The Studies Of Preparation And Applications Of Tetrapod-shape Zinc Oxide Whiskers

Tetrapod-like zinc oxide whisker (T-ZnOw) is one kind of multifunctional inorganic material with uniform three-dimensional structure. Based on the research status of the whiskers and its universal applications foreground, in this paper, the relationship between morphology and the preparation conditions of the nano whiskers was investigated with the help of modern apparatus such as XRD, SEM, EDS, TEM and HRTEM, and the growth mechanism and growth process of the whisker was also discussed. The photoluminescence property and photo-catalyst property of the whiskers, as well as the mechanical property and electric property of the T-ZnOw/polypropylene composite were also explored. A Series of research achievements were obtained:(1) Considering the high yielding cost of T-ZnOw in micro scale, which impeded its industrialization and applications because of the using of zinc source with high purity as the raw materials in the present several preparation methods, T-ZnOw in micro scale was first synthesized by the method of reactor preheating, with the zinc dross as the raw materials. The effects of environmental conditions and different zinc sources on the crystal morphology and yield of the products were investigated. And the optimal conditions to prepare T-ZnOw in micro scale with uniform morphology and high yield were found, which can be considered as a better technological process for the recovery and utilization of zinc secondary source.(2) The dynamic process based on the oxygen-controlling method under vacuum conditions was put out for the first time and adopted to synthesize nano T-ZnOw with the pure zinc pig as the raw material. The effects of catalyst, reaction temperature and the degree of the system vacuum on the morphology of the products were investigated. Nano whiskers with uniform morphology and controllable dimensions were successfully synthesized. With semicontinuous and dynamic characters, our method shows more possibility of industrialization when comparedwith the four methods to prepare whiskers that adopted by others.(3) The nucleation and growth mechanism of the whiskers crystal were primarily explored and the results show that, according to the experiment results, the growth of T-ZnOw was confirmed to submit to the vapor-solid mechanism. Octahedral multiple twin nucleus model that put forward by Iwanaga was found to be basically accord with the growth process of the whiskers in our experiments. According to the results of selected diffraction and high resolution electron microscope, octahedral multiple twin nucleus structure was found to exist in the central location of the nano tetrapod-shape zinc oxide whiskers, and the four legs were found to be single crystal with <001> growth direction.(4) The photoluminescence property and photo-catalyzing property of nano T-ZnOw were investigated in detail. It is indicated that at room temperature the PL spectrum of nano T-ZnOw was consisted of near band-edge UV emission that ascribing to the exciton emission and the broadened blue and green light emission that contributing to the crystal defects such as oxygen vacancy and zinc interstitial. The sharp absorbing peak in the UV-VIS extinction-spectrum of nano T-ZnOw indicates that the synthesized products in our experiment are of high crystal quality.(5) The nano T-ZnOw was used as photocatalyst for the first time. The reaction kinetics of the photodegradation experiment with methyl orange as the model compound was investigated. The effects of the content of the photocatalyst and the dimension of the whiskers on the photodegradation effect were explored. It was found that the photodegradation reaction followed the rule of first-order reaction. The optimal content of nano T-ZnOw is 2g/L, and the catalyzing effect increase with smaller dimensions of the whiskers. As compared to the nano TiO2 and nano ZnO with the same grain size, nano T-ZnOw showed better photodegradation effect and better stability, which mean that nano T-ZnOw could be a more suitable photocatalyst with great application potential.(6) The T-ZnOw /polypropylene composite was prepared byhot-pressing process. The effects of modification of T-ZnOw on the mechanical and electrical properties of the composite were investigated. It's found that T-ZnOw could effectively improve the electric-conductive property of the PP resin. The resistance ratio of the composite reduce to below 109n-cm when the content of the whisker is only 3%, which is more less than the content of other conductive particle or fibre fillers. The surface modification of T-ZnOw shows little influence on the conductive properties of the composite. The dielectric constant of composite increased with the increasing of the content of the whiskers and the surface modification of the whisker is verified to favor the reduction of the dielectric dissipation fraction of the composite. The dielectric properties of the composite were also influenced by the molecular structure of the coupling agents. The results of the experiments on the mechanical properties of the composite showed that the addition of whiskers modified by different coupling agents had different effect on the mechanical property of the composite due to the variety of the coupling mechnism. The strongest bond strength of interface between the two phases could be obtained when modified by coupling agent A151, which lead to the maximal tensile-strength and modulus. While best impact property could be realized when the whisker was modified with titanate coupling agents.