摘要:

In the absence of a published diagram, two versions of the liquidus surface of the ternary system CaSiO3‐BaSiO3‐SrSiO3were constructed from binary data. This information was adequate for a prediction of the temperature and composition of a ternary minimum or eutectic. This speculative interpolation, a more feasible approach than calculation under the circumstances, resulted in a useful working diagram which ultimately needs the test of experimental w

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07512.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The27Al and29Si magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) study of the kaolinite‐mullite transformation has shown the presence of Al in tetra‐ and pentacoordination in dehydroxylated kaolinite. The29Si NMR signal analysis of samples heated above 400°C demonstrates that the tetrahedral sheet of kaolinite begins to break down near 600°C and continues to do so to 900°C. From the27Al NMR signal evolution, it can be deduced that the exothermic peak at 980°C in DTA curves is associated with the modification of the coordination of Al, which changes from the tetra‐ or pentacoordination to the more stable octahedral coordination. Heating the sample at 880°C for 36 h produces the same transformation in the coordination of Al ions and the elimination of the exothermic peak at 980°C in the DTA diagram. After this transformation, all spectra show two tetrahedral lines characteristic of mullite, indicating that nuclei of mullite with low crystallinity are generated during the exothermic process which are not detected by XRD. At higher temperatures tetrahedral NMR peaks increase in intensity, yielding, at 1200°C, the 3:2 mull

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07513.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The analysis of X‐ray diffraction line profile broadening reveals the relationship between lattice microstrain and crystallite size for some microcrystalline quartz in natural quartzose rocks which crystallized slowly and statically. The mean microstrain of quartz microcrystallites increases proportionally with the reciprocal of the crystallite size and its magnitude reaches 0.18% (1.8×10−3) for crystallites ∼43 nm in diameter. This large lattice microstrain is ascribed to the internal pressure derived from the surface energy of the quartz microcryst

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07514.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The stress required for spontaneous fracture of glass films on a silicon substrate was found to be proportional to the reciprocal square root of the film thickness. A simple fracture theory, with an assumption of a wedgelike crack shape, explained this relationship well.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07515.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A TEM investigation was conducted on the structure of a second phase precipitated between the grains of a polycrystalline TiO2‐rich BaTiO3which was doped with 8 mol% Ca. This phase was identified as Ca‐stabilized Ba2Ti5O12with a 10‐layer orthorhombic structure and unit‐cell parameters a=0.990, b=1.131, and c=2

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07516.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Solid solutions of various compositions in the system LiAl5O8–LiFe5O8were prepared by calcining mixtures of Li2CO3, Al2O3, and Fe2O3. Lattice parameters of the solid solutions were determined by X‐ray diffraction (XRD). Samples of equimolar composition were also prepared with titanium and magnesium as dopants. The doped and undoped samples were annealed at 1050°C for up to 192 h in air. Annealing at this temperature, which is inside the miscibility gap for an equimolar composition, led to the decomposition of the originally single‐phase solid solution. The extent of phase transformation was followed by XRD. The fraction transformed was estimated using integrated peak intensities. The kinetic data were analyzed in light of the conventional kinetic equation and the previously derived equation which takes into account the diffusive and the interface transfer processes. It was observed that titanium enhances and magnesium suppresses the kinetics of phase separation. These results are rationalized on the premise that the predominant point defects are Schottky defects in this spinel

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07517.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The compressive stress for the shrinkage of a large pore during sintering has been analyzed by combining the effects of the pore size, the ratio of pore size to grain size, and the coordination number of the pore. Alumina has been selected to illustrate this model. The result shows that the compressive stress is a positive and increasing quantity during the sintering process with an increasing value depending on the rate of grain growth and pore shrinkage.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07518.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A nondestructive measurement of the surface stress and an indentation technique were used to determine the relationship between the fracture toughness and the surface compressive stress of a tempered glass plate. Ignoring the effect of surface compression, one can determine the fracture toughness concerned only with a change in the glass structure. It is found that the fracture toughness is lower for tempered glass than for annealed glass. It is indicated that the decrease is due to structural changes in the surface layer during the heat treatment in tempering; this is confirmed by infrared reflection spectroscopy.

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07519.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The phase diagram of the pseudobinary system Li2SO4–La2(SO4)3has been investigated by means of X‐ray diffraction and differential thermal analysis. LiLa(SO4)2is formed by a peritectic reaction in this system; the peritectic temperature is 653±3°C. The eutectic reaction of Li2SO4and LiLa(SO4)2occurs at 553±3°C; the composition at the eutectic point is 17 mol% La2(SO4)3. LiLa(SO4)2is monoclinic with a=1.375 nm, b=0.6744 nm, c=0.7068 nm, and β=105.4°. The ionic conductivity of LiLa(SO4)2has been studied from room temperature to 350°C and is found to be relatively low at room temperature or at lower temperatures. Its activation energy is 0.66 eV. Thus it is not suitable as a fast ion

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07520.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The influence of internal stresses, due to the thermomechanical mismatch between the fiber and the matrix, on the thermal expansion behavior of unidirectional fiber‐reinforced ceramics is considered. Using the composite cylinder model, the effective thermal expansion coefficients of the composite are calculated from the total strains, which consist of the strains due to temperature changes and the strains induced by the presence of internal stresses. The results reveal that when the fiber and the matrix have the same elastic constants, the rule of mixtures approach can be used to obtain the thermal expansion coefficients of the composite, as observed in previous analytical solutions. Also, for the case of low volume fractions of fibers with Young's moduli much larger than those of matrices, and the thermal expansion coefficients lower than those of matrices, the transverse thermal expansion coefficient of the composite is higher than that of either the fiber or the matrix. However, unlike previous studies, the present analysis provides a physical basis for this phenomenon in terms of the internal thermal stress state within the composit

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb07521.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY