.05lli 3 1.2630 5 a 2.0152 3 i . 2aai ¥ l 1.9976 3 1 . 200a ¥ 1 1.9338 a 1.1765 2

1.8608 a Philips camera 16 hour exposure Cobalt radiation*»-iron filter 30 Kv 0.9 ma % TRANSMITTANCE 100 60 80 20 0.4 0.6 0.8 1.0 WAVELENGTH MICRONS 1.2 THICKNESS- 2.94 2.94 THICKNESS- 0.5 % Vo0 . . % Vo0 0.5 — 0.25 0.25 — 0-GT- I4 -C T G 207- 1.4 % 20s 0 V2 1.6

SLCT GLASS) (SILICATE m m . . 2.0 1.8 100

80

cc. 40 fo 207-GT- CIS

THICKNESS- 2 . 9 4 m m .

20 0.25 % Cp203 0.20% Cf203 (SILICATE GLASS)

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 WAVELENGTH MICRONS 207-GT- Cll THICKNESS- 3.01 mm. — 0.25% Mn02

0.10 % M rt02 (SILICATE GLASS)

______I______I______I______1.4 1.6 1.8 2.0 WAVELENGTH MICRONS 100

80

GO

40

207- GT-CI3

THICKNESS— 2.94 m m . 20 — -0.25% F@p3

0.50% F@oO, (SILICATE CLASS)

0.4 0.60.8 1.0 1.2 1.41.6 1.8 2.0 WAVELENGTH MICRONS % % transmittance 60 80^ 40- 20 0.60.4 0.8 WAVELENGTH MICRONS 1,0 1.2 HCNS- 00 .0 3 THICKNESS- 2 C - T G - 7 0 2 02% Co304 0.25% — .0 Co,0A 0.10% 1.4 1.6 SLCT GLASS) (SILICATE mm 1.8 . -

2.0 & too

@0

o @o

M

207- GT-C17 THICKNESS - 2.99&M- 0.25% Ni203 0.20% Ni 0 (SILICATE GLASS)

0.4 0.6 o.e 1.0 1.2 1.4 1.6 1.8 2.0 WAVELENGTH MICRONS 100

80

H

2 0 7 -G T -C 9 THICKNESS-2.97 mm. 20 0.25 % CuO 0.50 % CuO (SILICATE CLASS

0.4 0.80.6 1.0 1.2 1.4 1.6 I.S 2.0 WAVELENGTH MI CRONS 2 0 7 -G T -C 2 I THICKNESS-2.96m 0.99 % CuO

i

o# 0.© 0 .© 1.0 1.2 1.4 1.6 2.0 WAVELENGTH MICRONS 100

2 0 7 -H X -C I

THICKNESS- 3.05 m m . so 0.99% CuO

20 Z\ 0.4 0.8 1.0 1.2 1.4 1.6 1.8 2.00.6 WAVELENGTH MICRONS Transmission 100 80 40 20 60 0 0 2 3 4 aeegh Microns Wavelength 5 6 THICKNESS 0 .0 -3 M ELT — 2 HRS. 2 2000°F MELT — 0 — GT2 — 207 7 8 mm 9 . 10 207 — HX-2 MELT — 2 HRS. 2000° F

THICKNESS — 3.02 m m .

Wavelength 100

207 JF9B MELT 2 HRS. 2000°F 80 THICKNESS - 3.05

c v>o V) wE c o k- I- 40

Wavelength Microns % TRANSMITTANCE 30 0 0 1 IO 0 4 0 5 GO 0 7 eo 1.0 ET RA- f HS800°F ° 0 0 HRS-8 if- TREAT- HEAT JF9A - 7 0 2 1.2 WAVELENGTH MICRONSWAVELENGTH 1.4 1.6 I U 13FIGUR 2.22 .0 2 .2 2 71 % TRANSMITTANCE 30 20 100 0 5 0 7 0 9 60 80- . 1.2 1.0 ET RA- HRS- F ° 0 0 -8 S R H 2 TREAT- HEAT JF7A - 7 0 2 WAVELENGTH- MICRONS WAVELENGTH- 1.4 1.6 FIGURE FIGURE Ik 1.8 2.96 M M 2.96 2.0 2.2 2.2 IMM. 2.2 ^T, A (3 too

2 0 7 - JF7B 9 0 HEAT TREAT-24-HRS.-800°F

6 0

7 Q

6 0

5 0 2 .47 MM .

2.96 M M 4 0

3 0

20

10

O I. 1.2 1.4 1.6 1.8 2.0 2.2 WAVELENGTH- MICRONS f 'IGUH15 *^3 £r

207- JFIIA HEAT TREAT- I HR.-800° F % % TRANSMITTANCE

WAVELENGTH-MICRONS 6 i.@ (MICRONS)

In X PLOT OF lTlKvs.lRX FOR 207JF DISPERSED PHASE GLASSES 0.01

"FIGURE 1? 100 % % TRANSMITTANCE - 0 4 CONSTANT SURFACE HEAT TREAT- I i HRS.BOO'F i I TREAT- HEAT JFIIB - 7 0 2 .2 . M M 3.22 . M M 3.67 . 14 . 16 2.0 1.6 1.6 1.4 1.2 AEEGH MICRONS WAVELENGTH FIGURE 18 .2 2 \ft

o 'b

S'

^S>0\ \ >r

*o\

*p> ' V ^ s x<& ^ N° \0> a * V?

' M^- 100

2 0 7 - JFI6A

THICKNESS - 3.02 mm. HEAT TREAT. 3 HRS. 800° F CONSTANT SURFACE

BEVEL DOWN c o BEVEL Up E c o

DS G I r

I i ,■. *. i — 6 7 8 9

Wavelength Microns 100

207- JF 16A

THICKNESS- 3.02 mm.

HEAT TREAT- 3 HRS.800 BEVEL UP 1 f £>*. VARIABLE SURFACE

c o 55 co £ — BEVEL CO H c Q D i3 w ro

Wavelength Microns 2 0 7 - JF 17

THICKNESS - 3.05 mm. HEAT TR EAT- 2jHRS. 800° F CONSTANT SURFACE

BEVEL D0WN

Wavelength 2 0 7 - JF17 THICKNESS- 3.0 5 mm. HEAT TREAT. - 2 5- HRS. 8 0 0 °F VARIABLE SURFACE

J — I i i ! I i 6 7 8 9 10

Wavelength Microns 207 - JFI8A THICKNESS-3.07mm. HEAT TREAT- 3 “ HRS.8 0 0 ° F CONSTANT SURFACE

2 3 4 5 6 7 8 9 10

Wavelength Microns 2 0 7 - J F 18 A THICKNESS- 3.07Ma. HEAT T R E A T -3-^ HRS.8 0 0 ° VARIABLE SURFACE Bh

2 0 7 - JFI8A COtSTAHT SURFACE SOURCE TO MONOCHROMATOR 4 0 CM ------NO POLARIZATION SAM PLE TO MONOCHROMATOR 2 0 CM ------INCIDENT LIGHT POLARIZED VERTICAL WAVELENGTH — 4 MICRONS ------INCIDENT UOHT POLARIZED HORIZONTAL — CROSSED POLARIZERS n s . transm ittance 0“ 00

4 5 315 7 0

90' 270*

50

135 2 2 5

180°

FIGUR1S 26 8£ 207- JFI8A

CONSTANT SURFACE SOURCE TO MONOCHROMATOR 4 0 CM ------NO POLARIZATION SAMPLE TO MONOCHROMATOR 2 0 CM TRANSMITTED LIGHT POLARIZED VERTICAL WAVELENGTH — 4 MICRONS TRANSMITTED LIGHT POLARIZED HORIZONTAL CROSSED POLARIZERS % TRANSMITTANCE

45' 70 315

6 0

SO

9 0 270' 50

7 0----- 135 225'

180°

F I G U R 2? fl6 2 0 7 - JFI8A VARIABLE SURFACE SOURCE TO MONOCHROMATOR 4 0 CM - INCIDENT LIGHT POLARIZED VERTICAL SAMPLE TO MONOCHROMATOR 2 0 CM 7 WAVELENGTH — 4 MICRONS - INCIDENT LIGHT POLARIZED HORIZONTAL — CR038ED POLARIZERS % TRANSMITTANCE

0° O-

30- 270° /!/

FIGURE 28 87 207- JF18 A VARIABLE 8URFACE SOURCE TO MONOCHROMATOR 4 0 CM NO PO LA RIZA TIO N SAMPLE TO MONOCHROMATOR 2 0 CM ------TRANSMITTED LIGHT-POLARIZED VERTICAL WAVELENGTH — 4 MICRONS ------TRANSMITTED LIGHT POLARIZED HORIZONTAL CROSSED POLARIZERS %TRANSMITTANCE O6

- -9?- -

270°

FIGURE 29 88

2 0 7 - J F I 6 A CONSTANT SURPASS SOURCE TO MONOCHROMATOR 40 CM HO, POLAC^ZATIO^ SAMPLE TO MONOCHROMATOR 20 CM INCIDENT LIGHT POLARIZED VERTICAL WAVELENGTH - 4 MICRONS INCIDENT LIGHT POLARIZED HORIZONTAL % TRANSMITTANCE °° ao

270° SO*

180*

FXGO'RE 30 89 2 0 7 -J F lS CONSTANT SURFACE SOURCE TO MONOCHROMATOR 4 0 CM NO POLARIZATION SAMPLE TO MONOCHROMATOR SO CM INCIDENT LIGHT FOLARIZED VERTICAL WAVELENGTH - 4 MICRONS INCIDENT LIGHT POLARIZED HORIZONTAL

U TRANSMITTANCE

0°

4 5 70 315 >s

90' 270°

5 0

eo

135 2 2 5

FIGURE 31 90 2 0 7 - J F 16 A constant surface- bevel up ( fixed) 207-JFI8A SOURCE TO MONOCHROMATOR 40 CM. CONSTANT SURFACE (ROTATED) WAVELENGTH — 4 MICRONS DISTANCE FROM SAMPLE TO MONOCHROMATOR ------IO CM. ------2 0 CM. ------30 CM. <%) TRANSMITTANCE

0°

120 315

4 0

2 7 0

4 0

60

6 0

135 2 2 5 120

180°

FIGURE 32 91 207—JFI6A CONSTANT SURFACE SOURCE TO MONOCHROMATOR 40 CM. DISTANCE FROJI SAMPLE TO MONOCKJCOTOR WAVELENGTH — 4 MICRONS 10 CM. ------L 20 CM. ------3 0 CM % TRAN3MITTANCE

4 5 .315

-GO

90 ° - -270'

7 0 25

8 0------180i*

FIGURE 33 32 207- JP 18A CONSTANT SURFACE DISTANCE FROM SAMPLE TO MONOCHROMATOR SOURCE TO t'OriOCHnOUATOR COCfcS. ______, n c m WAVELENGTH — 4 MICRONS 2 0 CTJ- 3 0 CM. % TRANSMITTANCE

45' -— 70— 315

9CT 2 7 0 °

TO 135'

IE(0"

FIGURE 3h /

93

SOURCE TO IsSOMCCHRO&l&TOR 4 0 CM 2 0 7 - J F I 8 B SAMPLE TO KWNOCHRCMATOR 2 0 CM CONSTANT SURFACE WAVE LENGTH — 4 MICRONS % TRANSMITTANCE

0° — i o —

6 0 315

30

40

9 0 2 7 0

4 0

SO

60 35 2 2 5

7 0 __ 180°

FIGURE 35 9k 207—JFI6A CONSTANT SURFACE SOURCE TO MONOCHRCWATOR 4 0 CtS. SAMPLE TO MOJJOCKROJJATOR 2 0 CU ------3 .0 2 MM. ------2 .03 MM. ------I .g o MM. % TRAMSMITTAKCE

0° -80

-70 315'

7 0 135' 225'

180

FIGURE 36 VII. DISCUS5I0H OF RESULTS

i A. Tellurium Dioxide Base Glass

The three basic glass compositions, 207-GT, 207-HX, and 207-JF are given in figures 10, 11, and 12j all exhibit superior infrared transmittances when compared with silicate glasses. It is to be noted that 207-HX and 207-JF do not transmit as far out into the in­ frared as does 207-GT, this probably the result of arsenic pent oxide in the former two compositions. This component contributed to the diminution of the absorption bands at 3*25 end U*9 microns. Its in­ clusion was a compromise between reducing these absorption bands and shifting the long wavelength cutoff toward the visible. On the other hand, the addition of CaF^ to the 207-HX composition to give 207-JF does not greatly affect the transmittance of the resulting glass (com­ pare Figures 11 and 12).

Both the 207-HX and 207-JF compositions exhibited a caustic effect on the platinum container during melting to so pronounced a degree that each container could not be used for more than four melts. An investigation is now underway to find refractories suitable for melting these tellurium dioxide glasses.

B. Radiation Absorption Studies

As previously stated, the primary reason for the additions of the transition element oxides to the tellurium dioxide base glass was

95 96 to study their respective absorption influences, particularly those which were located within the spectral region 1.0 to 2.0 microns.

The quantitative relations of these additions are shown in Figures 1 through 7? i» which are included for comparison the spectral transmit- tances of silicate glasses having approximately equal amounts of these same transition element oxides.

A study of the valence states and coordinations of these trans­ ition element oxides in tellurium dioxide glasses has been made, and is listed below.

1. Vanadium oxide. According to Weyl (HO), vanadium, oxide in silicate glasses gives absorption bands centering at O.U25, 0,62%, and 1.15 microns, respectively. These absorption bands are enhanced if the glass is melted under oxidizing conditions. The absorptions at O.U25 and 0.62£ microns were attributed to the vanadic (V ) ion, while the absorption band at 1.15 microns was thought to be the re­ sult of tetravalent vanadium (or the vanadyl, VO^^). Additions of up to 5 percent vanadium oxide were made to the tellurium dioxide glass with no absorption bands appearing in the O.U to 2.0 micron region of the spectrum (see Figure l). One possibility for the absence of the absorption bands attributable to vanadium oxide could be that this oxide is functioning as a glass network former in the tellurium dioxide glass, and does not exhibit its customary coloring action. It has been recently shown in this laboratory that vanadium oxide can function 97 as a glass network fox'raer (1*1, 1*2).

/ 2. Chromium oxide. The color imparted to silicate glasses by chromium oxide has been attributed to two valence states of the chrom­ ium ion (19). Trivalent chromium absorbs at 0.1*5 and 0.55 microns, while the hexavalent ion gives an absorption band at 0.6 microns.

Melting a chromium oxide containing glass under oxidising conditions tends to increase the trivalent ion content. The addition of chrom­ ium oxide to a tellurium dioxide glass produces absorption similar to the trivalent chromium ion (see Figure 2). On this basis, it may be concluded that chromium has a valence of three in this tellurium di­ oxide glass when melted under oxidising conditions.

3. Manganese oxide. This oxide gives two absorption bands in silicate glasses, one at 0.1*3 microns attributable to the divalent ion, and one at 0.5 microns as a result of the trivalent ion (19). In tellurium dioxide glasses (Figure 3)j manganese oxide gives a faint semblance of an absorption band at 0.5 microns, which may be attrib­ uted to tri valent manganese.

Iron oxide. The coloring action of iron oxide in silicate glasses has been attributed to both the divalent and tri valent ions

(19). The divalent farm, gives an absorption at 1.10 microns, whereas the tri valent form can be either colored or colorless, depending upon its coordination. Ferric iron with a coordination of four is thought 98 to function as a network former and gives strong absorption in the ultraviolet which extends into the blue, so that brown colors result.

The ferric ion with a coordination of six is thought to function as a

network modifier, and is practically colorless (19). Weyl and Rudow

(U3) have been able to show that -the colored iron complex can be rend­

ered colorless by the additions of fluorides to ferric thiocyanate in aqueous solution; they attributed this to the formation of the color- . less FeF^” anion. Increasing the concentration of the fluoride not only diminished the intensity of the absorption band which originated

in the blue end of the spectrum, but shifted it toward the ultraviolet with an apparent broadening of the band. According to Weyl (19), a

similar phenomenon can be anticipated in glasses, when the fluorine

ion replaces the oxygen ion. Iron oxide in a tellurium dioxide glass

gives an absorption in the blue end of the visible spectrum, which

might be the result of a stronger absorption in the ultraviolet. Since there are no absorptions in the near infrared, it may be concluded that

most of the iron is in the trivalent form in this glass.

Cobalt oxide. Figure £ shows the effects of cobalt oxide

In a tellurium dioxide glass. There is a region of complete opacity

from about 0*50 to about 0.70 microns, and a broad diffuse absorption band extending from 0.8 out to 2.0 microns. This latter absorption was

thought to be the superposition of three distinct bands having centers at 1.35, 1.50, and 1.70 microns, respectively. According to Weyl (19), 99 the absorption as given by cobalt oxide is the result of the divalent cobalt ion. , Weyl and Thurman (1*1+) have shown that the cobalt ion with a coordination of four produces absorption bands at 0,5$, 0.60, and

0.65 microns, while this ion with a coordination of six gives only one band at 0.55 microns. A tellurium dioxide glass, in which the concen­ tration of cobalt oxide was 0.0625 percent, revealed that the opaque region, 0.525 to 0.675 microns (Figure $), was the result of three bands, having centers at 0.55, 0.60, and 0.675 microns^ these closely resemble those found in silicates. It is probable that cobalt exists with coordination numbers of both four and six in this tellurium di­ oxide glass.

6. Nickel oxide. The absorption produced by nickel oxide in a tellurium dioxide glass is shown in Figure 6 and is a little diff­ erent than that found in most silicates. Weyl (19) has stated that the absorption may be attributed to the divalent nickel ion. Nickel with a coordination of six produces an absorption at about 0.1*1+ mi­ crons, while a four-fold coordination gives bands at 0.1+3, O.83 , and

1.30 microns, respectively. Xn most silicate glasses, there is a combination of these two coordinations. The data indicate that nickel is in six-fold coordination in these tellurium dioxide glasses.

7. Copper oxide. The addition of copper oxide to the tellur­ ium dioxide glass produces an absorption band at about 0.8 microns, 1 0 0 and this is not much different than that found in silicates (see Fig­ ure 7)* This band is probably due to the cupric (+2) ion, since the cuprous ion is colorless in most glasses (19).

Of all of these additions of the transition element oxides, copper oxide was the only one which gave a useful absorption band in the spectral region 1. 0 to 2.0 microns. In Figures 8 and 9 are shown the effects of increasing the concentration of this oxide to its ap­ parent saturation limit in a 20?“GT and a 207-HX base glass.

It appears that a selective radiation filter of the type de­ sired cannot be obtained by the absorption of radiation alone.

B. Radiation Scattering Studies The effect of prolonging the time of heat treatment of these

207-JF disperse phase glasses generally tends to move the region of selective scattering of radiation toward longer wavelengths as shown in the following tables

Sample Heat Treating Apparent Short Thick- Figure Number Time at 800°F Wavelength Cutoff ness Number

207-JF11A 1 hour < 1 . 0 microns 3.13 Km 16 207-JF11B 1-1/it < 1.0 3.22 17 207-JF9A 1-3/U l.P 2.92 13 207-JF7A 2 1.25 2.96 lit 207-JF7B 1.3 2.96 15 207-JF17t^2 1.3 3.05 22 207-JF16A 3 1.2 3.02 21 207-JF18A 3i 1.5 3.07 2U

The term “cutoff” is loosely used here to indicate the limit of rapidly 1 0 1 decreasing transmittance. These data indicate that a moderately ef­

fective radiation filter can be produced as the result of a controlled

formation of a disperse phase in a tellurium dioxide glass. This

type of filter presents unique possibilities in that the short x*ave-

length "cutoff" may be positioned over a range of wavelengths. It

does not have, therefore, the inherent restrictions characteristic

of absorbing ions in glass. The data obtained from the samples heat

treated in the Hoskins furnace (207~JF7-A, 207-JF7B, and 207-JF9A) con­

form satisfactorily with those obtained from the copper block furnace.

The method of heat treatment as given by the copper block fur-

nace was not entirely reproducible. This is evident when a comparison

is made of the transmittances of 207-JF16A and 207-JF17 (see Figures

21 and 2 2 ), the former heat treated for 3 hours, the latter 2-| hours. This limited reproducibility may have resulted from: (a) variations

in the compounding of the initial batch, (b) slight differences in the melted glass due to volatilisation of some of the constituents, (c) variations in the temperature of the glass melt as it was placed into

the annealing furnace, and (d) temperature fluctuations during heat

treatment.

As expected, increasing the duration of heat treatment for a

constant heating temperature of 8 0 0 °F, tends to increase the particle

size of the disperse phase in these tellurium dioxide glasses. This

Is based on the fact that the region of selective scattering of radia­

tion exhibited by these disperse phase glasses has a definite tendency 1 0 2 to move to longer wavelengths upon prolonging the heat treating time*

The transmittance data and visual evaluation of these glasses were not entirely consistent* The transmittance data obtained frcsa the IR-2 spectrophotometer indicated that the spectral region below the short wavelength "cutoff" of glasses 207-JF7A, 207-JF7B, 207-JF16A,

207-JF17, and 207“JFX8A was opaque. This was not entirely true, for these glasses appeared translucent when viewed in the beam of a strong projection lamp. The transmittance of 207-JFlBA v/as measured on the

DU spectrophotometer through the spectral region O.I4 to 1.0 microns, and gave 6,0 percent at 1 . 0 micron decreasing down to aero at 0 , 6 mi­ crons. Various factors could have contributed to the difference in transmittances as measured on these two instruments. The HJ spectro­ photometer is designed to operate efficiently in the ultraviolet and visible portions of the spectrum. By extending the measurements out to 1 . 0 micron, the long wavelength limit for accurate readings is prac­ tically exceeded. Furthermore, the phototube detector of the HJ spec­ trophotometer is sensitive over a large area, and is arranged so that it can detect both, scattered and directly transmitted radiation. The detector in the IR-2 spectrophotometer is a thermocouple of very small area, and the optical system is such that the thermocouple detects less scattered radiation than does the DU. These differences in the optical systems of the two instruments could readily account for this discrep­ ancy in the transmittance data. It must not be overlooked, however, that some visible light is transmitted by these disperse phase glasses. 103 The values of the logarithm of lc (the combined scattering and

absorption coefficients) plotted against the logarithm of the wave­ length % , for glasses 207-JFllA, 207-JF9A, 207-JF7B, and 207-JF7A

is shorn in Figure 17* The values of k were obtained by measuring

the intensities of transmitted radiation for at least two thicknesses of each glass in the spectral region, 1.0 to 2.3 microns, and the changes in transraittance with decreasing thickness for these glasses

are shown in Figures 13, li*, l£, and 1 6 . These calculations reveal that glasses 207-JF7A, 207-JF7B, and 207-JF9A apparently scatter radia­

tion in conformance with the Rayleigh equation for shorter wavelengths,

but appear to exceed the required inverse fourth power factor for

longer wavelengths. Sample 207-JFllA on the other hand appears to ex­ ceed this inverse fourth power wavelength factor over the entire spectral region measured. It will be recalled that this specimen ex­

hibited marked differences in transmittance upon decreasing its

thickness (see Figure 16). The evaluation of lc for the plot of Figure

17 was obtained from the thinner two sections of this specimen*

The fact that these disperse phase glasses appear to scatter

radiation selectively in excess of that predicted by the Rayleigh equation might be attributable to several factors. It is not believed that the absorption of the base glass could be contributing to this departure, since the transmittance of a non-heat treated glass is ap­ proximately constant over the spectral region 1.0 to 2.3 microns. This was assumed in the evaluation of k. It may be that the relative indices 1 0 1 ;

of the disperse phase and medium approached or were equal to unity within this spectral region, and this could result in a Christiansen filter effect. This type of radiation filter may be produced by sus­ pending a crystalline or glassy powder in a transparent medium, and depends for its filtering action upon the equality of the refractive

indices for a particular wavelength. At -the wavelength where the re­

fractive indices of the powder and the medium are equivalent (which was designated as % c ), the filter will exhibit a high transmittance; at other wavelengths it will exhibit reduced transmittance* The rea­ son for this high transmittance lies with the fact that only at this particular wavelength is the filter optically homogeneous. Radiation of this wavelength will pass through the filter unaffected, while

radiations of all other wavelengths will undergo refraction, reflec­ tion, and diffraction at each particle-medium interface, and are scattered. Barnes and Bonner (1*5) have studied the effect of particle size on the Christiansen transmittance peak of quartz particles, with

air as the suspending medium; these measurements were taken through the spectral region 3.0 to 10.0 microns. They found that as the part­

icle diameter of the quartz particles decreased from 60 to 0 microns,

the Christiansen transmittance peak had a tendency to increase in in­

tensity and become broader. A similar phenomenon may be taking place

in these disperse phase glasses, since the departure from the predicted

Rayleigh value of four for the wavelength exponent becomes more pro­ nounced as the duration of the heat treatment is decreased, resulting 105 in smaller particle diameters of the disperse phase. This is only a hypothesis, 'since the change in indices with wavelength of the dis­ perse phase and medium are not known. Unfortunately the efforts to determine the nature and structure of the disperse phase by means of

X—ray studies were not successful, so that no positive conclusions can be reached at present as to the cause of the departure of these calculated slopes to values greater than that predicted by the Ray­ leigh equation.

The unusual transmittance data of samples 207-JF11A and 11B

(Figures 16, l8, and 19), can be partially explained by the observa­ tions made on later samples. At the time that these measurements were taken, the effect of the orientation of each individual surface had not been discovered. If these specimens had been properly oriented, par­ ticularly sample 207-JF11B, it is probable that the change in transmit­ tance with decreasing thickness would have resulted in data more in line with the expected. The effect of preferred orientation of the sample on the trans­ mittance is shown in Figures 20 and 21 for sample 207-JF16A. These orientations include "constant" surface (bevel up and down), and "var­ iable" surface (bevel up and down). It is to be noted that there is a certain similarity between the transmittances obtained with these four orientations, with the transmittance of the "constant" surface (bevel up), being equivalent to the measurements for the "variable" surface

(bevel down). Conversely, the readings for the "constant" surface 1 0 6 (bevel down), are equivalent, to those for the "variable" surface (bevel up). '

A wedge-shaped sample in which the thickness of the specimen decreased as measured along the 2$ mm edge could account for such differences in transmittance as observed with orientations of "con­ stant" surface (bevel up and bevel down). However, a wedge-shaped sample of this type could not of itself have produced the difference in transmittance as observed with orientations of "constant11 surface

(bevel up) and "variable" surface (bevel up), since with these two orientations, the thickness of the specimen would have been the same. In this respect, the thicknesses of samples 207-JF16A, 17, 18A, 18B, and 19 were measured and found to vary not more than 2 percent. The effect on the transmittance obtained by sectioning the sam­ ple out of the central portion of the larger glass slab is shown in

Figures 22 and 23 (sample 207-JFl?). It will be recalled that this particular method of sample selection was used to reduce the possibili­ ties of a variation in optical density as a cause of these differences in transmittance. The transmittance measurements for this specimen were taken with the same orientations as used for 207-JF16A. These data are similar to those obtained on the previous specimen, although the results are not as pronounced (compare Figures 20 and 21, 22 and 2 3 ).

One reason for this effect not being as marked in 207-JFL7 when compared to 207-JF16A could be in the degree of "effective" heat treatment. Al­ though 207-JF16A was heat treated for 3 hours in comparison to the 2% 107 hour heat treatment given 2G7-JF17, the region of selective scattering

of radiation'begins at 1.2 microns in the former, while commencing at

1.3 in the latter. This difference in the 51 effective” heat treatment

is further emphasized when a comparison is made between the maximum

transmittances of these two samples; 207-JF16A transmits more than 80

percent at U. 25 microns, while 207-JF17 does not exceed this transmit­ tance at this wavelength (compare Figures 20 and 21, 22 and 23).

The transmittances for these four orientations of sample 207=

JF18A are analogous to, but more pronounced than, those of the two

previous samples (see Figures 2i* and 25). This was no doubt due to

the longer heat treatment of this specimen (3-V hours), with the region

of selective scattering of radiation shifting to longer wavelengths.

In comparing the transmittances of samples 207-JF16A, 207-JF17, and 207-JP18A, several relations should be noted. First, the selec­

tion of the beveled edge used for orientation was arbitrary, a3 was

also the case for all succeeding samples. Second, each of these three samples, for orientations of "constant” surface (bevel down) and "var­

iable” surface (bevel up), gave transmittances which approximate that

of a transparent glass over the spectral region 3*5 to 6.0 microns (compare Figures 20 and 21, 22 and 23* 21* and 25, with Figure 12). It was therefore assumed that -the measurements as obtained for these par­

ticular orientations were the result primarily of rectilinear or spec­

ular transmittance, and that there was little diffuse radiation being

detected. For orientations of "constant” surface (bevel up) and 1 0 8 "variable” surface (bevel down), these three specimens gave reduced transmittances within the spectral region, 3*5 6.0 microns. Third, the region of selective scattering commences at the same wavelength, regardless of the orientation of the specimen. Since these specimens were capable of almost rectilinear transmittance at h *0 microns, this wavelength was selected for the rotational transmittance studies.

The complete rotational transmittance of 207-JF18A is shown in

Figures 26, 27, 28, and 29. These include data for no polarisation, polarised incident light, analysed transmitted light, and crossed polarizers. These measurements were all taken with UO cm as the source to monochromator distance, the sample to monochromator distance being

20 cm. The wavelength selected for these measurements was I4.O microns, a wavelength removed from the region of selective scattering. In some cases, the use of these polarizing units seemed to have a tendency to increase the transmittance for a particular surface or orientation of surface as compared with no polarization. The results of these polar­ ization studies, however, were negative. One interesting feature of these rotational transmittance data of sample 207-JF1 8 A is that the re­ sultant pattern for the "constant” surface is equivalent to that of the "variable” surface, but displaced through 180°® This held not only for no polarization, but for incident polarized light, analyzed transmitted light, and crossed polarizers (compare Figures 26 and 28,

27 and 2 9 ), That this rotational transmittance effect was not characteristic 1 0 9 of only one sample was shown by the measurements on 207-JF16A (see

/ Figure 30)* These readings were taken for "constant" surface only, with no polarisation and polarised incident light. These data are

not dissimilar to those of 207-JF18A for a comparable optical system (compare Figures 30 and 26).

Sample 207-JF19 was obtained by sectioning the large glass

slab across its diagonal; this specimen was heat treated for 3 hours.

This particular method of sample selection was used to detenaine, if possible, vmether these optical effects were the result; of the melt­

ing and annealing procedures, or a function of the heat treatment.

The rotational transmittance for this specimen was measured for the

"constant” surface without polarization and with polarization in­

cident light (see Figure 31). It is seen that the asymmetry of the

resulting transmittances is similar to that obtained from 207-JF16A and 207-JF18A, but has been rotated through 90° (compare Figure 31

with Figures 30 and 26). The discussion of the rotational transrait- tances of sample 207-JF19 will be deferred until a later portion of this section.

One of the interesting features observed with these disperse

phase glasses is shown in Figure 32$ the result of crossing two of the glasses exhibiting rotational transmittances (207-JF16A and 207-

JF1 8 A). In this experiment, 207-JF16A was aligned within the optical

system so that the collimated incident beam impinged normally upon

its "constant" surface. The instrument was standardised to 100 per**

cent after the incident beam had passed through this sample. Item n o 207-JF2.8A ixas then placed In front of 207-JF16A, so that the incident beam impinged upon its "constant" surface (bevel up)® Transmittances were measured, with 207-JF18A being rotated 360°, in increments of hS°»

It is to be noted that these results are not unlike those which would be observed by crossing two ordinary polarizer3, i.e. a maximum and minimum of transmitted intensity is produced. At this point, however, the similarity ceases, Ordinaiy polarizers, when rotated, exhibit two maximum and minimum transmittances in 360°, these occurring al- ternately with every 90 of rotation. These disperse phase glasses, on the other hand, have only one maximum and minimum transmittance with rotation of 36.0°, these occurring 180° apart. The orientations of these two specimens leading to a maximum of transmitted intensity yields a transmittance reading of greater than 100 percent, ^his is only a relative value, since -the IE-2 spectrophotometer was standard­ ized not against an air path, but against sample 207-JF16A. These val­ ues of greater than ICO percent were determined by re-standardizing the IR-2 spectrophotometer against the two specimens oriented so as to give maximum transmittance, removing sample 207-JF18A, and then de­ termining the resulting transmittance of 207-JF16A. A simple calcu­ lation yielded the transmittance of the two samples as a unit. lvhese results indicate that more radiation is transmitted with two thick­ nesses of glass, than with one. It was during the studies on crossing these two specimens that the effect of the distance between sample and monochromator was observed® i n Up to this point, all measurements on rotational transmittance had been taken with a source to monochromator distance of Jj.0 cm, sample to mono­ chromator 20 cm. It was found, however, that the rotational transmit- tances could be varied by changing the distance from the sample to mcno- chrcmatorj til is held not only for the transmittances of the crossed glasses, but also for these specimens taken individually (see Figures

32, 33, and 3k). It is seen that the intensity of this transmittance effect is reduced with increasing distance from sample to monochroma­ tor for the crossed specimens, but increases with increasing distance for the samples taken individually. Wo explanation has been found for these contrary data.

The rotational transmittance of 207-JF18B (heat treated for 6 hours) is seen in Figure 35, these resulting from “constant0 surface with no polarization— and with polarised incident light. These data are to be compared with those of samples 207-JF16A, 207-JF18A, and 207-

JF1$B(Figures 30, 26, and 31). Samples 207-JF16A, 207-JF18A, and 207-

JF18B were obtained by cutting the large glass slab into half; 2Q7-JF19 was obtained by cutting the large glass slab across its diagonal. All of these specimens were heat treated with the upper melted surface placed up in the copper block; during grinding of all of these samples, this surface was designated as the “constant11 surface. There are two apparent variables, (a) the manner in which the samples were selected, and (b) the time of heat treatment. Samples 207-JF16A and 207-JF18A 1 1 2 were selected in the same manner and given heat treatments of 3 and 1 3^ hours respectively. Their rotational transmittances are similar, with maxima at 90° and 270°, and minima at 0° and l80° (see Figures

30 and 26). Item 207-JF18B was selected in the same manner as these

two samples, but was given a heat treatment of 6 hours. Its trans­ mittance pattern, although similar to the previous samples, has been

rotated U$°t with maxima occurring at h$° and 22%° , and minima at

13f>° and 315° (see Figure 35). Sample 207-JF19, on the other hand, was sectioned across the diagonal of the large glass slab, but was

given a heat treating time identical with that of 207-JF16A. Its ro­ tational transmittance gives maxima at 0° and 180°, and minima at 90°

and 270 (see Figure 3x). It must be admitted that these data are not consistent. It would appear, however, that the time of heat treat­ ment probably contributes more to this transmittance effect than does the method of sample selection.

The result of grinding on what was originally designated as the "constant” surface reveals that the previously adopted method of grinding does not appreciably influence the optical effects obtained

(see Figure 36). It is noted that the rotational transmittance ef­ fect is present for a thickness of 3*02 mm, practically disappears for a thickness of 2.06 ram, and reappears for a l.*>0 mm section. It would appear that this effect is a function of thickness of the specimen and concentration of the disperse phase. These data, however, do not 113 give a clue as to the cause of these optical effects. ; That these -unusual transmittance effects are not characteris­ tic of only one instrument was established by the data obtained from

the IR-3 spectrophotometer. The transmittances of samples 207-JF16A,

207-JF17, and 207-JF18A were measured on this instrument through the

spectral region 1.0 to 6.0 microns, with orientations of "constant"

surface (bevel up and down), and ‘’variable*’ surface (bevel up and

down) | these results compared favorably but were more pronounced than

those obtained from the IR-2 spectrophotometer for a comparable spec­

tral region and orientation of sample. The data from the IR-3 have

not been included, because at the time these measurements were taken,

this instrument was not in calibration for wavelength. These results,

therefore, could be treated only in a qualitative manner. The design

of the IR-3 spectrophotometer did not permit the complete rotational transmittance of these specimens to be easily measured.

Another aspect of these unusual optical properties is that these differences in transmittances are not observed when the beam incident upon the sample is convergent. This was brought to light when the transmittances of sample 207-JF16A were measured on the

Perkin-Elmer Double Beam Spectrophotometer, Model 21, -through the spectral region 1.0 to 6.0 microns, with orientations of “constant" surface (bevel up and down), and "variable" surface (bevel up and down). Mo difference in transmittance with direction or orientation could be found. Both the IR-2 anod IR-3 spectrophotometers impinge collimated radiation normally upon the sample.

Since' these rotational transmittance effects were not observed with a non-lieat treated glass, it may be concluded that these unusual

optical properties result from the presence of the disperse phase,

this produced by heat treatment. The length of the heat treatment

can also affect these transmittances. The X-ray diffraction work would seem to emphasize the first conclusion, since the data from a heat treated sample gave a pattern characteristic of a crystalline ma­

terial, while the data from a non-heat treated specimen resulted in a pattern characteristic of a glassy substance.

These differences in transmittance with rotation of the dis­ perse phase glasses may be partially due to the characteristics of the IR-2 spectrophotometer. This instrument was designed to impinge collimated radiation upon the specimen being tested, the entrance op­ tical element of the monochromator being a converging lens. It may be, with certain orientations of the disperse phase sample within the op­ tical system, that the transmitted radiation incident upon the converg­ ing lens of the monochromator is not collimated. At I4..O microns (the wavelength at which all of the rotational transmittance measurements were taken), these disperse phase glasses are capable of almost recti­ linear transmittance with certain orientations of the specimen, and these apparent transmittances were in all probability the result of collimated radiation incident upon the converging lens of the mono­ chromator. With other orientations of the sample, the transmittance 1XS at this wavelength was reduced* this possibly due to diffuse radia- ) tion incident upon this converging lens* Factors such as these may be contributing to the optical effects observed with the disperse phase glasses.

In comparing all of these rotational transmittances, especial­ ly those in which non-polariscd radiation was used, one feature stands

out. The asymmetry of the patterns obtained resembles that which

would be produced by crossing two ordinary polarizers. It is a possi­ bility that these disperse phase glasses are introducing some peculiar

type of polarisation which is not only detected, but analyzed in some

fashion by the monochromator of the IR-2 spectrophotometer. This

concept of the monochromator acting as an analyzer of polarized radia­ tion is not entirely out of line, since the transmitted radiation is

doubly dispersed through a prism before it Is finally detected. It is

possible that this transmitted radiation could be partially analyzed by

reflection (at or near Brewster’s angle), from the surfaces of this prism. In this event, it would appear that the use of the infrared polarizing units (as was the case in some of these rotational trans­ mittance experiments) would have given measurements indicating that this phenomenon was taking place. The actual data, however, do not

confirm this. This phenomenon of rotational transmittance has been discussed with various members of the Faculty, but no plausible solution resulted. They seem to believe that these effects are real and not merely the result of the fact that no instruments directly suited to this par­ ticular problem are available. VIII. SUMMARY AMD COMCLUSIOMS

In reviewing the information obtained during the course of this investigation, the following salient points may be established:

1. Tellurium dioxide functions as a glass network former* Some glasses derived from this oxide exhibit superior infrared transmittance when compared to silicate glasses, these being transparent from 0*1* to

6,0 microns*

2. The absorption bands (attributed to the presence of hydroxyls within this glass structure) constituted more of a problem than encoun­ tered in previous glass systems. Composition modifications are more effective in reducing the intensities of these absorption bands than was the control of the melting atmosphere.

3. Additions of inorganic colorants to the tellurium dioxide­ glasses studied generally produce specific absorption of visible and near infrared radiation not radically different from those In silicate glasses. The marked exception to this was vanadium oxide, which did not produce any absorption in the spectral region, O.li to 2.0 microns.

1*. Radiation absorption studies reveal that a filter which is opaque through the visible spectrum out to 1.5 microns and transparent at longer wavelengths, cannot be affected by additions of inorganic

1 1 7 1 1 8 colorants to these tellurium dioxide glasses.

S A moderately effective selective radiation filter of the type just described can be produced by a controlled formation of a disperse phase in these tellurium dioxide glasses* This disperse phase can be developed by a controlled heat treatment.

6. These types of radiation filters are characterised by the fact that the location of their short wavelength "cutoff*3 (limit of rapidly decreasing transmittance), may be shifted to longer or shorter wavelengths depending upon the duration of the heat treatment. The spectral region below the short xxavelength "cutoff" of these radiation scattering filters is not completely opaque. Additions of the favor­ able inorganic colorants to these disperse phase glasses upset the scattering relations and structures investigated.

7. The selective scattering of radiation exhibited by these disperse phase glasses appears to conform with the inverse fourth power wavelength factor as given by the Rayleigh radiation scattering equa­ tion, in some spectral regions. In other spectral regions these glass­ es apparently scatter radiation in excess of this fourth power factor.

8. A completely effective radiation filter could possibly be produced with a duplex or doublet unit, one portion of which absorbs the visible, the other portion selectively scattering the near infrared radiation. 119 9* These radiation scattering glasses appear to have a pre­ ferred orientation with regard to maximum transmittance. These differences in transmittance may be due in part to the optical ar­ rangement of the infrared spectrophotometer on which the measurements were taken, but it is thought that they seam to be primarily a func­ tion of the structure of the filters.

10o It is not thought that a divergence from plane parallel surfaces of the specimens could account for the observed effects.

11. The unique optical properties exhibited by these disperse phase glasses are not the result of ordinary polarisation.

12. The nature and sise of the particles of the disperse phase could not be determined by the microscopic and X-ray methods used.

It would appear that the surface has just been scratched in this work on disperse phase glasses. Undoubtedly radiation filters of this type can find wide application, particularly in scientific endeavors. The effect of rotational transmittance is very intriguing, and should be investigated in more detail. IXo BIBLIOGRAPHY

1. Gerlovin, J. I., Acad. Sci. USSR, 38, $, 170 (1938). 2. Florence, J. M., Glaze, F. W., Hahner, C. H., and Stair, R. J., J. Research K. B. S., hi, 623 (19U2).

3. Stair, R., Glaze, F. W., Ball, J. J,, Glas3 Ind., 30, 331 (19U9).

h. Florence, J. M. , Allahouse, C. C., Glaze, F. W., Hahner, C. H., J. Research N. 13. S., U5, 121 (1950).

5. Harrison, A. J., J. Ainer. Cer. Soc., 30, 363 (19U7).

6. Daniels, F,, Outlines of Physical Chemistry, John Wiley and Sons, Inc., New York, 19h^.

7. Herzberg, H., Infrared and Raman Spectrum, D. Van Nostrand Co., New York, i9h5. 8. Wood, R. M., Physical Optics, 3rd Ed., Macmillan Co., New York, 1936. 9. Anderson, S., j. Aaer. Cer. Soc., 33, h5 (1950).

10. Simon, I., and MacMahon, H. 0.s J. Amer. Cer. Soc., 36, 160 (1953).

11. Chothia, B. S., "Glass to Transmit Infrared Radiation,” Ph.D. Dis­ sertation, The Ohio State University, 19h9. 12. Lorey, F. D«, "The Development of Infrared Transmitting Glasses,” Master's Thesis, The Ohio State University, 3,950.

13. Shonebarger, F. J., "Glass to Transmit Infrared Radiations," Mas­ ter's Thesis, The Ohio State University, 1951* lh. Stanworth, J. E., J. Soc. Glass Tech., 3h, 217 (1952). 15. Pauling, L., The Nature of the Chemical Bond, Cornell University Press, Ithica, New York, 19UEH

1 6 . Zachariasen, W. H., J. Amer. Chem. Soc., 5U, 38hl (1932).

17. Goldschmidt, V. M., Vid-AKAD-SKR-Oslo, 8, 137 (1928).

1 2 0 1 2 1 18. Zsigmondy, R., Ann. Physik., h, 60 (1901).

1 19* VJeyl, W. A., Coloured Glasses, The Society of Glass Technology, Sheffi eld, l&igland, 1951*

20. Bachman, G. S., Glass Ind., 28, 631 (19l7).

21. Frits-Schmidt, M., Gohloff, G*, and Thomas, M., Z. tech. Physik., 11, 289 (1930). ”

22. Rayleigh, Lord, Phil. Mag., 1*7, 375 (1899). 23. Pile, G., Ann. Physik., 25, 337 (1908)<,

2U. Rayleigh, Lord, Proc. Royal Sec. (London), 90A, 219 (1911*).

25. Schuster, Aop Astrophys J., 21, 1 (1905).

26. Ryde, J. Wo, and Cooper, B. S., Proc. Roy. Soc. (London), 131A, U51 (1931).

27. Ryde, J. W . , and Yates, D. E., J. Soc. Glass Tech., 10, 27U (1926).

2 8 . Lax, C., Pirani, M., and Schoriborn, H., Licht und Lampe, 17, 173* 209 (1928).

29. Pfund, A. H., Phy. Review, 36 (1), 70 (1930).

30. Pfund, A. H., J. Opt. Soc. Am., 23, 375 (1933).

31. Pfund, A. H., J. Opt. Soc. Am., 2h„ Ik3 (193U).

32. Plummer, J. H., J. Opt. Soc. Am., 26, h3U (1936).

33* HLau, H. H., Ind. and Shg. Chem., 25, 81*8 (1933).

3U« Nacken, J., Jahrb Miner., 2, 133 (I9l5)« 35. Tammann, G., Kristalllsieren und Schmelzen, Leipzig, 1903.

36. Kitaigorodsky, I., and Kurovskaja, S, I., J. Soc. Glass Tech., 16, 210 (1932). 37. Mills, R. E., nA Polarizer for Infrared Radiation," Master*s Thesis, The Ohio State University, 1952. 122

3 8 . Berzelius, J. J., Annalen der Physik. und Chenie., 32, 577 (183U). * "

39. Lenher, V.3 and Wolensensky, E.a J. Amer. Chem. Soc., 35>* 718 (1913). ” "

I4.0 . VJeyl, VJ. A., Pincus, A. G. , and Badger, A. E., J. Amer. Cer. Soc., 22, 37h (1939). 1*1. Graham, H. Ao, ‘‘Vanadium Oxide as a Glass Network Former, ” Master*s Thesis, The Ohio State University, 195U. 1*2. Morris, A. S., “Vanadium Oxide Glass, Its Structure and Thermal Properties," Master’s Thesis, The Ohio State University, 195U. U3. VJeyl, VJ. A., and Rudou, H., Z..anorg. (hem., 226, 3l*l (1936).

U*. Weyl, W. A., and Thurman, E., Glastech. Ber., 11, 113 (1933)-

1*5. Barnes, R. B ., and Bonner, L. G., Phy. Rev., 1*9, 732 (1936). X. AUTOBIOGRAPHY

I, Charles L. McKinnis, was born in Cape Girardeau, Missouri, July 10, 1923. I received my secondary school education in the public schools of that city. The period 191*3 to 191*6 was spent in the Armed Forces. My undergraduate training was obtained at The

Southeast Missouri State College, Bachelor of Science (Chemistry

Major), 191*6, and The University of Missouri School of Mines and

Metallurgy, Bachelor of Science in Ceramic Engineering, 191*7- While a recipient of the A. P, Green Firebrick Company Fellowship in Ceramic Engineering, I received the degree Master of Science in

Ceramic Engineering from The University of Missouri School of Mines and Metallurgy in I9I48. From 191*8 to 195?0, I was employed by the

Pittsburgh Plate Glass Company in their Glass Division Research

Laboratory as a Research Engineer. In 195>0 I was appointed as an assistant to Dr. H. H. Blau at The Ohio State University, and acted in this capacity until I95>2 . During this period I enrolled in the Graduate School of The Ohio State University. I was appointed a

Research Associate by The Ohio State University Research Foundation in 1 9 5 2 , and have held this position for two years while completing the requirements for the degree Doctor of Philosophy.

123