CS240724B1 - The preparation of a blue-green zirconia ceramic pigment - Google Patents

Abstract

Method for preparing a blue-green ceramic pigment, the basis of which is zirconium silicate with a zirconium structure and each particle of which is colored to the resulting blue-green shade. The starting mixture contains, in addition to the chromophore in the form of vanadium ions, also molybdenum ions. The shade can be regulated by the mutual ratio of molybdenum and vanadium ions in the starting mixture. The pigment is suitable for coloring ceramic glazes, including high-temperature ones, to a blue-green shade.

Description

BACKGROUND OF THE INVENTION The present invention relates to a process for preparing a blue-green ceramic zirconium type pigrrtentium. Enhances synthesis; pigmentuty a- ^r ^ ^w revN shade který'byl 'hitherto achieved by mixing two separately-prepared pig-- ments of different colors - blue and green.

Zircon type pigments are among the best quality ceramic pigments. A stable and intensely colored blue zircon pigment is known. In view of the necessity of mixing the pigments in the preparation of the blue-green shade, it is necessary to ensure that the two shades are of the same type in order to ensure good homogeneity and reproducibility of the color shade in the glaze. However, the preparation of a stable and sufficiently colored green pigment of the purely zircon type is not yet solved.

The preparation of the blue ceramic zirconium pigment is based on a mixture, which usually contains, in a stoichiometric ratio, zirconia and silica, a chromophore in the form of ammonium vanadate or vanadium oxide, and a mineralizer, which are most often alkaline halides. Burning of this mixture produces a pigment formed by zirconium silicate microcrystals with a zircon structure. They are stained with vanadium ions, which are in tetravalent form as a substitute uncharged disorder at the zirconium site (V _Z1 ^x ), to a deep blue hue. By mixing this pigment with a pigment of a stable and saturated green hue and applying their mixture to the glaze, it would be possible to achieve a blue-green color. Known is a green zirconium-type pigment, whose preparation is again based on a mixture of the basic starting oxides - zirconium and silica - mineralizer and chromophore, which is most often chromium oxide or chromium compound, which is converted to oxide when the mixture burns. In the formation of zirconium microcrystals, the particles of colored chromium trioxide "grow" (enveloped) in them and give them a green color. However, the intensity of the green shade caused by these zirconia particles, which are sufficiently stable when applied to high temperature glazes, is relatively low. It is also known to prepare a green pigment by firing a mixture of zirconium, silica and vanadium oxides at high temperatures of 1200 to 1500 ° C, the mixture partially reacting to zirconium silicate. However, the degree of reaction is low, and thus the stability of the pigment when applied to the molten glaze is also low. It is a mixed pigment containing blue silicate particles and zirconia particles with surface-absorbed vanadium oxides having a yellow color. The resulting shade is then green, but the yellow-colored pigment component is less stable in the glaze.

The invention makes it possible to prepare a stable, zirconium-type ceramic pigment, intensely colored to an admixed nickel shade as a mixture of two pigments, but also to one, each particle of which is individually colored to the resulting shade. The essence of the preparation of the pigment according to the invention is that by dry blending of the individual components, a starting mixture containing by weight of the composition is prepared. 47 to 56% zirconia, 21 to 25.5% silica, 4 to 8% sodium hexafluorosilicate, 2 to 3.5% lithium hydroxide (LiOH, H2O), 1 to 2.8% sodium chloride, 4 up to 8% ammonium vanadate or 3.1 to 6.2% vanadium pentoxide and 4 to 15% ammonium molybdate [formula (NH4 is Mo7024.4HsO)] or 3.2 to 12.2% molybdenum trioxide, preferably prepared by mixing 50 up to 53% zirconium dioxide, 22.5 to 24% silica, 5.5 to 6.5% sodium hexafluorosilicate, 2.5 to 3.1 lithium hydroxide (Formula L1OH.H2O), 1.6 to 2.2% sodium chloride, 4.5 to 6% ammonium vanadate or 3.5 to 4.7% vanadium pentoxide and 5 to 9% ammonium molybdate [formula (NH4) eMo7O24.4 HzO] or 4 to 7.3% This mixture is fired at a rate of 3 to 20 ° C / min to a temperature of 600 to 850 ° C, and is held at this temperature for 1 to 4 h (depending on the temperature in said interval, depending on the type of oxide used) in the case of zirconium and according to the content of molybdenum ions in the mixture) During the calcination a strong mineralization effect of lithium hydroxide, sodium hexafluorosilicate and sodium chloride occurs. Ammonium molybdate or molybdenum trioxide releases active oxygen at a temperature of 500 ° C, which also has strong mineralization effects. This allows the reaction of zirconium silicate formation with the zirconium structure already at a relatively low firing temperature. Likewise, vanadium is converted from vanadate or vanadium pentoxide to the four-cylinder state, also with the release of active oxygen. The tubular and molybdenum ions are then trapped in the silicate structure as substitutional uncharged faults at the zirconium site - V _Zr ^x , MoZr ^x . The defect VZr ^x causes intense blue coloration of the silicate microcrystals, whereas the MoZr ^x defect is uncoloured and does not show any color at this stage of pigment preparation. After the firing is complete, the firing is washed with hot water, preferably with dilute hot mineral acid. This eliminates, in particular, the alkaline failure components which would decompose the silicate microcrystals during further heat treatment of the pigment according to the invention. The washed pigment is then calcined at a temperature greater than 1200 ° C for at least 10 min; for use in glazes with a glazing temperature greater than 1200 ° C, this pigment overhang is preferably not carried out. At temperatures above 1200 ° C, a portion of the blue-stained uncharged VZr ^x faults transitions on a beam loaded with 240724 V-type _Zr , which gives the silicate a green hue. The result is a blue-green tint of zirconia microcrystals and thus a blue-green pigment. Molybdenum ions, which are also present as silicates in the silicate structure, are able to change the charge of the vanadium ions. Depending on the ratio of vanadium and molybdenum ions in the starting mixture, the blue-green pigment shade can be varied.

The advantages of the preparation of the pigment according to the invention are described below.

The invention allows the preparation of a high-quality, thermally and chemically highly stable zirconium-type ceramic pigment intensely colored in blue-green. In this case, each pigment microcrystalline is individually colored to the resulting shade. Therefore, it is not a mixture of pigments and so application homogeneity of the glazes is ensured. The degree of pigment conversion to zirconium silicate is high. By varying the ratio of Mo _V ia and V _v ions in the starting mixture, the color shade of the pigment can be changed from the predominant blue through blue-green to the predominant green. The firing temperature of the starting mixture, and hence the formation of the silicate itself, is relatively low due to the mineralizing components; when using pigment in high temperature glazes, with a glazing temperature above 1200 ° C, it is not necessary to heat it separately (above 1200 ° Cj).

Example 1

100 g zirconium dioxide (ZrOa - purified haddeleyite mineral), 45 g silica (SiO2), 11.6 g sodium hexafluorosilicate (NazSiF6), 5.4 g lithium hydroxide (LiOH.H2O), 3.7 g sodium chloride (NaCl) , 10.7 g of ammonium vanadate (NH4VO3) and 12.6 g of molybdenum trioxide (M0O5) were dry blended and fired in an oven at 10 ° C / min at 700 ° C for 2 h. After separation by decantation and washing with water, the dried pigment containing 88% zirconium silicate, colored blue, was annealed to 1300 ° C for 20 minutes to obtain a blue-green pigment usable for coloring ceramic glazes with any glazing temperature. to blue-green.

EXAMPLE '20 2 g of zirconia (ZrO synthetic] 9 g of silicon dioxide (SiO2), 1.8 g of sodium hexafluorosilicate (Na 2 SiF6j ^L, 0.8 g of lithium hydroxide (LiOH. H2O), 0.6 g of sodium chloride ( NaCl), 1.4 g of vanadium pentoxide (V2O5) and 2.2 g of ammonium molybdate [(NH4) eMO7O24.4 H2O] were dry blended and fired in an oven at 15 ° C / min at 650 ° C, The slurry was hot leached with water and after separation by filtration, a blue pigment containing 85% zirconium silicate was obtained, usable directly for coloring high-temperature ceramic glazes (with a glazing temperature above 1200 ° C as a blue-green color shade).

Claims (1)

SUBJECT A process for preparing a blue-green zirconium ceramic pigment, characterized in that the dry blend starting mixture by mixing 47 to 56% zirconium oxide, 21 to 25.5% silica, 4 to 8% sodium hexafiluminosilicate, 2 to 3% by weight. 5% lithium hydroxide monohydrate, 1 to 2,8% sodium chloride, 4 to 8% ammonium vanadate or 3,1 to 6,2% ivanadium pentoxide and 4 to 15% ammonium molybdate (formula ()4) βΜθ7θ2ΐ. .4HaOj), or 3.2 to 12% molybdenum trioxide, preferably prepared by mixing 50 to 53% zirconia, 22.5 to the invention 24% silica, 5.5 to 6.5% sodium hexafluorosilicate, 2.5 to 3.1% lithium hydroxide monohydrate, 1.6 to 2.2% sodium chloride, 4.5 to 6% ammonium vanadate, or 3, 5 to 4.7% of vanadium pentoxide and 5 to 9% of ammonium molybdenum (formula (ΝΗ4) θΜθ7θ24.4 H2O) or 4 to 7.3% of molybdenum oxide are fired at 3 to 26 ° C / min to 600 to 850 ° C, held for 1 to 4 hours at this temperature, washed hot, preferably with dilute mineral acid, and optionally annealed at a temperature greater than 1200 ° C for at least 10 min.