Aluminum pigments encapsulated by inorganic-organic hybrid coatings and their stability in alkaline aqueous media.Introduction Lamellar lamellar /la·mel·lar/ (lah-mel´ar) 1. pertaining to or resembling lamellae. 2. lamellated (1). lamellar pertaining to or emanating from lamella. aluminum pigments ("aluminum flakes") have been used in solventborne metallic paints or inks for many years (1) due to their metallic appearance and "flop-effect." (2) Recently, growing importance of environmental considerations have led the paint and coatings industry to the development of coating systems with a reduced content of volatile organic compounds (VOC (Vertical Online Community) See vertical portal. ). (2,3) Waterborne coatings are the preferred way to solve the problem. However, since the waterborne coatings are mostly prepared in an alkaline medium, the aluminum pigments react with water: 2Al + 6[H.sub.2]O [right arrow] 2Al(OH)[.sub.3] + 3[H.sub.2] [up arrow] (Under neutral or slightly alkaline media) 2Al + 2O[H.sup.-] + 6[H.sub.2]0 [right arrow] 2Al(OH)[.sub.4.sup.-] + 3[H.sub.2] [up arrow] (Under strongly alkaline media) resulting in severe deterioration of metallic luster and dangerous pressure build up in the storage vessels. (1-7) As mentioned above, aluminum flakes, as a kind of metallic pigments, possess a bright, metallic luster. Therefore, corrosion inhibition of aluminum pigments must take care not to damage their appearance or shield their luster. In regard to aluminum sheets, focus is given to how to inhibit their corrosion in various conditions regardless of the luster. Considering the difference between corrosion inhibition of aluminum pigments and sheets, the method adopted for aluminum pigments stabilization in aqueous media can be divided into two principal categories (8): the adsorption adsorption, adhesion of the molecules of liquids, gases, and dissolved substances to the surfaces of solids, as opposed to absorption, in which the molecules actually enter the absorbing medium (see adhesion and cohesion). of corrosion inhibitors on the pigment surface (1,3-7,9-18) and the encapsulation of the pigment with a protective coating. (2,8,19-22) The encapsulation method is more promising since the protective layer can insulate the aluminum pigments from the corrosion medium. Inorganic coatings, such as Si[O.sub.2], show excellent mechanical strength, but poor compatibility with resins and other organic compounds contained in waterborne coatings. With regard to organic coatings, the poor adhesion of the coating material to the aluminum surface greatly limits their application. The combination of inorganic and organic compounds for the encapsulation of the aluminum pigments may be more effective and promising, but few reports have been found in this field until now. The sol-gel process, involving the hydrolysis hydrolysis (hīdrŏl`ĭsĭs), chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds. and condensation of the metal alkoxide (typically tetraethoxysilane (TEOS TEOS Tetraethylorthosilicate TEOS Tetra Ethyl Oxysilane TEOS Trusted E-Mail Open Standard )), has been used for corrosion protection of aluminum (8) by condensation of the sol-gel film as a barrier layer on the aluminum surface. Silane silane or silicon hydride Any of a series of inorganic compounds of silicon and hydrogen with covalent bonds and the general chemical formula SinH(2n + 2). coupling agents can be incorporated into the sol-gel network to enhance the adhesion between the inorganic surface and the organic compound. One of the well-known silane coupling agents is vinyltriethoxysilane (VTES VTES Vampire: The Eternal Struggle (trading card game) ), which can readily react with themselves and other metal alkoxides to form hybrid inorganic/organic polymers. (23) In addition, organic functional group of the silane coupling agent can further polymerize polymerize /po·lym·er·ize/ (pah-lim´er-iz) to subject to or to undergo polymerization. pol·y·mer·ize v. To undergo or subject to polymerization. with the organic monomers to form a polymeric layer. In this article, aluminum pigments encapsulated by novel inorganic-organic hybrid coatings were reported. The structure and morphology of the encapsulation was characterized by means of FTIR FTIR Fourier Transform Infrared (spectroscopy) FTIR Frustrated Total Internal Reflection FTIR Fourier Transfer Ir , SEM, and XPS (1) See XML Paper Specification. (2) A brand name for certain models of Inspiron laptops from Dell. . Furthermore, the stability of the coated aluminum pigments in alkaline aqueous media was also measured. Experimental Materials Raw materials used are listed in Table 1. Aluminum pigments (median particle size of 30 [micro]m) were washed with ethanol and distilled water before encapsulation, then dried under vacuum at 50[degrees]C. TEOS and VTES were purified by distillation prior to use. Styrene sty·rene n. A colorless oily liquid from which polystyrenes, plastics, and synthetic rubber are produced. Also called vinylbenzene. (St) monomer was washed with 100 mol [m.sup.-3] sodium hydroxide solution to remove inhibitor and purified by reduced pressure distillation. 2,2'-azobis (isobutyronitrile) (AIBN AIBN Australian Institute for Bioengineering and Nanotechnology (Brisbane, Australia) AIBN Azobis-Isobutyronitrile ), used as an initiator, was recrystallized prior to use. Absolute ethanol, ammonia solution, maleic acid anhydride anhydride (ănhī`drīd, –drĭd) [Gr.,=without water], chemical compound formed by removing water, H2O, from another compound; the anhydride can also react with water to form the original compound. (MAA MAA abbr. macroaggregated albumin ), divinylbenzene (DVB (Digital Video Broadcasting) An international digital television (DTV) standard that is the European and Far Eastern counterpart of the North American ATSC standard. ), and N-methyl-2-pyrrolidone (NMP NMP New Millennium Program (NASA) NMP National Military Park (National Park Service) NMP N-Methylpyrrolidone NMP Network Management Protocol NMP Not My Problem ) were used as received without further purification. Encapsulation Two grams of aluminum pigments and 50 mL of ethanol were put into a four neck-round bottom flask connected to a condenser condenser Device for reducing a gas or vapour to a liquid. Condensers are used in power plants to condense exhaust steam from turbines and in refrigeration plants to condense refrigerant vapours, such as ammonia and Freons. , thermometer, and nitrogen gas inlet/outlet. The solution was stirred at room temperature for 1 h and then heated to 40[degrees]C. About 3 mL ammonia and 5 mL distilled water diluted by 30 mL ethanol, TEOS and VTES also diluted by 30 mL ethanol, were added drop-to-drop over a period of 1 h to the solution simultaneously (the quantities of TEOS and VTES used in the experiment are listed in Table 2). The mixing solution was further stirred for 6 h. Then the solution was heated to 80[degrees]C. The monomer mixture of St, DVB, and MAA (dissolved in 10 mL ethanol) was dropped into the above-mixed solution over a 1-h period. (The quantities of the monomers used in the experiment are also listed in Table 2.) Simultaneously, a solution of 1% (on monomers, dissolved in NMP and diluted by 10 mL of ethanol) AIBN was added. The post-reaction time was 24 h. The solution was subsequently filtered and washed with ethanol. The resulting pigments were dried under vacuum at 60[degrees]C for 5 h. Characterization Fourier transform infrared (FTIR) measurements were carried out by using a Bruker Vector 33 spectrometer to characterize the functional groups of the pigments. The samples were ground with dried potassium bromide (KBr) powder, and compressed into a disk. The KBr disk was subjected to analysis by an IR spectrophotometer spectrophotometer, instrument for measuring and comparing the intensities of common spectral lines in the spectra of two different sources of light. See photometry; spectroscope; spectrum. . The scanning electron microscopy (SEM) investigations were performed with a Philips FEI FEI Fédération Équestre Internationale. XL-30 ESEM ESEM Environmental Scanning Electron Microscope ESEM International Symposium on Empirical Software Engineering and Measurement ESEM Experiment of Space Environment with Materials ESEM Ethernet Service Expansion Module . X-ray photoelectron spectroscopy X-ray Photoelectron Spectroscopy (XPS) is a quantitative spectroscopic surface chemical analysis technique used to estimate the empirical formula or elemental composition, chemical state and electronic state of the elements on the surface (upto 10 nm) of a material. (XPS) is a surface sensitive analysis technique. The XPS spectra were obtained on a Kratos Axis Ultra (DLD DLD Dihydrolipoamide Dehydrogenase (deficiency) DLD Domestic Long Distance DLD Digital Lifestyle Device DLD Deutsche Linux Distribution DLD Developmental Language Disorder DLD Don't Look Down (band) ) photo-electron spectrophotometer with a magnesium anode anode (ăn`ōd), electrode through which current enters an electric device. In electrolysis, it is the positive electrode in the electrolytic cell. anode Terminal or electrode from which electrons leave a system. (Mg K[alpha] 1253.6 eV). The pigments were irradiated with photons from a soft x-ray source with a well-defined energy. The survey scan was from 0 to 1100 eV to find atoms of surface. To evaluate the effect of the encapsulation described in this article, the stability test was carried out. About 0.6 gram of the encapsulated or unencapsulated aluminum pigments were dispersed in sodium hydroxide solutions at pH 11 in 60 mL glass bottles and stored at room temperature for 720 h. The hydrogen evolved was collected to estimate the effect of the encapsulation. The pH was adjusted to 11 if necessary. The corrosion protection efficiency (P, %) was calculated using the following equation: P = [[[V.sub.unenc] - [V.sub.enc]]/[V.sub.unenc]] x 100% where the [V.sub.unenc] and [V.sub.enc] are the evolved hydrogen volume of the unencapsulated and encapsulated aluminum pigments in the stability tests, respectively. Results and discussion Encapsulation process The flowchart for preparation of the hybrid inorganic and organic coatings is given in Fig. 1. The ethoxy eth·ox·y n. The univalent radical C2H5O. adj. Relating to or containing the ethoxy radical. group of the TEOS and VTES hydrolyze hydrolyze to performance hydrolysis. and condense in the ethanol/water media under catalysis catalysis Modification (usually acceleration) of a chemical reaction rate by addition of a catalyst, which combines with the reactants but is ultimately regenerated so that its amount remains unchanged and the chemical equilibrium of the conditions of the reaction is not of the ammonia solution. On the other hand, there is a layer of aluminum oxide on the surface of the aluminum pigments due to its exposure to the air. The surface of the aluminum oxide layer in a humid or moist environment has a significant population of hydroxyl groups. (24) These surface hydroxyls can participate in the sol-gel condensation reaction of the TEOS and VTES to form a chemical linkage, Si-O-Al, between the aluminum and the silicon sol-gel film. This chemical bond formation produces the strong interaction of the sol-gel layer with the aluminum surface. Moreover, the vinyl radical of the VTES can further polymerize with the St, DVB, and MAA. Herein, the DVB was used as crosslinker. The FTIR spectra of pure VTES, St-DVB-MAA copolymer copolymer: see polymer. , untreated aluminum pigments, TEOS- and VTES-coated (TV-coated) pigments and TEOS-VTES-St-DVB-MAA coated (TVSDM-coated) pigments are shown in Fig. 2. In the spectrum of TV-coated pigments, the new characteristic peaks near 1125 and 1082 [cm.sup.-1] appeared, which are assigned to the asymmetric stretch of the Si-O group. (25,26) This indicates that TEOS and VTES deposited on the surface of aluminum pigments. The shift of the band position near 1105 [cm.sup.-1] (pure VTES) to 1125 [cm.sup.-1] (TV-coated pigments) suggests the reaction of TEOS and VTES in the sol-gel process. The band near 3434 [cm.sup.-1] is assigned to the vibration modes of the Si-OH group, (27) which demonstrates that ethoxy group of TEOS and VTES hydrolyzed in the sol-gel reaction. In the spectrum of TVSDM-coated pigments, the new bands near 1608, 1496, 760, and 698 [cm.sup.-1] are assigned to the vibration modes of St and DVB, (28,29) while the bands near 1712 [cm.sup.-1] refer to the vibration modes of MAA. (30) To further demonstrate the copolymerization copolymerization (kōpäl´im  rizā´sh of St
with VTES, the FTIR spectra of pure VTES, St-MAA-DVB copolymer and
TVSDM-coated aluminum pigments are shown in Fig. 3. The absorption peak
near 1600 [cm.sup.-1] is attributed to stretch of C=C group. (25,27) As
seen from Fig. 3c, it is obvious that the peak of C=C bond disappeared,
indicating further polymerization polymerizationAny process in which monomers combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many thousands—may or may not all be the same. of St-MAA-DVB copolymer with vinyl group of VTES. [FIGURE 1 OMITTED] [FIGURE 2 OMITTED] [FIGURE 3 OMITTED] The SEM micrographs of the aluminum pigments are shown in Fig. 4. The surface of the uncoated aluminum pigments is basically smooth except for some granules Granules Small packets of reactive chemicals stored within cells. Mentioned in: Allergic Rhinitis, Allergies , which are tiny fragments of the aluminum pigments. Comparing the surface of the TV-coated aluminum pigments with that of uncoated aluminum pigments, it is clearly seen that many granules, which are congeries con·ge·ries n. (used with a sing. verb) A collection; an aggregation: "Our city, it should be explained, is two cities, or more of the hydrolysate hydrolysate /hy·drol·y·sate/ (hi-drol´i-sat) any compound produced by hydrolysis. protein hydrolysate of TEOS and VTES, appear on the surface of the aluminum pigments. As seen from Fig. 4c, the polymeric layer is obviously observed for the TVSDM-coated aluminum pigments. [FIGURE 4 OMITTED] Figure 5 presents the results of XPS measurements for further quantitative analysis of the elements and components on the surface of aluminum flakes. The spectrum of the bare Al flakes (Fig. 5a) shows signals due to the presence of oxygen (531.32 eV, O 1s); carbon (284.32 eV, C 1s) and aluminum atoms (73.32 eV, Al 2p). The characteristic peaks of Si 2s and Si 2p in Fig. 5b reveal that the presence of Si element on the surface of the particles is evident, which suggests that TEOS and VTES have been successfully bonded onto the Al flakes. In Fig. 5c, the characteristic peaks of Si 2s and Si 2p become more obvious compared with those in Fig. 5b; at the same time, the peak corresponding to Al element cannot be detected. Furthermore, the specification of elemental contents on the surface of the Al flakes is shown in Table 2. It is found that on the surface of the TVSDM-coated Al, the content of Al is zero, which also further demonstrates that the encapsulation of aluminum pigments was successfully prepared in our experiment. [FIGURE 5 OMITTED] Stability tests Figure 6 shows the time dependence of the hydrogen evolution for TV-coated and TVSDM-coated aluminum pigments. For comparison, the time dependence of the hydrogen evolution for the untreated aluminum pigments is also shown. Within about 100 h, the untreated aluminum pigments evolve hydrogen slowly. However beyond 100 h, the corrosion reaction accelerates and more hydrogen evolved. Within 120 h, the untreated pigments react completely. Within 720 h, both the TV-coated and TVSDM-coated pigments evolve much less hydrogen than the untreated pigments do, which reveals that the encapsulation layer formed on the surface of the aluminum pigments can protect them effectively. The comparison of the time dependence of the hydrogen evolution of the TV-coated pigments with that of the TVSDM-coated pigments shows the superiority of the latter. [FIGURE 6 OMITTED] Comparison of the hydrogen volumes evolved within 720 h for both TV-coated and TVSDM-coated aluminum pigments is shown in Fig. 7. There is a relationship between the hydrogen volume evolved within 720 h and the content of the TEOS or MAA in the polymeric network: the evolved hydrogen volume decreases with the increase of the content of the TEOS or MAA. The #5 and #8 (see Table 3) encapsulated aluminum pigments show best stability in the alkaline aqueous media of pH 11, the corrosion protection efficiency of which is both 99.8%. [FIGURE 7 OMITTED] Conclusions The investigation shows that the sol-gel method can be used to encapsulate aluminum pigments. However, specific conditions are necessary to achieve good stability in alkaline aqueous media. The most important factor is to form a protecting layer on the surface of the aluminum pigments. It was found that in the solgel process, the TEOS and VTES could condense on the aluminum pigments surface as a barrier layer and further copolymerize co·pol·y·mer·ize v. co·pol·y·mer·ized, co·pol·y·mer·iz·ing, co·pol·y·mer·iz·es v.tr. To polymerize (different monomers) together. v.intr. To react to form a copolymer. with St, DVB, and MAA monomers to form a compact protecting layer. The stability test shows that the sol-gel derived inorganic-organic hybrid coatings can give the aluminum pigments significantly improved storage stability in alkaline aqueous media. Acknowledgments We are grateful for the support of Miss Shu-Yi Zhu, Mr. Yang (for SEM), Mr. Jiang (for FTIR) and Mr. Yin (for XPS) for their experimental and measurement contributions. References 1. Miller, B, Paulus, A, Lettmann, B et al., "Amphiphilic am·phi·phil·ic adj. Of or relating to a molecule having a polar, water-soluble group attached to a nonpolar, water-insoluble hydrocarbon chain. Maleic Acid Copolymers as Corrosion Inhibitors for Aluminum Pigment." J. Appl. Polym. Sci., 69 2169-2174 (1998) 2. Batzilla, Th., Tulke, A., "Preparation of Encapsulated Aluminum Pigments by Emulsion Polymerization and their Characterization." J. Coat. Technol., 70 77-83 (1998) 3. Iriyama, Y, Ihara, T, Kiboku, M, "Plasma Polymerization of Tetraethoxysilane on Aluminum Granules for Corrosion Protection." Thin Solid Films, 287 169-173 (1996) 4. Muller, B, Schmelich, T, "High-Molecular Weight Styrene-Maleic Acid Copolymers as Corrosion Inhibitors for Aluminium Pigments." Corros. 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7. Muller, B, "Corrosion Inhibition of Different Metal Pigments in Aqueous Alkaline Media." Corros. Sci., 43 1155-1164 (2001) 8. Kiehl, A, Greiwe, K, "Encapsulated Aluminium Pigments." Prog. Organic Coat., 37 179-183 (1999) 9. Maayta, AK, Al-Rawashdeh, NAF NAF National Arbitration Forum NAF National Academy Foundation NAF National Abortion Federation NaF sodium fluoride NAF Naval Air Facility NAF National Ataxia Foundation NAF New America Foundation (think tank) , "Inhibition of Acidic Corrosion of Pure Aluminum by some Organic Compounds." Corros. Sci., 46 1129-1140 (2004) 10. Muller, B, "Corrosion Inhibition of Aluminium and Zinc Pigments by Saccharides." Corros. Sci., 44 1583-1591 (2002) 11. Foad El-Sherbini, EE, Abd-El-Wahab, SM, Deyab, MA, "Studies on Corrosion Inhibition of Aluminum in 1.0 M HCl and 1.0 M [H.sub.2]S[O.sub.4] Solutions by Ethoxylated Fatty Acids." Mater. Chem. Phys., 82 631-637 (2003) 12. Abd El Rehim, SS, Hassan, HH, Amin, MA, "Corrosion Inhibition of Aluminum by 1,1(lauryl amido)propyl propyl /pro·pyl/ (pro´pil) the univalent radical CH3CH2CH2—, from propane. pro·pyl n. A univalent organic radical, CH3CH2CH2, derived from propane. ammonium chloride in HCl Solution." Mater. Chem. Phys., 70 64-72 (2001) 13. Ashassi-Sorkhabi, H, Ghasemi, Z, Seifzadeh, D, "The Inhibition Effect of some Amino Acids Towards the Corrosion of Aluminum in 1 M HCl + 1 M [H.sub.2]S[O.sub.4] Solution." Appl. Surf. Sci., 249 408-418 (2005) 14. El-Etre, AY, "Inhibition of Acid Corrosion of Aluminum Using Vanillin va·nil·lin n. A white or yellowish crystalline compound found in vanilla beans and certain balsams and resins and used in flavorings and pharmaceuticals. ." Corros. Sci., 43 1031-1039 (2001) 15. Muller, B, "Aromatic 2-Hydroxy-Oximes as Corrosion Inhibitors for Aluminum and Zinc Pigments." Corros. Sci., 39 1469-1477 (1998) 16. Muller, B, "Polymeric Corrosion Inhibitors for Aluminum Pigment." React. Funct. Polym., 39 165-177 (1999) 17. Muller, B, "Stabilization of Aluminum Pigments in Aqueous Alkaline Media by Styrene Copolymers." J. Coat. Technol., 67 (846) 59-62 (1995) 18. Carpenter, et al, "Nitro-Substituted Polymeric Corrosion Inhibitors for Aluminum Flake Pigment." [P]. U. S. 5,389,139, 1995-2-14 19. Zabel, KH, Boomgaard, RE, Thompson, GE et al., "Properties of Ketimine/Acetoacetate Coated Aluminum Substrates." Prog. Organic Coat., 34 236-244 (1998) 20. Takashi, K, Kenji, Y, "Polymer Coated Aluminum Pigment having Water Dispersible Property and Method for Producing the Same." [P]. JP2004292690, 2004-10-21 21. Shuichi, N, Kazuo, K, "Resin-Coated Aluminum Pigment." [P]. JP2005146111A, 2005-6-9 22. Shuichi, N, "Silica-Coated Aluminum Pigment and its Manufacturing Method." [P]. JP2002088274, 2002-3-27 23. Tanoglu, M, McKnight, SH, Palmese, GR et al., "Use of Silane Coupling Agents to Enhance the Performance of Adhesively Bonded Alumina to Resin Hybrid Composites." Int. J. Adhesion Adhesives, 18 431-134 (1998) 24. Joshua Du, Y, Damron, M, Tang, G et al., "Inorganic/Organic Hybrid Coatings for Aircraft Aluminum Alloy Substrates." Prog. Oragnic Coat., 41 226-232 (2001) 25. Li, Y-S, Wright, PB, Puritt, R et al., "Vibrational Spectroscopic spec·tro·scope n. An instrument for producing and observing spectra. spec  tro·scop Studies of Vinyltriethoxysilane Sol-Gel and its
Coating." Spectrochim. Acta Part A, 60 2759-2766 (2004)
26. Yeh, J-M J-M Jelinski-Moranda (reliability model) , Weng, C-J, Liao, W-J et al., "Anticorrosively Enhanced PMMA-Si[O.sub.2] Hybrid Coatings Prepared from the Sol-Gel Approach with MSMA MSMA monosodium methanearsonate; an organic arsenical herbicide which can cause poisoning characterized by the signs of organic arsenic poisoning. as the Coupling Agent." Surf. Coat. Technol., 201 1788-1795 (2006) 27. Flis, J, Kanoza, M, "Electrochemical electrochemical /elec·tro·chem·i·cal/ (-kem´i-k'l) pertaining to interaction or interconversion of chemical and electrical energies. e·lec·tro·chem·i·cal adj. and Surface Analytical Study of Vinyl-Triethoxy Silane Films on Iron after Exposure to Air." Electrochim. Acta, 51 2338-2345 (2006) 28. Rong, Yu, Chen, H-Z, Li, H-Y et al., "Encapsulation of Titanium Dioxide Particles by Polystyrene via Radical Polymerization." Colloids Surf. A: Physicochem. Eng. Aspects, 253 193-197 (2005) 29. Deng, J, Yang, W, "Grafting Copolymerization of Styrene and Maleic Anhydride Binary Monomer Systems Induced by UV Irradiation." Eur. Polym. J., 41 2685-2692 (2005) 30. Switala-Zeliazkow, M, "Thermal Degradation of Copolymers of Styrene with Dicarboxylic di·car·box·yl·ic adj. Containing two carboxyl groups per molecule. Adj. 1. dicarboxylic - containing two carboxyls per molecule Acids--II: Copolymers Obtained by Radical Copolymerisation of Styrene with Maleic Acid or Fumaric Acid." Polym. Degrad. Stability, 91 1233-1239 (2006) [c] FSCT FSCT Federation of Societies for Coating Technology FSCT Fire Support Control Terminal and OCCA OCCA Oklahoma Court of Criminal Appeals OCCA Oil & Colour Chemists' Association OCCA Oregon Community College Association OCCA Orthodox Catholic Church of America OCCA Organized Crime Control Act OCCA Open Cooperative Computing Architecture 2007 L.-J. Li ([mailing address]), P.-H. Pi, X.-F. Wen, J. Cheng, Z.-R. Yang School of Chemical and Energy Engineering, South China University of Technology South China University of Technology (SCUT) is a Chinese university located in Guangzhou, capital of the Guangdong province in mainland China. In 1999, SCUT ranked No. 23 among Asia's Best Universities by Asiaweek[1]. , Guangzhou 510640, P.R. China e-mail: lilijunscut@yahoo.com.cn; lilijunscut@hotmail.com
Table 1: Raw materials
Materials Grade
Aluminum pigments [greater than or equal to]99%,
~30 [micro]m
Absolute ethanol [greater than or equal to]99.5%
Ammonia solution 25-28% (a)
Tetraethoxysilane [greater than or equal to]28.5% (b)
Vinyltriethoxysilane [greater than or equal to]98%
Styrene [greater than or equal to]99%
Maleic acid anhydride [greater than or equal to]99.5%
Divinylbenzene 55.2%
2,2'-azobis (isobutyronitrile) [greater than or equal to]99%
N-methyl-2-pyrrolidone [greater than or equal to]99.8%
Materials Manufacturer
Aluminum pigments Tianlong Trade Co., Ltd.
Absolute ethanol Union Chemical Industry Reagent Research
Institute
Ammonia solution Donghong Chemical Co., Ltd.
Tetraethoxysilane Guanghua Chemical Co., Ltd.
Vinyltriethoxysilane Kete Fine Chemical Industry Co., Ltd.
Styrene Lingfeng Chemical Reagents Co., Ltd.
Maleic acid anhydride Xingang Chemical Co., Ltd.
Divinylbenzene Shengzhong Fine Chemical Co., Ltd.
2,2'-azobis (isobutyronitrile) Kermel Chemical Reagents Development
Centre
N-methyl-2-pyrrolidone Kermel Chemical Reagents Development
Centre
(a) N[H.sub.3] content
(b) Si[O.sub.2] content
Table 2: Elemental content on the surface of aluminum flakes
Elemental content/%
Sample Si Al O C
Uncoated Al 0 26.094 22.101 51.805
TV-coated Al 18.900 9.743 40.006 31.351
TVSDM-coated Al 32.730 0 50.660 16.610
Table 3: Specifications of the materials used for encapsulation
Sample TEOS: VTES (molar ratio) St: MAA (molar ratio) P/%
#1 -- -- --
#2 1:1 -- 93.4
#3 3:2 -- 95.6
#4 3:1 -- 97.3
#5 1:1 4:1 99.8
#6 1:1 5:2 97.8
#7 1:1 1:1 95.6
#8 3:1 1:1 99.8
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