Materials Science Forum Vols. 654-656

Abstract: The investigation of the behavior of CO2 absorption into the low Al2O3 electric arc furnace (EAF) oxidizing slag under wet grinding was investigated in this paper. The slag was wet ground in the vibration ball mill in the presence of CO2 at room temperature. The observation of the CO2 absorption was made with constant pressure method. The CO2 absorption increased steeply in the early stage of grinding. It occurred simultaneously with the grinding and immediately ceased when the grinding was stopped. The CO2 absorption occurred at the interface between the slag and the water which was saturated with CO2. The CO2 absorption increased as the finer particles were formed by the grinding process, and as the interface between slag and water was increased by the vibration process. A large amount of CO2 absorption and high conversion ratio was observed in the oxidizing slag with low Al2O3 in comparison with those of the slag with the high Al2O3 content.

Abstract: A planetary ball milling (PBM) technique was employed to fabricate mechanically alloyed (MA processed) Al-Nb2O5 composite powder. Nano or sub-micron sized Nb2O5 particles were homogeneously embedded in the Al particles after milling for various periods. None of cracks, by-products and pores were observed in the areas between embedded Nb2O5 particulates and Al matrix powder after milling. The sequence of the in-situ reaction was confirmed by DSC, XRD measurements, optical microscopy and EPMA. The specific temperature of the in-situ reaction was between 650 and 700°C. Al-based metal matrix composites (MMC) reinforced with the sub-sieve sized θ-Al2O3 particulates and Al3Nb intermetallic compound were successfully fabricated by the in-situ reaction process. The substituted Nb by the in-situ reaction was fully reacted with Al to form the Al3Nb intermetallic compound during sintering. A number of sub-sieve sized θ-Al2O3 particulates and Al3Nb intermetallic compound formed by the in-situ reaction between Al and Nb2O5 were homogeneously distributed in the Al matrix during sintering. Nano sized θ-Al2O3 particulates are preferentially distributed near the Al3Nb intermetallic compound and no by-products are formed in the interfaces with the Al matrix.

Abstract: Hydrides with light elements such as MgH2, LiH, NH3 and NH3BH3 are known as high hydrogen containing materials. However, the high work temperature and the slow reaction rate limit the practical application of hydride systems. Those properties can be improved by the nano-composite materials. The nano-composite materials for hydrogen storage encompass a catalyst and composite hydrides at the nanometer scale. The catalyst increases reaction rate. The thermodynamic stability of the nano-composite materials can be controlled by the composite hydrides. In addition, the hydrogen absorption kinetics is accelerated by the nano-size materials and they may change the thermodynamic stability of the materials. In this study, we reviewed our experimental results on hydrogen storage properties of light weight nano-composite materials. The Mg-based nano-composite material with Nb2O5 showed excellent kinetics as compared with that of Mg. The Li-Mg-N-H system absorbed and desorbed above 5.5 mass % of H2 at 423K (8LiH ＋ 3Mg(NH2)2 3Li2.667MgN2H1.333＋8H2). We found that the H2 absorption and desorption of the MH-NH3 (M: Li, Na, K) system takes the following reaction path, MH + NH3  MNH2 + H2.