Kinetics Of Heterogeneous Processes Research Articles

On the Mechanisms Regulating the Plasma Composition and Kinetics of Heterogeneous Processes in a CF4 + CHF3 + Ar Mixture

On the Mechanisms Regulating the Plasma Composition and Kinetics of Heterogeneous Processes in a CF4 + CHF3 + Ar Mixture

MODIFICATION OF WOOD WITH FATTY ACIDS OBTAINED FROM SOAP STOCK

The paper considers the study of obtaining fatty acids from soap stocks. The proposed method of chemical processing of soap stock was applied for the first time and is not found in the previously published literature on the problems of chemical processing of vegetable oil waste. The composition of the isolated fatty acids of soap stock was studied by mass spectroscopy and the main chemical characteristics of the obtained fatty acids were determined. The isolated fatty acids are valuable not only as a feed additive for livestock, but also as a raw material for the chemical industry, in particular for the production of cellulose esters. The resulting fatty acids were used in the acylation of wood to obtain cellulose esters. The paper considers the kinetic regularities of the reaction of wood acylation with fatty acids of soap stock and studies the optimal conditions for the synthesis of cellulose esters from wood depending on the temperature and time of synthesis. The resulting products were investigated by IR spectroscopy, which proved the formation of an ester bond in the products obtained. When studying the kinetic regularities of the acylation of wood with fatty acids, the energy parameters were calculated in accordance with the kinetics of heterogeneous processes, which include the acylation of wood.

Formation and Chemical Transformations of Steel Corrosion Products in the Primary Systems of Nuclear Power Plants

Improvement of the corrosion situation during nuclear power plant (NPP) operation is associated with the enhancement of construction steel resistance against general (uniform) corrosion, with the routes of chemical transformations and corrosion product mass transfer in the coolant under different water chemistry conditions. Based on a look-back analysis of the obtained research results and a comparison of these results with those in available publications, the following conclusions were made: 1. The morphology of corrosion products formed on the inside surfaces of NPP systems has a four-layer structure. a. A layer of solid corrosion deposits tightly bonded with the surface is formed above the oxide film. b. Tightly bonded deposits are under loosely bonded (“loose” or dissipative) corrosive deposit layers that are dynamically balanced with the corrosion product particles dispersed in the water coolant. 2. By an aggregate state, the coarse/medium fractions (particle size more than 0.45 µm) and the fine fractions (particle size less than 0.45 µm) are conventionally referred to as nonsoluble and conditionally soluble corrosion products, respectively. 3. The chemical composition of all corrosion products depends on the presence of iron compounds, including the alloy element impurities (Cr, Ni, Mn, and Ti). 4. The radionuclide composition of all corrosion products is qualitatively the same and is presented by the activation products of reactor materials, such as 51Cr, 59Fe, 54Mn, 58Co, and 60Co. 5. The phase composition of solid corrosion products depends on the presence of ferrous (II) and ferric (III) iron oxide-hydroxide compounds whose ratio depends on water chemistry conditions: a. Under reducing water chemistry conditions, the phase composition of all corrosion products is determined by a spinel structure of magnetite (Fe3O4). b. Under oxidizing water chemistry conditions, the partial oxidation of ferrous (II) iron ions results in the formation of a defect structure of nonstoichiometric magnetite FeА 3+ [Fe2+ 1-хFe3+]BO4-х, where А and B are two nonequivalent positions in the magnetite structure. At х = 1, a nonstoichiometric magnetite structure changes into hematite, a α-Fe2O3 or maghemite γ-Fe2O3 structure. It is noted that the mathematical models nowadays used for describing the mass exchange and mass transfer of corrosion products in NPP primary systems do not consider physicochemical processes leading to the formation of such complex (phase, disperse, chemical, radionuclide) compositions of corrosion products. A widely known electrochemical mechanism that considers corrosion as a coupled anodic-cathodic process fails to explain actually observed steel dissolution and the contribution of soluble iron forms to oxide film formation on the corroding steel surface at potentials of cathodic polarization and anodic dissolution. This paper presents a diffusion model for corrosion product mass exchange and mass transfer in the steel-water coolant system as an alternative to the electrochemical model for general corrosion. This model is based on Frank-Kamenetkiy’s [Diffusion and Heat Transfer in Chemical Kinetics, Nauka (1987)] concept of the macroscopic kinetics of heterogeneous processes with simultaneous chemical transformations of the corrosion product ionic forms and the formation of solid-phase products in the water coolant and on the surface of corrosive steel. The diffusion model provided better insight into understanding how the phase, disperse, chemical, and radionuclide compositions of steel corrosion products are formed in the coolant of the NPP primary system.

Features of the Kinetics of Bulk and Heterogeneous Processes in CHF3 + Ar and C4F8 + Ar Plasma Mixtures

We carry out a comparative study of the kinetics of plasma-chemical processes and plasma composition in CHF3 + Ar and C4F8 + Ar mixtures under the conditions of a high-frequency (13.56 MHz) induction discharge. Using diagnostic methods and plasma modeling, the general features and differences of the plasma’s electrophysical parameters in the studied systems are established together with the key bulk processes that determine the stationary concentrations of neutral particles. Тhe CHF3 + Ar system in the range 0–75% Ar is shown to be characterized by lower values of the flux densities of the fluorine atoms and polymer of the forming radicals. Model analysis of the kinetics of the heterogeneous processes (etching, polymerization, degradation of the polymer film) confirmed the advantage of the C4F8 + Ar system of silicon etching anisotropy and etching selectivity compared to the SiO2/Si system.

New Regional Editor

Andrei Rotaru was born on the 9th of August 1983 in Craiova, Romania. Since November 2006, he is working at the National Institute for Laser, Plasma and Radiation Physics (INFLPR) Bucharest, Romania, where he currently holds the position of Researcher III (equiv. to Lecturer). Andrei has received his BSc in Chemistry and Physics from the Faculty of Chemistry of the University of Bucharest in 2006, specializing in Physical chemistry. Since 2004, he has carried out research in the field of thermal analysis and kinetics of heterogeneous processes (decomposition of various systems, including liquid crystals and dyes, complex inorganic materials and precursors, biomass and coal). He has also developed a software for performing kinetic computations (TKS-SP) and later on used this knowledge in studying, modelling and processing of thin films by laser-assisted techniques (mainly MAPLE). In 2007, Andrei has received an EPSRC grant, followed by a prestigious fellowship of the Roberto Rocca ‘‘Educational Program’’ for his doctoral studies in solid-state chemistry of ceramic materials at the University of St Andrews, United Kingdom. These more recent interests are related to the fabrication, thermal processing and characterization of novel electroceramic materials with tetragonal tungsten bronze structure. In general, a special interest was directed on modelling relaxation processes in polar dielectric ceramics and investigating the structure–properties relations to induce and control ferroelectricity and ferromagnetism. In 2011, he was the co-chairman of the 1st Central and East European Conference on Thermal Analysis and Calorimetry (CEEC-TAC1), and in 2008 a member of the scientific committee of the 14th International Congress on Thermal Analysis and Calorimetry (ICTAC14) in Brazil; he is a member of the International Confederation for Thermal Analysis and Calorimetry (ICTAC), Commission for Thermal Analysis and Calorimetry of the Romanian Academy (CATCAR), Kinetics committee at ICTAC, International Society for Optics and Photonics (SPIE), and president of the Central and Eastern European Committee for Thermal Analysis and Calorimetry (CEEC-TAC). Currently, he acts as an editor for thermal analysis at the Global Journal of Analytical Chemistry and as a reviewer for several journals: The Journal of Physical Chemistry, Journal of Thermal Analysis and Calorimetry, Thermochimica Acta, Journal of Applied Polymer Science, Dyes & Pigments, Chemical Industry & Chemical Engineering Quarterly, etc. Andrei has been an invited lecturer at several universities and institutes from Lithuania, Estonia, Slovakia, Czech Republic, Poland, and is directly involved and interested in A. Rotaru (&) INFLPR – National Institute for Laser, Plasma and Radiation Physics, Bvd. Atomistilor, nr 409, Magurele (Ilfov), Bucharest, Romania e-mail: andrei.rotaru@inflpr.ro Name: A. Rotaru

Thermogravimetric investigation of the oxidation of the ZrB2-SiO2 composite in the temperature range 800–1300°C

The kinetics and mechanism of high-temperature oxidation of the components of the ZrB2-SiO2 system are investigated using thermogravimetric and X-ray powder diffraction analyses. It is shown that the interaction between solid components of the ZrB2-SiO2 system, atmospheric oxygen, and the glass-forming melt can be adequately described by the equations of the formal kinetics of heterogeneous processes. The previously revealed effect of encapsulation of a high-melting compound by the glass-forming melt is confirmed. This effect manifests itself in the fact that, upon introduction of a silicon-containing component, the increment of the weight of a sample decreases as a result of the oxidation and the weight losses in the form of gaseous products decrease to almost zero.

Influence of the temperature of reactor wall on the kinetics of heterogeneous processes in H2 + Ar plasma

The results of experimental study of the recombination of hydrogen atoms in a positive glow gap and flowing afterglow of direct current discharge in H2 + Ar(0–95%) mixture are presented. On the basis of ESR measurements, the recombination probabilities are obtained for surfaces of quartz and molybdenum glass at different plasma parameters (pressure of 100–400 Pa, discharge current of 5–100 mA) and reactor wall temperatures (295–615 K). The values of activation energy for the recombination process are determined and the recombination mechanism is discussed.

KINETICS OF THE CARBON NANOMATERIALS OXIDATION

The distinction of the chemical activity of carbon nanomaterials is examined on the basis of chemical kinetics of heterogeneous processes. The activation energy for the oxidation by atmospheric oxygen of MWCNT (190±2 kJ·mol-1), fullerene C 60 (162±2 kJ·mol-1), amorphous carbon (124±2 kJ·mol-1), and synthetic diamond (166±2 kJ·mol-1) is evaluated. The use of the thermogravimetric analysis as a method of composition quantitative analysis of carbon nanomaterials is discussed.

Weibull distribution and kinetics of heterogeneous processes

The rate equation Qt/Q∞ = 1 − e−btn, where Qt/Q∞ is the fractional yield of an interface reaction at time t, was shown to be formally analogous to the Weibull distribution functions. Further correlation between the Weibull and the normal distributions did allow for a direct statistical interpretation of surface processes. Rates are thus defined by the well known parameters μ and σ. Geometrically incompatible processes were standardized on the basis of the exponent n and the shape parameter β of the Weibull distribution. For 3<n<4, processes obeyed the normal distribution, and for n<0.7, they obeyed the log normal distribution. By using the linearized probability plots, ambiguities imposed by the multiple logarithming of the above rate equation are avoided.