Compositions – Preservative agents – Anti-corrosion
Patent
1993-12-03
1996-08-27
Wu, Shean C.
Compositions
Preservative agents
Anti-corrosion
260DIG16, B01J 1300, C01G 3102, C09K 316
Patent
active
055498469
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the continuous preparation of vanadium pentoxide gels used for anti-static applications. The invention also relates apparatus for implementing the method.
The oxide of vanadium V.sub.2 O.sub.5 is an oxide which is particularly useful for obtaining compounds with satisfactory conductive properties for use in anti-static coatings.
It is known that it is possible to obtain vanadium oxide sols and that they have already been the subject of numerous studies. Thus, according to J. B. Donnet, in the Journal de Chimie Physique No 50, p.363 et seq (1953), these sols, which can be prepared by different methods (including the method of Erich Muller, which consists of spraying V.sub.2 O.sub.5 at melting point into cold distilled water), contain particles whose chemical nature has given rise to a certain amount of controversy. The article by Erich Muller which appeared in Kolloid Z. 8 P.302 (1911) mentions that V.sub.2 O.sub.5 is only very slightly soluble in water and that it is possible to obtain a sol, as indicated above, by spraying V.sub.2 O.sub.5 maintained at melting point into cold distilled water. A Revcolevschi, in the lecture given on 13 Dec. 1973 to the Societe d'Encouragement pour l'Industrie Nationale, described a new method for obtaining amorphous structures of oxides or mixtures of oxides. This method, known as hyperquenching, consists of rapidly cooling a substance in the liquid or vapour state. For quenching from the liquid state to be efficacious, it is necessary for the rate of cooling of the material to be exceptionally high at the time of the transition from liquid to solid. This assumes an extremely high rate of heat exchange at this precise moment. It has been shown that the mechanism of heat exchange by conduction is the most effective method if the following conditions are met: conductor of heat; small as possible.
A Revcolevschi proposes different methods for obtaining this result. It has been possible to obtain amorphous structures by these methods since the rate of quenching has been sufficiently rapid to fix the structure of the liquid state in the solid state.
Up till now, vanadium pentoxide (V.sub.2 O.sub.5) gels were produced by using a technique as described in the U.S. Pat. No. 4,203,769, namely in batches. According to the method described in this patent, the V.sub.2 O.sub.5 is melted in a furnace incorporating a quartz tube. The V.sub.2 O.sub.5 is optionally mixed with a doping agent such as silver. The furnace is raised to a temperature of approximately 1050.degree. C. The molten oxide is then cast into a quenching reactor, under agitation, containing distilled water at 20.degree. C. The outlet from the furnace is arranged at approximately 80 cm from the surface of the water in the quenching reactor. As soon as the desired concentration of V.sub.2 O.sub.5 is obtained (measured by weighing), the process is stopped. The molten V.sub.2 O.sub.5 remaining in the furnace is removed and the agitation of the gel in the quenching reactor is continued for approximately 30 minutes in order to obtain a uniform gel. Such a method has known drawbacks of batch manufacture, namely: the losses of molten oxide remaining in excess in the oven at the time the process is stopped (approximately 30% of the quantity of oxide); the stages during which the equipment is cleaned, requiring a considerable amount of time; non-uniform production from one batch to another. In addition, the yield of this type of method is relatively low. In fact, the maximum quantity of gel produced at 4% V.sub.2 O.sub.5 is 90 kg in 8 hours.
Thus one of the objects of the present invention is to provide a method allowing the continuous production of a vanadium pentoxide gel, optionally mixed with a doping agent.
Another object is to provide a method of manufacturing vanadium pentoxide gel making it possible, with a high yield, to obtain a gel with a constant concentration of vanadium pentoxide.
Yet another object of the present invention is to provide an apparatus enabling vanadium pentoxide t
REFERENCES:
patent: 3847788 (1974-11-01), Wallace
Legrand Annie F.
Tixier Jean P.
Eastman Kodak Company
Gerlach Robert A.
Wu Shean C.
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