Effect of synthesis temperature on the purity of product in hydriding combustion synthesis of Mg2NiH4

This paper describes the effect of synthesis temperature on hydriding combustion synthesis of Mg2NiH4 to improve the purity of product. The properties of the products were examined by means of X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The XRD patterns showed that the main phases of the products were Mg2NiH4 independently of the synthesis temperatures. However, when the samples were synthesized over 779 K, the eutectic temperature of magnesium and nickel system, most products contained a little Mg2NiH0.3. In contrast, in the products synthesized under the eutectic temperature, MgH2 and Ni existed with no Mg2NiH0.3: all Mg2Ni in the combustion synthesized products fully absorbed hydrogen and transferred to Mg2NiH4. These results revealed that the hydriding activity of the medium product from combustion synthesis of Mg2Ni depended on the synthesis temperature. In conclusion, to increase the activity of hydriding reaction and the storage capacity of products, and to avoid the evaporation loss of magnesium during combustion synthesis, a slightly lower synthesis temperature than the eutectic temperature is quite beneficial and available for hydriding combustion synthesis of Mg2NiH4. (C) 2002 Elsevier Science B.V. All rights reserved.