........ published in NEWSLETTER # 67
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........ published in NEWSLETTER # 67
REFRACTORY METALS IN MOLTEN SALTS: THEIR CHEMISTRY, ELECTROCHEMISTRY AND TECHNOLOGY
by Dr. D.H. Kerridge, Dept. of Engineering Materials, University, Southampton (U.K.)
Refractory metals are of ever increasing industrial importance and most are prepared, or processed, in molten salt solutions. Thus the understanding of the chemistry of refractory metals in the varied molten salts used is of prime importance, as are the electrochemical reactions of these metals which form the basis of their extraction.
The most significant of the papers delivered at this Advanced Research Workshop, held August 12 - 17th, 1997 in Apatity, Russia and well within the Arctic Circle, are published in this proceedings volume (NATO ASI SERIES 3-53) and describe the present status of the chemistry and electrochemistry of titanium, zirconium and hafnium; niobium and tantalum; chromium, molybdenum and tungsten; and rhenium: with, in some cases, their alloys with aluminium, tin and iron. The formation of their nitrides, borides, carbides and silicides was also covered for certain refractory metals. The molten salt solutions selected for study concentrated upon the alkali metal halides, particularly on the pure fluorides and pure chlorides together with fluoride-chloride mixtures. However, consideration was also given to the oxyanion metals, metaphosphates, nitrates and sulphates, together with molybdates and tungstates, both pure and containing fluoride.
Noteworthy reports included the 93Nb nuclear magnetic resonance of niobium solutions, in epitaxial growth of electrodeposited metals, spectroscopy (infrared, Raman, visible-ultraviolet) of molten salt solutions, together with thermodynamics and the effects of chemical reactions (acid-base, oxidation-reduction, disproportionation and cluster formation) and the influence of oxide content and oxoacidity, togethert with ligand absorption, on the electrowinning of metals. Other important practical parameters covered, included the synthesis and hardness of boride, carbide and silicide surface coatings; the possibilities of using non- consumable anodes in oxygen containing melts; and the recovery from scrap of expensive refractory metals and their subsequent separation by electrochemical means in fluoride-chloride and in sulphate melts.
In all there were 42 participants from ten NATO and cooperating partner countries who formed new scientific contacts and strengthened existing ones, whilst they shared the latest results of their research. Fortunately the latter is also possible for the readers of these proceedings, even if they did not have the good fortune to attend this ARW.
Reference books: 3-53, C179, C432