Abstract: A powder composition suitable for the pressureless thermal sintering of articles which may be used in aluminium electro-thermics contains titanium boride with boron and titanium hydride as densifying additives. During sintering these additives form titanium boride. As this is identical to the substance of the sintered article the additives therefore do not constitute impurities in the sintered article.

Abstract: A magnesium powder composition is used in a method for the reversible storage of hydrogen by absorption thereof in the magnesium to form the hydride which consists of an intimate mixture of magnesium powder and an inert powder which is stable under the conditions of formation and decomposition of the hydride. The stable inert powder, which prevents the agglomeration of the magnesium powder and maintains its hydrogen-storage capacity, is selected from the group which consists of metal powders such as manganese, iron, cobalt, nickel and copper, metal alloy powders such as iron-zinc alloys, and the oxides, carbides or nitrides of magnesium, calcium, boron, aluminum, silicon, titanium, zinc, vanadium, chromium, manganese and iron. The mixture is formed by intimately grinding the magnesium and inert powders together.

Abstract: A magnesium powder composition for the reversible storage of hydrogen by absorption thereof in the magnesium to form the hydride which consists of an intimate mixture of magnesium powder and an inert powder which is stable under the conditions of formation and decomposition of the hydride. The stable inert powder, which prevents the agglomeration of the magnesium powder and maintains its hydrogen-storage capacity, is selected from the group which consists of metal powders such as manganese, iron, cobalt, nickel and copper, metal alloy powders such as iron-zinc alloys, and the oxides, carbides or nitrides of magnesium, calcium, boron, aluminum, silicon, titanium, zinc, vanadium, chromium, manganese and iron. The mixture is formed by intimately grinding the magnesium and inert powders together.

Abstract: A titanium-iron-type alloy for the storage of hydrogen having an atomic composition corresponding to the formula Ti.sub.w Fe.sub.x M'.sub.y M".sub.z in which M' is a substituent for iron from the transition metals of group Vb or group VIb of the periodic system, M" is another iron substituent selected from the group which consists of nickel and manganese but which is nickel when M' is chromium and y and z are each between 0.01 and 0.2; w, representing the atomic concentration of titanium is at least equal to the sum x+y+z. The alloy can be charged with hydrogen, stored and desorbed from hydrogen.

Abstract: Silicon nitride-based powder composition enabling materials of densities exceeding 3.10 g/cm.sup.3 to be obtained by pressureless hot sintering. This composition contains, intimately mixed by pulverisation, Si.sub.3 N.sub.4 having a particle size not exceeding 1 .mu.m and up to 6% by weight of a densification aid comprising very finely ground magnesium oxide and aluminium oxide. This composition enables mechanical parts to be economically manufactured by moulding followed by sintering, their properties being practically equivalent to those of parts obtained by machining hot pressed blocks of Si.sub.3 N.sub.4.