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The effect of Al on the hydrogen sorption mechanism of LiBH<sub>4</sub>
Friedrichs, O.,Kim, J. W.,Remhof, A.,Buchter, F.,Borgschulte, A.,Wallacher, D.,Cho, Y. W.,Fichtner, M.,Oh, K. H.,Zü,ttel, A. Royal Society of Chemistry 2009 Physical chemistry chemical physics Vol.11 No.10
<P>We demonstrate the synthesis of LiBH<SUB>4</SUB> from LiH and AlB<SUB>2</SUB> without the use of additional additives or catalysts at 450 °C under hydrogen pressure of 13 bar to the following equation: 2LiH + AlB<SUB>2</SUB> + 3H<SUB>2</SUB>↔ 2LiBH<SUB>4</SUB> + Al. By applying AlB<SUB>2</SUB> the kinetics of the formation of LiBH<SUB>4</SUB> is strongly enhanced compared to the formation from elemental boron. The formation of LiBH<SUB>4</SUB> during absorption requires the dissociation of AlB<SUB>2</SUB>, <I>i.e.</I> a coupled reaction. The observed low absorption-pressure of 13 bar, measured during hydrogen cycling, is explained by a low stability of AlB<SUB>2</SUB>, in good agreement with theoretical values. Thus starting from AlB<SUB>2</SUB> instead of B has a rather low impact on the thermodynamics, and the effect of AlB<SUB>2</SUB> on the formation of LiBH<SUB>4</SUB> is of kinetic nature facilitating the absorption by overcoming the chemical inertness of B. For desorption, the decomposition of LiBH<SUB>4</SUB> is not indispensably coupled to the immediate formation of AlB<SUB>2</SUB>. LiBH<SUB>4</SUB> may decompose first into LiH and elemental B and during a slower second step AlB<SUB>2</SUB> is formed. In this case, no destabilization will be observed for desorption. However, due to similar stabilities of LiBH<SUB>4</SUB> and LiBH<SUB>4</SUB>/Al a definite answer on the desorption mechanism cannot be given and neither a coupled nor decoupled desorption can be excluded. At low hydrogen pressures the reaction of LiH and Al gives LiAl under release of hydrogen. The formation of LiAl increases the total hydrogen storage capacity, since it also contributes to the LiBH<SUB>4</SUB> formation in the absorption process.</P> <P> </P> <P>Graphic Abstract</P><P>LiBH<SUB>4</SUB> (LiBD<SUB>4</SUB>) is synthesized by hydrogenation of LiH (LiD) and AlB<SUB>2</SUB> without use of additional additives or catalysts. The reversible reaction mechanism is investigated. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b814282c'> </P>
Atomic diffusion induced degradation in bimetallic layer coated cemented tungsten carbide
Peng, Zirong,Rohwerder, Michael,Choi, Pyuck-Pa,Gault, Baptiste,Meiners, Thorsten,Friedrichs, Marcel,Kreilkamp, Holger,Klocke, Fritz,Raabe, Dierk Elsevier 2017 Corrosion science Vol.120 No.-
<P>We investigated the temporal degradation of glass moulding dies, made of cemented tungsten carbide coated with PtIr on an adhesive Cr or Ni interlayer, by electron microscopy and atom probe tomography. During the exposure treatments at 630 degrees C under an oxygen partial pressure of 1.12 x 10(-23) bar, Cr (Ni) was found to diffuse outwards via grain boundaries in the PtIr, altering the surface morphology. Upon dissolution of the interlayer, the WC substrate also started degrading. Extensive interdiffusion processes involving PtIr, Cr (Ni) and WC took place, leading to the formation of intermetallic phases and voids, deteriorating the adhesion of the coating. (C) 2017 The Authors. Published by Elsevier Ltd.</P>