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MgH2 and intermetallic hydride nanocomposites synthesized by mechanical ball milling

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One of the obstacles to the implementation of the Hydrogen Economy into automotive industry is a lack of viable hydrogen storage system. Relatively promising is hydrogen storage system based on solid state hydrides with high hydrogen capacities exceeding 6 wt. %. However, a number of high capacity hydrides have high desorption temperatures which are incompatible with the waste heat generated by an automotive PEM (Proton Exchange Membrane) fuel cell. The search for materials that match the DOE criteria for hydrogen storage materials to be used in automobile applications has been largely focused on hydride composites in the past ten years [1÷5]. Very recently, it has been shown [4, 5] that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems, substantially decreases linearly with increasing volume fraction of the constituent having lower desorption temperature. In the present work the composite approach is applied to the MgH2 + FeTi and MgH2 + LaNi5 systems. The composites with various volume fractions of both constituents were processed by controlled reactive milling (CRM) in a magneto-mill (under hydrogen atmosphere). Hydrogen desorption was tested using a Differential Scanning Calorimeter (DSC) and Temperature Programmed Desorption (TPD) analysis. The aim of this work is to analyze the influence of intermetallic additives on magnesium hydrogen decomposition process in MgH2 + FeTi and MgH2 + LaNi5 composites. experimental As-received commercial MgH2 powder (Sigma-Aldrich; ~98 wt. % purity; the remaining Mg), LaNi5 (Alfa Aesar, hydrogen storage grade) and cast FeTi intermetallic powder, were mixed to MgH2 + X wt. % FeTi and MgH2 + X wt. % LaNi5 (where X = 10, 30 and 50) compositions. As a reference MgH2 without additives was used. The FeTi intermetallic powder was obtained by melting pre-compressed Fe and Ti powders mixture and grinding the obtained ingot. Gr[...]

MgH2 based composites with LiAlH4 and LiNH2 complex hydrides

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The investigation of materials that could match the requirements for hydrogen storage system to be used in automobile applications has been mostly focused on complex hydrides in the past few years. Especially, since the work of Chen et al. [1], Luo [2] and Vajo et al. [3] on mixtures of LiNH2/LiH, LiNH2/MgH2 and LiBH4/MgH2, there have been many publications dedicated to complex hydrides that are thermodynamically destabilized by ball milling with other hydrides [4÷7]. The advantage of such reactions is that the relatively large enthalpies of complex hydrides can be decreased by providing an alternate reaction pathway that liberates hydrogen. It has also been observed that new phases could be formed during the high-energy ball milling of different ratios of known hydrides [2, 3]. Very recently, it has been shown [4, 5] that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems, substantially decreases linearly with increasing volume fraction of the constituent having lower desorption temperature. In the present work the composite approach is applied to the MgH2 + LiAlH4 and MgH2 + LiNH2 systems. The composites with various volume fractions of both constituents were processed by controlled mechanical milling (CMM) in a magneto-mill (under protective argon atmosphere). Hydrogen desorption was tested using a Differential Scanning Calorimeter (DSC) analysis. The aim of this work is to analyze the influence of intermetallic additives on magnesium hydrogen decomposition process in LiAlH4 and LiNH2 composites. experimental As-received commercial MgH2 powder (Sigma-Aldrich; ~98 wt. % purity; the rema[...]

The effect of porosity on thermal properties of TiB2-based Cu cermets obtained by ball milling and containerless HIP DOI:10.15199/28.2016.3.3


  The effect of porosity on microstructure and thermal properties of titanium diboride (TiB2) based cermets with Cu binder was investigated. It has been demonstrated a good wettability of the TiB2-Cu interfaces which allows for heat flow through it easily but formed microporosity (25÷32 %) and related structural defects in the sintered cermets affects the thermal conductivity. The specific heat changes exponentially with temperature and amounts to 0.37 J∙g-1K-1 at 298 K for the TiB2-Cu (20 vol. %) cermet with the lowest porosity. The X-ray diffraction (XRD) analysis confirmed that TiB2-Cu is the stable system and there was no reaction between TiB2 and Cu. The dependence of microstructure and composition on thermal properties of sintered the TiB2-Cu cermet alloys was discussed. Key words: titanium diboride, TiB2-Cu cermets, ceramic matrix composites (CMCs), hot isostatic pressing, HIP, thermal properties. Inżynieria Materiałowa 3 (211) (2016) 109÷114 DOI 10.15199/28.2016.3.3 1. INTRODUCTION Titanium diboride (TiB2) is one of a few refractory metal borides with an attractive combination of properties such as high melting point (3225°C), ultra-high hardness (25 GPa), high strength to density ratio, good thermal and electrical conductivity (96 W∙m-1K-1 and 22∙106 Wcm, respectively) and wear resistance [1, 2]. TiB2 can be used to produce dense constructive sintered materials for high-temperature structural applications as well as for control rod elements with a high-thermal neutron absorption in nuclear reactors. However, it is well known, that wide applications of TiB2 ceramic are limited due to poor sintering ability, which requires extremely high temperature [3, 4]. The interesting approach for obtaining the TiB2 based cermets is the sintering method by hot isostatic pressing (HIP). In this way by intensive mass transfer the sintering process is carried out in shorter time and at lower temperature. The lower temperatu[...]

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