Low-cost process of manufacturing transparent spinel

A high-yield and low-cost process of manufacturing a transparent object essentially consisting of magnesium aluminate spinel without metal dopants, comprising

• i) preparing an aqueous slurry comprising at least 55 wt % pure spinel powder, water, a dispersant, a pH-adjusting agent, and an organic agent to maintain low viscosity, said slurry lacking metal dopants;
• ii) milling the slurry of step i) in a ball mill for at least 24 hours, whereby obtaining a suspension of fine spinel particles in aqueous solution, wherein said organic agent enables to maintain low viscosity during said milling and over prolonged periods, and wherein the suspension contains at least 65 wt % non-aqueous components;
• iii) providing a mold without employing gypsum, having essentially the desired shape of said object, wherein the inner surface of the mold in contact with the slurry is a nano-pore filter essentially impermeable to the particles of said spinel powder, the mold being hermetically sealed except for an inlet of said mold and for the pores of said filter;
• iv) pouring said suspension of fine spinel particles of step ii) into said mold of step iii) through said inlet;
• v) connecting said inlet with pressure source and adjusting the pressure in said mold to up to 4 MPa, the pressure pushing the aqueous solution through said filter out of the mold;
• vi) keeping said pressure on until at least about 75% of the originally present liquid leaves the mold, whereby obtaining a green body;
• vii) extracting the green body from the mold and drying it in a humidity-controlled environment;
• viii) heating the body at between 680 and 720° C. until the organic materials are removed;
• ix) sintering at about 1600° C. for between 1.5 and 2.5 hours;
• x) subjecting the body to hot isostatic pressing at 1650° C. and at a pressure of between 50 and 200 MPa in argon atmosphere;
• and
• xi) annealing the body at about 1200° C. for 1 to 3 hours in air, and polishing said body to obtain said transparent object;
• thereby obtaining a transparent object without cracking problems essentially consisting of magnesium aluminate spinel in a high-yield and at a low-cost;
• and wherein the low scrap rate provides a yield of at least 75% based on the used spinel powder.