Thermal and Radiation Stability of Nanomaterials
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Thermal and Radiation Stability of Nanomaterials Rostislav A. Andrievski Institute of Problems of Chemical Physics, Russian Academy of Sciences 1 Semenov Prospect, Chernogolovka, Moscow Region, 142432, Russia ABSTRACT The kinetic/thermodynamic stabilization recent results of grain growth in nanomaterials (NMs)-based metals, alloys, and compounds are generalized. Due to their large share of interfaces which can act as the sinks for radiation defects, NMs show improved irradiation resistance such as the resistance to amorphization, hardening and swelling. Radiation defects will tend also to the nanostructure annihilation and transformation into amorphous state. Some unsolved problems are emphasized. INTRODUCTION It is well known that high level of physical/mechanical properties of NMs is due to a nanometric (1-100 nm) grain size (and correspondingly a large share of interfaces, triple and quadruple junctions), as well as an availability of segregations, nonequilibrium phases, residual stresses, nanopores, and other defects. Thus, almost all NMs (except supramolecular structures) are far from equilibrium state, and hence possess an excess of Gibbs free energy (ΔG). It follows from general considerations that the thermal activation and other effects, such as radiation, corrosion, deformation, and so on, can stimulate and enhance the diffusion, relaxation, recrystallization, and homogenization processes with partial or total annihilation of nanostructure and degeneration of high level properties. In this connection the NM stability is one of important problems in the new nanostructure development. While there are some reviews, papers, and books devoted to the consideration of the NM thermal/radiation stability (e.g., [1-8]), it seems to be interesting to give a short overview of this problem with accent on some little-explored and unexplored questions. THEORETICAL APPROACHES AND EXPERIMENTAL RESULTS Thermal stability It is evident that the nanostructure stabilization and grain growth decrease can be realized by reducing both the grain-boundary mobility (the so-called kinetic approach) and driving force (the so-called thermodynamic approach). In a first case, many drags such as nanoinclusions, nanopores, chemical ordering, triple junctions, quadruple junctions, and so on are considered for grain growth stopping. The second approach contains the reduction of the grain-boundary energy by solute segregation. The most known and old kinetic approach is the containment of grain growth by nanoinclusions or so-called Zener pinning. The division into two approaches is very conditional because in many practical cases these approaches are deeply intertwined (for example, when grain boundary segregations tend to decrease of the grain-boundary energy and functionate as nanoinclusions).
As applied to thermodynamic approach, it seems to be interesting and important some results on the development of thermodynamic description of NMs. The regular solution approximation is proposed to use for the estimation of ΔG for binary nanocrystalli
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