Transparent alumina microspheres

A process for making transparent Al.sub.2 O.sub.3 spheroids comprising the steps of:

• (i) making an aqueous sol of a material selected from a group consisting of aluminum isopropoxide and aluminum monohydrate;
• (ii) forming droplets of the sol from step (i) and dispersing said droplets in a particle forming fluid for chemical gelation which is substantially water immiscible, stirring the forming fluid to disperse the droplets and maintaining the droplets in the forming fluid for a sufficient time for them to gell;
• (iii) removing the gelled droplets from the forming fluid;
• (iv) drying the wet droplets from (iii);
• (v) pre-firing the dried droplets by heating gradually to a temperature of 800.degree.-1200.degree. C.;
• (vi) firing the droplets in the following sequence:
• (a) firing in dry oxygen at 1,800.degree.-1,975.degree. C. for 5-30 minutes followed by
• (b) firing in wet hydrogen at 1,800.degree.-1,975.degree. C. for 10-350 minutes in order to form hardened fired Al.sub.2 O.sub.3 spheroids;
• and
• (vii) allowing the Al.sub.2 O.sub.3 spheroids to cool.