Degradation of CoSb 3 in air was studied at 500, 600 and 700°C. The type and extent of degradation was evaluated on the basis of specimen mass change, scale thickness, visual inspection and systematic analysis of chemical composition, phase composition and microstructure of specimen surfaces, fractures and crosssections. It has been found that at the investigated temperatures, CoSb 3 is neither sufficiently stable nor oxidation-resistant. Antimony and cobalt react readily with oxygen by 500°C. The oxide scales are complex, with the predominant constituents being cobalt-antimony oxides, CoSb 2 O 4 and CoSb 2 O 6 . A tentative reaction mechanism is proposed.

Pulse magnetron sputtering was used to deposit Cr-5Si (at.%) thin layers onto CoSb 3 substrates to prevent degradation of the material at elevated temperatures. The quality of the protective layers was evaluated on the basis of oxidation tests in air at 500 and 600°C for up to 80 h. The surfaces, fractures and cross-sections of specimens were analyzed to assess integrity and adherence of the deposited layer as well as the extent of reaction and diffusion phenomena at interfaces. It was found that the Cr-5Si layer provided a satisfactory protection for CoSb 3 at 500°C. Promising results were obtained at 600°C.

No abstract

Role of Y 2 O 3 , CaO, MgO additives on structural and microstructural behavior of zirconia/mullite aggregates AIP Conf.Abstract. An alternative route was developed for the manufacturing of cobalt triantimonide and magnesium disilicide derivatives for thermoelectric applications [1,2]. The elemental powders were mixed in stoichiometric proportions, cold pressed into cylindrical preforms and heated in oxygen-free environment to initiate the exothermic reaction. According to DTA/TG measurements and observations under high-temperature microscope, the onset of reaction occurred at a temperature not exceeding the melting point of the more volatile component, i.e. antimony in the case of CoSb 3 and magnesium in the case of Mg 2 Si. The reaction products were additionally heat treated to secure homogenization. Dense sinters were obtained by hot uniaxial pressing of the obtained powders in moderate temperature-and-pressure conditions. Phase composition, chemical composition and microstructure of materials at consecutive manufacturing stages were systematically analyzed by XRD, TEM, SEM and EDS. Several advantages were identified in the proposed technology: absence of liquid phases, relatively short time of the synthesis, no need of milling for magnesium disilicide and easy disintegration into powder for cobalt triantimonide, possibility of insitu or ex-situ doping and grain size control.

No abstract