CS248541B1 - Grey-and-black- zirconium pigment - Google Patents

Abstract

Ceramic pigment based on it zirconium silicate with zirconium structure containing black particle inclusions of ruthenium trioxide they supply gray to black, ready to use zirconia-containing mixture and silica, inineralizers - hexafluorosilicate disodium, lithium hydroxide, chloride sodium and oxides, or ammonium or alkaline salts of hexavalent molybdenum or tungsten and ruthenium oxide or powdered oxide ruthenium or ruthenium compound by calcination to the oxide passing through its firing at temperatures of 580 to 900 ° C. The invention is a suitable gro use in ceramic industry. It makes it quite simple preparing a high quality pigment for toning glazes.

Description

BACKGROUND OF THE INVENTION The present invention relates to a gray-black zirconium pigment of the inclusion type and containing ruthenium dioxide

Zircon pigments, which are used in ceramics, are chemically, thermally and colored very stable means for dyeing glazes. They are based on zirconium silicate with a tetragonal spatially centered structure corresponding to the zirconium mineral formed in the process of preparing these pigments. In pure form, this silicate is uncoloured, but during its synthesis some impurities can be trapped into it, which then causes its coloration. They are, on the one hand, ions of certain transition metals incorporated into its structure as dyeing disorders; the number of these failure-ion-colored zircon pigments is limited and is not yet known in gray-black or black. Furthermore, there is a second type of admixture - particles of intensely colored compounds, which are embedded as so-called inclusions in synthesized zirconium microcrystals. These compounds would generally not withstand the aggressive action of molten ceramic glazes on their own. They would react with the ingredients in the glaze, causing a significant or complete loss of color. Therefore, they cannot be used for direct dyeing of glazes, but it is necessary to achieve ingrowth of these particles into zirconium microcrystals during pigment synthesis. The colored compound particles are then coated with colorless zirconium silicate and protected from the aggressiveness of the molten glaze. The resulting particles of this zirconia pigment are colored and can be used to effectively color ceramic glazes, including high temperature (glazing temperatures around 1300 ° C). However, the number of known compounds that can be used in this way to prepare zirconium inks pigments is limited, and a pigment of this type which is intensely gray-black to black is not yet known. Only zinc-2 248 541 pigments containing inclusions formed by some spinels, which are only light gray, are known. An intensely black substance is ruthenium dioxide, sometimes also referred to as ruthenium black. However, its direct use in ceramic glazes to achieve a gray-to-black shade is not possible. Although it is a chemically and thermally stable compound, it nevertheless does not resist high-temperature glazes during glazing and partially reacts with the glaze components with significant blacks loss. The color of the glaze is then irregular and uneven, despite the fact that the consumption of relatively expensive ruthenium dioxide would be too high in this way. Although low-temperature and medium-temperature glazes resist better when used directly, ruthenium dioxide will, however, again be disproportionately high; moreover, this oxide does not have good pigmentary properties in terms of dispersing the elution of its particles in the glaze. It is therefore not possible to achieve regular and even coloring with low-temperature and medium-temperature glazes when used directly.

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These drawbacks are overcome by the gray-gray zircon pigment according to the invention. It is based on the fact that the pigment consists of microcrystals of zirconium silicate having a zirconium structure containing inclusions of black ruthenium oxide particles. It is prepared from a mixture comprising 44 to 60% preferably 50 to 54% by weight of zirconium dioxide, 20 to 28% preferably 23 to 25% by weight of silica, 2 to 12% preferably 5 to 6% by weight of disodium hexafluorosilicate, 1.5 up to 7% preferably 2.5 to 4% by weight of lithium hydroxide, 0 to 6% preferably 1 to 2% by weight of sodium chloride, 2 to 20% preferably 4 to 7% by weight of the oxide or ammonium salt or alkali metal salt or an alkaline earth salt of hexavalent molybdenum or hexavalent tungsten and 0.1 to 20%, preferably 2 to 8% by weight of ruthenium oxide or powdered ruthenium, or a ruthenium compound by calcination of ruthenium dioxide. The mixture is heated at a rate of 0.5 to 40 ° C / min, preferably at a rate of 5 to 15 ° C / min to a temperature of 580 to 900 ° C, with a temperature of 600 to 750 ° C for a period of time and preferably 0. 5 to 2 h at this temperature. The use of temperature within the range is governed by the kind of starting zirconia and the amount of mineralizers - disodium hexafluorosilicate, lithium hydroxide, sodium chloride - within the ranges indicated for them. The mixture is fired to form zirconium silicate microcrystals with a zirconium structure as the pigment base. Their synthesis at relatively low firing temperatures is facilitated by the significant mineralization effects of disodium hexafluorosilicate in combination with lithium hydroxide ev. sodium chloride. In addition, the hexavalent molybdenum or tungsten compounds also contribute, by their mineralization effects, to obtain sufficient silicate yields at relatively low firing temperatures of the mixture. In the synthesis of zirconium microcrystals, intensely black ruthenium dioxide particles grow in them as so-called inclusions and give them a gray-to-black color shade, depending on the amount of ruthenium compound used in the range indicated. Molybdenum or tungsten ions are also incorporated into the silicate structure, which partially become tetravalent at the time of pigment formation (releasing active oxygen) and are captured as substitutional uncharged disorders at the zirconium site (Mo _z ^x , ^ Ζ _Γ ^χ ) ϊ however, they do not affect the actual color of the zirconium microcrystals. When powdered ruthenium is used, ruthenium dioxide is formed by its oxidation during firing. The active oxygen released from the molybdenum and tungsten compounds contributes to this. Similarly, when another ruthenium compound is used, it results in black ruthenium oxide particles, either by thermal decomposition or also with the aid of said oxygen. The product is a gray-to-black zircon pigment which gives it a gray-to-black shade when applied to a ceramic glaze. Optionally, the pigment leach may be washed with water or dilute mineral acid while hot to remove alkali residues from the mineralizers e, from the alkali metal salts of molybdenum and tungsten.

The pigment according to the invention is a highly stable zirconia pigment with an intense gray to black tint. Yippee

- 4,248,541 suitable for all types of ceramic glazes, including high-temperature glazes with a glazing temperature of about 1300 ° C. The high intensity of pigment shade is already achieved at relatively high

low ruthenium dioxide; the pigment allows an intense black to black glaze to be achieved even when used in relatively small amounts. The pigment lute is reacted to a zirconium silicate with a zirconium structure to a high degree (more than 80%). The energetic conditions for the preparation of the pigment are very advantageous, as the composition of the mineralizer takes place already at relatively low firing temperatures. Technological conditions of pigment preparation are also undemanding.

Example 1

100 g of mineral zirconia (purified baddeleyite), 46 g of silica, 11 g of disodium hexafluorosilicate, 6 g of lithium hydroxide monohydrate, 3 g of sodium chloride, 10 g of molybdenum oxide and 10 g of ruthenium dioxide were dry blended and fired in an oven a ramp rate of 10 ° G / min at 600 ° C for

1.5 h. The hot lime slurry contained 83% zirconium silicate and was intensely black. It is suitable for coloring ceramic glazes with any glazing temperature to black.

Example 2 g of synthetic zirconium dioxide, 25 g of silica, 6 g of disodium hexafluorosilicate, 3 g of lithium hydroxide, 2 g of sodium chloride, 10 g of dodecammonium dewaxate and 1 g of powdered ruthenium were dry blended and fired in an oven at 5 ° C / min, at 650 ° C for 1 h. The lime contained 81% zirconium silicate and was intensely gray. It is suitable for coloring ceramic glazes with any glazing temperature to gray.

Claims (1)

SUBJECT OF THE INVENTION 248 541 A black-black zirconium pigment consisting of zirconium silicate microcrystals having a zirconium structure, containing inclusions of black ruthenium dioxide particles and obtainable by heating at a rate of 0.5 to 40 ° C / min, preferably at a rate of 5 to 15 ° C / min to a temperature of 580 to 900 ° C, preferably to a temperature of 600 to 750 ° C with a holding time of 0.5 to 2 hours at this temperature of a mixture containing 44 to 60%, preferably 50 to 54% zirconia, 20 to 28%, preferably 23 to 25% silica, 2 up to 12%, preferably 5 to 6% disodium hexafluorosilicate, 1.5 to 7%, preferably 2.5 to 4% lithium hydroxide, 0 to 6%, preferably 1 to 2% sodium chloride, 2 to 20%, preferably 4-7% oxide, or ammonium salt, or an alkali metal salt or alkaline earth salt of hexavalent molybdenum or hexavalent tungsten and 0.1-20% preferably 2-8% ruthenium dioxide, or powdered ruthenium, or a ruthenium compound p ruthenium dioxide.