Thermal dissociation, steels

Two U.S. patents issued to the Barium Steel Corporation in 1957 claim the formation of the heptacarbonyls M(CO)7 (M = Ti, Zr, Hf) as intermediates for the purification of these metals (9,10). In this described refining process, the finely divided metal is treated with CO at 300-400°C and 4-8 atm. The resulting liquid heptacarbonyl compound is then thermally dissociated to the pure metal and CO. The alleged existence of these binary carbonyls seems highly unlikely without supporting evidence. 

Powder Formation. Metallic powders can be formed by any number of techniques, including the reduction of corresponding oxides and salts, the thermal dissociation of metal compounds, electrolysis, atomization, gas-phase synthesis or decomposition, or mechanical attrition. The atomization method is the one most commonly used, because it can produce powders from alloys as well as from pure metals. In the atomization process, a molten metal is forced through an orifice and the stream is broken up with a jet of water or gas. The molten metal forms droplets to minimize the surface area, which solidify very rapidly. Currently, iron-nickel-molybdenum alloys, stainless steels, tool steels, nickel alloys, titanium alloys, and aluminum alloys, as well as many pure metals, are manufactured by atomization processes. 

Detailed investigations of the reaction of Csl with boric acid in the condensed phase over the temperature range 400-1000 C under Ar, Ar-H2, and Ar—Ha-steam atmospheres were performed by Bowsher and Nichols (1985). The results showed that Csl decomposition in these reactions starts at temperatures above 400 °C and increases considerably beyond 700 °C, with the HI produced being partly converted to I2 (and/or iodine atoms) by thermal dissociation. Under such conditions, HI as well as I2 may react with the iron and nickel content of stainless steels under formation of the corresponding iodides (see below). Up to 960 °C, Csl and molten boric acid or boron oxide react in a diffusion-controlled reaction the rate of which is determined by the diffusion of the partners to the reaction zone. The reaction data measured in these experiments were consistent with Arrhenius law, showing an activation energy of 190 30kJ/mol. 

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