Use of plasma spraying in the manufacture of continuously graded and layered/graded molybdenum disilicide/alumina composites
- Rajendra U.
- Richard G.
- Maria I.
- David E.
Using platinum coatings on alumina (Al{sub 2}O{sub 3}) sheaths for thermocouples is a widely used practice in the glass industry. Protection of the thermocouple wires and alumina (Al{sub 2}O{sub 3}) sheathing is necessary to avoid corrosion and dissolution of the temperature-sensing unit. The cost associated with providing platinum coatings on the Al{sub 2}O{sub 3} sheath material can be prohibitively high when taking into consideration the infrastructure needed at the glass plants to maintain and secure an inventory of available platinum. There are also issues associated with improving the performance of the platinum coated Al{sub 2}O{sub 3}. The failure rate of the thermocouples can be as high as 50%. The U.S. glass industry has been in search of alternative materials that can replace platinum and still provide the durability and performance needed to survive in an extremely corrosive glass environment. Investigations by Y.S. Park et al have shown that molybdenum disilicide (MoSi{sub 2}) has similar performance properties in molten glass as some refractory materials that are currently being used in glass processing applications. Molybdenum disilicide is a candidate high temperature material for such applications because of its high melting temperature (2030 C), relative low density (6.24g/cm{sup 3}), high thermal conductivity (52 W/mK), a brittle to ductile transition near 1000 C, and stability in a variety of corrosive and oxidative environments. Additionally, the cost of MoSi{sub 2} is significantly lower as compared to platinum coatings. Plasma spraying has been shown to be a very effective method for producing coatings and spray formed components of MoSi{sub 2} and MoSi{sub 2} composites. Investigations on plasma spray formed MoSi{sub 2}-Al{sub 2}O{sub 3} composite gas injection tubes were shown to have enhanced high temperature thermal shock resistance when immersed in molten copper and aluminum. The composite tubes outperformed high-grade graphite and Sic tubes when immersed in molten copper and had similar performance to high-density graphite and mullite when immersed in molten aluminum. Energy absorbing mechanisms such as debonding (between the MoSi{sub 2} and Al{sub 2}O{sub 3} layers) and microcracking in the Al{sub 2}O{sub 3} layer contributed to the composites ability to absorb thermal stresses and strain energy during the performance test. Molybdenum disilicide and alumina are chemically compatible and have similar thermal expansion coefficients.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 977666
- Report Number(s):
- LA-UR-04-3828; TRN: US201012%%644
- Resource Relation:
- Journal Volume: 11; Journal Issue: 3; Conference: Submtted to ICCE-11, Hilton Head, South Carolina, August 8-13, 2004
- Country of Publication:
- United States
- Language:
- English
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