Preparation and characterization of ZrWMoO8 powders with different morphologies using hydrothermal method

Abstract

Materials that exhibit negative thermal expansion (NTE) property are of considerable scientific and technological interests [1–5]. Their use in composites facilitates the control of bulk thermal expansion properties to avoid cracks or separation at interfaces between the two components, which is especially needed for various applications in optics, electronics, and other fields where exact positioning of parts is crucial [6, 7]. For use in composite, an ideal NTE material should have isotropic and linear negative thermal expansion properties during a large temperature range including room temperature [8]. It is desirable that the material is thermodynamically stable over its NTE range and can be prepared in a low-cost and efficient way. The most promising NTE material to date is ZrW2O8 family due to its’ isotropic NTE property over a wide temperature range. The typical material, ZrW2O8, undergoes isotropic NTE behavior from 0.3 K to 1050 K [9,10]. Unfortunately, for use in composites, there are some drawbacks. For example, ZrW2O8 undergoes an order-disorder phase transition around 430 K and the linear coefficient changed from – 8.8 · 10 K to –4.9 · 10 K[11]. It also undergoes a phase transition to a more dense structure (with a significantly lower coefficient of NTE) at around 0.2 Gpa. While structurally related phases such as ZrMo2O8 and ZrW2–xMoxO8 solid solution do not undergo phase transition over the NTE temperature range, which makes it desirable in preparing composite materials [12–14]. Cubic ZrWMoO8 is a typical ZrW2–xMoxO8 solid solution. But it is difficult to prepare due to the volatilization of WO3 and MoO3 when conventional solid state techniques is used. The breakthrough in this area came when dehydration of the precursor method was put forward [15]. But this method was far from optimal because the solution usually was aged and gelatinized for weeks. Recently, a rapid synthetic route, hydrothermal method was approached and highly crystallized cubic ZrWMoO8 powders were achieved without the aging procedure [16]. As used as fillers in composites, for decreasing the innerstress, proper morphology is important. But to date, most NTE materials have been synthesized as powders without controlling in morphology due to the difficulty in synthesis. In this paper, ZrWMoO8 powders with different morphologies were prepared by hydrothermal method using HCl, HClO4, HNO3, H2SO4 and CH3COOH as acid media respectively. The influence of the kind of acid on the morphologies of the obtained ZrWMoO8 was also investigated. All the chemical reagents were analytical grade purity without further purification. In the typical procedure, zirconium oxynitrate [ZrO (NO3)2 5H2O], ammonium tungstate [N5H37W6O24 H2O] and ammonium molybdate [N5H37Mo6O24 H2O] were dissolved separately in distilled water according to the mole ratio of Zr:W:Mo=1:1:1. First, W solution and Mo solution were mixed, and then Zr solution was added slowly under vigorous stirring. After that, acid solution (HCl, HClO4, HNO3, H2SO4, CH3COOH(HOAc)) was added slowly to the above solution with continuous stirring for another 3 h. The Q.-Q. Liu J. Yang X.-J. Sun X.-N. Cheng (&) G.-F. Xu X.-H. Yan School of Materials Science and Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China e-mail: xncheng@ujs.edu.cn