| 摘要 |
1,223,639. Coated TiO 2 crystals. NATIONAL LEAD CO. 23 Aug., 1968 [29 Aug., 1967], No. 40535/68. Heading C1N. [Also in Division H1] TiO 2 in the form of crystals 0À2-5Á. in size, the majority of which are straight-edged, containing less than 0À2% Na or K compounds and less than 0.1% phosphate (calculated as oxides) is coated with at least one of the oxides Al 2 O 3 , TiO 2 , PbO, SiO 2 and ZnO, the amount of Al 2 O 3 being 0À05-0À3% and of the other oxides being 0À1-1À5%. Preparation is by: (a) hydrolysing a Ti/Fe sulphate solution to form TiO 2 hydrate, (b) bleaching, e.g. with H 2 SO 4 and Al, (c) washing to remove Fe salts but to retain 5-15% H 2 SO 4 , (d) treating a slurry of the TiO 2 with NH 3 , NH 4 OH, or (NH 4 ) 2 CO, to give a pH of 6À5-11, (e) washing to remove salts and to give a sulphate content of at most 0À3% SO 3 , (f) adding Na or K hydroxide or carbonate in amount of 0À4-2À0% by wt. calc. as oxide, (g) optionally adding a boron compound, in amount of 0À02-0À15% by wt. calc. as B 2 O 3 , (h) calcining at 900-1025‹ C. with K, at 875-925‹ C. with Na to form anatase, or at 925-1025‹ C. with Na to form rutile, (i) grinding to 0À2-5Á, e.g. by dry-milling, or preferably, by wet ball-milling with an alkaline dispersant (whereby the Na or K oxide content is reduced to 0À00-00À2%), (j) heating with an acidic salt of A1, Ti, Pb, Si or Sn, or a silicate, followed by neutralization, e.g. with NaOH, to a pH of 6-9 to precipitate the oxide on the TiO 2 , and (k) washing, drying and milling. In examples, the treating agents used were AlCl 3 , ZnO 2 , Pb acetate, TiCl 4 , TiCl 4 +ZnCl 2 , Na silicate + HCl. The product is photoconductive and may be dyed with fluorescein and used in copy paper. |
