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NIST Special Publication 945

Guide to the Nomenclature of Technology for Ceramic Systems

Vincent A. Hackley

!57

(0.945

•000 rhe National Institute of Standards and Technology was established in 1988 by Congress to "assist industry in the development of technology . . . needed to improve product quality, to modernize manufacturing processes, to ensure product reliability . . . and to facilitate rapid commercialization ... of products based on new scientific discoveries." NIST, originally founded as the National Bureau of Standards in 1901, works to strengthen U.S. industry's competitiveness; advance science and engineering; and improve public health, safety, and the environment. One of the agency's basic functions is to develop, maintain, and retain custody of the national standards of measurement, and provide the means and metliods for comparing standards used in science, engineering, manufacturing, commerce, industry, and education with the standards adopted or recognized by the Federal Government. As an agency of the U.S. Commerce Department's Technology Administration, NIST conducts basic and applied research in the physical sciences and engineering, and develops measurement techniques, test methods, standards, and related services. The Institute does generic and precompetitive work on new and advanced technologies. NIST's research facilities are located at Gaithersburg, MD 20899, and at Boulder, CO 80303. Major technical operating units and their principal activities are listed below. For more information contact the Publications and Program Inquiries Desk, 301-975-3058.

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'At Boulder, CO 80303. ^Some elements at Boulder, CO. NIST Svecial Publication 945

Guide to the Nomenclature of Particle for Ceramic Systems

Vincent A. Hackley

Ceramics Division Materials Science and Engineering Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-8520

February 2000

U.S. DEPARTMENT OF COMMERCE William M. Daley, Secretary

TECHNOLOGY ADMINISTRATION

Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY Raymond G. Kammer, Director National Institute of Standards and Technology Special Publication 945 Natl. Inst. Stand. Technol. Spec. Publ. 945, 24 pages (February 2000) CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2000

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, DC 20402-9325 Guide to the Nomenclature of Particle Dispersion Technology

Preface

It is generally agreed that measurements and standards play an integral role in the manufacture of ceramic materials. They enhance reliability by providing a basis for quantifying and comparing material properties during each of the manufacturing process, from raw materials to the finished product. Equally important is the establishment of a uniform and widely accepted nomenclature to permit the efficient exchange of scientific and technical information, and to provide a sound basis on which to standardize measurement methods and data reporting practices.

In June 1997, NIST established the Ceramic Processing Characterization Council (CPCC)"^ to assist the U.S. ceramics industry in the development of measurements and standards infrastructure. The CPCC is a voluntary, cooperative program among NIST, universities, private companies, other government research laboratories and private sector laboratories. A pnncipal goal of the consortium is to develop guidelines and recommended practices for the implementation of process measurements. Within the CPCC, the Dispersion & Working Group (DRWG) is responsible for addressing those measurement issues associated with in media. DRWG members quickly recognized the fundamental importance of terminology to any measurement-based strategy, and subsequently initiated a project to develop a uniform nomenclature for dispersion systems.

An ad hoc committee was formed, whose members included J.H. Adair (Penn State), J.A. Casey (IBM), R.A. Condrate (Alfred), M. Frey (3M), V.A. Hackley (NIST), W. Hunt (3M), A. Jillavenkatesa (NIST), M.J. Mayo (Penn State), G.Y. Onoda (NIST), P. Somasundaran (Columbia), and T. Wood (3M). The committee was charged with reviewing the technical content and language of the nomenclature, which I had volunteered to compile. Several revisions were passed through the committee before a draft version was circulated for comment by CPCC members at large. In addition to the committee review, two distinguished authorities in the particle science field, Bob Hunter at the University of Sydney and George Scherer at Princeton, were invited to review the nomenclature and provide input according to their respective areas of expertise. Their help is gratefully acknowledged.

In compiling this nomenclature, every effort was made to maintain a degree of uniformity with existing standards and conventions. To this end, the cooperation of the American Chemical Society and the International Union on Pure and Applied Chemistry (lUPAC) were instrumental.

To help put this nomenclature into practice, I have prepared this special publication. It is my general hope that it will serve as a resource to those working in particle dispersion applications, particularly in the ceramic sciences. It is my further hope that this document will serve to promote the establishment of a commonly recognized system of terminology throughout the ceramics community.

^ Formally known as the Ceramic Processing Characterization Consortium.

in Guide to the Nomenclature of Particle Dispersion Technology

Table of Contents

PREFACE Hi

I. INTRODUCTION 1

2. DEFINITIONS 1

2.1 Physical Description of Dispersed Systems 1 Related Terms 2 Recommendations 3 2.2 States of Subdivision (dispersed phase) 3 Definitions Based on Size 3 Definitions Based on Structure 3 Related Terms 4 Recommendations 5 2.3 Association and dissociation Processes 5 Association Processes 5 Dissociation Processes 6 Related Terms 6 Recommendations 7 2.4 Dispersion Stability 7 States of Stability 7 Stability Mechanisms 7 Interaction Terms 8 Related Terms 9 Recommendations 10 2.5 Interfacial and Electrokinetic Properties 10 The Interface 10 Adsorption Processes ' 11 Electrical Properties 12 Electrokinetic Effects 13 Related Terms 14

3. BIBLIOGRAPHY 16

3.1 Primary Sources 16 3.2 Secondary Sources 16

ACKNOWLEDGEMENTS 17

LIST OF REVIEWERS AND CONTRIBUTORS 17

INDEX TO DEFINED TERMS 18

iv Guide to the Nomenclature of Particle Dispersion Technology

GUIDE TO THE NOMENCLATURE OF PARTICLE DISPERSION TECHNOLOGY FOR CERAMIC SYSTEMS

1. INTRODUCTION framework for improved technical communication. The use of nomenclature for identifying dispersed particle systems, along with their The terms are organized into five

associated properties and components, is subsections, each dealing with a specific

often inconsistent and subject to aspect of dispersion: (1) physical description misinterpretation in the ceramic and of dispersed systems; (2) states of materials science literature. For example, subdivision; (3) association and terms for describing the state of association disassociation processes; (4) dispersion of in (e.g., aggregate or stability; and (5) interfacial and electrokinetic agglomerate) often carry specific properties. Acceptable alternative connotations that vary among different expressions and common abbreviations are authors. In an attempt to standardize usage of shown in parentheses adjacent to the defined dispersion terminology, and as a resource for term. In general, the American Chemical researchers, engineers and students, an Society's formalism for abbreviations has internally consistent system of nomenclature been adopted here."^ has been developed. In compiling definitions, a variety of sources were examined, In some cases, a definition may have two including lUPAC' recommendations, current parts; one more general in context and the and draft ASTM^ and ISO^ standards, and other more specific to ceramic applications. published materials drawn from both the Recommendations are also provided, for ceramic and the more general and instance, regarding the discontinuance of interface science literature (see the terms deemed ambiguous or obsolete, and are bibliography for a complete list of primary presented at the end of each subsection. and secondary sources). Within each definition, separately defined terms are identified in italics at their first

Definitions have been written first and occurrence. In addition, an alphabetized

foremost to serve those people in the index to defined terms is provided. ceramics field, but should be of equal utility to those involved in a broad range of dispersion-based non-ceramic applications. 2. DEFINITIONS

This is not, nor is it intended to be, an exhaustive compilation. Rather, this 2.1 Physical Description of Dispersed document focuses on commonly encountered Systems terms, and endeavors to provide a consistent Droplets or particles dispersed in a gaseous phase.

' International Union on Pure and Applied Chemistry ^ American Society for Testing and Materials ^ 2"" International Organization for Standardization The ACS Style Guide, Edition, 1997.

1 Guide to the Nomenclature of Particle Dispersion Technology

Continuous Phase consolidating the phase (e.g., by Constituting the dispersion medium, a slip-casting, tape-casting, or spray phase that exhibits continuity throughout drying). the dispersion; e.g., the Hquid in a suspension. Slurry A concentrated ceramic particulate Dispersed Phase (Discontinuous Phase) suspension.

In a dispersion, the phase that is distributed in the form of discrete discontinuities (particles, droplets or A liquid dispersion containing particles bubbles), in a second immiscible phase of colloidal dimensions. that is continuous. Suspension Dispersion A liquid in which solid particles are In general, a two-phase system in which dispersed. discontinuities of any kind (solid, liquid, ) are dispersed in a continuous phase Related Terms of a different composition or state; more specifically in the field of ceramics, the Heterodisperse term dispersion is used to describe a Describes a polydisperse particulate suspension of solid particles in a liquid system in which more than one discrete medium. size distribution mode occurs; e.g., bimodal, trimodal, etc. A dispersion consisting of two or more Monodisperse liquid phases. Realistically, all dispersions exhibit a finite spread in their particle size Hydrosol distribution. In practice, the term A sol in which forms the monodisperse can be used to identify a dispersion medium. dispersed system in which all particles are of nearly the same size, forming a Liquid Phase narrow (unimodal) distribution about an

Consisting of a condensed fluid; e.g., the average value. Numerically, a dispersion dispersion medium in a suspension. may be considered monodisperse if 90%

of the distribution (1.645a, where o is the Organosol standard deviation of the size

A sol in which an organic liquid forms distribution) lies within ±5% of the the dispersion medium. average size, (d):

Particulate Phase (Solid Phase) l^<0.05 The particles in a suspension, gel, or id) aerosol.

Polydisperse Slip Describes a dispersed system in which A term that refers to a suspension many particle sizes occur. In practice, a prepared for the expressed purpose of system may be considered polydisperse if

2

i Guide to the Nomenclature of Particle Dispersion Technology

less than 90% of the size distribution roughly 100 nm, and exhibit properties (1.645a, where a is the standard not normally associated with the bulk deviation of the size distribution) Hes phase (e.g., quantum optical effects).

within ±5% of the average size, (d): Colloid State of subdivision implying that the particles have at least in one direction a

dimension roughly between 1 nm and 1

|Lim. are significantly affected by Well-Dispersed when suspended in a A term used to describe a stable liquid. suspension in which the minimum particle size has been achieved. Ultrafine Recommendations State of subdivision implying that the particles have in any given direction a maximum dimension lying roughly Relative Concentration Terms between 1 \im and 10 ]xm. It is recommended that relative descriptive terms relating to particle Fine (Subsieve Range) concentration in suspension (e.g., dilute State of subdivision implying that the or concentrated) be defined in such a particles have in any given direction a manner that the reader has a clear maximum dimension less than roughly understanding of their relevance to the 37 [im. measurement or application at hand. For instance, in a light scattering (Sieve measurement, "dilute" may infer the Coarse Range) State of subdivision implying that the absence of multiple scattering, whereas in particles have in any given direction a an ultrasonic measurement this term may imply a linear response with dimension greater than roughly 37 [im. concentration. These conditions may vary by several orders of magnitude with Granule respect to particle concentration. State of subdivision generally referring to Concentration can also by defined on a dry particulates with dimensions lying more fundamental basis, taking into roughly in the 50 |Lim to 200 |Lim range; consideration the relative dominance of typically, granules are aggregates of finer thermal, hydrodynamic, or surface forces particles produced by spray-drying. in controlling suspension properties. Granulation is performed for ease of handling during subsequent consolidation 2.2 States of Subdivision (Dispersed operations. Phase) Deflnitions Based on Structure Deflnitions Based on Size Particle Nanosize (Nanophase) Any condensed-phase tridimensional discontinuity in a dispersed system may A special state of subdivision implying considered a particle; e.g., that the particles (or atomic clusters) generally be have average dimensions smaller than droplets in an emulsion or

5 )

Guide to the Nomenclature of Particle Dispersion Technology

dispersed in a liquid. The term is generally characterized by a loose normally used in reference to solid structure (low density). materials. An aggregate may also be regarded as a particle. Powder A relatively dry, undispersed Droplet accumulation of particulate matter with a Liquid-phase particle in an emulsion or macroscopic consistency. aerosol. Particulate Bicontinuous structure with a solid and a Composed of distinct particles. liquid component. The solid network may consist of particles or polymers, held Primary Particle together by covalent, ionic, or dispersion Smallest identifiable subdivision in a (physical) forces. The network may be particulate system. Primary particles may elastic, viscoelastic, or . The scale also be subunits of aggregates. of the mesh of the network (distance

between cross links) is of colloidal Microsphere dimensions. Refers to a spherical particle in the micrometer size range. A porous solid produced from a gel in

Aggregate such a way that very little shrinkage A cohesive mass consisting of particulate occurs. Typically, the term refers to subunits. materials made by supercritical extraction of the solvent, although structurally Hard-Aggregate equivalent materials can be made under An aggregate that cannot be easily ambient conditions by increasing network redispersed by the application of stiffness and/or elastic recovery, and by moderate mechanical agitation (shaking, reducing interfacial tension. stirring, or ultrasonication) and/or mild chemical treatment. Hard-aggregates Alcogel consist of subunits that have been A gel containing an alcoholic hquid chemically bonded or fused. phase.

Agglomerate Hydrogel In a suspension, an aggregate held A gel containing an aqueous liquid phase. together by physical or electrostatic forces. Xerogel Porous solid made by drying a gel under

Coagulate (Coagulum subcritical conditions. In a suspension, an aggregate formed by the addition of electrolyte. Related Terms

Floe Average Agglomeration Number (AAN) In a suspension, an aggregate formed by An estimate of the degree of the addition of a . Floes are agglomeration in a suspension. AAN is

4 Guide to the Nomenclature of Particle Dispersion Technology

the average number of primary particles characteristic dimension used in contained within an agglomerate. AAN is determining the MPS should be clearly calculated from the ratio of the median noted (e.g., mean size, median size, particle size, as determined by, for modal size, etc.). example, light scattering, or electrical zone sensing techniques, to Ultimate Working Unit the average equivalent spherical volume An individual particle or group of (Vbet) given by the BET gas adsorption particles that retains its structure method, such that: throughout a dispersion process and subsequent application. See also D^^ SSA 50 _ ( p AAN^ minimum particle size. BET Recommendations where V50 is the equivalent spherical volume calculated from the median Floccule diameter, D50 in jim, SSA is the specific It is recommended that this term not be surface area in m^/g and p is the particle used in the ceramic literature, (see Floe) density in g/cuv'. Hard, Soft Equivalent Spherical Diameter With the exception of the defined term

The diameter of a sedimenting particle hard-aggregate, it is recommended that determined from Stokes' law and such adjectives be avoided in the context assuming a spherical shape. The term is of dispersed phase structure. If their use sometimes used in conjunction with other is deemed necessary to convey material- measurement techniques and theoretical specific information, then the author constructs, where spherical geometry is should make a clear statement that assumed. defines the meaning and extent of usage.

Fractal 2.3 Association and Dissociation Processes A structure that has an irregular geometry under all scales of observation (i.e., it is Association Processes non-Euclidian). The fractal dimension of a species, Df, is the exponent to which a Aggregation characteristic length scale must be raised A general term defined as any process by to obtain proportionality with the overall which particles collect to form a cohesive size of the species. Destabilized mass or cluster; the resulting structure is suspensions tend to form aggregates with called an aggregate. fractal structures. In this case, Df has a value lying between 1 and 3, where Df=3 Agglomeration is a fully dense object. Formation of aggregates in a suspension through physical (van der Waals, Minimum Particle Size (MPS) hydrophobic) or electrostatic forces. The An experimental quantity operationally resulting structure is called an defined as the minimum particle size that agglomerate. can be achieved by a particular dispersion process as determined by an appropriate measurement technique. The

5 Guide to the Nomenclature of Particle Dispersion Technology

Coagulation sedimentation, or . A specific type of agglomeration in

which formation of aggregates is induced Perikinetic Aggregation by the addition of electrolyte to a The process of aggregation induced by

suspension. The resulting structure is Brownian motion. termed the coagulate or coagulum, while

the electrolyte additive is termed the Sol-gel coagulant. Process for making a gel from colloidal or molecular precursors. Formation of aggregates in a suspension Dissociation Processes mediated by polymeric species, that are either attached to the particles or exist Deagglom eration

freely in the suspending medium. The Reversal of agglomeration, i.e., the

resulting structure is called a floe, while dispersion of agglomerates to form a

the polymer additive is termed a suspension. flocculant. Polymer bridging is a flocculation process. Deflocculation

Reversal of flocculation, i.e., the Gelation dispersion offloes to form a suspension. Formation of a continuous (space-filling) solid network characterized by a finite Comminution static shear modulus (stress/strain ratio); Breaking down large pieces to the results from percolation of bonds required size; term commonly used in between particles or polymers. The association with milling of ceramic

resulting structure is termed a gel. slurries.

Fusion Process by which particles form Refers to the reversal of agglomeration irreversibly bonded structures; often by the addition of a strong acid or strong characterized by the appearance of base, such as HCl or NaOH. interparticle necks, (see also hard- aggregates) Related Terms

Heteroagglomeration, -Limited Rate Heterocoagulation, Heteroflocculation Refers to a rate of aggregation Generally refers to the aggregation of corresponding to the frequency of dissimilar particles; in ceramic encounter (collision rate) of the particles. applications, the formation of aggregates Each collision results in particle

by the cohesion between particles of adherence (i.e., a sticking probability

different materials (e.g., alumina and equal to 1). The rate of encounter is silica). controlled by the diffusion rate, which depends on the viscosity of the medium, Orthokinetic Aggregation the dimensions of the particles, and the The process of aggregation induced by concentration of the particles. hydrodynamic motions, such as stirring.

6 Guide to the Nomenclature of Particle Dispersion Technology

Reaction-Limited Rate rates that depend on the magnitude of the Refers to a rate of aggregation that is activation energy barrier that separates controlled by the reactivity of the them. panicles (i.e., the frequency of collisions resulting in particle sticking). Usually Kinetic Stability characterized by a sticking probability Most dispersed systems are much less than 1. A low sticking thermodynamically unstable, relative to probability results from the presence of their separate bulk phases; however, a an energy barrier. dispersion may exist for an appreciable length of time and therefore exhibit Syneresis kinetic stability. The term may be used in Spontaneous shrinking of a gel with reference to various destabilizing

exudation of hquid. processes, e.g., aggregation, coalescence, or sedimentation. Ultrasonication Application of high-energy, high- Stable Suspension frequency sound to a suspension in order A suspension that has sufficient kinetic

to disperse aggregates. Dispersion is stability to prevent the occurrence of thought to arise from the energy released significant aggregation as measured over during fluid cavitation. a relevant time frame. Stability may be ascertained by suitable experimental Recommendations means, such as particle size, turbidity, or sedimentation measurements. Sonication, Sonification

It is recommended that these terms not be Unstable Suspension used in the ceramic literature, (see A suspension that lacks kinetic stability Ultrasonication) as measured over a relevant time frame; a

highly unstable suspension is one that is 2.4 Dispersion Stability subject to rapid {diffusion-limited) aggregation. States of Stability Stability Mechanisms Colloidal Stability A physical state that characterizes the Electrostatic Stabilization relative ability of colloids to remain Mechanism in which aggregation is dispersed in a liquid; suspensions that do inhibited by the presence of a mutually not aggregate at a significant rate are said repulsive electrostatic potential that to be colloidally stable. The precise surrounds each particle. connotation depends on the time frame

under consideration. Colloidal stability is Steric Stabilization

a form of kinetic stability, and is Mechanism in which aggregation is therefore considered a metastable inhibited by the presence of an adsorbed thermodynamic state. From this polymer layer that is firmly anchored to perspective, aggregation may be the particle surface so as not to desorb described as a transition from a during collisions. In general, a steric metastable to a stable state, occurring at stabilizing agent has one portion of its

7 Guide to the Nomenclature of Particle Dispersion Technology

structure that exhibits low solubihty in increasing separation distance. The the dispersion medium and/or high primary maximum results from the fact affinity for the particle surface, and the that repulsive and attractive forces decay other portion is soluble in the medium. at different rates as a function of separation distance. In DLVO theory, a Electrosteric Stabilization large primary maximum acts as an energy

Mechanism in which aggregation is barrier, preventing aggregation of inhibited by the combined effects of particles into the primary minimum. electrostatic and steric stabilization. Usually associated with the adsorption of Primary Minimum polyelectrolytes onto the particle surface. The first appearance of a minimum in the interaction potential curve with Depletion Stabilization increasing separation distance. The

Mechanism in which aggregation is primary minimum results from the fact inhibited by the presence of free (non- that repulsive and attractive forces decay adsorbed) polymer due to the creation of at different rates as a function of

high-energy depletion zones (i.e., separation distance. In DLVO theory, a depleted of polymer compared to the bulk deep (negative) primary minimum acts as ) between closely interacting an energy well, allowing particles to particle surfaces. adhere and resulting in a loss of colloidal

stability. Interaction Terms Secondary Minimum DLVO A shallow energy minimum (usually of An abbreviation for a theory of the the order of a few kT) in the interaction stability of colloidal dispersions potential curve occurring at relatively describing the pair-wise interaction large separation distances beyond that of between charged particles in a dielectric the primary maximum. In the presence of medium. The theory, derived such an energy well, secondary minimum independently by Derjaguin and Landau, aggregation may occur. Because of the and by Verwey and Overbeek, calculates shallow nature of the secondary the opposing effects of attractive van der minimum, the aggregates formed are Waals forces and repulsive electrostatic held together weakly and as such tend to forces on the interaction potential. be unstable toward rather small energy inputs such as stirring. Interaction Potential The potential free energy between two Born (Hard Core) Repulsion surfaces, typically presented as a function As two surfaces are brought into close of separation distance. By convention, a contact, the attractive van der Waals

positive potential is mutually repulsive force between them increases

and a negative potential is mutually continuously. At some point in their attractive. approach, the electron of the two surfaces begin to overlap, giving rise to a Primary Maximum repulsive force termed the Bom or hard The first appearance of a maximum in the core repulsion. This results in a steep interaction potential energy curve with increase in the interaction potential curve

8 Guide to the Nomenclature of Particle Dispersion Technology

at very small interatomic separation Related Terms distances, becoming effectively infinite when interpenetration occurs. Critical Coagulation Concentration (ccc) Solvation (Structural) Forces The molar concentration of electrolyte, Non-DLVO forces that occur at extremely Co, necessary to induce rapid (diffusion- small separation distances (typically a limited) aggregation. Experimentally few molecular diameters) when particles determined by extrapolation of In W interact through an intervening fluid versus In Co to In W=0, where W is the medium. These forces arise whenever stability ratio. liquid are induced to order into quasi-discrete layers between surfaces, Coagulant and can result in a monotonically An electrolyte additive that induces increasing (repulsive), monotonically coagulation in a suspension. decreasing (attractive), or oscillatory interaction potential. In aqueous solvents Schulze-Hardy Rule these forces may be referred to as An empirical rule summarizing the hydration forces. general tendency of the critical coagulation concentration to vary Hamaker Constant inversely with the sixth power of the In the case of panicle interactions, a counterion charge number of added material constant that measures the electrolyte. relative strength of the attractive van der Waals forces between two surfaces. Lyotropic Series Particles interacting through an An ordered series of indicating, in intervening fluid medium will experience decreasing order, their effectiveness in a reduced attractive potential due to the influencing the behavior of colloidal presence of the third component. dispersions. Typically associated with an 's relative propensity to coagulate a Hard Sphere Interaction dispersion. A largely theoretical construct in which the interaction potential between Stability Ratio approaching particles is assumed to equal Ratio of the diffusion-limited to reaction- zero, except upon contact where it goes limited rate constants for aggregation. A abruptly to infinity (i.e., no large ratio indicates a high degree of interpenetration occurs). colloidal stability, whereas a ratio of unity indicates that diffusion-limited

Noninteracting conditions prevail and the system is If no barrier to particle approach, contact colloidally unstable. The rate constants and adherence exists, the particles are are determined experimentally from the said to be noninteracting. If the primary initial rates of aggregation. Usually minimum is sufficiently deep, every denoted by the symbol, W. collision will result in particles sticking together. The rate of aggregation will then be kinetically controlled (diffusion- limited rate).

9 Guide to the Nomenclature of Particle Dispersion Technology

Defoaming (Antifoaming) Agent Brownian (Thermal) Motion A that when present in small Random fluctuations in the density of amounts prevents the formation of a molecules in a liquid, due to thermal or aides in the coalescence of bubbles. energy, cause other molecules and small dispersed particles to move along

Dispersing Agent (Stabilizing Agent, random pathways. This random motion is

Dispersant) termed Brownian motion, and is most A substance that when present in small noticeable for colloidal particles. amounts facilitates the dispersion of aggregates and improves the kinetic Coacervation stability of particles. For example, When a colloidal suspension loses polyelectrolytes are often used as stability, a separation into two liquid

dispersing agents in ceramic processing. phases may occur. This process is termed

coacervation. The phase that is more

Surface Active Agent (Surfactant) concentrated in the colloid is the

A substance that lowers the interfacial coacervate, and the other phase is the tension between the solution in which it equilibrium solution. is dissolved, and other phases which are present (e.g., solid particles in a Recommendations suspension), and, accordingly, is positively adsorbed at the interface. Deflocculant, Dispersing Aid

It is recommended that these terms not be Polyelectrolyte used in the ceramic literature, (see A macromolecular substance that, on Dispersing Agent) dissolving in water or other ionizing solvent, dissociates to give polyions 2.5 Interfacial and Electrokinetic (polycations or polyanions) - multiply Properties charged ions - together with an equivalent amount of counter ions. A The Interface polyelectrolyte can be a polyacid, a polybase, a polysalt, or a polyampholyte. Interface Frequently used as dispersing agents in A boundary between two immiscible ceramic slurries. phases, at least one of which is condensed. Experimentally, the portion Sedimentation of the sample through which the first The settling of suspended particles or derivative of any concentration versus droplets due to the influence of gravity or location plot has a measurable departure an applied centrifugal field. from zero. In a suspension, the region of contact between the particle surface and Sedimentation Volume the suspending medium. The volume of particulate sediment formed in a suspension. If the sediment is Interfacial Region (Interphase) formed in a centrifugal field, the strength The region that exists between two of this field should be explicitly phases where the properties vary from indicated, otherwise normal gravity is those in the bulk. understood.

10 Guide to the Nomenclature of Particle Dispersion Technology

Surface Region approach of desolvated ions to the The tridimensional region, extending surface, and containing the ions or from the free surface of a condensed molecules that are specifically adsorbed. phase towards the interior, where the properties differ from the bulk. Outer Helmholtz Plane (OHP) At a charged interface, an imaginary Electrical Double Layer (EDL) plane representing the distance of closest The term describes the non-random array approach of solvated (hyrdrated) ions to of ions at an interface in which two the surface. Often equated with the oppositely charged layers coexist. For position of the shear plane. particles dispersed in a fluid, the EDL consists of the surface charge and the Shear Plane (Plane of Shear, Surface of solution charge. The solution charge may Shear) be further subdivided into Stem and In calculating the electrokinetic potential diffuse layers, which is often referred to from electrokinetic phenomena it is often as the triple layer model. assumed that a sharp plane separates the liquid adhering to the solid surface from

Double Layer Thickness the mobile liquid. This imaginary plane is Length characterizing the decrease of considered to lie close to the solid potential with distance from a charged surface. interface. Typically defined as 1/k, where

K is the Debye-Hiickel parameter. For Adsorption Processes low potentials it represents the distance over which the potential falls to lie, or Adsorption about one third, of the value of the The process by which a substance is surface potential. accumulated at an interface or in an interfacial region. Should not be

Diffuse Layer confused with absorption, which denotes The region surrounding a suspended accumulation inside a material or phase. particle in which non-specifically adsorbed ions are accumulated and Adsorbate distributed by the opposing action of the A substance that is adsorbed at the and thermal motion. interface or into the interfacial region of a substrate material, or adsorbent.

Stern Layer (Compact Layer) Counter and co-ions in immediate Adsorbent contact with a surface are said to reside in The substrate material onto which a the Stem layer, and form with the fixed substance is adsorbed. surface charge a molecular capacitor. Often equated with the immobile portion Adsorption Isotherm equilibrium of the electrical double-layer that exists The relationship between the the inside the shear plane. quantity of a substance adsorbed and composition of the bulk phase, at Inner Helmholtz Plane (IHP) constant temperature. At a charged interface, an imaginary plane representing the distance of closest

11 )

Guide to the Nomenclature of Particle Dispersion Technology

Specific Adsorption adsorbed molecules are in the position of Ions are specifically adsorbed when they closest approach to the substrate surface. are present in the Stem layer in amounts that exceed those expected from simple Multilayer Adsorption electrostatic considerations. Empirically, Adsorption in which more than a single ions that are specifically adsorbed have a layer of molecules is adsorbed at the noticeable effect on the isoelectric point. interface. Molecules adsorbed in excess of monolayer adsorption are not in the Non-Specific Adsorption position of closest approach to the Ions are non-specifically adsorbed when substrate surface. they are kept in the interphase only by long-range coulombic interactions. They Coadsorption are believed to retain their solvation shell The simultaneous adsorption of two or and in the position of closest approach to more species. the interface they are separated from it by one or more solvent molecular layers. Desorption Empirically, ions that are non-specific The process by which the amount of an

(indifferent) have no measurable effect on adsorbed substance is reduced. the value of the isoelectric point. Electrical Properties

Chemical Adsorption (Chemisorption Molecules are chemically adsorbed when Isoelectric Point (iep) they exist within the Stem layer and form For many ceramic systems, the pH at bonds with the surface groups, which which dispersed particles show no have a significant valence contribution. electrophoretic mobility and the zeta Empirically, ions that are chemically potential has a value of zero. More adsorbed have a noticeable effect on the generally, the pl value at which zeta is isoelectric point of a suspension and zero, where I is the potential determining exhibit a significant enthalpy (heat of ion. adsorption). Point of Zero Charge (pzc) Physical Adsorption (Physisorption) A particle carrying no fixed charge. The Adsorption in which the forces involved precise identification of pzc depends on are intermolecular (i.e., van der Waals, the definition adopted for surface charge. bonding) of the same kind as Typically for ceramic systems, the pH at those responsible for the non-ideality of which hydroxyl and adsorption is real and the condensation of just balanced to cancel net charge; here, , and which do not involve a the hydroxyl and proton are defined as significant change in the electronic the charge determining species. orbital patterns of the species involved. Surface Charge Density Monolayer Adsorption The quantity of electrical charge Adsorption in which only a single layer accumulated at a particle-solution of molecules becomes adsorbed at an interface, expressed per unit area; usually interface. In monolayer adsorption, all represented by the symbol oq.

) 12 Guide to the Nomenclature of Particle Dispersion Technology

Shear Plane Potential two phases determine the difference in The potential difference across the Galvani potential between these phases. mobile part of the electrical double layer They are often, but not always, identical at a charged solid-liquid interface; with the ions that stabilize a colloidal potential at the shear plane during an suspension formed from these phases. electrokinetic measurement. Synonymous with for the case of Co-ions particles suspended in a liquid. In systems containing large ionic species

(e.g., colloids), co-ions are those that, Streaming Potential compared to the large ions, have low When a liquid under a pressure gradient molecular mass and the same polarity. is forced through a capillary or porous For instance, in a suspension of plug, excess charges (ions) near the wall negatively charged particles containing are swept along by the liquid creating an sodium chloride, the chloride ions are co- accumulation of charge downstream. An ions and the sodium ions are counterions. electric field is also created, which opposes this accumulation. After a steady Counterions state has been established, the measured In systems containing large ionic species potential difference across the capillary (e.g., colloids), counterions are those that, or plug is called the streaming potential compared to the large ions, have low and is related to the pressure gradient and molecular mass and the opposite polarity. to the shear plane potential. For instance, in a suspension of negatively charged particles containing Zeta Potential (Electrokinetic Potential, sodium chloride, the sodium ions are Shear Plane Potential) counterions and the chloride ions are co-

The potential drop, ^, across the mobile ions. part of the electrical double layer, that is responsible for the electrokinetic Charge Reversal a charged particle is phenomena. C, is positive if the potential The process wherein increases from the bulk of the liquid caused to assume a new charge of the phase towards the shear plane. Certain opposite polarity. Such a change can be assumptions or estimations regarding the brought about by oxidation, reduction, double layer properties must be made in dissociation, adsorption, or ion exchange. order to calculate ^ from experimental data. It is therefore essential to indicate in Electrokinetic Effects all cases which equations have been used Electrokinetics in the calculation of t,. It can be shown, Referring to the relative motions of however, that for the same assumptions charged species in an electric field. The about the double layer properties, all field be applied, or it may be created electrokinetic phenomena must give the may the motion of a liquid or adjacent solid same value for the electrokinetic by potential. phase.

Electro-osmosis Potential Determining Ions When a liquid moves in response to an Those species of ions that by virtue of applied electric field, while an adjacent their equilibrium distribution between

13 Guide to the Nomenclature of Particle Dispersion Technology

solid phase remains stationary (e.g., in a potential difference termed the ultrasonic capillary or porous plug), this is called vibration potential. electro-osmotic flow. Fluid motion is due to the reaction of charged species within Ion Vibration Potential (I VP) the fluid, usually dissolved ions, to the The ultrasonic vibration potential of an applied field. ionic solution; also known as the Debye effect. Electrophoresis The motion of charged particles in an Colloid Vibration Potential (CVP) applied electric field. The ultrasonic vibration potential of a colloidal suspension. The resulting

Electrophoretic Mobility (Static, potential difference is related to the Dynamic) dynamic mobility of the particles; The electrophoretic velocity per unit field reciprocal effect to electrokinetic sonic strength, symbol |ie=v/£'.; \x,q is positive if amplitude. the particle moves toward lower potential and negative in the opposite direction. Electrokinetic Sonic Amplitude (ESA)

When measured in a d.c. electric field, |ie When a high-frequency alternating is referred to as the static mobility. When electric field is applied to a dispersion of measured in a high-frequency field it is charged colloids, the oscillatory referred to as the dynamic mobility, and electrophoretic motion of the particles relative to the surrounding medium given the symbol i^d or |i(a)). Dynamic results in a acoustic field mobility may be a complex quantity at measurable high frequencies. whose amplitude is related to the dynamic mobility; reciprocal effect of

Electroacoustics colloid vibration potential. The phase Referring to the electric-acoustic difference between the applied field and coupling in a fluid containing charged the resulting acoustic response can also to estimate the particle size colloids or ions; an effect that is be used responsible for the electrokinetic sonic distribution. amplitude, colloid vibration potential and ion vibration potential. Related Terms

Acoustophoresis Amphoteric The induced motion of particles Refers to a type of surface in which the (reactive site) is able subjected to an acoustic field. Charged same surface group particles will generate an electric field as to function as both an acid and a base. a result of this motion (see ultrasonic That is, the site may dissociate to release vibration potential). a proton or accept a proton.

Ultrasonic Vibration Potential (UVP) Zwitterionic When a sound wave propagates through a Refers to a type of surface in which two fluid containing charged particles (ions distinct surface groups (reactive sites) are or colloids), coherent acoustophoretic present. One is capable of dissociating to motion of the particles creates alternating release a proton (acid group), and the dipoles that generate a macroscopic

14 Guide to the Nomenclature of Particle Dispersion Technology

other is capable of accepting a proton charge numbers. (base group). Debye-Hiickel Parameter Hydrophilic A parameter in the Debye-Hiickel theory

May be used to describe the character of of electrolyte , denoted as k. For interaction of a particular atomic group aqueous solutions at 25 °C, k=3.288//

(or substance) with an aqueous medium. in reciprocal nanometers, where / is the In this usage the term has the relative ionic strength. See Thickness of the qualitative meaning of "water loving." Electrical Double Layer. The more general term, lyophilic ("solvent loving"), is used to distinguish Double Layer Compression (Screening) a class of colloidal systems. Increasing ionic strength causes the electrical potential near a charged surface

Hydrophobic to fall off more rapidly with distance.

The tendency of hydrocarbons (or of This is referred to as double layer lipophilic hydrocarbon-like groups in compression or screening, because the solutes) to form intermolecular double layer thickness shrinks as the aggregates in an aqueous medium, and Debye-Hiickel parameter increases with analogous intramolecular interactions. In increasing ionic strength. this usage the term has the relative

qualitative meaning of "water fearing." Electroviscous Effects The more general term, lyophobic For dispersions of charged particles, ("solvent fearing"), is used to distinguish these are those components of the a class of colloidal systems. viscosity connected with the charge on the particles. Indifferent (Supporting) Electrolyte

An ionic solution, whose constituents are Suspension Effect not electroactive (i.e., they have no The Donnan e.m.f. between a suspension

significant effect on the surface potential and its equilibrium liquid. The effect is of the material under study; no oxidative most commonly encountered with pH or reductive capacity) in the range of measurements in colloidal suspensions. applied potentials being studied, and whose ionic strength (and, therefore, Potentiometric Analysis contribution to the conductivity) is Analysis based on the measurement of usually much larger than the electrical potential using, for example, a concentration of an electroactive pH or ion-selective electrode.

substance to be dissolved in it. The ions Potentiometry is often combined with constituting an indifferent electrolyte are titrimetric analysis in the determination said to exhibit no specificity for the of particle surface charge. particle surface.

Titrant Ionic Strength The solution containing the active agent A measure of electrolyte concentration with which a titration is made.

given by /=y2^c, Zi', where c, are the

concentrations, in moles per liter, of the

individual ions, /, and Zj are their ion

15 Guide to the Nomenclature of Particle Dispersion Technology

Titration 3.2 Secondary Sources The process of determining the amount of a substance A by adding increments of Adsorption of Inorganics at Solid-Liquid substance B with provision for some Interfaces, Edited by M.A. Anderson and means of recognizing the point at which A.J. Rubin, Ann Arbor Science all of A has reacted. This allows the Publishers, Ann Arbor, MI, 1981. amount of A to be found from the known amount of B added up to this point. Chemical Processing of Ceramics, Edited by B.I. Lee and E.J. A. Pope, Marcel Titrimetric Analysis Dekker, NY, 1994. Analysis of test sample properties based on titration. Sample Preparation for the Determination of Particle Size Distribution of Ceramic Powders, 3. BIBLIOGRAPHY ISO/DIS 14703, 1998.

3.1 Primary Sources Particle Size Analysis: Dispersing Agents for Powders in , ISO Working Compendium of Chemical Terminology - Document 14887, 1997. lUPAC Recommendations, Compiled by V. , K.L. Loening, A.D. McNaught, Surface and Colloid Chemistry in and P. Sehmi, Blackwell Scientific Advanced Ceramics Processing, Edited Publications, Oxford, UK, 1987. by R.J. Pugh and L. Bergstrom, Marcel Dekker, NY, 1994. L.L. Schramm, The Language of Colloid and Interface Science - A Dictionary of Ultrasonic and Dielectric Terms, American Chemical Society, Characterization Techniques for Washington, DC, 1993. Suspended Particulates, Edited by V.A.

Hackley and J. Texter, American R.J. Hunter, Foundations of Colloid Ceramic Society, Westerville, OH, 1998.

Science, Volume 1, Oxford University

Press, Oxford, UK, 1989. C. J. Brinker and G.W. Scherer, Sol-Gel Science, Academic Press, NY, 1990. P.C. Hiemenz and R. Rajagopalan, Principles of Colloid and Surface D.F. Evans and H. Wennerstrom, The Chemistry, 3^^ Edition, Marcel Dekker, Colloidal Domain, VCH Publishers, NY, NY, 1997. 1994.

G.Y. Onoda and L.L. Hench, "Physical E. K. Fischer, Colloidal Dispersions, John Characterization Terminology," Chapter Wiley & Sons, NY, 1950. 5, pp. 35-37 in Ceramic Processing Before Firing, Edited by G.Y. Onoda and R.J. Hunter, Zeta Potential in Colloid L.L. Hench, John Wiley & Sons, NY, Science - Principles and Applications, 1978. Academic Press, NY, 1981.

16 Guide to the Nomenclature of Particle Dispersion Technology

D. Myers, Surfaces, Interfaces, and List of Reviewers and Contributors Colloids - Principles and Applications,

Chapter 10, "Colloids and Colloidal James H. Adair, Merrilea J. Mayo Stability," VCH Publishers, NY, 1991. The Pennsylvania State University, Particulate Materials Center D.H. Napper, Polymeric Stabilization of Colloidal Dispersions, Academic Press, Jon A. Casey NY, 1983. IBM, Materials Technology

R.H. Ottewill, "Stability and Instability in Robert A. Condrate Dispersed Systems," Journal of Colloid Alfred University, New York State and Interface Science, 58, 357-373 College of Ceramics (1977). Matthew Frey, William Hunt, Th.F. Tadros, "Control of the Properties Thomas Wood of Suspensions," Colloids and Surfaces, 3M Company, Ceramic Technology 18, 137-173 (1986). Center

Vincent A. Hackley, Ajit Jillavenkatesa,

Acknowledgements George Y. Onoda (retired) National Institute of Standards and A number of terms were included Technology, Ceramics Division courtesy of the American Chemical

Society from the book by L.L. Schramm. Robert J. Hunter Some definitions contained in the University of Sydney, School of Compendium of Chemical Terminology Chemistry, Australia were used, in part or in whole, courtesy of the International Union on Pure and George W. Scherer Applied Chemistry. Princeton University, Department of Chemical Engineering

Ponisseril Somasundaran Columbia University, Langmuir Center for Colloids and Interfaces

17 1 1

Guide to the Nomenclature of Particle Dispersion Technology

Index to Defined Terms

A D

AAN. See Average Agglomeration Number Deagglomeration, 6

Acoustophoresis , 14 Debye effect. 5ee Potential, Ion Vibration Adsorbate, 1 Debye-Hikkel Parameter, 15 Adsorbent, 11 Deflocculant. See Agent, Dispersing Adsorption, 11 Deflocculation, 6 Chemical, 12 Desorption, 12 Monolayer, 12 , 10 Multilayer, 12 Dispersing Aid. See Agent, Dispersing Non-Specific, 12 Dispersion, 2 Physical, 12 DLVO, 8 Specific, 12 Double Layer Compression, 15 Adsorption Isotherm, II Droplet, 4 Aerogel, 4

- Aerosol, 1 Agent E Antifoaming, 10 i?Z)L. See Electrical Double Layer Defoaming, 10 Electrical Double Layer, 1 Dispersing, 10 ' Electroacoustic, 14 Stabihzing, 10 electroactive. See Indifferent Electrolyte Surface Active, 10 Electrokinetic, 13 Agglomerate, 4 Electrokinetic Sonic Amplitude, 14 Agglomeration, 5 Electro-osmosis, 13 Aggregate, 4 Electrophoresis, 14 Aggregation, 5 Electroviscous Effects , 15 Orthokinetic, 6 Emulsion, 2 Perikinetic, 6 Equivalent Spherical Diameter, 5 Alcogel, 4 £Si4. See Electrokinetic Sonic Amplitude Amphoteric, 14 Average Agglomeration Number, 4 F

B F/oc, 4 Flocculation, 6 Born, 8 Floccule, 5 Brownian Motion, 10 Fractal, 5 Fusion, 6 c ccc. See Critical Coagulation Concentration G Charge Reversal, 13 Ge/, 4 Chemisorption, 12 , Gelation, 6 Coacervation, 10 Granule, 3 Coadsorption, 12 Coagulant, 9 Coagulate. See Coagulum H Coagulation, 6 Coagulum, 4 Hamaker Constant, 9 Co-ions, 13 Hard Core. See Bom Repulsion Co/tow/, 3 //arrf Sphere Interaction, 9 Comminution, 6 Hard-Aggregate, 4 Heteroagglomeration, Concentration. See Relative Concentration Terms 6 Counterions, 13 Heterocoagulation, 6

Heterodisperse , Critical Coagulation Concentration, 9 2 CVP. See Potential, Colloid Vibration Heteroflocculation, 6 hydration forces. See Solvation Forces 1 1 11

Guide to the Nomenclature of Particle Dispersion Teclinology

Hydrogel, 4 Liquid, 2 Hydrophilic, 15 Particulate, 2 Hydrophobic, 15 Solid, 2 Hydrosol, 2 Physisorption, 12

Inner Helmholtz, 1 I Outer Helmholtz, 1 Plane Shear, 11 iep. See Isoelectric Point of Point Zero Charge, 12 IHP. See Inner Helmholtz Plane of Polydisperse, 2 Indifferent Electrolyte, 15 Polyelectrolyte, 10 Interface, 10 Potential Interfacial Region, 10 Colloid Vibration, 14 Interphase, 10 Electrokinetic, 13 Ionic Strength, 15 Interaction, 8 Isoelectric Point, 12 lonVibration, 14 TVP. See Potential, Ion Vibration Shear Plane, 13 Streaming, 13 L Ultrasonic Vibration, 14 Zeta, 13 Layer Potential Determining Ions, 13 Compact, 11 Potentiometric Analysis, 15 Diffuse, 1 Powder, 4 lyophilic. See Hydrophilic Primary Maximum, 8 lyophobic. See Hydrophobic Primary Minimum, 8 Lyotropic Series, 9 pzc. See Point of Zero Charge

M R Microsphere, 4 Rate Particle Minimum Size, 5 Diffusion-Limited, 6 Mobility Reaction-Limited, 7 Dynamic, 14 Relative Concentration Terms, 3 Electrophoretic, 14 Static, 14

Monodisperse , 2 s MPS. See Minimum Particle Size Schulze-Hardy Rule, 9 Screening, 15 N Secondary Minimum, 8 Sedimentation, 10 , 3 Sedimentation Volume, 10 Noninteracting, 9 S/iear P&rne, 1 SiVwc Range. See Particle, Coarse o Slip, 2 Slurry, 2 OHP See Plane, Outer Helmholtz Sol, 2 Organosol, 2 Sol-gel, 6 Solvation Forces, 9 P Sonication, 7 Sonification, 7

Particle, 3 Stability Coarse, 3 Colloidal, 7 Fine, 3 Kinetic, 7 Stability Ratio, 9 Primal y, 4 Ultrafine, 3 Stabilization Particulate, 4 Depletion, 8 Peptization, 6 Electrostatic, 7 Phase Electrosteric, 8 Continuous, 2 Steric, 7 Forces, 9 Discontinuous, 2 Structural Range. See Particle, Fine Dispersed, 2 Subsieve

Supporting Electrolyte , 15

19 1 1

Guide to the Nomenclature of Particle Dispersion Technology

Surface Charge Density, 12 u Surface of Shear, 1

Surface Region, 1 Ultimate Working Unit, 5 Surfactant, 10 Ultrasonication, 1 Suspension, 2 UVP. See Potential, Ultrasonic Vibration Stable, 7 Unstable, 7 Suspension Effect, 15 w Syneresis, 1 Well-Dispersed, 3 T X Thermal Motion, 10 Xerogel, 4 Titrant, 15 Titration, 16

Titrimetric Analysis , 16 z triple layer model. 5£e Electrical Double Layer Zwitterionic, 14

2(9 .

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