DISPERSION OF ZIRCONIUM DIOXIDE AND ZIRCONIUM MIXED OXIDE
Dispersion of zirconium dioxide having a solids content of from 30 to 75 wt. %, based on the total amount of the dispersion, and a median value of the particle size distribution in the dispersion of less than 200 nm, obtainable by predispersing a zirconium dioxide powder and/or a zirconium mixed oxide powder having a ZrC>2 content of at least 70 wt. %, the powders being in the form of aggregated primary particles and having no internal surface and a BET surface area of the powder of 60±15 m2/g, in a dispersing agent in the presence of from 0.1 to 5 wt. %, based on the total amount of the dispersion, of a surface-modifying agent with an energy input of less than 200 KJ/m3, dividing the predispersion obtained into at least two part streams, placing these part streams under a pressure of at least 500 bar in a high-energy mill and decompress them via a nozzle, these part streams colliding with one another in a gas- or liquid-filled reaction chamber and thereby being ground, and optionally subsequently adjusting the dispersion to the desired content with further dispersing agent. It can be used for the production of ceramic layers, membranes and shaped articles.
1 . A dispersion of zirconium dioxide having a solids content of from 30 to 75 wt %, based on the total amount of the dispersion, and a median value of the particles in the dispersion of less than 200 nm, obtainable by predispersing a zirconium dioxide powder and/or a zirconium mixed oxide powder having a ZrO 2 content of at least 70 wt. %, the powders being in the form of aggregated primary particles and having no internal surface and a BET surface area of the powder of 60±15 m 2 /g, in a dispersing agent in the presence of from 0.1 to 5 wt. %, based on the total amount of the dispersion, of a surface-modifying agent with an energy input of less than 200 KJ/m 3 , dividing the predispersion obtained into at least two part streams, placing these part streams under a pressure of at least 500 bar in a high-energy mill and decompress them via a nozzle, these part streams colliding with one another in a gas- or liquid-filled reaction chamber and thereby being ground, and optionally subsequently adjusting the dispersion to the desired content with further dispersing agent.
2 . The dispersion of zirconium dioxide according to claim 1 , wherein the surface-modifying agent is 3-aminopropyltriethoxysilane, an ammonium salt of a polycarboxylic acid and/or a tetraalkylammonium hydroxide.
3 . The dispersion of zirconium dioxide according to claim 1 , wherein the dispersing agent is water.
4 . The dispersion of zirconium dioxide according to claim 1 , wherein the predispersed powder has a content of zirconium dioxide of at least 95 wt. %, of hafnium dioxide of from 0.5 to 4 wt. % and of chloride of not more than 0.05 wt. %.
5 . The dispersion of zirconium dioxide according to claim 1 , wherein the predispersed powder has a content of zirconium dioxide of at east 92 wt. %, of yttrium oxide of from 4.5 to 5.5 wt. % and of chloride of not more that 0.05 wt. %.
6 . The dispersion of zirconium dioxide according to claim 4 , wherein the BET surface area is 60±5 m 2 /g.
7 . The dispersion of zirconium dioxide according to claim 4 , wherein the powder has a tamped density of 100±20 g/l.
8 . The dispersion of zirconium dioxide according to claim 1 , wherein the solids content is 50±5 wt. %.
9 . The dispersion zirconium dioxide according to claim 1 , wherein a viscosity is less than 1,000 mPas in the shear gradient range of from 1 to 1,000 s −1 and at 23° C.
10 . The dispersion of zirconium dioxide according to claim 1 , wherein the dispersion is bimodal.
11 . A process for the preparation of the dispersion of zirconium dioxide according to claim 1 , comprising the steps:
a zirconium dioxide powder and/or a zirconium mixed oxide powder having a ZrO 2 content of at least 70 wt. %, the powder being in the form of aggregated primary particles having a BET surface area of 60±15 m 2 /g, is first introduced, all at once or in portions under dispersing conditions with an energy input of less than 200 kJ/m 3 , into the dispersing agent, preferably water, which contains at least one surface-modifying agent which is soluble in the dispersing agent and optionally additives for regulation of the pH, and a predispersion is produced in this way, the amount of powder being chosen such that the solids content is 30 to 75 wt. % and the amount of surface-modifying agent being chosen such that the content of surface modifying agent is 0.1 to 5 wt. %, in each based on the total amount of the predispersion, and
the predispersion is divided into at least two part streams, these part streams are placed under a pressure of at least 500 bar in a high-energy mill and are decompressed via a nozzle and allowed to collide in gas- or liquid-filled reaction chamber are thereby ground, and the dispersion is optionally subsequently adjusted to the desired content with further dispersing agent.
12 . The process according to claim 11 , wherein the dispersion which has already been ground once is circulated and is ground by means of the high-energy mill a further 2 to 6 times.
13 . The process according to claim 11 , wherein the pressure in the high-energy mill is 2,000 to 3,000 bar.
14 . The process according to claim 11 , wherein the maximum temperature during the preparation of the pre-(dispersion) is 40° C.
15 . (canceled)
16 . A method of producing ceramic layers, ceramic membranes, ceramic shaped articles, and polishing glass surfaces and metal surfaces, comprising casting, dry pressing, or cold isostatic pressing the dispersion onto a sample.