Nonequilibrium Chemical Composition Research Articles

High-Temperature Hydrogen Attack on 2.25Cr-1Mo Steel: The Roles of Residual Carbon, Initial Microstructure and Carbide Stability

High temperature hydrogen attack is a damage mechanism that occurs in critical steel components in petrochemical plants and refineries when the hydrogen penetrates the steel and reacts with the carbides within to produce pores containing methane. With the motivation of understanding the role of carbide stability on the reaction with hydrogen, samples of a classic 2frac{1}{4}Cr-1Mo steel were subjected to a variety of heat treatments that generate a corresponding variety of precipitates, prior to exposure to high-pressure hydrogen in an autoclave. Using quantitative carbide, porosity and microstructural characterisation, it has been possible to demonstrate the roles of four variables: (a) the carbon residue present in the ferrite; (b) the non-equilibrium chemical composition of carbide; (c) the fraction of the carbide that is closest to the thermodynamic equilibrium state and (d) the initial microstructural state, i.e., whether it is martensitic or bainitic prior to heat treatment.

Dynamic Model of a Non-equilibrium Chemical Composition Formation in the Shell of Single Neutron Stars

The process of a non-equilibrium chemical composition formation in the crust of a new born neutron star is considered, during cooling due to neutrino energy losses. A model is constructed for explaining accumulation of a large quantity of nuclear energy, which can maintain the X-ray luminosity of such compact objects for a long period of time. We studied numerically the dependence of the final chemical composition on various parameters of the model.

On the Formation of a Nonequilibrium Chemical Composition in the Shells of Neutron Stars

On the Formation of a Nonequilibrium Chemical Composition in the Shells of Neutron Stars

Synthesis of Functional Oxide Nanoparticles Through RF Thermal Plasma Processing

A method of synthesizing functional nanostructured powders through reactive thermal plasma processing has been developed. Nano-sized oxide powders, including titanium dioxide and some functional oxides, were synthesized by the oxidation of liquid precursors. Oxides with the prescribed cation ratio of the liquid precursor can be synthesized with this technique, and it is possible to precisely adjust the chemical composition, which is linked to the appropriate functions of ceramic materials. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, were used to vary the quench rate; therefore, the particle size of the resultant powders. The experimental results are well supported by numerical analysis on the effects of quench gases on the flow pattern and temperature field of thermal plasma as well as on the trajectory and temperature history of particles. Plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by conventional wet-chemical processes. Nano-sized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via reactive thermal plasma processing. The plasma-synthesized nanoparticles were spherical and hardly agglomerated, and high dispersion properties were observed, i.e., the plasma-synthesized TiO2 nanoparticles were individually dispersed in water.

Synthesis of Mixed-Phase TiO2 Nanopowders Using Atmospheric Pressure Plasma Jet Driven by Dual-Frequency Power Sources

Mixed-phase TiO2 nanopowders with different ratios of anatase and rutile have been successfully synthesized using atmospheric pressure plasma jet driven by dual-frequency power sources. The crystal structures of the TiO2 nanopowders were characterized by X-ray diffraction, SAED, HRTEM, and Raman shift spectroscopy. These results indicated that samples possessed anatase and rutile structure, in addition, the crystallinity of the TiO2 nanopowders increased and the chlorine contamination decreased with discharge RF power increasing. The photocatalytic activity of the TiO2 nanopowders was evaluated by decomposition methylene blue solution. The TiO2 nanopowders which were produced at the discharge RF power of 110 W had the highest photocatalytic activity. Optical emission spectroscopy (OES) was used to detect various excited species in the plasma jet. The results indicate that the various RF power significantly changes the intensities of emission lines (Ar, Ar+, Ti, Ti+, Ti2+, Ti3+ and O), which results in the TiO2 nanopowders a mixture of anatase and rutile phases. The nonequilibrium chemical composition could be formed in one step without anneal. It may have potential applications for synthesizing nanosized particles of high crystallinity by reactive nonthermal plasma processing.

Radiation-sustained nanocluster metastability in oxide dispersion strengthened materials

ODS materials constitute a new promising class of structural materials for advanced fission and fusion energy application. These Fe–Cr based ferritic steels contain ultra-high density of dispersion-strengthening nanoclusters conferring excellent mechanical properties to the alloy. Hence, guarantee the nanocluster stability under irradiation remain a critical issue. Nanoclusters are non-equilibrium multicomponent compounds (YTiCrO) forming through a complex nucleation pathway during the elaboration process. In this paper, it is proposed to observe the response of these nanoclusters when the system is placed far from equilibrium by means of ion beam. The results indicate that the Y, Ti, O and Cr atoms self-organized so that nanoclusters coarsened but maintain their non-equilibrium chemical composition. It is discussed that the radiation-sustained nanocluster metastability emerges from cooperative effects: radiation-induced Ostwald ripening, permanent creation of vacancies in the clusters, and fast Cr diffusion mediated by interstitials.

High-concentration niobium (V) doping into TiO2 nanoparticles synthesized by thermal plasma processing

Abstract

熱プラズマプロセスによる高機能ナノ粒子の合成

A method of synthesizing functional nanostructured powders through thermal plasma processing has been developed. Nano-submicron-size metal and carbide particles were synthesized through evaporation and subsequent condensation of powders in thermal plasma. The synthesis of nano-size titanium oxide powders was performed by the oxidation of solid and liquid precursors. The plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by the conventional wetchemical processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step via the reactive thermal plasma processing.

Synthesis of functional TiO2-based nanoparticles in radio frequency induction thermal plasma

Abstract A method of synthesizing functional nanostructured powders by using reactive thermal plasma processing has been developed. Nanosized TiO2 powders have been synthesized by the plasma oxidation of solid and liquid precursors. Quench gases, either injected from the shoulder of the reactor or injected counter to the plasma plume from the bottom of the reactor, are used to affect the quench rate and hence the particle size of the resultant powders. The experimental results are well supported by numerical analysis of the effects of the quench gas on flow pattern and temperature field of the thermal plasma as well as trajectory and temperature histories of the particles. The plasma-synthesized TiO2 nanoparticles showed phase preferences different from those synthesized by conventional wet processes. Nanosized particles of high crystallinity and nonequilibrium chemical composition were formed in one step by reactive thermal plasma processing. The plasma-synthesized nanoparticles were spherical and hardly agglomerated. Applications of highly functional nanoparticles are thought to require nanoparticles structured in the forms of (1) dispersoids, (2) fillers, and (3) patterns. For these purposes, plasma-synthesized nanocrystallites seem to be suitable.

Synthesis of ceramic nanoparticles with non-equilibrium crystal structures and chemical compositions by controlled thermal plasma processing

The synthesis of functional nanostructured powders has been developed through reactive thermal plasma processing. Nanosized particles of titanium oxide powder with high crystallinity and non-equilibrium chemical composition were synthesised by one-step processing based on the oxidation of solid and liquid precursors. Spherical carbon powders were treated in a reactive thermal plasma. Crystallinity, chemical composition, and surface morphology were changed in plasma-treated carbon powders. Plasma-treated carbon powders were used as the anode of a lithium-ion rechargeable battery, and improvements in discharge capacity and efficiency were recognized. The generation of pulse-modulated RF inductively coupled plasmas (PM-ICPs) was developed for the first time. The non-equilibrium states were recognized at the instances of pulse-on and pulse-off, and the concentration of chemically active radical species was increased. This offers a unique physico-chemical condition for materials processing.

プラズマプロセスを利用したナノ構造粉末材料の高機能化

Synthesis of functional nano-structured powders has been developed through the reactive thermal plasma processing. Spherical carbon powders, such as phenolic resin, glassy carbon and graphite powders, were treated in reactive thermal plasma. Crystallinity, chemical composition, and surface morphology were changed in plasma-treated carbon powders depending on the plasma conditions. Plasma-treated powders were applied to the anode of lithium-ion rechargeable battery, and improvement of the discharge capacity and the discharge efficiency was recognized. Also, the synthesis of nano-size titanium oxide powders has been performed by the oxidation of solid and liquid precursors. Plasma-synthesized TiO2 nano-particles showed the different phase preference from those synthesized by conventional wet processes. The nano-size particles of high crystallinity and non-equilibrium chemical composition were formed by one-step processing.

Mass Spectrometric Analysis of Nonequilibrium Airflows

Comprehensive measurements were made of the nonequilibrium chemical composition of arc-heated air expanding from reservoir temperatures and pressures of 2120 to 5380 K and 3.7 to 20.8 atm, respectively. A sampling probe containing a quadrupole mass spectrometer and a cryopump was used. Flow composition varied systematically with reservoir entropy, ranging from normal air to a highly nonequilibrium mixture containing 25 % atomic oxygen and 8 % nitric oxide. At low entropy, measured compositions compared favorably with finite-rate theory, but significant disagreement was evident at high entropy. Possible modifications to accepted reaction rates were investigated.

Definition of Temperature in Nonequilibrium Processes

The validity of using a multiple-temperature heat bath model for the description of nonequilibrium processes is examined. Several models have been proposed which utilize temperatures defined by statistical distribution functions or chemical mass action laws. Since, however, the heat bath model is described by classical thermodynamic temperatures which are defined in terms of heat exchange between a reversible engine and energy reservoirs, the validity of such models requires justification. It is shown that the classical thermodynamic temperature can sometimes be used to characterize a particular degree of freedom, such as vibration, even if it is not in equilibrium with the other degrees of freedom. However, it does not appear to be possible in general to associate a thermodynamic temperature with a nonequilibrium chemical composition. To demonstrate this, the entropy rise in vibrational and chemical nonequilibrium processes is computed using the concept of multiple temperatures and compared to the classical result. The results agree for vibrational nonequilibrium. For chemical nonequilibrium the results do not agree except for chemical systems in which the reactants and products have equal constant volume mass specific heats. An example of such a system is the ideal dissociating gas of Lighthill.