Thermodynamics of solid and liquid aluminium

Based on thermodynamic calculations, it is shown that in the temperature range of 298–1273 K, heating and cooling of aluminum are thermodynamically equilibrium processes. When aluminum is heated, the molar volume energy of Gibbs decreases and the molar boundary energy of nanocrystals increases. When aluminum is cooled, the molar volume energy of Gibbs increases and the molar boundary energy of nanocrystals decreases. Liquid aluminum is a nanostructured system. Dendritic microcrystals are formed from nanocrystals. They play a large role in the processes of changing the structure of aluminum during its heating and cooling.

Темплатный метод синтеза монодисперсных наночастиц MoS-=SUB=-2-=/SUB=-

Monodisperse molybdenum disulfide nanoparticles were synthesized in mesopores of spherical silica particles (mSiO2) served as a template. First, the pores of mSiO2 particles were impregnated with the precursor (ammonium tetrathiomolybdate solution). Then, the reduction of the filler in thermodynamically equilibrium conditions in H2S/H2 atmosphere was carried out. The template material (a-SiO2) was selectively etched from the composite mSiO2/MoS2 particles with HF to obtain individual MoS2 nanoparticles. The mean size of MoS2 nanoparticles determined by microscopic methods was found to be 3.5 nm. According to dynamic light scattering data, the nanoparticles had low size scatter (18%).

Численное исследование ударно-волнового нагружения металлических композитов на базе W и WC

The results of research on modeling shock-wave loading of metal composites – elkonites, which are sintered refractory materials tungsten, tungsten carbide or molybdenum impregnated with fusible metal silver or copper using thermodynamically equilibrium model TEC are presented. The investigation of the compressibility of such composites are related to the properties of the materials themselves and the possibility of creating samples based on them. Thermodynamic characteristics are calculated for these metals and compared with available data of shock-wave experiments. The model allows us to describe the dynamic loading of solid and porous alloys of various compositions such as Cu–W, Ag–W, Cu–WC, Ag-W. This model allows for targeted selection of material compositions of different porosity values and ratios of their components in order to obtain the specified characteristics for shock-wave loading of samples.

Thermodynamically Equilibrium Compositions of the Products Formed During the Filtration Combustion of the Metal-Containing Mixtures

Thermodynamic calculations for describing the compositions of the products formed in conditions of the filtration combustion of the metal-containing mixtures were carried out. The analysis of the equilibrium compositions of the products was carried out using the TERRA high-temperature thermochemical equilibrium calculation program. According to the results of calculations, the metals were divided into two groups. First one forms both the condensed and gaseous phases and in the second one ‒ metals that are only in the condensed phase. In case of the presence of metal compounds in the gas phase, as a rule, these are the following compounds: metals, oxides, hydroxides, hydrides, sulfides and metal sulfates. Metals of the second group cannot be subjected to mass transfer under conditions of the filtration combustion wave and will remain in solid combustion products (in ash).

Activating cement mixing water with the relaxation processes

The analysis of relaxation processes in water activated by thermal or ultraviolet radiation has been carried out. The activation of the mixing water leads to an earlier hardening of the cement. At the same time, activated water loses its properties with a relaxation time, which is equal to the activity time of melt water, which is explained by the common reasons for the origin of the increased reaction properties of activated water and melt water. These properties are due to the fact that activation increases the content of free water molecules. In the normal state, some of the water molecules enter the voids of fractal-clathrate structures. During thermal or radiation activation processes, characterized by certain relaxation times, these structures are destroyed, and free water molecules are released. But after the termination of activation, relaxation processes take place to restore thermodynamically equilibrium fractal-clathrate structures, and part of the free water is again captured by these structures. Therefore, the reactivity of water after the termination of activation decreases.

Environmental Characteristics of Modern Systems of Domestic Use of Fuel. Part 1

The analysis of the environmental component of the processes of natural gas burning in atmospheric burners of domestic gas stoves has been carried out. The computational and experimental studies of the harmful substances formation by combustion of natural gas have been performed. The chemical equilibrium of the NO–O2–NO2 system was considered. The thermodynamic analysis of transformation of the system during a process of natural gas (methane-air mixture) combustion has been tested. Despite an essential (sometimes – by the order(s)) difference between the thermodynamically equilibrium concentration of the nitrogen oxides [NOx]eq and the local, actually measured values [NOx] = [NO] + [NO2], the [NO]eq values could be served as the qualitative indicators of actual values of [NOx] concentrations. In the combustion processes natural gas and other fuels combustion at high temperatures [NO] >> [NO2] for both equilibrium and measured concentrations. By moderate and low local temperatures up to 600 K the equilibrium concentration [NO2]eq → [NO]eq in order of magnitude. Under some compositions of burning mixture the correlation could be set as [NO2] >> [NO], resulting in great danger for the human health. With regard to the formation of particularly toxic NO2 effluents observed in some cases, an influence of the reaction temperature and the composition of the combustible mixture on the possibility of nitrogen dioxide formation in the combustion products have been analyzed. A methodology for the experimental study of the harmful emissions formation has been proposed while the computerized firing rig has been developed for studying the combustion of hydrocarbon gases in burners of household stoves. An influence of the coefficient of primary air excess on the СО, NO, NO2 formation has been revealed and the possibility of appearance the emissions of a high concentration of nitrogen dioxide has been demonstrated.

Jackfruit as an Object of Drying: A Hygroscopic Study

Statics of drying is based on the laws of interaction between the gas medium and the dehydration facility, which seek a thermodynamically equilibrium state. Jackfruit is a wet thermolabile material. With a static equilibrium between the product and the environment, the water content in a hygroscopic state depends on the type of the product, its energy, humidity, and a number of parameters, e.g. temperature and partial pressure of the vapor on the surface. The paper introduces graphical dependences of the activity of water of jackfruit slices on humidity at various ambient temperatures. The authors also give its analogy in semilogarithmic coordinates. It helped to define a range of humidity that determined the type of connection between the moisture of the object and the dry residue. The laws of the mechanism of heat and mass transfer are relevant in determining the dynamics of the dehydration process. Their study can help to intensify the process of moisture removal with rational operating parameters. The present study featured the equilibrium states in the system, which made it possible to find the driving force of moisture transfer and to evaluate the heat carrier potential, as well as to substantiate the values of the parameters and the environment during storage and transportation of the finished dry product. The value of relative moisture content in equilibrium was determined by isothermal sorption curves. The value depends on the pre-treatment of the drying object, the conditions of its contact with the external environment, as well as by the energy and type of relationship between the dry residue and the moisture. The empirical results were arranged in the form of graphical dependences, which made it possible to theoretically obtain their mathematical approximation. The equations of dependence between the equilibrium moisture content of the material and the relative humidity of the vapor-air medium included a lot of constants, which also needed to be determined empirically. The mathematical dependences approximate the isothermal sorption curves, i.e. the relationship between the product’s moisture and water activity indices. The dependences can be used to conduct a thermodynamic analysis of the sorption process and determine the free, bound, and internal energies of the process of moisture absorption by the capillary-porous object of study. The hygroscopic examination of jackfruit is also necessary when making design decisions for the rational implementation of technological operations, including the storage and transportation of dry jackfruit slices.

Численное моделирование термодинамических параметров высокопористой меди

The modified equation of state is proposed for the calculation of thermodynamically equilibrium model TEС2 to improve the reliability of the description of thermodynamic parameters of shock-wave loading of pure materials and heterogeneous mixtures of different porosity. The parameters of the thermally consistent equation of state are determined for copper. A reliable description of the shock-wave loading of copper is obtained for a small number of fitting parameters determined by the experimental data. The thermodynamic parameters for copper of different porosity are modeled, the compression and temperature values along the shock adiabate are determined; the heat capacity value along the normal isobar is calculated. The results of calculations are compared with the known experimental results of different authors.