ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12376.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The dependence of an averaged ionic transport number and the ac conductivity on oxygen activity was determined at 500° and 600°C for Nb2O5‐doped Pb(Zr1‐∞Ti∞)O3(x=0.07, 0.10, 0.20, and 0.35). The electrical conductivity has ap‐character and indicates a complex dependence on [Ti] andPo2. ForPo2<10‐3atm the electrical conductivity increases linearly with [Ti]. For oxygen activities from 1 to 10‐8atm all PZT compositions showed some degree of electr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12377.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The kinetics of paste, bottle, and ball‐mill hydration of 3CaO SiO2and the effects of additions of electrolytes and alcohols were studied. Paste and bottle hydrations proceed through periods of induction, acceleration, and decay. If 3CaO SiO2is hydrated in an excess of H2O, as in bottle hydration, the reaction rate is lower than that for paste hydration. The ball‐mill hydration rate is much the highest and is controlled by the removal of the hydrate layer coating the 3CaO SiO2particles. Electrolytes always accelerate and alcohols retard the reaction rate. Experimental results are discussed with reference to modern theories of the 3CaO SiO2hydration mechan

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12378.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Through pores of hardened cement mortars were studied by gas transfer experiments. The permeabilities were the same for N2and H2. The pore size distribution of through pores was examined by back diffusion; the method was simplified by combining H2and N2gases. The permeability calculated from these results agreed with the experimental values of N2and H2. The neutralization rate of hardened cement was expressed asL2=kθ(t‐ti).The rate of neutralization was determined by the gas diffusion of both CO2and H

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12379.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The high oxygen pressure conductivity of high‐purity single‐crystal magnesium oxide at high temperatures varied as the 1/4 power of the oxygen partial pressure with a 3 eV activation energy; the low pressure conductivity varied as the ‐1/6 power of the pressure with an activation energy of 4 eV. The predominant defects proposed are (1) holes and singly ionized Mg vacancies at high pressure and (2) electrons and doubly ionized oxygen vacancies at low pressures. The effect of impurities was noted. Changes in the grain boundary conductance relative to the crystal conductance of MgO were observed as a function of temperature and pressure, but not as a function of grain boundary orientation, transport direction, or total impurity content. Increased high pressure ionic conductivity in polycrystalline material offered possible evidence for increased grain boundary diff

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12380.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

The ionic transport numbers of BeO, MgO, CaO, and SrO in single‐crystal and polycrystalline samples were examined under low oxygen potentials between 900° and 1180°C. The oxygen potentials were fixed by using metal/metal‐oxide electrodes in electrochemical cells with the samples of the alkaline earth oxides as solid electrolytes. The electromotive forces of these cells were compared with the emf values obtained from similar cells of high stability using high‐purity thoria‐based electrolytes. From the results it could be concluded that under comparable conditions of low oxygen pressure the electron transport number increases with increasing ionic radius of the group II element. Only BeO and MgO approach electrolytic behavior, and this occurs at relatively high oxygen pressures (>

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12381.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Data concerning the types of charge carrier responsible for electrical conduction in single‐crystal aluminum oxide are reviewed, and explanations are offered for discrepancies in terms of the experimental conditions. Measurements on undoped and Co2+and Mg2+doped crystals, made using a volume guard to avoid surface and gas conduction, are used to describe Al2O3as an ionic conductor with Al interstitial ions as the principal charge carriers at high oxygen activity. A defect model is proposed and the mobility of Ali3+, the concentration of Ali3+in undoped crystals, and the equilibrium constant for defect formation at high temperatures are estimate

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12382.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Barium titanate powders with average grain sizes of 0.07 and 0.65 μm were coated with an organic Nb ester, using a liquid‐solid mixing process. Small‐grained (1 to 3 μm) ceramic dielectrics from both powders and large‐grained (>50 μm) dielectrics from the 0.65 μm powder were fired using 0 to 2 at.% Nb. Microstructures, densities, and electrical resistivities were inv

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12383.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Effects of grain size and grain growth in Nb‐doped BaTiO3on temperature and frequency dependencies of the dielectric constant were investigated. When 0.65 μm powder is sintered to an average grain size of 1 μm, two dielectric constant peaks indicate the presence of Nb‐free BaTiO3and of Nb‐containing material. Single peaks are observed above room temperature after additional grain growth or when 0.07 μm powder is sintered to an average grain size of 1 μm. The Curie point of pure BaTiO3with 1 μm grains is 4 to 6°C lower than that of material with grains>10 μm. Thermodynamically, this behavior is accounted for by a phase inversion stress ∼ the room‐te

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12384.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Measurements of Nb diffusion into large‐ and small‐grained BaTiO3disks show a high ratio of grain boundary to bulk diffusivity. Well defined X‐ray diffraction lines are found in Nb‐doped BaTiO3only when significant grain growth occurs during sintering. When grain growth of a 0.65 μm grain size powder is limited at ∼1 μm, excess line broadening results. This is attributed to the simultaneous presence of Nb‐free and Nb‐rich regions. Because of its low bulk diffusivity little Nb penetrates into the original BaTiO3grain cores, and a solid solution forms only in the regions of recrystallization. When grain growth is limited, the “sintering reaction” results in a non‐homogeneous system; when appreciable grain growth occurs, most of the original grain cores are eliminated and an essentially unifo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1971.tb12385.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY