ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15941.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

It was possible to drive plastically blunted cleavage cracks through double cantilever beam specimens of impure MgO monocrystals in a series of small propagations. The forces required to propagate the cracks often defined a fairly constant apparent surface energy and provided an environment‐sensitive measure of toughness. Apparent surface energies between 1700 and 3100 ergs/cm2were obtained on MgO crystals tested in air. Values of apparent surface energy obtained from crystals tested in a low water content environment agreed well with values obtained on the same specimens in air, suggesting that water vapor in laboratory air does not significantly affect the toughness of MgO. Specimens tested while immersed in water, however, were approximately 30% tougher than those tested in air and exhibited a faceted fracture surface in contrast to the relatively smooth fracture surface produced in ai

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15942.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The creep of pure magnesia (99.9 +% MgO) was tested in transverse bending at temperatures from 1200° to 1500°C, strain rates near 10−2%/hr, and grain sizes of 4 to 50μ. In most cases, grain growth during the test affected the apparent creep behavior more than all the other variables combined. An analytical graphical method was used to separate the grain growth effect from other effects and to obtain more meaningful creep data. Creep occurred primarily by a viscous mechanism (Nabarro‐Herring type, cation‐lattice‐diffusion controlling) with a minor amount of plastic creep (dislocation climb). The agreement with previous creep dat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15943.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The creep of magnesia doped with 0.035 to 2.26 cation % of nine other oxides and three binary mixtures thereof and of three seawater products (about 96, 98, and 99.5y0 MgO) was evaluated in transverse bending at 1200° to 1500°C, with strain rates of about 10−2%/hr, and average grain sizes of 5 to 50p. The results obtained were compared with those for pure magnesia. Most additives accentuated the plastic (diffusion‐controlled) nature of the creep process presumably by pinning dislocations and/or slowing grain growth. In most cases the rate‐determining diffusing species seemed to be the cation, Mg, but in two cases it was suspected that oxygen boundary diffusion was controlling. Porosities above ˜10% appear to increase the temperature dependence of creep, probably by introducing boundary sliding. The agreement of the creep data with those of other diffusion‐controlled processes (electrical conductivity, sintering, and grain growth) is de

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15944.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Phase relations in air at 1300°C were determined for the system MgO‐Cr2O3−Fe2O3by conventional quenching techniques. Details of the phase equilibria were established for: (1) the sesquioxide solid solution between Cr2O3and Fe2O3, (2) the spinel solid solution field between MgCr2O4and MgFe2O4, and (3) the periclase solid solution field for MgO. Selected tie lines connecting coexisting compositions were established with X‐ray diffractometer data. Diffuse reflectance spectra, diffractometer intensity ratios, and lattice parameter measurements were obtained for quenched samples to study the structural inversion in the spinel series MgCr2O4

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15945.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The densification kinetics of magnesium aluminate spinel during vacuum hot‐pressing were studied between 1175° and 1460° C and from 500 to 5100 psi. A phenomenologi‐cal rate equation, which suggests a logarithmic relation between strain rate and porosity, excellently described the observed densification. Treating porosity as an independent variable was shown to be reasonable; it does not functionally restrict porosity as a modifier of the applied stress. The strain rate dependence on porosity decreased at a porosity of approximately 0.15. Below 1350° C the densification characteristics were similar to those reported for other oxide systems. At 1450°C an increase in the stress dependence of the densification rate and an interaction between stress and porosity suggested that plastic flow by dislocation motion was an operative mechanism during densif

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15946.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Electrical conductivities of binary alkali and thallous silicate glasses have been measured as a function of composition, temperature, and frequency. The best approximation to the activation energy for dc conduction can probably be obtained by extrapolating its frequency dependence to zero frequency, although values obtained at frequencies below 2500 hz do not differ greatly from the dc values. The plot of activation energy for conduction against modifier content consists of two straight lines of different slope. For all the alkali silicate glasses the break in slope occurs near 25 mole % alkali oxide and at an activation energy near 14.7 kcal/mole. The slope of the line below 25 mole % alkali oxide is proportional to the alkali ion radius. The behavior of thallous silicate glass is similar but not identical to that of the alkali silicates. It is concluded that (1) the reported conduction behavior does not result primarily from phase separation, (2) the principal contribution to the activation energy is probably the work required for a mobile ion to pass through the glass network rather than to leave its initial position, and (3) a structural change independent of the nature of the modifier cation occurs near a modifier content of 25 mole %.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15947.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Residual strain measurements on a series of sintered BeO tubes indicate that significant stresses developed during processing from the thermal expansion anisotropy. X‐ray topographic studies show that the resulting strains are preferentially located near grain and subgrain boundaries. Fine‐grained samples, 20μ and less, do not show pronounced subgrain structure and exhibit lower dislocation densities in the grain interiors than do coarse‐grained s

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15948.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The interrelation of hardness, modulus of elasticity, and porosity was investigated in four gypsum systems. Results suggest that intergrowth and interlocking of crystals significantly affect mechanical behavior, at least hardness and modulus of elasticity,E.In addition, both properties are related to porosity,p.This relation can be described empirically by the exponential expression E = Eoexp (— p

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15949.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The seven elastic compliances and seven elastic constants of single crystal calcium molybdate were determined by a resonance method. The compliance s16, which is zero for higher symmetry tetragonal crystals, need not be zero for crystals of lower tetragonal symmetry and contributes significantly to the orientation dependence of the elastic moduli of calcium molybdate. The values of the compliances and their standard errors (based on 41 measurements) in units of 10−11m2/N are s11= 0.974 + 0.005, s33= 0.958 ± 0.004, s44= 2.720 ± 0.009, s66= 2.471 ± 0.022, s12=−0.380 ± 0.010, s13=−0.230 ± 0.009, and s16= 0.4

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb15950.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY