Process for producing nanocrystalline alpha-AI2O3

Abstract

A process is claimed for producing nanocrystalline α-Al 2 O 3 that is characterized in that nuclei are added to aluminum chlorohydrate, which is subjected to thermal treatment within less than 30 minutes, the resultant agglomerates being comminuted.

1 . A process for producing nanocrystalline Al 2 O 3 , comprising the steps of adding a crystallization nuclei to aluminum chlorohydrate, thermally treating the combined crystallization nuclei and aluminum chlorohydrate for less than 30 minutes to form agglomerates, and comminuting the agglomerates. 
     
     
         2 . The process as claimed in  claim 1 , wherein the aluminum chlorohydrate is a compound having the chemical formula Al 2 (OH) x Cl y , wherein x is a number from 2.5 to 5.5 and y is a number from 3.5 to 0.5, and wherein the sum x+y is always 6. 
     
     
         3 . The process as claimed in  claim 1 , wherein the crystallization nuclei is very finely dispersed α-Al 2 O 3 , hematite or diaspore. 
     
     
         4 . The process as claimed in  claim 3 , wherein the very finely dispersed α-Al 2 O 3  crystallization nuclei has a mean particle size of less than 0.1 μm. 
     
     
         5 . The process as claimed in  claim 1 , wherein an aqueous suspension comprising aluminum chlorohydrate plus crystallization nuclei is first dried and the dried product is then calcined. 
     
     
         6 . The process as claimed in  claim 1 , wherein the thermally treating step is carried out in a sliding-bat furnace, chamber furnace, tube furnace, rotary kiln, microwave oven or in a fluidized-bed reactor. 
     
     
         7 . The process as claimed in  claim 1 , wherein the thermally treating step is carried out at temperatures below 1110° C. 
     
     
         8 . The process as claimed in  claim 1 , wherein the thermally treating step is carried out at from 700 to 1110° C. 
     
     
         9 . The process as claimed in  claim 1 , wherein an aqueous suspension comprising aluminum chlorohydrate and nuclei is injected directly into the calcination apparatus without prior removal of the water. 
     
     
         10 . The process as claimed in  claim 1 , wherein the thermally treating step is carried out in from 0.5 to 30 minutes. 
     
     
         11 . The process as claimed in  claim 1 , wherein the agglomerates are comminuted by wet or dry milling. 
     
     
         12 . The process as claimed in  claim 1 , wherein the agglomerates are comminuted by wet milling to form a suspension, and wherein at least one additive selected from the group consisting of acrylates, polyvinyl alcohols, polyethylene glycols, stearates and wax emulsions is added during or after the wet milling. 
     
     
         13 . The process as claimed in  claim 1 , wherein the agglomerates are comminuted by wet milling to form a suspension, and the suspension is spray-dryed. 
     
     
         14 . The process as claimed in  claim 1 , wherein the thermally treating step is carried out in from 0.5 to 10 minutes. 
     
     
         15 . The process as claimed in  claim 1 , wherein the thermally treating step is carried out in from 2 to 5 minutes.