DD290001A5 - METHOD FOR PRODUCING METAL OXIDE POWDERS - Google Patents

Abstract

The invention relates to a process for the preparation of finely dispersed metal oxide powders. These powders can be used in various fields of application, for example as a dye pigment, as a phosphor, as a polishing agent, as a starting material for high-performance oxide ceramics, as a sintering aid in ceramic production or as an adsorption material. The object of the invention is to provide a finely divided metal oxide powder with a narrow grain band. The invention has for its object to develop a method by which a fine basic precipitate can be obtained from a metal salt solution, which leads to a finely divided oxide powder with a low particle size after drying and calcination. This object is achieved according to the invention in that the reaction volume is brought into contact with a vigorous oxygen stream, with at least 6 l of gaseous oxygen being used for each cationate equivalent, and the recovered precipitate is further treated in a known manner. fine-particle, narrow grain band; vigorous oxygen flow; Kationenaequivalent}

Description

Field of application of the invention

The invention relates to a process for the preparation of finely dispersed Motalloxidpulvern. These powders can be used in various fields of application, for example as a dye pigment, as a phosphor, as a polishing agent, as a starting material for high-performance oxide ceramics, as a sintering aid in ceramic production or as an adsorption material.

Characteristic of the known state of the art

For the production of finely dispersed oxides, a variety of methods are known. They are based on mechanical, chemical or physical principles of particle formation. The mechanical methods of micro-crushing are most commonly used in the laboratory and on an industrial scale. However, apart from a limited fineness, the mechanical processes always involve the risk of additional material contamination. Also introduced with the mechanical distribution high lattice disorder of the powder crystallites can be disadvantageous in certain cases, for. B. affect the optical reflectivity. The physical methods that achieve fineness via evaporation, sputtering or sputtering are generally expensive in terms of apparatus and energy.

The most widespread have been found in chemical processes in which the oxide powder or a precursor which can be converted into the oxide powder by subsequent thermal treatment are synthesized directly in the chemical process. From the variety of chemical processes, the precipitation processes in aqueous solution protrude because a relatively satisfactory powder quality can be achieved with relatively little equipment. At the same time, the transmission in the small-scale to industrial scale poses no insoluble problems. As precipitation reactions have proven to be those in which the precipitate can be converted into the oxide even at relatively low temperatures. These are especially the precipitation of oxalates, carbonates and hydroxides (WP C 01 G / 324269) .The hydroxide precipitations have the advantage that no anion must be carried, which in the thermal conversion into the oxide by release of large amounts of gas, reaction of gaseous decomposition products with the Katione.i, incomplete reaction and / or increased environmental impact, can cause problems. However, the hydroxide precipitations also often have the disadvantage that the precipitate is amorphous or very fine crystalline. This occurs in particular when ammonia or another nitrogen base is used as the precipitant. This particular type of precipitation requires special measures of drying, which aim to reduce the surface tension of the solvent (exchange of water for organic solvents) or turn off completely (freeze-drying, supercritical drying). Nevertheless, oxide powders thus produced often have too wide a grain band and a high tendency to agglomerate.

Another characteristic is an often large increase in particle size with increasing calcination temperature, apparently a consequence of premature sintering at the contact points of the powder particles.

Object of the invention

The object of the invention is to provide a finely divided metal oxide powder with a narrow grain band.

Explanation of the essence of the invention

Gor invention has for its object to develop a method by which a fine basic precipitate can be obtained from a metal salt solution, which leads after drying and calcination to a finely divided oxide powder with a low particle size.

This object is achieved in that währer.d d & s precipitation process, the reaction volume is brought into contact with a strong flow of oxygen, wherein each precipitated cation at least 61 gaseous oxygen are used, and the recovered precipitate is further treated in a known manner.

For the introduction of the oxygen into the reaction volume, it is possible, for example, to use a simple injection into the precipitation suspension during the precipitation process at the location of the combination of metal halide solution and precipitation medium or an injection of the metal salt solution into the precipitate reservoir with an oxygen stream. The effect of the invention occurs, regardless of whether the metal cation is able to react with the oxygen in a redox process or not. However, the positive effect of the oxygen on the properties of the precipitate and the resulting oxide powder is lost,

when the oxygen larger amounts of another gas are mixed. Thus, the blowing of air instead of pure oxygen brings little or no improvement in product properties over precipitation without any contact of the precipitating / precipitation suspension with a gas stream. The surprising effect of the oxygen on the properties of the precipitate and oxide powders produced therefrom has not been clarified. Specifically, chemically sorted oxygen may specifically affect cohesiveness between the primary crystallites in the powder particles. Particularly noteworthy in the material produced under the influence of oxygen in addition to the narrower grain spectrum, only a relatively small change in the grain distribution function at low and medium calcination temperatures. In certain cases, z. As in cerium oxide powder occurs even a significant reduction in the average grain size.

Ausführungsbelsplele

1. 0.3 M Ce-III nitrate solution and 25% ammonia solution are simultaneously metered into a 3-liter laboratory beaker at room temperature (metering rate of the metal salt solution 0.5 l / h) that the measured with a glass electrode pH at 7.6 is located. An oxygen stream of 100 l / h is blown in through the dropping point of the metal salt solution via a glass tube.

At the same time the solution is stirred vigorously.

After completion of precipitation, the precipitate is filtered off, washed until free of nitrates and freeze-dried. The dry oxide hydrate is calcined in air.

The following particle sizes are established (Shimadzu centrifuge SA-CP-3, ultrasonic dispersion):

"to dso deodorant "Mm) mm) (Mi hydrate 0.1 0.6 8.8 CeO ₂ (at 500 ⁰ C for 1.5 h calcined) 0.2 0.5 2.5 CeO ₂ (at 65O ⁰ C for 1.5 h calcined) 0.1 0.6 4.0

If the precipitation is repeated in the same way but air is blown in place of oxygen, the particle sizes are as follows:

do dso deodorant (Mm) (Mm) (Mm) hydrate 0.1 0.5 2.5 CeO ₂ (calcined at 500 ° C, 1.5 h) 0.8 3.8 12.2 CeO ₂ (at 65O ⁰ C, 1.5 h calcined) 0.6 3.8 12.7

The X-ray detectable structure of the products in both cases corresponds to pure CeO ₆ , regardless of the type of gas used.

2. From a 0 3-M-iron sulfate solution is precipitated with ammonia solution at a pH = 8 iron oxide hydrate win described in Example 1, filtered, washed sulfate-free and calcined. The following particle sizes result:

dio dso dso dio d _M d " (Mm) (Mm) (Mm) (Mm) (Mm) (Mm) hydrate 0.4 1.0 1.8 0.90 1.7 2.8 Oxide after calcination (45O ⁰ C, 2 h, air) 0.1 0.4 1.2 0.3 1.1 1.8 If the precipitation is repeated in the same way but with the blowing through of air, the following particle sizes are established: hydrate Oxide after calcination 450 ° C, 2h, air)

If no gas is blown through the reaction volume during the otherwise analogous precipitation, the following values result:

(pm) (mm) (mm)

Oxide hydrate 0.2 2.0 5.7

Oxide after calcination

(450 ^° C, 2 h, air) 0.2 4.1 5.6

Claims (2)

1. A process for the preparation of metal oxide powders of high fineness and low particle size by precipitation of an oxide hydrate from an aqueous solution of the basic metal salts followed by drying and calcination of the precipitate, characterized in that during the precipitation process, the reaction volume with a stream of gaseous oxygen durchwirbe'i , wherein per cation equivalent at least 61 oxygen are introduced. 2. The method according to claim 1, characterized in that the metal salt solution with gaseous acid substance in the precipitated suspension wierd.