Keramisch onderzoek in Canada

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Ontwikkelingen in keramiek en glas

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History of the European Ceramic Society

The collective memory of a society is generally quite brief because of the continuous renewal of it membership. Therefore it seemed appropiate to document the initial phase and the development of th ECerS on the occoasion of its 20th anniversary

Electrical transport properties of beta-bismuth molybdate Bi2Mo2O9

Results are given for the electrical conductivity and ionic transport numbers of polycrystalline, sintered ß-Bi2Mo2O9 in the temperature region 300oC to 650oC and at partial oxygen pressures of 1-10-6 bar. The material shows mixed conductivity over the whole temperature and pressure region. The oxygen pressure dependence is explained by an acceptor controlled behaviour, with copper impurities and oxygen vacancies as the dominating defect

The chemistry of the carbothermal synthesis of β-SiC : reaction mechanism, reaction rate and grain growth

Evidence is given that in the present case the reaction mechanism of ß-SiC formation from silica and carbon is a direct solid-state reaction in which silica migrates over the silicon carbide surface to the carbon. A high value (440 kJ/mol) of activation energy is obtained for this reaction. This high value indicates that the reaction rate is determined by the diffusion of C atoms in carbon. As soon as the silica layers surrounding the silicon carbide particles have disappeared grain growth of ß-SiC occurs. The mechanism for grain growth of ß-SiC seems to be surface diffusion of Si and C atoms in SiC. The measured value of the activation energy for grain growth of ß-SiC is 450 kJ/mol. Grain growth of a-SiC results in platelets

Relations between composition and microstructure of sialons

The relation between compn. and microstructure of Sialon ceramics was studied. Fully dense yttrium-contg. a'- and a'+b'-Sialon ceramics were prepd. by gas pressure sintering. Addnl., the effect of La2O3 as a sintering additive was investigated. Exptl. results reveal that the typical microstructure of these Sialon ceramics consists of a cryst. phase of Sialons and a small fraction of amorphous phase remaining at grain boundaries. The compn. of the amorphous phase is very similar, both in a'- and b'-Sialon ceramics. However, the amt. of the amorphous phase increases with increasing amt. of oxides used in the starting mixts. The a'- and a'+b'-Sialons exhibit differences in grain size and grain morphol. The addn. of La2O3 to the starting mixts. promotes the incorporation of yttrium ions into the crystal lattice and leads to the formation of crystal defects in the a'-grains. [on SciFinder (R)