bluuebunny/crossref_metadata_2025 huggingface dataset:
Piezoelectric Ceramics
Authors: JAFFE HANS
Published: June 2006

The discovery of piezoelectric effects in electrically poled barium titanate ceramic, in the early l940, was a revolutionary contribution to the electromechanical transducer art. Since then, improved barium titanate ceramics adapted to a variety of practical needs have been developed, and a number of new piezoelectric oxide‐type compounds have been discovered. Among these the lead titanate zirconate group offers especially valuable properties. In addition to a survey of the field, the present paper presents new data on lead titanate zirconate over a range of compositions.
Immiscibility and Surface Tension of Some Simple Borates
Authors: SHARTSIS L. , SHERMER H. F. , BESTUL A. B.
Published: June 2006

This paper reports the minimum concentrations of second cations that must be added to phase‐separated binary borates to produce single‐phase glasses when batches of approximately 100 gm. are melted at 1300°C. and poured into an 8‐ by 10.5‐cm. steel mold at room temperature. Surface tensions are also reported for the melts at 900°, 1000°, 1100°, 1200°, and 1300°C. Alkali and alkaline‐earth cations and Pb++, Cd++, and Al+++ were used as auxiliary cations to make single phased the phase‐separated binary borates of the principal cations Ba++, Sr++, Ca++, Cd++, Zn++, and Mg++. Within any group of the periodic table the minimum homogenizing concentration increases with decreasing ionic radius of either the auxiliary or the principal cation. The surface tensions of layered binary melts are independent of cation identity and content, indicating an upper layer of nearly pure B2O3. For layered or unlayered ternary melts containing alkali auxiliary cations, surface tension increases with increasing cation content at rates that decrease with the ionic radius of either cation, indicating that in these layered ternary melts the cations enter the upper (B2O3‐rich) layer more freely than in the corresponding binary melts.
Solubility of Silica in Nitric Acid Solutions
Authors: ELMER THOMAS H. , NORDBERG MARTIN E.
Published: June 2006

The solubility and solution rates of porous glass and silica gel in nitric acid solutions at 95°, 65°, and 36° C. were determined. The solubility depends on the acid concentration, decreasing with increasing strength of free HNO3in accordance with the following equation: logC = ‐aN ‐ b, whereCis the silica solubility,Nis the acid normality, andaandbare empirical constants. The rate of solution of silica depends on acid concentration, the initial rate being a maximum at about 0.8N.The amount of silica dissolved is a function of time and acid concentration. For short periods of time (1 to 40 hours) a maximum amount of silica is dissolved in about 0.8NHNO3. For long periods of time this maximum is at 0.1Nor less. A curve showing the decrease in silica solubility with temperature in water is included.
Silica Structure Studies: V, The Variable Inversion in Cristobalite
Authors: HILL V. G. , ROY RUSTUM
Published: June 2006

It is demonstrated experimentally that even in the purest laboratory silicas available the temperature of the α‐β inversion in cristobalite is variable and depends on the structure of the starting material and on the temperature and length of heat‐treatment. It is shown that this variability is an index of the order achieved in the cristobalite structure quite independent of impurities. There is no specific order characteristic of a particular temperature; the completely ordered 3C stacking of cristobalite is the most stable cristobalite throughout the temperature range and has an α‐β inversion temperature of 267°± 2°C. All disordered cristobalites will tend toward the 3C 267° cristobalite with time. The conversion of cristobalite to tridymite involving the 3C→2 H stacking change does not alter the cristobalite inversion temperature, nor have any regular polytypes other than those recognized as tridymite been encountered.
Sintering Characteristics of Rare‐Earth Oxides
Authors: PLOETZ G. L. , KRYSTYNIAK C. W. , DUMAS H. E.
Published: June 2006

The sinterability of europium, samarium, gadolinium, and dysprosium pure oxides was investigated at various temperatures under both oxidizing and reducing conditions as well as hot pressing. Data are presented on the density, grain size, thermal expansion, resistance to water corrosion, and the microhardness of these oxides. Photomicrographs showing grain growth and microstructure are included. The results indicate that dysprosium oxide is the most stable of the four oxides investigated. It sinters with small grain size, is similar to alumina in coefficient of thermal expansion, and does not undergo a phase transformation.
Reactions Between Iron Oxides and Alumina‐Silica Refractories
Authors: MUAN ARNULF
Published: June 2006

Phase equilibrium data for the system FeO‐Fe2O2‐Al2O3‐SiO2 are used to evaluate the attack of iron oxides on alumina‐silica refractories under various idealized conditions which approach those occurring in practice. The extent of attack and the nature of the reactions at various levels of O2 pressure are discussed.
Mechanisms Involved in Securing Dense, Vitrified Ceramics from Preshaped Partly Crystalline Bodies
Authors: VINES R. F. , SEMMELMAN J. O. , LEE P. W. , FONVIELLE F. P.
Published: June 2006

The internal porosity of ceramics shaped before fusion has been improved by three firing techniques: (1) firing in vacuo, (2) firing in diffusible gas, and (3) finish firing and cooling under pressure. A method of measuring pore volume and texture has contributed to understanding the operating mechanics of these processes. This has led to recognition of the firing‐process requirements for different porcelains depending on their crystalline content, matured viscosity, service conditions, and performance specifications.
Variables Involved in Accelerated Alkali Resistance Testing of Porcelain Enamels
Authors: COX JOHN E.
Published: June 2006

Alkali test data were obtained for experimental and commercial porcelain enamels for test solutions of sodium hydroxide, sodium pyrophosphate, and commercial detergents. The effects of variations in volume and strength of solutions, time and temperature of testing, and the addition of bleaching agent were studied. The best correlation to detergent action was obtained with 1% sodium pyrophosphate. Results for sodium hydroxide varied greatly with solution strength. For some porcelain enamels the alkali resistance results, obtained with 5% sodium hydroxide, were contrary to those obtained with commercial detergents. The addition of a sodium hypochlorite type of bleach to detergent solution did not affect the degree of attack on porcelain enamels.
Oxidation Behavior of Silicon Carbide
Authors: ERVIN GUY
Published: June 2006

The oxidation of purified green silicon carbide in controlled atmospheres was studied by weight‐gain measurement and by observation of the surface reaction products, including optical measurement of the thickness of the oxide surface film. The rate of oxidation was much greater for silicon carbide in contact with fluid silicate glasses than for silicon carbide alone. In a vacuum of 0.1 mm., oxidation proceeded with loss of weight, because of the formation of volatile SiO2, and at a greater rate than at atmospheric pressure. It is postulated that the rate‐controlling process in the normal oxidation of silicon carbide is the formation of solid SiO2 on the surface.
Phase Equilibrium Studies in the System CaO‐Cr2O3‐SiO2
Authors: GLASSER F. P. , OSBORN E. F.
Published: June 2006

Results are presented of a study in air of mixtures in the system CaO‐Cr2O3‐SiO2. The phase equilibrium diagram shows relations at liquidus temperatures for all but the high‐lime part of the system. In this omitted part chromium in the mixtures oxidizes in air to higher valence forms. The compound Ca3Cr2Si3O12 (uvarovite) occurs at subsolidus temperatures, decomposing at 1370°C. to α‐CaSiO3 and Cr2O3. The inhibiting action of chromium oxide on the inversion of high‐temperature forms of Ca2SiO4 to the low‐temperature γ‐Ca2SiO4 is discussed in the light of new data. Evidence is presented for the existence of a pentavalent chromium compound, Ca3(CrO4)2, having solid‐solution relations with Ca3SiO4.
Fluoride Analysis of Glasses and Silicate Materials by Pyrohydrolysis Separation
Authors: ADAMS P. B. , WILLIAMS J. P.
Published: June 2006

Fluoride in a wide variety of glasses and silicate materials can be separated by pyrohydrolysis and then determined by titration with thorium nitrate. Pyrohydrolysis is accomplished by passing steam over a mixture of sample and uranium oxide (U3O3) at temperatures of approximately 1000°C. The average reproducibility of results is 2 relative % and the results are in general slightly higher than those obtained by conventional methods of separation. A determination can be completed in about 1 hour.
Structure and Physical Properties of Hardened Portland Cement Paste
Authors: POWERS T. C.
Published: June 2006

Methods of studying the submicroscopic structure of Portland cement paste are described, and deductions about structure are presented. The main component, cement gel, is deposited in water‐filled space within the visible boundaries of a body of paste. Space filled with gel contains gel pores; space not filled by gel or other solid material is capillary space. Hygroscopicity of cement gel, and capillary pores, accounts for various aspects of the properties and behavior of concrete. Data on gel and paste structure are used in discussing strength, permeability, volume stability, and action of frost.
Sintering of High‐Purity Nickel Oxide
Authors: IIDA YOSHIO
Published: June 2006

The results of an investigation of densification and grain growth during the sintering of high‐purity NiO in various atmospheres are presented. The sintering of NiO powders is divided into three stages. Grain growth during the third stage follows the empirical equation D2=K t, where D is the average grain diameter, K a rate constant, t the sintering time. The activation energy of grain growth was found to be 55 kcal. per mole. The shrinkage and weight loss during the sintering process in vacuum were larger than in argon, air, and oxygen. Grain growth during sintering also differed with the sintering atmosphere. It was concluded that the sintering process is not explained reasonably by the theory of a semiconductor.
Density Studies on the Function of Rare‐Earth tons in Glass Matrices
Authors: VICKERY R. C. , SEDLACEK R.
Published: June 2006

The effect on density of the inclusion of low concentrations of rare‐earth ions in lead silicate, soda‐lime, and phosphate glass matrices has been studied. Significant changes are noted in these density values that are particularly noticeable in phosphate glasses and least noticeable in lead glasses. It is considered that the variable function of the Pb2+ ion obscures the general effect of rare earths in lead silicate glasses; but in soda‐lime, and more specifically in phosphate glasses, evidence is highly satisfactory that the lanthanons (La through Lu) function only as network modifiers, and that scandium and yttrium in concentrations of >0.2 and 1.0 atomic % function strongly as network formers. This is shown to be in accord with concepts associating glass function with cation electronegativity.
Structural Interpretation of Immiscibility in Oxide Systems: III, Effect of Alkalis and Alumina in Ternary Systems
Authors: LEVIN ERNEST M. , BLOCK STANLEY
Published: June 2006

The structural interpretation of immiscibility expounded in Parts I and II is extended to include the effect of homogenizers, i.e., alkalis and alumina. Consistent with previous deductions, coordination configurations are postulated to illustrate the dominant role of the homogenizer cation in coordinating incompatible structural units of the melt. Two semi‐independent methods are used to arrive at a quantitative estimation of the amount of homogenizer required for complete miscibility in ternary silicate and borate systems. Both methods yield values of the proper order of magnitude when compared with the limited amount (both in extent and accuracy) of available observed data.
Initial Sintering of Alumina and Hematite
Authors: COBLE R. L.
Published: June 2006

Experimental measurements of the rate of shrinkage of pressed Al2O3 compacts, the neck growth between single‐crystal Al2O3 spheres and plates, and the effect of particle size on neck growth between single‐crystal Al2O3 spheres and plates are mutually consistent with the bulk diffusion sintering model. Tbe temperature dependence of the rate of shrinkage and neck growth in Al2O3 is characterized by an activation energy of 165 kcal. per mole. Apparent diffusion coefficients and temperature dependence calculated from the shrinkage of pressed compacts of Fe2O3 agree with measured diffusion coefficients for the diffusion of Fe in Fe2O3.
Calcium Carbonate Decomposition in Carbon Dioxide Atmosphere
Authors: HYATT EDMOND P. , CUTLER IVAN B. , WADSWORTH MILTON E.
Published: June 2006

Calcite crystal fragments of known surface area were decomposed in controlled carbon dioxide atmospheres. The decomposing sample was weighed continuously on an automatically recording thermobalance and a rate of weight loss per unit area was obtained. A rate expression involving actual and equilibrium CO2 pressures and the decomposition rate in pure nitrogen was derived. The mechanism of the decomposition is pictured as being a two‐stage phenomenon. Initially the CO2 leaves the CaCO3 cell and the residue of the CaO apparently assumes a metastable rhombohedral configuration similar to the original CaCO3. The second step of the reaction is the formation of well‐crystallized CaO from the active CaO. The active CaO thus acts as a bridge for this reversible reaction.
Thoria‐Urania Bodies and irradiation Studies
Authors: HOENIG C. L. , HANDWERK J. H. , KITTEL J. H. , BREDEN C. R.
Published: June 2006

Thoria‐urania fuels were irradiated bare and clad in metal jackets of stainless steel, Zircaloy‐II, and aluminum‐1 weight % nickel alloy. These specimens were irradiated in NaK (a sodium‐potassium eutectic alloy) and in water. Irradiation severity was based on the total metal‐atom burnup and on the surface heat flux, and the pellets were evaluated on the basis of dimensional stability, corrosion resistance, and visual analysis, The tests indicated that thoria‐urania solid‐solution bodies apparently are suitable for use as fuels in boiling‐water reactors.
Effects of High‐Conductivity Gases on the Thermal Conductivity of Insulating Refractory Concrete
Authors: WYGANT J. F. , CROWLEY M. S.
Published: June 2006

A method is described by which thermal conductivities can be determined in highly conductive gases without errors due to convection and radiation. Using a concrete composed of crushed insulating firebrick and aluminous cement, thermal conductivities were measured in helium. The k value rose slightly in helium at 1 atm. pressure, and much more in 200 lb. per sq. in. gauge helium. This was thought to be due to fracture of cell walls and greater helium permeation at high pressure. It is shown that several equations predict fairly accurately the k values in helium, using constants derived from k values in air. Calculations were made for K values in pure hydrogen, showing more than a 100% rise above those in air at moderate temperatures, and for k values in atmospheres containing various percentages of hydrogen.
Some Properties of Glasses in the System Barium Oxide–Boric Oxide–Silica
Authors: HAMILTON EDGAR H. , CLEEK G. W. , GRAUER O. H.
Published: June 2006

Densities, refractive indices, liquidus temperatures, and primary phases of glass compositions in the glassforming region of the system BaO‐B2O3‐SiO2 were determined. Anomalous changes in properties were observed for a continuous change in composition. The possibility that there is a relation between the compounds indicated by the phase diagram and the actual units in the glass is suggested.
Effects of the Exchangeable Ion on the Dehydration Properties of Vermiculite
Authors: ERNST W. S. , HAVENS I. F. , WILSON H. H.
Published: June 2006

Ion‐exchange studies were made on a selected vermiculite from South Carolina, the vermiculite having a base‐exchange capacity of about 100 me. per 100 gm. The material was saturated with magnesium, calcium, barium, sodium, and potassium ions, and differences in dehydration characteristics were noted. In general, it was found that the charge‐radius ratio of the exchangeable ion present exerts considerable influence on the amount and stability of the inter‐layer water present. No correlation between the nature of the exchangeable ion and the expandability of the vermiculite could be found.
Rate of Thermal Dehydration of Muscovite
Authors: HOLT J. BIRCH , CUTLER IVAN B. , WADSWORTH MILTON E.
Published: June 2006

By the use of an automatic thermogravimetric apparatus, weight loss versus time data were collected for muscovite at five different temperatures in the range 738° to 817°C. Initial sample weight rather than the external surface area was found to be a parameter of the rate of weight loss. A rate equation is presented that explains the observed logarithmic time dependence based on a model involving a systematic relief of strain during dehydration. These findings are supported by infrared spectra of muscovite in various stages of dehydration. It is also proposed that during dehydration aluminum ions in the octahedral layer shift from 6‐ to 4‐coordinated positions.
Colors and Magnetic Properties of Iron in Glasses of Various Types and Their Implications Concerning Structure: I, High Alkali Silicate Glasses
Authors: BISHAY ADLI
Published: June 2006

The effect of increase of alkali and the replacement of soda by potash and lithia was studied in glasses containing iron and melted under strongly reducing conditions. An increase of alkali in these glasses causes an increase in the absorption throughout the visible spectrum; this is attributed, from magnetic and optical measurements, to Fe2+04 incorporated in the molecular network of the glass structure and having a very low magnetic susceptibility as found in some black spinels (hercynite).
Internal Stresses in Model Ceramic Systems
Authors: FULRATH RICHARD M.
Published: June 2006

Model ceramic systems of crystals and glass fabricated by vacuum hot compaction were used to study methods of detection of internal stress on the crystalline phase. Effects of the volume fraction of the glass, compaction temperature and time, and crystal particle size in modifying induced internal stress are presented. These effects, together with X‐ray diffraction and wetting studies, indicate that internal stress development is closely connected to wetting of the crystal by the glass and the formation of a second crystalline phase. Limited results regarding influence of internal stress on strength of ceramic bodies indicate that increasing internal stress on the crystal phase decreases the modulus of rupture when the particle size of the crystal component remains constant. The results of this work indicate that the full potential of ceramic systems may not be realized with the presence of internal stress.
Stable and Metastable Equilibria in the Systems Y2O2‐Al2O3, and Gd2O3‐Fe2O3
Authors: WARSHAW I. , ROY RUSTUM
Published: June 2006

The phase equilibrium relations in the systems Y2O3‐Al2O3and Gd2O3‐Fe2O3were examined. Each system has two stable binary compounds. A 3:s molar ratio garnet‐type compound exists in both systems. The 1:1 distorted perovskite structure is stable in the system Gd2O3‐Fe2O3but only metastable in the system Y2O3‐AI2O3. This interesting example of metastable formation and persistence of a compound with ions of highZ/rvalues explains the discrepancies in the literature on the structure of the composition YA1O3. A new 2:1 molar ratio cubic phase has been found in the system Y2O3‐A12O3. Since silicon can be completely substituted for aluminum in this compound, the aluminum ions are presumably in fourfold coordination.
Piezoelectric and Dielectric Properties of Ceramics in the System Potassium—Sodium Niobate
Authors: EGERTON L. , DILLON DOLORES M.
Published: June 2006

High radial coupling coefficients are observed for compositions having up to 50 mole % sodium niobate additions to potassium niobate. The activity diminishes with additional sodium niobate content and disappears beyond about 98 mole % additions. Dielectric constants are relatively low, varying from 450 to 125, depending on composition. A.‐c. losses are high and d.‐c. resistivities are ∼1012ohm‐cm. The low dielectric constants and high coupling obtained in certain regions of the system make these materials promising for solid ultrasonic delay line use, especially where thin sectioned plates are required, as in high‐frequency thickness extensional or thickness shear mode transducers.
Electrical Insulating Properties of Porcelain Enamels on Copper
Authors: BERGERON C. G. , SCHWARZLOSE P. F. , FRIEDBERG A. L.
Published: June 2006

The electrical properties of copper oxide‐bearing porcelain enamels fired on sheet platinum and of the clear base porcelain enamel fired on sheet copper were measured. The dielectric constant, dissipation factor, and resistivity of the coatings were determined from room temperature to 700°F., and at frequencies varying from 0.1 to 100 kc. per second. The effect of firing time, firing temperature, and coating thickness on the copper ion content resulting in the coatings fired on copper was investigated. The copper ion concentration of the porcelain enamels fired on cop per was determined by X‐ray fluorescence analysis. Electrical measurements of coatings fired on platinum and on copper were correlated with the copper ion concentration of the coating. At concentrations in the coating below 5% CuO, some marked changes occurred in the electrical characteristics of the coatings as a function of CuO content. These changes were even more accentuated at elevated temperatures. At concentrations varying from 5% CuO to the saturation point of CuO in the coating (about 20% CuO for coatings fired at 1600°F.), the electrical properties of these coatings at room temperature were nearly unchanged throughout this range, whereas at elevated temperatures the general effect was that of a decrease in dielectric constant and dissipation factor as the CuO content was increased.
Phase Equilibria in the System Na2O – Nb2O5
Authors: SHAFER M. W. , ROY RUSTUM
Published: June 2006

Phase equilibria data, obtained both by differential thermal analysis and by quenching, are presented for the system Na2O‐Nb2O5. Five compounds corresponding to the formulas 3Na2O.1Nb206, lNa2O. 1Nb2O5, lNa2O 4Nb2O6, lNazO.7Nb2O5, and lNa2O. 10Nb2O6 have been found. The compound 3Naz0.lNb2O5 melts congruently at 992°C. The compounds 1Na2O. 4Nb2O6, lNa2O.7Nb2O, and 1Na2O. 1Onb2O5 melt incongruently at 1265°, 1275°, and 1290°C., respectively. The well‐known perovskite structure phase NaNbO3 was found to melt congruently at 1412°C. The transition temperatures in NaNbO5 were checked by thermal analysis and only the major structural changes at 368° and 640°C. could be detected. A new disordered form of NaNbO3 could be preserved to room temperature by very rapid quenching.
Piezoresistance and Piezocapacitance Effects in Barium Strontium Titanate Ceramics
Authors: SAUER H. A. , FLASCHEN S. S. , HOESTEREY D. C.
Published: June 2006

A large piezoresistance response to hydrostatic pressure is reported for a series of ceramic compositions in the system barium strontium lanthanum titanate (Ba, Sr, La)TiO2. This property appears to be closely associated with the Curie region (cubic‐tetragonal phase transition) and the phenomenon of a positive temperature coefficient of resistance for these same compositions. The piezoresistance coefficient, similar to the temperature coefficient of resistance, is positive in the Curie region, and is found to range up to the order of 700 X 10−12sq. cm. per dyne. Consistent with the observed piezoresistance effect, a positive piezocapacitive effect, ranging up to the order of 700 x 10−12sq. cm. per dyne, is observed in these compositions in the absence of the lanthanum impurity which produces semiconduction. It is suggested that these materials may be of interest in pressure‐sensitive devices such as acoustic transducers and pressure‐sensing elements and in techniques for measuring force and displacement.
Dielectric Studies of Some Borate and Phosphate Glasses
Authors: HIRAYAMA CHIKARA , RUTTER MILDRED M.
Published: June 2006

Some borate glasses, with sag points of 350° to 500°C., of high specific resistance and low power factor have been prepared. The power factor of the glasses has been measured to 250° C., and the resistivity has been measured up to temperatures approaching the transformation region. Borate glasses have higher resistivities and power factors than phosphate glasses. An increase in sag point of lead borate glasses by substitution of PbO with BaO, Al2O3, or SiO2 improves their dielectric properties. Depending on the type of glass, the dielectric constant varies linearly with the density of the glass.
Studies on 4CaOAl2.O3.13H2O and the Related Natural Mineral Hydrocalumite
Authors: BUTTLER F. G. , DENT GLASSER L. S. , TAYLOR H. F. W.
Published: June 2006

Single‐crystal X‐ray and electron‐diffraction studies show the existence in one polymorph of 4CaO.Al2O3. 13H2O of a hexagonal structural element with α= 5.74 a.u., c= 7.92 a. u. and atomic contents Ca2(OH)7‐ 3H2O. These structural elements are stacked in a complex way and there are probably two or more poly‐types as in SiC or ZnS. Hydrocalumite is closely related to 4CaO.A12O3.13H2O, from which it is derived by substitution of CO32‐for 20H‐+ 3H2O once in every eight structural elements; similar substitutions explain the existence of compounds of the types 3CaO Al2O3.CaY2‐ xH2O and 3CaO Al2O3 Ca Y xH2O. On dehydration, 4CaO.Al2O3.13H2O first loses molecular water and undergoes stacking changes and shrinkage along c. At 150° to 250°C., Ca(OH)2 and 4CaO.3Al2O3.3H2O are formed and, by 1000°C., CaO and 12CaO.7Al2O8. The dehydration of hydrocalumite follows a similar course, but no 4CaO.3Al2O3.3H2O is formed.
Apparatus for the Oscillating‐Heating Method of X‐Ray Powder Diffraction
Authors: ROWLAND R. A. , WEISS E. J. , LEWIS D. R.
Published: June 2006

An apparatus for obtaining the X‐ray powder diffraction pattern of a sample while its temperature is increasing at a constant controlled rate has been developed. This equipment is described in enough detail to permit duplicate construction. The program controller is continuously sensitive to the sample temperature and controls the amount of power supplied to the sample heater. Complete schematic details of the electronic circuitry are included, and mechanical details of the program generator are illustrated photographically. The dehydration of clays and related minerals is discussed to illustrate the use of this versatile apparatus. The first order diffraction maxima of water‐wet vermiculite and monoionic sodium, calcium, and magnesium montmorillonites are recorded while the sample temperature is increased at the rate of 5°C. per minute. This is then repeated with ethylene glycol substituting for the water. The temperatures of dehydration and of deglycolation depend on the nature of the exchange cation and are shown to increase in the order sodium < calcium < magnesium.
Ceramic and Dielectric Properties of Lead Metaniobate Electrical Ceramics
Authors: NELSON KARL E. , COOK RALPH L.
Published: June 2006

The effect of firing temperature and time on the weight loss, fired porosity, and dielectric properties of lead metaniobate was investigated. The amount of lead oxide lost was found to be a linear function of firing time and in addition increased rapidly as the firing temperature was increased. Specimens fired for 30 minutes at temperatures below 1275°C. had weight losses of less than 1% based on the amount of available PbO present, whereas specimens fired for the same length of time at temperatures greater than 1275°C. had weight losses up to 3.5%. Both a minimum and a maximum point were found in the fired porosity curve of lead metaniobate in the temperature range 1200° to 1350°C. When firing for 30 minutes, the minimum point occurred at about 1225°C. with a porosity value of 8% and the maximum point at 1300°C. with a porosity of 18%. The effect of porosity and weight loss on the dielectric properties of lead metaniobate is presented. The effect of replacing up to 0.7 mole fraction of the lead ion in lead metaniobate by cadmium was investigated. Cadmium additions lowered the Curie temperature and diluted the ferroelectric properties of lead metaniobate.
On the Formation of Fe2+ in the System MgO‐Fe2O3‐MgFe2O4 at High Temperatures
Authors: BLACKMAN L. C. F.
Published: June 2006

The formation of ferrous iron in the system MgO‐Fe2O3MgFe2O4 is of interest in connection with its deleterious effect on the microwave performance of magnesium ferrite, MgFe2O4. The partial reduction of ferric iron in the system at relatively low temperatures is discussed in terms of the preferential diffusion of iron, and its partial stabilization as ferrous iron from lattice energy considerations.
Ceramic Properties of Europium Oxide
Authors: CURTIS C. E. , THARP A. G.
Published: June 2006

Europium oxide of 99.7% purity was compacted into small bars and pellets which were fired at temperatures from 1050° to 1700°C. for 2 to 120 hours in atmospheres that were oxidizing, mildly reducing (open furnace), or strongly reducing. It was found that (1) europium oxide compacts fired in oxygen for 2 hours at 1500°C. bad attained a density of 90% of theoretical and were stable in boiling water, (2) compacts fired under mildly reducing conditions at 1500°C. for 2 hours had attained a density of 84% of theoretical and disintegrated in boiling water, and (3) those fired similarly in a hydrogen atmosphere began to fuse at 1500°C. The linear thermal expansion of the compacts fired at 1500°C. in the open furnace was 10.5 x 10‐6in. perin. per°C. between 0° and 1000 °C. and their molar specific heat between 0° and 800°C. was 33.3 cal. Careful investigation of the structural changes occurring in europium oxide with rising temperature revealed that (1) the low‐temperature (body‐centered cubic) form inverts slowly to the high‐temperature form at approximately 1050°C., (2) the high‐temperature form has monoclinic symmetry, and (3) it does not revert readily to the cubic form; its theoretical density was calculated to be 8.18 gm. per cm.3.
The KaoIinite‐Mullite Reaction Series: I, A Survey of Outstanding Problems
Authors: BRINDLEY G. W. , NAKAHIRA M.
Published: June 2006

This reaction series has been a subject of extensive investigation since the work of Le Chatelier in 1887. Nevertheless, major problems have remained concerned with the nature of metakaolin, the manner in which it transforms into a spinel‐type phase and mullite, and the relation of this spinel‐type phase to mullite. The present survey brings these problems into sharp focus and provides the necessary historical background fora new approach to their solution.
Apparent Temperatures Measured at Melting Points of Some Metal Oxides in a Solar Furnace
Authors: DIAMOND J. J. , SCHNEIDER S. J.
Published: June 2006

Six metal oxides (A12O3, TiO2, Nb2O5, Ta2O5, La2O3, and Dy2O3) were melted in a solar furnace and the apparent temperatures at their melting points were measured by means of a conventional optical pyrometer. The apparent temperatures of three of them (A12O3, TiO2, and Nb2O5) were 2025°, 1840°, and 1496°C. respectively, in close agreement with the melting points as determined by other investigators using other methods. The apparent temperatures of the other three varied widely and bore no relation to their melting points. The method therefore does not have general utility for the measurement of unknown melting points.
Structural Implications of the Electron Microscopy of Glass Surfaces
Authors: WARSHAW I.
Published: June 2006

Electron microscopy of fractured and polished surfaces of commercial silicate glasses by the preshadowed carbon replica technique reveals the presence of inhomogeneities in the glass ranging in size from 30 to 150 a.u. in diameter. Experiments were carried out to prove that the observed features resulted neither from the experimental technique used nor from the reaction of the glasses with atmospheric moisture. It is probable that these inhomogeneities are related to the bulk structure of the glass.
Structural and Thermal Expansions in Alkali Silicate Binary Glasses
Authors: TILTON LEROY W.
Published: June 2006

Two volume‐changing processes that should be considered in detail are (1) distention of networks by added oxides which may swell glass volumes in proportion to the added oxide volumes and (2) angular change in intertetrahedral bonding which may take place at and above annealing temperatures in proportion to the number of metal ions introduced by the modifications. Accordingly, the partial molar volumes of modifiers, νR, are assumed as those of their crystal or liquid states and the partial molar volumes of silica are computed from (1/νS) = 2.20 + 0.00057 (rm– 0.12) (1723 –t). Tentative glass volumes are then computed as Vg= SmνS+ rmνR by use of the mole fractions Sm and rm for silica and nonsilica, respectively. The excess of computed glass volumes, V0, over V as derived from observed densities is taken as a measure of the penetration of modifiers into the network cavities without corresponding distention of the network. By using the computed density of 1.95 for vitron, the value 2.20 for silica glass, and 2.30 as reported for irradiated silica, one can estimate that silica glass consists of 28% vitron and 72% disordered silica in the intervitron tissues. The values of Vg, –V mentioned are found to be in fair accord with expectations computable from the vitron theory.
Temperature Dependence of Plastic Yield Stress of Single Crystals of Magnesium Oxide
Authors: MAY J. E. , KRONBERG M. L.
Published: June 2006

The temperature dependence of the plastic yield stress of cleavage slabs of Norton Company magnesium oxide, containing approximately 0.2%, impurity, has been investigated up to 1000° C. for bending under three‐point loading. Previous thermal history has been found to be an important variable. In particular, annealing followed by a rapid quenching produces a marked softening, and at the same time causes a homogenization of the starting material. Such samples have been found to display inflections in strength versus temperature, corresponding to a minimum near 500°C. followed by a maximum near 700°C. At temperatures above those associated with the inflections the samples show a pronounced drop in load after yielding, and subsequent deformation occurs by jerky flow. The various observations have been discussed in terms of the interactions of dislocations with impurities that may be in precipitate or solution form, depending on past history and conditions at the time of testing. Some experimental information has also been obtained on the effect of strain rate on the plastic yield strength.
Cell Dimensions, Solid Solution, Polymorphism, and Identification of Mullite and Sillimanite
Authors: AGRELL S. O. , SMITH J. V.
Published: June 2006

X‐ray, optical, and chemical data are presented for sillimanites and for a wide range of natural and synthetic mullites. Single‐crystal X‐ray studies have revealed a new type of mullite (called S mullite) characterized by subsidiary sharp reflections in distinction to the extra diffuse reflections of common mullite (called D mullite). Atomic substitution of aluminum in D mullite leads to expansion of a and c but not of b, whereas substitution of iron and titanium in natural mullites gives a slight initial decrease in a and b followed by a subsequent increase; c increases uniformly for all concentrations. The data are consistent with solid solution ranging between the extremes 3Al2O3.2SiO2, 2Al2O3.‐SiO2, and 3(Al0.9Fe0.1)2O3.2SiO2. Cell dimensions of sillimanite vary only slightly. Consideration of the various methods of distinguishing mullite and sillimanite shows that the measurement of cell dimensions is the most reliable and for mullite has the added advantage that the S and D polymorphs may be distinguished and an estimate of the composition obtained for D mullite.
High‐Temperature X‐Ray Diffraction Investigation of the Uranium‐Carbon System
Authors: WILSON W. B.
Published: June 2006

The system UC‐UC2 was investigated at temperatures to 2200°C. utilizing high‐temperature X‐ray diffraction techniques. UC2, which has the CaC2 structure, was shown to transform to the CaF2 structure at 1820°C. Mean coefficients of expansion of UC, U2C3, and UC2 were determined. The decomposition of U2C3 to cubic UC2 and to UC saturated metastably with carbon was observed. Solubilities of UC in UC2 and UC2 in UC were determined near 1800°C. by a method based on lattice‐parameter measurements. The formation of, and existence conditions for, U2C3 were confirmed. It was observed that UC2 tends to decompose toward UC at the extreme temperatures, probably by loss of carbon to CO.
Ferroelectric Behavior in Barium Zirconium Metaniobate
Authors: GOODMAN G.
Published: June 2006

An unusual type of ferroelectric behavior has been observed in barium zirconium metaniobate, BaNb1.5Zr0.25O5.25. The orthorhombic, pseudotetragonal single crystal displays dielectric hysteresis only in its c direction, with normal dielectric properties in the a‐b plane. No evidence of a fist‐ or second‐order ferroelectric‐paraelectric transition has been observed up to 1400°C. The crystal melts incongruently at about 1525°C. A maximum in the dielectric constant occurs at 80°C. when measured at 103 c.p.s. but is not accompanied by any effect in the spontaneous polarization. The temperature of this k′ maximum has the frequency dependence of a dielectric relaxation process with an average activation energy of 0.2 e.v. These properties are consistent with the idea of a higher than second‐order ferroelectric‐paraelectric transition in this material. The dielectric behavior is explicable in terms of 180°“dipole aggregates” having a wide range of activation energies of reversal. There are suggestions in the technical literature of similar behavior in other materials.
The Structure of Some B2O3‐H2O Glasses
Authors: MELLER F. , MILBERG M. E.
Published: June 2006

Boron oxide glasses with compositions corresponding to B2O3, B2O3.0.42H2O, B2O3.0.50H2O, and B2O3.0.63H2) have been prepared and their structures have been studied. Diffractometric X‐ray scattering measurements have been made, and from these, radial distribution functions have been computed. Comparison of the radial distribution functions indicates that the fundamental triangular coordination characteristic of vitreous B2O3 is maintained in the water‐containing glasses. Consideration of the results of complementary infrared and nuclear magnetic resonance studies along with preliminary results of physical property measurements indicates that the glasses of high water content are heterogeneous. It is probable that disordered regions of high hydrogen bond density, approaching HBO2 in composition, are embedded in a matrix approximating vitreous B2O3.
Phase Equilibria in the System La2O3—Iron Oxide in Air
Authors: MORUZZI V. L. , SHAFER M. W.
Published: June 2006

Phase equilibria data are presented for compositions in the system La2O3‐iron oxide in air. Liquidus and solidus curves were obtained by the quenching method in the iron‐rich portion of the system. The remainder of the diagram was determined using a strip‐furnace technique. Two compounds have been found, the ortho‐rhombic perovskite LaFeO3 and a compound with the magnetoplumbite structure corresponding to a composition LaFe12O19. LaFeO3 was determined to melt congruently at about 1890°C. whereas LaFe12O19 has both a stability minimum and maximum at 1380° and 1421°C., respectively. The iron‐rich portion of the system is essentially ternary whereas the remainder can be considered to be a simple binary. Liquid compositions have been determined and are plotted in terms of the ternary system La2O3‐Fe2O3‐FeO.
Electron Microscope Studies of MuIIite Development in Fired KaoIinites
Authors: COMER JOSEPH J.
Published: June 2006

Preshadowed carbon replicas were used to follow changes in surface texture of poorly crystallized and well‐crystallized kaolinites after firing to various temperatures between 850° and 1200°C. X‐ray diffraction was used for phase identification. Mullite was observed consistently in preferred orientation on the large well crystallized kaolinite stacks but not on poorly crystallized specimens. Failure to detect mullite in preferred orientation in the latter may be due to flow of the reaction products which occurs in these specimens at temperatures below that at which mullite can be detected by electron microscopy or X‐ray diffraction.
Trapped Electrons in Irradiated Quartz and Silica: I, Optical Absorption
Authors: NELSON C. M. , WEEKS R. A.
Published: June 2006

Evidence is given for the correlation between an optical absorption band at 2300 a.u. and an electron spin resonance system developed in quartz after 60Co γ‐irradiation. The results of bleaching γ‐irradiated quartz and silica at 78°K. and at room temperature are presented and discussed. Also, further observations upon annealing these color centers are given.
Trapped Electrons in Irradiated Quartz and Silica: II, Electron Spin Resonance
Authors: WEEKS R. A. , NELSON C. M.
Published: June 2006

The correlation of two paramagnetic defects, observed by the electron spin resonance (ESR) technique, with two optical absorption bands produced by r‐ray or neutron irradiation is indicated. The peaks of the two absorption bards fall at ∼2100 8.u. and 2300 a.u. The effective g values for the ESR lines, for a crystal orientation with respect to the magnetic field of 100.1] parallel to H2, are 2.0006 plusmn; 0.0005 for the 2100 a.u. band, and there are two lines observed for the 2300 a.u. band at [g= 2.0007 and g= 2.00091 ± 0.0005. The correlation of the optical bands and ESR lines was established by a series of bleaching and annealing experiments. These experiments also establish the presence of another center which is not observed directly by either the optical or the ESR technique. ESR lines were observed which were attributed to a hyperfine interaction, A= 7.7 oersteds, of the g= 2.0006 (2100 a.u. band) defect with the Si29 isotope (I = 1/2, 4.7% abundance). Models for these defects, consistent with the experimental data, are suggested.
Synthesized Impurity Centers in Fused Silica
Authors: LELL E.
Published: June 2006

Fused silica has been prepared with controlled amounts (0.02 to 2.0%) of aluminum and lithium added. Absorption spectra and thermoluminescence reveal little difference between undoped specimens and those containing Li or Al alone. The simultaneous presence of Al and Li is essential to build up the absorption band at 2.3 e.v. (520 mμ) and increase the intensity of the bands at 4.1 e.v. (300 mμ) and 5.7 e.v. (220 mμ). A dependence between impurities and absorption of the three bands is given. Whereas all specimens show luminescence peaks at 120°C., those containing Al and Li simultaneously show an additional peak at 310°C.
X‐Ray Study of Phase Transitions in Ferroelectric PbNb2O6 and Related Materials
Authors: SUBBARAO E. C.
Published: June 2006

The phase transitions in PbNb2O6 and in compositions of the type Pb1+x (BxNb1‐x)O6, where B = Ti4+, Zr4+, or Sn4+, have been investigated between 25° and 650°C. using X‐ray and dilatometric techniques. The modified PbNb2o6 compositions possess orthorhombic PbNb2O6‐type structure, with the additional Pb2+ ions occupying vacant lattice sites. The lattice parameters a and c expand and b contracts during heating until, at the ferroelectric Curie temperature, a and b suddenly coincide and c expands slightly. Besides this phase change at the Curie temperature, the nonstoichiometric compounds show an additional phase transition in the range 450° to 300°C. depending on composition. The intermediate phase of Pbl+x(Ti2Nb1‐z)2O6 appears to possess orthorhombic symmetry.
The System UO2‐ZrO2
Authors: Evans P. E.
Published: June 2006

A phase diagram is proposed for the system UO2‐ZrO2 on the basis of earlier work and the results of new studies in which the mixed oxides were melted in a solar furnace to avoid contamination. X‐ray diffraction measurements were made on specimens melted in helium and on the same specimens after heating to 1350°C. in helium. The system shows a narrow two‐phase region about the eutectic at high temperatures which increases in extent at lower temperatures. The high‐temperature form of zirconia cannot be stabilized by the addition of UO2.
Surface Structure in Corundum: I, Etching of Dislocations
Authors: SCHEUPLEIN ROBERT , GIBBS PETER
Published: June 2006

Triangular etch pits, corresponding to the intersection of individual edge dislocations with the surface, have been observed in corundum single crystals after about 5 minutes of immersion in boiling phosphoric acid. Dislocations of both the (0001), (1120) and (1210), (1010) slip systems (where reference is made to the slip plane and slip direction, respectively) have been detected by this method. Edge dislocations of the (0001), (1120) system etched on surfaces close to and including the (1011) and {2021} planes. Dislocations of the {1210}, (1010) systems etched on the basal (0001) plane. The orientation dependence and technique of etching is described. The agreement with the Nye formula and with some of the expected properties of dislocations is cited as evidence that individual edge dislocations are actually detected. Typical photomicrographs of the etched surface in as‐received, deformed, flame‐polished, and polygonized crystals are shown. The dislocation structure produced in basally deformed crystals was found to depend critically on the constancy of the temperature during deformation. Crystals held at 2000°C. during bending exhibited dislocations arrayed in rows in the slip planes in good agreement with the Nye formula. Crystals bent while cooling (quench‐bent) had about twice as many dislocations as predicted by the Nye formula and these were distributed randomly. The possibility of vacancy condensation as a method for dislocation generation in quench‐bent crystals is discussed.
Some Phenomena Related to the Hydrophobicity of Silicate Glasses and Adsorbed Oxygen
Authors: ANDERSON SCOTT , KIMPTON D. D.
Published: June 2006

A number of silicate glasses have been melted which can be made to support a drop of water with a contact angle near 90°. It is demonstrated that the hydrophobicity is caused by a layer of semi‐chemisorbed oxygen. The oxygen is adsorbed at active centers which are related to the presence of octahedrally coordinated metal ions.
Gamma‐Ray Induced Coloring of Some Phosphate Glasses
Authors: BISHAY ADLI M.
Published: June 2006

The changes in gamma‐ray induced optical absorption in phosphate glasses resulting from changes in composition, conditions during melting, and additions of small amounts of some oxides are discussed. A resolution of the induced spectra showed that the observed absorption is due to the superposition of three bands at 2.3, 2.9, and 5.5 e.v. (540, 425, and 225 mü) and to a fourth band whose absorption peak is beyond 6 e.v. The ultraviolet induced absorption increases, whereas the visible absorption decreases in glasses melted under reducing conditions as opposed to those melted under normal conditions in air and on replacement of K+ by Na+ or Li+. A similar effect is produced on replacement of Ba++ by Pb++ and on the addition of T12O to a CaO‐P2O5 glass or the addition of As2O3 to a CaOP2O5, GeO2 glass. Additions of large amounts of GeO2 are accompanied by a decrease in the number of nonbridging oxygens and a decrease in the visible induced absorption. Replacement of Ca ++ by Ba++ ions showed an over‐all decrease in the induced absorption. The addition of small amounts of the oxides of germanium, titanium, iron, thallium, niobium, and arsenic showed an appreciable effect in inhibiting the visible induced coloration.