Structural mechanisms of fracture of nanocrystalline materials

Structural mechanisms and features of brittle and quasi-brittle fracture of nanocrystalline materials are theoretically analyzed. The role of size effects and internal stresses caused by a nonequilibrium structure during brittle trans-and intercrystallite fracture is studied. The dependence of the nanocrystalline material durability on the working stress and grain size is calculated. The conditions for certain mechanisms of plastic deformation to be operative in nanocrystalline materials are analyzed. The influence of the grain-boundary and dislocation mechanisms of plastic deformation on the conditions of nanocrack formation is studied. The dependence of the fracture toughness of nanomaterials on structure parameters is calculated.     

Use of the time-of-flight mass spectrometer to study the volatile products from mechanical degradation of polymers in a vibration grinder

Problems about the use of the mass-spectrometry method to study the compositions and kinetics of evolution of volatile products formed during the process of mechanical degradation of polymers in a vibration grinder are examined. A vibration ball mill was directly connected to the vacuum chamber of a time-of-flight mass analyzer. By use of this method, mass spectra of the volatile products evolved during vibration grinding of samples of polymethyl methacrylate, polytetrafluoroethylene, polyethylene, and poly-α-methylstyrene have been obtained. The possibility of studying the kinetics of evolution of volatile products as a function of the amplitude and duration of grinding has been shown in the case of polymethyl methacrylate and of polytetrafluoroethylene.     

Mechanism for mechanical destruction of ammonium bromide single crystals

Conclusions It was shown by the time-of-flight mass spectrometry method that a protonis transferred from the cation to the anion during the mechanical destruction of ammonium bromide single crystals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 924–926, April, 1978.     

An effective two reggeon two reggeon + particle vertex in Lipatov’s effective action and regge kinematics

The vertex of gluon production from the interaction between two reggeons associated with projectiles and two reggeons associated with targets is studied. The vertex can be used to calculate the collision cross section of two pairs of nucleons. The transversality of the vertex is verified along with its good behavior for large longitudinal momenta, which is essential for the vertex’s applicability. Poles are discussed for the zero values of longitudinal momenta. It is found that the poles remain, in contrast to the case of one projectile.     

Dielectric properties of single-crystal deuterated triglycine sulfate (DTGS) in ultra-weak low-and infra-low-frequency electric fields

The complex permittivity ɛ* is studied with separate readings for ɛ′ and ɛ″ at low and infralow frequencies and ultraweak fields. The effective conductivity λ is determined. An Arrhenius dependence is observed for ln ɛ′(1/T), ln ɛ″(1/T), and ln λ(1/T), both in the paraphase and in the polar phase. It is proposed that the conductivity of crystalline DTGS in the paraphase is an ion jump conductivity. Fiz. Tverd. Tela (St. Petersburg) 41, 1073–1075 (June 1999)     

Analysis of the Operation of Thermonuclear Inverted-Corona Targets with an Ultrathin Working Layer at the Iskra-5 Laser Facility

Journal of Experimental and Theoretical Physics - We report on the results of experiments performed on the Iskra-5 laser facility for studying the effect of the polydeuteroethylene (CD2)n working...     

Mechanodynamic diffusion of nitrogen molecules into armco-iron under its deformation in liquid nitrogen medium

Data on mechanodynamic penetration of nitrogen molecules are obtained under deformation of armco-iron samples. It is shown that molecular nitrogen diffuses into the surface layer of samples under their deformation in a liquid nitrogen medium, and the nitrogen concentration compares well with the helium concentration in samples deformed in a liquid helium medium and in some cases exceeds the latter.     

Photochemistry of the iron(III) complex with pyruvic acid in aqueous solutions

Photochemistry of the 1: 1 Fe^pIII complex with pyruvic acid (PyrH) in aqueous solutions was studied by stationary photolysis and nanosecond laser flash photolysis with the excitation by the 3rd harmonics of an Nd:YAG laser. The quantum yield of [FeIIIPyr]2+ under the excitation at 355 nm is 1.0±0.1 and 0.46±0.05 in the absence and in the presence of dissolved oxygen, respectively. In experiments on laser flash photolysis, a weak intermediate absorption in the region 580–720 nm was found. The absorption was ascribed to the [FeII…MeC(O)COO•]^p2+ radical complex. Laser flash photolysis of [FePyr]^p2+ in the presence of methyl viologen dications (MV^p2+) resulted in the formation of the MV•+ radical cations. The proposed reaction mechanism includes the inner-sphere electron transfer in the light-excited complex accompanied by the formation of the [Fe^pII…MeC(O)COO•]^p2+ radical complex followed by its transformation into the reaction products.     

Use of the helium medium for preparation of nano-sized powder materials by the example of industrial cement

Based on the phenomenon of the mechanodynamic diffusion of particles of the external medium in solids, a new in principle method has been proposed for the first time for producing nano-sized powder materials using industrial cement milled in a helium medium as an example. The temperature dependences of the extraction rate and the amount of helium in powders upon their heating in a temperature range of 20–1200°C have been obtained using mass spectrometry. It has been shown that milling of the cement powder of the M-400 brand using an MK-1 laboratory mill in helium leads to a considerable shift of its extraction curve towards lower temperatures compared with the air medium. The particle sizes of the powder milled in helium lie in a range of 5–10 nm, which is smaller than the powder size (～500 nm) after milling in the air medium by a factor of 100. The compression strength of cement samples obtained from the powders milled in helium increased by a factor of 2 compared with the strength of the samples from the initial material. The activation energies of helium extraction from the cement powders milled in helium and in air have been analyzed. The obtained results indicate a high efficiency of the method for producing nano-sized powder materials in the helium medium. The method can be used in the industrial scale based on the existing mill equipment with its minimal modernization.