Method for forming a titania-coated inorganic particle

Abstract

A method of forming a titania-coated inorganic particle comprising the steps of (a) stirring a mixture of a titania precursor such as a titanium alkoxide and an inorganic particle such as a hollow glass particles in an organic solvent such as an alcohol for more than 1 h to cause adsorption of the titania precursor on the surface of the inorganic particle; and (b) adding water dropwise to the mixture under stirring to convert the titania precursor to titania which then forms a coating on the inorganic particle. A method for forming a paint formulation, a titania-coated inorganic particle, a paint formulation comprising a titania-coated inorganic particle and use of a titania-coated inorganic particle in a paint formulation is also described.

Claims

1. A titania-coated inorganic particle, wherein said titania of the titania-coated inorganic particle is amorphous titania, and wherein said titania-coated inorganic particle has a density in the range of 0.1 g/mL to 1 g/mL.

2. The titania-coated inorganic particle of claim 1, wherein said titania coating of the titania-coated inorganic particle is of a thickness in the range of 50 nm to 300 nm.

3. The titania-coating inorganic particle of claim 1, wherein the titania coating is disposed on at least 90% of the surface of said inorganic particle.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIG. 1 is a reaction scheme showing the formation of a titania coating on the surface of a (a) hydrophilic hollow glass bead; and (b) hydrophobic hollow glass bead.

(3) FIG. 2 is a series of scanning electron microscopy (SEM) images of (a) K1 hollow glass beads at a magnification of ×350 and (b) the corresponding film after brush coating at a magnification of ×100.

(4) FIG. 3 is a series of SEM images of (a) K25 hollow glass beads at a magnification of ×100 and (b) the corresponding film after brush coating at a magnification of ×100.

(5) FIG. 4 is a series of elemental mapping images of titania-coated hollow glass beads where (a) and (b) are based on the sample HGB@TiO.sub.2-3.1/2:1/ethanol/80 (at a scale of 100 pin) and (c) and (d) are based on the sample HGB@TiO.sub.2-4.65/2:1/ethanol/80 (at a scale of 50 μm).

(6) FIG. 5 is a series of SEM images of (a) K25 hollow glass beads at a magnification of ×100, (b) HGB@TiO.sub.2-3.1/2:1/ethanol/80 at a magnification of ×100, (c) HGB@TiO.sub.2-4.65/2:1/ethanol/80 at a magnification of ×100, and (d) HGB@TiO.sub.2-4.65/2:1/water/80 at a magnification of ×100.

(7) FIG. 6 is a series of SEM cross-sectional images of (a) hollow glass beads at a magnification of ×7,000, (b) hollow glass beads at a magnification of ×9,000, (c) HGB@TiO.sub.2-4.65/2:1/water/80 at a magnification of ×15,000 and (d) HGB@TiO.sub.2-4.65/2:1/water/80 at a magnification of ×16,000.

(8) FIG. 7 is a schematic diagram illustrating a self-made temperature difference test box.

(9) FIG. 8 is a series of SEM images of (a) hydrophobic hollow glass bead (uncoated) at a magnification of ×100, with the inset at a magnification of ×1,000, and (b) HGB(Hydrophobic)@TiO.sub.2-4.96/2:1/ethanol/80 at a scale of 0.5 mm, with the inset at a scale of 25 μm.

(10) FIG. 9 is a series of elemental mapping images of (a), (b) HGB(Hydrophobic)@TiO.sub.2-4.96/2:1/ethanol/80, both at a scale of 30 μm.

(11) FIG. 10 is a series of photographs showing the dispersion of (a) original hydrophobic hollow glass beads and (b) titania-coated hydrophobic hollow glass beads in water.

(12) FIG. 11 is a graph showing the X-Ray Diffraction pattern of titania-coated hollow glass bead.

DETAILED DESCRIPTION OF DRAWINGS

(13) Referring to FIG. 1, there is provided a reaction scheme showing the formation of a titania coating on the surface of a (a) hydrophilic hollow glass bead; and (b) hydrophobic hollow glass bead.

(14) As shown in FIG. 1(a), the surface of a hydrophilic hollow glass bead 1 is shown. When the titania precursor such as titanium alkoxide is added to the hydrophilic hollow glass bead 1, after a sufficient long mixing time, the alkoxy group in titanium alkoxide may facilitate adsorption of titanium alkoxide on the surface of hydrophilic hollow glass bead 1 by reacting with the surface hydroxyl (—OH) groups to form —Ti—O-(hollow glass bead) covalent bonds (as seen in 2). When a controlled amount of water is added, hydrolysis occurs, converting some of the alkoxide groups to hydroxyl groups (as seen in 4). Polycondensation then occurs where titania seeds are formed on the surface of the hollow glass bead due to the relatively high concentration of titanium alkoxide on the surface of the hollow glass beads as compared with that in solution (as seen in 6). The titania seeds then facilitate the titania film formation on the surface of the hollow glass bead (as seen in 8).

(15) As seen in FIG. 1(b), the surface of a hydrophobic hollow glass bead 1′ is shown. When the titania precursor such as titanium alkoxide is added to the hydrophobic hollow glass bead 1′, after a sufficient long mixing time, the alkoxy group in titanium alkoxide may facilitate adsorption of titanium alkoxide on the surface of hydrophobic hollow glass bead 1′ (as seen in 2′) by physical bonds. When a controlled amount of water is added, hydrolysis occurs, converting some of the alkoxide groups to hydroxyl groups (as seen in 4′). Polycondensation then occurs where titania seeds are formed on the surface of the hollow glass bead due to the relatively high concentration of titanium alkoxide on the surface of the hollow glass beads as compared with that in solution (as seen in 6′). The titania seeds then facilitate the titania film formation on the surface of the hydrophobic hollow glass bead (as seen in 8′).

(16) Thus, the titanium alkoxides undergo hydrolysis (to form Ti—O—H bonds) and polycondensation to form three-dimensional structures with Ti—O—Ti bond when reacted with water. The morphology of titania is highly dependent on the relative reaction rate of hydrolysis and polycondensation, which is also strongly affected by the concentration of water. In order to achieve full coverage of hollow glass bead with titania, this requires careful control of mixing time, the molar ratio of water to titania precursor, and ratio of the titania precursor to the inorganic particle.

EXAMPLES

(17) Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Coating Titania on Surface of Hollow Glass Bead

(18) Tetrabutyl titanate (obtained from Sigma Aldrich of St. Louis of Missouri of the United States of America) was added to 72 mL of anhydrous ethanol. 0.6 g of K25 hollow glass bead (obtained from 3M Company of Minnesota of the United States of America), which is hydrophilic, was added into the solution with ratio of titanium alkoxide (molar) to hollow glass bead (g) in the range from 8 to 18 mmol/g and stirred for 2 hours. Water was added drop wise to the suspension at a molar ratio of water to tetrabutyl titanate in the range of 2:1 to 8:1 and stirred mechanically for 2 hours. The suspension was filtered and the titania coated hollow glass beads washed with water or ethanol. The titania coated hollow glass beads were dried at room temperature (of about 25° C.) or at temperature lower than 100° C. The titania coated hollow glass bead samples were collected and named as HGB@TiO.sub.2-A/B/C/D, where A represents the ratio of tetrabutyl titanate to hollow glass bead with unit of mL/g, B represents the molar ratio of water to tetrabutyl titanate, C represents the substance used to wash the sample, and D represents the temperature used to dry the sample.

(19) For coating titania or TiO.sub.2 onto the surface of hydrophobic hollow glass bead, the same process and parameters are utilized, and the sample is named HGB(hydrophobic)@TiO.sub.2-A/B/C/D.

Example 2

Paint Formulation

Example 2a

(20) HGB@TiO.sub.2-4.65/4:1/water/80 was added to binder A form paint. Binder A is a mixture of copolymer (which is Acronal® S 400, obtained from BASF SE of Ludwigshafen of Germany) and 20 wt % of calcium carbonate. The paint was coated onto a glass substrate. After each coating, the wet film was dried at room temperature (of about 25° C.) for 24 hours. The coating and drying operations were repeated. The thickness of the dry film ranged between 0.1 mm and 1 mm based on the coating times and wet film thickness control.

Example 2b

(21) the same steps as Example 2a was carried out here, but using sample HGB@TiO.sub.2-4.65/2:1/water/80.

Example 2c

(22) Pigments were added to binder A to form paint. The pigment is one of the following pigments: hollow glass bead, hollow glass bead and TiO.sub.2 physical mixture, TiO.sub.2 coated hollow glass bead, and HGB@TiO.sub.2-4.65/2:1/water/80. The paint was coated onto the surface of a biaxially oriented polypropylene (BOPP) film. After each coating, the wet film was dried at room temperature (of about 25° C.) for 24 hours. The coating and drying operations were repeated. The thickness of the dry film was around 1 mm. The BOPP film was peeled off to get the freestanding coating for thermal conductivity test.

Example 2d

(23) Pigments were added to binder B, which is Acronal® S 400 to form paint. The paint was coated onto a cement substrate. After each coating, the wet film was dried at room temperature (of about 25° C.) for 24 hours. The coating and drying operations were repeated. The thickness of the dry film ranged between 0.8 mm and 1 mm based on the coating times and wet film thickness control.

Example 2e

(24) Hollow glass bead K1 or K25 (3M) were added to Binder B Acronal® S 400 such that the concentration of the hollow glass bead in paint is 10 w %. This suspension was stirred, then the suspension was brush-coated on the surface of a BOPP film. The film was dried at room temperature for SEM test.

Example 3

Characterization and Performance Test of Sample

(25) Scanning electron microscopy (SEM, JEOL LV SEM 6360LA) and energy dispersive spectroscopy (JEOL JED-2300 EDX) were used to test the surface morphology, TiO.sub.2 dispersion, and TiO.sub.2 layer thickness of TiO.sub.2 coated hollow glass beads. Optima 5300 DV inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin-Elmer) was used to test the concentration of TiO.sub.2 in the TiO.sub.2 coated hollow glass bead. UV-VIS-NIR spectrophotometer UV-3600 (Shimadzu) with integrating sphere ISR 3100 was used to test the diffusive solar reflectance of the pigment.

(26) FIG. 2 shows the SEM images of (a) K1 hollow glass beads and (b) the corresponding film after brush coating as mentioned in Example 2e. The hollow glass beads possess isostatic crush strength of 250 psi and thermal conductivity of 0.047 W/(m.Math.K).

(27) FIG. 3 shows the SEM images of (a) K25 hollow glass beads and (b) the corresponding film after brush coating as mentioned in Example 2e. The hollow glass beads possess isostatic crush strength of 750 psi and thermal conductivity of 0.085 W/(m.Math.K).

(28) In order to make use of the thermal insulation property of hollow glass beads, it is necessary to maintain the integrity of the hollow glass bead after coating. Brush coating is the commonly used method to coat paint onto a surface. FIG. 2(b) shows that after brush coating, some of the hollow glass beads with isostatic crush strength of 250 psi were broken. FIG. 3(b) shows that hollow glass beads with isostatic crush strength of 750 psi can withstand the brush coating. Therefore, K25 hollow glass beads were selected for TiO.sub.2 coated hollow glass bead synthesis.

(29) FIG. 4 shows the results of elemental mapping using SEM EDS where the TiO.sub.2 coating on the surface of hollow glass beads was characterized. FIG. 4 shows that TiO.sub.2 can be coated onto hollow glass bead by using the disclosed method for samples HGB@TiO.sub.2-3.1/2:1/ethanol/80 (FIG. 4a) and of HGB@TiO.sub.2-4.65/2:1/ethanol/80 (FIG. 4b).

(30) FIG. 5 shows the surface morphologies of TiO.sub.2 coated hollow glass beads. It can be seen that TiO.sub.2 can be coated onto the surface of hollow glass beads without obvious freestanding TiO.sub.2 agglomerate formation (when comparing FIG. 5b, FIG. 5c and FIG. 5d to FIG. 5a). The ratio of titanium alkoxide (molar) to hollow glass bead (g) was controlled in the range from 8.4 to 18 mmol/g. The molar ratio of water to titanium alkoxide was controlled in the range from 2:1 to 8:1.

(31) FIG. 6 shows the cross sectional SEM images for TiO.sub.2 coated hollow glass bead confirming the formation of a TiO.sub.2 layer onto the surface of hollow glass beads. The thickness of the TiO.sub.2 layer is around 162 nm in FIG. 6c and 231 nm in FIG. 6d.

(32) Table 1 below shows the solar light reflectance property of the various samples based on the measurement of diffusive solar light reflectance of the sample powder. The results show that the samples washed by water showed higher diffusive solar light reflectance compared to that of samples washed by ethanol. For samples washed with ethanol, samples dried at room temperature showed higher performance compared to that of samples dried at 50° C. and 80° C. For samples washed with water, when the drying temperature was higher than 80° C., the diffusive solar light reflectance decreased. Therefore, drying temperature lower than 100° C. was favorable for TiO.sub.2 coated hollow glass bead synthesis considering the energy cost and the diffusive solar light reflectance performance.

(33) Table 1 also shows that TiO.sub.2 coated hollow glass bead samples had higher diffusive solar light reflectance than that of physical mixtures of TiO.sub.2 particles and hollow glass bead particles.

(34) TABLE-US-00001 TABLE 1 Diffusive solar light reflectance of various samples Diffusive solar Sample reflectance (%) HGB@TiO.sub.2-4.65/2:1/ethanol/room temperature 89.61 HGB@TiO.sub.2-4.65/2:1/ethanol/50 87.12 HGB@TiO.sub.2-4.65/2:1/ethanol/80 87.33 HGB@TiO.sub.2-4.65/2:1/ethanol/110 90.08 HGB@TiO.sub.2-4.65/2:1/ethanol/150 89.10 HGB@TiO.sub.2-4.65/2:1/water/room temperature 90.11 HGB@TiO.sub.2-4.65/2:1/water/50 90.64 HGB@TiO.sub.2-4.65/2:1/water/80 92.09 HGB@TiO.sub.2-4.65/2:1/water/110 90.15 HGB@TiO.sub.2-4.65/2:1/water/150 89.68 HGB@TiO.sub.2-3.1/2:1/ethanol/80 87.7 HGB@TiO.sub.2-5.43/2:1/ethanol/80 90.5 HGB@TiO.sub.2-6.5/2:1/ethanol/80 90.8 HGB@TiO.sub.2-4.65/8:1/water/80 99.96 HGB@TiO.sub.2-4.65/4:1/water/80 97.82 Physical mixture of HGB and TiO.sub.2* 95.92 Hollow glass bead 82.85 Amorphous TiO.sub.2 95.98 *TiO.sub.2 concentration in the physical mixture is the same as that of HGB@TiO.sub.2-4.65/4:1/water/80. The physical mixture was made by mixing specific amounts of hollow glass beads and amorphous TiO.sub.2 according to the weight ratio of hollow glass beads to TiO.sub.2 in HGB@TiO.sub.2-4.65/4:1/water/80.

(35) In order to test the effect of TiO.sub.2 on the density of TiO.sub.2 coated hollow glass beads, the density of TiO.sub.2 coated hollow glass beads was obtained by separated mass and volume measurement. The results (Table 2) show that TiO.sub.2 coating can tune the density of TiO.sub.2 coated hollow glass beads.

(36) TABLE-US-00002 TABLE 2 Density and TiO.sub.2 content of TiO.sub.2 coated hollow glass bead samples TiO.sub.2 Bulk concen- density ρ tration Sample (g/mL) (w %) ρ.sub.HGB@TiO2•ρ.sub.HGB. Hollow glass beads 0.1599 — — HGB@TiO.sub.2-4.65/2:1/ethanol/80 0.1955 20 1.223 HGB@TiO.sub.2-4.65/2:1/water/80 0.1954 20 1.222 HGB@TiO.sub.2-4.65/4:1/water/80 0.2658 50 1.662

Example 4

Characterization and Performance Test of Paint

(37) Total solar light reflectance was tested using UV-VIS-NIR spectrophotometer UV-3600 (Shimadzu) with integrating sphere ISR 3100 according to ASTM E903-96 and ASTM G159-98. Thermal conductivity was tested by using LFA 457 Microflash laser flash system (NETZSCH). Temperature difference test was conducted using the self-made temperature difference test box (shown in FIG. 7). The temperature of the center of the test box was recorded during the test. The temperature difference (ΔT) between test boxes with reference test board (T.sub.reference) and sample test board (T.sub.sample) can be calculated using the following equation: ΔT=T.sub.reference−T.sub.sample.

(38) Table 3 shows the solar light reflectance of paint formulated with TiO.sub.2 coated hollow glass beads, according to the methods listed in Examples 2a and 2b. The paint formulated with TiO.sub.2 coated hollow glass beads shows higher total solar light reflectance compared with that of paint formulated with hollow glass beads. When the concentration of HGB@TiO.sub.2-4.65/2:1/water/80 was 7.4 w %, and the volume concentration of HGB was the same as that of HGB@TiO.sub.2-4.65/2:1/water/80 in paint, the total solar light reflectance increased from 75.08% to 79.93%. The paint formulated with TiO.sub.2 coated hollow glass beads showed higher total solar light reflectance compared with that of paint formulated with TiO.sub.2 and hollow glass beads physical mixture. When the concentration of HGB@TiO.sub.2-4.65/2:1/water/80 was 17.4 w %, and TiO.sub.2 concentration in the physical mixture was the same as that of HGB@ TiO.sub.2-4.65/2:1/water/80, the total solar light reflectance increased from 83.64% to 85.74%.

(39) TABLE-US-00003 TABLE 3 Total solar light reflectance of cool paints formulated with TiO.sub.2 modified hollow glass beads Total Concen- solar light tration of Film reflectance pigment Coating thickness Sample (%) (w %) times (mm) Original binder 48.92 — 4 0.916 Hollow glass beads 75.08 * 4 1.000 HGB@TiO.sub.2- 79.93 7.4.sup.a 4 0.935 4.65/2:1/water/80 HGB@TiO.sub.2- 81.55 11.8 3 0.800 4.65/2:1/water/80 HGB@TiO.sub.2- 84.85 15.9 3 0.880 4.65/2:1/water/80 HGB@TiO.sub.2- 85.19 16.8 3 0.860 4.65/2:1/water/80 HGB@TiO.sub.2- 85.74 17.4 3 0.860 4.65/2:1/water/80 HGB TiO.sub.2 physical 83.64 17.4 3 0.850 mixture.sup.# HGB@TiO.sub.2- 86.27 18.9 3 0.860 4.65/4:1/water/80 HGB@TiO.sub.2- 87.36 20 3 0.863 4.65/4:1/water/80 *the volume concentration of HGB in the paint is the same as that of the TiO.sub.2 modified HGB in the paint.sup.a .sup.#TiO.sub.2 concentration in the physical mixture is the same as that of HGB@TiO.sub.2-4.65/2:1/water/80

(40) In order to test the effect of TiO.sub.2 coated hollow glass beads on the thermal conductivity of paint, paint was prepared according to the method of Example 2c. Table 4 shows that adding TiO.sub.2 coated hollow glass beads into the binder can decrease the thermal conductivity of the binder by 76%. Paint formulated with TiO.sub.2 coated hollow glass bead shows lower thermal conductivity than that of paint formulated with physical mixture of TiO.sub.2 and hollow glass bead.

(41) TABLE-US-00004 TABLE 4 Thermal conductivity of cool paint Thermal Concen- Sample conductivity tration of (name paint with pigment utilized) (W/m K) pigment (w %) Binder 0.559 NA Hollow glass bead* 0.098 * Physical mixture of hollow glass 0.150 16.8 bead and TiO.sub.2.sup.# HGB@TiO.sub.2-4.65/2:1/water/80 0.133 16.8 *The volume concentration of hollow glass bead in the binder is the same as that of HGB@TiO.sub.2-4.65/2:1/water/80 in the binder .sup.#The concentration of TiO.sub.2 in pigment composed of physical mixture of TiO.sub.2 and hollow glass bead is the same as that in TiO.sub.2 coated hollow glass bead HGB@TiO.sub.2-4.65/2:1/water/80

(42) In order to test the cooling performance of paint formulated with TiO.sub.2 coated hollow glass beads, a temperature difference test was conducted under sunlight irradiation. The results are shown in Table 5.

(43) TABLE-US-00005 TABLE 5 Temperature difference test for various formulated paints with different pigments.sup.# Cooling performance Sample 1 Sample 2 (° C.)* Weather condition Cement board Cement board coated 8.7 Date: 2 Aug. 2015 with paint which is Time: 12:30 PM-15:10 PM formulated with Address: 3 Research TiO.sub.2 coated hollow Link, Singapore glass bead.sup.a Temperature: 31-33° C. Feels like: 37-38° C. Wind: 16 km/h- 23 km/h Humidity: 66-55% Cement board coated Cement board coated 1.2 Date: 8 Oct. 2015 with paint which is with paint which is Time: 11:10AM-1:00 PM formulated with formulated with Address: 1 TiO.sub.2 and hollow TiO.sub.2 coated hollow Fusionopolis Place, glass bead physical glass bead Singapore mixture.sup.b Temperature: 32° C. Feels like: 36° C. Wind: 11 km/h Humidity: 55% Cement board coated Cement board coated 1.5 Date: 8 Oct. 2015 with paint which is with paint which is Time: 1:30 PM-2:15 PM formulated with formulated with Address: 1 hollow glass bead.sup.c TiO.sub.2 coated hollow Fusionopolis Place, glass bead Singapore Temperature: 32° C. Feels like: 35° C. Wind: 13 km/h Humidity: 52% *Cooling performance = T.sub.sample 1-T.sub.sample 2, T is the inner space temperature of test box with corresponding test board; .sup.#TiO.sub.2 coated hollow glass bead is HGB@TiO2-4.65/2:1/water/80, hollow glass bead is K25, TiO.sub.2 in physical mixture of TiO.sub.2 and hollow glass bead is amorphous TiO.sub.2 .sup.athe concentration of TiO.sub.2 coated hollow glass bead is 6 w %; .sup.bThe concentration of hollow glass bead and TiO.sub.2 are the same as that of TiO.sub.2 coated hollow glass bead in.sup.a; .sup.cThe volume concentration of hollow glass bead is the same as that of TiO.sub.2 coated hollow glass bead in.sup.a

(44) The results show that paint formulated with cool pigment developed in this application showed the highest cooling performance. The cool paint can decrease the room temperature of test box roofed with cement board by 8.7° C. The cooling performance of cool paint formulated with as-prepared cool pigment was also compared with that of the paint formulated with hollow glass bead only and physical mixture of hollow glass bead and TiO.sub.2, respectively. The results show that the cooling performance of cool paint formulated with as-prepared cool pigment in this application was at least 1.2° C. higher than that of hollow glass bead and physical mixture of hollow glass bead and TiO.sub.2. These results suggest the strong cooling performance of cool pigment developed in this application.

Example 5

Coating on Hydrophobic Hollow Glass Beads

(45) Here, TiO.sub.2 is also coated onto the surface of hydrophobic hollow glass bead (NIPO PTE LIMITED of Singapore) without obvious freestanding TiO.sub.2 agglomerate formation.

(46) FIG. 8(a) shows the SEM image of the original (uncoated) hydrophobic hollow glass bead while FIG. 8(b) shows the SEM image of the sample HGB(hydrophobic)@TiO.sub.2-4.96/2:1/ethanol/80. This shows that the TiO.sub.2 was able to form a uniform coating on the surface of hydrophobic hollow glass beads without any free standing TiO.sub.2 agglomerate formation. This is also confirmed by the elemental mapping image in FIG. 9(a) and FIG. 9(b). FIG. 10 shows the dispersion of (a) original hydrophobic hollow glass beads in water and (b) TiO.sub.2 coated hydrophobic hollow glass bead in water. The dispersion of hydrophobic hollow glass beads in water was increased due to the TiO.sub.2 coating.

(47) These results suggest the wide application scope of this application to coat TiO.sub.2 onto the surfaces of both hydrophilic and hydrophobic hollow glass beads.

(48) FIG. 11 shows the XRD pattern of TiO.sub.2 coated hollow glass beads (that are hydrophobic). FIG. 11 shows that after subtracting the XRD pattern of hollow glass bead and substrate, TiO.sub.2 coated hollow glass beads does not show any peak, suggesting the amorphous structure of TiO.sub.2 in the TiO.sub.2 coated hollow glass beads.

Comparative Example

(49) The titania-coated hollow glass beads were compared against a number of market products. In market, most cool paints focus on utilization of only solar light reflectance property and some paint products have both solar light reflectance and low thermal conductivity properties. Some products from companies in the market which show the certified properties are shown in Table 6.

(50) TABLE-US-00006 TABLE 6 Comparison with market products Total solar light Thermal TiO.sub.2 reflectance conductivity content Product (%) (W/mK) (w %) Company FECOAT 1000 85* No thermal  7-10.sup.# BASF UF 1001 WHITE insulation property mentioned Thermoshield 84.sup.$ 0.142.sup.$ 10-30.sup.$ Thermoshield White Australia Pty Ltd HGB@TiO.sub.2-  85.19 0.133.sup.  3.4 — 4.65/2:1/water/80 *The data is obtained from Energy Star (https://www.energystar.gov/productfinder/product/certified-roofproducts/?scrollTo=103&search_text=&energy_star_partner_isopen=1&brand_name_isopen=&zip_code_filter=&product_types=Select+a+Product+Category&energy_star_partner_filter=BASF + Corporation) .sup.#FECOAT 1000 UF 1001 WHITE Safety Datasheet 2015, version 3.1 .sup.$The data is obtained from company website: http://www.thermoshield.com.au/technical-data.html

(51) Comparing market products with the TiO.sub.2 coated hollow glass beads of the application, when the total solar light reflectance is almost the same, the content of TiO.sub.2 used in this application is much lower. Comparing the disclosed cool paint with Thermoshield White, the thermal conductivity of the disclosed cool paint is lower. It is common knowledge in industry that using high content of TiO.sub.2 will induce high total solar light reflectance, however, TiO.sub.2 is expensive and possesses a large carbon footprint. In this application, TiO.sub.2 is coated uniformly onto the surface of hollow glass bead without any obvious free standing agglomerates, which will make full use of the effective interfacial surface area. This therefore results in achieving high total solar reflectance with lower content of TiO.sub.2.

INDUSTRIAL APPLICABILITY

(52) The disclosed method may be able to form titania-coated inorganic particles that are used in a formulation. The titania-coated inorganic particles may be used in a paint formulation to impart desired properties such as high solar light reflectance, low thermal conductivity and/or high emissivity.

(53) The disclosed method may avoid the problem of freestanding agglomerates of titanium dioxide particles. The disclosed method may not require controlling the crystal phase of titanium dioxide. The disclosed method may control the rate of TiO.sub.2 coating formation by controlling the ratio between the titania precursor, inorganic particles and water. The disclosed method may not require the use of pH control or temperature control. The disclosed method may not require the use of pre-heating or complicated post-treatment steps.

(54) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.