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The interfacial shear strength of SiC/glass composites fabricated either under vacuum or in argon gas by hot-pressing was estimated using a single-fiber pullout test as a function of the loading rate. The interfacial shear strength of the composite fabricated under vacuum depended insignificantly on the loading rate. On the contrary, for the composite fabricated in argon gas, loading rates strongly influenced the interfacial shear strength as well as the interfacial debonding behavior. The influence of loading rates on the interfacial shear strength in the latter composite could result from the presence of the Si-O bond, whose strength is affected by slow crack growth along the fiber-matrix interface. These results indicate that the fracture behavior of fiber-reinforced ceramics whose interfacial shear strength depends on the loading rate can differ widely under dynamic and static loading.

Mullite/SiC continuous fiber composites were fabricated by hot-pressing under different processing conditions. The interfacial shear strength was measured during the pull-out test, and the effect of fabrication conditions on interfacial debonding behavior was discussed. The debonding length during the pull-out test was quantitatively evaluated using acoustic emission. The interfacial shear strength was evaluated by stress analysis. The control of interfacial shear strength was achieved by controlling the hot-press temperature. An increase of load was found during the pull-out process after complete debonding. In order to explain the increased load, a new model is presented.

It is proposed that reduced transformation zone widths in Mg-PSZ in cyclically versus critically propagated cracks are due to reductions in the crack-tip toughness, consistent with an intrinsic cyclic fatigue mechanism. Cyclic fatigue crack growth in Mg-PSZ was observed in situ in a SEM. Following cyclic fatigue, the samples were critically broken and the fracture surfaces observed. Extensive crack bridging by the precipitate phase was observed near the crack tip, and it is proposed that this crack bridging significantly affects the material's intrinsic toughness. Frictional degradation of the precipitate bridges occurs during cyclic loading and hence reduces the critical crack-tip stress intensity factor for crack propagation. Reductions in the critical crack-tip stress intensity factor also lead to reductions in the transformation zone widths during cyclic loading and hence the level of crack-tip shielding caused by phase transformation. This appears to be the mechanism of cyclic fatigue. A degree of uncracked ligament bridging was also observed and is linked with the frequency of random large precipitates. However, analysis shows that its effect upon crack growth rates under cyclic load is limited.

Compacts of TiB{sub 2} with densities approaching 100% are difficult to obtain using pressureless sintering. The addition of SiC was very effective in improving the sinterability of TiB{sub 2}. The oxygen content of the raw TiB{sub 2} powder used in this research was 1.5 wt%. X-ray photoelectron spectroscopy showed that the powder surface consisted mainly of TiO{sub 2} and B{sub 2}O{sub 3}. Using vacuum sintering at 1,700 C under 13--0.013 Pa, TiB{sub 2} samples containing 2.5 wt% SiC achieved 96% of their theoretical density, and a density of 99% was achieved by HIPing. TEM observations revealed that SiC reacts to form an amorphous phase. TEM-EELS analysis indicated that the amorphous phase includes Si, O, and Ti, and X-ray diffraction showed the reaction to be TiO{sub 2} + SiC {yields} SiO{sub 2} + TiC. Therefore, the improved sinterability of TiB{sub 2} resulted from the SiO{sub 2} liquid phase that was formed during sintering when the raw TiB{sub 2} powder had 1.5 wt% oxygen.

Compacts of TiB{sub 2} with densities approaching 100% are difficult to obtain using pressureless sintering. The addition of SiC was very effective in improving the sinterability of TiB{sub 2}. The oxygen content of the raw TiB{sub 2} powder used in this research was 1.5 wt%. X-ray photoelectron spectroscopy showed that the powder surface consisted mainly of TiO{sub 2} and B{sub 2}O{sub 3}. Using vacuum sintering at 1,700 C under 13--0.013 Pa, TiB{sub 2} samples containing 2.5 wt% SiC achieved 96% of their theoretical density, and a density of 99% was achieved by HIPing. TEM observations revealed that SiC reacts to form an amorphous phase. TEM-EELS analysis indicated that the amorphous phase includes Si, O, and Ti, and X-ray diffraction showed the reaction to be TiO{sub 2} + SiC {yields} SiO{sub 2} + TiC. Therefore, the improved sinterability of TiB{sub 2} resulted from the SiO{sub 2} liquid phase that was formed during sintering when the raw TiB{sub 2} powder had 1.5 wt% oxygen.

Addition of alumina particles to silicon carbide results in strongly improved toughness values. In order to come to a better understanding of this phenomenon, crack propagation is simulated for a 20 vol% alumina particles-dispersed silicon carbide composite material using the Body Force Method. Special emphasis is paid to the influence of graded compositions. Numerically obtained crack paths are compared to crack paths generated experimentally by Vickers indentations. Moreover, mechanical properties of the investigated material were measured experimentally. Microstructural toughness variations as well as the direction of crack propagation are found to be strongly influenced by residual stresses due to the mismatch between thermal expansion coefficients of alumina and silicon carbide and by the actual crack location. According to tensile residual stresses in the radial direction cracks approaching a particle are deviated circumferentially in the matrix around the particle. Moreover, the failure behavior of cracks propagating into a zone of increasing or decreasing volume fraction of alumina particles is found to behave differently as residual stress fields superimpose in the case of particle clustering. ©.

Stable Al2O3–SiC–YAG hybrid composites were successfully fabricated by reaction of Al2O3 and Y2O3 and incorporation of SiC. The hot-pressed bodies consisted of uniformly dispersed grains of microsized YAG particulates and nanosized SiC particulates in an Al2O3 matrix. Although the grain size of monolithic A12O3 increases markedly with increased temperature, the grain size of the Al2O3–SiC–YAG hybrid composites was effectively restrained due to grain-boundary pinning by the particulates.

5-O- and 6-O-Methyldihydrostreptomycin have been prepared from dihydrostreptomycin by a sequence of reactions involving methylation of a selectively protected derivative (4) with diazomethane in the presence of tin(II) chloride. The structures of the final products were confirmed by their 13C-NMR spectra and the TACu method.