Seversk Technological Institute of National Research Nuclear University “MEPhI”

V. L. Sofronov, Professor, Dean of Technological Faculty, e-mail: sofronov@ssti.ru
A. S. Buynovskiy, Professor, Department of Chemistry and Technology of Contemporary Energetics’ Materials, Technological Faculty
A. N. Zhiganov, Head of the Institute, Professor
A. Yu. Makaseev, Deputy Head of the Institute
Yu. N. Makaseev, Assistant Professor, Department of Chemistry and Technology of Contemporary Energetics’ Materials, Technological Faculty

This article contains the results of research to develop nonpolluting, low-waste, «dry» fluoride technology of getting magnetic materials based on rare earth metals such as Nd—Fe—B. At the same time there have been formulated physical-chemical basis of the proposed technology and experimentally studied the main stages of this technology: fluorination of raw materials (oxides, metal concentrates, waste, magnetic, and other industries) by element fluorine, calciethermic out-of-furnace fluoride recovery to produce compact ingots of alloys and ligatures, making magnets by the method of powder metallurgy using mechanical or hydride grinding, as well as waste recycling. The thermodynamic analysis carried out in the processes of fluorination of oxides and metallothermic recovery of rare earth compounds and transition metals has shown that these processes are irreversibly shifted toward the formation of the reaction products. There are results of investigations of the kinetics of the fluorination and calciethermic restoration carried out by thermogravimetric plants. Mathematical processing of experimental data on the fluorination of neodymium and iron oxides showed that they were adequately described by an equation of decreasing surface and the activation energy E_a = (87,0 ± 7,0) kJ/mol. There have been given the experimental research results of all stages of getting magnet materials. These researches were done on the apparatus made by the authors. The analyses of properties of raw materials and got products were made by using modern physical-chemical methods: spectral-emission, atomic-absorption, spectral ISP, conductometric, gaschromatographic and others. There are also research results of the effect of factors on the yield and quality of the out-of-furnace recovery smelting (RS) of alloys: Fe and Nd trifluorides content, moisture and volatile impurities (F₂, HF) in fluorides; the scale of the RS; an excess of the reducing agent, material, shape, dimensions of the crucible, the material and the thickness of the crucible lining, the quantity of Fe additions in the form of powder, etc. Samples of the magnets made by powder metallurgy method from ingots of RS alloys correspond to technological condition specifications for the magnets. A scheme for recycling of various wastes is offered.

The work is made within the bounds of the state agreement P509 of 14^th of May, 2010 on the Federal goal-oriented program “Scientific and science-pedagogical personnel of innovative Russia” for 2009–2013.

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