Process for preparing pure silver chromate for electrochemical cells

Claim 2

A process of preparing silver chromate of greater than 99.5% purity for use as a positive active material in an electrochemical generator having a lithium negative electrode and a non-aqueous electrolyte comprising reacting concentrated chromate and silver salt solutions in the presence of a concentrated bichromate solution to yield said silver chromate, at least said chromate solution being added progressively into the bichromate solution in such a manner as to maintain the pH thereof at a value which prevents precipitation of silver oxide.

Claim 3

A process according to claim 1 in which equivalent quantities of said concentrated silver salt solution and of said concentrated chromate solution are both added progressively to said concentrated bichromate solution, both being added in such a manner as to maintain the pH of said last-named solution at a value which is low enough to prevent precipitation of silver oxide.

Claim 4

A process according to claim 1 wherein said chromate solution is of lithium chromate.

Claim 5

A process for preparing silver chromate of greater than 99.5% purity for use in a non-aqueous electrolyte type electrochemical generator comprising the steps of reacting concentrated silver salt solution with a concentrated solution of a soluble bichromate and chromic acid to precipitate silver bichromate, placing said silver bichromate precipitate in aqueous suspension and then reacting said precipitate in suspension with a concentrated solution of a soluble chromate selected from the group consisting of magnesium chromate, sodium chromate, potassium chromate, lithium chromate and ammonium chromate, to precipitate silver chromate, said solution of a soluble chromate being gradually added to said precipitate in suspension in such a manner as to maintain the pH thereof at a value not greater than 4.5 to prevent precipitation of silver oxide.

Claim 6

A process for preparing silver chromate of greater than 99.5% purity for use in a non-aqueous electrolyte type electrochemical generator comprising the steps of reacting concentrated silver salt solution with a concentrated solution of a soluble bichromate and chromic acid to precipitate silver bichromate, placing said silver bichromate precipitate in aqueous suspension and then reacting said precipitate in suspension with a concentrated solution of a soluble chromate selected from the group consisting of magnesium chromate, sodium chromate, potassium chromate, lithium chromate and ammonium chromate, to precipitate silver chromate, said solution of a soluble chromate being gradually added to said precipitate in suspension in such a manner as to maintain the pH thereof at a value not greater than 4.5 to prevent precipitation of silver oxide.

Claim 7

A process for preparing silver chromate of greater than 99.5% purity for use as a positive active material in an electrochemical generator having a lithium negative electrode and a non-aqueous electrolyte comprising the steps of heating in the proportions of 100 cc of 0.26M magnesium bichromate solution having a pH of 4.5 to boiling point; then adding 80 cc of a 2.53M magnesium chromate solution containing 0.202 moles of chromate and 122 cc of concentrated silver nitrate solution containing 0.410 grams of silver to the boiling magnesium bichromate solution to precipitate silver chromate of said silver nitrate solution and said magnesium chromate solution, at least said magnesium chromate solution being added progressively into the bichromate solution in such a manner as to avoid increase of said pH above 4.5 to prevent precipitation of silver oxide, washing the precipitated silver chromate and then heating the washed silver chromate to effect drying thereof.

Claim 8

A process for preparing silver chromate of greater than 99.5% purity for use as a positive active material in an electrochemical generator having a lithium negative electrode and a non-aqueous electrolyte comprising the steps of heating in the proportions of 100 cc of 0.26M magnesium bichromate solution having a pH of 4.5 to boiling point; then adding 80 cc of a 2.53M magnesium chromate solution containing 0.202 moles of chromate and 122 cc of concentrated silver nitrate solution containing 0.410 grams of silver to the boiling magnesium bichromate solution to precipitate silver chromate of said silver nitrate solution and said magnesium chromate solution, at least said magnesium chromate solution being added progressively into the bichromate solution in such a manner as to avoid increase of said pH above 4.5 to prevent precipitation of silver oxide, washing the precipitated silver chromate and then heating the washed silver chromate to effect drying thereof.

Claim 9

A process according to claim 5 wherein said silver nitrate solution and said chromate solution are added simultaneously and progressively to said boiling magnesium bichromate solution in such a manner as to maintain the pH of said last-named solution at a value which avoids increase of said pH above 4.5.

Claim 10

A process according to claim 5 wherein said silver nitrate solution is first added to said boiling magnesium bichromate solution and thereafter adding said chromate solution thereto.

Claim 11

A process according to claim 5 wherein said silver nitrate solution and said chromate solution are added alternatively to said boiling magnesium bichromate solution, each addition being limited to avoid increase in pH of the magnesium bichromate solution above 4.5.

Claim 12

In the process for preparing silver chromate of greater than 99.5% purity for use in an electrochemical cell, the steps comprising preparing a solution of a bichromate and chromic oxide, adding a silver salt to said solution to yield silver bichromate as precipitate, then placing said silver bichromate in suspension in water and then adding a concentrated soluble chromate to the suspension of silver bichromate to yield silver chromate as precipitate.

Claim 13

In the process for preparing silver chromate of greater than 99.5% purity for use in an electrochemical cell, the steps comprising preparing a solution of a bichromate and chromic oxide, adding a silver salt to said solution to yield silver bichromate as precipitate, then placing said silver bichromate in suspension in water and then adding a concentrated soluble chromate to the suspension of silver bichromate to yield silver chromate as precipitate.

Claim 14

In the process according to claim 9, wherein said suspension in water is elevated to boiling point.

Claim 15

In a process for preparing silver chromate of greater than 99.5% purity for use in an electrochemical cell, the steps of preparing a concentrated magnesium chromate solution by reacting chromic oxide with magnesium oxide, preparing a solution of a bichromate and chromic oxide, adding a silver salt to said solution to yield silver bichromate as precipitate, then placing said silver bichromate in suspension in water and gradually adding to said suspension said concentrated magnesium chromate solution to yield silver chromate as precipitate.

Claim 16

In a process for preparing silver chromate of greater than 99.5% purity for use in an electrochemical cell, the steps of preparing a concentrated magnesium chromate solution by reacting chromic oxide with magnesium oxide, preparing a solution of a bichromate and chromic oxide, adding a silver salt to said solution to yield silver bichromate as precipitate, then placing said silver bichromate in suspension in water and gradually adding to said suspension said concentrated magnesium chromate solution to yield silver chromate as precipitate.

Claim 17

In a process of preparing silver chromate of greater than 99.5% purity for use in an electrochemical cell, the steps of preparing silver bichromate suspension in water, and adding to said suspension a concentrated soluble chromate solution to yield said silver chromate of greater than 99.5% purity as precipitate, said soluble chromate being added gradually into the bichromate suspension in such a manner as to maintain the pH level thereof at a value which is low enough to prevent precipitation of silver oxide.

Claim 18

In a process of preparing silver chromate of greater than 99.5% purity for use in an electrochemical cell, the steps of preparing silver bichromate suspension in water, and adding to said suspension a concentrated soluble chromate solution to yield said silver chromate of greater than 99.5% purity as precipitate, said soluble chromate being added gradually into the bichromate suspension in such a manner as to maintain the pH level thereof at a value which is low enough to prevent precipitation of silver oxide.

Claim 19

In the process according to claim 12 wherein said suspension in water is elevated to the boiling point.

Claim 20

A process for preparing silver chromate of greater than 99.5% purity for use in a non-aqueous electrolyte type electrochemical generator comprising the steps of reacting concentrated silver salt solution with a concentrated solution of a soluble bichromate and chromic acid to provide in situ a suspension of a precipitate of silver bichromate, and then reacting said precipitate in suspension with a concentrated solution of a soluble chromate selected from the group consisting of magnesium chromate, sodium chromate, potassium chromate, lithium chromate and ammonium chromate, to precipitate silver chromate, said solution of soluble chromate being gradually added to said precipitate in suspension in such a manner as to maintain the pH thereof at a value not greater than 4.5 to prevent precipitation of silver oxide.

Claim 21

A process for preparing silver chromate of greater than 99.5% purity for use in a non-aqueous electrolyte type electrochemical generator comprising the steps of reacting concentrated silver salt solution with a concentrated solution of a soluble bichromate and chromic acid to provide in situ a suspension of a precipitate of silver bichromate, and then reacting said precipitate in suspension with a concentrated solution of a soluble chromate selected from the group consisting of magnesium chromate, sodium chromate, potassium chromate, lithium chromate and ammonium chromate, to precipitate silver chromate, said solution of soluble chromate being gradually added to said precipitate in suspension in such a manner as to maintain the pH thereof at a value not greater than 4.5 to prevent precipitation of silver oxide.

Claim 22

A process according to claim 14 wherein the cation of the soluble bichromate is the same as the cation of the soluble chromate.