Search

One of the well-known ways of metal foam production consists of adding powder which releases gaseous decomposition product at high temperatures into a melted metal. When producing aluminum foams, titanium hydride powder is most frequently used, while its main disadvantage is its insufficient thermal stability. This results in a premature gas loss in the process of the powder introduction into a melted metal matrix. The paper discloses approaches to suppression of the undesirable premature titanium hydride decomposition by means of its preliminary thermal treatment, as well as the external pressure elevation over that of the system being processed during the foam formation. A method of using the thermally treated powder is proposed, in order to obtain aluminum foam samples having a required geometry and sufficiently uniform porous structure.

Results of studies of current-conducting properties of titanium hydride powders oxidized by air oxygen at different modes in order to form oxide and oxohydride coatings at the particles surface which enhance heat resistance of the hydride are presented. Method of impedance spectroscopy is used to determine contribution of resistance of the formed coatings and contribution of resistance of the grains of titanium hydride powders into the powder impedance. Method aspects of conducting measurements of the impedance of powder materials by stepwise sample compression are discussed. General approach to experimental data processing related to study of metal hydrides which contain shielding films of various chemical compositions at the particle surface is described.

The oxidation of titanium hydride powder by air oxygen and the influence of oxidation conditions on the degree of oxidation of hydride particles, specific gas content in the powder, and kinetics of its thermal decomposition were studied. The resistometry method was used to determine the effective activation energy of oxidation of titanium hydride by air oxygen. The content of the surface nonconducting phase formed by titanium oxide and oxohydride films under various oxidation conditions was estimated.

The influence of the granulometric properties of powdered metal on the density dependence of its conductivity is studied by the example of metallic scandium. It is found that a decrease in the grain size leads to an increase in the compression force necessary to rupture oxide films at the sites of grain contact and thereby carry the powder to the conducting state. It is shown that this force correlates with the content of scandium oxide forming a film on the grain surface. When the grain size range expands, the conductivity critical index decreases substantially because of an increase in the density of a conducting percolation cluster formed by the contacting metallic bases of the grains.