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Home , Potassium chloride, Rubidium carbonate, Rubidium hydride, Rubidium sulfate, Titanium tetraiodide

March 25, 1969 W. L. Wilson 3,434,799 FROCESS FOR PREPARING PIGMENTARY DIoxIDE Filed April 14, 1965

INVENTOR WILLIAM L. WIL5ON FG, 2. BY Chila..., ATTORNEYS 3,434,799 United States Patent Office Patented Mar. 25, 1969 1. 2 of at least 1500, usually at least 1700, and a blue under 3,434,799 m tone (tint tone) for a particle size distribution range be PROCESS FOR PREPARNG PGMENTARY TTANIUM DOXDE low 1.0 micron, preferably, 0.2 to 0.5 micron. William L. Wilson, Barberton, Ohio, assignor to PPG In the practice of this invention, it has been discovered Industries, Inc., a corporation of Pennsylvania that the pigmentary and optical properties, particularly Continuation-in-part of application Ser. No. 190,140, undertone (tint tone), of rutile pigment Apr. 25, 1962. This application Apr. 14, 1965, Ser. can be substantially increased by reacting the titanium No. 448,121 tetrahalide with an oxygenating gas in the vapor phase Int, C. C01g 23/04 in the presence of a silicon source or additive selected U.S. C. 23-202 11. Claims O from the group consisting of metallic silicon and a silicon compound and a further source which will provide at least one selected from the group consisting of , ABSTRACT OF THE DISCLOSURE , , and cesium. The preparation of pigmentary titanium dioxide by va To more specifically describe the process of this inven por phase oxidation of titanium tetrahalide is described. 5 tion, reference is made to the drawing, and FIGURES 1 A process for improving the pigmentary properties of the to 3, inclusive which depict apparatus for practicing the pigment by conducting the oxidation reaction in the pres process invention. ence of additives, particularly silicon and potassium is FIGURE 1 describes a diagrammatic cross-section view discussed. of a concentric orifice-annulus burner fitted in a furnace. 20 FIGURE 2 further illustrates the construction of the burner of FIGURE 1, representing a view along line I-I CROSS-REFERENCE TO RELATED APPLICATIONS of FIGURE 1. This application is a continuation-in-part of U.S. ap FIGURE 3 illustrates a diagrammatic cross-section view plication Ser. No. 190,140, filed Apr. 25, 1962, now U.S. of a burner which may be fitted in the furnace of FIGURE Letters Patent 3,214,284. 25 1 to produce pigmentary titanium dioxide according to the This invention relates to a process for producing pig process of this invention. mentary titanium dioxide having superior optical proper Referring to FIGURES 1 and 2, reaction zone chamber ties by the vapor phase oxidation of a titanium tetrahalide of furnace A comprises a concentric steel shell 1 and an selected from the group consisting of titanium tetrachlo internal lining of firebrick 5 (or other heat resistant insu ride, titanium tetraiodide, and . 30 lation). At the lower part of furnace A is a conical bot Titanium dioxide is currently produced commercially by tom terminating at outlet 7. At the upper part of furnace at least two different basic processes, the so-called A' is a burner A. process and the process. The latter involves the Burner A is composed of three concentric tubes, 2, 3, vapor phase reaction of titanium tetrahalide and an oxy and 4. Tube 3 is arranged so as to circumscribe tube 4 genating gas at a temperature of at least 800° C., usually 35 (forming annulus 6) and tube 2 is arranged so as to cir 1000 to 1400° C., in the absence or presence of a fluidized cumscribe tubes 3 and 4 (forming annulus 9). Each of bed, e.g., as disclosed in U.S. Letters Patent 2,964,386, the tubes 2 and 3 are evenly spaced from the wall of the U.S. Letters Patent 2,240,343, issued to Muskat, U.S. tube it circumscribes. This is more clearly shown in FIG Letters Patent 2,394,633, issued to Pechukas et al., or U.S. lure 2, which shows the tube arrangement taken along line Letters Patents 2,968,529 and 3,069,281, issued to William 40 I-I of FIGURE 1. L. Wilson. The oxygenating gas may comprise any oxidiz In the operation of the reactor of FIGURES 1 and 2, ing or oxygenating agent, such as , air, oxides of an oxygenating gas typically preheated 900° C. to 1750 , H2O, oxides of , or mixtures of C. is fed to the upper opening in tube 4, while an inert Sale. gas at room temperature up to the temperature of the Pigmentary titanium dioxide has unique optical proper 45 oxygenating gas is fed to the opening at the top of tube ties which make it useful, particularly in the paint indus 3. The inert gas may comprise , nitrogen, bro try. Such optical properties, for example, tinting strength mine, , , helium, krypton, Xenon, carbon di and undertone, are a function of particle size, dispersion oxide, or mixtures thereof. Concurrently therewith, tita and color. Pigmentary titanium dioxide of a given particle nium tetrahalide is fed to the opening at the upper part size distribution range, e.g., mean diameter of 0.2 to 0.5 50 of tube 2. The titanium tetrahalide has a temperature of micron, may be prepared by the vapor phase oxidation 140 C. to about 1200° C. processes of Muskat, Pechukas, or Wilson, noted herein Referring to FIGURE 3, burner B, which may be fitted before, as well as by other processes, e.g., Canadian Pat in furnace A of FIGURE 1 in replacement of burner ent 517,816, issued to Krchma et al., or British patent A, is composed of three concentric tubes annularly ar specifications 876,672 and 922,671. 55 ranged. Central oxygenating gas tube 12 is circumscribed However, it has been discovered that the Surface ac by tube 11, which in turn is circumscribed by tube 10 tivity of the titanium dioxide particles produced by the such that there is formed annuli 17 and 16. Tube 11 is, aforementioned processes may be such that electrostatic provided with an annular lip 13, at its lower end and charges or forces are set up between individual particles tube 10 is provided with annular lip 14, such that the whereby the particles come together and combine in groups 60 titanium tetrahalide and inert gas streams are emitted of two or more. Such grouping is termed chaining or ag from the annuli 17 and 16 in a direction substantially gregation. The result of such grouping, chaining, or aggre perpendicular to the direction of flow of the oxygenating gation is a deficient pigment having less than optimum gas from tube 12. In operation, burner B is fed in the dispersibility and decreased optical properties, particular same manner as burner A of FIGURE 1. ly undertone. 65 It has been discovered that if titanium dioxide is pre The silicon source or additive and the selected ion of pared in accordance with the present invention, there is potassium, zinc, rubidium, and cesium can be added to produced a pigmentary titanium dioxide particle having gether or separately to the inert stream or added together optimum dispersion and undertone for a given particle or separately in one of the reactants, e.g., titanium size distribution range. More particularly, there is pro 70 tetrahalide or oxygenating gas. duced a raw, uncoated pigmentary titanium dioxide par When the process is operated in accordance with U.S. ticle having high, superior dispersion, a tinting strength Letters Patents 3,069,282 and 3,105,742 and a combusti 3,434,799 3 4. ble carbon-containing or -containing fuel is fed into (C4H9)SiH, the reaction zone 30, the silicon source and selected ion (CHg) Si (silicon tetrabutyl), can also be introduced separately or together directly to CHSiH, the reaction zone 30 independently of the inert stream, (C5H11)2SiH2, reactants, and combustible fuel. (C5H11)SiH, Thus, in the practice of this invention, the silicon source 5 (C5H11) Si (silicon tetraisoamyl), can be added directly to the reaction Zone 30 or incor C6H13SiH, porated with one or more streams of inert gas, reactants, (C6H13)2SiH2, or fuels being fed to the zone. Likewise, the selected ion (CH3)3SiH, of potassium, zinc, rubidium, and cesium can be added (C6H13) Si, directly to the Zone 30 or incorporated with one or more O CH-15SiH, streams being fed to the zone. The selected ion may be (CH15)2SiH2, added separately or in conjunction with the silicon source. (CH15)SiH, The silicon source and the selected ion additives can (CH15) Si, be added directly to the reaction Zone as an atomized (C6H5) Si (silicon tetraphenyl), spray in a solid, liquid, or gaseous state. (CHT) Si (silicon tetra-m-tolyl or tetra-p-tolyl), Furthermore, such additives may be added to the Zone (C6H5CH2) Si (silicon tetrabenzyl), by employing an inner furnace wall 5 constructed of a (C12H9)4Si (silicon tetraxenyl), ceramic or firebrick material which contains either one (CH3)3CH5Si (trimethylphenylsilane), or both of the silicon and ion additives. Such material is 20 (CH3)2(C6H5)2Si (dimethyldiphenylsilane), gradually eroded into the reaction zone due to the high CH3(CH) Si (methyltriphenylsilane), temperature oxidation environment in Zone 30, as noted (C2H5)3CH5Si (triethylphenylsilane), for example in British patent specification 672,753. (C2H5)2(C6H5)2Si (diethyldiphenylsilane), One or both of the additives may also be introduced C2H5 (CH5)3Si (ethyltriphenylsilane), into the reaction Zone by employing a ceramic dedusting (CH3) (C2H5) (n-CH) (C6H5)Si (methylethyl edge, as disclosed in copending U.S. application Ser. No. propylphenylsilane), 379,825, filed July 2, 1964, which contains a source of (C2H5) (n-CH) (i-CH) (CH2C6H5) Si (ethyl-n- the ion and/or silicon, e.g., a lava stone containing about propyl-i-butylbenzylsilane), 0.5 to 1.5 percent by weight potassium. (CH5)SiH (triphenylsilane), Such additives are further introduced by employing a 30 (CHCH2)SiH (tribenzylsilane); baffle, as disclosed in copending U.S. application Ser. No. organosilicon or alkylhalosilanes such as 376,980, filed June 22, 1964, now U.S. Patent 3,382,042, CHSiHCl, which is constructed out of a silicon or selected ion con CHSiHCl2, taining material. CHSiCl3, The silicon source is added to the process in an amount CHCISiH, sufficient to insure the presence of 0.01 to 8.0 percent by CHCl2SiH, weight SiO2, basis the weight of the TiO2, in the reac CClSiH, tion Zone. CHCl2SiHCl, The selected metallic ion source of potassium, Zinc, CHCISiHCl, rubidium, and cesium is added to the process in an amount 40 CHCISiHCl, sufficient to insure the presence of 0.00001 to 4.0, prefer CH5SiHCl, ably 0.001 to 0.1, percent by weight of the selected ion in C2H5SiHCl2 the reaction zone, basis the weight of the TiO2. CHSiCl3, Silicon source as employed herein defined as any com CHSiHCl, pound of silicon (including metallic silicon) which will CHSiHCl, oxidize to silica (SiO2) at a temperature of 1500 C. or CHSiCl3: less. silicon halides such as SiCl, (), Specific silicon compounds envisioned not by way ol SiBra (silicon tetrabromide), limitation are the silicon or such as Sila (), SiH4 (monosilane), SiF (silicon tetrafluoride), SiH (), SiHaCl (monochlorosilane), SiHs (), SiH2Cl2 (dichlorosilane), SiHo (tetrasilane), SiHCl (trichlorosilane), Sish 12 (pentasilane), SiHaBr (monobromosilane), Sigh14 (hexasilane), SiH2Bra (dibromosilane), SiH16, SiHBr3 (tribromosilane), Sigh18, SiHa (monoiodosilane), SigH20, SiHgI (diiodosilane), Silo H22; SiHI (triiodosilane), alkylsilanes such as 60 SiHF (monofluorosilane), CH3SiHa (monomethylsilane), SiH2F2 (difluorosilane), (CH3)2SiH (dimethylsilane), SiHF (trifluorosilane), (CH3)SiH (trimethylsilane), SiCl2 (silicon dichloride), C2H5SiH (monoethylsilane), SiBr2 (silicon dibromide) SiI (silicon diiodide), (C2H5)2SiH (diethylsilane), 65 SiF2 (silicon difluoride), Si2Cl6 (silicon trichloride), (CH) SiH (triethylsilane), SigBr (silicon tribromide), (CH3) Si (silicon tetramethyl), Sigis (silicon triiodide), (C2H5) Si (silicon tetraethyl), SigFs (silicon trifluoride), CHSiH, 70 SiICl3 (silicon iodotrichloride), (CH)2SiH, SilCls (silicon iododichloride), (CH)SiH, SiBrCl3 (silicon bromotrichloride), (CH)4Si (silicon tetrapropyl), SiBr2Cl2 (silicon bromodichloride), CHgSiH, SiFCl3 (silicon fluorotrichloride), SiFiCl2 (silicon fluorodichloride),

3,434,799 9 10 (potassium acid acetate), KCHO2H2O (potassium K2C2O4'H2O (potassium oxalate), KHC2O4 (potassium acetylsalicylate), KNH2 (), oxalate), KHCO4/2 H2O, KHCOHO, KNH4CHOs KHC2O4H2C2O4.2H2O, KO, K2O2, K2O3, KO (potassium tartrate), KAuO2xH2O, KN KCHSO4. (), KCH5O23H2O (potassium benzo (potassium phenyl sulfate), KPO4, KHPO, ate), K2B2H6 (potassium ), K2B2H6O (potassi um dihydoxy diborane), K2B5 H (potassium pentabo KPO 3H2O rane), KBO (potassium metaborate), KBO 8H2O (po (potassium pyrophosphate), KPOs. tassium tetraborate), KBOa'4H2O (potassium pentabo The cesium ion source can be elemental cesium or a rate), KBO /2 H2O (potassium peroxyborate), 10 Cesium compound. Examples not by way of limitation of Cesium compounds include both organic and inorganic KCAHBO compounds such as CsC2H5O2 (cesium acetate), (potassium borotartrate), KBrO (), KBr (), KAuBra, 5 (cesium aluminum sulfate), CsCH5O3 (cesium benzo KCrO2Cr (OH) CrO4 ate), CsBrO3 (cesium bromate), CsBr (cesium mono (potassium chromate, basic), bromide), CsBrs (cesium tribromide), CsBrCII (cesium bromochloroiodide), CsIBr2 (cesium dibromoiodide), KCr(SO4)2 12H2O CsIgBr (cesium bromodiiodide), Cs2CO3 (cesium carbo (potassium chromium sulfate), KC6H5OHO (potas 20 nate), CshCO3 (cesium carbonate hydrogen), CsCIO sium citrate), KH2C6H5O1 (, mono (cesium chlorate), CsClO4 (cesium perchlorate), CsCl basic), KOCN (), KCN (potassium cy (cesium chloride), CSAuCl4 (cesium chloroaurate), anide), KC2H5SO4 (potassium ethyl sulfate), K2GeF6 (potassium fluogermanate), K2C20H10Os (potassium flu CsBraCl orescein derivative), KPFs (potassium hexafluorophos (cesium chlorodibromide), CsBrCl (cesium dichlorobro phate), KF (), KF•2H2O, KHF2, mide), CsICl2 (cesium dichloroiodide), CssnCls (cesium KSiF6 (potassium fluosilicate), KAu(CN)2, KBF4 (po chlorostannate), CsCrO4 (cesium chromate), CsCn tassium fluoborate), K2HPO3 (potassium mono hydrogen (cesium cyanide), CsP (cesium fluoride), CsSiF6 (cesium orthophosphite), KH2PO3 (potassium dihydrogen ortho fluosilicate), CsCHO2 (cesium formate), CsCHO-HO, phosphite), KHCH4O4 (potassium hydrogen phthalate), CSH (cesium ), CsCH (cesium hydroxide), CsIO KC6HNO (potassium picarate), KC12HsO4 (potassium (cesium iodate), CsIO4 (cesium metaperiodate), CsI piperate), KCH5O2 H2O (potassium propionate), (cesium monoiodide), Csils (cesium triiodide), CsI (cesi KCHSO4. um pentaiodide), CsCls, CsBris, Csfs, CsNO (cesium (potassium propyl sulfate), KHC6HsOs (potassium acid 35 nitrate), CsNO3HNO3 (cesium hydrogen nitrate), d-saccharate), KCH5O3 (potassium Salicylate), KC15H1904 (cesium dihydrogen nitrate), CsNo (cesium nitrite), (potassium santoninate), K2SiO3 (potassium metasili Cs2C2O4 (cesium oxalate), Cs2O (cesium monoxide), 4) Cs2O3 (cesium peroxide), Cs2O3 (cesium trioxide), CsC, cate), KHSi2O5 (potassium hydrogen disilicate), (cesium Superoxide), CshCaH4O4 (cesium hydrogen KC18H3502 phthalate), CsPh(SO4)2.12H2O (cesium rhodium sul (potassium stearate), K2C4H4O4.3H2O (potassium suc fate), CsCHsO3 (cesium salicylate), Cs2SO4 (cesium cinate), KHC4H4O4 (potassium hydrogen succinate), Sulfate), CshSO4 (cesium hydrogen sulfate), KHCHO-2H2O, KFSO (potassium fluosulfonate), KThFs 4H2O (potassium fluothorate), KTiF6H2O (po tassium fluotitanate), KazrF6 (potassium fluozirconate), (cesium sulfide), Cs2S2 (cesium disulfide), CsSHO, KCHO (), K2C3HPOs (potassium Cs2S3 (cesium tetrasulfide), Cs2S5 (cesium pentasulfide), glycerophosphate), KH (), KOH (po Cs2S6 (cesium hexasulfide). The rubidium ion source can be elemental rubidium tassium hydroxide), KIO (), or a rubidium compound. Examples not by way of limi KIO HIO tation of rubidium compounds include both organic and (potassium acid iodate), KIO-2HIO3, KIOA (potassium inorganic compounds such as RbCHO (rubidium ace metaperiodate), KI, KI3 (potassium triiodide), KCl3, KF, tate), Rb Al(SO4)2.12H2O (rubidium aluminum sulfate), KF3, KBr, KBr3, KC3H5OxH2O (potassium lactate), RbBrO3 (rubidium bromate), RbBr (rubidium bro KC12H2O (potassium laurate), K2C4H4Os (potassium mide), RbBra (rubidium tribromide), Rb1 BrCl (rubidium malate), KCH2(SO3)2 (potassium methionate), bromochloroiodide), Rb1 Bra (ribidium dibromoiodide), RbBrCl (rubidium dichlorobromide), RbBrC1 (rubid 2KCHSO4. HO ium chlorodibromide), Rb2CO3 (), (potassium methyl sulfate), K2C10Hs (SO3)2·2H2O (po 60 RbHCO3, RbClO3 (rubidium chlorate), RbClO (rubid tassium -1,5-disulfonate), KIBr2 (potassium ium perchlorate), RbCl (), RbICI dibromoiodide), K2SnBrs, KCl CaCl2 (potassium calci (rubidium dichloroiodide), RbCrO4 (rubidium chro um chloride), K2C10H14O4.5H2O (potassium d-campho imate), Rb2Cr2O (rubidium dichromate), RbBF (rubid rate), K2CO3 (), K2CO3'xH2O, ium fluoride), Rb2SiF (rubidium fluosilicate), RbFSOs KHCO3 (potassium hydrogen carbonate), K2C2O6 (po (rubidium fluosulfonate), RbH (), tassium peroxycarbonate), (KCO)6 (potassium carbon RbOH (), Rb|O (rubidium iodate), yl), KClO3 (), KClO4 (potassium per RbC4 (rubidium metaperiodate), RbI (rubidium io chlorate), KC, KClO, KICA (potassium chloroiodate), dide), Rb (rubidium triiodide), RBI-4SO, RbMnO, KICl2, KOSCls (potassium chloroosmate), K2RhCls (po (rubidium permanganate), RbNO (rubidium ni tassium pentachlorohodite), KCrO4 (potassium chro 70 trate), RbNOHNO (rubidium hydrogen nitrate), mate), KCr2O (), KCrO3 (po RbNO3'2HNO3, Rb2O (rubidium monoxide), RbC), tassium peroxychromate), KNO3 (), RbAOs (rubidium trioxide), RbC), (rubidium superoxide), KN (), KNO2 (), Rb2SO4 (), RbHSO4 (rubidium hydro KC18H38O2 (potassium oleate), KC18H38O2C18H34O2 (po gen Sulfate), Rb2S (rubidium monosulfide), Rb2S-4HO, tassium acid oleate), KOsO4.2H2O (potassium osmate), 75 Rb2S2 (rubidium disulfide), Rb2S (rubidium trisulfide), 3,434,799 1. 2 Rb2S5 (rubidium pentasulfide), Rb2S (rubidium hexa The reaction Zone 30 was preheated and maintained sulfide), RbHCHOs, Rb2O (rubidium peroxide). at 1000 C. The zinc ion source can be metallic zinc or a zinc Varying amounts of SiCIA were added to the TiCl, and compound. Examples not by way of limitation of varying amounts of KCI were added to the oxygen stream. Zinc compounds include both organic and inorganic The results are tabulated in Table I. The SiC added to compounds Such as Zn(C2H8O2)2 (), the TiCl4 and the KCl added to the O2 are expressed in mole percent, basis TiCl4. ZnAlO4 (zinc aluminate), Zn(NH2)2 (zinc amide), TABLE Zn(CH5O2)2 (zinc benzoate), 3ZnO2B2O3 (zinc bo Run No. SiC in KCI in O: Tinting Strength, Undertone, rate), Zn(BrO3)2 6H2O (Zinc bromate), ZnBr2 (zinc TiCl TiO2 TiO2 None None 1,500 Brown 10. bromide), Zn(CHO)22H2O zinc butyrate), 0.13 None 1,630 Brown 4. 0.27 None 1,590 Do. Zn (C6H11O2)2 None 0.006 1,500 Brown 2 None 0.02 1,420 Do. (zinc caproate), ZnCO3 (zinc carbonate), None 0.02 1,510 Brown None 0.04 1,560 Do. Zn(CIO ) 2 4H2O None 0.04 1,530 Brown 2 0.13 0.006 i,600 Blue 4. (zinc chlorate), ZnCl2 (), ZnCrO4 (Zinc 0.2 0.003 1,670 Neutral. 0.27 0.004 1,640 Blue 2. chromate), ZnCr2O3.H2O (zinc dichromate), 0.27 0.006 1,580 Blue 4. Zn3 (C6H5O) 2 2HO (zinc citrate), Zn(CN)2 (zinc cyanide), Example II Zn(H2O)6GaF5H2O The process operation conditions of Example I were (zinc fluogallate), Zinfa (zinc fluoride), ZnSiF 6H2O repeated. The addition of SiCl, to the reaction zone 30 25 was constant, 0.27 mole percent, basis TiCl4. (zinc fluosilicate), Zn(HSO CHO), Different (anions) were added to the reaction zone Zn(OH)HSO CHO with the SiCl, feeding an atomized aqueous chloride solu (zinc formaldehydesulfoxylate), Zn(CHO)2 (zinc for tion of each ion. The results are shown in Table II. TABLE II mate), ZnC4H4OHO, ZnCH4O6.2H2O (zinc tartrate), 30 Zn(SCN)2 (zinc thiocyanate), Zn(CHO).2H2O (zinc Added Atomized Chloride Tinting Valerate), Zn(NH3)2Cl2 (Zinc diaminezinc chloride), Run No. Anioll fams per Strength. Undertone Zn(CH2CH2CH2CH3)2 (zinc di-n-butylzinc), Zn(CH5)2 ter (zinc diethylzinc), Zn(CH3)2 (zinc dimethylzinc), 1------K------200 (KCl).------1,580 Blue 4. 2------Cs------200 (CsCl)------1,610 Blue 3. Zn(C6H5)2 (zinc dihpenylzinc), Zn(CH2CH2CH3)2 (zinc 3--- Zn------200 (ZnCl).-- --- 1,670 Brown. di-n-propylzinc), Zn(C6H4CH3)2 (zinc di-o-tolyzinc), 4. - Na------200 (NaCl). - - - , 610 Brown 5, 5- - - Ce------200 (CeCl3).-- --- 1,630 Brown 2. Zn(CHO2)22H2O (Zinc formate), ZnCaO (zinc gal 6.-- --- Ce------400 (CeCis). --- 1,640 Brown 5 -- Li------200 (LiCl)------1,690 Do.

late), ZnCHOP (zinc glycerophosphate), Zn(OH)2 8.-- - Ba------200 (BaCl2). 1,630 Brown 4 (zinc hydroxide), Zn(IO), (zinc iodate), 9- - - s - 1,650 Brown 3 1,610 Brown 4 1,650 Brown 2 Zn (zinc ), Zn(CH3O2)23H2O (zinc dil-lactate), Zn(CH3O2)22H2O (Zinc d-lactate), Zn(C11HO2)2 The results summarized in Table II illustrate the effect (zinc laurate), Zn(MnO4)28H2O (zinc permanganate), on undertone when a selected ion, e.g., K, CS, or Zn, Zn(NO3)2.3H2O (zinc nitrate), ZnN (zinc nitride), ZnO is added to the reaction zone with a silicon source. (Note (), Zn(CHO2)2 (zinc acetylacetonate), Runs 1 to 3). Zn(CHsO4)2 (zinc 1-phenol-4-sulfonate), Zn3(PO4)2 However, when other selected ions of the Group I-A (zinc ortho phosphate), Zn3(PO4)2.4H2O, metals, e.g., Na, Li, or ions of Group II-A, e.g., Ba or Sr, are added with the same silicon Source (Runs Zn3 (PO4) 2 8HO 4 to 9), there is no apparent effect on Undertone when Zn(PO4)22H2O, Zn2PO (zinc pyrophosphate) Zn2P compared with Runs 10 and 11 where no anions are (zinc phosphide), Zn(H2PO2)2·H2O (zinc hypophos added. phite), zinc picrate, Zn(CH5O)2.3H2O (zinc salicylate), The tinting strength of pigmentary titanium dioxide ZnSeO4.5H2O (zinc Selenate), ZnCO2H2O, ZnCO4 may be determined by any of several methods known in (zinc oxalate), zinc oleate, ZnSiO (zinc metasilicate), the paint industry. One such method is the Reynold's zinc stearate, ZnSO4 (), hydrates of zinc sul 5 5 Blue Method, A.S.T.M. D-332-26, "1949 Book of fate, ZnS, ZnSHO, ZnSO (zinc sulfite). A.S.T.M. Standards,” Part 4, page 31, published by The following are typical examples: American Society for Testing Material, Philadelphia, Pa. Tint tone or undertone of a titanium dioxide pigment Example I Sample is determined by visually comparing a paste of 60 the pigment with a paste of a selected standard. A burner having the configuration of burner B in FIG In Examples I and II hereinbefore, a paste of each URE 3 was employed in conjunction with reaction sample and Standard was prepared in accordance with chamber A of FIGURE 1. A.S.T.M. D-332-36 using carbon black to tint each sam (TiCl) at 1000 C. and 14.7 ple paste to the same depth of grey as the standard. pounds per square inch absolute pressure was flowed at The standard used in the Examples I and I has an oil the rate of 80 millinoles per minute through annulus 17 absorption rating of 20.9 as determined by A.S.T.M. into reaction zone 30. The TiCl, contained 3 mole per D-281-31, an average particle size of 0.25 micron as de cent of aluminum trichloride (AlCl), basis the TiCl4. termined with an electron micrograph, and an assigned Simultaneously, oxygen at 1000 C. and 14.7 pounds undertone value of Blue 2. per square inch absolute pressure was flowed at 96 milli The samples obtained in Examples I and II were com moles per minute through pagssage 15 (tube 12) into the pared with the standard and an undertone value assigned reaction zone 30. to the Sample by stating whether the sample was bluer or A 40 mole percent chlorine shroud (basis (TiCl) at browner than the designated standard. 1000 C. and 14.7 pounds per square inch absolute pres The more blue a pigment is, the more pleasing are the Sure was flowed through annulus 16. 75 optical properties of a paint prepared from the pigment. 3,434,799 13 14 Conversely, the more brown the pigment, the less pleas from 0.01 to 8.0 weight percent silicon dioxide, based on ing the optical properties of the paint. titanium dioxide, and in the presence of a separate added The undertone scale used herein ranges from a Brown Source of a member selected from the group consisting of 10 to a Blue 6 as shown hereinafter in Table III. potassium, rubidium and cesium which is sufficient to pro TABLE I vide from 0.00001 to 4 weight percent, based on titanium dioxide, of said member. Brown ------10 7. In a process for preparing pigmentary titanium di Do ------9 oxide by vapor phase oxidation of titanium tetrachloride Do ------8 With OXygenating gas, the improvement which comprises Do ------7 conducting Said oxidation in the presence of a silicon Do ------6 O and a source of potassium, said silicon halide being Do ------5 present in an amount, which, when oxidized, is sufficient Do ------4 to form from 0.01 to 8.0 weight percent silicon dioxide, Do ------3 based on titanium dioxide, and said potassium source Do ------2 being present in an amount Sufficient to provide from Do ------1. 0.00001 to 4 weight percent, based on titanium dioxide, Neutral ------of potassium. Blue ------8. In a process for preparing pigmentary titanium di Blue (Standard) ------2 Blue ------3 Oxide by vapor phase oxidation of titanium tetrahalide 20 Selected from the group consisting of titanium tetra Do ------4 chloride, titanium tetrabromide and titanium tetraiodide Do ------5 in a reaction Zone, the invention which comprises improv Do ------6 ing the optical properties of titanium dioxide so produced While the invention has been described by reference to by introducing a source of silicon and a separate source specific details of certain embodiments, it is not intended of potassium into said reaction zone. that the invention be construed as limited to such details 9. A process according to claim 8 wherein said source except insofar as they appear in the appended claims. of silicon is introduced in an amount which, when I claim: oxidized, is sufficient to form from 0.01 to 8.0 weight per 1. In a process for preparing pigmentary titanium cent silicon dioxide, based on titanium dioxide, and where dioxide by vapor phase oxidation of titanium tetrahalide 30 in said potassium source is introduced in an amount suffi Selected from the group consisting of titanium tetra cient to provide from 0.00001 to 4 weight percent po chloride, titanium tetrabromide and titanium tetraiodide tassium, based on titanium dioxide. with oxygenating gas, the invention which comprises in 10. A process according to claim 8 wherein said source proving the optical properties of titanium dioxide so pro of silicon is silicon tetrachloride and wherein said source duced by conducting said oxidation in the presence of an of potassium is potassium chloride. added Source of silicon and a separate added source of a ii. In a process for preparing pigmentary titanium member selected from the group consisting of potassium, dioxide by vapor phase oxidation of titanium tetrachloride rubidium and cesium. With oxygenating gas, the improvement which comprises 2. A process according to claim 1 wherein the source conducting said oxidation in the presence of silicon tetra of silicon is selected from the group consisting of metallic () chloride and potassium chloride, said silicon tetrachloride silicon and a silicon halide. being present in an amount sufficient to form from 0.01 3. A process according to claim 1 wherein the source to 8.0 weight percent silicon dioxide, based on titanium of silicon is present in an amount which, when oxidized, dioxide, and said potassium chloride being present in an is sufficient to form from 0.01 to 8.0 weight percent silicon annount Sufficient to provide from 0.00001 to 4 weight dioxide, based on titanium dioxide. percent potassium ion, based on titanium dioxide. 4. A process according to claim 1 wherein from 0.00001 to 4 weight percent, based on titanium dioxide, References Cited of a member selected from the group consisting of po tassium, rubidium and cesium is present. UNITED STATES PATENTS 5. A process according to claim 1 wherein the source 3,208,866 9/1965 Lewis et al. ------23-202 XR of silicon is a silicon halide and the source of potassium 3,068,113 12/1962 Strain et al. ------106-300 is a potassium halide. 6. In a process for preparing pigmentary titanium di EDWARD STERN, Primary Examiner. oxide by vapor phase oxidation of titanium tetrachloride with oxygenating gas, the improvement which comprises U.S. C. X.R. conducting Said oxidation in the presence of an added 106-300 Source of silicon which, when oxidized, is sufficient to form