Heterocoagulation-spray drying process for the inclusion of ceramic pigments

The improvement of the physico-chemical resistance of hematite pigment in ceramic bodies has been pursued through its inclusion into a transparent and refractory matrix of silica or zirconia. The inclusion process was accomplished by heterocoagulation followed by spray-drying. The heterocoagulation process was optimised through an electrokinetic technique, that measured the ζ potential of both matrix and pigment as a function of pH and of different amounts of dispersing agents. Suspensions of pigment and matrix were designed in order to achieve the maximum surface charges. The heterocoagulated mix was then spray-dried in order to avoid any separated coagulation of pigment and matrix and to obtain a well granulated powder suitable for application in ceramic bodies. A stable red-coloured ceramic pigment for low firing applications was obtained starting from amorphous silica as matrix and hematite as colorant.