ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12200.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Relaxation phenomena were observed in sintered Y2O3at frequencies from 10−3to 105Hz at 150°, 200°, 255°, 306°, and 357°C. The observed dispersion is predicted approximately by a theory requiring exponential decay of the polarization. The theory describing the larger lower‐frequency relaxation should be based on an interfacial mechanism with an inter‐granular region of higher conductivity. Electrode effects cannot be ruled out, however, on the basis of the present work. The most probable basis for the theory describing the smaller higher‐frequency relaxation is defect‐dipol

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12201.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Polycrystalline BaTiO3prepared from alkoxy‐derived high‐purity submicron powders was studied. Highly dense bodies with uniform grain size were obtained typically by uniaxial cold‐pressing at 3000 psi and isostatic pressing at 30,000 psi followed by sintering at 1300° to 1350°C in air for 0.5 to 1 h. Using the same consolidation parameters and intimate mixing of residual concentrations of highly active fine‐particulate rare‐earth oxides to act as grain‐growth inhibitors, nearly theoretically dense bodies with a uniform microstructure and 1 to 1.5 μm grain size were obtained. Typical microstructures with well‐defined 90° and 180° domain patterns characteristic of BaTiO3: were observed. Also, an example of a checkerboard pattern resulting from a 〈111〉 ingrown twin plane in the structure which is independent of the Curie temperature was found. Electrical measurements on the undoped material indicated room‐temperature dielectric constant and tan δ values of 5000±500 and 4×10−3, respectively. Very highkvalues and dissipation factors were observed with the L

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12202.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The effects of adsorbed H2O on the dielectric properties of ultrafine BaTiO3particulates of varying particle size and environmental history were determined. The dielectric behavior depends strongly on surface hydration. No particle size dependence of dielectric constant was found for dehydroxylated surfaces in ultrafine particulate (unsintered) BaTiO3materials. For equivalent particle sizes, the ac conductivity is sensitive to surface morphology. Reactions with H2O vapor appear to account for the variations in dielectric properties. Surface dehydration was effectively accomplished by washing as‐received powders in isopropano

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12203.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Fine particle size, high‐purity BaTiO3powder was used to fabricate sintered and hot‐pressed specimens. A second phase, BaTi3O7, frequently developed in samples fired at high temperatures. The dielectric properties of many specimens had frequency dispersions characteristic of interfacial polarization or other related space charge effects. Controlled particle size specimens were fabricated by hot‐pressing and the temperature dependence of their dielectric properties was evaluated as a function of heat trea

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12204.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The uv absorption spectra caused by Pb in bulk silicate glasses and in a film sputtered from 1.08 PbO·SiO2glass are measured. Lead causes a strong absorption band between 5 and 6 eV. Vacuum uv measurements on the sputtered film reveal a second, much larger, absorption band that has a maximum near 7.6 eV and that is tentatively attributed to excitation of an O ion bonded to a Pb2+ion

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12205.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The kinetics and mechanism of eutectoid decomposition of CuFe5O8were studied by X‐ray diffractometer, electron probe microanalyzer, and reflecting‐light microscope techniques. The isothermal decomposition curves were sigmoidal and the maximum rate of decomposition occurred at ∼600°C. Sigmoidal‐type curves indicated that the decomposition proceeded by a process of nucleation and growth. Kinetic data were best expressed by Avrami's equation with n≃2 and n≃4 below and above 850°C, respectively. A “site saturation” mechanism is suggested. Bainite‐type and pearlite‐type microstructures were observed below and above 800°C, respectively. Grain boundaries were active sites in

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12206.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Apatites can be used as bioceramic materials for tooth and bone implants. Infrared (4000 to 400 cm−1) and laser‐Raman spectra were obtained for hydrothermally prepared hydroxyapatites with the general formula X10(PO4)6(OH)2where X= Ca2+Sr2+, Ba2+, or Pb2+Fundamental vibrational modes were identified and empirical band assignments made. Analysis of the vibrational spectra led to the reassignment of thev2mode to a higher wave‐number, lower‐intensity band (e.g. ∼470 cm−1for Ca hydroxyapatite). Effects of solid‐state interaction were noted in the vibrational spectra and interpreted by factor‐group analysis. An “effective” factor group C6h, which neglects the locations of the OH−ions, best describes the vibrational spectra o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12207.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Magnesium ferrite of composition Mg0.993Fe2.007O4was quenched from 1000°, 1150°, and 1295°C. The rate of inversion at 450°C was followed by Curie temperature measurements in a thermo‐gravimetric analyzer. The inversion process possessed the features of a nucleation and growth transformation. It is postulated that short range order within the octahedral sub‐lattice plays an important role in cation ordering in Mg

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12208.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Nonlinear deflections and radial surface stresses in thin elastic circular plates laterally deformed into symmetrical concave shapes are analyzed. The deformations are induced by loading each plate with a small center ring while the plate is resting on a ring of nearly the same diameter as the plate. The rings and plate are coaxial, i.e. concentric. Center deflections up to 3 and 4.5 times the plate thickness were predicted for ring‐diameter ratios of 0.5 and 0.2, respectively. The predicted deflection profiles at various loads agreed quite well with those which were determined experimentally on a chemically strengthened glass plate. This analysis provides a new criterion for using the coaxial‐ring loading method for flexural strength testing of brittle materi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12209.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY