摘要:

Optical transmittance and crystal‐lattice distortion and their relation were studied in hot‐pressed La‐doped Pb zirconate‐titanate (PLZT) ferroelectric ceramics at the ferroelectric‐antiferroelectric morphotropic phase boundary. In the thermally annealed condition, the crystal system of PLZT at the FE‐AFE morphotropic phase boundary was pseudotetragonal and similar to the antiferroelectric phase (AFEβ) appearing in Pb(Zr, Ti)O3and (Pb, Sr)ZrO3. Optical transmittance and crystal‐lattice distortion change monotonically with respect to the Zr/Ti ratio, and the optical transmittance increases approximately linearly with decreasing lattice distortion. In view of these relations and the temperature dependence of the optical transmittance, it is suggested that light scattering in PLZT ceramics is caused mainly by the variation in refractive index encountered as the light travels from one domain or grai

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18998.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

A cell was set up consisting of a reference melt and a mixture of sodium metasilicate and sand at 1100°C. Since the liquid phase of the mixture continuously changed composition as the reaction proceeded, the emf also changed and provided a method of studying the rate of reaction. In the early stages of the reaction, the emf obeyed an equation derived from the assumption that the rate of attack on the sand particles was directly proportional to their surface area and to the chemical potential gradient of Na2O across a boundary layer

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18999.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

An imaging technique was developed for measuring the thermal conductivity and diffusivity of small disks of refractory oxides at temperatures ranging from 1500°K to the melting point of the material. One face of the sample is exposed to the radiant heat flux of an arc‐imaging furnace. A shutter instantaneously cuts off incident radiation, and the cooling of the specimen is recorded with a motion‐picture camera. The flux re‐radiated by the nonirradiated face of the sample is measured with a thermopile. Thermal conductivity and temperatures in the bulk of the sample are determined by computational analysis. Experimental data are fitted to computed cooling‐temperature curves to determine thermal diffusivity. This technique was applied to pure and stabilized ZrO2, Y2O3,

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19000.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Studies were continued on the effects of surface‐active environments on the hardness and the rates of drilling and abrasive wear of mono‐ and polycrystalline Al2O3. Changes in hardness induced byn‐alcohols and various aqueous environments were correlated with changes in ζ‐potential, hardness being maximum at the point of zero charge (pzc). Diamond‐core drilling rates exhibited a similar relation. Studies of the environment‐sensitive abrasive wear of both mono‐ and polycrystalline Al2O3on a diamond‐impregnated metallographic wheel revealed more complicated behavior. The wear rate of Al2O3undern‐alcohols is markedly dependent on the viscosity of the environment, with little or no correlation with ζ‐potential being evident. Studies using methanol‐water mixtures indicated, on the other hand, a slight viscosity dependence and the converse correlation with ζ‐potential to that observed in diamond‐core drilling, i.e. the rate of material removal was lowest at the pzc. Tests in aqueous solutions revealed no dependence on viscosity, but a strong inverse dependence on ζ‐potential, wear rate again being lowest at the pzc. These and other results are interpreted in terms of the various influences of adsorbed species on the near‐surface fl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19001.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The 1780°C isothermal section of the reciprocal quasiternary system Si3N4‐SiO2‐BeO‐Be3N2was investigated by the X‐ray analysis of hot‐pressed samples. The equilibrium relations shown involve previously known compounds and 8 newly found compounds: Be6Si3N8, Be11Si5N14, Be5Si2N6, Be9Si3N10, Be8SiO4N4, Be6O3N2, Be8O5N2, and Be9O6N2. Large solid solubility occurs in β‐Si3N4, BeSiN2, Be9Si3N10, Be4SiN4, and β‐Be3N2. Solid solubility in β‐Si3N4extends toward Be2SiO4and decreases with increasing temperature from 19 mol% at 1770°C to 11.5 mol% Be2SiO4at 1880°C. A 4‐phase isotherm, liquid +β‐Si3N4(ss)Si2

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19002.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Transformational superplasticity associated with the eutectoid reaction in the Bi2O3‐Sm2O3system was observed and characterized in hypoeutectoid and hypereutectoid compositions. Transformational strain varied linearly with applied stress and exhibited a stress‐axis intercept, or threshold stress, that is related to the proeutectoid microconstituent. Results are explained quantitatively using the analysis by Greenwood and Johnson and a creep mechan

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19003.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The effect of heat treatment on the microstructure of Li2O‐Al2O3·SiO2glass‐ceramics which contain crystals of either Li2SiO3, Li2Si2O5, or both was investigated quantitatively. Strength determinations for abraded rods were correlated with heat treatment on the basis of both size and distribution of crystals and the type and amount of crystal phases present. The presence of Li2Si2O5crystals enhanced the strength, whereas the presence of Li2SiO3crystals did not change the strength of the abraded parent glass. The interrelation between strength and microstructure is discu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19004.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The solubility of WC in TiC was found to vary from 50 mol% at 2050°C to 75 mol% at 2350°C; WC was precipitated from solid solutions containing 75 mol% WC‐25 mol% TiC and 65 mol% WC‐35 mol% TiC at 1900°C. The precipitated WC occurred as well‐aligned ribbon‐shaped particles. The crystallographic orientation of the precipitate and the matrix established by electron diffraction techniques is [100]WC[110]TiCand [010]WC[001′]TiC. The interfacial planes were (001) for WC and (111) for TiC solid solution. Diffraction spot splitting occurred for all reflections of precipitated WC except the 001 type, indicating that compression of WC along the [110] direction took place, resulting in an apparent orthorhombic symmetry. This phenomenon was explained on the basis of the specific volumes and the difference in thermal expansion coefficient between WC and the solid solution. Tungsten carbide precipitated rapidly in the presence of Co, with all the WC precipitating in the form of platelets randomly oriented around the matrix grains. The hardness of the solid solutions 65 mol% WC‐35 mol% TIC and 75 mol% WC‐25 mol% Tic increased ∼10% and ∼23%, respectively, after they wer

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19005.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The wetting of several new materials for gas turbine engines, e.g. SiC, Si3N4, and C, by liquid Si and binary Si alloys containing Cu, Fe, and B was determined by the sessile drop method. All contact angles measured were<90°. Hot‐pressed SiC, Si3N4, and Refel SiC are easily wet by Si; wetting is controlled by the balance of interfacial energies. Carbon is wet well by Si, but wetting is controlled by reaction and, in some carbons, by infiltration of Si into C. Additives to Si such as B and Fe can form compounds in reaction zones during wetting at interfacial are

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19006.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Strength losses in diboride ceramics resulting from load cycling near ultimate strength and from thermal cycling to 3000°F were investigated. Specimen configurations included notched and unnotched flexural specimens as well as specimens oriented in 3 orthogonal directions with respect to the billet pressing direction. Flexural fatigue testing for 2 to 8 million cycles produced no failures when stress levels were below 80% of flexural control strengths. Static loading of specimens that survived the fatigue test revealed no strength deterioration as a result of stress cycling. Thermal exposure produced an oxide coating; strength reductions caused by thermal cycling could be correlated with the thickness of this coating

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb19007.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY