Hot pressing of TiB2 has been investigated with particular emphasis on the evolution of secondary phases originating from the initial surface oxide layer on the TiB2 powders. Carbothermal reduction of the surface oxides during sintering was also investigated by adding carbon to the TiB2 powder. TiO1−xCx was shown to be the main secondary phase in hot‐pressed TiB2, and carbon was shown to strongly influence on sintering process and the amount, composition and distribution of the secondary phase TiO1−xCx. The formation of TiO1−xCx is discussed in relation to volatile boron oxide, which reacts with the graphite die to produce CO gas, which further may cause transport of carbon into TiB2 during sintering before pore closure. Finally it was demonstrated that the density could be controlled by addition of carbon to the TiB2 powder.

Preferential grain growth is reported for hot pressed titanium diboride (TiB2) prepared at 1800°C and 50 MPa. Orientation imaging microscopy and X‐ray diffraction revealed that the grains in the material were preferentially orientated with the [001] direction parallel to the mechanical field. The experimental findings are discussed, with emphasis on the anisotropic properties of TiB2.

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The processing of aluminum nitride (AlN) ceramics in aqueous media requires the use of a surface layer to protect the surface of the particles against hydrolysis. This surface layer might influence the densification, affecting the reactions between AlN and sintering additives. The present paper describes a thermodynamic and experimental approach to evaluate the effects of a phosphate-based protecting surface layer on the densification of AlN in the presence of YF 3 -CaF 2 as sintering aids, and to predict the densification behavior during sintering using thermodynamic assessments. Based on thermodynamic calculations and the measured weight loss of the samples during heating to sintering temperature, the chemical reactions occurring during firing were proposed. The proposed reactions were related to the experimental results as well as the final properties of the AlN samples, namely, thermal conductivity, microstructure, secondary phases, and density. II. Experimental ProcedureAlN powder was supplied by HC Starck (Grade C), Germany, having an average particle size, d 50 , B0.33 mm, a specific surface area of B6 m 2 /g, and an oxygen content of 2.5 wt% O, according to the information given by the supplier. CaF 2 (Grade-325 J. Smialek-contributing editor The S.M. Olhero wishes to thanks to Funda@a˜o para a Cieˆncia e Tecnologia of Portugal (FCT) for the financial support under the grant SFRH/BD/8754/2002.

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