摘要:

Transformational plasticity associated with the monoclinic‐to‐cubic phase transition at 730°C in Bi2O3was observed and characterized. This phenomenon is explained in terms of Greenwood and Johnson's model of internal stress‐induced deformation, proceeding, in this instance, by a time‐dependent, grain‐size‐sensitive creep mechanism, probably grain‐boundary sliding. Criteria are proposed for choosing other prospective transformationally plastic ceramics; they are met by Bi2WO6, which also exhibits extensive transformat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18978.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

High Na vapor pressure, peritectic decomposition, and high reactivity of the melt complicate the growth of α‐alumina crystals. These difficulties were overcome by using a high‐pressure (300 psig) growth chamber, Na2O‐rich melts, and Ir for all surfaces in contact with the melt. These procedures were combined with the edge‐defined film‐fed growth technique to produce single‐crystal β alumina tube

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18979.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The subsolidus miscibility gap for the TiO2‐SnO2system was redetermined. The critical temperature, 1430°C, is intermediate between that determined by Padurow, 1330°C, and that determined by Garcia and Speidel, 1475°C. Although the phase boundary is slightly asymmetric (the critical composition occurs at 47 mol% TiO2), it fits the regular‐solution model down to 1200°C. Calculations of the coherent spinodal using the regular‐solution model indicated depression of the spinodal belowTc, by 105°, 310°, and 387° for composition fluctuations along the [001],, anddirections, respectively. These depressions of the spinodal are much greater than those calculated by Stubican and Schultz; this discrepancy is believed to result from an error in the latter workers’ calculations. During the present work, positive deviations from Vegard's law were found in this system. Both the magnitude and the sign of the deviation can be predicted using a theory based on nonlinear second‐

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18980.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

In the bending of symmetrically loaded circular plates of brittle material, e.g. glass, which are supported between flexible gaskets at the periphery, large errors can result in estimating the stresses and deflections in the plate if it is assumed that the plate is simply supported. This paper uses the exact numerical solution, given elsewhere, in comparing the exact stresses and deflections with those obtained by assuming simply supported edges. It is shown that gasket width and stiffness are important in controlling the maximum stress. The deviation from an assumption of simple support is greatest when the plate is thin.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18981.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The dynamic reaction of SiO2with CaO (1:2 mol ratio) was studied at temperatures up to 1500°C, especially those>1400°C. Simultaneous TG and DTA, high‐temperature X‐ray diffraction (horizontal sample), and high‐temperature microscopy and dilatometry were used. The reactants (CaCO3and quartz) were finely ground and mixed in stoichiometric amounts. Thermogravimetry was used to ascertain that the samples were representative and homogeneous. The reaction mechanism in the dynamic thermal synthesis of Ca2SiO4was elucidated and confirmed by high‐temperature X‐ray

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18982.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The final stage of the reaction mechanism elucidated in Part I of this paper is amenable to quantitative analysis. The reaction between an SiO2‐rich liquid phase and CaO is the rate‐determining step. Measurements were made by DTA and high‐temperature X‐ray diffraction. Activation parameters calculated from the kinetic data agree well with the proposed reaction me

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18983.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The reactivity with water of 3CaO· SiO2stabilized in the tri‐clinic and monoclinic forms with MgO was studied by monitoring the heat of hydration using conduction calorimetry. The early heats of hydration increase moderately when the MgO content brings the sample near the monoclinic‐triclinic transition point. Reactivity increases markedly when samples with high MgO contents are annealed. Annealing appears to cause separation of some of the MgO and also eventually converts monoclinic samples to the triclinic form. Samples containing<0.9% MgO showed a slight reduction in reactivity after they were annealed, but pure 3CaO· SiO2was unaffected. Preparation of the samples and their examination by X‐ray diffraction and chemical extraction methods are described. Possible explanations for the hydration behavior are di

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18984.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

A method for recovering the temperature distribution in glass from remotely sensed spectral emission data was studied. The temperature distribution, which was related analytically to the spectral emerging intensity, was determined by an optimization technique that minimizes the difference between measured and calculated emissions. The method was evaluated by measuring spectral emission from heated glass using both a spectrometer and a spectroradiometer. Data were taken from 600 to 900 K for window glass samples with different back‐surface boundary conditions. The recovered temperature profiles obtained using data from both measuring instruments were compared with each other and with temperature profiles predicted from a combined conduction‐radiation heat‐transfer analysis. When only 2 unknown coefficients were used to represent the temperature distribution, the recovered and predicted profiles agreed with

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18985.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Ceramic electrolytes derived from β‐alumina are cracked by electrolysis under certain conditions. Cracks form only when Na+ions migrate through the ceramic and are converted to metallic Na, as in the charging of an Na‐S battery. The origins of mechanical damage are postulated and examined. A plausible mechanism consists of ceramic dissolution at preexisting surface cracks; it depends on the interaction of capillarity, stress, and selective removal of electrolyte from crack tips by effluxing Na. Relative solute fluxes are calculated for each contributing process. The proposed model is shown to account for many of the experimental observations, most notably a threshold current density below which no degradation is appa

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18986.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The formation of afwillite in tricalcium silicate pastes initiated by ding with crystals was studied to determine the effects on development of tensile strength. Afwillite forms in pastes only when fresh surfaces of both tricalcium silicate and afwillite seed are exposed by initial grinding. Higher early strengths reflect increased rates of hydration in seeded pastes, but strengths at later ages are lower than those of untreated pastes. At all ages tensile strength is lower at a given degree of hydration in seeded pastes than in unseeded ones; this behavior is considered to result from changes in pore‐size distribution which occur as afwillite forms. Afwillite initially forms concomitantly with calcium silicate hydrate gel but later arises from conversion of the ge

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb18987.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY