| With the oil crisis and air pollution coming worse and worse, the using of clean energy of hydrogen, as well as, hydrogen fuel cell has become one of the main orientation of new energy in this age, in which the development of the Mg-based hydrogen storage alloy with excellent properties is a very important research subject. Hydriding Combustion Synthesis (HCS), a new materials processing technology proposed to produce hydrogen storage alloys recently, offers many advantages, such as short processing time, simple equipment and low energy requirements. In addition, its product also shows excellent performance, such as high activity, high purity and no activation process. Owing to its potential important values in preparing of hydrogen storage alloy, HCS has drawn great attention internationally recently. But the research of HCS is just at the beginning in our country now.In order to introduce the advanced synthesis technology and set up basal conditions for the research of HCS of Mg-based hydrogen storage alloy in our country, in this study, a series of primary research on the development of HCS reaction apparatus and the preparation of pure Mg-based hydrogen storage alloy-Mg2NiH4 by HCS were carried out and some conclusions on the process parameters of HCS have been also obtained.A simple HCS reaction apparatus was developed to meet the experimental requirements of hydrogen pressure of 6MPa, working temperature of 600℃ and direct measurement and control of the sample temperature. It involved the design of apparatus, selection of material, manufacture and testing according to the practical situation and a great deal of investigation.Pure Mg2NiH4 has been obtained by the simple HCS reaction apparatus developed under the lower pressure (≤1.5MPa). The purity of products was analyzed by X-ray diffraction (XRD). Meanwhile, the effects of main parameters such as hydrogen pressure, synthesis temperature, and the holding time at hydriding temperature on product purity were studied. Some results were obtained as follows: Comparing with the hydrogen pressures of l.0MPa and 0.5MPa, the purity of Mg2NiH4 obtained in the initial pressure of 1.5MPa increased obviously. Under this pressure, with the increasingof synthesis temperature and its holding time, the synthesis of Mg2Ni was promoted. Those results were explained by the mechanism of the combustion synthesis of Mg2Ni including solid-solid diffusion reaction between magnesium and nickel and the liquid-trigger of reaction mechanism. The increasing of the holding time at 653 K, the temperature of hydriding reaction from Mg2Ni to Mg2NiH4, can promote the hydriding reaction. However, long holding time at high synthesis temperature is disadvantageous to the hydriding of Mg2Ni because of the compaction of Mg2Ni during a long course of sintering accompanied. It is very significant and important to balance the two aspects: the high activity of product of Mg2Ni for hydriding reaction and the completion of the reaction of combustion synthesis Mg2Ni. In the initial pressure of 1.5MPa, pure Mg2NiH4 was obtained under different conditions, such as, holding 120min at synthesis temperature of 808K and 60min at Mg2Ni hydriding temperature of 653K; holding 60min at synthesis temperature of 850K and 90min at 653K.The effect of hydriding reaction of Mg on the purity of products of HCS was also studied under different pressures and different synthesis temperatures with changing cycles of hydriding and dehydriding and the holding time at the hydriding reaction of Mg. The relationships of hydriding reactions of Mg, synthesis of Mg2Ni and hydriding reaction from Mg2Ni to Mg2NiH4 were investigated firstly by means of XRD and SEM. It was found that with the hydriding reaction of Mg processed, the synthesis of Mg2Ni was accelerated and the hydriding activity of Mg2Ni increased obviously. The main reason is that the volume expansion of Mg during hydriding introduced not only crack and the pulverizing particles that accelerate the synthesis reaction of Mg2Ni, but also larger pores,...
|
PDF Full Text Request