Patent GB-499153-A (GB)
Title: Improvements in or relating to the manufacture of white titanium pigments
IPC: C09C1/36
Filed: 1937-08-24
Abstract: White titanium pigments having a controlled colour tone are prepared by calcining the pigments, or pigment-forming materials, at temperatures of the order of 850-1000 DEG  C., in the presence of a light-reflectance controlling agent which is present in a quantity not exceeding 0,1 per cent by weight based on the weight of the finished pigment and which consists of one or more of the elements yttrium, molybdenum, palladium, tin, lanthanum, erbium, tungsten, platinum, gold and thorium, which may be present either in the elemental form or in the form of compounds. Specified reflectance controlling agents are oxalates and tartrates of the metals, potassium molybdate, ammonium molybdate, potassium palladinate, sodium stannate, sodium tungstate, calcium tungstate, yttrium nitrate, molybdic chloride, palladium chloride, lanthanum sulphate, erbium sulphate tungstic chloride, platinic chloride, auric chloride and thorium sulphate, while the metals themselves, or alloys thereof, may be used.  These may be added at any convenient stage prior to calcination, and amounts of 0,001 per cent are often sufficient. Mixtures of the agents may be used.  The invention is applicable to the production of titanium dioxide pigments, composite titanium pigments, and titanates suitable for pigments.  According to examples: (1) sodium tungstate solution is added to a slurry of washed hydrated titanium compounds, the mixture well stirred, the solids separated and calcined at 850-1000 DEG  C., and pulverized; (2) sheelite is added to ilmenite prior to digestion, and the pigment is obtained by hydrolysis, washing, calcination and pulverization; (3) potassium molybdate solution is added to titanium sulphate solution, and the pigment is obtained by hydrolysis, washing, calcination and pulverization; (4) tungstic acid is dissolved in a solution of potassium carbonate, the resulting solution added to washed hydrated titanium compounds, and the pigment obtained as before; (5) a mixture of blanc fixe and a solution of titanium sulphate is subjected to hydrolysis; to the composite pigment is added gold chloride, and the treated composite pigment is calcined and pulverized; (6) hydrated titanium compounds are treated with a solution of sodium tungstate, and intimately mixed with blanc fixe, followed by calcination and pulverization; (7) ilmenite is digested with concentrated sulphuric acid containing potassium molybdate, and the pigment obtained as before; (8) a digestion cake obtained by treating ilmenite with concentrated sulphuric acid is dissolved in weak sulphuric acid containing molybdenum, and the pigment is obtained by clarification, hydrolysis, washing, calcination and pulverization.  U.S.A. Specification 1,892,693 is referred to.  The Specification as open to inspection under Sect. 91 is not limited to the use of an amount of light-reflectance controlling agent which does not exceed 0,1 per cent.  Further, it is not limited to the preparation of titanium pigments, but mentions also the preparation of other white pigments such as zinc oxide, zinc sulphide and lithopone.  This subject-matter does not appear in the Specification as accepted.