Thermal shock graphite

Sihcon nitride has good strength retention at high temperature and is the most oxidation resistant nitride. Boron nitride [10043-11 -5] has excellent thermal shock resistance and is in many ways similar to graphite, except that it is not an electrical conductor. 

A siHcon carbide-bonded graphite material in which graphite particles are distributed through the siHcon carbide matrix has high thermal shock resistance and is suitable for appHcations including rocket nose cones and nozzles and other severe thermal shock environments (155) (see Ablative materials). 

The resistance of graphite to thermal shock, its stabiUty at high temperatures, and its resistance to corrosion permit its use as self-supporting vessels to contain reactions at elevated temperatures (800—1700°C), eg, self-supporting reaction vessels for the direct chlorination of metal and alkaline-earth oxides. The vulnerabiUty of cemented joints in these appHcations requires close tolerance ( 0.10 mm) machining, a feat easily accompHshed on graphite with conventional metal machining equipment. 

This wear is caused primarily from high thermal and mechanical stress, chemical attack, attack by iron and slag, oxidation, and severe thermal shock. Thus the design of the hearth wall and the concepts employed ate just as important as the carbon or graphite materials chosen for the refractory material. Despite their benefits and properties, no carbon or graphite material can overcome the problems of an improper hearth wall design concept. 

Alumina—graphite refractories, almost all continuous casting ware, have come into much greater use as continuous casting has spread in steelmaking. These refractories are used in shrouds that conduct the molten metal from the ladle to the tundish, in the subentry tubes that take the metal from the tundish to the mold, in isostatically pressed stopper rods, and in shroud tubes for slab and bloom casters. The alumina—graphite compositions are used in these products because of the thermal-shock resistance and corrosion resistance they impart to the product. 

Fig. 4. The performance of several grades of graphite and graphite composites subjected to thermal shock loading.

Meehanite HE Flake graphite-pearlitic cast iron all-round material for general use with good thermal shock resistance... 

Isobe, Y., Shirakawa, H., Son, P., and Miyake, M., Thermal Shock Resistance of Chemically V apor-Deposited Molybdenum Coatings on Graphite, / of the Less CommonMetals., 152 251-260(1989)... 

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