Anomalous solid state reaction between SiC and Pt
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I. INTRODUCTION
Solid state reactions between metals and ceramics have long been an important subject in both scientific and engineering fields. Recently, studies1"4 of compatibility between metals and ceramics have attracted considerable attention due to the need for developing better ceramic (fiber, whisker, or particulate forms) reinforced metal matrix composites and metal/ceramic joinings for applications under extreme environments. In composite materials, a subject of great interest is the solid state reaction (or interfacial reaction) between the reinforcements and matrices. There exists a technical dilemma with regard to the desired extent of interaction between the reinforcement and the matrix. A strong metallurgical bond between them through solid state reaction is essential in order to make composites with good structural integrity. Nevertheless, extensive interaction causes degradation of the reinforcement, which in turn impairs the overall mechanical properties of the composite material. Other important issues to be addressed are the thermal, physical, and mechanical properties of the reaction product(s). Among the ceramic reinforcements being used in metal matrix composites, SiC whisker is a popular one. As a result, understanding the chemical reactions between SiC and various types of metal substrates is important from an engineering point of view. To our knowledge, reaction in the Pt-SiC system has not been reported before. A study of solid state reaction between SiC and Pt would provide insights into the chemical reaction and give further understanding about metal/ ceramic interfaces. a)Current
address: Lockheed Research and Development Division, O-9310, B-204, 3251 Hanover Street, Palo Alto, California 94304. J. Mater. Res., Vol. 5, No. 3, Mar 1990
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In this paper, an intriguing solid state reaction between Pt and SiC is reported. Since the reaction behavior at 900 °C is similar to that at 1000 °C, the emphasis is on the results obtained at 900 °C. II. EXPERIMENTAL PROCEDURES
Rectangular pieces of j8-SiC (hot-pressed) and Pt of about 1 to 2 mm thick were used in the experiments. The SiC samples were polished with a diamond disk of 15 jxm grit and the Pt samples were polished with alumina slurries of 0.3 fim particle size. The samples were then ultrasonically cleaned in acetone and water and dried by compressed air. The diffusion couples were formed by pressing two reactant samples together in a specially designed pressure clamp. The couples were then loaded into a tube furnace flushed with a protective He gas. The samples were annealed at 900° and 1000 °C for various times. Upon finishing the anneals, the samples were air cooled. To examine the reaction between Pt and SiC, crosssectional views of the reaction zone were prepared. Scanning electron microscopy (SEM), scanning Auger microscopy (SAM), laser Raman microprobe, and x-ray diffraction were used to characterize the reaction behavior and chemistry of the reaction product. III. RESULTS AND
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