CS258931B1 - Process for preparing a gray ceramic zirconium pigment - Google Patents

Abstract

The pigment is of the zircon type with inclusions of manganese dioxide. It is prepared from the decomposition products obtained by the decomposition of zirconium mineral with a mixture of potassium and sodium hydroxide at temperatures above 600 °C. The alkaline ions in the decomposition products then act as the alkaline component of the mineralizer of the pigment's own synthesis... Hydrofluoric and hydrochloric acids are used as the halide component, with which the basic products are precipitated. After admixture of a chromophore in the form of a manganese compound, the mixture is fired at 600 to 1,000 °C to a gray pigment.

Description

The invention relates to a process for preparing a gray ceramic pigment containing manganese dioxide; The starting zirconium raw material for pigment preparation is zirconium mineral.

The basis of zircon pigments used for coloring ceramic glazes is synthetic zirconium silicate with a structure corresponding to the zirconium mineral. Silicate is colorless in pure form, but it can be trapped in its synthesis! different admixtures, which can then become a color.

There are two groups of coloring agents. The first is the ions of some transition elements that are incorporated into the zirconium structure as dyeing disorders. However, their number is limited and there are no known silicates that add a gray shade. The second group consists of particles of intensely colored compounds, which, as so-called inclusions, are embedded in the microcrystals of zirconium silicate, which they color. The particles of the above mentioned compounds cannot usually be used separately for dyeing ceramic glazes, as they would not withstand the aggressive environment of their melts when directly applied, they would react with the glaze components, which would lead to a complete or significant loss of color.

Therefore, these particles should be protected from the aggressive environment of the molten glaze with a layer of zirconium silicate. This is achieved by the ingrowth of the particles into the zirconium microcrystals formed. The resulting zirconium pigment particles can then color ceramic glazes, including high-temperature glazes with a glazing temperature of about 1300 ° C.

However, the number of color compounds that can be used to prepare zirconium pigments of the inclusions type is limited.

Indeed, dyeing the silicate microcrystals with inclusions to be applicable to the glazes can only be achieved if the ingrowth is actually effective. This happens when the coloring compounds are in the form of microparticles, preferably formed only at the time of synthesis of the zirconium microcrystals and serve as a seed for their further growth.

Moreover, the formation of these microparticles and their existence should be possible at high temperature in the reaction medium of the exothermic silicate formation process, which contains an aggressive melt with alkali and halide ions. This process is then very effective if the zirconium silicate formation reaction runs slower and the silicate is formed on inclusions in uniform, regular and sufficiently thick layers. For the preparation of gray zircon pigments of the inclusions type, only the use of some spinels and the use of ruthenium dioxide are known so far. Spinels as inclusions, however, only give a light gray shade of zircon pigments. Ruthenium dioxide is not a commercially available and cheap raw material.

These drawbacks are overcome by the gray zirconium pigment according to the invention, which contains manganese dioxide inclusions. The particles of this oxide are intensely black, but their entrapment into zirconium microcrystals has not been known. Indeed, the use of manganese compounds in the most commonly used starting materials for the synthesis of zirconium pigments, starting from zirconia and silica, does not lead to the formation of a gray pigment. When these mixtures are fired, the conversion of manganese compounds to black manganese dioxide particles, which are less stable in the reaction medium and at these temperatures, is not effectively associated with the exothermic formation of zirconium silicate, which would be immediately coated and thus further protected in the synthesis environment.

Therefore, the preparation of the pigment according to the invention consists in utilizing zirconium mineral decomposition products containing alcolic-zirconium silicates. These then allow the synthesis of zirconium silicate by a slower and less exothermic process. A suitable method for obtaining these substances is the decomposition of the zirconium mineral by alkaline melting. According to the invention, a mixture of potassium hydroxide and sodium hydroxide is used as flux.

Its decisive advantage over other alkaline fluxes (eg sodium) is its low consumption per unit of zirconium.

In decomposition products, the alkali content is then very low and there is no need to leach them before the actual pigment synthesis. Conversely, they can even be used in the next stage (in pigment synthesis) as an alkaline component of a mineralizer.

The process according to the invention for preparing a gray ceramic pigment from zirconium mineral consists of the preparation of zirconium mineral decomposition products obtained from 7 wt. parts of the mineral decomposed, at a temperature above 600 ° C, preferably at a temperature of 750 to 900 ° C, by means of 2 to 5, preferably 3.2 to 4.5 wt. parts by weight of a mixture of hydroxides containing potassium and sodium hydroxide in mutual mass. a ratio of 3 to 1: 1, preferably in wt. ratio of 1.8 to 1.3: 1. The decomposition temperatures used correspond to those of the ceramic industry, respectively. they are lower and decomposition takes place to a high degree (above 90%). Advantageously, waste hardening baths from the engineering industry, which are essentially a mixture of potassium hydroxide and sodium in mass, can be used as fluxes. ratio of about 3: 2. According to the invention, these alkali are used only in relatively small masses. so that zirconium pigment can be prepared directly from the decomposition products without leaching them.

In addition, the degradation products represent directly a mixture of zirconium potassium potassium silicate and zirconium disodium silicate, preferably for the synthesis of the gray zirconium pigment of the invention. The potassium and sodium ions contained therein act as an active alkaline component of the synthesis mineralizer. The halide components of the mineralizer are added in the form of hydrohalic acids. Therefore, the decomposition products, further according to the invention, after cooling, are sprinkled with hydrofluoric acid, preferably a concentration of 15 to 25% by weight. % in an amount corresponding to at least 1 wt. %, preferably from 1.2 to 1.5 wt. of hydrofluoric acid and further sprinkling with hydrochloric acid, preferably a concentration of 12 to 22 wt. %, in an amount corresponding to at least 0.5, preferably C, 6 to 0.8 wt. parts of hydrogen chloride. Since acids of lower concentrations, i.e. diluted, are preferably used, various waste acids can also be used.

Thereafter, chromoform is added in an amount of 0.1 to 5, preferably 1 to 2 wt. parts of the manganese compound, preferably manganese carbonate. Various manganese or sludge waste compounds may also be used; however, they need to contain manganese in the bivalent state. The presence of even small amounts of tetravalent and high-grade manganese reduces the resulting gray pigment shade. In fact, it violates the condition of the formation of dyeing microparticles of manganese dioxide upon firing at the time of the zirconium silicate synthesis.

The mixture of decomposition products sprinkled with acids and with an added chromophore is then fired according to the invention at a temperature of 600 to 1000 ° C, preferably at a temperature of 700 to 850 ° C.

After evaporation, it is optionally leached with water or mineral acid, preferably at temperatures above 60 ° C. However, since the alkali content of the stillage is not high, there is no need for washing and the stillage can be directly applied to the ceramic glaze.

The final product of the process of the invention is a gray ceramic pigment consisting of microcrystals of silica: zirconia having a zirconium structure in which black manganese dioxide particles are embedded, which give an intensely gray shade. The manganese dioxide particles are completely coated with a layer of thermally and chemically highly stable zirconium silicate.

This protects them when applied to ceramic glazes from the aggressive environment of the molten glaze. A gray pigment can therefore be used to achieve a gray tint in ceramic glazes, including, high temperature glazes, with a glazing temperature of about 1300 ° C.

The amount of manganese dioxide in the pigment can be used to control the gray shade of the pigment and the glaze from light gray to intense gray and gray-black.

Advantages of the method of preparation of gray ceramic pigment according to the invention:

• The pigment flux is high both in terms of stability, the degree of conversion to zirconium silicate (80 to 90%), but to the extent of the gray shade intensity which can be controlled by the amount of chromoform added from light gray to gray-black.

- cheaper basic raw material - zirconium mineral - is used for pigment preparation,

- the mineral degradation temperatures and the actual pigment synthesis are favorable and correspond to (or lower) the temperatures used in the synthesis of ceramic pigments and in the ceramic industry in general,

- the consumption of alkaline flux for decomposition is low and a waste hardening bath of mechanical engineering containing potassium and sodium hydroxide can be successfully used; In addition, alkali ions in decomposition products‘ are also used as the alkaline component of the mineralizer in the actual pigment synthesis,

- Waste dilute acids may also be used as the halide component of the pigment synthesis mineralizer,

- various manganese wastes may be used as chromoform,

- the degree of mineral degradation achieved is high (about 90%) and the yield of the entire pigment preparation according to the invention is also high (representing 80 to 90% by weight of the starting zirconium),

- the preparation of the pigment does not require a demanding leaching operation of the mineral decomposition products with the difficult processing of the extracts into a zirconium and siliceous component,

- all intermediates and products are in solid phase and in free-flowing form, so handling and firing of the pigment are simple operations in this respect.

Example 1 g of zirconium mineral (containing 96% zirconium silicate) was decomposed with a hydroxide mixture containing 24 g of potassium hydroxide and 16 g of sodium hydroxide at 800 ° C for 2 h. The decomposition proceeded from 93 t. After decomposition products were decomposed 55 g of hydrofluoric acid 20% wt. concentration and 33 g of hydrochloric acid 17 wt. centrrii.ee. The mixture was further admixed with 8.5 g of manganese carbonate, and the mixture was fired at 800 ° C for 2 h. . The pigment was applied in an amount of 10 wt. % to a high temperature ceramic glaze with a glazing temperature of 1300 ° C, which gave the same gray shade.

Example 2

100 g of zirconium mineral (containing 94% zirconium silicate) was decomposed with 43 g of spent mechanical quenching bath containing potassium hydroxide and sodium hydroxide in wt. ratio 3: 2, at 900 ° C for 1 h. The decomposition proceeded from 94%. After cooling, the decomposition products were sprayed with 40 g of hydrofluoric acid 38% by weight. concentration and 22 g of hydrochloric acid 35 wt. concentration. 6 g of manganese hydroxide were added thereto and the mixture was fired at 800 ° C for 1 h. The lime was washed with boiling water and the remaining phase was 87 g of gray zirconium pigment containing 83% zirconium silicate. The pigment was applied in an amount of 6 wt. % to a borosilicate glaze having a glazing temperature of 1040 ° C, which gave the same gray shade.

Claims (1)

SUBJECT. b Process for the preparation of a gray ceramic pigment from zirconium mineral, characterized in that decomposition products of zirconium mineral obtained from 7 wt. parts of the mineral by decomposition at a temperature above 600 ° C, preferably at a temperature of 750 to 900 ° C, with 2 to 5, preferably 3.2 to 4.5 wt. parts by weight of the mixture of hydroxides containing potassium and sodium in a ratio by weight of 3 to 1: 1 to each other, preferably in a weight ratio. a ratio of 1.8 to 1.3: 1 and sprinkled after cooling with hydrofluoric acid, preferably a concentration of 15 to 25 wt. %, in an amount corresponding to at least 1 wt. %, preferably from 1.2 to 1.5 wt. % of hydrogen fluoride and further sprinkled with hydrochloric acid, preferably a concentration of 12 to 22 wt. %, in an amount corresponding to at least 0.5, preferably 0.6 to 0.8 wt. 0.1 to 5, preferably 1 to 2 wt. parts of a manganese compound, preferably a carbonate, and are fired at a temperature of 600 to 1000 ° C, preferably at a temperature of 700 to 850 ° C, and after firing optionally further leached with water or mineral acid, preferably at temperatures above 60 ° C.