CS249963B1 - Process for preparing intense pink ceramic paint - Google Patents

Abstract

A low-temperature three-component mineralizer is used, containing sodium molybdenum, sodium hexafluorosilicate and lithium hydroxide, which in combination with chloride or ferrous fluoride (preferably ferrous chloride tetrahydrate) enables the formation of zirconium silicate from the starting oxides (silicon and zirconium) even at a low firing temperature, simultaneously with the formation of coloring hematite particles, which are thus very effectively captured in the emerging zirconium silicate structure. The colorant is suitable for intensive coloring of ceramic glazes, especially borosilicate glazes, to a pink shade.

Description

The present invention relates to a process for preparing a ceramic colorant which, when applied, imparts an intense pink color to the ceramic glazes. It is a dye of zircon - hematite type prepared at relatively low firing temperatures.

Ceramic dyes based on zirconium silicate with a zircon structure are prepared by firing a mixture containing generally in a stoichiometric ratio of zirconium dioxide and silica and compounds with mineralizing effects (most commonly sodium halides) together with compounds providing coloring oxides, in the case of a pink dye. is either ferrous sulfate or ferric oxide hydroxide.

Firing of these mixtures should be carried out at temperatures higher than 750-800 ° C, usually at temperatures between 900-1000 ° C. The mechanism of formation of this dye shows that a truly intense pink shade can only be achieved with simultaneous formation of hematite staining particles and colorless microcrystals of zirconium silicate with a zirconium structure into which the hematite is trapped and stained.

Upon firing, the iron compound is partially converted from the starting mixture, by reaction with mineralizers, to the ferrous halide. It then reacts with the silica starting to form hematite and silica tetrahalide, which reacts with the zirconium starting material to form microcrystals of zirconium silicate.

However, the direct use of ferrous halides in the starting mixtures used to prepare pink zirconium pigments has not been effective due to the relatively high firing temperatures necessary to effect the reaction of forming zirconium silicates in these mixtures. temperatures substantially lower.

The process according to the invention consists in using a starting mixture containing 42 to 48% by weight of an intense pink zirconia-hematite dye. % zirconia, 19 to 23 wt. 10 to 30 wt. % chloride ev. % ferrous fluoride, preferably ferrous chloride tetrahydrate and 12 to 17 wt. %, preferably 13.5 to 15.5 wt. % of a three-component low temperature mineralizer.

Due to the relatively low silicate formation temperature (about 600 ° C), made possible by the low-temperature mineralizer, the transition of ferrous halides to hematite takes place virtually concurrently with the formation of zirconium silicates. Thus, the hematite staining particles are trapped in the zirconium microcrystals very effectively and give them an intense red-pink coloration.

The low temperature three-component mineralizer comprises sodium molybdate (dihydrate), sodium hexafluorosilicate and lithium hydroxide (monohydrate), in a molar ratio of 1: 0.76 to 1.00: 2.51 to 3.20, preferably 1: 0.83 to 0.93 : 2.70 to 3.00.

The calcination of the starting mixture shows both the strong mineralization effects of lithium ions released from the hydroxide and the effects of silica tetrafluoride released from hexafluorosilicate, which can immediately react with zirconium oxide to form zirconium silicate.

As a result, the weak exothermic reaction of the formation of silicates starts. In this phase, the strong mineralization effects of the active oxygen released from the sodium molybdate are very beneficial. The significant overall mineralization effects of the ternary mineralizer thus allow sufficient reacting of the starting oxides (silica and zirconium) to zirconium silicate with a zircon structure already at temperatures of about 600 ° C.

The active oxygen released from the molybdate also strongly contributes to the oxidation of the ferrous component to the ferrous component and thus to the formation of dyeing hematite at temperatures corresponding to the formation of silicate.

The halide anions released from the ferrous halide also have a beneficial effect on the silicate formation reaction, as they attract additional silica grains into the reaction to form a highly reactive silica halide.

All components of the starting mixture are dry blended and the mixture is baked at a temperature of 600 to 640 ° C for 1 to 3 hours (depending on the type of ZrOj used) the temperature rise rate is relatively high: 5 to 10 ° C / min to the firing temperature was reached most rapidly and no premature oxidation of Fe ¹¹ to Fe ¹¹¹ occurred, i.e. before the temperature of silicate formation occurred.

Preferably, a coating of at least 1 cm of powdered thermally stable powder is applied to the starting mixture, loosely poured in the baking vessel, and to the ongoing reactions of inert material (e.g. finely ground mineral zircon, ev. already baked zirconhematite dye.

Due to a certain consistency of the fired mixture, after cooling the layer of powdered material can be easily removed without any contamination of the product. The slurry can still be removed with hot water to remove its soluble fractions prior to application to the glaze.

The advantages of the process according to the invention reside in the quality of the colorant which shows a high degree of reaction to zirconium silicate with a relatively high content of hematite retained therein; when applied to ceramic glazes, it is colored intensely pink.

A further advantage is in the low, energy-efficient, very favorable firing temperature and also in the technological undemanding of dye preparation.

Example 1 *

100 g of purified baddeleyite (ZrO2) mineral, 45 g of silica, 50 g of ferrous chloride tetrahydrate and 35 g of low temperature three-component mineralizer containing 16 g of sodium molybdate dihydrate, 11 g of sodium hexafluorosilicate and 8 g of lithium hydroxide monohydrate were dry over a 1 to 1.5 cm layer of ground zirconium mineral in a porcelain vessel and heated at 10 ° C / min to 620 ° C, which was held for 2 h.

After cooling and pouring off the zirconium mineral layer, the lime was extracted with hot water; The dye obtained is suitable for coloring ceramic, especially borosilicate, glazes to an intense pink.

Example 2 g of synthetic zirconia, 39.5 g of silica, 22 g of ferrous fluoride and 29 g of a low temperature mineralizer containing 13 g of sodium molybdate dihydrate, 9.5 g of sodium hexafluorosilicate and 6.5 g of lithium hydroxide monohydrate were dry mixed. and in a ceramic vessel overlaid with a 1 to 2 cm layer of the prepared leached pink dye (from Example 1) and heated at a rate of 5 ° C / min to 630 ° C, which was held for 2 h. heat usable as pink ceramic dye.

Claims (2)

A process for preparing an intense pink ceramic dye of the zirconia-hematite type, characterized in that the starting mixture comprises 42 to 48% by weight of zirconia, 19 to 23% by weight of silica, 10 to 30% by weight of iron chloride or fluoride and 12 to 17% by weight, preferably 13.5 to 15.5% by weight of a three-component low temperature mineralizer comprising sodium molybdate dihydrate, sodium hexafluorosilicate and lithium hydroxide monohydrate in a molar ratio of 1: 0.76 to 1: 2.51 to 3.2, preferably 1% by weight : 0.83 to 0.93: 2.7 to 3 is premixed dry and then heated at a rate of 5-10 ° C / min to 600-640 ° C, which is maintained for 1 to 3 hours. 2. A method according to claim 1, characterized in that the heating of the mixture is carried out when the mixture is overlaid with an at least 1 cm thick layer of zirconium mineral or already fired zircon-haemalt dye.