Blackwell Publishing Journal Backfiles 1879-2005
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
The microhardness–nanostructure correlation of a series of silica/silicon oxycarbide porous composites has been investigated, as a function of pyrolysis temperature, Tp. The pyrolyzed products have been studied by means of scanning electron microscopy, mercury porosimetry, chemical analysis, solid-state 29Si-NMR, X-ray diffraction, Raman spectroscopy, and microindentation hardness. Two distinct regimes are found for the microhardness behavior with Tp. In the low-temperature regime (1000°C ≤Tp 〈 1300°C), the material response to indentation seems to be dominated by the large amount of pores present in the samples. In this Tp range, low microhardness values, H, are found (〈110 MPa). Above Tp= 1300°C, a conspicuous H increase is observed. In this high-temperature regime (Tp= 1300–1500°C), microhardness values are shown to notably increase with increasing pyrolysis temperature. The H behavior at Tp= 1300–1500°C is discussed in terms of (i) the volume fraction of pores and the average pore size, (ii) the bond density of the oxycarbide network, and (iii) the occurrence of a nanocrystalline SiC phase.
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