摘要:

The subsolidus phase equilibria of the MgO─V2O5─SiO2system was studied by solid‐state reaction and powder X‐ray diffractometry. The resulting ternary is discussed with respect to corrosion of magnesia‐ and silica‐containing refractories by vanadium‐con

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05521.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The distribution of initiation loads for cone cracking during Vickers indentation is studied by direct experimental observation of the indentation process and by simulation. Observations on three different glasses show that cone cracks initiate at the edge of the contact impression and yield distributions of initiation loads with nonzero minima. The simulations, based on a model of an expanding indentation impression in a random array of active crack nuclei, yield distributions of initiation loads with minima of zero. Cone cracks at sharp contacts are concluded to be initiated from nuclei generated by the contact process itself, rather than by nuclei preexisting on the contact surface.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05522.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The Madelung energies of A2+(B1/32+B2/35+) O32‐and A2+(B2/33+B1/36+) O32‐systems were calculated for different dopants on the A‐site. The theoretical results show that the higher‐valence dopant enhances the 1/2‐type (1:1) ordered arrangement of B‐site cations in A2+(B1/32+B2/32+)O32‐, whereas the lower‐valence dopant promotes the 1:1 ordering in A2+(B2/33+B1/36+)O32‐, and no doping promotes the 1/3‐type (1:2) ordering in the both systems. These calculation results are in agreement with the experimental observations of donor‐ and accep

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05523.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Based on the surface properties of aqueous silica, boehmite, and SiC‐whisker dispersions, SiC‐whisker‐reinforced lithium aluminosilicate (LAS) matrix composites were fabricated by a mixed colloidal processing route. The composites were characterized by a uniform spatial distribution of SiC whiskers throughout the matrix. The fracture toughness increased from 1.3 MPa.m1/2for the LAS specimen to 5.0 MPa.m1/2for the hot‐pressed composite (950°C and 20 MPa for 20 min) containing 20 wt% SiC whisker. The increase in fracture toughness appears to result mainly from crack deflection and crack bridging by whiskers with some additional toughenings from load transfer and whisker

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05524.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Because of their preferred orientation, the addition of boron nitride dispersions to hot‐pressed boron carbide was found to result in a considerable degree of anisotropy in thermal conductivity of the resulting composite, indicated by an increase in the thermal conductivity perpendicular to the hot‐pressing direction by as much as a factor of 3 at the highest boron nitride volume fractions of this study, and a decrease in the thermal conductivity parallel to the hot‐pressing direction by as much as a factor of 2. The composite data were found to be below the values expected from composite theory, which may represent indirect evidence for the existence of an interfacial thermal ba

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05525.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Thin films of 52/48 PZT have been deposited on Ni–Ti shape memory alloys using a sol–gel spin‐on method. Micrometer‐thick PZT films adhere well to the alloy for strains as large as 0.4%, and they retain their ferroelectric properties during repeated cycling through the shape memory transfo

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05526.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The effects of a 5.8‐y exposure to low‐earth‐orbit environment upon the mechanical properties of five commercial glasses and a low‐expansion‐coefficient glass‐ceramic have been examined. The radiation components of the earth‐orbit environment did not degrade the mechanical strength of the samples examined within the limits of experimental error. Statistical problems arising from the low frequency of micrometeorite or space debris impacts upon the samples precluded statistically valid measurement of impacted sample strengths. Upper bounds for the magnitude of the impact event damage upon the strengths for impacted samples have be

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05527.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Belite crystals give six sets of twinned αH′l‐phase lamellae upon transition from α to αH′. During further cooling a remelting reaction occurs within the crystals with heterogeneous nucleation and growth of a liquid phase on the lamella boundaries. The liquid, spherical in shape (∼0.1 μm in diameter), is made up of 70 wt% Fe2O3, 20 wt% CaO, and 10 wt% SiO2at 1100°C and vitrified on r

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05528.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The deposition rate of SiC on carbon‐coated Nicalon fibers from methyltrichlorosilane in hydrogen was measured as a function of temperature, pressure, total flow rate, and simulated reactant depletion. The results, together with kinetic information on the stability of methyltrichlorosilane, led to two conclusions: (1) two different mechanisms of deposition can occur depending on whether the methyltrichlorosilane has an opportunity to dissociate into separate silicon‐ and carbon‐containing precursors, and (2) the deposition rate is strongly reduced by the generation of byproduct HCl. The data were fitted to a simple etch model to obtain a kinetic expression that accounts for the significant effect o

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05529.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Magnesium sulfate's attack on cement‐based materials results in massive deposition of gypsum and brucite accompanied by decalcification of calcium silicate hydrate (CSH) (the binding material of the cement). Magnesium silicate hydrate (MSH) appears as a late‐stage product, mainly on deteriorated surfaces, and replaces the decalcified CSH. MSH appears as an inhomogeneous phase forming an intimate mixture with brucite. The Mg:Si ratio of the MSH is lower than the equivalent Ca:Si ratio of the CSH and is probably close to 1. The deterioration itself is primarily attributed to the decalcification of the CSH rather than its replacement by

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05530.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY