AU2006352688A1 - Processes for the hydrothermal production of titanium dioxide - Google Patents

Description

WO 2008/088312 PCT/US2006/049545 TITLE PROCESSES FOR THE HYDROTHERMAL PRODUCTION OF TITANIUM DIOXIDE FIELD OF THE INVENTION 5 The present invention relates to processes for the hydrothermal production of titanium dioxide from titanyl hydroxide. BACKGROUND Titanium dioxide (TiO 2 ) is used as a white pigment in paints, plastics, paper, and specialty applications. Ilmenite is a naturally occurring 10 mineral containing both titanium and iron with the chemical formula FeTiO 3 . Two major processes are currently used to produce TiO 2 pigment the sulfate process as described in "Haddeland, G. E. and Morikawa, S., "Titanium Dioxide Pigment", SRI international Report #117" and the 15 chloride process as described in "Battle, T. P., Nguygen, D., and Reeves, J.W., The Paul E. Queneau International Symposium on Extractive Metallurgy of Copper, Nickel and Cobalt, Volume 1: Fundamental Aspects, Reddy, R.G. and Weizenbach, R.N. eds., The Minerals, Metals and Materials Society, 1993, pp. 925-943". 20 Lahti et al (GB 2221901 A) disclose a process for the production of titanium dioxide pigment including hydrothermal crystallization in an aqueous acid medium below 300 "C. Crystallization aids are mentioned, but the compositions of the crystallization aids are not given. The present invention provides a hydrothermal crystallization 25 process for the production of titanium dioxide. The use of specific crystallization directors, or additives, promotes the formation of rutile, anatase, or brookite. Variation of process operating parameters can lead to either pigmentary-sized or nano-sized rutile. SUMMARY OF THE INVENTION 30 One aspect of the present invention is a process comprising: WO 2008/088312 PCT/US2006/049545 a) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry; b) adding to the titanium-containing slurry 0.16 to 20 weight percent of a free acid selected from the group 5 consisting of HC, H 2

C

2 04-2H 2 0, HNO 3 , HF, and HBr to form an acidified titanium-containing slurry; c) adding to the acidified titanium-containing slurry 0.01 to 15 weight percent of a rutile-directing additive to form a mixture; 10 d) heating the mixture to a temperature of at least 150 *C but less than 374 0C for less than 24 hours in a closed vessel to form rutile and a residual solution; and e) separating the rutile from the residual solution. 15 Another aspect of the present invention is a process comprising: a) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry; b) adding to the titanium-containing slurry 0.16 to 0.41 20 wt% of a free acid selected from the group consisting of HCI, HNO 3 , HF, H 2

C

2 O4-2H 2 0, and HBr to form an acidified titanium-containing slurry; c) adding to the acidified titanium-containing slurry 0.5 to 15 weight percent of a pigmentary rutile-directing 25 additive to form a mixture; d) heating the mixture to a temperature of at least 220 OC but less than 374 0C for 24 hours or less in a closed vessel to form pigmentary rutile and a residual solution; and 2 WO 2008/088312 PCT/US2006/049545 e) separating the pigmentary rutile from the residual solution. A further aspect of the present invention is a process comprising: 5 a) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry; b) optionally adding less than 0.16 wt% of an acid selected from the group consisting of HCI, HF, HBr, HNO 3 , and

H

2

C

2 0 4 2H 2 0 or up to 20 wt. % of H 2

SO

4 to the 10 titanium-containing slurry to form an acidified slurry; c) adding 0.01-15 weight percent of an anatase-directing additive to the slurry to form a mixture; d) heating the mixture to a temperature of at least 150 "C but less than 374 *C for 24 hours or less in a closed 15 vessel to form anatase and a residual solution; e) separating the anatase from the residual solution. These and other aspects of the present invention will apparent to one skilled in the art in view of the following disclosure and the appended claims. 20 BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a scanning electron micrograph (SEM) image of pigmentary rutile TiO 2 produced hydrothermally at 250 0C in an embodiment of the present invention. FIGURE 2 is a scanning electron micrograph (SEM) image of 25 silica/alumina surface-coated rutile TiO 2 product according to an embodiment of the present invention. FIGURE 3 is an X-ray powder pattern of hydrothermal synthesized TiO 2 containing about 80% brookite according to an embodiment of the present invention. 3 WO 2008/088312 PCT/US2006/049545 FIGURE 4 shows the particle size distribution of TiO 2 product synthesized from TiOSO 4 -derived titanyl hydroxide at 250 0 C vs. commercial chloride process pigmentary rutile according to an embodiment of the present invention. 5 DETAILED DESCRIPTION Titanium dioxide is known to exist in at least three crystalline mineral forms: rutile, anatase, and brookite. Rutile crystallizes in the tetragonal crystal system (P42/mnm with a = 4.582A, c = 2.953A); anatase crystallizes in the tetragonal crystal system (141/amd with a = 3.7852A, c 10 9.5139A); brookite crystallizes in the orthorhombic crystal system (Pcab with a = 5.4558A, b = 9.1819A, c = 5.1429A). The particle size of titanium dioxide influences the opacity of products utilizing TiO 2 . Titanium dioxide product in the particle size range 100 to 600 nanometers is desired for use as pigment. Titanium dioxide with a particle size less than 100 15 nanometers is referred to as nano-sized. Hydrothermal crystallization involves conversion of an amorphous titanyl hydroxide intermediate to titanium dioxide in the presence of water at relatively mild temperature conditions compared to the calcination temperatures (ca. 1000 0C) typically utilized in commercial titanium dioxide 20 production. Titanyl hydroxide (titanic acid) is believed to exist as TiO(OH) 2 (beta- or meta-titanic acid), Ti(OH) 4 or TiO(OH) 2

-H

2 O (alpha- or ortho titanic acid) or TiO(OH) 2 -xH 2 0 (where x>1). [J. Barksdale, Titanium: Its Occurrence, Chemistry, and Technology, 2 nd Ed., Ronald Press: New York (1966)]. Titanyl hydroxide can be produced by either of the known 25 commercial processes for titanium dioxide production, the chloride process or the sulfate process. Additionally, titanyl hydroxide can be produced by other processes which have not yet been commercialized, such as extraction of titanium-rich solutions from digestion of ilmenite by hydrogen ammonium oxalate. Reaction temperatures in the hydrothermal 30 crystallization process range from as low as 150 0C up to the critical point of water (374 0C) with reaction pressures on the order of the corresponding vapor pressure of water. Reaction times are less than 24 4 WO 2008/088312 PCT/US2006/049545 hours. The use of specific phase-directing crystallization aids, or additives, can be used to control the titanium dioxide phase and morphology produced. Variation of the range of process conditions such as control of the acid concentration in the reaction mixture can be used to 5 selectively control the resulting titanium dioxide particle size, crystallography, and morphology. The rutile phase of titanium dioxide can be formed at 150 to 374 0 C with the addition of rutile-directing additives. Rutile-directing additives are those that promote the formation of the rutile TiO 2 phase in the crystallized 10 product. Examples of rutile-directing additives include the halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium, and the group I and group 11 metals. Pigmentary rutile titanium dioxide can be produced at 220 to 3740C with the addition of pigmentary rutile-directing additives. Pigmentary rutile-directing additives are those that promote the formation 15 of the rutile TiO 2 phase in the crystallized product, with the product particle size in the desired pigmentary particle size range of 100-600 nm. Examples of pigmentary rutile-directing additives include the rutile directing additives disclosed herein above. Preferred examples of pigmentary rutile-directing additives include ZnCl 2 , ZnO, MgCl 2 , and NaCI. 20 Nano-sized rutile titanium dioxide can be produced with the addition of any one of the previously mentioned rutile-directing additives at temperatures as low as 150 0C. The anatase phase of titanium dioxide can be produced at similar process temperatures with the addition of anatase-directing additives. 25 Anatase-directing additives are those that promote the formation of the anatase TiO 2 phase in the crystallized product. Examples of anatase directing additives include KH 2

PO

4 , Al 2

(SO

4

)

3 , ZnSO 4 , and Na 2

SO

4 . The brookite phase of titanium dioxide can be produced at temperatures of 150 to 374 OC with the use of brookite-directing additives. Brookite-directing 30 additives are those that promote the formation of the brookite T10 2 phase in the crystallized product. Examples of brookite-directing additives include AICl 3 6H 2 0, alpha-A1203, AI(OH) 3 , and AIOOH. 5 WO 2008/088312 PCT/US2006/049545 The processes of the present invention for the production of rutile include mixing titanyl hydroxide with water to form a slurry. After mixing the titanyl hydroxide with water, the resulting slurry is acidified by addition of a specified concentration of free acid. Free acid is defined herein as the 5 amount of acid above what is needed to neutralize any residual basic species remaining in the titanyl hydroxide from prior processing. The acid and free acid concentration is selected to facilitate the phase-directing action of the additives noted above as well as to control the resulting TiO 2 particle size. For producing rutile TiO 2 , the added acid may be selected 10 from the group HCI, HNO 3 , HF, HBr, or H 2

C

2 0 4 2H 2 O. The concentration of the acid can affect the resulting particle size of the titanium dioxide obtained from the process. The process of the present invention can produce either nano-sized or pigmentary-sized rutile titanium dioxide. Increasing acid concentration tends to decrease the particle size of the 15 resulting titanium dioxide. Pigmentary-sized particles have a large market and thus are frequently the desired particle size. To the acidified slurry is added a phase-directing additive in a concentration of 0.01 to 15 weight percent to form a mixture. Phase directing additives such as those cited previously aid in crystallization of 20 the desired phase and in controlling the resulting particle morphology. The mixture containing the phase directing additive and the acidified slurry is then charged into a closed vessel and heated to a temperature of at least 150 0C and less than the critical point of water (374 'C). The pressure developed in the autoclave is the vapor pressure of the 25 mixture, which is approximately the vapor pressure of the major constituent, water. The mixture is held at temperature for 24 hours or less. This procedure is referred to as a hydrothermal treatment. The time at temperature is a factor in determining the particle size of the resulting titanium dioxide, where in general, depending upon the reaction 30 conditions, increasing time at temperature leads to increasing particle size. During the hydrothermal treatment in the closed vessel, the charged mixture is converted to the desired phase of titanium dioxide and a 6 WO 2008/088312 PCT/US2006/049545 residual solution. The titanium dioxide may be separated from the residual solution using standard techniques such as filtration or centrifugation. Titanium dioxide is frequently supplied to the pigment market with a coating such as silicon and aluminum oxides which may be added in an 5 additional process step. To produce anatase, the above described processes for rutile production are followed except the phase-directing additive is replaced by an anatase-directing additive, as disclosed herein above. The addition of acid is optional but less than 0.16 wt% of an acid selected from the group 10 HCI, HF, HBr, HNO 3 , and H 2

C

2 0 4

-

2

H

2 0 may be added to the slurry, or up to 20 wt% H 2

SO

4 . If the brookite phase is desired, the above described process for rutile production is followed except an NH 4 0H or NH 3 solution is added to the titanium-containing slurry to raise its pH to greater than 9, and the 15 phase-directing additive is replaced by a brookite-directing additive, as disclosed herein above. The brookite phase is usually formed as a mixture of brookite, anatase, and rutile along with a residual solution. EXAMPLES EXAMPLE I 20 Preparation of a Titanyl Hydroxide Precipitate from Reagent Grade Ammonium Titanyl Oxalate A mixture containing 150g of a reagent grade ammonium titanyl oxalate monohydrate (Acros; CAS# 10580-03-7) and 1200g of deionized water was added to a 4L glass beaker. The mixture was agitated by a 25 magnetic stir bar for 30 minutes at room temperature and filtered via a 0.45[tm disposable nylon filter cup to remove any insoluble impurities. The filtrate was collected and transferred back into the 4L glass beaker and heated to 800C on a hot plate with constant agitation. Concentrated

NH

4 0H (28-30wt% NH 3 ; CAS# 1336-21-6) was gradually added to titrate 30 the ammonium titanyl oxalate solution to pH 8.0-8.3, while the temperature of the mixture was maintained at 80'C. The reaction mixture was kept at 7 WO 2008/088312 PCT/US2006/049545 temperature for an additional 15 minutes and then filtered via a 24cm #54 Whatman paper filter to yield 463g of titanyl hydroxide precipitate. The titanyl hydroxide precipitate was collected and reslurried with 2L of deionized water at room temperature. The mixture was heated to 60*C on 5 a hot plate with agitation and held at this temperature for 20 minutes. A small amount of concentrated NH 4 0H solution was added to maintain the solution pH at 8.0-8.3. The solution was then filtered via a 24cm #54 Whatman paper filter to yield 438g of wet titanyl hydroxide cake. The wet cake was then washed by resuspending the material in 2L of deionized 10 water and filtering at room temperature to remove residual oxalate. The washing step was repeated until the conductivity of the filtration liquid dropped below 100 pS. The resulting titanyl hydroxide precipitate had an estimated solid content of 1Owt% and was found to have an amorphous X ray powder pattern with no distinctive anatase-like or rutile-like peaks. 15 Elemental C-N analysis revealed that the synthesized titanyl hydroxide precipitate contained 0.2%C and 2.7%N on a dry basis. EXAMPLE 2 Hydrothermal Crystallization of Nano-Size Rutile TiO 2 from Reagent Grade Ammonium Titanyl Oxalate Derived Titanyl Hydroxide Precipitate 20 A mixture consisting of 4g of a reagent grade ammonium titanyl oxalate derived titanyl hydroxide precipitate (refer to Example I for precipitate preparation and characterization), 0.0102g of ZnCl 2 (reagent grade, CAS# 7646-85-7), and 3.9g of a dilute HCI solution was diluted with deionized water to a concentration of 4 grams of TiO 2 per 100 grams of 25 slurry. The dilute HCI solution was prepared by combining 2.8g of a 12.1 N reagent grade HCI solution (CAS# 7647-01-0) and 32.6g of deionized water. The mixture containing the titanium precipitate was added to a 1OmL gold tube with a welded bottom. The top of the gold tube was then crimped, and the tube was inserted vertically into a 1 L Zr-702 pressure 30 vessel. To facilitate heat transfer inside the 1 L reactor, water was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed in water, and it contained a thermocouple 8 WO 2008/088312 PCT/US2006/049545 for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. This added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. The reactor was heated to an internal 5 temperature of 2500C via the use of an external electrical heating jacket and held at this temperature for 8 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 350C on a hot plate. It was then filtered via a 0.2gm nylon membrane and washed with deionized water. The wet 10 Ti0 2 cake was dried in a 750C vacuum oven for 13-14 hours to yield 0.3g of TiO 2 powder. The recovered TiO 2 product was 100% rutile with an average crystal domain size of 34nm as determined by X-ray powder diffraction. The material had a mono-modal particle size distribution and a d 50 of 131nm (d 1 o = 92nm; d 9 o = 197nm). Scanning electron microscopy 15 images confirmed that the primary particles of the synthesized TiO 2 product were of nano-size on the order of 150nm. EXAMPLE 3 Hydrothermal Crystallization of Pigmentary Rutile TiO 2 at 2500C from Reagent Grade Ammonium Titanyl Oxalate Derived Titanyl Hydroxide 20 Precipitate (10mL Scale) A mixture consisting of 4g of a reagent grade ammonium titanyl oxalate derived titanyl hydroxide precipitate (refer to Example 1 for precipitate preparation and characterization), 0.0582g of ZnC1 2 (reagent grade, CAS# 7646-85-7), and 2.1g of a dilute HCl solution was diluted with 25 deionized water to a concentration of 4 grams of TiO 2 per 100 grams of slurry. The dilute HC solution was prepared by combining 2.8g of a 12.1 N reagent grade HCI solution (CAS# 7647-01-0) and 33.3g of deionized water. The mixture containing the titanium precipitate was added to a I0mL gold tube with a welded bottom. The top of the gold tube was then 30 crimped, and the tube was inserted vertically into a 1 L Zr-702 pressure vessel. To facilitate heat transfer inside the 1L reactor, water was added to submerge the bottom half of the inserted gold tube. The reactor 9 WO 2008/088312 PCT/US2006/049545 thermowell was also immersed in water, and it contained a thermocouple for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. This added argon pressure, along with the autogenous hydrothermal pressure was contained inside 5 the sealed reaction vessel. The reactor was heated to an internal temperature of 250*C via the use of an external electrical heating jacket and held at this temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 350C on a hot plate. It was then filtered 10 via a 0.2l.m nylon membrane and washed with demonized water. The wet TiO 2 cake was dried in a 750C vacuum oven for 13-14 hours to yield 0.3g of TiO 2 powder. The recovered TiO 2 product was 100% rutile with an average crystal domain size of 54nm as determined by X-ray powder diffraction. The particle size distribution of the material had a d 1 0 of 15 220nm, d 50 of 535nm, and d 9 o of 930nm. Scanning electron microscopy images confirmed that the primary particles of the synthesized TiO 2 product were of pigmentary size on the order of 200-500nm. EXAMPLE 4 Hydrothermal Crystallization of Pigmentary Rutile TiO 2 at 250*C from 20 Reagent Grade Ammonium Titanyl Oxalate Derived Titanyl Hydroxide Precipitate (1 L Scale) A mixture consisting of 140g of a reagent grade ammonium titanyl oxalate derived titanyl hydroxide precipitate (refer to Example 1 for precipitate preparation and characterization), 2.2182g of ZnCI 2 (reagent 25 grade, CAS#7646-85-7), 7g of a 12.1 N reagent grade HCI solution (CAS# 7627-01 -0), and 175g of deionized water was added to a 1L Zr-702 pressure vessel. 50psig argon pressure was brought into the reactor prior to heat-up. The added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. 30 The reaction mixture was agitated by a pitch blade impeller at a constant speed of 130rpm. The reactor was heated to an internal temperature of 2500C via the use of an external electrical heating jacket and held at this 10 WO 2008/088312 PCT/US2006/049545 temperature for 16 hours. The reactor internal temperature was measured by a thermocouple inside the reactor thermowell, which was immersed in the reaction mixture. After the completion of the hydrothermal crystallization reaction, the TiO 2 slurry was recovered from the zirconium 5 reactor and found to have a pH of 1.1. It was then filtered at room temperature via a 0.2p m disposable nylon filter cup and washed thoroughly with deionized water to yield 20.11 g of a wet TiO 2 cake with an estimated solid content of 55wt%. The TiO 2 produced was 100% rutile with an average crystal domain size of 55nm as determined by X-ray io powder diffraction. The material had a mono-modal particle size distribution and a d 5 o of 802nm (d 10 = 453nm; d 90 = 1353nm). The primary particles of the synthesized TiO 2 product were pigmentary in size on the order of 200-500nm as determined by scanning electron microscopy (see Figure 1). 15 The pigmentary rutile TiO 2 was then surface treated via a standard chloride-process technology to encapsulate the TiO 2 base material with a silica/alumina coating. X-Ray fluorescence spectroscopy of the coated product indicated a SiO 2 composition of 3.1wt% and an A1 2 0 3 composition of 1.5wt%. The material had an acid solubility value of 0.2% (relative to a 20 commercial specification of <9%), which indicated the production of a photo-durable TiO 2 product. Scanning electron microscopy images of the surface treated TiO 2 confirmed the uniform deposition of the silica/alumina coating on the TiO 2 particles (see Figure 2). EXAMPLE 5 25 Hydrothermal Crystallization of Pigmentary Rutile TiO 2 at 250 0 C from Capel llmenite Ore Derived Titanyl Hydroxide Precipitate A mixture consisting of 2.7g of a Capel ilmenite ore .(Iluka, Australia) derived titanyl hydroxide precipitate (1 5wt% solid), 0.0583g of ZnC 2 (reagent grade, CAS# 7646-85-7), and 3.2g of a dilute HCI solution was 30 diluted with deionized water to a concentration of 4 grams of TiO 2 per 100 grams of slurry. The dilute HCI solution was prepared by combining 2.8g of a 12.1 N reagent grade HCI solution (CAS# 7647-01-0) and 48.9g of 11 WO 2008/088312 PCT/US2006/049545 deionized water. The mixture containing the titanium precipitate was added to a 1OmL gold tube with a welded bottom. The top of the gold tube was then crimped, and the tube was inserted vertically into a 1 L Zr-702 pressure vessel. To facilitate heat transfer inside the I L reactor, water 5 was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed in water, and it contained a 0 thermocouple for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. This added argon pressure, along with the autogenous hydrothermal pressure was 10 contained inside the sealed reaction vessel. The reactor was heated to an internal temperature of 250 0 C via the use of an external electrical heating jacket and held at this temperature for 24 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 35 0 C on a hot plate. It was then filtered 15 via a 0.2ptm nylon membrane and washed with deionized water. The wet TiO 2 cake was dried in a 75*C vacuum oven for 13-14 hours to yield 0.25g of TiO 2 powder. The recovered TiO 2 product was 94% rutile with an average crystal domain size of 45nm as determined by X-ray powder diffraction. Scanning electron microscopy images of the TiO 2 product 20 revealed primary particles of super-pigmentary size, on the order of 500 1000nm. The material exhibited a bi-modal particle size distribution with a significant percentage of the particles in the pigmentary range of 500 1000nm (d 10 = 104nm; d 5 o = 610nm; d 9 o = 1199nm). EXAMPLE 6 25 Lower Temperature (s; 235 0 C) Hydrothermal Crystallization of TiO 2 from Reagent Grade Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate A mixture consisting of 4g of a reagent grade ammonium titanyl oxalate derived titanyl hydroxide precipitate (refer to Example 1 for 30 precipitate preparation and characterization), 0.0582g of ZnC 2 (reagent grade, CAS#7646-85-7), and a small amount (as shown in Table 6-1) of a dilute HCI solution was diluted with deionized water to a concentration of 12 WO 2008/088312 PCT/US2006/049545 4-5 grams of TiO 2 per 100 grams of slurry. The dilute HCI solution was prepared by combining 2.8g of a 12.1N reagent grade HCI solution (CAS# 7647-01-0) and 32.6g of deionized water. The mixture containing the titanium precipitate was added to a 1OmL gold tube with a welded bottom. 5 The top of the gold tube was then crimped, and the tube was inserted vertically into a 1L Zr-702 pressure vessel. To facilitate heat transfer inside the 1 L reactor, water was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed in water, and it contained a thermocouple for determining the reactor internal 10 temperature. 50psig argon pressure was brought into the reactor prior to heat-up. The added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. The reactor was heated to an internal temperature as specified in Table 6 1 via the use of an external electrical heating jacket and held at this 15 temperature for 24 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 35 0 C on a hot plate. It was then filtered via a 0.2 m nylon membrane and washed with deionized water. The wet TiO 2 cake was dried in a 75 0 C vacuum oven for 13-14 hours, and the resulting TiO 2 20 powder was characterized by X-ray powder diffraction and particle size distribution. The product characterization data showed that a pigmentary rutile TiO 2 product was produced at a hydrothermal temperature of 235*C (6-A). Scanning electron microscopy images of the material confirmed that its primary particles were of pigmentary size on the order of 200 25 500nm. A nano-size rutile TiO 2 product with a mono-modal particle size distribution was observed at 2200C (6-F). Lowering the reaction temperature further to 2000C favored the formation of the anatase phase (6-G); however, the percent of nano-size rutile in product was found to improve with increasing HCI concentration (6-1). 30 13 WO 2008/088312 PCT/US2006/049545 TABLE 6-1 Lower Temperature (s 235 0 C) Hydrothermal Crystallization of TiO 2 Ti0 2 Product Rxtn. Dilute HCI Domain Sample Temp. Phase d 5 o (g) Size ("C) (% Rutile) (nm) (nm) 6-A 235 2.0 99 59 548 6-B 235 2.4 100 51 350 6-C 235 3.0 100 38 144 6-D 220 2.0 68 44 191 6-E 220 2.4 94 39 156 6-F 220 3.0 100 37 142 6-G 200 2.0 30 34 53 6-H 200 2.4 47 33 92 6-1 200 3.0 87 28 103 5 EXAMPLE 7 Additive Effect on Hydrothermal Crystallization of TiO 2 from Reagent Grade Ammonium Titanyl Oxalate Derived Titanyl Hydroxide Precipitate A mixture consisting of 4-5g of a reagent grade ammonium titanyl oxalate derived titanyl hydroxide precipitate (refer to Example 1 for 10 precipitate preparation and characterization) and 0.025g of a mineralizing salt (as shown in Table 7-1) was diluted with deionized water to a concentration of 4-5 grams of TiO 2 per 100 grams of slurry. A small amount of acid (as shown in Table 7-1) was added to the mixture to lower its pH to approximately 1. The acidic mixture containing the titanium 15 precipitate and the mineralizing salt was charged into a 10mL gold tube with a welded bottom. The top of the gold tube was then crimped, and the tube inserted vertically into a 1L pressure vessel. To facilitate heat transfer inside the 1 L reactor, water was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed 14 WO 2008/088312 PCT/US2006/049545 in water, and it contained a thermocouple for determining the reactor internal temperature. 50-60psig of argon pressure was brought into the reactor prior to heat-up. The added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed 5 reaction vessel. The reactor was heated to an internal temperature of 2500C via the use of an external electrical heating jacket and held at this temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 35*C on a hot plate. It was then filtered via a 0.2pjm nylon io membrane and washed with deionized water. The wet TiO 2 cake was dried in a 750C vacuum oven for 13-14 hours, and the resulting TiO 2 powder was characterized by X-ray powder diffraction and particle size distribution. The product characterization data showed that among the 18 tested mineralizing salts, ZnCl 2 , ZnO, MgC 2 , and NaCl were found to is promote both rutile formation and the growth of equiaxed TiO 2 crystals. Additives KBr, KCI, LiCl, SnCl 4 , ZnF 2 , NH 4 F, and NaF were found to be rutile phase directing but had no significant effect on crystal morphology.

KH

2

PO

4 , A1 2

(SO

4

)

3 , ZnSO 4 , and Na 2

SO

4 favored the formation of the anatase phase, while the presence of AICl 3 , A1 2 0 3 , and Al(OH) 3 negatively 20 affected the formation and growth of the TiO 2 particles. 15 WO 2008/088312 PCT/US2006/049545 TABLE 7-1 Additive Effect on TiO 2 Formation TiO 2 Product Sample Additive Acid Domain d50 Phase* Size (nm) (nm) 7-A N/A HOI 100% R 36 144 7-B ZnC 2 HCI 100% R 41 185 7-C ZnO HCI 100% R 47 179 7-D MgCl2-6H 2 0 HCI 100% R 42 145 7-E NaCl HCI 100% R 40 144 7-F KBr HCI 100% R 39 152 7-G KCI HCI 98% R; 2% A 29 117 7-H LiCI HCI 100% R 37 147 7-1 SnC 4 HCI 100% R 26 112 7-J ZnF 2 HCI 100% R 32 132 7-K NH 4 F HCl 88% R; 12% A 30 124 7-L NaF HO 90% R; 10% A 31 131 7-M KH 2

PO

4 HCI 100% A 19 68 7-N A1 2

(SO

4

)

3

H

2

SO

4 100% A 13 47 7-0 ZnSO 4

-H

2 0 H 2

SO

4 100% A 14 51 7-P Na 2

SO

4 . H 2

SO

4 100% A 13 49 77% R; 9% A, 7-Q AIC1 3 -6H 2 0 HCI 23 73 14%B 50%R; 28% A, 7-R alpha-A1 2 0 3 HCI 18 36 22%B 23% R; 56% A, 7-S AI(OH) 3 HCI 14 48 21%B * R = Rutile; A = Anatase; B = Brookite Rutile/anatase mixtures were quantified using a calibrated XPD technique based on multiple known standard mixtures. Rutile/anatase/brookite mixtures were estimated using 5 Whole Pattern Fitting (WPF) and Rietveld refinement of crystal structures in JADE* XPD analysis software (JADE* v.6.1 @ 2006 by Materials Data, Inc., Livermore, CA). 16 WO 2008/088312 PCT/US2006/049545 EXAMPLE 8 Reaction pH Effect on Hydrothermal Crystallization of TiO 2 from Reagent Grade Ammonium Titanyl Oxalate Derived Titanyl Hydroxide Precipitate A mixture consisting of 3g of a reagent grade ammonium titanyl 5 oxalate derived titanyl hydroxide precipitate (refer to Example I for precipitate preparation and characterization) and a small amount of ZnCl 2 (reagent grade, CAS#7646-85-7, as shown in Table 8-1) was diluted with deionized water to a concentration of 3-4 grams of TiO 2 per 100 grams of slurry. Varying amounts of a dilute HCI solution were added to the titanyl 10 hydroxide slurry as reported in Table 8-1. The mixture was then charged into a 1 OmL gold tube with a welded bottom. The top of the gold tube was crimped, and the tube inserted vertically into a 1 L Zr-702 pressure vessel. To facilitate heat transfer inside the I L reactor, water was added to submerge the bottom half of the inserted gold tube. The reactor 15 thermowell was also immersed in water, and it contained a thermocouple for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. The added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. The reactor was heated to an internal 20 temperature of 250*C via the use of an external electrical heating jacket and held at this temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 350C on a hot plate. It was then filtered via a 0.2pm nylon membrane and washed with deionized water. The wet 25 TiO 2 cake was dried in a 75*C vacuum oven for 13-14 hours, and the resulting TiO 2 powder was characterized by X-ray powder diffraction and particle size distribution. The product characterization data indicated that under hydrothermal reaction conditions, control of reaction pH was critical to determining TiO 2 crystal phase and morphology. An increase in HCl 30 concentration favored the formation of rutile but had a negative impact on TiO 2 crystal growth. Pigmentary rutile TiO 2 was observed at an acid concentration of 0.0018 moles of HCI per 3g of titanyl hydroxide precipitate 17 WO 2008/088312 PCT/US2006/049545 (8-B). Increasing the HCI concentration further led to the production of nano-size rutile TiO 2 . TABLE 8-1 REACTION PH EFFECT ON TIO 2 FORMATION TiO 2 Product HCI ZnC1 2 Domain Example Phaseds (mol) (g) Size d 50 (% Rutile) (n) (nm) (nm) 8-A 0.0007 0.2301 68 35 117 8-B 0.0018 0.1447 100 52 584 8-C 0.0028 0.0735 100 44 233 8-D 0.0038 0.2896 100 36 142 5 EXAMPLE 9 Seeding Effect on Hydrothermal Crystallization of TiO 2 from Capel Ilmenite Ore Derived Titanyl Hydroxide Precipitate A mixture consisting of 2.7g of a Capel ilmenite ore (Iluka, Australia) derived titanyl hydroxide precipitate (1 5wt% solid), 0.0583g of ZnC1 2 10 (reagent grade, CAS# 7646-85-7), 0.02g of a rutile seed derived from TiOC 2 (100% rutile by X-ray powder diffraction; d1o = 56nm, d 50 = 86nm, d 9 o = 143nm), and 2.9g of a dilute HCI solution was diluted with deionized water to a concentration of 4 grams of TiO 2 per 100 grams of slurry. The dilute HCI solution was prepared by combining 2.8g of a 12.1N reagent 15 grade HCI solution (CAS# 7647-01-0) and 48.9g of deionized water. The mixture containing the ore derived titanium precipitate and the rutile seed was added to a 10mL gold tube with a welded bottom. The top of the gold tube was then crimped, and the tube was inserted vertically into a 1 L Zr 702 pressure vessel. To facilitate heat transfer inside the 1 L reactor, 20 water was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed in water, and it contained a thermocouple for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. This added argon pressure, along with the autogenous hydrothermal pressure was 18 WO 2008/088312 PCT/US2006/049545 contained inside the sealed reaction vessel. The reactor was heated to an internal temperature of 250 0 C via the use of an external electrical heating jacket and held at this temperature for 24 hours without agitation. After the completion of the hydrothermal reaction, the TiO 2 slurry was recovered 5 from the gold tube and warmed to 350C on a hot plate. It was then filtered via a 0.2tim nylon membrane and washed with deionized water. The wet TiO 2 cake was dried in a 750C vacuum oven for 13-14 hours, and the resulting TiO 2 powder was characterized by X-ray powder diffraction and particle size distribution. The TiO 2 product (9-A) was 97% rutile with an io average crystal domain size of 30nm as determined by X-ray powder diffraction. The material had a bi-modal particle size distribution and a d 5 o of 155nm (d 10 = 99nm; d 9 0 = 4893nm). For comparison, an unseeded TiO 2 product (9-B) was also synthesized under the same hydrothermal reaction conditions. The unseeded TiO 2 was 68% rutile with an average crystal 15 domain size of 40nm as determined by X-ray powder diffraction. The material also exhibited a bi-modal particle size distribution with a d 50 of 462nm (d10 = 162nm; d 9 o = 3513nm). The data suggest that the presence of the TiOCl 2 derived rutile seed promotes the formation of the rutile phase but negatively impacts TiO 2 particle growth. 20 TABLE 9-1 Seeding Effect on Hydrothermal Crystallization of Tio 2 from Capel Ilmenite Ore Derived Titanyl Hydroxide Precipitate .l TiO 2 Product Rutile Dilute ZnC 2 Domain Example Seed Phaseds HCI (g) (g) Size (g) (% Rutile) (nm) (nm) 9-A 0.02 2.9 0.0583 97 30 155 9-B 0.00 2.9 0.0583 68 40 462 19 WO 2008/088312 PCT/US2006/049545 EXAMPLE 10 Oxalate Effect on Hydrothermal Crystallization of TiO 2 from Reagent Grade Ammonium Titanyl Oxalate Derived Titanyl Hydroxide Precipitate A mixture consisting of 4g of a reagent grade ammonium titanyl 5 oxalate derived titanyl hydroxide precipitate (refer to Example I for precipitate preparation and characterization) and a small amount of a dilute HCI solution (as shown in Table 10-1) was diluted with deionized water to a concentration of 7-8 grams of TiO 2 per 100 grams of slurry. The dilute HCI solution was prepared by combining 4.3g of a 12.1N reagent 10 grade HCI solution (CAS# 7647-01-0) with 14.5g of water. Varying amounts of Na 2

C

2

O

4 were added to the titanyl hydroxide slurry to adjust its oxalate concentration. The grams of Na 2

C

2 0 4 (reagent grade, CAS# 62 76-0) added are reported in Table 10-1. The mixture was then charged into a 10mL gold tube with a welded bottom. The top of the gold tube was 15 crimped, and the tube inserted vertically into a 1L Zr-702 pressure vessel. To facilitate heat transfer inside the 1 L reactor, water was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed in water, and it contained a thermocouple for determining the reactor internal temperature. 50psig argon pressure 20 was brought into the reactor prior to heat-up. The added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. The reactor was heated to an internal temperature of 250 0 C via the use of an external electrical heating jacket and held at this temperature for 16 hours without agitation. After the 25 completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 35 0 C on a hot plate. It was then filtered via a 0.2pm nylon membrane and washed with deionized water. The wet TiO 2 cake was dried in a 75 0 C vacuum oven for 13-14 hours, and the resulting TiO 2 powder was characterized by X-ray powder diffraction and 30 particle size distribution. Based on the product characterization data, the presence of oxalate in the initial titanyl hydroxide mixture was found to promote the formation of the rutile phase under hydrothermal reaction 20 WO 2008/088312 PCT/US2006/049545 conditions; however, the TiO 2 particle size decreased with increasing initial oxalate concentration. TABLE 10-1 Oxalate Effect on TiO 2 Formation Dilute TiO 2 Product Na 2

C

2

O

4 Domain Example HCI Phase d 50 (g) Size (g) (% Rutile) (nm) (nm) 10-A 0.8 0 60 51 68 10-B 0.8 0.157 90 18 54 10-C 1.8 0 100 39 400 10-D 1.8 0.080 100 31 131 5 EXAMPLE 11 Hydrothermal Crystallization of Brookite TiO 2 A mixture consisting of 80g of a Capel ilmenite ore (Iluka, Australia) derived titanyl'hydroxide precipitate, 8g of concentrated NH 4 0H solution (28-30wt% NH 3 , CAS# 1336-21-6), 0.4g of a nano-size rutile seed (100% 10 rutile by X-Ray powder diffraction: d1 0 = 118nm, d 50 = 185nm, d 9 o = 702nm), and 173g of deionized water was added to a IL PTFE lined Hastelloy* B-3 pressure vessel. The wetted reactor components, including the thermowell, agitator shaft, and impeller were made of Zr-702 metal to minimize TiO 2 contamination by metal corrosion products under 15 elevated temperature and pH conditions. 90psig argon pressure was brought into the reactor prior to heat-up. The added argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. The reaction mixture was agitated by a pitch blade impeller at a constant speed of 90rpm. The reactor was heated to an 20 internal temperature of 2200C via the use of an external electrical heating jacket and held at this temperature for 8 hours. The reactor internal temperature was measured by a thermocouple inside the reactor thermowell, which was immersed in the reaction mixture. After the completion of the hydrothermal crystallization reaction, the TiO 2 slurry was 21 WO 2008/088312 PCT/US2006/049545 recovered from the reactor and found to have a pH of 9.5. The slurry was combined with 160g of deionized water and charged into a 1 L round bottom flask. The mixture was agitated via a magnetic stir bar at a temperature of 800C for approximately 5 hours under reflux conditions. 5 The TiO 2 slurry was then filtered via a 0.2pm disposable nylon filter cup while it was still hot. The resulting wet TiO 2 cake was washed thoroughly with 800C deionized water, and it was then dried in a 750C vacuum oven for approximately 12 hours to yield 8g of TiO 2 powder. The recovered TiO 2 product contained as much as 25% amorphous material as 10 determined by X-ray powder diffraction (XPD). The relative amount of the three crystalline TiO 2 phases in this product (see Figure 3) was estimated using Whole Pattern Fitting (WPF) and Rietveld refinement of crystal structures in JADE® XPD analysis software (JADE® v.6.1 @2006 by Materials Data, Inc., Livermore, CA). This analysis indicated the 15 recovered crystalline product consisted of 10% rutile, 10% anatase, and 80% brookite. The material exhibited a mono-modal particle size distribution and a d 50 of 86nm (d 10 = 49nm; d 9 o = 159nm). EXAMPLE 12 Hydrothermal Crystallization of Pigmentary Rutile TiO 2 at 250*C from 20 Titanyl Sulfate (TiOSO 4 ) Derived Titanyl Hydroxide Precipitate A mixture consisting of 3.4g of a reagent grade titanyl sulfate derived amorphous titanyl hydroxide precipitate (12wt% solid, 0.00wt% carbon, 0.62wt% nitrogen), 0.0582g of ZnCl 2 (reagent grade, CAS# 7646 85-7), and 2.2mL of a 0.96N HCI solution was diluted with deionized water 25 to a concentration of 4 grams of TiO 2 per 100 grams of slurry. The mixture was added to a 1 OmL gold tube with a welded bottom. The top of the gold tube was then crimped, and the tube was inserted vertically into a I L Zr 702 pressure vessel. To facilitate heat transfer inside the 1 L reactor, water was added to submerge the bottom half of the inserted gold tube. 30 The reactor thermowell was also'immersed in water, and it contained a thermocouple for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. This added 22 WO 2008/088312 PCT/US2006/049545 argon pressure, along with the autogenous hydrothermal pressure was contained inside the sealed reaction vessel. The reactor was heated to an internal temperature of 250 0 C via the use of an external electrical heating jacket and held at this temperature for 24 hours without agitation. After the 5 completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 35 0 C on a hot plate. It was then filtered via a 0.2ptm nylon membrane and washed with deionized water. The wet TiO 2 cake was dried in a 75 0 C vacuum oven for 13-14 hours to yield 0.32g of TiO 2 powder. The recovered TiO 2 product was >99% rutile with an 10 average crystal domain size of 58nm as determined by X-ray powder diffraction. The material exhibited a bi-modal particle size distribution with a significant percentage of the particles in the pigmentary range of 500 1000nm (d 10 = 92nm; d 50 = 284nm; d 9 o = 789nm) (refer to Figure 4). EXAMPLE 13 15 Hydrothermal Crystallization of Nano-Size Rutile TiO 2 at 250 0 C from Titanium Oxychloride (TiOCl 2 ) Derived Titanyl Hydroxide Precipitate A mixture consisting of 4.Og of a reagent grade titanium oxychloride derived amorphous titanyl hydroxide precipitate (1 Owt% solid, 0.00wt% carbon, 0.55wt% nitrogen), 0.0584g of ZnCl 2 (reagent grade, CAS# 7646 20 85-7), and 2.5mL of a 0.96N HCI solution was diluted with deionized water to a concentration of 3 grams of TiO 2 per 100 grams of slurry. The mixture was added to a 1OmL gold tube with a welded bottom. The top of the gold tube was then crimped, and the tube was inserted vertically into a 1 L Zr 702 pressure vessel. To facilitate heat transfer inside the 1 L reactor, 25 water was added to submerge the bottom half of the inserted gold tube. The reactor thermowell was also immersed in water, and it contained a thermocouple for determining the reactor internal temperature. 50psig argon pressure was brought into the reactor prior to heat-up. This added argon pressure, along with the autogenous hydrothermal pressure was 30 contained inside the sealed reaction vessel. The reactor was heated to an internal temperature of 2500C via the use of an external electrical heating jacket and held at this temperature for 24 hours without agitation. After the 23 WO 2008/088312 PCT/US2006/049545 completion of the hydrothermal reaction, the TiO 2 slurry was recovered from the gold tube and warmed to 35*C on a hot plate. It was then filtered via a 0.2ptm nylon membrane and washed with deionized water. The wet TiO 2 cake was dried in a 75 0 C vacuum oven for 13-14 hours to yield 0.24g 5 of TiO 2 powder. The recovered TiO 2 product was 100% rutile with an average crystal domain size of 30nm as determined by X-ray powder diffraction. The material exhibited a mono-modal particle size distribution with a d 50 of 125nm (d 10 = 83nm; d 9 o = 207nm). In Examples 14 to 24, the crystallization of TiO 2 particles was 10 carried out hydrothermally in the presence of strong acids and various metal chloride mineralizers. Amorphous hydrous titanium oxide precipitate (sometimes represented as TiO(OH) 2 -nH 2 O with n ~ 32, (Example I provides precipitate preparation and characterization) was added to water to produce a slurry typically in the 33 - 50 weight % range. These slurries 15 were acidified with strong mineral acids to give pH values typically in the 1 - 2 range. In certain experiments, metal chloride salts were added at levels ranging from 0.5 to 20% of the weight of the amorphous TiO(OH) 2 -nH 2 O. The mixtures were placed into gold reaction tubes, which were then crimped closed, as opposed to sealed, to allow for pressure 20 equilibration. The gold tube with its contents was then placed into an autoclave. The temperature of the experiments ranged from 250 to 350 0 C and the pressure was autogenous, ranging from 40 to 170 atmospheres, respectfully. Typical reaction times varied from 1 to 72 hours with a preferred time of between 18 to 24 hrs. Under various experimental 25 conditions, listed herein, faceted rutile TiO 2 primary particles of pigmentary dimensions could be produced. There was a strong correlation between average crystallite size and primary particle size. From the scanning electron micrographs, the primary particles were essentially the pigment particles. Secondary 30 particles were loosely agglomerated primaries. PSD measurement alone without electron microscopy confirmation was highly problematic. The wide breadth of particle size was most likely associated with concentration 24 WO 2008/088312 PCT/US2006/049545 gradients owing to lack of agitation. Mineralizer affected not only primary particle size, but also crystalline phase formation and crystal habit. The presence of chloride tended to result in the formation of equiaxed rutile particles, nitrate tended to form acicular rutile particles, and sulfate forms 5 anatase. The presence of ZnCl 2 mineralizer resulted in the formation of pigmentary particles at lower temperature. The presence of ZnC 2 mineralizer also resulted in a higher degree of agglomeration of the primary particles. EXAMPLE 14 to Hydrothermal Crystallization of -Pigmentary Rutile TiO 2 at 350 0 C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate A mixture consisting of 20.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate and 100 ml of a 0.1N HCI solution was charged into a 125 ml glass vessel specifically designed to fit into a high 15 pressure autoclave (maximum pressure rating = 1000 atmospheres). The glass vessel incorporated an open trap to allow for pressure equilibration. The pH of the mixture prior to crystallization was 2.3. The sealed autoclave was externally heated to 3500C and developed an autogenous hydrothermal pressure of 172 atmospheres. The autoclave was held at 20 temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the glass vessel, filtered and washed with de-ionized water, and allowed to air dry. The recovered TiO 2 product was predominantly rutile (84% rutile/16% anatase) with an average crystal domain size of 38.5 nm as determined by 25 X-ray powder diffraction. Scanning electron microscopy images of the TiO 2 product revealed equiaxed primary particles of pigmentary size, on the order of 200-500nm. The material exhibited a mono-modal particle size distribution with a significant percentage of the particles in the pigmentary range of 500-1000 nm (d 10 = 414 nm; d 50 = 732 nm; d 9 o = 1183 30 nm). 25 WO 2008/088312 PCT/US2006/049545 EXAMPLE 15 Hydrothermal Crystallization of Pigmentary Rutile TiO 2 at 350*C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate A mixture consisting of 6.0 grams of an ammonium titanyl oxalate 5 derived titanyl hydroxide precipitate and 10 ml of a 1.0 N HCI solution was charged into a 15 ml gold tube with a welded bottom. The top of the gold tube was then crimped to allow for pressure equilibration, and the tube was inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The pH of the mixture prior to crystallization 10 was 1.3. The sealed autoclave was externally heated to 350 0 C and developed an autogenous hydrothermal pressure of 163 atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the gold tube, filtered and washed with de-ionized 15 water, and allowed to air dry. The recovered TiO 2 product was 100% rutile with an average crystal domain size of 56.9 nm as determined by X-ray powder diffraction. Scanning electron microscopy images of the TiO 2 product revealed a majority of equiaxed primary particles of pigmentary size, on the order of 200-500nm, and some super-pigmentary-sized 20 primary particles ( 1 pm). The material exhibited a mono-modal particle size distribution with a significant percentage of the particles in the pigmentary range of 500-1000 nm (d 1 0 = 358 nm; d, 0 = 746 nm; d 90 1378 nm). EXAMPLE 16 25 Hydrothermal Crystallization of Pigmentary Rutile TiO 2 at 350"C from Capel Ilmenite Ore (Iluka, Australia)-Derived Titanyl Hydroxide Precipitate A mixture consisting of 6.0 grams of a Capel ilmenite ore (Iluka, Australia)-derived titanyl hydroxide precipitate and 10 ml of a 1.0 N HCI solution was charged into a 15 ml gold tube with a welded bottom. The 30 top of the gold tube was then crimped to allow for pressure equilibration, and the tube was inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The sealed autoclave 26 WO 2008/088312 PCT/US2006/049545 was externally heated to 350'C and developed an autogenous hydrothermal pressure of 165 atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the 5 gold tube, filtered and washed with de-ionized water, and allowed to air dry. The recovered TiO 2 product was 100% rutile with an average crystal domain size of 42.3 nm as determined by X-ray powder diffraction. Scanning electron microscopy images of the TiO 2 product revealed a majority of equiaxed primary particles of pigmentary size, on the order of 10 200-500nm, and some super-pigmentary-sized primary particles (A pm). The material exhibited a bi-modal particle size distribution with a significant percentage of the particles in the pigmentary range of 500-1000 nm (d 10 = 99 nm; d 5 o = 156 nm; d 9 o = 622 nm). EXAMPLE 17 15 Hydrothermal Crystallization of Anatase TiO 2 at 350 0 C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate A mixture consisting of 6.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate and 6 ml of a 0.2 N HCI solution was charged into a 15 ml gold tube with a welded bottom. The top of the gold 20 tube was then crimped to allow for pressure equilibration, and the tube was inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The pH of the mixture prior to crystallization was 4.7. The sealed autoclave was externally heated to 350 0 C and developed an autogenous hydrothermal pressure of 170 atmospheres. 25 The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the gold tube, filtered and washed with de-ionized water, and allowed to air dry. The recovered TiO 2 product was 100% anatase with an average crystal domain size of 20.3 nm as determined by 30 X-ray powder diffraction. 27 WO 2008/088312 PCT/US2006/049545 EXAMPLE 18 Hydrothermal Crystallization of Nano-Sized Rutile TiO 2 at 2500C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate A mixture consisting of 6.0 grams of an ammonium titanyl oxalate 5 derived titanyl hydroxide precipitate and 10 ml of a 1.0 N HNO 3 solution was charged into a 15 ml gold tube with a welded bottom. The top of the gold tube was then crimped to allow for pressure equilibration, and the tube was inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The pH of the mixture prior to 10 crystallization was 2.2. The sealed autoclave was externally heated to 250 0 C and developed an autogenous hydrothermal pressure of 39 atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the gold tube, filtered and washed with de 15 ionized water, and allowed to air dry. The recovered TiO 2 product was 100% rutile with an average crystal domain size of 27.0 nm as determined by X-ray powder diffraction. Scanning electron microscopy images of the Ti02 product revealed a majority of nano-sized acicular primary particles, on the order of 100 nm in length with an aspect ratio (length/width) of 20 between 2 and 5. The material exhibited a mono-modal particle size distribution with the majority of the particles in the nano-sized range of 50 200 nm (d 0 = 77 nm; d 50 = 115 nm; d 9 o = 171 nm). EXAMPLE 19 Hydrothermal Crystallization of Anatase TiO 2 at 3500C from Ammonium 25 Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate A mixture consisting of 6.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate and 10 ml of a 1.0 N H 2

SO

4 solution was charged into a 15 ml gold tube with a welded bottom. The top of the gold tube was then crimped to allow for pressure equilibration, and the 30 tube was inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The pH of the mixture prior to crystallization was 1.6. The sealed autoclave was externally heated to 28 WO 2008/088312 PCT/US2006/049545 350"C and developed an autogenous hydrothermal pressure of 170 . atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the gold tube, filtered and washed with de 5 ionized water, and allowed to air dry. The recovered TiO 2 product was 100% anatase with an average crystal domain size of 44.5 nm as determined by X-ray powder diffraction. The material exhibited a bi-modal particle size distribution (d 10 = 98 nm; d 5 o = 154 nm; d 9 o = 700 nm). EXAMPLE 20 10 Hydrothermal Crystallization of Pigmentary TiO 2 at 3500C from Ammonium. Titanyl Oxalate:Derived Titanyl Hydroxide Precipitate with 0.5 Mol% Mineralizers Mixtures consisting of 6.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate, 0.5 mol% a) LiCl, b) NaCl, and c) 15 SnC 4 mineralizers, and 10 ml of a 1.0 N HCI solution were each charged into 15 ml gold tubes with a welded bottom. The top of the gold tubes was then crimped to allow for pressure equilibration, and the tubes were inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The pH of the mixtures prior to crystallization 20 was 1.3. The sealed autoclave was externally heated to 350*C and developed an autogenous hydrothermal pressure of 157 atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurries were recovered from the gold tubes, filtered and washed with de 25 ionized water, and allowed to air dry. The recovered TiO 2 products were 100% rutile. Average crystal domain sizes of 54.5 (LiCI), 64.6 (NaCI), and 54.7 (SnCl 4 ) nm, were determined by X-ray powder diffraction. These materials exhibited bi-modal particle size distributions (LiCI: d 10 = 122 nm; d5o = 307 nm; d 9 O = 818 nm; NaCl: d 10 = 153 nm; d 50 = 523 nm; d 9 o = 1026 30 nm;.SnC 4 : d 10 = 84 nm; d 5 o = 169 nm; d 9 0 = 719 nm). 29 WO 2008/088312 PCT/US2006/049545 EXAMPLE 21 Hydrothermal Crystallization of Pigmentary and Super-Pigmentary TiO 2 at 350 0 C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate with Increasing Mol% of NaCI Mineralizer 5 Mixtures consisting of 6.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate, a) 0, b) 10, and c) 20 mol% NaCl mineralizer, and 10 ml of a 1.0 N HCI solution were each charged into 15 ml gold tubes with a welded bottom. The top of the gold tubes was then crimped to allow for pressure equilibration, and the tubes were inserted 10 vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The sealed autoclave was externally heated to 350*C and developed an autogenous hydrothermal pressure of 158 atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 15 slurries were recovered from the gold tubes, filtered and washed with de ionized water, and allowed to air dry. The recovered TiO 2 products were 100% rutile. Average crystal domain sizes of 31.1 (0 mol% NaCI), 44.8 (10 mol% NaCI), and 54.6 (20 mol% NaCI) nm, were determined by X-ray powder diffraction. The materials exhibited mono-modal, tri-modal, and 20 mono-modal particle size distributions, respectively, (0 mol % NaCI: d 10 = 93 nm; d 50 = 131 nm; d 90 = 192 nm; 10 mol% NaCl: d 10 = 58 nm; d 5 o = 167 nm; d 9 o = 572 nm; 20 mol% NaCI: d 10 = 349 nm; dro = 604 nm; d 9 o = 948 nm). EXAMPLE 22 25 Hydrothermal Crystallization of Pigmentary and Super-Pigmentary TiO 2 at 350*C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate at High Solids Loading - approximately 1g TiO 2 /mI concentrated HCI A mixture consisting of 10.0 grams of an ammonium titanyl oxalate 30 derived titanyl hydroxide precipitate and 1 ml of a concentrated 12 N HCI solution was charged into a 15 ml gold tube with a welded bottom. The top of the gold tubes was then crimped to allow for pressure equilibration, 30 WO 2008/088312 PCT/US2006/049545 and the tube was inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The sealed autoclave was externally heated to 3500C and developed an autogenous hydrothermal pressure of 170 atmospheres. The autoclave was held at 5 temperature for 16 hours without agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurry was recovered from the gold tube, filtered and washed with de-ionized water, and allowed to air dry. The recovered TiO 2 product was 100% rutile. An average crystal domain size of 66.4 nm was determined by X-ray powder diffraction. The 10 material exhibited a bi-modal particle size distribution (d 10 = 411 nm; d9 0 = 784 nm; do = 5503 nm). EXAMPLE 23 Hydrothermal Crystallization of Pigmentary TiO 2 at 250 0 C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate with ZnCl 2 15 Mineralizer Mixtures consisting of 3.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate, 0.14 gram of ZnCl 2 mineralizer, and 2 ml of a 1.0 N HCI solution, and 4 ml of deionized water were each charged into 15 ml gold tubes with a welded bottom. The top of the gold tubes was 20 then crimped to allow for pressure equilibration, and the tubes were inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The sealed autoclave was externally heated to 250"C and developed an autogenous hydrothermal pressure of 39 atmospheres. The autoclave was held at temperature for 16 hours without 25 agitation. After the completion of the hydrothermal reaction, the resultant TiO 2 slurries were recovered from the gold tubes, filtered and washed with de-ionized water, and allowed to air dry. The recovered TiO 2 products were 100% rutile. An average crystal domain size of 47.0 nm was determined by X-ray powder diffraction. The material exhibited a mono 30 modal particle size distribution (d 10 = 345 nm; d 5 0 = 669 nm; d 9 0 = 1108 nm). 31 WO 2008/088312 PCT/US2006/049545 EXAMPLE 24 Hydrothermal Crystallization of Pigmentary TiO 2 at 250"C from Ammonium Titanyl Oxalate-Derived Titanyl Hydroxide Precipitate with MgC 2 and CaC 2 Mineralizer 5 Mixtures consisting of 6.0 grams of an ammonium titanyl oxalate derived titanyl hydroxide precipitate, 0.43 grams of MgC12-6H 2 0 and 0.34 grams of CaC12-2H 2 0 mineralizer, respectively, 4 ml of a 1.0 N HCI solution, and 8 ml of deionized water were each charged into 15 ml gold tubes with a welded bottom. The top of the gold tubes was then crimped 10 to allow for pressure equilibration, and the tubes were inserted vertically into a high-pressure autoclave (maximum pressure rating = 1000 atmospheres). The sealed autoclave was externally heated to 250*C and developed an autogenous hydrothermal pressure of 39 atmospheres. The autoclave was held at temperature for 16 hours without agitation. After the 15 completion of the hydrothermal reaction, the resultant TiO 2 slurries were recovered from the gold tubes, filtered and washed with de-ionized water, and allowed to air dry. The recovered TiO 2 products were 100% rutile. An average crystal domain size of 54.4 nm for MgCl 2 and 42.5 nm for CaCl 2 was determined by X-ray powder diffraction. The materials exhibited bi 20 modal particle size distributions (MgCl 2 : d 10 = 75 nm; d 50 = 654 nm; d 9 o = 1317 nm and CaC 2 : d 10 = 99 nm; d 5 o = 162 nm; d 9 0 = 612 nm). 32

Claims (3)

1. A process comprising: f) mixing amorphous titanyl hydroxide with water to obtain 5 a titan iu m-contain ing slurry; g) adding to the titanium-containing slurry 0. 16 to 20 weight percent of a free acid selected from the group consisting of [101, 1- 2 C 2 0 4 -21- 2 0, HNO 3 , HF, and HBr to form an acidified titanium-containing slurry; 10 h) adding to the acidified titanium-containing slurry 0.01 to 15 weight percent of a rutile-directing additive to form a mixture; i) heating the mixture to a temperature of at least 150 cC but less than 374 oC for less than 24 hours in a closed 15 vessel to form rutile and a residual solution; and j) separating the rutile from the residual solution.

2. The process of claim o wherein the rutile-directing additive is selected from the group consisting of halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium, and the group I and group 11 metals. 20 3. A process comprising: f) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry; g) adding to the titanium-containing slurry 0.16 to 0.41 wt% of a free acid selected from the group consisting of 25 [101, HNO 3 , HF, 1- 2 C 2 0 4

21- 2 0, and HBr to form an acidified titan ium-containing slurry; h) adding to the acidified titanium-containing slurry 0.5 to 15 weight percent of a pigmentary rutile-directing additive to form a mixture; 30 i) heating the mixture to a temperature of at least 220 OC but less than 374 0C for 24 hours or less in a closed 33 WO 2008/088312 PCT/US2006/049545 vessel to form pigmentary rutile and a residual solution; and j) separating the pigmentary rutile from the residual solution. 5 4. The process of claim 3 wherein the pigmentary rutile directing additive is selected from the group consisting of halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium, and the group I and group 1I metals. 5. The process of claim 3 wherein the pigmentary rutile 10 directing additive is selected from the group consisting of ZnC 2 , ZnO, MgC 2 , and NaCl. 6. A process comprising: a) mixing amorphous titanyl hydroxide with water to obtain titanium-containing slurry; 15 b) adding to the titanium-containing slurry 0.3 to 20 weight percent of a free acid selected from the group consisting of HCI, H 2 C 2 04-2H20, HNO 3 , HF, and HBr to form an acidified titanium-containing slurry; c) adding 0.01 to 15 weight percent of a rutile-directing 20 additive selected from the group consisting of the halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium and the group I and group Il metals to the acidified titanium-containing slurry to form a mixture; d) heating the mixture to a temperature of at least 150 'C 25 but less than 250 0C for less than 24-hours in a closed vessel to form nano rutile and a residual solution; e) separating the nano rutile from the residual solution. 7. The process of claim 6 wherein the rutile-directing additive is 30 selected from the group consisting of halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium, and the group I and group 11 metals 34 WO 2008/088312 PCT/US2006/049545 8. A process comprising: f) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry; g) optionally adding less than 0.16 wt% of an acid selected s from the group consisting of HCl, HF, HBr, HNO 3 , and H 2 C 2 0 4 -2H 2 0 or up to 20 wt. % of H 2 SO 4 to the titanium-containing slurry to form an acidified slurry; h) adding 0.01-15 weight percent of an anatase-directing additive to the slurry to form a mixture; 10 i) heating the mixture to a temperature of at least 150 *C but less than 374 *C for 24 hours or less in a closed vessel to form anatase and a residual solution; j) separating the anatase from the residual solution. 9. The process of claim 8 wherein the anatase-directing 15 additive is selected from the group consisting of KH 2 PO 4 , A1 2 (SO 4 ) 3 , ZnSO 4 , and Na 2 SO 4 . 10. A process comprising: a) mixing amorphous titanyl hydroxide with water to obtain a titanium-containing slurry; 20 b) adding a NH 4 0H/NH 3 solution to the titanium containing slurry such that the slurry has a pH greater than 9.0; c) adding to the slurry 0.01 to15 weight percent of a brookite-directing additive to the titanium-rich slurry to 25 form a mixture; d) heating the mixture to a temperature of at least 150 0 C but less than the 374 0 C for 24 hours or less in a closed vessel to form brookite and a residual solution; e) separating the brookite from the residual solution. 30 35 WO 2008/088312 PCT/US2006/049545 11. The process of claim 10 wherein the brookite-directing additive is selected from the group consisting of AICI 3 -6H 2 0, alpha-A1 2 0 3 , AI(OH)3, and AIOOH. 36