초록 ▼

Procedure for making Al2O3 spheroids, 600 micrometers in diameter or less, utilizes an AlOOH sol containing 0.25% weight percent MgO (in the form of Mg(NO3)2ㆍ6H2O) and HNO3. The sol is dispersed into droplets in a particle forming fluid (e.g., 2-ethylhexanol) where gelling occurs. The gelled spheroi

Procedure for making Al2O3 spheroids, 600 micrometers in diameter or less, utilizes an AlOOH sol containing 0.25% weight percent MgO (in the form of Mg(NO3)2ㆍ6H2O) and HNO3. The sol is dispersed into droplets in a particle forming fluid (e.g., 2-ethylhexanol) where gelling occurs. The gelled spheroids are collected, dried and pre-fired in air at temperatures less than 1,200°C. for up to about 12 hours. The dried and prefired beads are fired in a 2-step process at temperatures of about 1,850-1,950°C. in the following sequence: a first dry oxygen firing for about ten minutes, followed by a wet hydrogen firing for up to 350 minutes. Reasonably transparent microspheres having crystallites in the range of 5-100 micrometers are obtained with little intergranular porosity, and their density is estimated to be near theoretical.

대표청구항 ▼

A solid, transparent, polycrystalline spheroid useful as a retroreflective lens element and having a diameter less than about 500 micrometers, consisting essentially of alpha alumina having crystallites of about 5 to 200 micrometers in largest dimension. A process for making transparent Al2O3 sphero

A solid, transparent, polycrystalline spheroid useful as a retroreflective lens element and having a diameter less than about 500 micrometers, consisting essentially of alpha alumina having crystallites of about 5 to 200 micrometers in largest dimension. A process for making transparent Al2O3 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°-1200°C.; (vi) firing the droplets in the following sequence: (a) firing in dry oxygen at 1,800°-1,975°C. for 5-30 minutes followed by (b) firing in wet hydrogen at 1,800°-1,975°C. for 10-350 minutes in order to form hardened fired Al2O3 spheroids; and (vii) allowing the Al2O3 spheroids to cool.