No abstract

621.762The formation of hydride phases under high-energy ball-milling of Mg and Mg + 10 mass% Fe powders in hydrogen under a pressure of 1.2 MPa has been studied. The influence of iron content and dispersion degree of the Mg-alloys upon thermal stability and decomposition temperature of the hydride phase of the alloys was investigated by thermal desorption, x-ray diffraction, and differential thermal analyses. It was established that addition of 10 mass% of iron to magnesium contributes to higher dispersion degree of the magnesium hydride obtained via milling in hydrogen under pressure. The hydride contains maximum amount of weak-and medium-bound hydrogen. The latter is mainly concentrated in the region of grain boundaries, the quantity of which increases with increase in dispersion degree. The formation of new boundaries and accumulation of defects in these regions are accompanied by an increase in thermodynamic potential, which causes a decrease in both the temperature of decomposition of the hydride phase by 100°C and its thermal stability.

621.762Methods have been applied from scanning electron microscopy, hydrogen thermal desorption, XRD, and differential thermal analysis on the effects of grain size and alloying with boron as regards the thermal stability and decomposition temperatures of hydride phases in mechanical alloys in the Ti − B − H system. The alloys were prepared by high-energy processing for 50 h in a planetary ball mill with mixtures of TiH 1.9 + 9 mass% B + 13 mass% Ti and also with TiH 1.9 + 50 mass% TiB 2 at speeds of 1000 rpm, in addition to mixtures of TiH 1.9 + 40 mass% B and TiH 1.9 + 50 mass% TiB 2 , which were treated for 20 min at speeds of 1680 rpm. The dispersal on mechanical treatment and the addition of boron to the titanium hydride powder have substantial effects on the thermal stability. The processing of the mixture TiH 1.9 + 9 mass% B + 13 mass% Ti lasting 50 h in argon gave temperatures for the dissociation of the Ti(B, H) x hydride phase in the mechanical alloy lower by 300 deg than the decomposition temperature for the initial titanium hydride TiH 1.9 . The mechanisms have been identified for the effects of the dispersal and boron alloying on the thermal stability of the titanium hydride.