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The structure and phase formation of porous liquid phase sintered silicon carbide (porous LPS-SiC), containing yttria and alumina additives have been studied. The present paper is focused on the system Y-Al-Si-C-O. The systems Al-Si-C-O and Y-Si-C-O have been studied in previous papers [J. Eur. Ceram. Soc. (in press) parts I and II]. The reaction products of the interaction of Al2O3 /Y2O3 with SiC and resulting microstructures were analysed by model experiments. The influences of different sintering atmospheres, namely argon and Ar/CO and different temperatures have been investigated. Thermodynamic calculations and sintering experiments reveal that silicides or carbides can be formed in addition to stable oxides. The main parameters controlling the formation of the different reaction products are the free carbon content, the oxygen activity and the temperature. Using CO containing atmospheres, the decomposition of the oxide additives can be effectively suppressed and stable porous LPS-SiC can be produced.

Hybrid foams consist of two different interpenetrating or particulate-embedded foam-material classes and, therefore, an enhanced multifunctionality of the material and of the final product can be expected. This paper illustrates the concept of hybrid foams with two selected examples. The cells of an open-cell steel host-foam are filled either with a polymer foam or a newly developed direct ceramic foam. The results of compression tests and non-destructive resonance-frequency-damping analyses are presented. An improvement in the deformation is observed for the metal-polymer hybrid foam, while the deformation behavior changes from brittle to ductile for the metal-ceramic hybrid foams. Additionally, the damping and Young's modulus of the metal foam are enhanced by the interpenetrating direct foamed ceramic.

High porosity permeable materials have been manufactured on the basis of the highly uniform structure of foamed polyurethane since the 1950 s. This paper shows the development of open cell foams based on all kinds of steels, titanium alloys, and also open-cell molybdenum foams made by a powder metallurgical replication technique. Such materials show a wide range of physical and mechanical properties, which may be adapted to various requirements. The automotive industry, for example, needs high-temperature resistant materials with high permeability and good strength for catalytic conversion. For orthopaedic implants, the network-like metal foams made of titanium, tantalum, or steel exhibit a bone-like structure. The powder metallurgical replication route represents an economic method to process open-cell metal foams with a unique combination of properties for a wide range of applications.

This paper describes the manufacture of an oxidation protection layer for reticulated silicon carbide foams. The produced foams are investigated by light microscopy, XRD and electrical measurements. The protection efficiency is estimated by weight change, image analysis and electrical resistance. The results indicate a feasible way to protect SiC foams against oxidation.

The structure and the electrical properties of porous and dense liquid-phase sintered silicon carbide ceramics (LPS-SiC), containing yttria and alumina additives, have been studied. The electrical resistance of LPS-SiC-materials varies in a wide range. This paper is focused on the influence of porosity on the electrical resistance of the sintered SiC. The porosity was controlled by the SiC grain size. Porous LPS-SiC materials were found to have substantially lower electrical resistance in comparison to dense materials of the same type. The structure of the materials was investigated by XRD and FESEM. The porous materials consist of large grains due to the coarser starting powders in comparison to the dense materials. This results in a reduction of the dissolved and re-precipitated fraction of the SiC during sintering. Using the in-lens SEM mode, the high conductivity of the formed rims of the SiC grains could be shown. These observations reveal that the rim volume of dense LPS-SiC is much more extended than the rims of porous materials showing the higher conductivity.