Method for producing particulate material by freeze drying

Claim 1

THE METHOD OF FREEZE DRYING AQUEOUS SOLUTIONS OF METAL SALTS WHICH COMPRISES FREEZING SUCH SOLUTIONS IN THE FORM OF DROPLETS AND REMOVING THE SOLVENT FROM SAID FROZEN DROPLETS BY SUBLIMATION, WHEREIN THE IMPROVEMENT COMPRISES INCORPORATING IN SAID SOLUTIONS, PRIOR OF FREEZING, AND IN ADDITION TO SAID METAL SALTS, AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF AMMONIUM HYDROXIDE ALKYL AMMONIUM HYDROXIDES WHEREIN THE ALKYL SUBSTITUENTS CONTAN FROM 1-4 CARBON ATOMS AND SALTS OF ETHYLENE DIAMINE TETRAACETIC ACID, WHICH RAISES THE FREEZING POINT OF SAID SOLUTION AND REDUCES ANY TENDENCY TO SUPERCOOL.

Claim 2

THE METHOD OF FREEZE DRYING AQUEOUS SOLUTIONS OF METAL SALTS WHICH COMPRISES FREEZING SUCH SOLUTIONS IN THE FORM OF DROPLETS AND REMOVING THE SOLVENT FROM SAID FROZEN DROPLETS BY SUBLIMATION, WHEREIN THE IMPROVEMENT COMPRISES INCORPORATING IN SAID SOLUTIONS, PRIOR OF FREEZING, AND IN ADDITION TO SAID METAL SALTS, AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF AMMONIUM HYDROXIDE ALKYL AMMONIUM HYDROXIDES WHEREIN THE ALKYL SUBSTITUENTS CONTAN FROM 1-4 CARBON ATOMS AND SALTS OF ETHYLENE DIAMINE TETRAACETIC ACID, WHICH RAISES THE FREEZING POINT OF SAID SOLUTION AND REDUCES ANY TENDENCY TO SUPERCOOL.

Claim 6

A method for forming particulate material of at least one water soluble metal salt, comprising: freezing droplets of an aqueous solution of said at least one salt within a time period of up to one second by introducing the droplets into a liquid refrigerant, the refrigerant having a volume sufficient to maintain a solution-to-refrigerant volume ratio within the range of 1:2 to 1:100, whereby substantial coalescence of the droplets is avoided during freezing, collecting the frozen droplets at a temperature below the freezing point of the solution, and removing the water from the frozen droplets by sublimation, wherein the improvement comprises adding to the solution prior to freezing at least one additive selected from the group consisting of ammonium hydroxide, tetraalkyl ammonium hydroxide, R4N (OH) , where R is selected from the group consisting of ethyl, methyl, propyl and butyl, and salts of ethylene diamine tetraacetic acid, the additives being added in an amount below that at which a precipitate of the metal salt is formed, whereby supercooling of the solution droplets during freezing and melting of the frozen droplets during sublimation are substantially avoided.

Claim 7

A method for forming particulate material of at least one water soluble metal salt, comprising: freezing droplets of an aqueous solution of said at least one salt within a time period of up to one second by introducing the droplets into a liquid refrigerant, the refrigerant having a volume sufficient to maintain a solution-to-refrigerant volume ratio within the range of 1:2 to 1:100, whereby substantial coalescence of the droplets is avoided during freezing, collecting the frozen droplets at a temperature below the freezing point of the solution, and removing the water from the frozen droplets by sublimation, wherein the improvement comprises adding to the solution prior to freezing at least one additive selected from the group consisting of ammonium hydroxide, tetraalkyl ammonium hydroxide, R4N (OH) , where R is selected from the group consisting of ethyl, methyl, propyl and butyl, and salts of ethylene diamine tetraacetic acid, the additives being added in an amount below that at which a precipitate of the metal salt is formed, whereby supercooling of the solution droplets during freezing and melting of the frozen droplets during sublimation are substantially avoided.