Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1994-03-23
1996-02-27
Bos, Steven
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
423 92, 423275, 423 87, 423DIG12, 423592, 252518, C01G 1902, H01B 100
Patent
active
054946522
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for obtaining particles of metal oxide; the invention relates also to the resulting oxide particles as veil as their use as antistatic agent, particularly for photographic films.
The metal oxide powders have various applications, particularly in the field of antistatic or conductive compositions.
A technique well known to prepare these oxides consists in precipitating a hydroxide from a salt, and then recovering this hydroxide and submitting it to a calcination treatment at a high temperature, higher than 500.degree. C. and even 1000.degree. C. During this calcination treatment, various phenomena can occur which modify the texture or the crystalline morphology of the metal oxide particles, and produce a sintering, i.e., a clustering of these particles. As a result, materials in the form of particles exhibiting irregular sizes are obtained. With these particles, it is difficult to prepare dispersions and coating compositions in order to obtain thin conductive or antistatic layers. Moreover, the physical properties of such layers are not very reproducible. Therefore, a mechanical treatment such as grinding, is necessary to obtain finer particles and more homogeneous powders, in order to render these materials suitable for the applications considered. However, grinding causes crystalline defects to appear in the particles, which defects must be often resorbed by means of an additional thermal treatment.
In some cases, the hydroxide precipitation is a coprecipitation, because either a second metal hydroxide or an insoluble salt of another metal is coprecipitated with the hydroxide. An example is the initial step for preparing hexaferrites of alkaline-earth metals, where a ferric hydroxide and an alkaline-earth metal carbonate are coprecipitated. This precipitate is then thermally processed at about 1000.degree. C. in order to obtain the hexaferrite. In order to promote the reaction between hydroxide and carbonate, it is known to add a promoter which can be an alkali metal borate, PbO, Bi.sub.2 O.sub.3, an alkali metal ferrite, a molybdate, an alkali metal chloride or sulfate. This method which consists in calcinating the hydroxide/carbonate mixture in the presence of the promoter, in order to accelerate a chemical reaction, is disclosed in U.S. Pat. No. 3,793,443.
However, U.S. Pat. No. 3,810,973 indicates that using, as a flux, compounds such as B.sub.2 O.sub.3, alkali metal borates or halides gives variable results and accordingly, proposes to form a sodium chloride and potassium chloride mixture in situ in order to promote the formation of a ferrite.
U.S. Pat. No. 4,401,643 discloses a method for preparing barium ferrites whereby a mixture of mixed barium and iron carbonate and of sodium salt is obtained by coprecipitation; then, this mixture is heated at a temperature higher than 680.degree. C., but lower than the sodium salt melting temperature and a finely divided ferrite powder is obtained, which is separated from the sodium salt.
Moreover, the technical literature discloses the preparation of numerous metal oxides such as ZnO, SnO.sub.2, In.sub.2 O.sub.3, MgO, TiO.sub.2, by precipitating and calcinating the corresponding hydroxide. In this literature, it is not mentioned or suggested to use a promoter or a flux during the calcination step.
From the foregoing, it can be stated that it is still a problem to obtain metal oxides in the form of fine, homogeneous particles exhibiting a determined morphology and appropriate conductive properties. The thermal treatment of oxides and the sintering it generates remain an obstacle in this regard.
The present invention is directed to an improved method for obtaining, in a simple and economical manner, a fine powder of metal oxide exhibiting electrically conductive properties.
The method consists in preparing a hydroxide precursor of a metal oxide, mixing this precursor with an inorganic compound having a melting point lower than the crystallization temperature of said metal oxide and then submitting the resulting mixture t
REFERENCES:
patent: 3793443 (1974-02-01), Arendt
patent: 3810973 (1974-05-01), Arendt et al.
patent: 4233282 (1980-11-01), Arendt
patent: 4246143 (1981-01-01), Sonoda
patent: 4401643 (1983-08-01), Hibst et al.
patent: 4614669 (1986-09-01), Yannopoulos
patent: 5112433 (1992-05-01), Dawson et al.
Bos Steven
Eastman Kodak Company
Lorenzo Alfred P.
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