Jean-Marc Heintz

Sintering mechanisms of 0.99 SnO2-0.01 CuO mixtures

The densification kinetics of 0.99 SnO2-0.01 CuO molar mixtures have been studied between 850 and 1150 °C. Both experimental analyses and theoretical modelling show the role of a liquid phase for sintering temperatures Ts ≥ 940 °C: sintering is controlled by a liquid phase after a fast shrinkage due to grain rearrangement. The analytical formulation of the shrinkage behaviour suggests that dissolution at the solid-liquid interface is the limiting process when Ts ≤ 1000 °C and diffusion is the limiting step at higher temperatures.

Densification of 0·99SnO20·01CuO mixture: Evidence for liquid phase sintering

Abstract The sintering of a 0·99SnO 2 ue5f80·01CuO molar mixture was studied at 1150°C in air. A fast and high densification was observed: the compactness obtained can reach 98·7%. After grain rearrangement, the simultaneous changes in shrinkage and grain size observed versus time were in agreement with a liquid phase sintering mechanism. It was shown that copper dissolves into the SnO 2 rutile type structure. The electrical behaviour of the material obtained was in agreement with an interstitial position for copper ions.

Interface analysis in Al and Al alloys/Ni/carbon composites

Nature of fibre/matrix interfaces existing in Al/C composites were investigated depending on the presence of a nickel interlayer deposited on carbon fibres and on the composition of the aluminium matrix. Auger and electron microprobe analyses were used. The role of the nickel layer on the chemical evolution of the system after a 96 h heat treatment at 600°C is discussed. The presence of this nickel layer limits the diffusion of carbon into aluminium, and thereby, eliminates the formation of a carbide interphase, Al3C4, which is known to lower the mechanical properties of Al/C composites. The mechanisms differ according to the composition of the matrix. In the case of pure aluminium, an Al-Ni intermetallic is formed after thermal annealing. It does not react with the carbon fibre and so inhibits the growth of Al3C4. In the case of the alloyed matrix (AS7G0.6), the dissolution of the Ni sacrificial layer, after annealing, does not lead to the same Al-Ni intermetallic but a thin nickel layer remain in contact with the carbon fibre avoiding formation and growth of Al3C4 carbide. This difference of behaviour is tentatively ascribed to the presence of silicon that segregates at the fibre/matrix interface.

Spark plasma sintering and decomposition of the Y3NbO7:Eu phase

The spark plasma sintering (SPS) of Eu3+-doped Y3NbO7 niobate phase was investigated to obtain dense ceramics. Although SPS allowed obtaining high-density ceramics, decomposition of the niobate phase occurred at high temperature and was promoted by the SPS process, which limited its use as an optical material. The niobate phase has been prepared by two synthesis methods: a solid-state route and a sol–gel method. The purity, density and microstructure of the dense ceramics were analyzed after spark plasma sintering. Translucent ceramics were only obtained from sol–gel powders after SPS at 1600xa0°C during 20xa0min with a heating rate of 5xa0°C/min. The sintering study of the pure niobate phase showed that during SPS process and especially in the presence of the high electrical field the Y3NbO7 phase is metastable at 1600xa0°C. A decomposition of the niobate compound is clearly demonstrated by luminescence measurements when high heating rates were used.