Mechanochemical Procedures Research Articles

Direct synthesis of pure complex aluminium hydrides by cryomilling

Simple mechanochemical procedures can be used for the solid-state preparation of stable complex aluminium hydrides as hydrogen storage materials. For the synthesis of unstable complex hydrides, cryomilling at temperatures at which product decomposition does not take place under milling conditions appears to be a viable method. To probe the potential of cryomilling for the synthesis of complex aluminium hydrides, the reactions of different alkaline hydrides with AlH 3 were tested under these conditions.

Mineral induced mechanochemical degradation: The imazaquin case

The potential role of mechanochemical processes in enhancing degradation of imazaquin by soil components is demonstrated. The investigated components include montmorillonite saturated with Na +, Ca 2+, Cu 2+and Al 3+, Agsorb (a commercial clay mix), birnessite and hematite. The mechanical force applied was manual grinding of mixtures of imazaquin and the minerals, using mortar and pestle. The degradation rates of imazaquin in these mixtures were examined as a function of the following parameters: time of grinding, herbicide load (3.9, 8.9, 16.7 and 26.6 mg imazaquin per g mineral), temperature (10, 25, 40 and 70 °C), acidic/basic conditions, and dry or wet grinding. Dry grinding of imazaquin for 5 min with Al-montmorillonite or with hematite resulted in 56% and 71% degradation of the imazaquin, respectively. Wet grinding slightly reduced the degradation rate with hematite and entirely cancelled the enhancing effect of grinding with Al-montmorillonite. Wet grinding in the presence of the transition metals: Ni 2+, Cu 2+, Fe 3+ added as chlorides was carried out. Addition of Cu 2+ to Na-montmorillonite loaded with imazaquin was the most effective treatment in degrading imazaquin (more than 90% of the imazaquin degraded after 5 min of grinding). In this treatment, Cu-montmorillonite formation during the grinding process was confirmed by XRD and accordingly, grinding with Cu-montmorillonite gave similar degradation values. LC–MS analysis revealed that the mechanochemical transformation of imazaquin resulted in the formation of a dimer and several breakdown products. The reported results demonstrate once again that mechanochemical procedures offer a remediation avenue applicable to soils polluted with organic contaminants.

Modification of the high-doped GaAs surface region by its exposure to 150 keV proton beam

The interaction of 150 keV protons with a high-doped n-GaAs crystal has been investigated by X-ray diffraction at grazing incidence (XRDGI), photoreflectance (PR), photoluminescence (PL) and scanning electron microscopy (SEM). The measurements confirmed that simultaneous with almost full loss of the semiconducting properties of the surface crystal region after applying the 1015 proton/cm2 dose, (111) oriented extended type of crystalline defect was formed. These defects have been identified as the (111) planes rotated by ∼40° with respect to the (111) planes of the undisturbed GaAs cubic structure. They are located at the hydrogenated GaAs layer/GaAs interface and induced by two effects: formation of microcracks prolonged throughout the implanted layer in 111 direction up to undisturbed GaAs crystal and strain arising at the corresponding interface. The role of the surface microcracks formed in the uppermost part of the reference sample as a consequence of unsuitable mechano-chemical polishing procedures in the evolution of the effect observed is also discussed.