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Bulk copper, copper-graphene and copper-graphite composites were produced from copper-thermally expanded graphite (TEG) powder mixtures with 0-3 wt.% TEG contents via modified powder metallurgy process that includes powder milling in a planetary mill at 350 rpm for 5 hours, compaction, and vacuum annealing at 1030 °C for 1 hour. Phase composition and microstructure of the composites were analysed by XRD and SEM techniques. According to Raman spectroscopy, TEG transforms into a few layer graphene flakes in case of composites with 0.1-1 wt.% of carbon additive, while for 3 wt.% of carbon additive it remains in the form of graphite. The addition of 0.1 wt.% TEG results in the tensile strength increase up to 160 MPa (from 93 MPa for pure copper specimen synthesized via the similar synthesis route). Vickers hardness obtained for Specimens under the study is independent fromthe composite composition.

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A high temperature Knudsen effusion method was used to study the composition of vapour and partial vapour pressures of species in multicomponent borosilicate glasses. Data on the activities of metaborates of alkali metals were obtained. Using an acid–base concept the relative volatility of these glasses was compared and discussed. © 1998 John Wiley & Sons, Ltd.

Nickel matrix composites are important materials for various engineering applications. The present paper describes the fabrication of bulk graphene-nickel (Gr-Ni) and reduced graphene oxide-nickel (rGO-Ni) composites by powder metallurgy technique using various graphene sources, namely, thermally exfoliated graphite (TEFG) and reduced graphene oxide (rGO) and the investigation of the mechanical properties of the composites. Homogeneous distribution of graphene derivatives in the composite matrices was confirmed for all compositions by XRD and Raman spectroscopy. It was proved that different Gr sources in the initial powder mixtures result in some different graphene derivatives type in the composites produced. Nevertheless, scanning electron microscopy data demonstrated that the microstructure of the samples produced using the different graphene sources is rather similar. It was shown that the mechanical properties of the composites are very sensitive to the type of graphene derivative chosen at low additive contents. TEFG addition results in the decreased values of tensile strength, ductility, and elongation for all compositions. It was shown that 0.1 wt.% of rGO addition resulted in the 34 % elongation-to-failure increase with no change in the UTS value of composite. The 0.1 wt.% rGO-Ni composite showed the increased elongation and the tensile strength value comparable to pure nickel specimen. Fractography tests revealed the difference in the mechanical behaviour of rGO-Ni and Gr-Ni composites.

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A new approach has been applied to study processes which take place during the thermochemical action of air (or other) plasma on heat protection materials. Vaporization processes of the borosilicate coating of 'Buran's' heatprotective tiles, both the initial state and after re-entry simulation testing (up to 100 landings), were investigated by the Knudsen mass spectrometric effusion method. Modelling of the thermochemical action of the shock-layer plasma onto the front surfaces of real-scale tiles was carried out by using an induction plasma generator of 500 kW power. It was established that the thermochemical action of the plasma causes, essentially, a decrease of vapour pressure over the coating. However, despite this decrease, the pressures observed are significantly higher than those over the SO,-B,O, system at the same temperature, due to gas-phase SiO production by reaction between boron and silicon oxides and SiB4, which are contained in the coating. The data available allow one to postulate the presence of the SiBO molecule in the gas phase. Data on mass-loss rates obtained by direct measurements after re-entry simulation compared well with the values calculated from mass spectrometric data. It is suggested that the difference observed is caused by thermochemical action of atomic oxygen on the coating.