Pigments stable at high temperatures

Claim 1

A temperature-stable spinel in the form of acicular particles having a length of 0.01 to 0.13 micron and consisting essentially of oxygen, iron, and at least one metal, said spinel corresponding to the formula XFe.sub.2 O.sub.4 wherein X is said other metal, said other metal being one selected from the group consisting of Cu, Ca, Cd, Co, Ba, Sr, and Mn.

Claim 8

A method of making a pigment having good stability at high temperatures, said method consisting essentially of the steps of forming a first aqueous solution consisting essentially of water, a soluble ferrous salt, and at least one other salt, said salt being a soluble salt of a non-ferrous metal selected from the group consisting of copper, calcium, cadmium, cobalt, barium, strontium, manganese, and lithium, said ferrous salt and said non-ferrous salt being present in said solution in proportions such that the respective quantities of iron and other metal which are present will yield, when said solution is so adjusted in pH as to cause precipitation, the formation of a substantial quantity of a precipitate oxidizable to a spinel of the formula XFe 2 O 4 , or YFe 5 O 8 in which X is a metal selected from the group consisting of Cu, Cd, Ca, Co, Ba, Sr, and Mn, and Y is Li, mixing with said first aqueous solution a second aqueous solution to form a reaction mixture, said second solution containing a substantial proportion of a soluble alkalizing compound selected from the group consisting of the carbonates, bicarbonates, and hydroxides of the alkali metals, the said second solution being used in such quantity and the said first and second solutions being in such a state of dilution that there results upon said mixing the formation of a precipitate in the form of particles of sub-micron size, the liquid phase of said reaction mixture being as a result of such precipitation substantially completely depleted in its content of lithium ions and metal ions having a valence greater than one; oxidizing the said precipitate to form a spinel in aqueous solution; then heating said aqueous solution having said spinel therein to a temperature of from about 75° to 100° C.; and recovering said spinel.

Claim 9

A method of making a pigment having good stability at high temperatures, said method consisting essentially of the steps of forming a first aqueous solution consisting essentially of water, a soluble ferrous salt, and at least one other salt, said salt being a soluble salt of a non-ferrous metal selected from the group consisting of copper, calcium, cadmium, cobalt, barium, strontium, manganese, and lithium, said ferrous salt and said non-ferrous salt being present in said solution in proportions such that the respective quantities of iron and other metal which are present will yield, when said solution is so adjusted in pH as to cause precipitation, the formation of a substantial quantity of a precipitate oxidizable to a spinel of the formula XFe 2 O 4 , or YFe 5 O 8 in which X is a metal selected from the group consisting of Cu, Cd, Ca, Co, Ba, Sr, and Mn, and Y is Li, mixing with said first aqueous solution a second aqueous solution to form a reaction mixture, said second solution containing a substantial proportion of a soluble alkalizing compound selected from the group consisting of the carbonates, bicarbonates, and hydroxides of the alkali metals, the said second solution being used in such quantity and the said first and second solutions being in such a state of dilution that there results upon said mixing the formation of a precipitate in the form of particles of sub-micron size, the liquid phase of said reaction mixture being as a result of such precipitation substantially completely depleted in its content of lithium ions and metal ions having a valence greater than one; oxidizing the said precipitate to form a spinel in aqueous solution; then heating said aqueous solution having said spinel therein to a temperature of from about 75° to 100° C.; and recovering said spinel.