Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1996-05-07
1998-03-03
Gorgos, Kathryn L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
42218604, 42218626, B01J 1908
Patent
active
057230277
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to a method for the continuous preparation of a powder by reacting at least two reagents in a plasma arc, in which one first and one second reagent are fed to the plasma arc which is maintained by a voltage applied between a first and a second electrode, whereby at least the first reagent is electrically conductive and is used as the first electrode.
2. Background Information
Furthermore, the invention pertains to a device for the continuous preparation of a powder by reacting at least one first and one second reagent in a plasma arc, with a feed arrangement for feeding at/east the first reagent to the feed opening of a plasma chamber which has an interior tapering in the direction of a passage lying opposite the feed opening, and with at least two electrodes which are connected to a generator for maintaining the plasma arc in the plasma chamber, whereby the first electrode is formed by the first reagent.
Plasma is a complex medium which is obtained at very high temperatures of e.g. 3000.degree. C. It is very reactive so that chemical reactions take place at a high velocity. Plasma is formed by the ionization of a gas resulting from the electric discharge of a direct current, from high-frequency discharge, and from microwave discharge. Examples of present-day use are: Reduction of iron ore by injecting iron ore (oxide) and coal into a plasma burner; by injecting numerous metal oxides Cr.sub.2 O.sub.3, SiO.sub.2, CaO and MgO.
Plasma arcs are used primarily in metallurgy at temperatures exceeding 1500.degree. C. They consume large quantities of electric energy. They require electrodes which after use become waste, and therefore contribute to environmental pollution.
An induction plasma can in fact be produced without electrodes, although its performance is weaker, as described in the documentation "nes Plasmas Industriels" of the French Ministry of Instruction, Research and Higher Education (La Documentation Francaise, No. 10, 1986).
A method and a device according to the type described are known from the Swiss patent specification CH 281 749. It describes a method for preparing metal halogenides, whereby an anode is produced consisting of a mixture of minerals of the corresponding metals and of carbon, and an arc in a halogen-containing atmosphere is generated between this anode and a carbon cathode, thus forming metal halogenide.
The anode is used up during this process. Due to the inhomogeneity of the anode material, the plasma burns unevenly. Moreover, the preparation of the electrode is time-intensive and costly.
A device according to the type described is known from the British patent specification GB 959,027. The plasma injection device described therein has a plasma chamber and a feed arrangement for feeding a metal wire charged as an electrode to the plasma chamber. At its underside, the feed arrangement is provided with an outlet for the wire extending coaxially to the interior of the plasma chamber which opens upward in the direction of the feed arrangement. The interior of the plasma chamber tapers downward in the direction of an outlet nozzle.
It has been demonstrated that with the known device the plasma produced in the plasma chamber cannot be stabilized sufficiently.
SUMMARY OF THE INVENTION
Thus, on one hand, the present invention has the objective of proposing a simple and economical method for the continuous and reproducible preparation of a powder by reacting at least two reagents in a plasma arc and, on the other hand, of providing a device which guarantees a homogeneous and uniform plasma and thus reproducible results.
In terms of the method, this objective was met according to the invention by feeding the first reagent to the plasma arc in fluid form.
The first reagent can be present, for example, in the form of a melt, a liquid, a suspension, a dispersion, a gel, or a shakable or pourable powder. It is not necessary to prepare a solid electrode that contains the first reagent. Signs of wear and tear or so
REFERENCES:
patent: 2157498 (1939-05-01), Reinecke et al.
patent: 2837654 (1958-06-01), Berghaus et al.
patent: 3101308 (1963-08-01), Sheer et al.
patent: 3708409 (1973-01-01), Bainbridge
patent: 4801435 (1989-01-01), Tylko
patent: 5196102 (1993-03-01), Kumar
patent: 5562809 (1996-10-01), Sorokin
French Ministry of Instruction and Higher Education, "Les Plasmas Industriels", No. 10, (1986), pp. 107 to 111 (and English language translation thereof), (no month available).
Patent Abstracts of Japan, of JP-62111373, (May 1987), vol. 11, No. 328.
Gorgos Kathryn L.
Mayekar Kishor
W.C. Heraeus GmbH
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