Process for the preparation of anhydrous aluminum fluoride

Claim 2

The process of claim 1, wherein the treatment of ammonium fluoride and the aluminum oxide is conducted in an aqueous ammoniacal solution having a weight ratio of free ammonia to ammonium fluoride in the range of between 0.25:1 and 0.5:1, and the concentration of ammonium fluoride is above 25 weight percent.

Claim 3

The process of claim 1, wherein an aluminum oxide is used which has been previously treated to dehydrate it.

Claim 4

The process of claim 1, wherein an aluminum oxide is used containing between 0.5 and 1.1 mol of H2O pro mol Al2O3 and which has been obtained from an aluminum oxide hydrate richer in H2O by partial dehydration.

Claim 5

The process of claim 1, wherein an aluminum oxide is used which has been previously heated to dehydrate it, the heating being carried out in such a way, that during the first hour the temperature of 230* C. is not surpassed.

Claim 6

The process of claim 1, wherein the treatment of the ammonium fluoride solution with the aluminum oxide or hydrate thereof is carried out at a temperature in the range of between 65* C. and 125* C.

Claim 7

The process of claim 1, wherein the treatment of the ammonium fluoride solution with the aluminum oxide or hydrate thereof is conducted under pressure in a closed reaction vessel.

Claim 8

The process of claim 1, wherein the heating of the mixture of triammonium hexafluoroaluminate and unconverted aluminum oxide or aluminum oxide hydrate is conducted at a temperature range of between about 480* C. and 550* C.

Claim 9

The process of claim 1, wherein the aluminum fluoride is formed in a metastable modification by heating the mixture of triammonium hexafluoroaluminate and aluminum oxide or aluminum oxide hydrate to temperatures between 480* C. and 550* C. gradually or stepwise in a period lasting at least 20 minutes.

Claim 10

The process of claim 1, wherein the mixture of solids obtained in step B is granulated or pelletized.

Claim 11

The process of claim 11, wherein the mixture of solids obtained in step B is granulated or pelletized while being still humid.

Claim 12

A process for the preparation of anhydrous aluminum fluoride from ammonium fluoride and an aluminum oxide by the intermediate formation of triammonium hexafluoroaluminate, which comprises the steps of A. treating an aqueous solution of ammonium fluoride with a quantity of aluminum oxide or aluminum oxide hydrate at least approximately twice that required for the formation of triammonium hexafluoroaluminate, whereby an intimate mixture of triammonium hexafluoroaluminate and unconverted aluminum oxide or aluminum oxide hydrate is formed. B. separating the so-formed mixture of triammonium hexafluoroaluminate and unconverted aluminum oxide or aluminum oxide hydrate from its mother liquor, and C. heating the mixture of triammonium hexafluoroaluminate and unconverted aluminum oxide or aluminum oxide hydrate up to about 900* C., whereby the triammonium hexafluoroaluminate is decomposed to form aluminum fluoride.