摘要:

The present investigation did not confirm the conclusion of Ruffet al.that certain compositions within the system CaO‐ThO2‐ZrO2might solidify in the vitreous state. Although many ZrO2‐rich samples were translucent after they were melted in an induction plasma torch, X‐ray diffraction indicated a crystalline structure of the fluorite type. When samples were annealed at 1400°C, the metastable phase decomposed, and translucency was lost. A section of the system at 1600°C is presented, together with a preliminary description of a pyrochlore‐type compound with the approximate composition 2CaO

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11434.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO‐Al2O3‐SiO2system were studied by DTA, X‐ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO2or TiO2. Up to 10 wt% CeO2was also added to some glasses. Metastable solid solutions with the high‐quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce2Ti2O4(Si2O7). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO2, but no crystalline TiO2was detected. In the presence of CeO2, TiO2was a more effective catalyst than ZrO2. Although CeO2lowered the melting temperatures of the glass‐ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crysta

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11435.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Quantitative studies of diffuse X‐ray scattering and measurements of magnetization are reported for (Fe,Mg)O with 15.7 cation % Fe held in a reducing atmosphere at 1400°C and quenched. The diffuse scattering is greater for fast cooling than for slow cooling; in both cases, spinel precipitation occurs, but the amount is much larger in the latter case. From this scattering, short‐range order parameters were determined for the clustering between cations, and displacements were obtained between cations and anions. From the magnetic measurements the size of magnetic Fe ion clusters was obtained. Computer simulations of the cation arrangement with the measured short‐range order parameters indicate that the magnetic clusters cannot be accounted for by nearest‐neighbor Fe2+]clusters. However, clusters of Fe ions related by first‐ and/or second‐neighbor vectors are of the size found from the m

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11436.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

A semiempirical model for intermediate‐stage sintering is developed based on simultaneously occurring volume and grain‐boundary diffusion mechanisms of mass transport and explicitly incorporating the effects of grain growth. The sintering equation derived depends strongly on the reduction of pore number density associated with grain growth and is independent of the mechanism of grain growth. The time and temperature dependencies of densification predicted by the equation, which are tested using data for metal and ceramic powders, agree well with observations. The data indicate that grain‐boundary diffusion contributes negligibly to densific

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11437.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The diffusion coefficient and the electric mobility of sodium (22Na) ions in a sodium silicate glass (25 mol% Na2O) were measured simultaneously at 300°C in an experiment of the type used by Chemla, where the diffusion heat treatment is made in a constant dc electric field. The diffusion coefficient remained unchanged with an applied electric field. The correlation factor in the Nernst‐Einstein relation calculated from the simultaneously measured diffusion coefficient and electric mobility was 0.5±0

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11438.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Hydrated calcium silicates containing Al3+]or Fe3+]were prepared by autoclaving C3S and β‐C2S in the presence of C3A or C2F at 190°C. Al3+]and Fe3+]diffuse into the crystal lattice of α‐C2SH and C3SH1.5. Solid solutions containing Al3+]and Fe3+]were placed in contact at 25°C with sources of sulfates, either in aqueous stirred suspensions or as pastes. Al3+]and Fe3+]remain stable in the solid solution, inhibiting the formation of ettringite. This absence of ettringite can explain the resistance of autoclaved cement pastes and concretes to sulfate

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11439.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The impact resistances and fracture mirror radii (rm) of rods of several ceramic materials were measured. The fracture stresses (σf) were determined from σfvs rm−1/2curves obtained from fiexural strength tests. An analysis, based on the assumption that the principal factor contributing to the impact energy absorbed is the energy (Ue) required to deflect the specimen to the fracture stress, indicated that the impact energy absorbed (U) per unit of specimen cross‐sectional area (A) increased in proportion to the square of the maximum stress. The analysis also indicated that the slopes of the curves ofU/Avs σf2are proportional to the reciprocal of Young's modulus. Experimental data for several materials are consistent with this an

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11440.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The standard Gibbs free energies of formation of CuAlO2and CuAl2O4were determined in the range 700° to 1100°C, using emf measurements on the galvanic cells (1) Pt,CuO +] Cu2O/CaO‐ZrO2/O2,Pt; (2) Pt,Cu +] CuAlO2+] Al2O3/CaO‐ZrO2/ Cu +] Cu2O,Pt; and (3) Pt,CuAl2O4+] CuAlO2+]Al2O3/CaO‐ZrO2/O2,Pt. The results are compared with published information on the stability of these compounds. The entropy of transformation of CuO from tenorite to the rock‐salt structure is evaluated from the present results and from earlier studies on the entropy of formation of spinels from oxides of the rock‐salt and corundum structures. The temperatures corresponding to 3‐phase equilibria in the system Cu2O‐CuO‐Al2O3at specified O2pressures calculated from the present results are discussed in reference to availab

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11441.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Phase equilibria in the system MgO‐B2O3were investigated using DTA and quenching techniques. The system contains 4 invariant points. The compounds MgO·2B2O3and 2MgO·B2O3melt incongruently at 995° and 1312°C, respectively, whereas 3MgO·B2O3melts congruently at 1410°C. A eutectic occurs at 1333°C and

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11442.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

The strength degradation of soda‐lime‐silica glass during dynamic loading was studied by using a fracture‐mechanics approach. The theoretical and experimental results indicate that subcritical flaw growth during loading causes the strength degrad

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1975.tb11443.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY