| The development of the domestic magnesium industry, properties, applications and preparation methods of primary magnesium and magnesium alloy are overviewed in the thesis. It's the opinion of the author that there are grave defects in traditional methods: moltensalt electrolysis and silicothermic reduction of oxides. The former process is complex, needs vast investment, and emits toxic gases like chlorine gas; treatment of production wastes is overburden costly; erosion of the production equipments and plant buildings is badly, and maintenance cost overwhelming. The flaws in the process of magnesium extraction by silicothermic reduction of oxides are: ?high production cost with the higher cost of major reductant, ferrosilicon (75%);(2) short service life, but high price of reduction retort, which is made of high Ni-Cr alloy; (3) Since the retort is vacuumed inside and heated under the normal pressure outside, small-size retort, low forced filling rate, low production capacity and thermal efficiency, batch production and low productivity are lead to.Introduction of vacuum technology in magnesium extraction, high Ni-Cr alloy is substituted by cheaper carbon and reduction retort by internal heating vacuum furnace; scale of vacuum furnace is free of the limit of retort cubic capacity;thermal efficiency and production of single equipment are raised, cost decreased andworking conditions improved. Since all reactions take place in the closed vacuum furnace, there is less influence upon environment.Through inter-link retrieve, relevant papers are absent domestic; and abroad are scarce. R.Winand, the most epitomized, solved only how to produce magnesium vapor through magnesia reduction by carbon, conditions and devise of condenser used to condense the vapor into liquid or solid critical magnesium was not touched upon. Extended test ended deplorably due to clogging.Thermodynamic calculation gives that: the process, magnesia reduced by carbon in vacuum, is feasible, that by comparison with atmosphere carbothermic reduction, vacuum method decreases reaction temperature by 300~400癈,and that reaction efficiency is enhanced under the situation of reduction temperature higher than or equal to 1352癈,homologous dew point higher than 651癈( melting point of magnesium).Laboratory test results in improver reduction rate by enhancing reduction temperature and elongating reduction time, additionally by adding appropriate fluoride. During reducing process, vacuum degree changes with time and by which decides the reduction rate and completeness. The condition, of magnesia reduction by coal in the vacuum, is: C:MgO (molar ratio) is 3:1, calcium fluoride, which is 10% of total weight, is added as catalyst, the reaction temperature is raised above 1500癈 and holding-time is 30-40min.The better crystalline state and heavy fibrous structure solid magnesium lump condensates, growing vertically on condensation face, are succeeded to acquire in laboratory tests. The condensed magnesium have a layered growth and the purity of condensed magnesium is up to 99%, which are superior to former researches only getting magnesium powers.The novel vacuum furnace is employed in laboratory study. Compared with atmosphere magnesium carbothermic reduction furnace, this new one has the merits of high automation, easy manipulation and fine safety. Vacuum coking, vacuum carbothermic reduction process and magnesium vapory condensation process can be carried out in a furnace. And the whole reduction process, without gas H2 or N2, can directly yield very high purity magnesium lump condensates, then omits the following process of distilling magnesium powders, shortens the whole flow sheet-IV-Abstractand improves the operation security.The dissertation integrates coal chemistry and coking with vacuum metallurgy to bring up vacuum coking procedure. Updated analysis and test procedure such as SEM, EPMA, XRD, are exploited to explore the law behind coking varied ratio of magnesia and coal in vacuum to get semi-coking material. The doctoral t...
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