THERMALLY STABLE COLOR PIGMENTS WITH NANOFIBER COATING

Abstract

A method to coat oxide-based color pigments with an ultrasound-assisted coating of nanofiber or other nanostructures in order to enhance heat-fastness and color performance to said color pigments is presented. In particular, the present invention provides a method to coat oxide-based color pigments with nano-coating materials, including but not limited to, alumina and/or silica at different dosage levels, with nanospike, nanoneedle, nanoplate, and/or nanoflower morphology towards enhancing the heat-fastness and color performance of said color pigments.

Claims

1. A method of increasing the thermal stability of iron oxide pigments comprising: placing iron oxide pigment in a coating material precursor solution, wherein the coating material precursor solution is a precursor of one or more of aluminum oxide and silicon oxide; treating the iron oxide pigment and the coating material precursor solution with ultrasound at a temperature of less than 100 C. to promote nanoparticle formation on the iron oxide pigment; and growing a coating from the coating material precursor solution to grow nanoparticles of one or more of the aluminum oxide and the silicon oxide on a surface of the iron oxide pigment such that the resulting iron oxide pigment is thermally stable to a temperature of at least 230 C.

2. The method according to claim 1, wherein the aluminum oxide precursor is an aluminum sulphate.

3. The method according to claim 1, wherein the silicon oxide precursor is tetraethylortho silicate or aminopropyl triethylsilane.

4. The method according to claim 1, wherein the iron oxide pigment is FeOOH yellow iron oxide.

5. The method according to claim 1, wherein the nanoparticles are selected from nanofiber. nanoneedle, nanospike, nanoplate, or nanoflower morphologies, or mixtures thereof.

6. The method according to claim 1, wherein the ultrasound treatment is applied for a period of approximately 5 minutes to 120 minutes.

7. The method according to claim 1, wherein the temperature during ultrasound treatment is approximately 40-80 C.

8. The method according to claim 1, wherein the pH during the ultrasound treatment is controlled to between approximately 7-8.

9. The method according to claim 1, wherein the ultrasound-treated material is aged for a period of between approximately 5 minutes and approximately 240 minutes.

10. The method according to claim 1, wherein the ultrasound treatment occurs at a frequency in between approximately 40 and 55 kHz inclusive.

11. The method according to claim 1, wherein the ultrasound treatment occurs at a frequency where the ultrasound wavelength is approximately an integral multiple of a rod length of the iron oxide pigment.

12. Yellow iron oxide pigment coated with one or more of aluminium oxide and silicon oxide nanoparticles selected from nanofibers, nanoneedles, nanospikes, nanoplates, nanoflowers, or mixtures thereof that is thermally stable to at least approximately 230 C., made by the process of claim 1.

13. The coated yellow iron oxide pigment according to claim 12, wherein the aluminum oxide precursor is an aluminum sulphate.

14. The coated yellow iron oxide pigment according to claim 12, wherein the silicon oxide precursor is tetraethylorthosilicate or aminopropyl triethylsilane.

15. The coated yellow iron oxide pigment according to claim 12, wherein the temperature during ultrasound treatment is approximately 40-80 C.

16. The coated yellow iron oxide pigment according to claim 12, wherein the pH during the ultrasound treatment is controlled to between approximately 7-8.

17. The coated yellow iron oxide pigment according to claim 12, wherein the ultrasound-treated material is aged for a period of between approximately 5 minutes and approximately 240 minutes.

18. The coated yellow iron oxide pigment according to claim 12, wherein the ultrasound treatment occurs at a frequency in between approximately 40 and 55 kHz.

19. The coated yellow iron oxide pigment according to claim 12, wherein the ultrasound treatment occurs at a frequency where the ultrasound wavelength is approximately an integral multiple of a rod length of the yellow iron oxide pigment.

20. Yellow iron oxide pigment coated with one or more of aluminium oxide and silicon oxide nanoparticles selected from nanofibers, nanoneedles, nanospikes, nanoplates, or nanoflowers or mixtures thereof that is thermally stable to at least approximately 230 C.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0022] The above and other objects and features of the present invention will become apparent from the following description of the present invention, when taken in conjunction with the accompanying drawings, in which:

[0023] FIG. 1 shows a graphical illustration with TEM images of preparation of hierarchical core/shell Fe.sub.3O.sub.4 @ SiO.sub.2 @ -AlOOH @Au micro/nanoflowers.

[0024] FIG. 2 shows a TEM image of FeNi.sub.3/Al.sub.2O.sub.3 core/shell nanocomposites.

[0025] FIG. 3 shows a TEM image of a TiO.sub.2@AlOOH core/shell particle.

[0026] FIG. 4A shows one TEM image of hierarchical Al.sub.2O.sub.3 and SiO.sub.2 coating structure on yellow iron oxide.

[0027] FIG. 4B shows another TEM image of hierarchical Al.sub.2O.sub.3 and SiO.sub.2 coating structures on yellow iron oxide.

[0028] FIG. 4C shows the EDX spectrum of hierarchical Al.sub.2O.sub.3 and SiO.sub.2 coating structures on yellow iron oxide.

[0029] FIG. 5 shows a transmission electron microscopic image of yellow iron oxide rods.

[0030] FIG. 6 shows a transmission electron microscopic image of yellow iron oxide rods with alumina nanofiber coating.

[0031] FIG. 7A shows one embodiment of a nanofiber coating for 45 kHz frequency of EDX spectra.

[0032] FIG. 7B shows another embodiment of a nanofiber coating for 45 kHz frequency of EDX spectra.

[0033] FIG. 7C shows the TEM image corresponding to the one embodiment of a nanofiber coating for 45 kHz frequency of EDX spectra as shown in FIG. 7A.

[0034] FIG. 7D shows the TEM image corresponding to another embodiment of a nanofiber coating for 45 kHz frequency of EDX spectra as shown in FIG. 7B.

[0035] FIG. 8A shows a TEM image at a high magnification, revealing almost no nanofiber coating for a 25 kHz frequency.

[0036] FIG. 8B shows a TEM image at high magnification and an EDX spectrum, revealing almost no nanofiber coating for a frequency of 35 kHz.

[0037] FIG. 8C shows a TEM image at high magnification and an EDX spectrum, revealing almost no nanofiber coating for a frequency of 130 kHz.

[0038] FIG. 9 shows a TGA plot for yellow iron oxide rods with alumina nanofiber coatings, depicting the start of a phase transformation at 264 C. (lower line) as well as the first derivative (upper line) revealing a complete phase transformation at 265-300 C.

[0039] FIG. 10 shows yellow iron oxide rods with alumina nanofiber coatings, revealing a color change for temperatures over 240 C.

[0040] FIG. 11A shows a TEM image at a low magnification, revealing almost no nanofiber coating for frequency of 25 kHz.

[0041] FIG. 11B shows a TEM image at a medium magnification, revealing almost no nanofiber coating for a frequency of 25 kHz.

[0042] FIG. 11C shows a TEM image at a high magnification, revealing almost no nanofiber coating for a frequency of 25 kHz.

[0043] FIG. 12A shows a TEM image at a low magnification, revealing almost no nanofiber coating for a frequency of 25 kHz.

[0044] FIG. 12B shows a TEM image at a medium magnification, revealing almost no nanofiber coating for a frequency of 25 kHz.

[0045] FIG. 12C shows a TEM image at a high magnification, revealing almost no nanofiber coating for a frequency of 25 kHz.

[0046] FIG. 13A shows a TEM image of YIOs coated with alumina-needles without ultrasound. The arrow indicates the area of interest.

[0047] FIG. 13B shows a higher magnification TEM image of YIOs coated with alumina-needles without ultrasound. The arrow indicates the area of interest.

[0048] FIG. 13C shows an EDX spectrum of YIOs coated with alumina-needles without ultrasound. The arrow indicates the area of interest.

[0049] FIG. 14A shows a TEM image of YIOs coated with alumina-needles at 45 kHz ultrasound. The arrow indicates the area of interest.

[0050] FIG. 14B shows a higher magnification TEM image of YIOs coated with alumina-needles at 45 kHz ultrasound. The arrow indicates the area of interest.

[0051] FIG. 14C shows an EDX spectrum of YIOs coated with alumina-needles at 45 kHz ultrasound.

[0052] FIG. 15 shows TGA results YIO coated with alumina under sonication at 25 Mit.

[0053] FIG. 16 shows TGA results of YIO coated with alumina under sonication at 45 kHz.

[0054] FIG. 17A shows a TEM image at a low magnification, revealing almost no nanofiber coating for frequency of 130 kHz.

[0055] FIG. 17B shows a TEM image at a medium magnification, revealing almost no nanofiber coating for a frequency of 130 kHz.

[0056] FIG. 17C shows a TEM image at a high magnification, revealing almost no nanofiber coating for a frequency of 130 kHz.

[0057] FIG. 18A shows a TEM image at a low magnification, revealing almost no nanofiber coating for a frequency of 35 kHz.

[0058] FIG. 18B shows a TEM image at a medium magnification, revealing almost no nanofiber coating for a frequency of 35 kHz.

[0059] FIG. 18C shows a TEM image at a high magnification, revealing almost no nanofiber coating for a frequency of 35 kHz.

[0060] FIG. 19A shows a TEM image of typical alumina-coated YIO at 130 kHz.

[0061] FIG. 19B shows an EDX result for the corresponding alumina-coated YIO at 130 kHz.

[0062] FIG. 20A shows a TEM image of typical alumina-coated YIO at 35 kHz.

[0063] FIG. 20B shows an EDX result for the corresponding alumina-coated YIO at 35 kHz.

DETAILED DESCRIPTION OF THE INVENTION

[0064] The present invention is further illustrated by the following embodiments and examples which may only be used for illustrative purpose but are not intended to limit the scope of the presently-claimed invention. The present inventors have invented a method to coat color pigments with coatings (FIGS. 2 and 3) of nanofibers (FIG. 1) or other nano-structures such that the color pigments are enhanced in heat-fastness (FIGS. 9 and 16), color performance (FIG. 10), and oil repulsion performance (oil absorption of raw yellow iron oxide rod: 0.431 g per gram of iron oxide; oil absorption of yellow iron oxide with alumina nanofiber coating: 0.349 g per gram of iron oxide). The method involves application of ultrasound to promote growth of nano structures on pigment particles. The present invention is more economical and practical over the prior art presented in Table 1.

[0065] In particular, the present invention may be carried out at relatively low temperatures of less than 100 C. In a further aspect, the methods of the present invention may be carried out at temperatures of approximately 80 C. or less or approximately 60 C. or less. In one aspect, the method may be carried out at temperatures ranging from 5 C. to 35 C.

[0066] In the present invention, precursor solutions or suspensions are mixed with iron oxide pigments. In particular, precursor solutions or suspensions of aluminum oxide and/or silicon oxide are used to form coatings of aluminum oxide and/or silicon oxide of various morphologies.

[0067] While the iron oxide is subjected to the precursor coating solution or suspension of aluminum oxide and or silicon oxide, ultrasound is applied for approximately 5-120 minutes at a frequency between approximately 40 and 55 kHz inclusive.

[0068] Following the ultrasound treatment, further growth of the nanostructured coatings is promoted during an aging process. The resultant nanoparticle-coated iron oxide is thermally stable to a temperature of at least approximately 230 C. Note that ultrasound is applied to promote growth of a nanostructured coating on the iron oxide pigment. That is, ultrasound is not merely used to disperse various mixture components, it is used to cause the growth of the nanostructured coatings. Without being bound by any particular mechanism, it is speculated that treatment with ultrasound and, in particular, treatment with a resonant frequency of ultrasound, may assist in the nucleation and growth of various nano structures. It is understood that particularly useful frequencies of ultrasound may vary with the size and geometry of containers and the volume of the mixture, the amount and size of the starting materials, etc. and that, for some container configurations, treatment at other than resonant frequencies may best promote nanostructure growth. Thus the particular frequencies set forth above have been shown to promote nanostructure crystal growth for the conditions set forth in the Example. However, those of ordinary skill in the art will appreciate that other frequencies may promote crystal growth with larger batch sizes, larger containers, larger mixture volumes, etc.

[0069] For aluminum oxide coatings, precursor solutions include anhydrous Al.sub.2(SO.sub.4).sub.3, Al.sub.2(SO.sub.4).sub.3.9H.sub.2O, Al.sub.2(SO.sub.4).sub.3.12H.sub.2O, Al.sub.2(SO.sub.4).sub.3.16H.sub.2O, Al.sub.2(SO.sub.4).sub.3.18H.sub.2O and any Al.sub.2(SO.sub.4).sub.3 hydrates. For silicon oxide coatings, precursor solutions include silicates and silanes such as, for example, tetraethylortho silicate and aminopropyl triethylsilane.

[0070] The iron oxide pigment may be placed in suspension and added to a coating solution of a coating precursor material for coating growth from a precursor solution. In an exemplary embodiment, the iron oxide pigment coated is FeOOH yellow iron oxide pigment.

[0071] With more details provided in an exemplary embodiment, 50-500 grams of yellow iron oxide slurry may be dispersed in 300-3000 milliliter of water upon sonication for 5-180 minutes. The dispersed yellow iron oxide may be heated to 40-80 C. with vigorous stirring using mechanical stirrer. 50-500 grams of aluminum sulphate hydrate may be dissolved in 70-350 milliliter of water by heating and stirring. The solution may be transferred to a burette. 1-10 M sodium hydroxide solution may be prepared and transferred to another burette. Aluminum sulphate and sodium hydroxide solutions may be added simultaneously to the dispersed yellow iron oxide under ultrasonication at 40-80 C. while controlling the pH at 7-8. Aging may be performed as the mixture is stirred vigorously at 40-80 C. for another 5-240 minutes. The product may then be collected and washed with large amounts of water.

Example 1

[0072] This example relates to the coating of yellow iron oxide with alumina or silica of different morphologies. FIGS. 4A to 4C and FIGS. 5 to 6 depict coatings of alumina nanoneedles and alumina nanofibers. To produce the alumina coatings on the iron oxide, the following experimental conditions are used: FeOOH (100 g) yellow iron oxide pigment was well dispersed in a beaker with 600 mL deionized water by ultrasound sonication (45 kHz) and stirring for 3 hours.

[0073] Al.sub.2(SO.sub.4).sub.3.9H.sub.2O (186.8 g) was dissolved in minimal amount of deionized water and acidified with 0.1 M H.sub.2SO.sub.4 before solvation. The acidic solution was heated and stirred using a stirrer bar.

[0074] Well-dispersed FeOOH was heated to the temperatures shown in Table 3 and vigorously stirred using mechanical stirrer.

[0075] The acidic aluminium sulphate solution and concentrated NaOH solution were added together dropwisely into the FeOOH mixture with ultrasound sonication (45 kHz). The pH value of the mixture was controlled at 7-8.

[0076] After adding all acidic aluminium sulphate solution, the final concentration of the FeOOH mixture was made up to 100 g/L with deionized water.

[0077] Following ultrasonic treatment, aging is performed to grow the various coatings on the iron oxide. The aging conditions are shown in Table 4.

[0078] The product was collected by filtration and air-dried overnight.

[0079] Ultrasound frequency resonance with yellow iron oxide rod length (714.3137.5 nm) for an ordered coating. While four ultrasound frequencies (130 kHz, 45 kHz, 35 kHz, and 25 kHz) were tested, 45 kHz produces the most satisfactory coating properties (FIGS. 7A-7D; 14A-14C); 130 kHz (FIGS. 17A-17C; 19A-19B), 35 kHz (FIGS. 18A-18C; 20A-20B), and 25 kHz (FIGS. 11A-11C; 12A-12C; 15) show significantly less nanofiber coating (FIG. 8A-8C). The yellow iron oxide coating without ultrasound shows a thin layer of coating but no nanofibers (FIGS. 13A-13C).

[0080] The wavelength, , of the ultrasound can be determined by: =v/f, where v is the velocity and f is the frequency of the ultrasound. Table 2 below shows the wavelengths of the ultrasound at the aforementioned frequencies.

TABLE-US-00002 TABLE 2 Wavelengths of treating ultrasound at frequencies where nanofiber coating occurs Wavelength Velocity Frequency (nm) (m/sec) (kHz) 7622.22 343 45 2638.46 343 130 9800 343 35 13720 343 25
It can further be observed that nanofiber coating occurs at treating ultrasound frequencies where the ultrasound wavelengths are of approximately integral multiples of the yellow iron oxide rod length (714.3137.5 nm). These may be considered, for the experimental container conditions above, as resonant frequencies for the particular size of the starting material and may be particularly useful for promoting nanostructure coating growth.

[0081] Further experimental conditions for this working example are presented in Table 3 and Table 4:

TABLE-US-00003 TABLE 3 Experimental condition of coating process Experiment Temperature No. Al.sub.2O.sub.3 % SiO.sub.2 % ( C.) 1 0.1 60 2 0.3 60 3 0.5 60 4 1 60 5 3 60 6 5 60 7 5 1 60 8 5 5 60 9 5 10 60 10 10 25 11 10 60 12 10 80

TABLE-US-00004 TABLE 4 Experimental condition of aging process Experiment Temperature No. ( C.) pH Time 1 60 6.0 30 mins 2 60 9.0 30 mins 3 60 6.0 1 hour 4 90 6.0 30 mins

[0082] Table 5.

[0083] The table shows the quantified color changes of commercially available yellow iron oxide rods (raw material of YS23(R17-068), prior art yellow iron oxide rods with standard alumina coating (standard Al.sub.2O.sub.3 coated YS23(R17-066), and yellow iron oxide rods with alumina nanofiber coating under 45 kHz ultrasound according to the present invention (modified Al.sub.2O.sub.3 coated YS23(R17-067). All of the samples were tested according to W/B, that is, the mixing method with white and black.

TABLE-US-00005 Mass Tone Tint Tone Trial/Formula dE dL da db Strength % dE dL da db Strength % Std 1. Color Standard Al.sub.2O.sub.3 coated 4.7 1.43 0.78 4.41 105.82 3.99 3.27 1.25 1.92 74.24 Raw YS23(R17-066) material Modified A1.sub.2O.sub.3 coated 4.23 1.41 0.74 3.92 104.07 3.82 3.18 1.16 1.79 75.04 of YS23 YS23(R17-067) (R17-068) 2. Heat stability02.3 + 0 Standard 220 C. 2.41 1.51 0.56 1.79 103.93 1.48 0.87 0.52 1.08 102.18 R17-066 Al.sub.2O.sub.3 coated 30 min YS23(R17- 240 C. 3.81 2.33 0.86 2.88 106.07 2.22 1.5 0.93 1.35 105.85 066) 30 min Modified 220 C. 1.73 1.18 0.47 1.18 103.87 1.09 0.73 0.4 0.7 102.63 R17-067 Al.sub.2O.sub.3 coated 30 min YS23(R17- 240 C. 3.13 1.99 0.72 2.31 105.68 2 1.32 0.63 1.36 104.56 067) 30 min Raw material 220 C. 6.24 3.63 1.38 4.88 108.2 4.22 2.67 1.57 2.87 108.68 R17-068 of YS23(R17- 30 min 068) 240 C. 11.76 6.77 2.77 9.21 116.28 8.4 5.34 3.26 5.6 119.22 30 min

INDUSTRIAL APPLICABILITY

[0084] Accordingly, the first objective of the presently claimed invention relates to a method to coat oxide based color pigments with a coating of nano-sized materials of different morphologies in order to enhance the heat-fastness and color performance of said color pigments. In particular, the present invention provides a method to coat oxide-based color pigments with nano-sized coating materials, including but not limited to, alumina and/or silica at different dosage levels, with nanofiber, nanoneedle, nano spike, nanoplate, nanoflower morphology towards enhancing the heat-fastness and color performance to said color pigments for cement coloring, road painting, and other high-performance pigments, etc.