| abstract |
A molded article is made from a mixture of (a) a sinterable inorganic powder and (b) a moldable binder comprising oxygen-containing wax. Suitable powders are of metal oxides or double oxides, metal carbides, nitrides and borides; e.g. Al2O3, MgO, Y2O3, MgAl2O4 or Pb1-xLaxZr1-yTiyO3 (x = 0-1 and y = 0-1); the powder is preferably of size 5-100 mu m. The binder can be a natural or synthetic wax or higher fatty acid, a synthetic hydrocarbon wax or petroleum wax may be blended therewith; it preferably forms 15 to 60% by volume of the mixture, and contains not less than 50% by weight of oxygen-containing wax such as a higher fatty acid or ester or glyceride thereof, or oxidized paraffin. The mixture is kneaded, granulated if necessary, and shaped by injection molding or extrusion in a machine used for shaping plastics or ceramics, and heated to a temperature above that at which the binder melts (e.g. to 800 DEG C for oxidized microcrystalline wax) so that the binder is removed. The remaining shaped powder is then sintered in known manner (e.g. at 1700 DEG C for 3 hours for Al2O3). The method is useful in making translucent ceramics, without cracks or foams due to evaporation of binder. |