Simulation of the structural state of amorphous phases in nanoscale SiO2 synthesized via different methods

The structural state in nanoscaled SiO₂ is probed experimentally via X-ray diffraction and the simulation method. The aerosil nanoparticles and nanoparticles synthesized via the electron beam evaporation are compared. The nanoparticles for all samples are shown to be in the amorphous state. The amorphous state of a SiO₂ unit lattice is simulated via the molecular dynamics. The full-profile refinement of parameters for a simulated SiO₂ phase (the Rietveld method) has allowed the complete structural information to be established at varying the specific surface. The unit cell parameters, the spatial atomic distribution and the degree of cell node occupation are determined, as well. The specific surface area is shown to decrease in aerosil nanoparticles and to increase in tarkosil nanoparticles with the increasing binding energy of atoms in a cell.

     

Local strain distribution in Ni3Ge crystals

We have used a net method to study the distribution of stresses on two facets of Ni₃Ge crystals deformed compressionally to a deformation ε=14 and 16% (near destruction) at experimental temperatures of 77 and 673 K, respectively. It is shown that the stress distribution is inhomogeneous over the sample. Stresses which exceed the average are distributed randomly over the sample at low temperature and in more localized fashion at T=673 K. The temperature has a significant influence on the nature of the deformation distribution. It is shown that the Shannon entropy of the normal distribution of local deformation values is determined only by the variance of random quantities. It is observed that as the temperature is raised to 673 K the Shannon entropy falls or we observe a self-organization of the local volume deformations. State Architecture and Construction Academy, Tomsk. V. D. Kuznetsov Physicotechnical University, Tomsk State University, Siberia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 87–92, March, 1997.     

Dislocation dynamics and thermal hardening of alloys with L12 superlattice

We studied the effect of superdislocation velocities on thermal hardening of alloys with the L1₂ superlattice. We estimate the activation energy for self-stopping of dislocations due to changes in the elastic field of moving dislocations as compared with immobile dislocations. We calculate the velocity of a dislocation loop element, taking into account interactions with dislocations. We show that, because of deformation stress, superdislocations can move at nearly the speed of sound. This, in turn, can help reduce the activation energy for self-stopping processes of superdislocations by a factor of 1.3 to 5.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–61, February, 1996.     

Role of fractal dimension in internal stress fields of Ni3Fe single crystals

In this paper, using the similarity method we have determined the fractal dimension of the dislocation structure of Ni₃Fe single crystals in chaos and in the stage of cell wall formation. We have established that in chaos D=1.04, and at the walls D=1.08. For a linear dependence =_f+·G·b·^1/2, the internal stresses increase by a factor of 1.1 in chaos and 1.22 in the cells, while the internal energy increases by a factor of 1.22 and 1.48 respectively. We discuss the mechanisms for roughening the dislocation structure.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–37, January, 1995.     

Analysis of fragmentation of deformation in Ni3Ge single crystals

The strain distribution on two faces ofNi ₃Ge single crystals compressed to a strain ε-14.16% at T=77.673K was studied by the grid method. It is shown that temperature has a significant effect on the strain distribution. Fragmentation of local strain due to shape change in specimens during active loading was established by the method of main components. Tomsk State Architecture-Construction Academy, Tomsk 634003. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 1, pp. 154–159, January–February, 1998.     

Compression and heating of spherical fusion targets by indirect (x-ray) drive on the Iskra-5 facility

Experiments have been carried out using the Iskra-5 facility in order to study the behavior of x-ray targets in response to a highly symmetric x-ray field. Results are presented of experiments using targets in the form of a spherical copper hohlraum coated with gold on the inside, with six laser entrance holes and a glass microtarget filled with DT gas located at the center. In some experiments the central capsule was coated with a plastic ablator layer of varying thickness. An analysis of the experimental results showed that on the whole, they are satisfactorily described by spherically symmetric gasdynamic calculations. Zh. éksp. Teor. Fiz. 114, 155–170 (July 1998)     

Evolution of Distribution of Dislocations in Ni3Ge Single Crystals During Deformation

The evolution of the distribution of dislocations in Ni₃Ge single crystals subjected to deformation in uniaxial compression is studied. The dislocation ensemble in the material under review is found to be of a chaotic homogeneous type. Contact interactions between dislocations prevail, and a linear relation of the spacing between dislocations to the length of dislocation segments is observed for stoppers of an arbitrary type. An equation is derived for the probability density function of the fraction of mobile dislocation segments. The solution to the equation is the normal distribution law. This solution can be extended to parameters that are functions of the dislocation density or spacing between dislocations. The experimental histograms of the spacing between dislocations and of that between arbitrary stoppers with a high significance level obey the lognormal law for all degrees of reduction studied.