Methods for the preparation of iron whiskers in chemical transport reactions of thermal dissociation of iron penta and dodecacarbonyls and carbidocarbonyl clusters Fe 5 С(СО) 15 were described. The morphology, structure, and chemical composition of the whiskers were studied. The main factors determining the growth rate and mechanical properties of the whiskers were revealed. A model for the mechanism of thermal dissociation of iron carbonyls was proposed. This process was shown to be a chain radical ion reaction initiated via the scheme of activating complex formation. Analogies between the thermal dissociation of iron carbonyls in the adsorption layer and the known radical ion processes in the liquid and gas phases were found.Metal whiskers are characterized by high ratios (20-25) of the length to apparent diameter and represent a peculiar type of inorganic material finding wide use in the recent time due to its perfect crystal structure and, as a consequence, a high mechanical strength, a considerable resistance toward oxidation, and unique electrophysical properties. In particular, they are used for the develop ment of new composite materials with metallic and poly meric matrices and for the production of magneto dielectric cores and high efficiency emitters. 1 Different methods for growing metal whiskers in the solid, liquid, and gas phases are known. Of these methods the simplest and most promising is the gas phase thermal dissociation of metal carbonyls during a transport reac tion in which the chemical nature of the starting compo nents changes. The formation of small amounts of iron whiskers (IW) from iron pentacarbonyl (IPC) and hydro gen was observed for the first time in a chamber of an electron microscope. 2,3 However, lacking data on the mechanism of metal carbonyl dissociation did not allow a preparative method of α iron IW preparation to develop. The purpose of this work was to search for optimum con ditions of preparing α iron whiskers from iron carbonyls, to reveal the main factors affecting the formation of the structure, chemical and phase compositions of iron whis kers, and to establish a scheme of thermal dissociation of metal carbonyls.
ExperimentalIron pentacarbonyl Fe(СО) 5 , iron dodecacarbonyl Fe 3 (СО) 12 , and carbidocarbonyl cluster Fe 5 С(СО) 15 were used as starting compounds for studying thermal dissociation.Industrial IPC was purified by distillation. Iron dodecacarbonyl was synthesized by refluxing IPC and triethylamine in an aqueous solution followed by treatment with hydrochloric acid and purified by washing with water, metha nol, and hexane. 4,5 Iron carbidocarbonyl cluster Fe 5 С(СО) 15 was synthesized according to a previously described procedure. 6,7All carbonyls used are volatile and easily decompose, which makes it possible to significantly decrease the tem perature of thermal dissociation compared to that, e.g., of oxides, to reject the use of explosive and corrosion active me dia (hydrogen, chlorine, etc.), and to use supports of different shapes. Wire and plates of dif...
