Session BB5.5

4:45 PM BB5.5
SILICATES AND OTHER NATURAL MATERIALS. Pavel Chraska, Karel Neufuss, Blahoslav Kolman, Jiri Dubsky, Institute of Plasma Physics, Prague, CZECH REPUBLIC.

In connection with utilization of the high throughput of WSP, a search for special materials, which are non-expensive but have interesting properties, have been extensively conducted. In this regard very promising materials are silicates and natural materials, such as Zircon, various Garnets and Basalt. Zircon - ZrSiO₄ - is a natural mineral used for various applications as a refractory bulk material. On plasma spraying Zircon decomposes into t-ZrO₂ and glassy SiO₂. Such a combination exhibits some interesting properties, such as a high thermal shock resistance, very good corrosion resistivity, low wettability, etc. Garnets as a group are relatively common in highly metamorphosed rocks. The general formula for garnets is A₃B₂(SiO₄)₃, where A represents divalent elements such as iron, magnesium, calcium, etc., and B represents a trivalent metal. Regardless of the type of the feedstock garnet, all plasma sprayed deposits were in the amorphous (glassy) state. Two types of the amorphousness were observed - one with amorphous peaks and the other without, suggesting a certain redistribution and inhomogeneity of the chemical composition. Porosity of all the plasma sprayed deposits was very low, mostly below 4-5 %. For one garnet type - almandine Fe₃Al₂(SiO₄)₃ - the porosity reached an exceptional value below 2 %. Adhesion to a steel substrate was similar to an alumina coating's adhesion - both without a bond coat. Excellent coatings were made of basalt. All the deposits, regardless of the spraying parameters, were in glassy state with a very low porosity (2.5 to 3 %), consisting of closed spherical pores. Practically no cracks were observed, offering thus a very low gas permeability of free-standing pipes, produced by spraying. Generally, it is evident that WSP, due to its very high temperature and energy dissipation, is capable of good melting and depositing of even large quantities of these materials with very interesting properties.
Support of grant GACR 104/96/1353 is gratefully acknowledged.

SESSION BB6: NEAR-NET FABRICATION
Chairs: Enrique J. Lavernia and John E. Smugeresky
Thursday Morning, December 4, 1997
Essex North/Center (W)