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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>
New Estimates for the Shadow Economies all over the World
Friedrich Schneider,Andreas Buehn,Claudio E. Montenegro 한국국제경제학회 2010 International Economic Journal Vol.24 No.4
This paper presents estimations of the shadow economies for 162 countries, including developing, Eastern European, Central Asian, and high income OECD countries over 1999 to 2006/2007. According to our estimations, the weighted average size of the shadow economy (as a percentage of 'official' GDP) in Sub-Saharan Africa is 37.6%, in Europe and Central Asia (mostly transition countries) 36.4% and in high income OECD countries 13.4%. We find that an increased burden of taxation (direct and indirect ones), combined with (labour market) regulations and the quality of public goods and services as well as the state of the 'official' economy are the driving forces of the shadow economy.