Yubo Zhang

Giant Phase Transition Properties at Terahertz Range in VO2 films Deposited by Sol–Gel Method

VO(2) films were fabricated on high-purity single-crystalline silicon substrate by the sol-gel method, followed by rapid annealing. The composition and microstructure of the films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The results indicated a polycrystalline nature with high crystallinity and compact nanostructure for the films, and the concentration of +4 valence vanadium is 79.85%. Correlated with these, a giant transmission modulation ratio about 81% of the film was observed by terahertz time domain spectroscopy. The experimentally observed transmission characteristics were reproduced approximately, by a simulation at different conductivities across the phase transition. According to the effective-medium theory, we assumed that it is important to increase the concentration of +4 valence vanadium oxide phases and improve the compactness of the VO(2) films for giant phase transition properties. The sol-gel-derived VO(2) films with giant phase transition properties at terahertz range, and the study on their composition and microstructure, provide considerable insight into the fabrication of VO(2) films for the application in THz modulation devices.

Curing of polyester powder coating modified with rutile nano-sized titanium dioxide studied by DSC and real-time FT-IR

Polyester powder coating modified with 2 mass% of rutile nano-sized titanium dioxide (nano-TiO2) was prepared by melt-blend extrusion method. The nano-TiO2 dispersion state in the powder coating matrix was analyzed by field emission scanning electron microscopy (FE-SEM), which presented a well dispersion of modified nano-TiO2 in the polyester powder coating. The effect of nano-TiO2 on the curing of polyester powder coating was investigated by differential scanning calorimeter (DSC). Kissinger and Crane methods were used to study the activation energy (E) and reaction order (n) of the coating. The results indicated that 2 mass% of nano-TiO2 additive played a prompting role in the curing of polyester powder coatings, due to the hydroxyl functional groups existed on the surface of nano-TiO2. Furthermore, real-time Fourier transform infrared (FT-IR) spectroscopy with a heating cell was also employed to record the curing actions, of which results were consistent with the DSC experiments.

Effects of TiO2 Interlayers on the Optical Switching of VO2 Thin Films Grown by Sol-Gel Process: Effects of TiO2 Interlayers on the Optical Switching of VO2 Thin Films Grown by Sol-Gel Process

为了提高VO 2 薄膜的热致相变性能, 采用复合结构与掺杂相结合的方法, 首先通过溶胶-凝胶法在云母基底上制备锐钛型TiO 2 薄膜, 再在光致亲水性处理的TiO 2 /云母基底上涂覆V 2 O 5 以及掺钨V 2 O 5 水溶胶, 然后经热处理获得VO 2 /TiO 2 及V x W 1- x O 2 /TiO 2 复合薄膜. 采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、傅立叶变换红外光谱仪(FTIR)研究薄膜的物相, 表面形貌以及热致相变特性. 结果表明, VO 2 /TiO 2 复合薄膜晶体生长为(011)面择优取向; V x W 1- x O 2 /TiO 2 复合薄膜产生多种取向. TiO 2 中间层有助于使VO 2 薄膜生长致密, 相变温度降低, 更使V x W 1- x O 2 /TiO 2 复合薄膜滞后温宽降至约4℃.为了提高VO 2 薄膜的热致相变性能, 采用复合结构与掺杂相结合的方法, 首先通过溶胶–凝胶法在云母基底上制备锐钛型TiO 2 薄膜, 再在光致亲水性处理的TiO 2 /云母基底上涂覆V 2 O 5 以及掺钨V 2 O 5 水溶胶, 然后经热处理获得VO 2 /TiO 2 及V x W 1- x O 2 /TiO 2 复合薄膜。采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、傅立叶变换红外光谱仪(FTIR)研究薄膜的物相、表面形貌以及热致相变特性. 结果表明, VO 2 /TiO 2 复合薄膜晶体生长为(011)面择优取向; V x W 1- x O 2 /TiO 2 复合薄膜产生多种取向。TiO 2 中间层有助于使VO 2 薄膜生长致密, 相变温度降低, 更使V x W 1- x O 2 /TiO 2 复合薄膜滞后温宽降至约4℃。

Calorimetric Reaction Rate Determination with the Characteristic Kinetic Parameter Method

On the basis of the theory of thermokinetics proposed in the literature, a novel thermokinetic method for determination of the reaction rate, the characteristic parameter method, is proposed in this paper. Mathematical models were established to determine the kinetic parameters and rate constants. In order to test the validity of this method, the saponifications of ethyl benzoate, ethyl acetate and ethyl propionate, and the formation of hexamethylenetetramine were studied with this method. The rate constants calculated with this method are in agreement with those in the literature, and the characteristic parameter method is therefore believed to be correct.In the light of the characteristic parameter method, we have developed further two thermo-kinetic methods, the thermoanalytical single and multi-curve methods, which are convenient for simultaneous determination of the reaction order and the rate constant. The reaction orders and rate constants of the saponifications of ethyl acetate and ethyl butyrate and the ring-opening reaction of epichlorohydrin with hydrobromic acid were determined with these methods, and their validity was verified by the experimental results.