Materials Chemistry最新文献

The high temperature phase transformation of hydrazonium sulfate, N₂H₆SO₄ has been studied using DSC. The enthalpy of phase transition is found to be 3.63 ± 0.1 kJ mole⁻¹. The phase transition temperature is found to decrease with the increase of particle size. It appears that the strain energy and not surface energy, is responsible for the phase transformation. The molar volume of the salt increases during the transformation as found by the dilatometric experiment involving percentage of linear thermal expansion. On cooling, the transformation from the high temperature modification to orthorhombic form is incomplete and extends over a wide range of temperature.

Surface modifications induced by rolling temperature on various HSLA steels are investigated. The main effect of the temperature is the formation of a surface oxide barreer and the diffusion of carbon towards the bulk, leading to the formation of a different steel composition at the surface.

The consequences of it as concerns some further surface treatments (in particular the phosphatization) are evidenced.

An original device for direct analysis of the mechanochemical evolution of solid-gas systems has been developed.

The volume of gas evolved or occluded during the mechanical reaction is measured under constant gaseous pressure and temperature.

Grinding experiments have been performed on several hydroxydes and hydrates. They show that this method is very convenient for the systematic study of the thermodynamic and kinetic characteristics of solid-gas reactions carried out either by grinding or by mechanical treatment and subsequent thermolysis.

Glass formation and phase equilibria of the MnO-TeO₂ system in the 0 to 50 mol% MnO range are studied. It is found that the glass-formation region in air is larger than in an inert atmosphere and varies within 10 to 37 mol% MnO.

The existence of four tellurites of manganese is confirmed and the nature of their melting is established.

Carbon segregation followed by graphite formation was studied on a fcc cobalt single crystal, both starting from a clean and a sulfur covered surface. The presence of one monolayer of sulfur atoms was found to affect greatly the graphite formation. In isothermal conditions at high temperatures, the graphite film covers completely the cobalt surface, in any case. However, the time necessary depends on the sulfur coverage and on the surface region. In the most perfect areas of the surface the decrease in the rate of graphite precipitation was found to reach two orders of magnitude.

A coating of Cu₅Si on Cu was prepared by treating copper with monosilane at 700°C and its behaviour in oxygen at high temperature investigated. The protective efficiency of this coating is good as no oxidation could be detected up to 600°C. At higher temperatures, the oxidation scale consists of three layers respectively of Cu₂O in contact with the metal, SiO₂, and CuO. The kinetic curves are of sigmoidal type. Their first part corresponds probably to a nucleation process leading to the formation of the silica layer. In the following stages, the reaction rate is assumed to be controlled by the simultaneous diffusion of oxygen and copper through the SiO₂ and CuO layers.

The Raman spectra of Ge_xAs_yS_z glasses have been studied in the ternary composition region of GeS₂-As₂-S. Dominant features of the obtained spectra were discussed and the structural units forming the disordered structural network of Ge_xAs_yS_z glasses were identified as: GeS₄ tetrahedra, AsS₃ pyramids, As-S-S-As bent chains and S_n (n = 2–4) chain segments. At high sulfur concentrations a part of the sulfur is dissolved in the structural network in the form of S₈ molecules.

In deaerated media containing hydrogen sulfide, the inhibition of the corrosion of steel by homologous series of aliphatic amines and imidazolines was measured potentiokinetically. The data obtained were correlated successfully to the hydrophobicity and the polarity (calculated parameter) of these molecules by means of Hansch relationship.