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141 Le Chatelier, Henri Louis
SUBJECT AREA: Metallurgy[br]b. 8 November 1850 Paris, Franced. 17 September 1926 Miribel-les-Echelle, France[br]French inventor of the rhodium—platinum thermocouple and the first practical optical pyrometer, and pioneer of physical metallurgy.[br]The son of a distinguished engineer, Le Chatelier entered the Ecole Polytechnique in 1869: after graduating in the Faculty of Mines, he was appointed Professor at the Ecole Supérieure des Mines in 1877. After assisting Deville with the purification of bauxite in unsuccessful attempts to obtain aluminium in useful quantities, Le Chatelier's work covered a wide range of topics and he gave much attention to the driving forces of chemical reactions. Between 1879 and 1882 he studied the mechanisms of explosions in mines, and his doctorate in 1882 was concerned with the chemistry and properties of hydraulic cements. The dehydration of such materials was studied by thermal analysis and dilatometry. Accurate temperature measurement was crucial and his work on the stability of thermocouples, begun in 1886, soon established the superiority of rhodium-platinum alloys for high-temperature measurement. The most stable combination, pure platinum coupled with a 10 per cent rhodium platinum positive limb, became known as Le Chatelier couple and was in general use throughout the industrial world until c. 1922. For applications where thermocouples could not be used, Le Chatelier also developed the first practical optical pyrometer. From hydraulic cements he moved on to refractory and other ceramic materials which were also studied by thermal analysis and dilatometry. By 1888 he was systematically applying such techniques to metals and alloys. Le Chatelier, together with Osmond, Worth, Genet and Charpy, was a leading member of that group of French investigators who established the new science of physical metallurgy between 1888 and 1900. Le Chatelier was determining the recalescence points in steels in 1888 and was among the first to study intermetallic compounds in a systematic manner. To facilitate such work he introduced the inverted microscope, upon which metallographers still depend for the routine examination of polished and etched metallurgical specimens under incident light. The principle of mobile equilibrium, developed independently by Le Chatelier in 1885 and F.Braun in 1886, stated that if one parameter in an equilibrium situation changed, the equilibrium point of the system would move in a direction which tended to reduce the effect of this change. This provided a useful qualitative working tool for the experimentalists, and was soon used with great effect by Haber in his work on the synthesis of ammonia.[br]Principal Honours and DistinctionsGrand Officier de la Légion d'honneur. Honorary Member of the Institute of Metals 1912. Iron and Steel Institute Bessemer Medal.Further ReadingF.Le Chatelier, 1969, Henri Le Chatelier.C.K.Burgess and H.L.Le Chatelier, The Measurement of High Temperature.ASDBiographical history of technology > Le Chatelier, Henri Louis
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