The influence of additives on the reaction kinetics and for microstructure refinement in LiBH 4-MgH 2 composites is investigated in detail. Indications on the rate limiting processes during the reactions are obtained by comparison of the measured reaction kinetics to simulations with one specific rate limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in-situ Xray diffraction (XRD) measurements. During desorption, the hydrogen is released at a constant rate, which possibly is correlated to the one-dimensional growth of MgB 2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy (TEM) images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of the microstructure on the reaction kinetics.

The orientation distribution function (ODF) of the crystallites of polycrystalline materials can be calculated from experimentally measured pole density distribution functions (pole figures). This procedure, called pole-figure inversion, can be achieved by the series-expansion method (harmonic method). As a consequence of the (hkl)-(hkl) superposition, the solution is mathematically not unique. Rather it contains a range of possible solutions (kernel) which is only limited by the positivity condition of the distribution function. The complete distributio 9 functionf(g) can be split into two parts f(g) and f(g) expressed by even-and odd-order terms of the series expansions. For the calculation of the even part f(g), the positivity condition for all pole figures contributes essentially to an 'economic' calculation of this part, whereas, for the odd part, the positivity condition of the ODF is the essential basis. Both of these positivity conditions can be easily incorporated in the series-expansion method by using several iterative cycles. This method proves to be particularly versatile since it makes use of the orthogonality and positivity at the same time.

The current physiological in vitro tests of Mg degradation follow the procedure stated according to the ASTM standard. This standard, although useful in predicting the initial degradation behavior of an alloy, has its limitations in interpreting the same for longer periods of immersion in cell culture media. This is an important consequence as the alloy’s degradation is time dependent. Even if two different alloys show similar corrosion rates in a short term experiment, their degradation characteristics might differ with increased immersion times. Furthermore, studies concerning Mg corrosion extrapolate the corrosion rate from a single time point measurement to the order of a year (mm/y), which might not be appropriate because of time dependent degradation behavior. In this work, the above issues are addressed and a new methodology of performing long-term immersion tests in determining the degradation rates of Mg alloys was put forth. For this purpose, cast and extruded Mg-2Ag and powder pressed and sintered Mg-0.3Ca alloy systems were chosen. DMEM Glutamax +10% FBS (Fetal Bovine Serum) +1% Penicillin streptomycin was used as cell culture medium. The advantages of such a method in predicting the degradation rates in vivo deduced from in vitro experiments are discussed.

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Sintering of magnesium powder is strongly inhibited by a stable oxide layer that is formed immediately after exposure to air. In contrast to e.g. titanium, no solubility of oxygen in solid magnesium is reported; therefore, the oxide layer is not dissolved during sintering. In this study, different methods are investigated in order to overcome this problem. It is shown that magnesium can be sintered if the sintered parts are surrounded by magnesium getter material. Calcium additions improve sinterability. The optimum calcium content lies in the range of 0.6 wt%.