Graphite 234 Subject

T. Fukunaga, K. Nagano, U. Mizutani, H. Wakayama, Y. Fukushima, Structural change of graphite subjected to mechanical mrUing. J. Non-Cryst. Solids, 232-234 (1998) 416-420. 

Development of chlorine electrode materials has benefited from the experience of chlor-alkali electrolysis cell technology. The main problem is to find the best compromise between cycle life and cost. Porous graphite, subjected to certain proprietary treatments, has been considered a preferable alternative to ruthenium-treated titanium substrates. The graphite electrode may undergo slow oxidative degradation, but this does not seem to be a significant process. 

Heavy-ion induced X-ray emission applied to thick samples features several advantages, which are related to the small sample size assayed. As an example, with a 1 MeV u Kr + beam of 3mm diameter, the weight of graphite subjected to analysis would be less than 15 pg. Consequently problems associated with their target analysis (absorption of X-rays interference due to the substrate in the case of thin layer analysis) using X-ray methods are avoided. 

By subjecting boron nitride (a white powder) to high pressure and temperature small crystals of a substance harder than diamond, known as borazon, are obtained. This pressure-temperature treatment changes the structure from the original graphite-like layer structure (p. 163) to a diamond-like structure this hard form can withstand temperatures up to 2000 K. 

Very small synthetic diamonds have been made industrially by subjecting graphite to pressures in the range 5.5-b.9 GN m , at temperatures between 1500 and 2700 K. The diamonds produced are very small but competitive with natural diamonds for use in industrial cutting and grinding wheels. 

Among nonmetallic materials, glass, chemical stoneware, enameled steel, acid-proof brick, carbon, graphite, and wood are resistant to iodine and its solutions under suitable conditions, but carbon and graphite may be subject to attack. Polytetrafluoroethylene withstands Hquid iodine and its vapor up to 200°C although it discolors. Cloth fabrics made of Saran, a vinyHdene chloride polymer, have lasted for several years when used in the filtration of iodine recovered from oil-weU brines (64). 

The anodes can be made of graphite which tolerates high current densities without passivation, but are subject to gradual corrosive attack causing a... 

Carbon steels heated for prolonged periods at temperatures above 455°C (8.50°F) may be subject to the segregation of carbon, which is transformed into graphite. When this occurs, the structural strength of the steel will be affected. Killed steels or low-alloy steels of chromium and molybdenum or chromium and nickel should be considered for elevated-temperature seivices. 

Elucidation of the phase relationships between the different forms of carbon is a difficult field of study because of the very high temperatures and pressures that must be applied. However, the subject is one of great technical importance because of the need to understand methods for transforming graphite and disordered forms of carbon into diamond. The diagram has been revised and reviewed at regular intervals [59-61] and a simplified form of the most recent diagram for carbon [62] is in Fig. 5. 

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

Tube and shell heat exchangers, small distillation columns, reactors, valves, pumps and other items are available in impregnated grapliite. Graphite can be joined only by cementing, which embrittles on aging. It is prone to mechanical damage, particularly when subjected to tensile stresses. 

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