Yellow pigments stable at high temperatures

Claim 1

A transparent, temperature-stable spinel in the form of acicular particles having a length of 0.01 to 0.13 microns and consisting essentially of oxygen, iron, and at least one other 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 magnesium, zinc and tin.

Claim 6

A method of making a transparent yellow 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 magnesium, zinc, and tin, 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 , in which X is a metal selected from the group consisting of magnesium, zinc, and tin 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 metal ions having a valence greater than one; oxidizing at 15° to 35° C. 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 7

A method of making a transparent yellow 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 magnesium, zinc, and tin, 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 , in which X is a metal selected from the group consisting of magnesium, zinc, and tin 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 metal ions having a valence greater than one; oxidizing at 15° to 35° C. 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.