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  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G23/00—Compounds of titanium
  • C01G23/04—Oxides; Hydroxides
  • C01G23/047—Titanium dioxide
  • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/46—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates
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  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
  • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
  • C09C1/36—Compounds of titanium
  • C09C1/3607—Titanium dioxide
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  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/50—Solid solutions
  • C01P2002/52—Solid solutions containing elements as dopants
  • C01P2002/54—Solid solutions containing elements as dopants one element only
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/60—Compounds characterised by their crystallite size
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/77—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by unit-cell parameters, atom positions or structure diagrams
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/01—Particle morphology depicted by an image
  • C01P2004/03—Particle morphology depicted by an image obtained by SEM
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/51—Particles with a specific particle size distribution
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/51—Particles with a specific particle size distribution
  • C01P2004/52—Particles with a specific particle size distribution highly monodisperse size distribution
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer

Definitions

• a further aspect of the present invention is a process comprising: 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 O 4 ⁇ H 2 O or up to 20 wt.
• FIGURE 1 is a scanning electron micrograph (SEM) image of pigmentary rutile TiO 2 produced hydrothermally at 250 0 C in an embodiment of the present invention.
• FIGURE 2 is a scanning electron micrograph (SEM) image of 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.
• FIGURE 4 shows the particle size distribution of Ti ⁇ 2 product synthesized from TiOSO 4 -derived titanyl hydroxide at 250 °C vs. commercial chloride process pigmentary rutile according to an embodiment of the present invention. DETAILED DESCRIPTION
• 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 nanometers is referred to as nano-sized.
• 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 Ti ⁇ 2 phase in the crystallized product.
• examples of rutile-directing additives include the halides, oxalates, oxides, and hydroxides of zinc, tin, ammonium, and the group I and group Il metals.
• Pigmentary rutile titanium dioxide can be produced at 220 to 374 0 C with the addition of pigmentary rutile-directing additives.
• Pigmentary rutile-directing additives are those that promote the formation 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.
• pigmentary rutile-directing additives include the rutile- directing additives disclosed herein above.
• Preferred examples of pigmentary rutile-directing additives include ZnCI 2 , ZnO, MgCI 2 , and NaCI.
• 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 0 C.
• the anatase phase of titanium dioxide can be produced at similar process temperatures with the addition of anatase-directing additives.
• 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 , AI 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 0 C with the use of brookite-directing additives. Brookite-directing additives are those that promote the formation of the brookite TIO 2 phase in the crystallized product.
• brookite-directing additives examples include AICI 3 -6H 2 O, alpha-AI 2 O 3 , AI(OH) 3 , and AIOOH.
• 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 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 TiC» 2 particle size.
• 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 the desired phase and in controlling the resulting particle morphology.
• 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 HCI, HF, HBr, HNO 3 , and H 2 C 2 O 412 H 2 O may be added to the slurry, or up to 20 wt% H 2 SO 4 .
• brookite phase is desired, the above described process for rutile production is followed except an NH 4 OH or NH 3 solution is added to the titanium-containing slurry to raise its pH to greater than 9, and the 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.
• a mixture containing 15Og of a reagent grade ammonium titanyl oxalate monohydrate (Acros; CAS# 10580-03-7) and 120Og of deionized water was added to a 4L glass beaker.
• the mixture was agitated by a magnetic stir bar for 30 minutes at room temperature and filtered via a 0.45 ⁇ m disposable nylon filter cup to remove any insoluble impurities.
• the filtrate was collected and transferred back into the 4L glass beaker and heated to 80 0 C on a hot plate with constant agitation.
• 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 1L Zr-702 pressure vessel.
• 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.
• 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 ZnCI 2 (reagent grade, CAS# 7646-85-7), and 2.1 g 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 12.1 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 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.
• 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 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.
• 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 0.2 ⁇ m nylon membrane and washed with deionized water. The wet TiO2 cake was dried in a 75°C 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 ⁇ > of 220nm, d 50 of 535nm, and dgo 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.
• 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.
• the reactor internal temperature was measured by a thermocouple inside the reactor thermowell, which was immersed in the reaction mixture.
• the TiO 2 slurry was recovered from the zirconium reactor and found to have a pH of 1.1. It was then filtered at room temperature via a 0.2 ⁇ m disposable nylon filter cup and washed thoroughly with deionized water to yield 20.11g of a wet TiO 2 cake with an estimated solid content of 55wt%.
• the Ti ⁇ 2 produced was 100% rutile with an average crystal domain size of 55nm as determined by X-ray powder diffraction.
• the material had an acid solubility value of 0.2% (relative to a 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).
• the top of the gold tube was then crimped, and the tube was inserted vertically into a 1 L Zr-702 pressure vessel.
• water was added to submerge the bottom half of the inserted gold tube.
• the reactor thermowel Ol 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 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.
• the Ti ⁇ 2 slurry was recovered from the gold tube and warmed to 35°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 C C vacuum oven for 13-14 hours to yield 0.25g of Ti ⁇ 2 powder.
• 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 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 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 temperature for 24 hours without agitation.
• 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 Ti ⁇ 2 cake was dried in a 75°C vacuum oven for 13-14 hours, and the resulting Ti ⁇ 2 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- 500nm.
• a mixture consisting of 4-5g of a reagent grade ammonium titanyl oxalate derived titanyl hydroxide precipitate (refer to Example 1 for 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 T1O2 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 precipitate and the mineralizing salt was charged into a 1OmL 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.
• KH 2 PO 4 , AI 2 (SO 4 ) 3 , ZnSO 4 , and Na 2 SO 4 favored the formation of the anatase phase, while the presence Of AICI 3 , AI 2 O 3 , and AI(OH) 3 negatively affected the formation and growth of the TiO 2 particles.
• Rutile/anatase mixtures were quantified using a calibrated XPD technique based on multiple known standard mixtures. Rutile/anatase/brookite mixtures were 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). EXAMPLE 8
• the wet 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 HCI 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 (8-B). Increasing the HCI concentration further led to the production of nano-size rutile T1O 2 .
• This 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 25O 0 C via the use of an external electrical heating jacket and held at this temperature for 24 hours without agitation.
• the T ⁇ O2 slurry was recovered from the gold tube and warmed to 35°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°C vacuum oven for 13-14 hours, and the resulting Ti ⁇ 2 powder was characterized by X-ray powder diffraction and particle size distribution.
• the TiO 2 product (9-A) was 97% rutile with an average crystal domain size of 30nm as determined by X-ray powder diffraction.
• 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 domain size of 40nm as determined by X-ray powder diffraction.
• the wetted reactor components including the thermowell, agitator shaft, and impeller were made of Zr-702 metai to minimize TiO 2 contamination by metal corrosion products under 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 internal temperature of 220 0 C 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.
• the TiO 2 slurry was recovered from the reactor and found to have a pH of 9.5.
• the slurry was combined with 16Og 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 80 0 C for approximately 5 hours under reflux conditions.
• the TiO 2 slurry was then filtered via a 0.2 ⁇ m disposable nylon filter cup while it was still hot.
• the resulting wet TiO 2 cake was washed thoroughly with 80 0 C deionized water, and it was then dried in a 75°C vacuum oven for approximately 12 hours to yield 8g Of TiO 2 powder.
• the mixtures were placed into gold reaction tubes, which were then crimped closed, as opposed to sealed, to allow for pressure 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.
• faceted rutile TiO 2 primary particles of pigmentary dimensions could be produced.
• 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 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.
• a mixture consisting of 6.0 grams of an ammonium titanyl oxalate- 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 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.
• the resultant Ti ⁇ 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 with an average crystal domain size of 56.9 nm as determined by X-ray powder diffraction. Scanning electron microscopy images of the TiO2 product revealed a majority of equiaxed primary particles of pigmentary size, on the order of 200-500nm, and some super-pigmentary-sized primary particles ( ⁇ ⁇ m).
• a mixture consisting of 6.0 grams of an ammonium titanyl oxalate- 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 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.
• 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 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 350°C and developed an autogenous hydrothermal pressure of 170 atmospheres. The autoclave was held at temperature for 16 hours without agitation.
• 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 Ti ⁇ 2 product was 100% anatase with an average crystal domain size of 44.5 nm as determined by X-ray powder diffraction.
• the sealed autoclave was externally heated to 350 0 C and developed an autogenous hydrothermal pressure of 158 atmospheres.
• the autoclave was held at temperature for 16 hours without agitation.
• 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.
• 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.
• 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.
• 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.

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