bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of Percent Crystallinity of Partly Devitrified Glass by X‐Ray Diffraction
Authors: OHLBERG S. M. , STRICKLER D. W.
Published: June 2006

An X‐ray diffractometer method similar to one used to determine the crystallinity of stretched rubber has been applied to partly devitrified glass. Percent crystallinity is equated to 100(Ig, –Ix)/ (Ig– IB). Ig, Ix, IB are respectively the noncrystalline scattering intensities measured at a single value of 2θ for the parent glass (zero crystallinity), the partly devitrified glass, and a mechanical mixture of crystalline compounds chemically equivalent to the parent glass. The value of 2θ is selected such that the noncrystalline scattering is high for the parent glass and at the same time is free of crystalline scattering in the case of the partly devitrified glass and of the mechanical mixture. The assumptions and approximations inherent in the method are discussed and their validity is tested. The method is rapid, virtually independent of the crystalline species present, and accurate to ±5% or better.
Irreversible Compressibility of Silica Glass as a Means of Determining the Distribution of Force in High‐pressure Cells
Authors: CHRISTIANSEN E. B. , KISTLER S. S. , GOGARTY W. B.
Published: June 2006

The theoretical distribution of force over two types of cells used at pressures up to 160,000 atm is considered and compared with experimental results obtained by using silica glass as a pressure indicator. Experimental data for the pressure‐irreversible density‐change relation of silica glass to pressures of 200,000 atm are reported. Differences between results of the present investigation and those of previous investigations are discussed.
Mathematical Treatment of Glass Corrosion Data
Authors: HOGANSON D. K. , HEALY J. H.
Published: June 2006

Acid corrosion data obtained at elevated temperatures were related mathematically in a multiple regression form. The mathematical model was tested satisfactorily for several glasses corroding in four mineral acids at different concentrations.
Hot Pressing of Potassium‐Sodium Niobates
Authors: JAEGER R. E. , EGERTON L.
Published: June 2006

Compositions in the system KNbO3‐NaNbO2 have been hot‐pressed to yield ceramics with relative densities greater than 99%. Because these materials lack any degree of pyroplastic behavior, temperatures approaching those required for air sintering are needed. These hot‐pressed specimens exhibit a finer microstructure than that obtainable by conventional processing. Enhanced piezoelectric coefficients are observed, and in certain compositional regions radial coupling coefficients have been increased from 32 to approximately 48%. Dielectric constants increase with densification and ac losses remain relatively high. The fine structure and improved piezoelectric activity, especially near the equimolar composition, make these materials desirable for electromechanical transducers, particularly in the 10 to 20 Mc per second range. The rate equation of Murray, Live, and Williams for hot‐pressing ceramics was found to apply in this system.
Some Studies of Effect of High Pressure on a Lithia‐Alumina‐Silica Glass
Authors: EPPLER R. A. , GIARDINI A. A. , TYDINGS J. E.
Published: June 2006

The effect of near‐hydrostatic pressure on the synthesis of a lithia‐alumina‐silca glass was studied. It was found that the fusion of the oxides to form a glass melt was seriously impeded. A study also was made of the effect of hydrostatic pressure on the crystallization of a previously synthesized glass of similar composition. The approach to equilibrium in the system was found to be more rapid than at atmospheric pressure. In addition, a minor amount of a phase which could not be synthesized directly from the melt (α‐spodumene) was found.
An Electron Microscope Study of Pyrolytic Graphite
Authors: COY WILLIAM J.
Published: June 2006

An electron microscope study of pyrolytic graphite is presented in which subgrains of 0.1μ are shown. The effect of a cathodic vacuum etch on transverse and normal sections is given. Cracks in the structure are shown to be approximately 4μ long, parallel, and separated by 1μ.
The Ternary System CaO—MnO—SiO2
Authors: GLASSER F. P.
Published: June 2006

Phase equilibrium data resulting from quenching experiments are presented for the ternary system CaO‐MnO‐SiO2. An atmosphere of controlled oxygen pressure having Po2, ≅ 10−6 atm at 1555°C was used to maintain the manganese in the divalent state. The ternary liquidus surface is largely one of low‐lying liquidus temperatures. Three ternary liquidus minima dominate this surface. These have the following compositions (in weight percent CaO, MnO, and SiO2): (a) 5.0, 48.4, and 46.6%, (b) 17.5, 45.0, and 37.5%, and (c) 15.0, 53.0, and 32.0%. Temperatures measured at these points are (a) 1265° C, (b) 1195°C, and (c) 1204°C. Isofracts of the quenched glasses are presented. Crystallization paths of ternary mixtures are represented by a series of fractionation curves and selected isothermal planes. Partition of manganese between coexisting pairs of crystalline phases (e.g., meta‐silicate, olivine, and (Ca,Mn)O solid solutions) favors concentration of manganese in the more basic phase. Subsolidus equilibria involving these phases and also Ca3Si2O7 and Ca3SiO5 are discussed. Ca3Si2O7 and Ca3SiO6 do not admit any appreciable amounts of Mn++ into their lattices.
Dynamical Flow Properties of Single Crystals of Sapphire, I
Authors: KRONBERG M. I.
Published: June 2006

The tensile deformation of sapphire was studied as a function of the temperature and of the strain rate. The ranges of the two variables were approximately 1200° to 1700°C and 10−3 to 10−1in. per in. per minute. The work showed the existence of a relatively sharp temperature transition between completely brittle fracture and massive plastic flow, the specific transition temperature being sensitively related to the strain rate. For the limits of the rate range used, the transition temperature increased from approximately 1270° to 1520°c. In going through a range of only a few degrees of temperature near the transition, it was possible to obtain either no plastic flow on the low‐temperature side or a relatively large amount of the order of a 100% extension on the high‐temperature side. The stress‐strain relation for plastic flow was found to be characterized by a pronounced yield‐point drop; i.e., the stress required to initiate macroscopic flow was approximately double that required for subsequent flow. The magnitudes of both the upper and lower yield stresses were temperature sensitive and both decreased approximately exponentially with increasing temperature for a given strain rate. An inverse dependency of a similar kind was found for the effect of strain rate under conditions of isothermal testing. On the other hand, the fracture stress before yielding was found to be essentially independent of both temperature and strain rate, lying in a scatter band of approximately 16,000 to 20,000 psi. As the testing temperature at a given strain rate was lowered, the plastic yield stress therefore rose sharply. The transition temperature between ductile and brittle behavior was interpreted to correspond to the temperature at which the upper yield stress equaled the fracture stress. Since the lower yield stress was only half the upper yield stress, extensive flow then became possible whenever the transition temperature for yielding was exceeded.
Observations on Normal Grain Growth of Magnesia and Calcia
Authors: DANIELS A. U. , LOWRIE R. C. , GIBBY R. L. , CUTLER IVAN B.
Published: June 2006

It is generally agreed that the rate of grain growth in metallic systems may be expressed by an equation that describes the square of the average diameter as being proportional to the time of annealing at constant temperature. The proportionality constant is exponentially dependent on temperature as normally expected in a rate expression according to the theory of reaction kinetics. The purpose of this study was to check the applicability of these equations to metallic oxide systems. Reagent‐grade MgO and CaO prepared from reagent‐grade CaCl2 obeyed the grain‐growth expressions reasonably well. Strong temperature dependence of the growth rate of both materials was attributed to impurities. Activation energies of 110 and 60 kcal per mole were calculated for CaO and MgO, respectively. Both values are higher than would be anticipated for grain‐boundary diffusion in high‐purity materials. Although porosity varied considerably for various isotherms, no effect of porosity on grain growth was detected. The data, however, were considered to be insufficient to warrant strong conclusions concerning this variable.
Rheological Factors for Attapulgite Suspended in Water
Authors: GABRYSH A. F. , EYRING H. , CUTLER I.
Published: June 2006

Stress‐strain curves and stress‐relaxation curves were determined at various temperatures (1° to 70°C) and concentrations (16 to 22 wt%) for attapulgite suspended in water. Stress‐relaxation experiments were conducted under different conditions on samples which were relaxed for various durations of time between successive cyclic deformations. The flow properties are given in terms of rheopexy and thixotropy. The flow curve (for shear rates 0 to 700 per second versus shear stress) shows, first, a rheopectic hysteresis loop which changes on repeated shearing to a reversible and reproducible non‐Newtonian flow curve. After resting the system for about 12 hours, the resulting flow curve shows a thixotropic loop. Viscosity as a function of pH shows an inversion at pH ⋍ 6.3. A model for explaining the observed facts is proposed. The script S type of looped‐over flow curves showing both rheopectic and thixotropic characteristics is explained in terms of breakage of “logjammed” and crystalline bundles. A plot of the yield‐point viscosities versus the reciprocal of temperature for the rheopectic and thixotropic curves shows activation energies of about 1 and 2 kcal respectively. An autographic rotational viscom‐eter was designed and utilized to obtain the data reported so that the objectionable effects of frictional heating in the sample were minimized. The calibration response of the viscometer to a glycerol standard shows good agreement with published viscosity data.
Kinetics of Initial Sintering of Vacuum‐Reduced Titanium Dioxide
Authors: WHITMORE D. H. , KAWAI TOSHIHIKO
Published: June 2006

Observations of sphere‐to‐plate bonding of vacuum‐reduced monocrystalline rutile have been carried out over the temperature range 1200° to 1275°C. The rate law governing the interfacial growth between sphere and plate indicates that the predominant mechanism of material transport in this sintering process is volume diffusion. In the light of the reasonably satisfactory agreement between the oxygen self‐diffusion coefficients calculated from the present sintering data and those directly observed by Haul and Just utilizing an isotopic exchange technique, it is likely that oxygen ion diffusion is the rate‐determining step in the sintering experiments described.
Role of Cerium in Suppression of Gamma‐Ray Induced Coloring of Borate Glasses
Authors: BISHAY ADLI M.
Published: June 2006

The role of cerium in the suppression of gamma‐ray induced coloration in glass has been found to depend on the relative concentration of Ce3+ to Ce4+ ions as well as on the total cerium content. In a borate glass having high ultraviolet transmission, it has been found that both Ce3+ and Ce4+ ions are necessary to suppress the optical absorption bands induced in the visible region. The role of cerium can be explained on the basis of a change in its oxidation state as a result of gamma irradiation. It is postulated that the cerous ions, by the reaction Ce3+→ Ce4++e, suppress the induced visible band at 2.36 ev (525 mμ), which may result from positive hole centers. High cerous ion concentration results, however, in an induced center (Ce3++e) which absorbs in the visible at about 1.9 ev (650 mμ). The presence of Ce4+ ions near Ce3+ prevents the formation of this center possibly by the reaction Ce4++e→ Ce3+. These induced opposite changes in the oxidation state of cerium tend to maintain a balance in the ratio of Ce3+ to Ce4+ ions in the glass during irradiation, and the suppression of the visible bands depends on this ratio.
Temperature Dependence of Elastic Constants of Vitreous Silica
Authors: SPINNER SAM
Published: June 2006

The relation between the elastic moduli and temperature from room temperature to about 1300°C was determined for a group of vitreous silica specimens by a dynamic resonance method. All the curves were approximately parabolic in shape, reaching a maximum near 1050° to 1200°C. At the maximum value, Young's modulus was more than 11% higher and the shear modulus was about 9% higher than their room‐temperature values. Poisson's ratio was then computed to rise from about 1/6 at room temperature to about 1/5 at the temperature of maximum elastic modulus. Small but significant differences were observed in the temperature‐modulus curves for specimens from different sources. These differences were found to be related to differences in the infrared transmission curves.
Dielectric Properties of Glasses in the System Nb2O5–Na2O–SiO2
Authors: HIRAYAMA CHIKARA , BERG DANIEL
Published: June 2006

The effect of niobia on the dielectric properties of glasses in the system Nb2O5–Na2O–SiO2 has been studied from 100 to 1010 cps. The dielectric constant is high even at frequencies up to 1010 cps. The Nb5+ ion, with its small ionic radius and high charge, reinforces the network and raises the dielectric constant.
Experimental Evaluation of Beam‐Bending Method of Determining Glass Viscosities in the Range 108 to 1015 Poises
Authors: HAGY H. E.
Published: June 2006

The method of determining the viscosity of a glass by the viscous bending of a simple beam is experimentally compared with the fiber‐elongation technique. For a standard soda‐lime‐silica glass, beam‐bending viscosity data are found to agree well with fiber‐elongation measurements reported by the National Bureau of Standards. An apparatus using the beam‐bending principle is described with which reliable viscosity measurements for glasses are obtained in the range 108 to 1015 poises at temperatures up to 1500°C.
Glass Formation and Recrystallization in the Lithium Metasilicate Region of the System Li2O–Al2O3–SiO2
Authors: EPPLER R. A.
Published: June 2006

The stability of the vitreous state in the lithium metasilicate region of the system Li2O–Al2O3–SiO2 was found to be a function of the concentration of lithia. The higher the lithia content, the less stable was the glass. The devitrification of glasses in this system was studied. In addition to the phases present at or near the liquidus, it was found that the β‐eucryptite–β‐quartz solid solution phase was metastable over most of the region. The Li2O–SiO2, β‐Li2O–Al2O3–4SiO2 solid solution, β‐Li2O–Al2O3–2SiO2 solid solution triple point was estimated to be near 62.5% SiO2, 17% Al2O3, and 20.5% Li2O (by weight). The thermal expansions of bodies in this region were measured and the values obtained are explained in terms of the phases present.
Influence of TiO2 on Properties of Glasses in the System K2O–PbO–SiO2–TiO2 and Its Relation to Structure
Authors: RAO Bh. V. JANAKIRAMA
Published: June 2006

By a progressive weight percent substitution of TiO2 for SiO2 at various rations of concentration of K2O and PbO, the entire region of glass formation in the quaternary system K2O–PbO–SiO2–TiO2 was covered with 51 glass compositions. The properties of these glasses were determined and studied with respect to the role of TiO2 in the system. The results indicated that the dielectric constant increased progressively with increasing TiO2 concentration whereas the dissipation factor showed an overall decrease, when measured at 1 Mc and 25°C. Density and the refractive index increased progressively with increasing TiO2 concentration but deviated from the additive relation. Chemical durability, expansivity, and softening temperature vs. composition curves showed definite inflections. The effect of TiO2 on oxygen packing indicated that Ti4+ strengthens the network in lower concentrations and weakens the network in higher concentrations in this system. It appears to be likely that Ti4+ changes its coordination number form 4 to 6.
Phase Relations in the Garnet Region of the System Y2O3–Fe2O3–FeO–Al2O3
Authors: VAN HOOK H. J.
Published: June 2006

Liquidus equilibrium relations for the air isobaric section of the system Y2O3–Fe2O3–FeO–Al2O3 are presented. A Complete solid‐solution series is found between yttrium iron garnet and yttrium aluminum garnet as well as extensive solid solutions in the spinel, hematite, orthoferrite, and corundum phases. Minimum melting temperatures are raised progressively with the addition of alumina from 1469°C in the system Y–Fe–O to a quaternary isobaric peritectic at 1547°C and composition Y0.22Fe1.08Al0.70O2.83* Liquidus temperatures increase rapidly with alumina substitutions beyond this point. The thermal stability of the garnet phase is increased with alumina substitution to the extent that above composition Y0.75Fe0.65Al0.60O3 garnet melts directly to oxide liquid without the intrusion of the orthoferrite phase. Garnet solid solutions between Y0.75Fe1.25O3 and Y0.75Fe0.32‐Al0.93O3 can be crystallized from oxide liquids at minimum temperatures ranging from 1469° to 1547°C, respectively. During equilibrium crystallization of the garnet phase, large changes in composition occur through reaction with the liquid. Unless care is taken to minimize temperature fluctuations and unless growth proceeds very slowly, the crystals may show extensive compositional variation from core to exterior.
Reactions Between Alkaline‐Earth Sulfates and Cirstobalite
Authors: BROWNELL W. E.
Published: June 2006

The decomposition of magnesium and calcium sulfates was measured preliminary to measuring the reactions between alkaline‐earth sulfates and cristobalite. Since gaseous sulfur oxides were evolved in the processes, a starch‐iodide titration was used to determine the amounts of decomposition and reaction with time. Magnesium sulfate decomposed at temperatures above 900°C, before reaction with cristobalite. Calcium sulfate was found to react with cristobalite previous to thermal decomposition with an accompanying evolution of sulfur dioxide. Strontium and barium sulfates reacted with cristobalite at progressively higher temperatures. The applications of the data to the sulfur problems in the production of clay products are discussed.
Barium Zirconate‐Lead Titanate Ferroelectric Ceramics
Authors: BRATSCHUN W. R.
Published: June 2006

Hot‐pressed barium zirconate‐lead titanate ceramics have been examined to determine crystal‐line symmetry and dielectric, ferroelectric, and piezoelectric properties. Barium zirconate additions to lead titanate form solid solutions with a decreasing tetragonal c/a axial ratio until at 60PbTiO3–40BaZrO3 to 75PbTiO3–25BaZrO3 the ceramics have coercive forces low enough to permit polarization. High‐coercive‐force piezo‐electric ceramics are formed with kp up to 0.30 and d33 up to 110 × 10−12 coulombs per newton.
Preparation of Thin Mullite Films
Authors: WILLIAMS J. C. , SINCLAIR W. R. , KOONCE S. E.
Published: June 2006

Aluminosilicate glass films having compositions approximately that of mullite produced by reactive sputtering of aluminum‐silicon alloys are discussed. Data are given on the speed of deposition under certain conditions for a variety of metal and ceramic substrates. Mullite crystals with the needle habit are formed from the initial amorphous film by subsequent heat treatment of about 1 hour at temperatures of 1100° to 1400°C. The number and size of the crystals are affected by firing conditions, composition, and thickness of the film and by nucleating agents such as carbon on the surface of the film as indicated by transmission electron micrographs of unsupported films. The reaction of the oxide films with some supporting ceramic substrates has also been studied.
Phase Studies in BeO–Metal Oxide Systems Using a Porous‐Collector Technique
Authors: CHAPMAN A. T.
Published: June 2006

The phase relations in high‐temperature BeO–metal oxide systems were investigated by means of a porous‐collector technique. In this technique, which was found to be applicable to simple eutectic oxide systems with fluid melts, the liquid formed during heating of a water‐shaped specimen was absorbed in a porous collector. The lowest temperature at which the liquid formed and the material balance were used to establish the eutectic temperature and composition. The eutectics in four binary systems were determined as (1) ZrO2–BeO, 2045°× 10°C, 59 ± 2 mole % BeO, CeO2–BeO, 1890°× 20°C, 63 ± 3 mole % BeO, (3) MgO–BeO, 1860°× 10°C, 69 ± 2 mole % BeO, and (4) MgO–ZrO2, 2080°× 10°C, 65 ± 3 mole % MgO. Experiments in the ternary system MgO–ZrO2–BeO indicated an extensive region of solid solubility in the ZrO2‐rich portion of the system and a eutectic plane at 1720°× 10°C.
Studies of Early Stages of Paste Hydration of Cement Compounds, II
Authors: CHATTERJI S. , JEFFERY J. W.
Published: June 2006

The paste hydration of mixtures of alite, C3A, and C4AF with and without gypsum and/or NaOH was studied by electron‐optical and X‐ray diffraction techniques. In the absence of both gypsum and NaOH, a foil‐like reaction product and hexagonal calcium aluminate hydrates were formed first. Any CO2, present formed calcium carboaluminate. With time the foils changed to splines of CSH, and hexagonal aluminate hydrates changed to cubic C3AH6. When no gypsum was present, NaOH solution retarded the formation of hexagonal aluminates at the very early stages of hydration; it did not have much effect on the later hydration processes. With gypsum but without alkali, a foil‐like product and ettringite formed first. Later the foils changed to splines of CSH and ettringite to monosulfate. Alkali, in the presence of gypsum, hastened the formation of splines of CSH. The results suggest that the hydration of alite, even after 14 days, goes through the solution phase.
High‐Temperature Firing of Basic Refractories
Authors: VAN DRESER M. L. , BOYER W. H.
Published: June 2006

An investigation was conducted to determine the hot modulus of rupture strength, the tendency to burst under iron oxide attack, the tendency to creep, and the hot‐load‐bearing strength of chromite‐bearing basic refractories fired from 1400° to 2000°C. Petrographic examination was employed to define the mechanisms of improved bonding which resulted from firing at high temperatures. The results of these physical and chemical tests and the observed microstructure indicated that a greatly improved, highly stabilized basic refractory could be obtained by proper brick design and firing to temperatures of approximately 1700°C. Control of design features such as total silica content, chromite/periclase ratio, and chromite sizing was found to be necessary to achieve superior properties through high‐temperature firing.
Deformation and Fracture of Polycrystalline Lithium Fluoride
Authors: SCOTT WILLIAM D. , PASK JOSEPH A.
Published: June 2006

Techniques for the fabrication of polycrystalline LiF test specimens were developed and evaluated using single‐crystal LiF as a control. An etch was developed which revealed dislocations on all crystallographic faces of LiF. Large‐grained polycrystalline specimens tested in four‐point loading underwent 0.076 to 0.798% plastic strain before fracture. In most cases their yield stress was similar to that for single crystals favorably oriented for flow on {110}〈110〉 slip systems. Deformation was inhomogeneous among the grains because of differences in orientation with respect to the applied stress and within individual grains because of interactions at grain boundaries. Grain boundaries were barriers to slip, but stresses resulting from slip in one grain were transmitted to neighboring grains and often caused local deformation near the boundary. In one case, local boundary slip occurred on an (010) plane. Three‐grain junctions were areas of high residual stresses, and fractures originated at boundaries at or near three‐grain junctions. Fractures were mixed transgranular and intergranular.
Diffusionless Phase Transformations in Zirconia and Hafnia
Authors: WOLTEN G. M.
Published: June 2006

A study, by high‐temperature diffractometry, of the monoclinic‐tetragonal phase changes in pure ZrO2 and HfO2 disclosed that the hysteresis loops associated with the transformations have similar shapes which are typical of many martensitic phase changes, but that the widths of the loops differ greatly for the two materials, being about 200°C for zirconia and only 20° to 30°C for hafnia. The temperature‐induced transformations are predominantly athermal. The nature of these and similar transformations is discussed. The reversible formation of a cubic form of ZrO2 above 2200°C was confirmed.
Thermal Shock Analysis of Spherical Shapes, II
Authors: HASSELMAN D. P. H. , CRANDALL W. B.
Published: June 2006

A new approach has been used to calculate the maximum temperature difference to which a brittle ceramic sphere can be subjected without failure. The modified method of calculation and some new data have made possible a better correlation between these calculated values and measured values obtained in earlier work.
Valence Changes of Iron and Manganese in Manganese Ferrite
Authors: BUESSEM W. R. , BUTLER S. R.
Published: June 2006

The gain in weight of manganese ferrite was measured at several oxygen pressures and temperatures above 1200°C with a controlled atmosphere thermobalance. The phase boundaries were determined where necessary and the weight gain was measured within the one‐phase field. The lattice constant was also determined from high‐angle X‐ray reflections (2θ× 160°) on specimens quenched in mercury from the same oxygen pressures and temperatures at which the weight gain was measured. The lattice constant was found to decrease with increasing oxidation. The results show that iron and/or manganese coexist in several valence states within the stability range of the single‐phase material.
Relation of Single‐Crystal Elastic Constants to Polycrystalline Isotropic Elastic Moduli of MgO
Authors: CHUNG DAE‐HYUN , SWICA JOSEPH J. , CRANDALL WILLIAM B.
Published: June 2006

The three elastic compliance coefficients of synthetic periclase were determined in the kilocycles per second frequency range by a resonance method. Polycrystalline elastic moduli on dense‐formed MgO were measured. The calculated isotropic elastic moduli for polycrystalline MgO obtained from the single‐crystal constants are in good agreement with experimental values measured on the dense MgO at the theoretical density point. The measured Young's modulus and the shear modulus of polycrystalline MgO are found to be 30.50 and 12.90 × 1011 dynes per cm2 respectively. The results of the present investigation are compared with the earlier work in the megacycles per second frequency range. A theoretical analysis is made to establish the validity of the present values. Schemes of averaging the single crystalline elastic constants for polycrystalline behavior are reviewed for crystals of cubic symmetry.
High‐Pressure Effects on Oxide Glasses: II, Subsequent Heat Treatment
Authors: MACKENZIE J. D.
Published: June 2006

The annealing or volume variation with time of both silica and boron oxide glasses densified in the rigid state was studied. Appreciable annealing of silica glass was observed at temperatures as low as 200°C and of boron oxide glass at even room temperature. This anomalous volume flow depended on temperature, time, and specific volume and was characterized by small apparent relaxation times and activation energies. The differences between this type of volume relaxation and other properties such as delayed elasticity, cold flow, and stabilization are discussed. Devitrification to α‐cristobalite observed at temperatures as low as 500°C is attributed to the presence of shear stresses.
Electron Microscopy of Sintered Beryllia
Authors: RAU ROBERT C.
Published: June 2006

Porosity, etching characteristics, and general microstructural features of extruded and sintered beryllium oxide were studied by electron microscope observation of surface replicas. Both pore structures and etching characteristics were shown to be related to the hemimorphic hexagonal crystal structure of BeO. A form of twinning possible only in hemimorphic systems was also observed.
Grain Growth in Ca0.16Zr0.84O1.84
Authors: TIEN T. Y. , SUBBARAO E. C.
Published: June 2006

Isothermal grain growth in Ca0.16Zr0.84O1.84, a cubic solid solution of the fluorite type, was studied between 1600° and 2000°C. The grain size increased as the 0.4 power of time. The growth rate was found to be slower than in metals. The activation energy for grain‐boundary migration was about 80 kcal per mole. The influence of sintering atmosphere on grain growth is shown.
Pressure Sintering: Mechanisms and Microstructures for Alumina and Magnesia
Authors: VASILOS T. , SPRIGGS R. M.
Published: June 2006

Pressure sintering (or hot‐pressing) of pure alumina and magnesia in graphite dies and in ceramic dies over the range 1100° to 1700°C and 4000 to 10,000 psi has been shown to be very useful in fabricating these materials with controlled microstructures (e.g., very high relative density and fine grain size or controlled larger grain sizes) without the use of additives to control grain size. Apparent diffusion co‐efficients calculated for the densification process are orders of magnitude greater than for pressureless sintering, which might be explained by enhanced diffusion under stress. Alternatively, however, lower calculated coefficients which are more in agreement with pressureless‐sintering data result when pressure correction terms, modified by porosity, are applied to existing relations. It is concluded that the consistency in calculated diffusion coefficients as well as the reasonable comparison of activation energies suggests that, for the pressures used, densification beyond the initial stages is a diffusion‐controlled process.
Barium Titanates With Improved Insulation Resistance and Time Constant
Authors: HOH S. R. , PIRIGYI F. E.
Published: June 2006

An experimental study was conducted to improve the insulation resistance and time constant of ceramic barium titanates. It was found that the purity of the barium titanate had a notable effect, and several additives were found which improved the time constants by several orders of magnitude. The insulation resistance at elevated temperatures could be improved substantially by additions of high‐fluorine compounds of such cations as uranium and chromium.
Kinetics of Vapor‐Phase Hydration of Magnesium Oxide
Authors: LAYDEN GEORGE K. , BRINDLEY G. W.
Published: June 2006

Magnesium oxide prepared by calcining the carbonate at 1000°C was sintered at 1800°C and ground under methanol. Well‐sized 2 to 5 and 5 to 10μ fractions were separated. After outgassing at 550°C in vacuum, the powders were hydrated at various temperatures to 98°C in a wide range of water vapor pressures, and the reaction was followed gravimetrically with a silica helix balance. At low temperatures and vapor pressures, where nucleation is exceedingly slow, the hydration of prenucleated samples was studied. The results are interpreted on the basis of a model in which an interface reaction controls the progress of the reaction. The reaction rate varies with the water vapor pressure p according to a function (p/p* ‐ 1), where p 0.3 psat. and appears to correspond to the equilibrium adsorption pressure. This suggests that the reaction depends on an adsorbed water vapor film which has free access to the reacting surface. The reaction rate constant varies with temperature according to an Arrhenius‐type equation, with an activation energy 16,100 cal per mole.
Rheological Factors for Bentonite Suspensions
Authors: GABRYSH W. F. , EYRING H. , LIN‐SEN PAN , GABRYSH A. F.
Published: June 2006

The flow behavior of bentonite colloidal suspensions is given in terms of the stress‐strain relations with respect to variables of concentration, suspension medium, hydrogen‐ion concentration, temperature, and the successive application of shear stress. Repeated cycling (successive reruns of upcurve and downcurve) caused thixotropic hysteresis loops which decreased in size to a final constant and reproducible flow curve. A hysteresis loop did not appear for a mixture of less than 20 wt% bentonite and glycerin. The flow curves are discussed in terms of bondings in “cardhouse” and “blockhouse” models for dilute and concentrated suspensions respectively. Eyring's rate theory of viscosity is discussed briefly in terms of the well‐known generalized viscosity equation

which was applied successfully to given flow curves. Physical and chemical characterizations are compared in terms of thixotropic flow models for aqueous, glycerol, and oil (Bentone grease) suspensions.
Elastic Energy at Fracture and Surface Energy as Design Criteria for Thermal Shock
Authors: HASSELMAN D. P. H.
Published: June 2006

The physical properties which affect the propagation of cracks in specimens fractured by thermal shock are discussed. The driving force for crack propagation is provided by the elastic energy stored at fracture. The mechanism of energy dissipation which will tend to arrest the propagating cracks is provided by the “effective surface energy” required to produce the newly formed crack surfaces. An expression is derived applicable to a body of spherical shape for the mean area traversed by cracks nucleated by thermal shock. Three numerical examples are given for materials with widely different physical properties, and their fracture behavior is predicted. Good agreement with experiment was obtained. Thermal shock damage resistance parameters suitable for the relative comparison of the “degree of damage” to be expected in materials fractured by thermal shock are proposed. The criteria for a low degree of damage are high values of Young's modulus of elasticity, Poisson's ratio, and effective surface energy and low values of strength. Recommendations are made for the selection of materials for severe thermal shock, where the best materials available are known to fail.
Diffusion Sintering: II, Initial Sintering Kinetics of Alumina
Authors: JOHNSON D. LYNN , CUTLER IVAN B.
Published: June 2006

The initial sintering kinetics of alumina have been studied by measuring the isothermal shrinkage of compacts of several alumina powders in air. The shrinkage of these compacts can best be described by a grain‐boundary vacancy diffusion model for the temperature range 1200° to 1600°C. The behavior of the compacts is consistent with the model after an initial shrinkage has occurred. The magnitude of this initial shrinkage is constant for identical specimens and is independent of the sintering temperature.
Residual Stresses in Two‐Phase Systems as Determined by Changes in Transition Temperature
Authors: BOGARDUS E. HAL , ROY RUSTUM
Published: June 2006

Differences in thermal expansion between glass and crystal and between halide and oxide produce hydrostatic and nonhydrostatic pressures (negative or positive) in polyphase bodies which result in marked changes in the phase‐transition temperature of one of the phases. In the glass‐plus‐crystal systems, the tensile strength of the matrix is not exceeded and reasonable agreement between calculated and experimental values is obtained. The magnitude of maximum lowering in the transition temperature of a particular system is shown to be in the hundreds of degrees centigrade. In a crystalline halide matrix, high tensile stresses cause fractures in the halide and therefore substantial discrepancies between the experimental and calculated values.
The System Manganese Oxide–Cr2O3 in Air
Authors: SPEIDEL D. H. , MUAN ARNULF
Published: June 2006

The quenching technique has been used to determine equilibrium relations in the system manganese oxide‐Cr2O3 in air in the temperature range 600° to 1980°C. The following isobaric invariant situations have been determined: At 910°± 5°C tetragonal Mn3O4 solid solution, cubic Mn3O4 solid solution (=spinel), Mn2O3 solid solution, and gas coexist in equilibrium. Cubic Mn3O4 solid solution, Cr2O3 solid solution, liquid, and gas are present together in equilibrium at 1970°± 20°C. The invariant situation at which cubic Mn3O4 solid solution, Mn2O3 solid solution, Cr2O3 solid solution, and gas exist together in equilibrium is below 600°C.
High‐Temperature Energy Relations in Borates: Alkaline‐Earth and Lead Borate Compounds and Their Glasses
Authors: STEWART DANIEL R. , RINDONE GUY E.
Published: June 2006

The high‐temperature energy relations in some alkaline‐earth and lead borate glasses and compounds of the same compositions are reported. The data obtained with a continuous high‐temperature calorimeter and by solution calorimetry in 2N nitric acid were combined to give heat content versus temperature curves from 25° to 1100°C. The heats of fusion, entropies of fusion, entropy changes vs. temperature, and the free‐energy changes from crystal to glass at 25°C are given. Previously unavailable X‐ray diffraction data for strontium diborate and calcium diborate are reported.
Initial Temperatures of Zirconia Phase Changes and Solid‐Solution Reactions
Authors: SMOOT THOMAS W. , RYAN JOSEPH R.
Published: June 2006

Mixtures of zirconia with yttria, magnesia, calcia, ceria, and combinations of calcia and magnesia were investigated by X‐ray diffraction at temperatures up to 2870°F. The initial stabilizing reactions occurred at temperatures ranging between 900° and 2700°F. Magnesia apparently showed the lowest temperature of initial reaction and yttria the highest. Combinations of calcia and magnesia showed initial solid solution at temperatures lower than calcia but higher than magnesia, although magnesia seemed to be the first to react. Inconclusive evidence indicated that some exsolution occurred in some combinations when temperatures were lowered.
Structure of Nickel Oxide Containing Alumina
Authors: GILLAM E. , HOLDEN J. P.
Published: June 2006

X‐ray powder patterns have been used to measure the thermal expansion of (a) nickel oxide, (b) nickel aluminate, and (c) nickel oxide containing alumina and ignited at 1300°C in air. The results show that any solid solution that occurs must be restricted to less than 1 mole % of the solute. An X‐ray line‐broadening effect was found in the ignited and quenched nickel oxide containing alumina. This is attributed to heterogeneous lattice strains associated with a limited solid solution of nickel aluminate in nickel oxide at ignition temperatures and reprecipitation during quenching to room temperature.
Infrared Absorption Spectra of Sodium Silicate Glasses from 4 to 30μ
Authors: HANNA RINOUD , SU G‐J.
Published: June 2006

The infrared absorption spectra of sodium silicate glasses of molar composition Na2O·xSiO2 (where = 5, 4, 3, and 2) were determined with unpolarized radiation in the 4 to 30μ region. The glass spectra showed a definite similarity to the spectra of α‐quartz, with lattice vibrational bands around 1066,786, and 464 cm−1. As x decreased, some bands shifted toward lower frequencies indicating a decrease in the force constant. No new frequencies were found in the silicate glasses which did not have counterparts in α‐quartz.
Volatility of UO2±x and Phase Relations in the System Uranium—Oxygen
Authors: CHAPMAN A. T. , MEADOWS R. E.
Published: June 2006

The volatility of UO2±x and the phase relations in the system uranium‐oxygen were studied using thermogravimetric techniques. Chemical reactions describing the loss of uranium from UO2±x at temperatures between 1100° and 2200°C in oxygen pressures between approximately 102 and 10−6 torr are proposed. Results were obtained requiring the consideration of UO4(g) as the uranium‐bearing vapor species above UO2±x. Evidence supporting the existence of UO4(g) included the volatilization of material with an oxygen‐to‐uranium ratio of 4 during the decomposition of UO2+x(0.Z > × > 0) to near‐stoichiometric UO2 in vacuum above 1500°C and the dependence of the evaporation rate of the uranium dioxide on the oxygen pressure between 1200° and 1500°C. The equilibrium oxygen pressures over compositions between UO2.02 and UO2.63 in the UO2+x and U3O8‐y regions and over the boundary between these phases were measured between 1000° and 1600°C. The equilibrium oxygen‐to‐uranium ratio of UO2±x was less than 2 above 1700°C in vacuum.
Infrared Absorption Spectroscopy in Zirconia Research
Authors: McDEVITT NEIL T. , BAUN WILLIAM L.
Published: June 2006

Infrared absorption spectra are shown for monoclinic ZrO2 and for cubic stabilized ZrO2. Nine bands are reported in monoclinic ZrO2 in the region 800 to 200 cm−l, whereas only one broad band is observed in cubic ZrO2 over the same frequency range.
Lattice Defects in Tetragonal ZrO2
Authors: HOCH MICHAEL
Published: June 2006

The activity of zirconium in the tetragonal ZrO2 phase was measured at 2200° to 2300°K as a function of composition by studying the reaction

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From the variation of the zirconium activity with composition, the pairwise interaction energy E11 between vacancies in the oxygen lattice was evaluated at ‐4.6 ± 1.0 kcal per mole.
Axial Thermal Expansion of TetragonaI ZrO, Between 1150° and 1700°C
Authors: LANG S. M.
Published: June 2006

The lattice constants for three samples of tetragonal ZrO2 were measured in a high‐temperature X‐ray diffractometer in the range 1150° to 1700°C in an ambient air atmosphere. The unrefined lattice constants were the same for these materials only after each had been previously heat‐treated at 1550° to 1750°C in an ambient air atmosphere. The thermal expansions of the two axes are linear and are given by: a value, A = 3.5882+ 4.50 X 10+(T), within 0.0013 A; and c value, A = 5.1882+ 7.57 × 10−5(T), within 0.0022 A, where T is in °C for the range 1150° to 1700°C. The lattice constant values are a= 3.6399 A and c= 5.2758 A at 1150°C and a= 3.6782 A and c= 5.3397 A at 1700°C.
Structure‐Property Relations for Pyrolytic Graphite
Authors: COFFIN I. F.
Published: June 2006

The mechanical and physical properties of pyrolytic graphite are closely related to the structure produced during its deposition. It is shown how various features of the deposited structure can be predicted with some accuracy. These features include the structure of isolated nodules, the influence of various substrate conditions, and the effects of continuous nucleation. The effect of these structures on properties is discussed and the relation of the residual stress state to the deposition conditions is explained.
Structure of Borosilicate and Borogermanate Melts at 1300°C; a Viscosity and Density Study
Authors: RIEBLING E. F.
Published: June 2006

An improved counterbalanced sphere viscometer‐densitometer was used to obtain information at temperatures between 1000° and 1400°C for (a) molten B2O3, (b) a series of borosilicate melts containing up to 55 mole % SiO2, and (c) a series of borogermanate melts containing up to 65 mole % GeO2. The dependence on composition of these structure‐sensitive parameters was used to develop a model for the alteration of molten B2O8 by other network‐forming species. The B/Si or B/Ge ratio is shown to be a significant factor in determining melt structure. The silicon (or germanium) atoms appear to be widely separated in the B2O2 solvent for compositions in the 0 to 10‐20 mole % SiO2 (or GeO2) region. The evidence suggests that a gradual microclustering of SiO2 (or GeO2) accompanies moderate departures from ideality for B2O3 in the 10‐20 to 60 mole % SiO2 (or GeO2) region. Extensive micro‐clustering of SiO2 (or GeO2), approaching network formation, appears to occur in the 60 to 100 mole % SiO2 (or GeO2) region; some of the boron atoms remain in clusters and/or are forced to adopt a tetrahedral configuration in this region.
Resistivity Anomaly in Doped Barium Titanate
Authors: HEYWANG W.
Published: June 2006

The barrier‐layer model previously proposed to explain the anomalous increase in resistivity that occurs in doped BaTiO3 has been reexamined in the light of data obtained from more recent experiments. The picture thus obtained describes correctly and quantitatively the resistivity anomaly and the frequency and voltage dependence of the resistivity in the entire temperature range investigated (‐180° to +200°C). The activation energy of the donors and of the surface states as well as the density of states in BaTiO3 were determined and are in close agreement with other investigations. Comments are made regarding the uncertainty of the nature of the surface states.
Magnetic Properties of Chromium Chrysoberyl
Authors: SANTORO R. P. , NEWNHAM R. E.
Published: June 2006

Magnetic susceptibility data between 4.2° and 300°K have been obtained for the (Al,Cr)2BeO4 solid‐solution series. Chromium chrysoberyl is antiferromagnetic with a Néel temperature near 28°K; above 60°K it obeys the Curie‐Weiss law with θ= 13OK and an effective atomic moment of 3.2 Bohr magnetons. A four‐sublattice Weiss model consistent with the experimental results is presented.
Mechanical Behavior of Magnesium Oxide at High Temperatures
Authors: DAY R. B. , STOKES R. J.
Published: June 2006

Magnesium oxide crystals show a wide variety of deformation and fracture modes under tension. These modes are determined by the number of slip systems operating concurrently in a given volume. (1) At low temperatures, slip is confined to a single (110) (110) system and plasticity is limited by stress concentrations which develop where slip switches from one plane to another. (2) At intermediate temperatures, (110) (110) slip systems at 90° can interpenetrate but those at 60° cannot. Mechanical properties then depend on the initial slip distribution. When slip is confined to 90° systems there is little work hardening and crystals neck down to a knife‐edge ductile fracture. When slip is confined to 60° systems, crystals work harden and fracture by cleavage. (3) At high temperatures, dislocations can interpenetrate on all systems and polygonization can occur. After easy glide the crystals work harden and elongate over 100% before fracturing in a completely ductile manner. The transition temperature from one mode to another depends on strain rate.
Introduction of Particle‐Size Distribution into Kinetics of Solid‐State Reaction
Authors: SASAKI HIROMU
Published: June 2006

A theory to introduce particle‐size distribution of the reacting component into Carter's equation on solid‐state reaction is described. The particle‐size distribution is defined as follows: The reacting component is divided according to particle size into groups and the mean particle sizes of each group are set in a geometrical series. By introducing the particle size distribution into the equation, the reacted fractions of the groups can be mathematically determined. The theory was applied to the solid‐state reaction of lead zircon‐ate from lead oxide and zirconium oxide having a particle size distribution. Using the measured particle‐size distribution of the zirconium oxide and the overall fraction of zirconium oxide reacted, an activation energy of about 100 kcal per mole was determined.
Surface Charge of Alumina and Magnesia in Aqueous Media
Authors: ROBINSON McDONALD , PASK J. A. , FUERSTENAU D. W.
Published: June 2006

By streaming potential measurements, the zero point of charge (zpc) of or‐Al2O3 having a fully hydroxylated surface was found to occur at pH 9.2 ± 0.2. By calcining the alumina at temperatures above 1000°C, the zpc was lowered to about pH 6.7. By aging the calcined material in water at room temperature for a period of weeks, the surface was rehydroxylated and the zpc increased. The zpc of MgO occurred at pH 12.5 f 0.5. Because of its high solubility, the zpc of MgO was not affected by heat treatment.