I.A. Bryukhanov

The role of water in the elastic properties of aluminosilicate zeolites: DFT investigation

The bulk and Young moduli and heats of hydration have been calculated at the DFT level for fully optimized models of all-siliceous and cationic zeolites with and without water, and then compared to the corresponding experimental data. Upon the addition of water, the monovalent alkali ion and divalent alkaline earth ion exchanged zeolites presented opposite trends in the elastic modulus. The main contribution to the decrease in the elastic modulus of the alkali ion exchanged zeolites appeared to be a shift of cations from the framework oxygen atoms upon water addition, with the coordination number often remaining the same. The contrasting increase in elastic modulus observed for the divalent (alkaline earth) ion exchanged zeolites was explained by cation stabilization resulting from increased coordination, which cannot be achieved within a rigid zeolite framework without water.

Theoretical Aspects of Methanol Carbonylation on Copper-Containing Zeolites

The experimental data have been considered to match the theoretical mechanisms proposed previously to describe processes of oxidative carbonylation of methanol on copper-containing catalysts. The schemes examined cover methoxy intermediates, carbomethoxy intermediates, carbonates, and Cu(OCH3)2Cu binuclear clusters. The attack of the first methanol molecule on copper carbonate has been simulated in terms of the isolated cluster (8R) model with periodic boundary conditions (on CuMOR zeolite), and parameters of the individual steps involving description of the transition states have been evaluated.

Mechanisms and rate of dislocation nucleation in aluminum-copper alloys near Guinier-Preston zones

This article is devoted to a molecular dynamics simulation study of partial dislocation loop nucleation with respect to its mechanism and rate, and its propagation process under high shear stress in aluminum-copper alloys. The mechanisms of dislocation nucleation near Guinier-Preston (GP) zones of various diameters and concentrations have been analyzed. Dislocation nucleation rates near plain GP Cu-zones with diameters of 3.5, 7.5, and 13.5 nm and at various concentrations have been calculated using the mean lifetime method with temperatures in range of 100 and 700 K. It has been found that depending on the temperature and applied stress, the dislocation can nucleate either from the edge, or from the plain area of a GP zone. The dislocation nucleation is preceded by a generation of defect clusters that are formed due to local opposite atomic shifts in two adjacent (111) planes by the half-length of a Burgers vector of a partial dislocation. The expansion of a partial dislocation loop can be accompanied by...

Nucleation of dislocations in aluminum alloys with copper

The influence of copper impurities on the nucleation of dislocations in aluminum has been investigated using the method for determining the average lifetime of the metastable state. The primary data have been obtained using the molecular dynamics method. The obtained dependences of the dislocation nucleation rate on the shear stress in pure aluminum and aluminum solid solutions with copper have been plotted in the Arrhenius form. It has been found that, with an increase in the copper concentration, the activation parameters for these dependences decrease. It has been shown that an increase in the temperature leads to an increase in the sensitivity of the dislocation nucleation rate to stresses in aluminum solid solutions with 0.1–3.0 at % Cu, in contrast to pure aluminum in which the sensitivity is almost independent of the temperature. The dependences of the dislocation nucleation rate on the copper concentration and temperature over the entire range of stresses have been discussed based on the obtained approximations.