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Particle size and purity control study on ZrW2O8 powders using coprecipitation method
Materials Science & Engineering B 246 (2019) 27–33
Contents lists available at ScienceDirect
Materials Science & Engineering B journal homepage: www.elsevier.com/locate/mseb
Particle size and purity control study on ZrW2O8 powders using coprecipitation method ⁎
T
⁎
Yan Zhanga, Yingkui Guoa, , Lei Chenb, , Yujin Wangb, Guangwei Zhanga, Yuansong Zhoua a
Inorganic Nonmetallic Materials and Engineering Department, School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150000, PR China b Institute of Advance Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: ZrW2O8 powder Coprecipitation method Particles size Calcination temperature
ZrW2O8 powders with different particles size are synthesized by coprecipitation method. The effects of pH, PEG and calcination temperature on the phase, morphology and particle size of ZrW2O8 powders were investigated. The purity of the ZrW2O8 powder is also detected by XRF, and the optimal parameters of the coprecipitation method are obtained. The coprecipitation precursor is prepared by adding PEG400 into W6+ solution with a preferred pH of 2, and then calcined at 600 °C for 2 h and 1160 °C for 2 h to obtain the small particles size ZrW2O8 powder with narrow particle size distribution. The average particle size of ZrW2O8 powder is about 0.51 μm. The purity of ZrW2O8 powder is 97.95% with 2.05% ZrO2 as impurity due to the thermodynamic instability of ZrW2O8 and the volatilization of WO3 at high temperature.
1. Introduction ZrW2O8 material has negative thermal expansion (NTE) property ranging from 0.3 K to 1050 K, the negative thermal expansion coefficient is about −9 × 10−6 K−1 [1], which has been widely used in electronic device, optical microscope with high precision, precision optical lens, gums filler material and substrate material, etc. The potential application of ZrW2O8 material has stimulated interest in the synthesis of ZrW2O8 powder. How to simply obtain the high purity ZrW2O8 powders with small size is becoming a very important issue, and has caused wide broad concern over the recent years. There are a variety of methods for fabrication ZrW2O8 powder, such as the solid phase method [2], the coprecipitation method [3], the sol-gel method [4], hydrothermal method [5], combustion method [6], microwave synthesis method [7], and spray drying method [8]. Although the ZrW2O8 powder prepared by sol-gel method and hydrothermal method can get a small particle size and high purity [9,10], it entails considerable time and complex process, maybe take several weeks [11,12]. Solid phase method is a traditional simple method to prepare ZrW2O8 powder, while the particle size is always about 5–15 μm by common fabrication process [13,14]. Thus, the ZrW2O8 powder needs to be further grinded, and some impurity would be introduced into the fine ZrW2O8 powder. The coprecipitation method is attractive fabrication process to synthesis some small particle size powders. Sun et al. [15] have fabricated the ZrW2O8 ⁎
powder by coprecipitation method with 2.5 μm, then have successfully synthesized ZrW2O8 powder with the size of 0.4 μm by coprecipitation method particles via zirconium oxynitrate, ammonium tungstate and PEG-20000, when the value of nPEG/nmetal is 0.032 [16]. While, the detail particle size adjustment and purity refinement of synthesis ZrW2O8 powder are still no reported in detail. In this study, based on an overall consideration of purity and particle size of ZrW2O8 powder, the coprecipitation method was employed to prepare the ZrW2O8 powder via zirconium chloride and ammonium tungstate with different value of PH. The particles size and its distribution of ZrW2O8 powder were investigated by laser particle size analyzer and scanning electron microscopy (SEM) to evaluate the influence of pH value and amount of PEG in precursor solution. The purity of ZrW2O8 powder under the different calcination temperature are also further investigated by X-Ray Diffraction (XRD) and X-ray fluorescence (XRF). 2. Experimental method The raw materials are oxygen zirconium chloride (ZrOCl2·8H2O) and ammonium tungstate ((NH4)5H5[H2(WO4)6]·H2O) (Pharmaceutical group co., LTD, China). The compositional concentration of ZrOCl2·8H2O and (NH4)5H5[H2(WO4)6]·H2O are calculated according to the adequate molar ratios of ZrO2 and WO3. The (NH4)5H5[H2(WO4)6]·H2O is dissolved in distilled water and vigorously
Corresponding authors. E-mail addresses: [email protected] (Y. Guo), [email protected] (L. Chen).
https://doi.org/10.1016/j.mseb.2019.05.019 Received 21 October 2017; Received in revised form 25 April 2019; Accepted 17 May 2019 Available online 04 June 2019 0921-5107/ © 2019 Elsevier B.V. All rights reserved.
Materials Science & Engineering B 246 (2019) 27–33
Y. Zhang, et al.
Table 1 Compositional design of ZrW2O8 powder with different fabrication parameters. Code
pH = 1.5 pH = 2.0 pH = 2.5 pH = 3.0 pH = 3.5 pH = 4.0
Temperature (°C)
1160
W0 W200 W2000
PEG dissolve solution
PEG (wt.%) 200
400
2000
W W6+ W6+ W6+ W6+ W6+
– – – – – –
4.0 4.0 4.0 4.0 4.0 4.0
– – –
Zr4+ W6+ Zr4+ W6+ Zr4+ W6+
1.5 – – 1.5 1.5 –
– – – – – –
1.5 – 1.5 – – 1.5
6+
– –
stirred to prepare 0.04 mol/L W6+ solution with a preferred pH being 1.0, in order to increase the solubility of (NH4)5H5[H2(WO4)6]·H2O in the solution. Simultaneously, ZrOCl2·8H2O is also added in distilled water to prepare 0.02 mol/L Zr4+ solution when the pH is adjusted to 6.0. The different dispersing agents (PEG) are pre-dissolved in Zr4+ solution and W6+ solution as shown in Table 1. The 0.02 mol/L Zr4+solution is added to the 0.04 mol/L W6+ solution immediately, and then the pH of the solution is adjusted to the range of 1.5–4.0 by adding a certain concentration of hydrochloric acid (HCl) or ammonium hydroxide (NH3·H2O). During the coprecipitation, the reaction solution is vigorously stirred for 1 h. Subsequently, the reaction solution is placed for 12–24 h conducting aging process. The synthesis coprecipitation are dried in 100 °C in drying oven after vacuum filtration overnight, and then the products are put in furnace for 600 °C/2h and 1140–1200 °C/ 2h. It is more important to note that the products need to be quenched into an ice-water bath quickly for avoiding decomposition of ZrW2O8 materials, attributing that ZrW2O8 has only a narrow temperature range thermodynamic stability in 1105–1231 °C [17,18]. Phase identification is carried out by using X-ray Diffraction (Netherlands Panalytical instruments co., Ltd) with Cu-Ka radiation. The particle size and morphology of synthesized powders are observed by scanning electron microscopy (SEM, America FEI Quanta 200FEG). The particle size distribution is counted by LA-920 laser particle size analyzer (HORIBA). The phase purity was carried out using X-ray fluorescence (Netherlands Panalytical instruments co., Ltd).
Fig. 1. XRD patterns of the ZrW2O8 powder obtained via precursors prepared with different value of pH: (a) pH = 1.5; (b) pH = 2.0; (c) pH = 2.5; (d) pH = 3.0; (e) pH = 3.5; (f) pH = 4.0.
particle size of d90 is about 1.15 μm. The distribution becomes wider when the value of pH is 1.5, 2.5 and 3, about 5.65 μm, 5.87 μm and 4.47 μm, respectively. By adjusting the pH value of solution and adding amount of dispersant, the solution particles dispersion can be adjusted with the change of solution Zeta potential. In general, the metal oxides would absorb water vapor in the air to form a similar structure in the hydroxyl groups on the particle surface. However, in the acidic or alkaline liquid medium, the separation process occurs as follows:
In an acidic medium: M− OH + H+ = M− OH+2 In an alkaline medium: M− OH + OH− = M− O− + H2 O The degree of dissociation depends on the pH of the solution. In alkaline media, the surface of the dispersed phase particles is negative charged. While, in acidic medium, the surface of a dispersed phase particle is positive charged. Therefore, the concentration of H+ and OH− increases or decreases with the pH value of the solution adjusting. Electric potential changes have an appreciable influence on the balance between the attraction and repulsive force on the surface of colloidal particles. The solution viscosity changes accordingly, the best form of dispersion achieves when the viscosity reaches the minimum [19]. According to DLVO theory [17], the relation between VA (van der Waals attracting potential energy) and VR (repulsive potential energy between particles due to double electric layers) and the total potential energy VT between two particles are shown in equation (1):
3. Results and discussion 3.1. pH Fig. 1 shows the XRD patterns of ZrW2O8 powder obtained via precursors prepared with different value of pH. All the ZrW2O8 powders are successfully fabricated and no obvious peaks of impurity phase can be detected. All the peaks of ZrW2O8 powders are coordinated with standard diffraction peaks of ZrW2O8 based on the PDF cards (501868). There is no influence of PEG on the formation of ZrW2O8 phase, due to decomposing completely before 900 °C as the pervious reference reports [17]. Fig. 2 shows SEM images of the ZrW2O8 powder obtained via precursors prepared with different value of pH. The optimization particle size of ZrW2O8 powder can be obtained when the value of pH is 2 and the particle size is about 0.5–0.6 μm, which is smaller and more uniform than that of ZrW2O8 powder synthesized at any other value of pH. Fig. 3 shows particle size distribution of the ZrW2O8 powder with different value of pH. The results of particle size distribution are consistent with the SEM images of the ZrW2O8 powder. The average particle size is about 0.51 μm in pH 2. Its distribution is the narrowest, the
VT = VA + VR
(1)
When the distance between particles H = R-2r is very small, the gravitational potential energy VA of van der Waals is shown in equation (2):
VA =
−Ar 12H
(2)
H is the shortest distance between particles; R is the distance between the two particle centers; r is the particle radius; A is the Hamaker constant. When the particles are nano-micron in size, the repulsive potential energy VR generates between particles due to double electric layers is shown in equation (3):
VR ∝ exp(−k(R − 2r )) 28
(3)
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Fig. 2. SEM images of the ZrW2O8 powder obtained via precursors prepared with different value of pH: (a) pH = 1.5; (b) pH = 2.0; (c) pH = 2.5; (d) pH = 3.0; (e) pH = 3.5; (f) pH = 4.0.
changing addition sequence of PEG in solution. As shown in Fig. 4, the main diffraction peaks are assigned to the ZrW2O8 powder according to the PDF cards (50-1868). While, some weak peaks of m-ZrO2 can be observed, which is attributable to the decomposition of ZrW2O8 to form ZrO2 and WO3. Fig. 5 shows SEM images of the obtained ZrW2O8 powder prepared via different PEG. The ZrW2O8 powder is irregular shape in different PEG. The ZrW2O8 powder has different degrees growth, which distribution is relatively uniform and the particle size is smallest in W2000. Fig. 6 shows particle size distribution of the precursors prepared with changing addition sequence of PEG in solution. The particle size of ZrW2O8 powder has a widest distribution when using sequence of W0,
From equation (3), the thicker the double electric layer (1/k) is, the greater the repulsive potential energy generates between particles. Therefore, the total potential energy VT between particles presented repulsive barrier making it difficult for particles to reunite. In the present study, when the value of pH is 2, the thickness of the double layer of solution is suitable to form larger the exclusion barrier, so that the powder is dispersible and not easy to reunite. Therefore, the powder distribution of ZrW2O8 is relatively uniform with the smallest particle size.
3.2. The solution dissolved PEG Fig. 4 shows XRD patterns of the ZrW2O8 powder obtained via
Fig. 3. Particle size distribution of the ZrW2O8 powder obtained via precursors prepared with different value of pH: (a) pH = 1.5; (b) pH = 2.0; (c) pH = 2.5; (d) pH = 3.0; (e) pH = 3.5; (f) pH = 4.0. 29
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adsorption layer has a regular vertical extension. If the space resistance forces the system to a decentralized state, the dispersion effect is satisfied. This is the role of macromolecular weight PEG. But after reaching the full layer of adsorption, the excess adsorption molecules form a branched chain in the adsorption layer and the adsorption layer is complicated. This is affected by small molecular weight PEG. As a result, the solution has better dispersibility when the solution dissolving small molecular weight PEG is mixed into the solution dissolving macromolecular weight PEG. Besides, PEG is eliminated as gas when the calcining process, which has a certain impact on the powder. This made the particle size smaller. The dispersion of ZrW2O8 powder is improved, and the particle sizes are reduced.
3.3. Temperature Fig. 7 shows XRD patterns of the ZrW2O8 powders calcinated at different temperature from 1140 °C to 1200 °C. All the precursors are prepared at a pH of 2 with the PEG2000 dissolving in W6+ solution and PEG200 dissolving in Zr4+ solution correspondingly. From the Fig. 7 (A), the main diffraction peaks of powders are assigned to ZrW2O8, while some peaks of ZrO2 as impurities are also detected. The peaks intensity of ZrO2 increase with increasing the calcination temperature based on the XRD enlarged patterns ranging of 26–32° as shown in Fig. 7(B), which is attributed to the thermodynamic stability of ZrW2O8 and the volatilization of WO3 at high temperature [21]. With the temperature increasing, the volatilization of WO3 becomes more obvious, and the amount of residual zirconium oxide increases subsequently. From Fig. 7(B), the peak position of ZrW2O8 is slightly shifted to high angle. The 2theta (2θ) increasing with the d decreasing indicates the reduction of the cell parameters, which indicates that the volume of ZrW2O8 is shrinking as the temperature increase [22]. This is the negative thermal expansion of ZrW2O8 as the literature reported [23,24]. Fig. 8 showed SEM images of the ZrW2O8 powders calcinated at different temperature. The ZrW2O8 powder has irregular shape at different temperature. The ZrW2O8 powder distribution is relatively uniform and the particle size increases with increasing the calcination temperature. The ZrW2O8 powder particle size is the largest when temperature is 1200 °C. Fig. 9 showed particle size distribution images of the ZrW2O8 powders calcinated at different temperature. The average particles size and particle size distribution of ZrW2O8 powder are similar when calcinated at 1140 °C and 1160 °C. While, the particle size of ZrW2O8 powder begins to show a growth trend when the calcination temperature is more than 1180 °C. The particle size d90 of ZrW2O8 powder obtained at 1180 °C and 1200 °C is about 2.27 μm and 2.57 μm, respectively. The optimization calcination temperature of the powder is 1160 °C, and the average particle size d50 is about 0.77 μm with the narrow distribution. Thus, it is certain that the precursors prepared in this case that the W6+ solution is incorporated with PEG400 and then adjusted the value of pH to 2. Subsequently, the precursors are calcined at 600 °C for 2 h and 1160 °C for 2 h to obtain high purity ZrW2O8
Fig. 4. XRD patterns of the precursors prepared via different addition sequence of PEG in solution: (a) W0; (b) W20; (c) W2000.
the average particles size d50 of ZrW2O8 powder is about 5.12 μm and d90 is about 10.10 μm. For using W2000, the average particle size of powder gets minimized, the particle size d50 of powders is about 0.88 μm with narrow distribution. This deduces that when Zr4+ solution (dissolving small molecular weight of PEG) mixes with W6+ solution (dissolving macromolecular weight long chain PEG), the solution has the best dispersibility. Thereby, ZrW2O8 powder with the smaller particles size and narrower distribution is synthetized under this circumstances. This result is consistent with SEM images. It is reported in the literature the particle size is reduced by adding appropriate dispersant (PEG) [15]. Particles size is reduced from 10 μm to 2 μm after adding PEG2000 into solution. The particles size synthetized in present study is smaller than that in the literature reported. PEG is a kind of non-ionic surfactant, which is used in nanopowder preparation. It only has two kinds of hydrophilic base (ether-base and hydroxy) without hydrophobic base, its molecular chain presents a snake form in water solution, and it is easy to build a strong hydrogen bond with hydroxide gel surface, so as to form a large molecule hydrophilic membrane on the surface of the colloidal particles. As a result, the effects of high electrostatic and space resistance are caused. The intergranular reunite is controlled by the surface tension between particles, which reduces due to the influence of high electrostatic and space resistance. The space resistance of the particles increases with the addition of PEG, the powder agglomeration is reduced with it [20]. Particles are separated because the macromolecular weight PEG form long chain in solution and are coated by the small molecular weight PEG. As PEG forming a complete single adsorption layer on the particle surface, the Van der Waals force between particle becomes small. The
Fig. 5. SEM images of the precursors prepared via different addition sequence of PEG in solution: (a) W0; (b) W20; (c) W2000. 30
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Fig. 6. Particle size distribution images of the precursors prepared via different addition sequence of PEG in solution: (a) W0; (b) W20; (c) W2000.
Fig. 7. XRD patterns of the ZrW2O8 powders calcinated at different temperature: (a) 1140 °C, (b) 1160 °C, (c) 1180 °C, (d) 1200 °C; (A) XRD patterns of the ZrW2O8 powders calcinated at 1140–1200 °C, (B) XRD enlarged patterns ranging of 26–32°.
Fig. 8. SEM of the ZrW2O8 powders calcinated at different temperature: (a) 1140 °C; (b) 1160 °C; (c) 1180 °C; (d) 1200 °C. 31
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Fig. 9. Particle size distribution images of the ZrW2O8 powders calcinated at different temperature: (a) 1140 °C; (b) 1160 °C; (c) 1180 °C; (d) 1200 °C. Table 2 XRF results of ZrW2O8 powder. Zr (at %)
W (at %)
O (at %)
Zr (mol %)
W (mol %)
ZrW2O8 (mol)
ZrO2 (mol)
ZRW2O8 (at%)
ZrO (at %)
17.40
63.80
18.80
35.48
64.52
0.32
0.03
97.95
2.05
powder with small particles size and narrow distribution. The purity of ZrW2O8 powder is also detected by XRF as listed in Table 2, which is indicated that the purity of optimized ZrW2O8 powder is about 97.95 at. % and the ZrO2 is the only impurity in the ZrW2O8 powder.
of ZrW2O8 synthesized by solid phase method, Rare Metal. 32 (2008) 38–42. [3] X.L. Du, X.H. Qu, M.L. Qin, R.S. Guo, The negative expansion coefficient material ZrW2O8 prepared by coprecipitation method, J. Univ. Sci. Technol. Beijing 29 (2007) 925–927. [4] X.J. Sun, X.N. Cheng, J. Yang, Q.Q. Liu, Synthesis and property study on negative thermal expansion ZrW2O8 powders using the citric acid sol-gel method, J. Funct. Mater. 46 (2015) 08023–08027. [5] X.J. Sun, X.N. Cheng, J. Yang, Q.Q. Liu, Effect of acids on the morphology and negative thermal expansion analysis of ZrW2O8powders prepared by the hydrothermal method, Ceram. Int. 39 (2013) 165–170. [6] X. Yan, X.N. Cheng, X.B. Yang, C.H. Zhang, Combustion synthesis of ZrW2O8 and preparation of its composite with near zero thermal expansion, Key Eng. Mater. 353–358 (2007) 1235–1238. [7] X.Y. Kong, J.S. Wu, Z.P. Zeng, ZrW2O8 microwave synthesis characterization and negative expansion behavior, J. Chin. Ceram. Soc. 27 (1999) 265–269. [8] D.M. Christina, D.I. Van, S. Hoste, Synthesis of the negative thermal expansion compound ZrW2O8 by the spray drying technique, Eng. Mater. 206 (2002) 11–14. [9] L.M.S. And, C.M. Lukehart, Zirconium tungstate (ZrW2O8)/polyimide nanocomposites exhibiting reduced coefficient of thermal expansion, Chem. Mater. 17 (2005) 2136–2141. [10] L. Jiang, W.F. Shangguan, Hydrothermal preparation and photocatalytic water splitting properties of ZrW2O8, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 25 (2010) 919–923. [11] K. Kanamori, T. Kineri, R. Fukuda, K. Nishio, M. Hashimoto, H. Mae, Spark plasma sintering of sol–gel derived amorphous ZrW2O8 nanopowder, J. Am. Ceram. Soc. 92 (2010) 32–35. [12] X. Xing, Q. Xing, R. Yu, J. Meng, J. Chen, G. Liu, Hydrothermal synthesis of ZrW2O8 nanorods, Phys. B Phys. Condensed Matter 371 (2006) 81–84. [13] S. Nishiyama, T. Hayashi, T. Hattori, Synthesis of ZrW2O8 by quick cooling and measurement of negative thermal expansion of the sintered bodies, J. Alloy. Compd. 417 (2006) 187–189. [14] X. Yang, J. Xu, H. Li, X. Cheng, X. Yan, In situ synthesis of ZrO2/ZrW2O8 composites with near-zero thermal expansion, J. Am. Ceram. Soc. 90 (2010) 1953–1955. [15] X.J. Sun, J. Yang, Q.Q. Liu, X.N. Cheng, Synthesis and primary particle size control study on negative thermal expansion ZrW2O8 powders using co-precipitation method, Chin. J. Inorg. Chem. 21 (2005) 1412–1416. [16] X.J. Sun, J. Yang, Q.Q. Liu, X.N. Cheng, Synthesize ZrW2O8 powders with different particle size by co-precipitation method and characterize the negative thermal expansion property, J. Funct. Mater. 38 (2007) 3184–3187. [17] A. Fedorova, T. Kämpf, M. Scheffler, Study of phase decomposition in ZrW2O8, Adv. Eng. Mater. 18 (2016) 1118–1122. [18] J.P. Li, C. Yang, S.H. Meng, F.J. Yi, Y.H. Li, Effect of the cooling ways on the
4. Conclusions The high purity ZrW2O8 powder with small particle size is fabricated using the coprecipitation method. The particles size and particles size distribution of ZrW2O8 powder are appreciably affected by pH and the solution dissolved PEG. The optimization fabrication process for obtaining the small particles size ZrW2O8 powder with narrow particle size distribution is that PEG400 is firstly added into W6+ solution for preparation precursor with a preferred pH of 2, and then calcined at 600 °C for 2 h and 1160 °C for 2 h. The purity of ZrW2O8 powder reaches about 97.95% based on the XRF results. The particles size d50 and d90 of ZrW2O8 powder is about 0.51 μm and 1.15 μm, respectively. Acknowledgements This work is partially supported by the National Natural Science Foundation of China (Grant Nos.: Nos. 51172052, 51602074 and 51621091) Natural Science Foundation of Heilongjiang Province (Grant No. E2016026), China Postdoctoral Science Foundation (Grant No. 2016M600246), and Heilongjiang Postdoctoral Foundation (Grant No. LBH-Z16084). Program for New Century Excellent Talents in University (No. NCET-13-0177) are also greatly appreciated. References [1] L.H.N. Rimmer, M.T. Dove, K. Refson, The negative thermal expansion mechanism of zirconium tungstate ZrW2O8, Physics 17 (2016) 1089–1094. [2] L.S. Tong, J.Z. Fan, B.L. Xiao, T. Zhuo, The effect of sintering process on the purity
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[22] X.P. Chen, L.M. Fang, G.A. Sun, F. Peng, B. Chen, D.W. He, L. Jing, Preparation and pressure-induced cubic-to-orthorhombic phase transition in ZrW2O8, J. High Pressure Phys. 29 (2015) 59–62. [23] G. Ventura, M. Perfetti, Thermal Properties of Solids at Room and Cryogenic Temperatures, Springer Netherlands .5 (2014) 81–91. [24] X.M. Zhao, Y.L. Kang, Q.H. Han, Austenite isochronal transformation kinetics of 1000 MPa cold rolled dual phase steel, Beijing KejiDaxueXuebao J. Univ. Sci. Technol. Beijing 35 (2013) 195–200.
properties and microstructure of ZrO2/ZrW2O8 ceramic composites, Key Eng. Mater. 697 (2016) 381–385. [19] H.T. Zhu, C.Y. Zhang, J.Y. Yang, Y.Y. Hou, Studies on gelcasting of zirconia-alumina ceramic, Shandong Ceram. 22 (1999) 3–7. [20] X.J. Sun, J. Yang, Q.Q. Liu, X.N. Cheng, Effect of preparation method on particle size and negative thermal expansion property of negative thermal expansion ZrW2O8 powders, Chin. J. Inorg. Chem. 22 (2006) 1635–1639. [21] Y. Wang, J. Wang, L. Wang, The influence of sintering temperature on ZrW2O8 prepared by solid phase method, Heat Treatment 25 (2010) 22–23.
33
Contents lists available at ScienceDirect
Materials Science & Engineering B journal homepage: www.elsevier.com/locate/mseb
Particle size and purity control study on ZrW2O8 powders using coprecipitation method ⁎
T
⁎
Yan Zhanga, Yingkui Guoa, , Lei Chenb, , Yujin Wangb, Guangwei Zhanga, Yuansong Zhoua a
Inorganic Nonmetallic Materials and Engineering Department, School of Materials Science and Engineering, Harbin University of Science and Technology, Harbin 150000, PR China b Institute of Advance Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: ZrW2O8 powder Coprecipitation method Particles size Calcination temperature
ZrW2O8 powders with different particles size are synthesized by coprecipitation method. The effects of pH, PEG and calcination temperature on the phase, morphology and particle size of ZrW2O8 powders were investigated. The purity of the ZrW2O8 powder is also detected by XRF, and the optimal parameters of the coprecipitation method are obtained. The coprecipitation precursor is prepared by adding PEG400 into W6+ solution with a preferred pH of 2, and then calcined at 600 °C for 2 h and 1160 °C for 2 h to obtain the small particles size ZrW2O8 powder with narrow particle size distribution. The average particle size of ZrW2O8 powder is about 0.51 μm. The purity of ZrW2O8 powder is 97.95% with 2.05% ZrO2 as impurity due to the thermodynamic instability of ZrW2O8 and the volatilization of WO3 at high temperature.
1. Introduction ZrW2O8 material has negative thermal expansion (NTE) property ranging from 0.3 K to 1050 K, the negative thermal expansion coefficient is about −9 × 10−6 K−1 [1], which has been widely used in electronic device, optical microscope with high precision, precision optical lens, gums filler material and substrate material, etc. The potential application of ZrW2O8 material has stimulated interest in the synthesis of ZrW2O8 powder. How to simply obtain the high purity ZrW2O8 powders with small size is becoming a very important issue, and has caused wide broad concern over the recent years. There are a variety of methods for fabrication ZrW2O8 powder, such as the solid phase method [2], the coprecipitation method [3], the sol-gel method [4], hydrothermal method [5], combustion method [6], microwave synthesis method [7], and spray drying method [8]. Although the ZrW2O8 powder prepared by sol-gel method and hydrothermal method can get a small particle size and high purity [9,10], it entails considerable time and complex process, maybe take several weeks [11,12]. Solid phase method is a traditional simple method to prepare ZrW2O8 powder, while the particle size is always about 5–15 μm by common fabrication process [13,14]. Thus, the ZrW2O8 powder needs to be further grinded, and some impurity would be introduced into the fine ZrW2O8 powder. The coprecipitation method is attractive fabrication process to synthesis some small particle size powders. Sun et al. [15] have fabricated the ZrW2O8 ⁎
powder by coprecipitation method with 2.5 μm, then have successfully synthesized ZrW2O8 powder with the size of 0.4 μm by coprecipitation method particles via zirconium oxynitrate, ammonium tungstate and PEG-20000, when the value of nPEG/nmetal is 0.032 [16]. While, the detail particle size adjustment and purity refinement of synthesis ZrW2O8 powder are still no reported in detail. In this study, based on an overall consideration of purity and particle size of ZrW2O8 powder, the coprecipitation method was employed to prepare the ZrW2O8 powder via zirconium chloride and ammonium tungstate with different value of PH. The particles size and its distribution of ZrW2O8 powder were investigated by laser particle size analyzer and scanning electron microscopy (SEM) to evaluate the influence of pH value and amount of PEG in precursor solution. The purity of ZrW2O8 powder under the different calcination temperature are also further investigated by X-Ray Diffraction (XRD) and X-ray fluorescence (XRF). 2. Experimental method The raw materials are oxygen zirconium chloride (ZrOCl2·8H2O) and ammonium tungstate ((NH4)5H5[H2(WO4)6]·H2O) (Pharmaceutical group co., LTD, China). The compositional concentration of ZrOCl2·8H2O and (NH4)5H5[H2(WO4)6]·H2O are calculated according to the adequate molar ratios of ZrO2 and WO3. The (NH4)5H5[H2(WO4)6]·H2O is dissolved in distilled water and vigorously
Corresponding authors. E-mail addresses: [email protected] (Y. Guo), [email protected] (L. Chen).
https://doi.org/10.1016/j.mseb.2019.05.019 Received 21 October 2017; Received in revised form 25 April 2019; Accepted 17 May 2019 Available online 04 June 2019 0921-5107/ © 2019 Elsevier B.V. All rights reserved.
Materials Science & Engineering B 246 (2019) 27–33
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Table 1 Compositional design of ZrW2O8 powder with different fabrication parameters. Code
pH = 1.5 pH = 2.0 pH = 2.5 pH = 3.0 pH = 3.5 pH = 4.0
Temperature (°C)
1160
W0 W200 W2000
PEG dissolve solution
PEG (wt.%) 200
400
2000
W W6+ W6+ W6+ W6+ W6+
– – – – – –
4.0 4.0 4.0 4.0 4.0 4.0
– – –
Zr4+ W6+ Zr4+ W6+ Zr4+ W6+
1.5 – – 1.5 1.5 –
– – – – – –
1.5 – 1.5 – – 1.5
6+
– –
stirred to prepare 0.04 mol/L W6+ solution with a preferred pH being 1.0, in order to increase the solubility of (NH4)5H5[H2(WO4)6]·H2O in the solution. Simultaneously, ZrOCl2·8H2O is also added in distilled water to prepare 0.02 mol/L Zr4+ solution when the pH is adjusted to 6.0. The different dispersing agents (PEG) are pre-dissolved in Zr4+ solution and W6+ solution as shown in Table 1. The 0.02 mol/L Zr4+solution is added to the 0.04 mol/L W6+ solution immediately, and then the pH of the solution is adjusted to the range of 1.5–4.0 by adding a certain concentration of hydrochloric acid (HCl) or ammonium hydroxide (NH3·H2O). During the coprecipitation, the reaction solution is vigorously stirred for 1 h. Subsequently, the reaction solution is placed for 12–24 h conducting aging process. The synthesis coprecipitation are dried in 100 °C in drying oven after vacuum filtration overnight, and then the products are put in furnace for 600 °C/2h and 1140–1200 °C/ 2h. It is more important to note that the products need to be quenched into an ice-water bath quickly for avoiding decomposition of ZrW2O8 materials, attributing that ZrW2O8 has only a narrow temperature range thermodynamic stability in 1105–1231 °C [17,18]. Phase identification is carried out by using X-ray Diffraction (Netherlands Panalytical instruments co., Ltd) with Cu-Ka radiation. The particle size and morphology of synthesized powders are observed by scanning electron microscopy (SEM, America FEI Quanta 200FEG). The particle size distribution is counted by LA-920 laser particle size analyzer (HORIBA). The phase purity was carried out using X-ray fluorescence (Netherlands Panalytical instruments co., Ltd).
Fig. 1. XRD patterns of the ZrW2O8 powder obtained via precursors prepared with different value of pH: (a) pH = 1.5; (b) pH = 2.0; (c) pH = 2.5; (d) pH = 3.0; (e) pH = 3.5; (f) pH = 4.0.
particle size of d90 is about 1.15 μm. The distribution becomes wider when the value of pH is 1.5, 2.5 and 3, about 5.65 μm, 5.87 μm and 4.47 μm, respectively. By adjusting the pH value of solution and adding amount of dispersant, the solution particles dispersion can be adjusted with the change of solution Zeta potential. In general, the metal oxides would absorb water vapor in the air to form a similar structure in the hydroxyl groups on the particle surface. However, in the acidic or alkaline liquid medium, the separation process occurs as follows:
In an acidic medium: M− OH + H+ = M− OH+2 In an alkaline medium: M− OH + OH− = M− O− + H2 O The degree of dissociation depends on the pH of the solution. In alkaline media, the surface of the dispersed phase particles is negative charged. While, in acidic medium, the surface of a dispersed phase particle is positive charged. Therefore, the concentration of H+ and OH− increases or decreases with the pH value of the solution adjusting. Electric potential changes have an appreciable influence on the balance between the attraction and repulsive force on the surface of colloidal particles. The solution viscosity changes accordingly, the best form of dispersion achieves when the viscosity reaches the minimum [19]. According to DLVO theory [17], the relation between VA (van der Waals attracting potential energy) and VR (repulsive potential energy between particles due to double electric layers) and the total potential energy VT between two particles are shown in equation (1):
3. Results and discussion 3.1. pH Fig. 1 shows the XRD patterns of ZrW2O8 powder obtained via precursors prepared with different value of pH. All the ZrW2O8 powders are successfully fabricated and no obvious peaks of impurity phase can be detected. All the peaks of ZrW2O8 powders are coordinated with standard diffraction peaks of ZrW2O8 based on the PDF cards (501868). There is no influence of PEG on the formation of ZrW2O8 phase, due to decomposing completely before 900 °C as the pervious reference reports [17]. Fig. 2 shows SEM images of the ZrW2O8 powder obtained via precursors prepared with different value of pH. The optimization particle size of ZrW2O8 powder can be obtained when the value of pH is 2 and the particle size is about 0.5–0.6 μm, which is smaller and more uniform than that of ZrW2O8 powder synthesized at any other value of pH. Fig. 3 shows particle size distribution of the ZrW2O8 powder with different value of pH. The results of particle size distribution are consistent with the SEM images of the ZrW2O8 powder. The average particle size is about 0.51 μm in pH 2. Its distribution is the narrowest, the
VT = VA + VR
(1)
When the distance between particles H = R-2r is very small, the gravitational potential energy VA of van der Waals is shown in equation (2):
VA =
−Ar 12H
(2)
H is the shortest distance between particles; R is the distance between the two particle centers; r is the particle radius; A is the Hamaker constant. When the particles are nano-micron in size, the repulsive potential energy VR generates between particles due to double electric layers is shown in equation (3):
VR ∝ exp(−k(R − 2r )) 28
(3)
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Fig. 2. SEM images of the ZrW2O8 powder obtained via precursors prepared with different value of pH: (a) pH = 1.5; (b) pH = 2.0; (c) pH = 2.5; (d) pH = 3.0; (e) pH = 3.5; (f) pH = 4.0.
changing addition sequence of PEG in solution. As shown in Fig. 4, the main diffraction peaks are assigned to the ZrW2O8 powder according to the PDF cards (50-1868). While, some weak peaks of m-ZrO2 can be observed, which is attributable to the decomposition of ZrW2O8 to form ZrO2 and WO3. Fig. 5 shows SEM images of the obtained ZrW2O8 powder prepared via different PEG. The ZrW2O8 powder is irregular shape in different PEG. The ZrW2O8 powder has different degrees growth, which distribution is relatively uniform and the particle size is smallest in W2000. Fig. 6 shows particle size distribution of the precursors prepared with changing addition sequence of PEG in solution. The particle size of ZrW2O8 powder has a widest distribution when using sequence of W0,
From equation (3), the thicker the double electric layer (1/k) is, the greater the repulsive potential energy generates between particles. Therefore, the total potential energy VT between particles presented repulsive barrier making it difficult for particles to reunite. In the present study, when the value of pH is 2, the thickness of the double layer of solution is suitable to form larger the exclusion barrier, so that the powder is dispersible and not easy to reunite. Therefore, the powder distribution of ZrW2O8 is relatively uniform with the smallest particle size.
3.2. The solution dissolved PEG Fig. 4 shows XRD patterns of the ZrW2O8 powder obtained via
Fig. 3. Particle size distribution of the ZrW2O8 powder obtained via precursors prepared with different value of pH: (a) pH = 1.5; (b) pH = 2.0; (c) pH = 2.5; (d) pH = 3.0; (e) pH = 3.5; (f) pH = 4.0. 29
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adsorption layer has a regular vertical extension. If the space resistance forces the system to a decentralized state, the dispersion effect is satisfied. This is the role of macromolecular weight PEG. But after reaching the full layer of adsorption, the excess adsorption molecules form a branched chain in the adsorption layer and the adsorption layer is complicated. This is affected by small molecular weight PEG. As a result, the solution has better dispersibility when the solution dissolving small molecular weight PEG is mixed into the solution dissolving macromolecular weight PEG. Besides, PEG is eliminated as gas when the calcining process, which has a certain impact on the powder. This made the particle size smaller. The dispersion of ZrW2O8 powder is improved, and the particle sizes are reduced.
3.3. Temperature Fig. 7 shows XRD patterns of the ZrW2O8 powders calcinated at different temperature from 1140 °C to 1200 °C. All the precursors are prepared at a pH of 2 with the PEG2000 dissolving in W6+ solution and PEG200 dissolving in Zr4+ solution correspondingly. From the Fig. 7 (A), the main diffraction peaks of powders are assigned to ZrW2O8, while some peaks of ZrO2 as impurities are also detected. The peaks intensity of ZrO2 increase with increasing the calcination temperature based on the XRD enlarged patterns ranging of 26–32° as shown in Fig. 7(B), which is attributed to the thermodynamic stability of ZrW2O8 and the volatilization of WO3 at high temperature [21]. With the temperature increasing, the volatilization of WO3 becomes more obvious, and the amount of residual zirconium oxide increases subsequently. From Fig. 7(B), the peak position of ZrW2O8 is slightly shifted to high angle. The 2theta (2θ) increasing with the d decreasing indicates the reduction of the cell parameters, which indicates that the volume of ZrW2O8 is shrinking as the temperature increase [22]. This is the negative thermal expansion of ZrW2O8 as the literature reported [23,24]. Fig. 8 showed SEM images of the ZrW2O8 powders calcinated at different temperature. The ZrW2O8 powder has irregular shape at different temperature. The ZrW2O8 powder distribution is relatively uniform and the particle size increases with increasing the calcination temperature. The ZrW2O8 powder particle size is the largest when temperature is 1200 °C. Fig. 9 showed particle size distribution images of the ZrW2O8 powders calcinated at different temperature. The average particles size and particle size distribution of ZrW2O8 powder are similar when calcinated at 1140 °C and 1160 °C. While, the particle size of ZrW2O8 powder begins to show a growth trend when the calcination temperature is more than 1180 °C. The particle size d90 of ZrW2O8 powder obtained at 1180 °C and 1200 °C is about 2.27 μm and 2.57 μm, respectively. The optimization calcination temperature of the powder is 1160 °C, and the average particle size d50 is about 0.77 μm with the narrow distribution. Thus, it is certain that the precursors prepared in this case that the W6+ solution is incorporated with PEG400 and then adjusted the value of pH to 2. Subsequently, the precursors are calcined at 600 °C for 2 h and 1160 °C for 2 h to obtain high purity ZrW2O8
Fig. 4. XRD patterns of the precursors prepared via different addition sequence of PEG in solution: (a) W0; (b) W20; (c) W2000.
the average particles size d50 of ZrW2O8 powder is about 5.12 μm and d90 is about 10.10 μm. For using W2000, the average particle size of powder gets minimized, the particle size d50 of powders is about 0.88 μm with narrow distribution. This deduces that when Zr4+ solution (dissolving small molecular weight of PEG) mixes with W6+ solution (dissolving macromolecular weight long chain PEG), the solution has the best dispersibility. Thereby, ZrW2O8 powder with the smaller particles size and narrower distribution is synthetized under this circumstances. This result is consistent with SEM images. It is reported in the literature the particle size is reduced by adding appropriate dispersant (PEG) [15]. Particles size is reduced from 10 μm to 2 μm after adding PEG2000 into solution. The particles size synthetized in present study is smaller than that in the literature reported. PEG is a kind of non-ionic surfactant, which is used in nanopowder preparation. It only has two kinds of hydrophilic base (ether-base and hydroxy) without hydrophobic base, its molecular chain presents a snake form in water solution, and it is easy to build a strong hydrogen bond with hydroxide gel surface, so as to form a large molecule hydrophilic membrane on the surface of the colloidal particles. As a result, the effects of high electrostatic and space resistance are caused. The intergranular reunite is controlled by the surface tension between particles, which reduces due to the influence of high electrostatic and space resistance. The space resistance of the particles increases with the addition of PEG, the powder agglomeration is reduced with it [20]. Particles are separated because the macromolecular weight PEG form long chain in solution and are coated by the small molecular weight PEG. As PEG forming a complete single adsorption layer on the particle surface, the Van der Waals force between particle becomes small. The
Fig. 5. SEM images of the precursors prepared via different addition sequence of PEG in solution: (a) W0; (b) W20; (c) W2000. 30
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Fig. 6. Particle size distribution images of the precursors prepared via different addition sequence of PEG in solution: (a) W0; (b) W20; (c) W2000.
Fig. 7. XRD patterns of the ZrW2O8 powders calcinated at different temperature: (a) 1140 °C, (b) 1160 °C, (c) 1180 °C, (d) 1200 °C; (A) XRD patterns of the ZrW2O8 powders calcinated at 1140–1200 °C, (B) XRD enlarged patterns ranging of 26–32°.
Fig. 8. SEM of the ZrW2O8 powders calcinated at different temperature: (a) 1140 °C; (b) 1160 °C; (c) 1180 °C; (d) 1200 °C. 31
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Fig. 9. Particle size distribution images of the ZrW2O8 powders calcinated at different temperature: (a) 1140 °C; (b) 1160 °C; (c) 1180 °C; (d) 1200 °C. Table 2 XRF results of ZrW2O8 powder. Zr (at %)
W (at %)
O (at %)
Zr (mol %)
W (mol %)
ZrW2O8 (mol)
ZrO2 (mol)
ZRW2O8 (at%)
ZrO (at %)
17.40
63.80
18.80
35.48
64.52
0.32
0.03
97.95
2.05
powder with small particles size and narrow distribution. The purity of ZrW2O8 powder is also detected by XRF as listed in Table 2, which is indicated that the purity of optimized ZrW2O8 powder is about 97.95 at. % and the ZrO2 is the only impurity in the ZrW2O8 powder.
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4. Conclusions The high purity ZrW2O8 powder with small particle size is fabricated using the coprecipitation method. The particles size and particles size distribution of ZrW2O8 powder are appreciably affected by pH and the solution dissolved PEG. The optimization fabrication process for obtaining the small particles size ZrW2O8 powder with narrow particle size distribution is that PEG400 is firstly added into W6+ solution for preparation precursor with a preferred pH of 2, and then calcined at 600 °C for 2 h and 1160 °C for 2 h. The purity of ZrW2O8 powder reaches about 97.95% based on the XRF results. The particles size d50 and d90 of ZrW2O8 powder is about 0.51 μm and 1.15 μm, respectively. Acknowledgements This work is partially supported by the National Natural Science Foundation of China (Grant Nos.: Nos. 51172052, 51602074 and 51621091) Natural Science Foundation of Heilongjiang Province (Grant No. E2016026), China Postdoctoral Science Foundation (Grant No. 2016M600246), and Heilongjiang Postdoctoral Foundation (Grant No. LBH-Z16084). Program for New Century Excellent Talents in University (No. NCET-13-0177) are also greatly appreciated. References [1] L.H.N. Rimmer, M.T. Dove, K. Refson, The negative thermal expansion mechanism of zirconium tungstate ZrW2O8, Physics 17 (2016) 1089–1094. [2] L.S. Tong, J.Z. Fan, B.L. Xiao, T. Zhuo, The effect of sintering process on the purity
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