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