Journal of the American Ceramic Society

KELL, R. C.; GREENHAM, A. C.; OLDS, G. C. E.

doi: 10.1111/j.1151-2916.1973.tb12684.xpmid: N/A

The compounds SrZrO3 and CaZrO3 combine high permittivity with low loss and positive temperature coefficient of permittivity. Temperature‐stable materials were produced by forming solid solutions between these zirconates and zirconates or titanates having negative coefficients. The properties of temperature‐stable compositions in the systems Ca(Zr,Ti)O3 and (Ba,Sr)(Zr,Ti)O3 were investigated. At 4 GHz the relative permittivities were from 29 to 35 and the loss tangents from 3 to 11×10−4. Both permittivity and microwave loss increased as the principal alkaline‐earth ion was changed from Ca to Sr to Ba, but the higher losses could be reduced by adding ∼1 mol% Nb or Ta. Dense fine‐grained ceramics with the properties required for microwave applications were prepared.

HASKELL, R. W.

doi: 10.1111/j.1151-2916.1973.tb12685.xpmid: N/A

The thermodynamics of spinodal decomposition is presented in detail on the basis of Hillert's one‐dimensional model. The flux equation governing the initial kinetics of such processes is also developed. Similarities and comparisons to the Cahn‐Hilliard phenomenological theory are noted.

MORRIS, WILLIAM G.

doi: 10.1111/j.1151-2916.1973.tb12686.xpmid: N/A

The nonlinear volt‐ampere characteristics and small‐signal ac capacitance and resistance of sintered ZnO containing 0.5 mol% Bi2O3 were measured. Many of the electrical properties are related directly to the microstructure, which consists of conductive ZnO grains separated by a continuous amorphous Bl2O3, phase. The origin of the nonlinear conduction in the intergranular phase was confirmed by experiments with evaporated thin films. The proposed conduction mechanism in varistors containing ZnO and Bi2O3 is a combination of hopping and tunneling in the amorphous phase.

BATHA, H. DEAN; WHITNEY, E. DOW

doi: 10.1111/j.1151-2916.1973.tb12687.xpmid: N/A

The kinetics of the thermal decomposition of silicon nitride, Si3N4(s)→3Si(l)+2N2(g), were studied from 1490° to 1750°C using a static system. The reaction was followed by measuring the rate of increase of N2 pressure in the system as a function of time. In the initial stages, the decomposition followed first‐order kinetics, with the rate constant expressed as: In the later stages, the experimental data followed the Jander solid‐state kinetic law, with the Jander rate constant given by: The effects of excess Si and of Ar and N2 atmospheres on the reaction kinetics are also reported.

CHIN, G. Y.; UITERT, L. G.; GREEN, M. L.; ZYDZIK, G. J.; KOMETANI, T. Y.

doi: 10.1111/j.1151-2916.1973.tb12688.xpmid: N/A

Single crystals of NaCl, NaBr, KCl, and KBr containing divalent additions of Ca2+, Sr2+, and Ba2+ were tested mechanically. In the solution‐treated condition, the yield strength, σv, as determined from compression testing in a 〈100〉 direction is essentially dependent on the concentration of the dopant only and is independent of the species of either the dopant or of the host material. All crystals soften on aging, with the exception of the NaCl:Ca2+, NaBr:Ca2+, and NaBr:Sr2+ systems. In addition, correlation was good between σv, and the Knoop hardness number, H, obtained by indentation with the long axis of the indenter aligned in 〈100〉. The equation is of the form σv=C(H–H0), where C≅ 0.21 for all four halide families and H0 is near the hardness value of the pure halides. Furthermore, H0≅5×10−3E111, the Young's modulus in the 〈111〉 direction. Hence σv≅0.21H–10−3E111.

SANDERS, D. M.; HENCH, L. L.

doi: 10.1111/j.1151-2916.1973.tb12689.xpmid: N/A

An approach is developed for understanding formation of gel films on glass surfaces during water exposure. Compositional and microstructural data from ir reflection spectroscopy, scanning electron microscopy, and electron microprobe analysis are used with parameters defined from solution‐analysis data to produce an SiO2 composition profile of the corroded surface. This model profile is compared with a measured profile and used to interpret differences in corrosion resistance of binary Li2O‐ and Na2O‐SiO2 glasses. Effects of corrosion temperature on surface gel structure are also discussed.

TOMOZAWA, MINORU; OBARA, RICHARD A.

doi: 10.1111/j.1151-2916.1973.tb12690.xpmid: N/A

An equation was derived which relates the change in the metastable immiscibility temperature, ΔTm, caused by a minor third component and the corresponding liquidus temperature change, ΔTl. This relation is expressed as where Tm and Tl are the initial immiscibility temperature and liquidus temperature, respectively, S is the entropy of binary liquid, and ΔS is the change in the configurational entropy. For a qualitative estimate, the relation ΔTm∼ΔTl is satisfactory. To evaluate the above equation quantitatively, the entropy must be known. The entropy equation of Charles based on the number of nonbridging oxygen pairs and bridging oxygen atom was used and a reasonable estimate was made of the change of the immiscibility temperatures for selected systems.

EHMAN, MICHAEL F.; AUSTERMAN, S. B.

doi: 10.1111/j.1151-2916.1973.tb12691.xpmid: N/A

A hydrochloric acid chemical etchant for BeO was refined and evaluated. The etchant, when used for 20 min at 120°C on chemically polished surfaces, produces distinctive pits at dislocations intersecting the (0001) and (101) surfaces. Correspondence of etch pits and dislocations was inferred by comparing the enlargement of pits with etching time and the constancy of pit density with continued etching. On {1010} surfaces, the etchant is not sensitive to sites of defect emergence and hence leaves a relatively flat, featureless surface. The etch rates and activation energies are given for {0001}, {1010}, and {101} surfaces. The reaction mechanism is discussed.