Time and Temperature Factors in Construction of Rock Strength Criteria

Using the synthesis of the kinetic concept on solid strength and the Coulomb - Mohr strength theory as the base, the failure conditions taking into account the time and temperature factors are obtained.     

Simulation Studies of Electronic Properties and Atomic Ordering in the b-Si3N4 – Mg – O SYSTEM

Simulation studies of the electronic structure, interatomic bonds, chemical composition, and atomic ordering in solid solutions Si_6–x Mg_xO_2x N_8–2x of the β-Si₃N₄ – Mg – O system and solid solutions Si_6–x Mg_xO_xN_8–2x X_x (X = S, Se) and Si_6–x Mg _x/2M _x/2O_xN_8–x (M = C, Si, Ti, Ge, Zr, Sn, and Pb) are carried out using the strong-coupling energy-band method. Stabilization of solid solutions Si_6–x Mg_xO_2x N_8–2x is accomplished in the presence of S, Se or Zr. In these solutions, Mg and O atoms are capable of forming quasi-unidimensional structures (dopant, or impurity, channels) similar to those predicted for β-sialons.     

Effect of Vacancies on the Electronic Structure and Bonding of Zirconium Nitride

The electronic structure and bonding configuration of cubic (B1 type) Zr- and N-deficient zirconium nitride phases were investigated using self-consistent linearized muffin-tin-orbital calculations in the atomic-sphere approximation for a supercell containing eight atoms. Interatomic interactions were analyzed in terms of the crystalline orbital overlap population calculated by the semiempirical tight-binding method. The results are compared with earlier calculations and available experimental data on the electronic structure of nonstoichiometric ZrN.     

Effect of magnetism on the solubility of 3d elements in BCC iron: Results of first-principle investigations

The methods of quantum-mechanical simulation have been used to study alloys of bcc iron with 3d transition metals in the ferromagnetic and paramagnetic states. It has been shown that the main factor that determines the solubility of the 3d elements is their electronic structure. The energy of the solution, mixing, and effective interatomic interactions vary regularly depending on the position of the element in the Periodic Table and on the magnetic state of the matrix. In some cases, depending on the magnetic state, changes in these quantities lead to the violation of the Hume-Rothery rules that determine the solubility of substitutional elements in alloys. The results obtained help us to understand the microscopic mechanisms that determine the solubility of alloying elements and their effect on the phase stability and structural state of steels.     

Modeling the structure of sialon ceramics

The zone method of strong bonding is used to consider the processes of ordering of Si, O, and cation vacancy admixtures in sialon ceramic materials. A model of the microstructure of polytypes in the Si - Al - O - N system is suggested. Transleted from Ogneupory i Technicheskaya Keramika, No. 8, pp. 21 – 24, August, 2000.     

First-principles study of 4d solute diffusion in nickel

Diffusion of the 4d transition elements in Ni has been investigated within the five-frequency model framework using migration energy barriers calculated from the first principles. Agreement with counterintuitive experimental/calculated data is observed; atoms in the middle of 4d row have the smallest atomic radii while exhibiting the lowest diffusivity as compared to larger atoms at the beginning and the end of 4d row. We show that 4d solute diffusion is controlled mainly by the size misfit. The larger atoms have higher solute–vacancy binding energies and lower migration barriers. Both were shown to correlate with a displacement of the equilibrium solute position toward the adjacent vacancy. The difference in mechanisms controlling sp- and transition elements diffusion rates in Ni is discussed.     

Electronic structure of high-temperature ZrO2Cz

Semiempirical band-structure calculations are used to examine the electronic structure and bonding configuration of metastable fluorite phases ZrO₂C_z containing interstitial carbon or substitutional carbon and zirconium vacancies. The results are used to analyze the existing models for the solid-state transformations involved in the carbon reduction of oxides.     

Effect of Al, Si, B, and C Impurities on the Electronic Structure and Bonding of Zirconium Nitride

The electronic structure and bonding configuration of cubic (B1 type) ZrN-based substitutional solid solutions containing Al, Si, B, or C atoms on the Zr and/or N sites were investigated using self-consistent linearized muffin-tin-orbital calculations in the atomic-sphere approximation. The total and partial densities of states, cohesion energy of the solid solutions, and charge states of the constituent atoms were evaluated. Interatomic interactions were analyzed using the semiempirical tight-binding method. The results were used to discuss the possible mechanisms of formation of ternary ZrN-based solid solutions and compare their chemical stability.