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Research of MicaFe3O4 Pearlescent Pigment by CoPrecipitation1

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  • Research of MicaFe3O4 Pearlescent Pigment by CoPrecipitation1

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As the pH value is the most important parameter in coprecipitation of Fe3+ and Fe2+, the other 4 param eters were fixed firstly, namely the condition of reac tion temperature was 30°C, t[r] (1)ISSN 10876596, Glass Physics and Chemistry, 2011, Vol 37, No 3, pp 330–342 © Pleiades Publishing, Ltd., 2011 Research of Mica/Fe3O4 Pearlescent Pigment by CoPrecipitation1 Liang Xiaojuana, c, Xu Haiquanb, Chen Jingb, Sun Juncaia, Yang Yuxiangb,*, and Liu Xiangnongd a Dalian Maritime University, Dalian, 116026, P R China Department of Chemistry, East China University of Science and Technology, Shanghai, 200237, P R China *email: yuxyang@online.sh.cn c College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, 325035, P R China d Testing Center, Yangzhou University, Yangzhou, 225009, P R China b Received May 19, 2010 Abstract—Experiments on preparation of mica/Fe3O4 pearlescent pigment were performed to discuss influ ences of several crucial parameters on final products The samples were characterized by XRD, HRSEM, FTIR and color measurement, the content of Fe3O4 on the mica surface was also analyzed by XPS It was found that the smoothness, compactness and colour deepness of the coating were influenced by different pH values and temperatures The optimum preparation parameters of mica/Fe3O4 pearlescent pigment were obtained: the value of pH ≥ 9.2; the concentration of sodium hydroxide was 0.5 mol/l; the concentration ratio of Fe3+ to Fe2+ was 1.6 : 1; the velocity of magnetic stirring was 138 ≤ v ≤ 151 r/min; reaction temperature was 70–80°C; calcination temperature was 350°C and calcination time was h Keywords: coprecipitation, pearlescent pigment, mica DOI: 10.1134/S1087659611030084 INTRODUCTION Mica is elastic, curving and highly resistant to abra sion and wearing, as well as heating Moreover, mica is insoluble in acid and alkali solution, and it is chemical stable, so it is a good substrate for preparation of pearl escent pigment At present, oxide compounds depos ited on the mica surface to prepare pearlescent pig ment include: TiO2, ZrO2, SnO2, Cr2O3, Fe2O3, Al2O3, SiO2, ZnO, Fe3O4, and so on [1–4] Usually preparation of mica/Fe3O4 is under condi tion of certain pH value and temperature Firstly a cer tain molar ratio salt solution of Fe2+ and Fe3+ is put in to the mica suspension to coprecipitate to form Fe3O4, then the resulting product is calcined in inert atmosphere to produce mica/Fe3O4 In a second method, bivalent iron salt reacts directly with certain amount of oxidant, then it is precipitated in mica sus pension and calcined in inert atmosphere to produce mica/Fe3O4 [2] In another method, Fe2O3 is depos ited on the mica surface, then calcined to prepare mica/Fe3O4 through controlling the amount of reduc ing gas [3, 4] But there are problems in these methods: when using oxidant to oxidize bivalent iron, it is very difficult to control the accurate proportion, because the bivalent iron itself can be easily oxidized in the air; and when mica/Fe2O3 is reduced in reducing atmo sphere, the demands for eduipment and operation are The article is published in the original higher All these limit the largescale production and development of mica/Fe3O4 composites Recent years, there are few researches on Fe3O4 deposited on the mica surface to prepare pearlescent pigment in China Comparing to separate Fe3O4 or mica, mica/Fe3O4 has one or more layers of mica When the light shines on the surface of Fe3O4, it is par tially reflected and partially penetrates into mica, then reflected again, resulting in one more mica reflecting light, which will further penetrate into the surface layer of Fe3O4 and interfere with the reflecting light of Fe3O4 surface Owing to different colors and sizes, mica/Fe3O4 not only features a graceful gloss, but also possesses colour sensation, gentle or twinkle appear ance, which help it to gain more and more applica tions in industries In this paper coprecipitation method was used to produce pearlescent pigment by depositing the newlyformed nano Fe3O4 particles onto mica surface under controlled pH conditions, the effects of pH values, temperatures, sodium hydroxide concentrations, molar ratios of C Fe3+ / C Fe2+ , on the smoothness, compactness and colour deepness of the coating were determined EXPERIMENTAL Instruments and Equipments Constantflow pump, peristaltic pump BT501J, pH controller DICAWOP24000G210E, temperature 330 (2) RESEARCH OF MICA/Fe3O4 PEARLESCENT PIGMENT BY CoPRECIPITATION 331 Preparation of mica/Fe3O4 All reagents were analytically pure, and the distilled water used was boiled for five minutes to eliminate oxygen mica/Fe3O4 was synthesized as follows: first, by 100 ml of boiled distilled water and 10 g of mica were put into a beaker, and then the suspension was made by magnetic stirring In the atmosphere of nitro gen, a certain molar ratio of the mixed solution of FeCl3 ⋅ 6H2O and FeCl2 ⋅ 4H2O was put into the beaker with a peristaltic pump, then a certain amount of sodium hydroxide solution was dropped into the bea ker under controlled pH conditions by using pH con troller After all reactants were added, the suspension was stirred for half an hour to complete the reaction Then the product was filtered, washed and dried at 60°C in vacuum, then the dry product was calcined in tube type electricresistance furnace at 350°C for h in nitrogen gas flow In the experiment the coprecipitation method was used to coat one layer of nanometer Fe3O4 on the mica surface The experimental principle is described by the following reactions: mica/Fe2+/Fe3+ + OH– mica/Fe(OH)2/Fe(OH)3, mica/Fe(OH)2/Fe(OH)3 mica/FeOOH + Fe2+ mica/FeOOH, mica/Fe3O4 + H+ In an ideal situation the ratio of Fe3+ to Fe2+ should be : 1, but in actual operation Fe2+ is easily oxidized in the air, therefore, for obtaining the mica surface coated with highpurity Fe3O4, the oxidation of Fe2+ should be taken into consideration, and the ratio of Fe3+ to Fe2+ should be smaller than : [5] Determination of Percent of Coated Fe3O4 in the Sample Structure analyses As seen from Fig 1, the mica diffraction peak appears at 17.5, 26.5, 35.8, and 45.1° The Fe3O4 coated mica sample was prepared under the condition of pH 9.2, CNaOH equals to 0.5 mol/l, C Fe3+ / C Fe2+ at 1.6 : 1, and v: 138~151 r/min at the temperature of 75°C, corresponding to the 2M1 white mica (001) reflection peak: 5.06 (004), 3.36 (006), 2.51 (008), and 2.01 Å (0010), respectively [6] All (001) reflection peaks intensity are strong in Fig 1, moreover, the peak shape is sharp and symmetrical, indicating that the crystallinity of the chosen in the experiment mica was high The diffraction peak of the chosen in the experiment Fe3O4 appeared at 2θ = 30, 35.4, 43.1, 53.7, 57.1 and 62.8°, corresponding to 2.98 (220), 2.53 (311), 2.10 (400), 1.70 (422), GLASS PHYSICS AND CHEMISTRY Vol 37 No Intensity, a.u indicating controller WMZK01, tubular resistance furnace SK2212, electiric vacuum drying oven, Color i5 type color measurement device 311 200 511 422 400 440 10 20 30 40 50 60 70 80 2θ, deg Fig XRD patterns of mica (1), nanometer Fe3O4 parti cles (2), Fe3O4 coated mica sample (3) 1.61 (511), and 1.48 Å (440) crystal face of cubic phase Fe3O4, respectively [7] After mica surface was coated by Fe3O4, the diffraction peaks of the sample appeared at 2θ = 17.5, 26.5, and 45.1°, corresponding to the characteristic diffraction peak of mica; while weak dif fraction, peaks appeared at 2θ = 35.4, 43.1, 57.1, and 62.8°, corresponding to the characteristic diffraction peak (311), (400), (511), and (440) of Fe3O4, indicat ing that Fe3O4 has been coated the mica surface Determination of Fe3O4 Coating Rate on the Mica Surface The external standard method [8] was used to cal culate the content of Fe3O4 coated the mica surface, which is described as follows: Cs = fs Hs , (1) Ci = fi Hi , (2) then (1) : (2) and obtains: C H i = F i , Hs Cs (3) where Hs and Hi are peak intensity of mica and Fe3O4, Cs and Ci are mass concentration of mica and Fe3O4 respectively, and F is a proportional coefficient In this study analytical pure Fe3O4 and dry mica were mixted uniformly with mass ratio of : 1, : 2, : 4, : 6, : 8, and : 9, respectively, and the mixed samples were determined by XRD The peak intensity corresponding to Fe3O4 was determined, using the strongest characteristic peak (311) as main base peak It is found that the normalized XRD peak (311) inten sity was directly proportional to the mass ratio of pure Fe3O4 to mica, and thus the standard curve was plotted by normalized XRD peak (311) intensity versus per 2011 (3) XRD peak (311) intensity 332 XIAOJUAN et al Quantification of Color Characteristic of the Product 0.6 0.5 0.4 0.3 0.2 0.1 0.2 0.4 0.6 0.8 Percent of coated Fe3O4, % 1.0 Fig Standard curve of normalized XRD peak (311) intensity versus percent of coated Fe3O4 cent of coated Fe3O4 to determine the percent of coated Fe3O4 in the sample (Fig 2) ΔE *ab = Generally the CIE 1976 L* a* b* color coordinates system, which was stipulated by International Illumina tion Committee in 1976, is used to quantify the color char acteristic of Fe3O4 coated mica sample At present, this coordinate system is taken as industrial standard to appraise pigment color intensity precisely [9, 10], where L* stands for luminance value, a* and b* stand for chro maticity coordinate, a* represents red (+), green (–); b* represents yellow (+), blue (–) The color difference in two measurements, such as chromaticity difference between two different pigments, can be shown through the ΔE *ab parameter from the L* a* b* color coordinate system Therefore, the color instrumental measurement was used to determine L*, a*, and b* value of different kinds of Fe3O4 coated micas prepared in the experiment, and the black ferric oxide pigment produced by German Baier pig ment Ltd Co is taken as the standard substance to com pare with Then the product quality was determined by calculating ΔE *ab as follows: 2 ( L *Sample – L *Standard ) + ( a *Sample – a *Standard ) + ( b *Sample – b *Standard ) The higher the ΔE *ab value, the more significant the pearly luster effect is [11] The standard colorimetric parameters are determined: L* = 38.80, a* = +0.39, b* = –0.57, and colorimetric parameters of various coated samples determined under different conditions are shown in Tables 1–5 RESULTS AND DISCUSSION Influence of Different Parameters on Coating and Pearly Luster Effect Influence of different pH values on coating and pearly luster effect According to the condition in preparation of nanoFe3O4 coated mica, five parame ters were selected in the experiment: the coprecipita tion pH value of Fe3+ and Fe2+ [12], the NaOH con centration used in precipitation, the molar ratio of Fe3+ to Fe2+ [13], the stirring speed and crystallization temperature of preparation of nanometer Fe3O4 mem brane [14] And orthogonal experiments of these parameters were designed to prepare mica/Fe3O4 by liquid phase coprecipitation method As the pH value is the most important parameter in coprecipitation of Fe3+ and Fe2+, the other param eters were fixed firstly, namely the condition of reac tion temperature was 30°C, the concentration of sodium hydroxide solution was 0.5 mol/l, the ratio of Fe3+ to Fe2+ was 1.364 : 1, as well as the velocity of magnetic stirring was 138 ≤ v ≤ 151 r/min, then the influence of pH value on coating shape was studied The high resolution scanning electron microscope (HRSEM) patterns of Fe3O4 coated mica under dif ferent pH condition are shown in Fig Figure 3a is the HRSEM pattern of mica substrate, showing that the surface of mica was bright and clean before mica was coated by nanoFe3O4 particles, and the mica changed into different shape after coating, as shown in Fig 3b–3f As demonstrated in Fig 3c, when pH value was exactly the coprecipitation pH value of Fe3+ and Fe2+, the Fe3O4 particles were quite evenly coated on the mica surface with the average particle diameter within 70–80 nm, thus the coating layer was very com pacted and smooth But when the pH value was lower or higher than 9.2, the density and smoothness of the coating layer are poor Figure 3b is the HRSEM pattern of Fe3O4 coated mica when pH was 8.9, it indicates that the coating layer was not compact and uniform, and the coating rate was the lowest However the value of a* and b* of the sample were the highest (Table 1), and the sample showed obvious red and yellow, it is possibly because Fe2O3 held a major proportion in the sample It is related to the coprecipitation pH value of Fe3+ and Fe2+, according to the solubility product rule, when the pH value was low, Fe3+ preferentially formed βFeOOH in solution, then Fe2O3 was easily produced by calcination, leading to the sample showing red When the pH value was higher than 9.2, namely pH was 9.8 or 10.1 (Figs 3e, 3f), the agglomeration phenom enon of Fe3O4 coating on the mica surface was very seri ous, and the surface was uneven, many “holes” appeared GLASS PHYSICS AND CHEMISTRY Vol 37 No 2011 (4) RESEARCH OF MICA/Fe3O4 PEARLESCENT PIGMENT BY CoPRECIPITATION (а) μm (b) 100 nm (c) 100 nm (d) 100 nm (e) 100 nm (f) 100 nm 333 Fig HRSEM patterns of influence of different pH values on the product: mica substrate (a); pH 8.9 (b); pH 9.2 (c); pH 9.5 (d); pH 9.8 (e); pH 10.1 (f) on the mica surface Moreover, the higher the pH value is, the more “holes” appeared on the mica surface, a* and b* achieved the maximum value, and the sample appeared obvious red and yellow This is because when the pH value of the solution is higher than the coprecip itation pH value of Fe3+ and Fe2+, it is easier to produce GLASS PHYSICS AND CHEMISTRY Vol 37 No Fe(OH)3 than to produce Fe(OH)2, besides Fe3O4 and βFeOOH were produced much faster than their depos iting on the mica surface, causing the instantly produced massive mixture particles depositing unevenly and agglomerating on the mica surface, leading to many “holes” emergence 2011 (5) 334 XIAOJUAN et al Table Colorimetric parameters and the percent of coated Fe3O4 in the coated samples at different pH values Colorimetric parameter L* a* b* * ΔE ab Fe3O4 coating, % Note: t = 30°C; CNaOH pH value 8.9 9.2 9.6 9.8 10.1 47.31 1.51 3.15 43.76 1.09 2.12 41.82 1.32 2.35 43.18 1.50 2.61 42.39 1.46 2.52 9.35 5.69 4.30 5.53 4.86 29.39 33.40 21.82 32.50 36.52 = 0.5 mol/1; Fe3+ : Fe2+ = 1.364 : 1; 138 r/min ≤ Influence of Different Sodium Hydroxide Concentrations on Coating Effect The pH value of the solution has an effect on coat ing layer, besides, the sodium hydroxide solution con centration, causing Fe3+ and Fe2+ to coprecipitate, is also a parameter which can’t be ignored If the initial coprecipitation sodium hydroxide solution concen tration is relatively high, the iron ion will bond with OH– ion during the process of dropping iron salt into alkali As a result the local OH– ion concentration will be oversized and the pH value of the solution will increase greatly Furthermore, it will cause the copre cipitation reaction rate to be much too quick and the size of the obtained magnetic particles on the mica surface to be large On the other hand, if the initial co precipitation sodium hydroxide solution concentra tion is relativly low, the OH– ion concentration of the solution will drop more slowly A low sodium hydrox ide solution concentration will be more preeminent in preparation of coating particles on the mica surface with tiny and even particles Therefore, when parameters were fixed, viz, the reaction temperature was 30°C, the coprecipitation response pH was 9.2, Fe3+ : Fe2+ ratio was 1.364 : and the velocity of magnetic stirring was 138 ≤ v ≤ 151 r/min, then the influence of the initial coprecipitation NaOH concentration on shape of coating layer was studied Under the conditions of CNaOH being 2, 1.5, 1.0, 0.5, and 0.25 mol/l respectively, HRSEM patterns of Fe3O4 coat ing layer on mica are shown in Fig As shown in Fig 4, when the NaOH concentration was mol/l, the Fe3O4 particles agglomerated seri ously on the mica surface, as a result, the coating layer was neither smooth nor compact This is because excessive high local OH– ion concentration induced Fe3+ ion and Fe2+ ion to hydrolyze fast, so the size of the produced Fe3O4 increased and agglomeration par ticles with different sizes and shapes were produced Therefore, the Fe3O4 deposited unevenly on the mica surface and formed the coating layer with uneven sur face As seen in Fig 4a, the coating layer has many “holes”, showing an uncompact structure v ≤ 151 r/min As the NaOH solution concentration decreased in turn, agglomeration phenomenon decreased accord ingly, when the NaOH solution concentration was 0.5 mol/l, compared to other samples, the coating layer showed more smooth and compact, and the coating rate achieved the maximum Therefore, a suit able alkali concentration is critical for forming smooth and compact coating layer (as shown in Figs 4c, 4d) The suitable alkali concentration can cause the pH value of solution to be close to the coprecipitation pH of Fe3+ ion and Fe2+ ion, producing uniform and sphere nanometer Fe3O4 particles in the solution, which were able to subsequently deposit evenly on the suspending mica surface When the NaOH solution concentration was 0.25 mol/l, the alkali concentration was excess low, and the pH value of solution was low in the initial stage, causing Fe3+ easily to precipitate sep arately, leading to red βFeOOH producing And the particles in the solution agglomerated, accompanying with formation of acicular substance, it is not benefi cial to preparation of pure Fe3O4 coating layer on mica Thus, there was obtained a little Fe3O4 and it deposited nonuniformly on the mica surface, form ing uneven and uncompact coating layer (as shown in Fig 4e) The sodium hydroxide concentration also has a sig nificant influence on pearly luster effect, and small size Fe3O4 produced by low concentration sodium hydroxide was coated smoothly on the mica surface, increasing the pearly luster effect obviously When the sodium hydroxide concentration was 0.5 mol/l, ΔE *ab value achieved the maximum, showing that the pearly luster effect was obvious (Table 2) When the sodium hydroxide concentration was 1.5 mol/l, although ΔE *ab value is only the second to the former, mean while, both a* value and b* value of the sample achieved the maximum, so it showed obvious red and yellow, and the Fe3O4 coating layer on the mica surface was not smooth GLASS PHYSICS AND CHEMISTRY Vol 37 No 2011 (6) RESEARCH OF MICA/Fe3O4 PEARLESCENT PIGMENT BY CoPRECIPITATION (а) 100 nm (b) 100 nm (c) 100 nm (d) 100 nm 335 100 nm (e) Fig HRSEM patterns of influence of different sodium hydroxide concentrations (mol/l) on coating shape of the product: (a), 1.5 (b), 1.0 (c), 0.5 (d), 0.25 (e) Influence of Different Molar Ratios of C Fe3+ / C Fe2+ on Sample Coating Effect According to the document [12], the molar ratio of C Fe3+ / C Fe2+ affects the appearance of nanoFe3O4, and possibly affects the sample coating effect in further In the initial solution, the trivalent iron and biva lent iron exist in ion form Fe2+ is possibly oxidized to GLASS PHYSICS AND CHEMISTRY Vol 37 No Fe3+, so when the iron solution is made, the molar ratio of Fe3+ to Fe2+ should be smaller than the stoichi ometric ratio (2 : 1) in the chemical equation Thus, when parameters were fixed, namely the reaction temperature t was 30°C, pH of coprecipitation was 9.2, CNaOH was 0.5 mol/l, the velocity of magnetic stir ring was 138 ≤ v ≤ 151 r/min, we investigated the influ ence of the initial molar ratio of C Fe3+ / C Fe2+ on coat 2011 (7) 336 XIAOJUAN et al Table Colorimetric parameters and the percent of coated Fe3O4 in the coated samples at different sodium hydroxide con centrations Colorimetric parameter Sodium hydroxide concentration, mol/1 0.25 0.5 1.0 1.5 2.0 L* 46.33 49.24 45.71 48.02 47.32 a* 1.58 1.39 1.41 2.08 1.94 b* 3.62 3.80 3.13 4.62 4.39 * ΔE ab 7.86 11.36 7.90 10.71 9.98 31.59 43.20 29.39 40.08 31.40 Fe3O4 coating, % Note: t = 30°C; pH = 9.2; Fe3+ : Fe2+ = 1.364 : 1; 138 r/min ≤ v ≤ 151 r/min Table Colorimetric parameters and the percentage of coated Fe3O4 in the coated samples at different C Fe3+ / C Fe2+ ratios Colorimetric parameter C Fe3+ / C Fe2+ 1.2 : 1.4 : 1.6 : 1.8 : 2.0 : L* 43.71 42.82 43.45 43.54 43.57 a* 1.68 1.62 1.39 2.00 2.97 b* 3.06 2.88 2.69 3.62 4.72 * ΔE ab 6.24 5.44 5.77 6.53 7.58 53.45 42.75 34.32 48.10 47.51 Fe3O4 coating, % Note: t = 30°C; pH = 9.2; CNaOH = 0.5 mol/l; 138 r/min ≤ v ≤ 151 r/min ing shape Under the conditions of C Fe3+ / C Fe2+ being 1.2 : 1, 1.4 : 1, 1.6 : 1, 1.8 : and 2.0 : 1, the HRSEM patterns of Fe3O4 coating layer on mica are shown in Fig respectively As shown in Fig 5a, when C Fe3+ / C Fe2+ was 1.2 : 1, the Fe2+ is excessive, so not only Fe3O4 deposited on the mica surface, but also excessive Fe(OH)2 agglom erated on the mica surface Fe(OH)2 itself is white pre cipitate, and it is extremely unstable, as soon as it meets with air, it immediately combines with oxygen to FeO ⋅ xFe2O3 ⋅ yH2O form, which is easily oxidized further to red iron oxide crystal [14], resulting in the coating layer being unsmooth and incompact There fore, even if the product was calcined in nitrogen atmosphere it still showed red color, moreover the high values of a* and b* of the samples (Table 3) also dem onstrate that As C Fe3+ / C Fe2+ molar ratio increased, the smoothness and compactness of coating layer on mica surface also increased accordingly, as shown in Figs 5b, 5c When C Fe3+ / C Fe2+ was 1.6 : 1, the coating layer on mica surface is relatively smooth and com pact, because hydrated colloidal Fe(OH)3 and Fe(OH)2 can effectively deposit onto the mica surface at the same time, forming smooth and compact Fe3O4 coating layer at this molar ratio When C Fe3+ / C Fe2+ ≥ 1.8, excessive Fe3+ formed red βFeOOH in the coprecipitation, accumulating anomalously on the mica surface The HRSEM image shows some small and also large “holes”, as shown in Figs 5d, 5e, indicating that the compactness of the coating layer on the mica surface is poor under this condition Molar ratio of C Fe3+ / C Fe2+ also has a significant influence on the sample chromaticity coordinate parameters a* and b* When the total amount of Fe3+ is more than the amount of Fe3+ participated in the coprecipitation with Fe2+ under the condition of GLASS PHYSICS AND CHEMISTRY Vol 37 No 2011 (8) RESEARCH OF MICA/Fe3O4 PEARLESCENT PIGMENT BY CoPRECIPITATION (а) 100 nm (b) 100 nm (c) 100 nm (d) 100 nm 337 100 nm (e) Fig HRSEM patterns of influences of different molar ratio of Fe3+ to Fe2+ on product appearance: 1.2 : (a), 1.4 : (b), 1.6 : (c), 1.8 : (d), 2.0 : (e) C Fe3+ / C Fe2+ being 2.0, the redundant Fe3+ then has strong tendency to form red βFeOOH, leading to the red color deepening, and a* and b* value achieve the maximum as a result When ferric iron quantity is excessive low, namely C Fe3+ / C Fe2+ is 1.2, divalent iron is excessive, the produced ferrous hydroxide will con tinue to be oxidized to iron hydroxide Then it was cal GLASS PHYSICS AND CHEMISTRY Vol 37 No cined to ferric oxide form, and finally transformed into ferric oxide (showing red), causing the red value to increase, as well as the value of a* and b* The above results are shown only when C Fe3+ / C Fe2+ is 1.6, a* and b* achieve the minimum value with the quite high ΔE *ab value, showing obvious pearly luster effect (Table 3) 2011 (9) 338 XIAOJUAN et al (а) 100 nm (b) 100 nm (c) 100 nm (d) 100 nm Fig HRSEM patterns of influence of different stirring speeds (v, r/min) on product appearance: 110–124 (a), 124–138 (b), 138–151 (c), 151–166 (d) Influence of Stirring Speed on Coating Effect The Fe3O4 coating layer of sample exhibits always an extremely thin lamellar crystalline structure, which is the basis for showing pearl luster But this structure is sensitive to shear action, if the shear force is too small, the Fe3O4 nanoparticles cannot precipitate evenly on the mica substrate, and if the shear force is oversized, the Fe3O4 nanorparticles will flake off the mica substrate This shows that the shear force can influence both the coating and pearly luster effect, therefore, the stirring speed plays a major role on the coating and pearly luster effect, and a moderate stir ring speed may be beneficial to obtain a good pearly luster effect In order to study the influence of stirring speed on coating effect, parameters were fixed, namely the reaction temperature was 30°C, the pH value of co precipitation was 9.2, CNaOH was 0.5, the C Fe3+ / C Fe2+ was 1.6 : 1, and the influence of stirring speed on coat ing shape was studied On the condition of different stirring speeds v, the HRSEM images of Fe3O4 coat ing layer on mica surface are shown in Fig When the stirring speed v was 110–124 r/min, local agglomeration on the mica surface was serious, leading to the coating layer being neither smooth nor compact (Fig 6a) As can be seen from Table 4, the coating rate and ΔE *ab value of Fe3O4 on the mica sur face were low, indicating the poor pearly luster effect This is because the stirring speed was too slow, result ing in insufficient stirring, as the stirring speed increased, the smoothness and compactness of Fe3O4 coated mica were improved gradually When the stir ring speed v was 138–151 r/min, the smoothness and compactness of the coating layer on mica surface exhibit optimum (Fig 6c), attribute to the appropriate shear force As shown from Table 4, when stirring speed was 124–138 r/min, ΔE *ab value achieved the maximum, indicating that the pearly luster effect was the best, but the Fe3O4 coating rate was low The result showed that the shearing force has different influences on pearly luster effect and coating rate When the stirring speed v increased to 151–166 r/min, the coating rate reduced appreciably, “holes” appeared partly on the coating layer of mica surface, and the Fe3O4 agglomeration accumulated partly on GLASS PHYSICS AND CHEMISTRY Vol 37 No 2011 (10) RESEARCH OF MICA/Fe3O4 PEARLESCENT PIGMENT BY CoPRECIPITATION 339 Table Colorimetric parameters and the percentage of coated Fe3O4 in the coated samples at different stirring speeds Colorimetric parameter v, r/min 110–124 124–138 138–151 151–166 L* 42.30 46.65 43.11 41.15 a* 0.95 1.13 0.99 1.07 b* 1.50 2.39 1.61 1.98 * ΔE ab 4.16 8.17 4.07 3.53 21.44 31.32 45.75 38.79 Fe3O4 coating, % Note: t = 30°C; pH = 9.2; CNaOH = 0.5 mol/l; Fe3+ : Fe2+ =1.6 : Table Colorimetric parameters and the percent of coated Fe3O4 in the coated samples at different temperatures Colorimetric parameter Temperature, °C 65 70 75 80 L* 54.13 54.04 54.60 52.54 a* 0.92 0.95 1.12 1.34 b* 2.34 3.21 2.78 3.82 * ΔE ab 15.61 15.71 16.17 14.46 Fe3O4 coating, % 30.71 36.96 50.75 40.97 Note: pH = 9.2; CNaOH = 0.5 mol/l; Fe3+ : Fe2+ = 1.6 : 1; 138 r/min ≤ v ≤ 151 the coating membrane of the mica surface, leading to the smoothness and compactness reducing It is possi bly because the hydrated Fe3O4 coating partly fell off as the stirring speed increased and as a result, agglom eration occured and “holes” appeared on parts of mica surface Influence of Coating Temperature on Coating Effect In the process of coating Fe3O4 particles on the mica surface, the coating temperature is also a very essential parameter In this experiment parameters were fixed, namely coprecipitation response pH value was 9.2, CNaOH was 0.5 mol/l, the stirring speedy was 138–151 r/min and C Fe3+ / C Fe2+ was 1.6 : 1, then the influence of coating temperature on coating shape was studied As shown in Figs 7a–7d, temperature has a signif icant influence on Fe3O4 coating layer on mica sur face The higher the coating temperature, the more compact the Fe3O4 coating layer was put on mica sur face, indicating that coating speed increases as tem perature increases and the coating reaction is a endot GLASS PHYSICS AND CHEMISTRY Vol 37 No hermic reaction When the coating temperature rose to 70 or 75°C, the compactness of Fe3O4 coating layer on mica surface was relatively perfect (Figs 7b, 7c) As shown in Table 5, after an increase of tempera ture, both luminance value L* and ΔE *ab of the sam ples increased significantly, showing that the pearly luster effect increased obviously And a* and b* value of the sample increased along with the temperature, so does the red value When the temperature reached 80°C, the red value achieved the maximum, it is likely because that unstable Fe2+ changed into Fe3+ after increase of temperature It is also noted from the results of Table 1–5, all the luminance values L* of Fe3O4 coating layer on mica are higher than that of the black ferric oxide pigment standard substance produced by the German Baier Pigment, Ltd Co The ΔE *ab value is above 4, showing obvious pearly luster effect But both a* value and b* value of all samples are higher than those of the stan dard substance, demonstrating that the chromaticity of pinkish red and yellow of the samples prepared in the experiment are obviously at the high level 2011 (11) 340 XIAOJUAN et al (а) 100 nm (b) 100 nm (c) 100 nm (d) μm Fig HRSEM patterns of influence of different temperature (°C) on product appearance: 65 (a), 70 (b), 75 (c), 80 (d) 13 4 Intensity, CPS 2 Fe2O3, Fe 2p Fe2O3, Fe satellite FeO, Fe 2p FeO, Fe satellite 740 730 720 710 Binding evergy, eV 700 Fig XPS patterns of the content of Fe2O3 and FeO on the mica surface XRay Protoelectron Spectroscopy (XPS) It is general that Fe3O4 is usually partially oxidized to Fe2O3 inevitably in Fe3O4 preparation, and they are difficultly differed by the general analyses techniques So in these papers, Xray photoelectron spectroscopy was used to analyze the percentage of Fe3O4 and Fe2O3 in the sample under the optimum condition The spectrums of iron characteristic peak integral chart of the two components are shown in Fig Figure shows the XPS integral chart of the two components on the mica surface The binding energy peak of 2p of iron (in Fe2O3 and FeO) was 710.6 and 724.08 eV respectively [15] The molar ratio of Fe2O3 to FeO on the mica surface is calculated as 1.26 : (a little higher than : 1), the result indicates that there was a little Fe2O3 on the mica surface besides major Fe3O4 The reason for the existence of a little Fe2O3 in the coating layer is that during the experiment the copre cipitation pH was within an alkaline scope and strong alkali NaOH was used as precipitating agent On the one hand, Fe3+ has a tendency of forming goethite; on GLASS PHYSICS AND CHEMISTRY Vol 37 No 2011 (12) RESEARCH OF MICA/Fe3O4 PEARLESCENT PIGMENT BY CoPRECIPITATION the other hand, the strong alkaline medium as precip itating agent can easily cause the formation of non magnetic iron compound Fe2O3 [16, 17] Therefore, there was a little Fe2O3 mixed in magnetic Fe3O4 nanoparticles Transmittance, % a FarFTIR Analyses Iler once mentioned in his patent that coating compact Fe3O4 membrane on micro surface is a chemistry bonding action [18] In order to confirm this statement, we determined mica, Fe3O4 as well as the mica/Fe3O4 sample by far infrared spectrum within the scope of 50–650 cm–1 wave number, and the results are shown in Fig In Fig 9, the characteristic wide absorption peaks at 512.1 and 421.6 cm–1 belong to Si–O vibration of mica [19, 20], and the strong absorption peaks at 228.7, 171.5, 143.6, 115.7, 95.7, and 69.1 cm–1 belong to the stretching vibration of AlO4 unit [21] in the mica Fe3O4 had obvious absorption peaks, among them, one wide absorption peak is at 553.4 cm–1, one small peak at 351.2 cm–1, and one sharp absorption peak at 384.4 cm–1 are all attributed to the character istic absorption peak of Fe3O4 stretching vibration; while one small peak at 437.6 cm–1, a pair of sharp peaks at 301.9 and 278.0 cm–1 are attributed to the characteristic absorption peaks of FeIII–O [22]; a pair of absorption peaks at 168.9 and 156.9 cm–1 belong to the stretching vibration of the FeO4 tetrahedron unit [23] When the mica was coated with Fe3O4, the far infrared spectrum changed greatly, the characteristic wide absorption peak of mica moved from 512.1 to 502.8 cm–1, while wide absorption peak of mica at 421.6 cm–1 disappeared As for the Fe3O4 after the coating reaction was finished, the characteristic absorption peaks of the Fe3O4 stretching vibration at 553.4 and 384.4 cm–1, as well as the FeIII–O absorp tion peak at 437.6 cm–1 all disappeared, meanwhile, a pair of new peaks appeared at 418.9 and 611.8 cm–1 respectively, attributed to Fe–O stretching vibration in Fe–O–Si [24] As shown in Fig 9, both the two absorption peaks of FeIII–O at 301.9 and 278.0 cm–1 turned weaker, so did the stretching vibration absorp tion peak of Fe3O4 at 351.2 cm–1 However three absorption peaks of the stretching vibration of the AlO4 unit at 228.7, 171.5, and 115.7 cm–1 turned stronger, but the peak position had not changed yet The Fig also shows that the stretching vibration absorption peaks of AlO4 unit at 95.7 and 69.1 cm–1 shifted to lower wave number, the absorption peak of AlO4 unit at 143.6 cm–1 and two absorption peaks of stretching vibration of the FeO4 unit disappeared It is found that a new sharp absorption peak appeared at 150.3 cm–1, probably because that the AlO4 unit in GLASS PHYSICS AND CHEMISTRY Vol 37 No 341 b c 600 500 400 300 200 Wavenumber, cm–1 100 Fig Fe3O4 (a), mica (b), sample synthesized under the optimum condition (c) mica formed a Fe–O–Al bond with the FeO4 unit, demonstrating that the mica is coated with nano Fe3O4 particles through Al–O–Fe bond CONCLUSIONS The deposition of one kind of smooth and compact nanometer Fe3O4 coated mica was studied The effects of pH value, sodium hydroxide concentration, C Fe3+ / C Fe2+ molar ratio, stirring speed and tempera ture on Fe3O4 coating rate and smooth on the mica surface were investigated The results indicate that, when the sodium hydrox ide concentration is 0.5 mol/l, pH value is exactly the coprecipitation pH of Fe3+ and Fe2+, the coating is smooth and the coating rate is also relatively high Moreover, the pearly luster effect is significant Exces sive Fe3+ or Fe2+ has a bad influence on coating perfor mance, and when C Fe3+ / C Fe2+ is 1.6, the coating is rel atively smooth and compact and the pearly luster effect is obvious From the point of coating rate and pearly luster effect, stirring speed at 138 r/min ≤ v ≤ 151 r/min and the reaction temperature at 70–75°C is quite appropriate Through XPS analyses and far infrared analyses of the sample in the coating process we found that, a Al–O–Fe bond had formed between1 Fe3O4 mem brane and the surface of the mica particles, indicating that there is a chemical bonding action between them ACKNOWLEDGMENTS Project supported by the National Natural Science Foundation of China (no 20971043) and Zhejiang Province Science Foundation (no 2006C1118) 2011 (13) 342 XIAOJUAN et al REFERENCES Prengel, C., 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AND CHEMISTRY Vol 37 No 2011 (14)
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