Study of diamond/mullite composites by sol/gel and hot press sintering methods
Date
2011-04-15
Authors
Govo, Simbarashe Piniel
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Abstract
A study has been conducted into the synthesis of 10wt% diamond/ mullite composites
through two methods: First through the hot press sintering of alumina and silica in
stoichiometric composition for 3:2 mullites (mullite formed in situ) at 1400, 1450 and
1500oC. Second through the sol/ gel process. The sol/ gel method only provided the basis
for future development with no further discussion of the results while the hot press
sintering method yielded composites with residual cristobalite and corundum phases.
Achieved densities of the composites were 93.7, 94.6 and 95.8% of the theoretical density
with respect to sintering temperatures of 1400, 1450 and 1500oC for compact samples by
the first method. Hardness – measured by Vickers indentation – of the composites
decreased with increase in temperature with 15.5 ± 0.33GPa achieved at the lowest
sintering temperature investigated. The decrease in hardness was attributed to the
structural degradation of diamond to non-diamond carbon forms with increase in
temperature as observed from Raman spectra of each of the composites. X-ray traces
showed an increase in the mullite content with increase in temperature. The fracture
toughness of compacts initially hot press sintered from alumina and silica in
stoichiometric composition for 3:2 mullite with no diamond added decreased with
increase in sintering temperature with 4.75 ± 0.10MPa·m1/2 achieved at the lowest
sintering temperature investigated. Further discussion to the structure and physical
properties is presented.
Description
MSc, School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment
Keywords
sintering methods, composites, diamond, mullite