Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Patent
1997-08-28
1999-11-02
Wyszomierski, George
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
75363, 75369, B22F 922
Patent
active
059762179
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method for the chemical reduction, consisting of one or more stages of reaction, of powdered metal compounds as the material to be reduced, to powdered metal or to powdered metal compounds at a lower oxidation state than the predetermined final product, in a temperature controlled reaction chamber with input and output openings for the material to be reduced, for the gaseous reducing medium and, alternatively, for the carrier gas. The method is particularly suitable for the reduction of refractory powdered metal oxide into powdered metal, for example, the reduction of en oxide to tungsten, or even of molybdenum oxide to molybdenum.
Until now, the methods of powder metallurgy have dominated the manufacture of refractory metals and their further processing. As a result, the quality of the powdered metal, particularly the purity and the grain structure, has a decisive influence on the quality of the powder-metallurgical products produced from it.
The specialist has therefore always ascribed great importance to the production steps of metal extraction, which produce pure powdered metal directly. This especially concerns the reduction of powdered metal oxides of refractory metals, for example W.sub.4 O.sub.11 or MoO.sub.3 to pure metallic powder in one or more stages of reduction.
It is therefore noteworthy, that these oxides have predominantly been reduced in pusher-type furnaces for decades, for reasons unchanged up to the present. For this processing, the powdered oxides are smeared into a thin layer in tablet-like ceramics or metal seers and directed (pushed) step by step, at an established rate for several hours through a high temple pusher-type furnaces with zones of different temperature and different atmospheric conditions. As a rule, hydrogen gas is introduced as the reducing agent. The processing times and therefor the reduction times are around 10.sup.3 -2.times.10.sup.4 seconds. The specific throughput, measured as tons of material to be produced per unit volume (m.sup.3 ) of the reaction chamber and hour, is approximately 0.04 for pusher-type furnaces.
Another known method for reducing these types of metallic compounds which is seldom used in practice, is the so led rotary kiln method Here the charging stock of the material to be reduced moves in a rotary kiln tilted slimly from the horizontal. The processing times are comparable to that of pusher-type kilns. Here, adequate furnace dwelling or reduction times are likewise in the range of 10.sup.3 -10.sup.4 seconds and the specific throughput is approximately 0.055 tons per cubic meter and hour.
Both of these methods have a disadvantage which has been known for a long time, namely the small specific throughput of the powder to be reduced, relative to the size of the installation. The source of the small specific throughput is the restricted access of the reducing gas to the powder surface of the material to be reduced.
To overcome the discussed disadvantages of rotary kilns and pusher-type kilns, it has been proposed to undertake the reduction in a fluidized bed oven In this method, the metal compound to be reduced is brought as powdered charging stock into a temperature controlled reaction chamber on a metal grating, By the reducing gas, mixed with a carrier gas if necessary, flows from below through the material to be reduced, which is positioned on the grating, thereby stirring up the material, bringing it into a quasi-fluid gas particle phase, and reducing it to powdered metal in contact with the same.
Yet even in this method, the dwelling time of the material to be reduced in the reaction chamber for adequate homogeneous reduction of the particles is 10.sup. -10.sup.4 seconds. Accordingly, the specific throughput of the material to be reduced is around one power of ten above that of pusher-type and rotary kilns.
The sources of these unsatisfactorily long dwelling or reaction times are the partial reoxidation of already reduced particles in the charging stock, and the unavoidable formation of
REFERENCES:
patent: 3234007 (1966-02-01), Blocher, Jr. et al.
patent: 4859236 (1989-08-01), Patrician et al.
patent: 5125964 (1992-06-01), Buerkel et al.
Kneringer Gunter
Kock Wolfgang
Resch Joachim
Schwarzkopf Technologies Corporation
Wyszomierski George
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