GB1418641A - Treatment of material by an arc discharge plasma - Google Patents

Abstract

1418641 Plasma heating MAX-PLANCKGES ZUR FORDERUNG DER WISSENSCHAFTEN eV 16 Nov 1972 [20 Nov 1971 29 July 1972] 52989/72 Heading H5H [Also in Division C7] Material 24 is treated by an arc discharge plasma between axially spaced electrodes 16 18 at least one of which is annular in a vessel 10 maintained at an average pressure below atmospheric by introducing the material 24 to a region in the plasma close to a position where an axial magnetic field B has such a high value, e.g. > 10 KGaus, preferably at least 20 KG and more preferably between 30 and 60 KG that the product wt of the electron gyration frequency w, and the time t which is defined as the reciprocal of the mean collision frequency, is greater than 1, and the arc plasma is of annular form and rotates about the axis, and recovering the treated material 36 from a space radially outside the region w is defined as the frequency at which electrons rotate about a line of magnetic flux. Both electrodes may be annular as shown, with outer and inner insulating, e.g. quartz or ceramic extensions 20a, 20b and 22a, 22b secured to their outer and inner peripheries. The extensions are of hyperbolic form to conform to the field lines of the magnetizing coil 30. An electromagnetic needle valve 26, 28 introduces measured doses of material to the high intensity field region through the longer inner extension 20b of the upper electrode. The vessel 10 is evacuated through conduit 12. The pressure on the axis is high and decreases radially so that treated material is centrifuged to the vessel walls. The electrodes may be of any closed loop shape, e.g. disc, rectangular, elliptical or triangular. The lower electrode 18 may be rod shaped. The magnetic coil 30 may be a superconducting coil requiring no power supply during use. Chemical elements may be recovered from their compounds, e.g. titanium, zirconium, vanadium, tantalum and aluminium; chemical compounds may be produced; fusible materials may be treated, or liquids, vapours and gases and mixtures or dispersions may be treated by the process. If the treated material 36 is capable of forming a volatile metal halide it may be removed by introducing a halogen to the discharge vessel. Chromium, niobium, tantalum, silicon titanium, uranium, vanadium, and zirconium are suitable metals. When ilmenite (FeTiO 3 + Fe 2 O 3 ) is introduced to the plasma iron and titanium deposit on the quartz vessel 10. Iodine vapour introduced to the vessel forms TiI 4 and FeI 2 . At 200‹ C. the TiI 4 is volatile enabling it to be pumped away leaving the still solid FeI 2 behind. The TiI 4 vapour is decomposed on a Ti surface at 1000 to 1200‹ C., the liberated iodine being free for recycling. Instead of a halogen, a halide which is capable of giving off free halogen atoms to the treated material may be used.