Effects of Cr, W, and Mo on the High Temperature Oxidation of Ni-Based Superalloys

The oxidation behavior of Ni–9.5Co–(8~12)Cr–(2.5~5.5)Mo–(4~8)W–3Al–5Ti–3Ta–0.1C–0.01B alloys was investigated at 850 °C and 1000 °C The mass change, the phase of oxides, and the cross-sectional structure of specimens were analyzed after cyclic oxidation tests. The oxide scale was composed mainly of Cr2O3 and NiCr2O4, but NiO, TiO2, and CrTaO4 were also found. Al2O3 was formed beneath the Cr oxide layer. The Cr oxide layer and internal Al oxide acted as barriers to oxidation at 850 °C, while Al oxide was predominantly protective at 1000 °C. Cr increased the mass gain after oxidation test at both temperatures. Mo increased the oxidation rate at 850 °C but decreased the oxidation rate at 1000 °C. W slightly increased the mass gain at 850 °C but did not produce a significant effect at 1000 °C. The effects of Cr, Mo, W, and the temperature were discussed as well as the volatilization of oxides, the valence number of elements, and diffusion retardation.

Quantum chemical valence indices from the one-determinantal difference approach

The recently introduced quadratic (two-electron) valence indices, ionic and covalent, derived from the Hartree–Fock finite-difference approach, are applied to selected organic and inorganic molecules to demonstrate their utility in monitoring chemical bonding patterns in molecular systems. The indices are defined in terms of differerences between simultaneous probabilities of finding two electrons on specified atoms, calculated from the molecular and separated-atom-limit (SAL) wave functions, respectively, in the UHF approximation. The total quadratic valence number represents the overall number of chemical bonds in the system under consideration; it is interpreted as the molecular expectation value of the difference operator of the molecular and SAL density operators. This interpretation leads to a new set of ionic atomic and diatomic valence components; these modified valence numbers are discussed using the two-orbital model in the UHF scheme. A new procedure is proposed for dividing the one-center contributions to the bond valences; it generates effective bond orders in qood agreement with chemical expectations. The new valence quantities are tested on selected typical molecules and prototype hydrogen-bonded dimers. A more extensive study has been carried out on small-ring propellanes, to examine changes in bond valences between bridgehead atoms in selected systems. Key words: chemical valence: UHF difference approach; chemical bond: two-electron model; bond multiplicities; ionic/covalent bond components; propellanes: valence study.

The quark–gluon phase in strong interacting matter

A system of free quarks and gluons in thermal and in chemical equilibrium has been investigated in the context of hadronic phase transitions. The dependence on temperature of various quantities (i.e., chemical potentials and number and energy densities) was obtained. Calculations of number and energy densities at a given critical temperature have been performed for different valence number densities. A brief discussion of a phase transition occurring in the laboratory is also given.