Mixed phase oxide pigments

Mixed-phase oxide pigments are manufactured by high temperature (800-1000 °C) solid state reactions of the individual oxide components in the appropriate quantities. The preparation of nickel antimony titanium yellow, for example, involves reaction of Ti02, NiO and Sb203 carried out in the presence of oxygen or other suitable oxidising agent to effect the necessary oxidation of Sb(m) to Sb(v) in the lattice. 

The formation of rutile mixed phases in the system Ti-Ni-Sb-0 is described in detail in [3.92], When nickel ions are to be included in the pigment and antimony trioxide is used to provide the antimony ions, oxygen must be present to ensure that nickel and antimony occupy the titanium sites in the lattice. If oxygen is excluded, only small amounts of nickel and antimony are taken up in solid solution, and no useful products are formed. The presence of oxidizing agents (e.g., nitrates) is necessary for the production of antimony-containing mixed metal oxide pigments. 

When mixed-phase rutile pigments are used in special paint systems, (e.g., stoving or acid-catalyzed lacquers), inorganic surface treatment in an aqueous medium can improve the gloss and flocculation properties. For example, an aqueous pigment suspension is first treated with a surfactant, and then coated with metal hydroxides or oxide hydrates [3.93],... 

There are no standard methods for the chemical analysis of mixed metal oxide pigments. They are first decomposed (e.g., with peroxide in the case of rutile mixed phases, or soda/borax for the spinels) and the appropriate methods are then used to determine the elements. 

In many inorganic pigments, lanthanides and transition elements are responsible for color. Metal oxides and oxide hydroxides are, however, also important as colored pigments because of their optical properties, low price, and ready availability. Colored pigments based on oxides and oxide hydroxides are either composed of a single component or mixed phases. In the latter, color is obtained by incorporation of appropriate cations. 

Pigment industry raw material for the production of chromium-containing stains and pigments based on mixed metal oxide phases... 

The chrome yellow pigments [4344-37-2], C.I. Pigment Yellow 34 77600 and 77603, are pure lead chromate or mixed-phase pigments with the general formula Pb(Cr,S)04 [3.131] (refractive index 2.3-2.65, density ca. 6 g/cm3). Chrome yellow is insoluble in water. Solubility in acids and alkalis and discoloration by hydrogen sulfide and sulfur dioxide can be reduced to a minimum by precipitating inert metal oxides on the pigment particles. 

Production. In large-scale production, lead or lead oxide is reacted with nitric acid to give lead nitrate solutions, which are then mixed with sodium dichromate solution. If the precipitation solutions contain sulfate, lead sulfochromate is formed as a mixed-phase pigment. After stabilization the pigment is filtered off, washed until free of electrolyte, dried, and ground. 

Chem. Descrip. Inorg. mixed-phase pigments with structure of rutile titanium dioxide and other metal oxides Uses Pigment for surface coatings and plastics Features In combination with org. pigments for luminous hues suitable high processing temps. 

Winchell (1931) gives a preparation method for an amorphous form of altirniniim oxide, the conditions being stated as calcination of an aluminium hydroxide at 925°C for some hours . At 1000-1200 C for 1 hour this compound converts to corundum (. v.), so samples may have mixed phases. Heaton (1928) notes that synthetic aluminium oxide has been used as a substrate for lake pigments. 

Listed hy the Colour Index (1971) under Cl 77500/Cl Pigment Brown 29 as chromium iron brown (chromium(lll) iron(lll) oxide, (Fe,Cr)203), and described as a mixed phase pigment based on iron oxide-chromium oxide . 

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