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Preparation and color performance control of Cr2O3 green pigment through thermal decomposition of chromium hydroxide precursor
Materials Letters 117 (2014) 244–247
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation and color performance control of Cr2O3 green pigment through thermal decomposition of chromium hydroxide precursor H.L. Zhang a,b, S.T. Liang a,b,c, M.T. Luo a,b, M.G. Ma a,b,d, P.P. Fan a,b,e, H.B. Xu a,b,n, P. Li a,b, Y. Zhang a,b a National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China b Key Laboratory of Green Process and Engineering, Chinese Academy of Sciences, Beijing 100190, China c University of Chinese Academy of Sciences, Beijing 100190, China d School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300401, China e New Materials and Function Coordination Chemistry Lab, Qingdao University of Science and Technology, Qingdao 266042, China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 November 2013 Accepted 2 December 2013 Available online 11 December 2013
Cr2O3 green pigment was prepared through the thermal decomposition of chromium hydroxide precursor, which was precipitated by Cr(NO3)3 and NaOH solutions. The color performance of asprepared Cr2O3 is comparable to the commercial pigment when the precursor was precipitated from 0.25 mol/L Cr(NO3)3 solution. When increasing the concentration of Cr(NO3)3 solution, the color of Cr2O3 becomes more reddish and much darker. The structure and morphology of different precursors and Cr2O3 samples were characterized. Amorphous precursor with non-agglomerated particles, which could be obtained by controlling the concentration of Cr(NO3)3 solution, was found to be a prerequisite for preparing Cr2O3 pigment with good color performance. & 2013 Elsevier B.V. All rights reserved.
Keywords: Cr2O3 green pigment Chromium hydroxide Color performance Microstructure Particles
1. Introduction Due to its excellent performance in wear, corrosion and chemical resistance, Cr2O3 green pigment has been widely used in ceramics, coatings, printing and construction materials [1,2]. There are several processes for the production of Cr2O3 [1–4]: the reduction of an alkali dichromate by sulfur or ammonium salt; the thermal decomposition of CrO3; the hydrogen reduction of an alkali chromate and the subsequent thermal decomposition of CrOOH; the thermal decomposition of chromium hydroxide (Cr (OH)3 xH2O). The former two processes have been employed in the industrial production but the consequent environmental pollutions are unresolved. The third one is a cleaner process developed by our laboratory and several Cr2O3 green pigments have been successfully fabricated [3,4]. The last one is also a cleaner process as the by-product is H2O. However, the color of Cr2O3 decomposed by Cr(OH)3 xH2O was reported to be reddish and dark [5]. Bearing in mind that Cr(OH)3 xH2O is a common compound in chromate production, it is of great importance if the
n Corresponding author at: National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China. Tel.: þ86 10 82544810; fax: þ86 10 82544810. E-mail address: [email protected] (H.B. Xu).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.12.010
color of Cr2O3 decomposed by Cr(OH)3 xH2O could be improved further. As the important precursor for Cr2O3, the preparation and decomposition process of Cr(OH)3 xH2O have captured the intention of researchers [6–9]. The thermal behavior of Cr(OH)3 xH2O was found to differ depending on the preparation condition [6]. When the preparation condition of Cr(OH)3 xH2O changed, the morphology and particle size of Cr2O3 decomposed changed accordingly [8,9]. It is well known that color performances of Cr2O3 pigments are in close relation with their crystal structures, particle sizes and morphologies, etc. [1–4], so it is reasonable to deduce that these Cr2O3 samples would vary in the color performance. The present work is focused on the preparation of Cr2O3 pigment through thermal decomposition of Cr(OH)3 xH2O precipitated by Cr(NO3)3 and NaOH solutions. The concentration of Cr (NO3)3 solution was modulated and Cr2O3 pigment with color performance comparable to the commercial sample was produced. The key factor for preparing Cr2O3 pigment with good color performance through thermal decomposition of Cr(OH)3 xH2O was analyzed. 2. Experimental procedure Cr(NO3)3 9H2O and NaOH of analytical purity were used. Distilled water was home-made. At 95 1C, 1.0 mol/L NaOH solution
H.L. Zhang et al. / Materials Letters 117 (2014) 244–247
was added at a rate of 5 mL/min into 240 mL Cr(NO3)3 solution with vigorous stirring. The addition was stopped when the pH reached the desired value. The reaction mixture was kept stirring for 3.5 h. After the precipitate was filtrated, watered, dried and grinded, Cr(OH)3 xH2O precursor was obtained. The precursor was calcinated at 950 1C for 1.5 h to produce Cr2O3 pigment. Preparation conditions of different precursors were summarized in Table 1. The color parameters (CIE-Lnanbn) of Cr2O3 samples were reported using the International Commission on Illumination (CIE-Lnanbn, 1976) colorimetric system and the same testing method previously reported [3]. A Datacolor 110 colorimeter (Datacolor CO., LTD, USA) equipped with an illuminant D65 and 101 complementary observer was employed. The infrared spectra of the samples diluted in KBr were recorded by a Spectro GX Fourier transform infrared (FT-IR) Spectrometer (Perkin-Elmer, USA). X-ray diffraction (XRD) patterns were recorded using a Rigaku diffractometer employing Cu Kα radiation. The morphologies of samples were investigated using a JSM-6700F NT scanning electron microscope (SEM).
Table 1 Preparation conditions of precursors and the color parameters of Cr2O3 samples. Commercial pigment S1 was listed as reference. Desired Concentration pH value of Cr(NO3)3 solutions (mol/L)
Precursors Cr2O3 samples
Ln
an
bn
1.5 1.5 1.0 1.0 0.25 0.25 /
P-1.5-10 P-1.5-6.5 P-1.0-10 P-1.0-6.5 P-0.25-10 P-0.25-6.5 /
42.12 39.45 44.53 47.84 47.39 54.39 51.06
14.54 14.16 15.72 15.72 18.30 18.77 17.28
12.52 11.86 14.64 13.53 15.40 16.85 18.92
10 6.5 10 6.5 10 6.5 /
C-1.5-10 C-1.5-6.5 C-1.0-10 C-1.0-6.5 C-0.25-10 C-0.25-6.5 S1
245
3. Results and discussion The color parameters of Cr2O3 samples are listed in Table 1. Remarkable variances in color were observed. Commercial Cr2O3 pigment (named as sample S1) from a foreign manufacturer produced through the reduction of Na2Cr2O7 with (NH4)2SO4, was chosen as the standard sample. Compared to S1, C-1.5-10 and C-1.5-6.5 are more reddish and much darker, with larger values of an about 14 and smaller values of Ln around 40. When Cr(NO3)3 solution with lower concentration was employed, the value of an decreased, i.e., the color of Cr2O3 became greener. The value of an decreases by more than 4 when the concentration of Cr (NO3)3 solutions decreases from 1.5 to 0.25. Meanwhile, the value of bn increases from 11–12 to 15–17 and large improvement in the lightness is achieved. Finally, the hues of C-0.25-10 and C-0.25-6.5 are comparable to S1. Their an values are smaller than S1, indicating that these samples are even greener compared with the commercial pigment. Their Ln values fluctuate from 47 to 54 and their bn values are around 16, which means that they are bright bluish-green pigments. To explore the cause of the remarkable variances in color, the structure and morphology of different precursors and Cr2O3 samples were characterized. Due to the fact that the change regularities with concentrations are similar under different pH values, a batch of precursors (P-1.5-10, P-1.0-10 and P-0.25-10) and Cr2O3 samples (C-1.5-10, C-1.0-10 and C-0.25-10) were chosen for demonstration. FT-IR spectra patterns of the precursors and Cr2O3 samples are shown in Fig. 1. All the precursors are Cr(OH)3 xH2O according to their characteristic bands at around 3400, 1630, 1480, 1370, 940 and 515 cm 1 [10–12]. Only slight variation in the relative strength can be detected (Fig. 1(a)). They are amorphous as no diffraction peak was found in their XRD spectra (Supplementary data). IR bands characteristic of Cr2O3 were well developed in the spectra of Cr2O3 samples (Fig. 1(b)) [6,10,12]. Slight variation in the shoulder around 690 cm 1 might be related to different morphology [6]. XRD patterns demonstrate that these Cr2O3
Fig. 1. FT-IR spectra of chromium hydroxide precursors and Cr2O3 samples. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
246
H.L. Zhang et al. / Materials Letters 117 (2014) 244–247
samples are all well crystallized pure Cr2O3 (JCPDS No. 38-1479) (Supplementary data). SEM pictures of Cr(OH)3 xH2O precursors are shown in Fig. 2. Particles in P-0.25-10 (Fig. 2(a)) were non-agglomerated and loosely attached to each other. Differently, many agglomerated structures were found in P-1.0-10 (Fig. 2(b)). This phenomenon was more obvious in P-1.5-10 and the sizes of the agglomerates were larger (Fig. 2(c)). Kinetics of precipitation is controlled by concentration when other elements such as pH, temperature and adding rate are constant. A very fast rate of formation at high concentration tends to result in conglomerations of precipitated particles. Non-agglomerated particles were precipitated from Cr (NO3)3 solutions under proper concentration whereas only hard agglomerates were obtained under higher concentration [12]. In this work, 0.25 mol/L might be in the appropriate range where non-agglomerated particles were precipitated. Metal oxides formed through the thermal dehydration of their hydroxides could preserve the texture of their precursors [13]. The influence of concentration on the kinetics of precipitation leads to differences in stacking manners of the precursors (Fig. 2). Precursors having different stacking manners and different surface energies would decompose into Cr2O3 with different morphologies [8,14]. SEM pictures of Cr2O3 samples are shown in Fig. 3. Similar to S1 (Fig. 3(d)), isometric grains and a uniform size distribution were observed in C-0.25-10 (Fig. 3(a)). However, some large grains, of irregular shapes and varying sizes, were observed
in C-1.0-10 (Fig. 3(b)). In C-1.5-10 (Fig. 3(c)), the amount and size of irregular grains increase while the grain shape and size distribution become more non-uniform. Particle morphology and size distribution could affected strongly the hue, the light scattering and the tinting strength of pigment [1,15]. Pigments with uniform size and shape always exhibit good performance and high purity of hue [2,15]. For Cr2O3, lighter greens with yellowish hues are obtained with finely divided pigments [1]. Irregular grain shapes and non-uniform size distributions in Cr2O3 decomposed by precursors with large agglomerates, might be the causation for the deterioration of their color performances. Accordingly, Cr(OH)3 xH2O precursor with non-agglomerated particles might be a prerequisite for preparing Cr2O3 pigment with good color performance.
4. Conclusions Cr2O3 pigment with color performance comparable to the commercial sample was obtained through thermal decomposition of Cr(OH)3 xH2O precipitated by 0.25 mol/L Cr(NO3)3 and 1 mol/L NaOH solutions. When Cr(NO3)3 solutions with higher concentrations such as 1.0 and 1.5 mol/L were used, large agglomerates were formed in the precursors. These precursors would decompose into Cr2O3 with irregular grain shapes and non-uniform size distributions, which lead to the deterioration of color. For fabricating Cr2O3
Fig. 2. SEM pictures of Cr(OH)3 xH2O precursors, (a) P-0.25-10, (b) P-1.0-10, (c) P-1.5-10.
Fig. 3. SEM pictures of Cr2O3 samples, (a) C-0.25-10, (b) C-1.0-10, (c) C-1.5-10, (d) S1.
H.L. Zhang et al. / Materials Letters 117 (2014) 244–247
pigment with good color performance, the preparation condition of Cr(OH)3 xH2O should be controlled to obtain precursor with non-agglomerated particles. Acknowledgements This research was financially supported by the National Natural Science Foundation of China (No.11204304 and 51204154) and the National Basic Research Program (973 Program) of China (No. 2013CB632601 and 2013CB632606). The authors thank Lu Shi for providing language help. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.12.010.
247
References [1] Buxbaum G, Pfaff G. Industrial inorganic pigments. 3rd ed. Weinheim: WileyVch; 2005. [2] Zhu JL, Wu SN. Pigment technology. 2nd ed. Beijing: Chemical Industry Press; 2002. [3] Liang ST, Zhang HL, Luo MT, Luo KJ, Li P, Xu HB, et al. Ceram Int. http://dx.doi. org/10.1016/j.ceramint.2013.08.107 (Sep 5). [4] Li P, Xu HB, Zhang Y, Li ZH, Zheng SL, Bai YL. Dyes Pigm 2009;80:287–91. [5] Jiang QP, Chen N, Zhang GQ, Chen Y, Du JB. Inorg Chem Ind 2013;45:54–5. [6] Music S, Maljkovic M, Popovic S, Trojko R. Croat Chem Acta 1999;72:789–802. [7] Kim DW, Shin SI, Lee JD, Oh SG. Mater Lett 2004;58:1894–8. [8] Pei ZZ, Zhang X. Mater Lett 2013;93:377–9. [9] Kohli N, Singh O, Singh RC. Sens Actuators, B 2011;158:259–64. [10] Onjia AE, Milonjić SK, Čokeša D, Čomor M, Miljević N. Mater Res Bull 2003;38:1329–39. [11] Bai YL, Xu HB, Zhang Y, Li ZH. J Phys Chem Solids 2006;67:2589–95. [12] Ocaña M. J Eur Ceram Soc 2001;21:931–9. [13] Zhao Y, Yang J, Frost RL. J Raman Spectrosc 2008;39:1327–31. [14] Kim DW, Oh SG. Mater Lett 2005;59:976–80. [15] Bittler K, Ostertag W. Angew Chem Int Ed Engl, 19; 1980; 190–6.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation and color performance control of Cr2O3 green pigment through thermal decomposition of chromium hydroxide precursor H.L. Zhang a,b, S.T. Liang a,b,c, M.T. Luo a,b, M.G. Ma a,b,d, P.P. Fan a,b,e, H.B. Xu a,b,n, P. Li a,b, Y. Zhang a,b a National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China b Key Laboratory of Green Process and Engineering, Chinese Academy of Sciences, Beijing 100190, China c University of Chinese Academy of Sciences, Beijing 100190, China d School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300401, China e New Materials and Function Coordination Chemistry Lab, Qingdao University of Science and Technology, Qingdao 266042, China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 November 2013 Accepted 2 December 2013 Available online 11 December 2013
Cr2O3 green pigment was prepared through the thermal decomposition of chromium hydroxide precursor, which was precipitated by Cr(NO3)3 and NaOH solutions. The color performance of asprepared Cr2O3 is comparable to the commercial pigment when the precursor was precipitated from 0.25 mol/L Cr(NO3)3 solution. When increasing the concentration of Cr(NO3)3 solution, the color of Cr2O3 becomes more reddish and much darker. The structure and morphology of different precursors and Cr2O3 samples were characterized. Amorphous precursor with non-agglomerated particles, which could be obtained by controlling the concentration of Cr(NO3)3 solution, was found to be a prerequisite for preparing Cr2O3 pigment with good color performance. & 2013 Elsevier B.V. All rights reserved.
Keywords: Cr2O3 green pigment Chromium hydroxide Color performance Microstructure Particles
1. Introduction Due to its excellent performance in wear, corrosion and chemical resistance, Cr2O3 green pigment has been widely used in ceramics, coatings, printing and construction materials [1,2]. There are several processes for the production of Cr2O3 [1–4]: the reduction of an alkali dichromate by sulfur or ammonium salt; the thermal decomposition of CrO3; the hydrogen reduction of an alkali chromate and the subsequent thermal decomposition of CrOOH; the thermal decomposition of chromium hydroxide (Cr (OH)3 xH2O). The former two processes have been employed in the industrial production but the consequent environmental pollutions are unresolved. The third one is a cleaner process developed by our laboratory and several Cr2O3 green pigments have been successfully fabricated [3,4]. The last one is also a cleaner process as the by-product is H2O. However, the color of Cr2O3 decomposed by Cr(OH)3 xH2O was reported to be reddish and dark [5]. Bearing in mind that Cr(OH)3 xH2O is a common compound in chromate production, it is of great importance if the
n Corresponding author at: National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China. Tel.: þ86 10 82544810; fax: þ86 10 82544810. E-mail address: [email protected] (H.B. Xu).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.12.010
color of Cr2O3 decomposed by Cr(OH)3 xH2O could be improved further. As the important precursor for Cr2O3, the preparation and decomposition process of Cr(OH)3 xH2O have captured the intention of researchers [6–9]. The thermal behavior of Cr(OH)3 xH2O was found to differ depending on the preparation condition [6]. When the preparation condition of Cr(OH)3 xH2O changed, the morphology and particle size of Cr2O3 decomposed changed accordingly [8,9]. It is well known that color performances of Cr2O3 pigments are in close relation with their crystal structures, particle sizes and morphologies, etc. [1–4], so it is reasonable to deduce that these Cr2O3 samples would vary in the color performance. The present work is focused on the preparation of Cr2O3 pigment through thermal decomposition of Cr(OH)3 xH2O precipitated by Cr(NO3)3 and NaOH solutions. The concentration of Cr (NO3)3 solution was modulated and Cr2O3 pigment with color performance comparable to the commercial sample was produced. The key factor for preparing Cr2O3 pigment with good color performance through thermal decomposition of Cr(OH)3 xH2O was analyzed. 2. Experimental procedure Cr(NO3)3 9H2O and NaOH of analytical purity were used. Distilled water was home-made. At 95 1C, 1.0 mol/L NaOH solution
H.L. Zhang et al. / Materials Letters 117 (2014) 244–247
was added at a rate of 5 mL/min into 240 mL Cr(NO3)3 solution with vigorous stirring. The addition was stopped when the pH reached the desired value. The reaction mixture was kept stirring for 3.5 h. After the precipitate was filtrated, watered, dried and grinded, Cr(OH)3 xH2O precursor was obtained. The precursor was calcinated at 950 1C for 1.5 h to produce Cr2O3 pigment. Preparation conditions of different precursors were summarized in Table 1. The color parameters (CIE-Lnanbn) of Cr2O3 samples were reported using the International Commission on Illumination (CIE-Lnanbn, 1976) colorimetric system and the same testing method previously reported [3]. A Datacolor 110 colorimeter (Datacolor CO., LTD, USA) equipped with an illuminant D65 and 101 complementary observer was employed. The infrared spectra of the samples diluted in KBr were recorded by a Spectro GX Fourier transform infrared (FT-IR) Spectrometer (Perkin-Elmer, USA). X-ray diffraction (XRD) patterns were recorded using a Rigaku diffractometer employing Cu Kα radiation. The morphologies of samples were investigated using a JSM-6700F NT scanning electron microscope (SEM).
Table 1 Preparation conditions of precursors and the color parameters of Cr2O3 samples. Commercial pigment S1 was listed as reference. Desired Concentration pH value of Cr(NO3)3 solutions (mol/L)
Precursors Cr2O3 samples
Ln
an
bn
1.5 1.5 1.0 1.0 0.25 0.25 /
P-1.5-10 P-1.5-6.5 P-1.0-10 P-1.0-6.5 P-0.25-10 P-0.25-6.5 /
42.12 39.45 44.53 47.84 47.39 54.39 51.06
14.54 14.16 15.72 15.72 18.30 18.77 17.28
12.52 11.86 14.64 13.53 15.40 16.85 18.92
10 6.5 10 6.5 10 6.5 /
C-1.5-10 C-1.5-6.5 C-1.0-10 C-1.0-6.5 C-0.25-10 C-0.25-6.5 S1
245
3. Results and discussion The color parameters of Cr2O3 samples are listed in Table 1. Remarkable variances in color were observed. Commercial Cr2O3 pigment (named as sample S1) from a foreign manufacturer produced through the reduction of Na2Cr2O7 with (NH4)2SO4, was chosen as the standard sample. Compared to S1, C-1.5-10 and C-1.5-6.5 are more reddish and much darker, with larger values of an about 14 and smaller values of Ln around 40. When Cr(NO3)3 solution with lower concentration was employed, the value of an decreased, i.e., the color of Cr2O3 became greener. The value of an decreases by more than 4 when the concentration of Cr (NO3)3 solutions decreases from 1.5 to 0.25. Meanwhile, the value of bn increases from 11–12 to 15–17 and large improvement in the lightness is achieved. Finally, the hues of C-0.25-10 and C-0.25-6.5 are comparable to S1. Their an values are smaller than S1, indicating that these samples are even greener compared with the commercial pigment. Their Ln values fluctuate from 47 to 54 and their bn values are around 16, which means that they are bright bluish-green pigments. To explore the cause of the remarkable variances in color, the structure and morphology of different precursors and Cr2O3 samples were characterized. Due to the fact that the change regularities with concentrations are similar under different pH values, a batch of precursors (P-1.5-10, P-1.0-10 and P-0.25-10) and Cr2O3 samples (C-1.5-10, C-1.0-10 and C-0.25-10) were chosen for demonstration. FT-IR spectra patterns of the precursors and Cr2O3 samples are shown in Fig. 1. All the precursors are Cr(OH)3 xH2O according to their characteristic bands at around 3400, 1630, 1480, 1370, 940 and 515 cm 1 [10–12]. Only slight variation in the relative strength can be detected (Fig. 1(a)). They are amorphous as no diffraction peak was found in their XRD spectra (Supplementary data). IR bands characteristic of Cr2O3 were well developed in the spectra of Cr2O3 samples (Fig. 1(b)) [6,10,12]. Slight variation in the shoulder around 690 cm 1 might be related to different morphology [6]. XRD patterns demonstrate that these Cr2O3
Fig. 1. FT-IR spectra of chromium hydroxide precursors and Cr2O3 samples. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
246
H.L. Zhang et al. / Materials Letters 117 (2014) 244–247
samples are all well crystallized pure Cr2O3 (JCPDS No. 38-1479) (Supplementary data). SEM pictures of Cr(OH)3 xH2O precursors are shown in Fig. 2. Particles in P-0.25-10 (Fig. 2(a)) were non-agglomerated and loosely attached to each other. Differently, many agglomerated structures were found in P-1.0-10 (Fig. 2(b)). This phenomenon was more obvious in P-1.5-10 and the sizes of the agglomerates were larger (Fig. 2(c)). Kinetics of precipitation is controlled by concentration when other elements such as pH, temperature and adding rate are constant. A very fast rate of formation at high concentration tends to result in conglomerations of precipitated particles. Non-agglomerated particles were precipitated from Cr (NO3)3 solutions under proper concentration whereas only hard agglomerates were obtained under higher concentration [12]. In this work, 0.25 mol/L might be in the appropriate range where non-agglomerated particles were precipitated. Metal oxides formed through the thermal dehydration of their hydroxides could preserve the texture of their precursors [13]. The influence of concentration on the kinetics of precipitation leads to differences in stacking manners of the precursors (Fig. 2). Precursors having different stacking manners and different surface energies would decompose into Cr2O3 with different morphologies [8,14]. SEM pictures of Cr2O3 samples are shown in Fig. 3. Similar to S1 (Fig. 3(d)), isometric grains and a uniform size distribution were observed in C-0.25-10 (Fig. 3(a)). However, some large grains, of irregular shapes and varying sizes, were observed
in C-1.0-10 (Fig. 3(b)). In C-1.5-10 (Fig. 3(c)), the amount and size of irregular grains increase while the grain shape and size distribution become more non-uniform. Particle morphology and size distribution could affected strongly the hue, the light scattering and the tinting strength of pigment [1,15]. Pigments with uniform size and shape always exhibit good performance and high purity of hue [2,15]. For Cr2O3, lighter greens with yellowish hues are obtained with finely divided pigments [1]. Irregular grain shapes and non-uniform size distributions in Cr2O3 decomposed by precursors with large agglomerates, might be the causation for the deterioration of their color performances. Accordingly, Cr(OH)3 xH2O precursor with non-agglomerated particles might be a prerequisite for preparing Cr2O3 pigment with good color performance.
4. Conclusions Cr2O3 pigment with color performance comparable to the commercial sample was obtained through thermal decomposition of Cr(OH)3 xH2O precipitated by 0.25 mol/L Cr(NO3)3 and 1 mol/L NaOH solutions. When Cr(NO3)3 solutions with higher concentrations such as 1.0 and 1.5 mol/L were used, large agglomerates were formed in the precursors. These precursors would decompose into Cr2O3 with irregular grain shapes and non-uniform size distributions, which lead to the deterioration of color. For fabricating Cr2O3
Fig. 2. SEM pictures of Cr(OH)3 xH2O precursors, (a) P-0.25-10, (b) P-1.0-10, (c) P-1.5-10.
Fig. 3. SEM pictures of Cr2O3 samples, (a) C-0.25-10, (b) C-1.0-10, (c) C-1.5-10, (d) S1.
H.L. Zhang et al. / Materials Letters 117 (2014) 244–247
pigment with good color performance, the preparation condition of Cr(OH)3 xH2O should be controlled to obtain precursor with non-agglomerated particles. Acknowledgements This research was financially supported by the National Natural Science Foundation of China (No.11204304 and 51204154) and the National Basic Research Program (973 Program) of China (No. 2013CB632601 and 2013CB632606). The authors thank Lu Shi for providing language help. Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.12.010.
247
References [1] Buxbaum G, Pfaff G. Industrial inorganic pigments. 3rd ed. Weinheim: WileyVch; 2005. [2] Zhu JL, Wu SN. Pigment technology. 2nd ed. Beijing: Chemical Industry Press; 2002. [3] Liang ST, Zhang HL, Luo MT, Luo KJ, Li P, Xu HB, et al. Ceram Int. http://dx.doi. org/10.1016/j.ceramint.2013.08.107 (Sep 5). [4] Li P, Xu HB, Zhang Y, Li ZH, Zheng SL, Bai YL. Dyes Pigm 2009;80:287–91. [5] Jiang QP, Chen N, Zhang GQ, Chen Y, Du JB. Inorg Chem Ind 2013;45:54–5. [6] Music S, Maljkovic M, Popovic S, Trojko R. Croat Chem Acta 1999;72:789–802. [7] Kim DW, Shin SI, Lee JD, Oh SG. Mater Lett 2004;58:1894–8. [8] Pei ZZ, Zhang X. Mater Lett 2013;93:377–9. [9] Kohli N, Singh O, Singh RC. Sens Actuators, B 2011;158:259–64. [10] Onjia AE, Milonjić SK, Čokeša D, Čomor M, Miljević N. Mater Res Bull 2003;38:1329–39. [11] Bai YL, Xu HB, Zhang Y, Li ZH. J Phys Chem Solids 2006;67:2589–95. [12] Ocaña M. J Eur Ceram Soc 2001;21:931–9. [13] Zhao Y, Yang J, Frost RL. J Raman Spectrosc 2008;39:1327–31. [14] Kim DW, Oh SG. Mater Lett 2005;59:976–80. [15] Bittler K, Ostertag W. Angew Chem Int Ed Engl, 19; 1980; 190–6.