Lead chromate pigment with improved thermal stability
AssigneeE. I. Du Pont de Nemours and Company
InventorJames Francis Higgins
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Abstract
Dense silica-coated lead chromate pigment prepared by adding from 0.2% to 1% by weight of a soluble silicate compound to an aqueous solution of chromate, and, optionally, at least one of sulfate and molybdate, contacting the aqueous solution with an aqueous lead salt to precipitate the base lead chromate pigment, treating the pigment with at least one hydrous oxide, and applying from 2% to 40% by weight of dense, amorphous silica to the treated lead chromate pigment. The resulting dense silica-coated lead chromate pigment exhibits higher thermal stability in plastics than conventional dense silica-coated lead chromate pigment.
Claims5
A dense silica-coated chromate pigment prepared by the steps of
- i. adding from 0.2% to 1% by weight of a soluble silicate compound, calculated as SiO.sub.2 and based on the weight of the base lead chromate pigment, to an aqueous solution of a soluble salt of chromate and, optionally, at least one soluble salt selected from the group consisting of sulfate and molybdate,
- ii. contacting the aqueous solution of step (i) with an aqueous lead salt to precipitate the base lead chromate pigment,
- iii. treating the base lead chromate pigment with at least one hydrous metal oxide, and
- iv. applying a coating of dense, amorphous silica to the treated lead chromate pigment of step (iii) in an amount from 2% to 40% by weight, calculated as SiO.sub.2 and based on the weight of the dense silica-coated lead chromate pigment.
Dependencies are inferred from the claim text.