Papers by Author: Yuriy S. Nechaev

Abstract: In the present study, the extraordinary, i.e., not yet reproduced by anybody, data of Rodrigez, Baker, Gupta et al. on the “super” storage of hydrogen in activated graphite nanofibers (GNFs) were analyzed and interpreted in approximation of the first-order sorption processes. Our developed methodology was used for processing, analysis and interpretation of thermal desorption and thermogravimetric spectra of hydrogen in the GNF samples. The analysis has shown that there is a real possibility of reproducing of the modified extraordinary results, but only in the case of revealing the know-how technology of the activation treatment of the GNF samples.

Abstract: We present results of the constructive critical analysis and interpretation of some recent studies (Blavette, Sauvage, Wilde and others) at the atomic scale (using three-dimensional atom-probe field-ion microscopy) of impurity nanosegregation at dislocations, including “Cottrell atmospheres”, and grain boundaries in deformed intermetallics and metallic materials, and their relevance to mechanical properties and diffusion processes.

Abstract: Based on the results of the thermodynamic analysis of a number of experimental data, and in the light of the Kaibyshev-Valiev discovery, the possibility of periodic formation of a liquid-like state in the nanoregions of extremely "non-equilibrium" grain boundaries and in other structural defect regions in metallic polycrystals during their superplastic deformation and intense plastic deformation is considered. It is also considered important differences between the liquid-like state and the glass-like (amorphous) state.

Abstract: In this analytical review, some thermodynamic, physical and nanotechnological aspects of the graphene/graphane problem are considered (in a correlation), relevance to developing a much simpler and efficient method (in comparison with the megabar compression dynamic and static ones) of producing a high-density solid molecular hydrogen carrier. It is achieved by the hydrogen intercalation (at the cost of the hydrogen association energy) in closed multigraphane (carbohydride-like) nanostructures of the megabar strength properties. The limiting density value (0.7±0.2 g/cm3(H2)) of such intercalated high-purity reversible hydrogen carrier corresponds to a megabar compression. The “volumetric” hydrogen capacity is of 0.3±0.1 g/cm3(system), and the “gravimetric” one being ≥ 15 wt %( H2). Such a hydrogen storage nanotechnology can exceed and/or correspond to the known U.S. DOE requirements-targets on the hydrogen on-board storage for 2015 (www.eere.energy.gov /hydrogenandfuelcells), with respect to the hydrogen capacities (0.081 g/cm3(system), 9.0 wt %( H2)), safety, reversibility and purity.

Abstract: Empiric evaluations of fundamental characteristics of interactions of gaseous hydrogen with different kinds of graphite and novel carbonaceous nanomaterials and revealing the micromechanisms have been carried out. The approaches used were those of the thermodynamics of reversible and irreversible processes for analysis of the adsorption, absorption, diffusion, TPD and other experimental data and comparing the analytical results with first-principle calculations. Such analysis of a number of the known experimental and theoretical data has shown a real possibility of the multilayer specific adsorption (intercalation) of hydrogen between graphene layers in novel carbonaceous nanomaterials, relevance for solving the bottle-neck problem of the hydrogen on-board storage in fuel-cell-powered vehicles, and other technical applications.

Abstract: An annotated analytical essay of possible nanofabrication and nanotechnology applications is presented with respect to: (1) some techniques and original results [1-4] concerning the regularities and micromechanisms (physics) of the hydrogen fluoride gas activator influence on the diffusion-controlled oxidation processes of titanium, zirconium and zirconium-based alloys with niobium, and also – on nitriding, boriding and carbiding a series of refractory metals (Ti, Zr, Nb, Mo, W, Ta); (2) some techniques, original results and physics of the diffusion-controlled formation processes of the compound-like nanosegregation [5-13] and the results [13-23] on the liquid-like phase at grain boundary regions in metals and alloys. In the scope of this review, a constructive analysis, the Arrhenius-type treatment, and the original data interpretation [16-21] has been carried out for the first time; (3) some techniques, original analytical results, and physics [24, 25] of the diffusion-controlled processes of the hydrogen multilayer intercalation (physisorption of a condensation or clustering type) with carbonaceous nanostructures. The main objective of the given analytical essay is to attract the researchers’ attention to the expediency of such a non-conventional data analysis and interpretation.

Abstract: New possible nanotechnology applications of some original developments and results of studying the regularities and micromechanisms (physics) of the hydrogen °uoride gas activa- tor in°uence on oxidation of titanium, zirconium and zirconium-based alloys with niobium, and also - on nitriding, boriding and carbiding a series of refractory metals (Ti, Zr, Nb, Mo, W, Ta) are elaborated. The new possible nanotechnology applications of the techniques and physics of creating a compound-like nanosegregation or the liquid-like nanosegregation at grain bound- aries in nanostructured metals, i.e. creating of speci¯c cellular type natural nanocomposites, are considered as well.

Abstract: Specific phase transitions to the compound-like impurity nanosegregation structures at dislocations and grain boundaries in metals and their influence on diffusion-assisted processes are considered, mainly, on the basis of the thermodynamic analysis of the related experimental data. The following systems and aspects are in detail considered: (1) the hydride-like nanosegregation of hydrogen at dislocations and grain boundaries in palladium and their influence on the apparent characteristics of hydrogen solubility and diffusivity in palladium; (2) the physics of the anomalous characteristics of diffusion of Fe and other transition impurities in crystalline Al at elevated temperatures, the role of the compound-like nanosegregation (CLNS) of Fe and the others at dislocations and grain boundaries in Al, analysis of the Mössbauer and diffusion data on CLNS of Fe at grain boundaries and dislocations in Al; (3) some new physical aspects of internal oxidation and nitridation of metals (for Cu-0.3%Fe alloy/Cu2O surface layer, and for (Ni-5%Cr) alloy / N2 gas), the role of the compound-like impurity nanosegregation at dislocations and grain boundaries, study results on the deviations from the classical theories predictions and their interpretation. The possibility is considered of nanotechnology applications of the study results for creation of nanostructured metals with compound-like nanosegregation structures at grain boundaries, in order to obtain specific physical and mechanical properties of such a cellural-type nanocomposites. In particular, it can be complex hydride-like, carbide-like, nitride-like, carbide-nitride-like, oxide-like or intermetallide-like nanosegregation structures at grain boundaries of nanostructured metals.

Abstract: Urgent open questions and their solution ways are considered of the thermodynamic stimuli and mechanisms of the enhanced Fickian diffusion mass-transport providing the unusual structuralphase transformations in metallic materials undergoing the intensive cold deformation, those can not be described in the framework of the conventional phase diagrams.

Abstract: As the critical constructive analysis, with using the thermodynamic and crystal-chemical approaches, of the related experimental data is shown, the anomalous (with respect to the Al selfdiffusion characteristics (DAl - the self-diffusion coefficient, D0Al - the entropy (frequency) factor of the self-diffusion coefficient, QAl – the self-diffusion activation energy (enthalpy)) quantities of D*, D0*, Q* of the transition impurity Fickian diffusion in Al in many cases can be of the apparent character (related to the known Oriani model), whereas the normal quantities of D, D0, Q (i.e., close to DAl, D0Al, QAl), and the anomalously low quantities of D⊥, Q⊥, D0⊥ can be as the true characteristics of the impurity Fickian diffusion in the normal Al lattice (bulk) and in the compound-like nanosegregation (CLNS) structures at dislocations, respectively.