GB393474A - Improvements in or relating to pigments - Google Patents

Abstract

Pigments are obtained by heating together oxygen-containing compounds of titanium, antimony, and chromium, in the presence of an element which is electropositive to the other three constituent elements at high temperatures, i.e. an element which combines as a base with the other constituents. The products are insoluble in water, acids, and alkalis, and inert to most chemical reagents at high temperatures. They have high opacity and covering power. In colour they range from light yellow through orange and brown to olive. They may be used in the manufacture of pottery, paints, cements, and rubber articles. Titanium dioxide, rutile, and titanium lithopone may be employed as sources of titanium; antimony may be introduced as the trioxide, pentoxide, tetroxide, or as antimonite or antimonate. Chromium may be introduced as chromium trioxide, chromic oxide, chromates, or dichromates. The electropositive element employed is ordinarily sodium or potassium, but other elements such as calcium, strontium, barium, magnesium, aluminium, zinc, tin, silver, lead, nickel, cobalt, lanthanum, and cadmium may be used. In the ceramic industry where the clay contains sodium or calcium, this may constitute the source of the electropositive element. Preferably, the ingredients are mixed in such proportions that the atomic ratios of chromium to antimony and of chromium to titanium are not greater than unity, and that the ratio of the weight of chromium to that of the electropositive element is not greater than the ratio of the atomic weight of chromium to twice the equivalent weight of the electropositive element. The pigment may be made by mixing the constituents intimately and then calcining the mixture in an oxidizing atmosphere. Intimate mixing is facilitated by mixing with water. The temperature at which the mixture is calcined is preferably above 800 DEG C. One of the components may be mixed with ceramic raw material which is then formed into the desired article, fired, dipped into a suspension containing the remainder of the pigment ingredients, and again fired. If desired, all the ingredients may be mixed with the ceramic material which is then formed into tableware, fired, coated with transparent glaze, and again fired. Alternatively, the pigment may be mixed with a suspension of ceramic material and applied as a coating on a coloured or uncoloured body. In examples, the following mixtures are specified:--titanium dioxide, antimony trioxide, chromic acid, and caustic soda; titanium dioxide, sodium antimonate, and chromic acid; magnesium carbonate, stannic oxide, strontium carbonate, cadmium oxide, nickel carbonate, aluminium oxide, sodium silicate, kaolin, or feldspar, and titanium dioxide, antimony trioxide, and chromic acid; lead chromate, titanium dioxide, and antimony trioxide.