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OUCHI, HIROMU; NISHIDA, MASAMITSU; HAYAKAWA, SHIGERU
doi: 10.1111/j.1151-2916.1966.tb13171.xpmid: N/A
Effects of additives on the piezoelectric properties of Pb(Mg1/3Nb2/3)O3‐PbTiO3‐PbZrO3 ceramics in a perovskite‐type structure are described. The tetragonality of Pb(Mg1/3Nb2/3)0.375‐Ti0.375Zr0.25O3 ceramics increased with the addition of NiO, Cr2O3, or Fe2O3 but decreased with the addition of MnO2 or CoO. The dielectric and piezoelectric properties of the base composition were improved markedly through selection of additives in proper amounts. Addition of NiO yielded a high dielectric constant and planar coupling coefficient for compositions at the morphotropic transition boundary. High mechanical Q‐factors and low electrical dissipation factors were obtained by addition of MnO2. Addition of both NiO and MnO2 produced a mechanical Q‐factor of 2051 and a planar coupling coefficient of 0.553. The resonant frequency of Pb(Mg1/2Nb2/3)0.4375Ti0.4375 zr0.125O3 containing MnO2 had very low temperature and time dependence. The microstructure indicated that ceramics with a high mechanical Q‐factor had a fine, uniform grain structure. Addition of Cr2O3 retarded grain growth and addition of MnO2, NiO, CoO, or Fe2O3 promoted grain growth in the ternary system.
SCHWARTZ, MICHAEL; MACKENZIE, J. D.
doi: 10.1111/j.1151-2916.1966.tb13172.xpmid: N/A
Glasses in the system CaO–SiO2 were prepared with the composition varying from 40 to 55 mole % CaO. The Na2O impurity content ranged from 0.01 to 1.30 mole %. The electrical resistivity was insensitive to the Na2O content but decreased with increasing CaO concentration. The activation energy for conduction ranged from 33.54 to 31.23 kcal/mole as the CaO concentration increased. The conduction mechanism was considered in terms of three arbitrary parameters: (1) equivalent oxygen packing density, (2) ionic radius, and (3) ion‐oxygen attraction.
MOCHEL, ELLEN L.; NORDBERG, MARTIN E.; ELMER, THOMAS H.
doi: 10.1111/j.1151-2916.1966.tb13173.xpmid: N/A
Removal of soda from a glass surface at high temperature can, on cooling, give appreciable strengthening due to lowering of the expansion coefficient at the surface. Soda depletion has been accomplished previously by treating a high‐expansion soda‐lime glass with SO2 in the presence of oxygen and water. The depletion rate can be doubled by using dispersed platinum to catalyze the oxidation of SO2 to SO3 before the gas reacts with soda from the glass. The data are consistent with the soda depletion being Fickian both with and without the catalyst. Alumina in the glass composition markedly increases the strength which can be attained by sulfur oxide treatment. Although the percentage of soda retained in the leached layer increases, the total amount of soda removed from the glass also increases as alumina increases. It must follow that the depth of the layer is increased.
doi: 10.1111/j.1151-2916.1966.tb13174.xpmid: N/A
Reactions occurring during the heating of pyrite depend on the atmosphere. Fe2O3 is formed under good oxidizing conditions; FeS is formed when the atmosphere is low in oxygen. This is shown by DTA, X‐ray diffraction, and total sulfur determinations on iron sulfides, on their mixtures with illitic clays and inert materials, and particularly on shales. The importance of the steam that evolves from the clay is shown. A mechanism for the reactions involving pyrite during the firing of a brick is discussed.
PASSMORE, E. M.; DUFF, R. H.; VASILOS, T.
doi: 10.1111/j.1151-2916.1966.tb13175.xpmid: N/A
Creep of polycrystalline MgO was studied using four‐point transverse bending at 1380° to 1800°K and stresses from 1000 to 5000 psi. The effects of temperature, stress, and grain size on the creep rate were determined for grain sizes from 2 to 20μ. Activation energies for creep decreased sharply with increasing grain size from 96,000 cal/mole at 2μ to 54,100 cal/mole at 5.5μ and then remained constant over the grain‐size range 5.5 to 20μ. Creep was attributed in part to a stress‐directed diffusional mechanism controlled by extrinsic oxygen ion diffusion in the 5.5 to 20μ grain sizes, although the calculated ionic self‐diffusion rates were higher than those predicted by the Nabarro‐Herring theory. It is suggested that the discrepancy may be due to a vacancy formation mechanism, which is consistent with the observed formation of dislocation substructure and preferentially distributed porosity during creep, as well as with the observed decrease in creep rate with increasing creep strain.
doi: 10.1111/j.1151-2916.1966.tb13176.xpmid: N/A
The compound BaFeO3‐x exists in many forms, the hexagonal phase having a wide range in oxygen content (BaFeO2.63–2.92). The other phases have the limited compositions and the distinct structures of perovskite: triclinic I, BaFeO2.50; triclinic II, BaFeO2.64–2.67; rhombohedral I and II, BaFeO2.62–2.64; and tetragonal, BaFeO2.75–2.81. The phases contain Fe4+ ions correlating with the oxygen content. The hexagonal phase shows a continuous change in oxygen content with temperature down to BaFeO2.63. The perovskitelike phases, however, show characteristic transformations. The triclinic I phase oxidizes to the triclinic II form at 320° to 500°C and to the hexagonal form at 720° to 915°C in oxygen. These transformations are related to oxidation‐reduction of iron ions (Fe3+⇌ Fe4+).
doi: 10.1111/j.1151-2916.1966.tb13177.xpmid: N/A
Infrared spectra of binary and ternary compositions in the glassy state and in the devitrified crystalline state in the system GeO2‐P4O10‐V2O5 were studied and compared with infrared spectra of crystalline spinels, which are known to contain V5+ ions in sixfold coordination. Results indicated that the fundamental vibration frequency of the V—O bond occurred at wave number 1015 cm−1. The spectra also provided evidence that the V5+ ion existed in sixfold coordination in the glassy state, as well as in the devitrified crystalline state, and that the VO6 octahedron retained its identity even at low concentrations and melting temperatures of 1450°C. Conductivity measurements indicated that, as the concentration of V2O5 decreased below the critical range of 5 to 10 mole %, there was an abrupt loss in the electronic conductivity of the glasses; the conductivity decreased with increasing concentration of the lower valence states of vanadium. A mechanism of conduction compatible with the structure of glasses in the system is suggested to explain these observations.
doi: 10.1111/j.1151-2916.1966.tb13178.xpmid: N/A
When a magnesia‐chrome refractory is heated in air a reaction layer develops around the chromite grains. This layer is magnesioferrite at 800°C; above 800° it comprises a solid solution of spinel of the type Mg(Al,Cr,Fe3+)2O4 and a magnesiowustite solid solution. As the temperature increases, the composition of the spinel in the reaction layer changes toward enrichment in chromium and aluminum and impoverishment in iron. A direct‐bond chromite‐periclase, well defined at about 1750°C, is formed essentially by diffusion. In slowly cooled specimens the average composition of the spinel in the reaction layer in the direct bond approximates to Mg(Al0.05Cr0.40‐Fe0.10)2O4. The order of diffusion of the individual ions from chromite to periclase is: Fe ≫ Cr > Al. This order can be explained by considering the charge and size of ions involved and the energy required to create cation vacancies. In specimens quenched from high temperatures the concentration of the magnesium‐rich phases in the silicate pockets increases in the direction of the periclase grains whereas the calcium‐rich phases are concentrated at the center of the pockets.
doi: 10.1111/j.1151-2916.1966.tb13179.xpmid: N/A
Young's modulus, shear modulus, and modulus of rapture for two chemically strengthened glasses were determined at high temperatures. The Young's modulus and shear modulus decreased with increasing temperature, with a sharp inflection slightly above room temperature. The region of inflection indicated an internal friction peak. For comparison Young's modulus and shear modulus were determined as a function of temperature on a thermally tempered soda‐lime‐silica glass and on a semitempered borosilicate glass. Curves of these moduli, in contrast to those for the chemically strengthened glasses, did not reveal regions of inflection. The modulus of rupture is not affected by short exposure to heat up to 260°C., but decreases appreciably when exposed to temperatures above 204°C for 200 hr or more. Deflection measurements at room temperature showed that the two chemically strengthened glasses had about five times as much delayed elasticity as did thermally tempered soda‐lime‐silica glass.
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