Papers by Keyword: Enthalpy

Abstract: This study investigates the thermodynamics of manganese ion adsorption on nanozeolite to assess the nanomaterial’s heavy metal removal efficiency from surface water, industrial water, and groundwater. Using Isothermal Titration Calorimetry (ITC), the thermodynamic profile of nanozeolite is obtained, demonstrating a low equilibrium binding affinity. The thermodynamic signature showed favorable binding mechanisms, primarily from the change of entropy, suggesting spontaneous reactions. Meanwhile, the enthalpy change of adsorption increases as temperature rises, while ∆G and T∆S decrease. Using proper thermodynamic conditions, nanozeolite may efficiently remove manganese from different water sources.

Abstract: A thermodynamic model for cellular glass pore-formation has been developed on the basis of natural volcanic silicate and aluminosilicate glasses. The energy expenses for heating the materials, chemical reactions, breaking the structural bonds of water hydrates, evaporation of the released water, and pore formation of the glass mass are determined sequentially. The enthalpy and Gibbs energy of the complex gas-forming agent HNO₃ + SiC are calculated.

Abstract: One of the effective ways to improve the quality of semi-finished products made from aluminum alloys is to eliminate the columnar and fan-shaped structure in them, refine the grain and achieve homogeneity, is modification and alloying. Modification of the melt is carried out using ligatures and allows a significant increase in the casting rate without fear of an excessive increase in the degree of zonal segregation during crystallization, as well as ensuring the uniformity of the chemical composition over the section. An important role in the quality of modification is also played by the manufacturing technology of the master alloy itself, which should ensure an increase in the cooling rate during crystallization. To obtain an alloy with the required properties, the quality of the charge materials used must be considered. First of all, this concerns master alloys, which are used for alloying and modifying the alloy. The most common for the manufacture of ingots and shaped castings are master alloys containing boron or boron and titanium. The boron content in these ligatures is 1-5%. It is generally accepted that a large amount of boron (except for the rise in the cost of the alloy itself) upon accelerated cooling promotes the refinement of the internal structure of the grain, but can lead to an increase in large inclusions of TiB2.

Abstract: High entropy alloys (HEAs) are equimolar multi-principal-element alloys (MPEAs) that are different from traditional solvent-based multicomponent alloys based on the concept of alloy design. Based on initial work by Yeh and co-workers, HEAs were postulated to exhibit four “core” effects: high entropy, sluggish diffusion, lattice distortion, and cocktail effect. Out of these four proposed core effects, “high entropy” and “sluggish diffusion” effects were most debated in the literature as these core effects directly affect the thermodynamic and kinetic understanding of HEAs. The initial work on HEAs by several researchers utilized these effects to indirectly support the experimentally observed “unique” properties, without independent investigation of these core effects. The presumed implications of these core effects resulted in justification or generalization of properties to all HEAs, e.g., all HEAs should exhibit high temperature stability based on high entropy effect, high temperature strength owing to limited grain growth, good diffusion barrier application due to sluggish diffusion kinetics, etc. However, many recent studies have challenged these core effects, and suggested that not all HEAs were observed to exhibit these core effects.

Abstract: To effectively interpret the fluid flow dynamics in the molten metal pool, a numerical model was established. The moving repetitive Gaussian laser pulse is irradiated in the work piece. The consideration of laser scanning speed makes the transport phenomena complex. The continuity and momentum equations are solved to get the flow velocity of the molten metal in the melt pool. The energy equation is solved to know the temperature field in the work piece. The algebraic equations obtained after discretization of the governing equations by Finite Volume Method (FVM) are then solved by the Tri Diagonal Matrix Method. Enthalpy-porosity technique is used to capture the position of the melt front which determines the shape of the melt pool. Marangoni convection is considered to know its effect on the shape of the melt pool. The surface tension coefficient is taken as both positive and negative value while calculating the Marangoni force. The two possible cases will cause the Marangoni force to distort the flow dynamics in the melt pool . It's dominance over the buoyancy force in controlling the melt pool shape is focused in the present study. Further, the present model will present an insight to the consequences of laser scanning velocity over the melt pool dimensions and shape.

Abstract: In this paper, the Mg-Al hydrotalcite-like compound (Mg-Al-HTLC) was synthesized by hydrothermal method at 373K. Structure and morphology of Mg-Al-HTLC was obtained with X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infra-red spectroscopy(FTIR). A series of polar and non-polar molecules were used for probes, surface properties of Mg-Al-HTLC was studied by inverse gas chromatography (IGC) at 353K, 363K, 373K, 383K respectively. The retention volume was utilized for evaluating the free energy of adsorption (-ΔG^SP), the dispersive component of the surface energy(γ_s^D), as well as the enthalpy and entropic component(ΔH^SP, -ΔS^SP). XRD results reveal that the Mg-Al-HTLC has high crystallinity and perfect layered structure. The results of IGC show that Mg-Al-HTLC would adsorb straight-chain alkanes spontaneously, and the values of γ_s^D were similar at all temperature. It reveals Mg-Al-HTLC is a material with particular characteristics of both acid and base. This study illustrates that, as a method to evaluate the surface properties of material , IGC method is dependable and significant.

Abstract: Cellulose is a good bio-based material for rich resources and recyclability. Paraffin is widely used in the field of energy storage and temperature regulation due to its excellent heat storage properties and mature preparation technology. In this paper, the cellulose fibers with energy storage and temperature regulation were prepared by wet spinning process using paraffin as phase change material. Field Emission Scanning Electron Microscope (FE-SEM), X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) were utilized to characterize the morphology structure, crystalline properties, phase transition properties and heat resistance of fibers and so on. The results showed that the fiber surface without holes and paraffin was uniformly distributed in the cellulose matrix, and paraffin was not easily overflow during the process of phase change. Paraffin and cellulose substrate had good compatibility due to the interaction of hydrogen bonding, and 30% of paraffin did not cause a significant impact on the degree of crystallinity and thermal stability of cellulose fibers. Enthalpy of the resultant functional fibers could reach 27.44 J/g, and the thermal decomposition temperature was over 300 °C. The fibers possessed the phase change ability and certain mechanical properties. Furthermore, it was found that the fibers still had good resistance to washing under extreme conditions.

Abstract: Cutting temperature always highly reaches over to 1000°C when high speed machining with PCBN tools. Diffusion of tool material element may have important influence on tool wear at such high temperature., the diffusion wear and oxidation wear have become the major wear mechanism. In this paper, the rules of diffusion wear and oxidation wear for PCBN cutting tools are proposed and analyzed based on thermodynamics theory. Dissolution concentrations in typical normal workpice materials of PCBN tool material at different temperature are then calculated. Diffusion reaction rules in high temperature are developed and analyzed using Gibbs free energy criterion. The machining tests were conducted using the PCBN tools at different cutting speeds of 50, 95,100 and 180 m/min, feed of 0.1, 0.2mm and depth of cut of 0.1, 0.8, 1, and 1.5 mm respectively on PUMA300LM numerically-controlled lathe. It was found that the theoretical results were uniform with the experimental data; the results will provide useful references for tool material design and selection.

Abstract: The article presented the processes of pyrolysis and gasification of biomass leading to the preparation of liquid hydrocarbon fractions in the synthesis of Fischer-Tropsch and processes HTU. Preliminary thermogravimetric testing of biomass samples was conducted on the STA 449 F3 Jupiter® coupled with the gases analyzer – spectrometer QMS 403 Aëolos. These studies were carried out for samples of cereal straw, crushed to a state of dry dust. The temperature regime provided that the samples were heated to the temperature of 750 °C at the heating rate of 10 K/min. Gases (nitrogen, argon or carbon dioxide) were used with flow rates of 60 mL/min. The results, along with discussion, are presented in graphs - TG curves and mass spectrum.

Abstract: Metal matrix composites are regarded to be one of the most predominant classifications in composites. The thermal characterization of metal matrix composites using Differential Scanning Calorimetry is a resourceful technique for the determination of heat flow distribution, specific heat capacity and enthalpy. The measurement of the thermal properties of materials is fundamental for the better understanding of the thermal design. Differential Scanning Calorimeter (DSC) is a technique that measures the difference in the heat flow to a sample and to a reference sample as a direct function of time or temperature under heating, cooling or isothermal conditions. In the present research, evaluation of specific heat capacity and enthalpy are accomplished for Al 6061, Silicon Carbide and Graphite hybrid metal matrix composites from room temperature to 300°C based on heat flow response. Based on endothermic and exothermic processes, the heat flow can be shown clearly depending on heating rate and gradual variation in temperature. The heat flow and heating rate are beneficial in the estimation of specific heat capacity for different percentage compositions of the hybrid composites.