The impact of bead milling on the thermodynamics and kinetics of the structural phase transition of VO<sub>2</sub> particulate materials and their potential for use in thermochromic glazing

The thermodynamics and kinetics of the structural phase transition from monoclinic VO2(M) to rutile VO2(R) and were studied for particulate materials obtained by bead milling of VO2(M) powder. Using wet bead milling, we decreased the particle size of VO2(M) powder from ∼1 μm to 129 nm. With progressive milling, the switching enthalpy decreased from 47 J g−1to 29 J g−1due to a loss of crystallinity. The switching kinetics were studied using Friedman's differential isoconversional method. The activation energy || decreases with increasing difference between the actual temperature of the material and its switching temperature (). Furthermore, || decreases with progressive milling, and kinetic asymmetry is induced. For milled particulate materials, || is lower for the switch from VO2(R) to VO2(M) than for the opposite switch. For hydrothermally synthesized nanoparticles, || is in the same order of magnitude, albeit with inverse switching asymmetry. Latter may result from different defects that are introduced during both preparation techniques. Applying layers of milled particulate material to glass sheets yielded thermochromic coatings with luminous transmission of 40.7% and solar modulation of 8.3%. This demonstrates that milled VO2particles have potential for use in energy efficient thermochromic windows.

对通过球磨VO₂(M)粉末获得的颗粒材料，研究了从单斜晶系VO₂(M)到金红石型VO₂(R)的结构相变的热力学和动力学。通过湿式球磨，我们将VO₂(M)粉末的粒径从约1μm减小到129nm。随着球磨的进行，由于结晶度的降低，转变焓从47 J g⁻¹降至29 J g⁻¹。采用弗里德曼微分等转化率法研究了转变动力学。活化能||随着材料的实际温度与其转变温度( )之间差值的增大而降低。此外，||随着球磨的进行而降低，并且产生了动力学不对称性。对于球磨后的颗粒材料，从VO₂(R)到VO₂(M)的转变的||比相反转变的要低。对于水热合成的纳米粒子，||处于相同的数量级，尽管具有相反的转变不对称性。后者可能是由两种制备技术过程中引入的不同缺陷导致的。将球磨后的颗粒材料层涂覆在玻璃板上，得到了透光率为40.7%、太阳调制率为8.3%的热致变色涂层。这表明球磨后的VO₂颗粒在节能热致变色窗户方面具有应用潜力。