Thermal Conductivity and Thermal Diffusivity of Liquid Indium–Tin Alloys

Thermal-conductivity and thermal-diffusivity coefficients of indium–tin alloys have been determined using the laser flash method over the temperature range from the liquidus line to 1173 K. Measurements were performed using the setup LFA-427 of NETZSCH company in an argon protective atmosphere, and cells were produced from molybdenum. The equations for temperature dependences of the thermal conductivity and thermal diffusivity of In–Sn alloys have been obtained. The results of measurements were compared with data available in the literature.     

Thermal Conductivity and Thermal Diffusivity of Pulse-Heated W–Re Alloys

Results are reported for the thermal conductivity and thermal diffusivity as a function of temperature for four W–Re alloys (4.0, 21.24, 24.07, and 31.09 mass% of Re) over a wide temperature range covering the solid and liquid states. The measurements allow the determination of specific heat and dependences among electrical resistivity, temperature, and density of the alloys into the liquid phase. The thermal conductivity is calculated using the Wiedeman–Franz law. Additionally, data for thermal conductivity and thermal diffusivity of the constituent elements, tungsten and rhenium, are presented for the first time. Both metals have been previously studied with the same experimental technique.     

High-Temperature Pyrometric Measurement of Thermal Diffusivity by a Flash Method: Co–Si and Co–Ge Systems

The paper deals with an automated system for measuring the thermal diffusivity of metals and alloys by a flash method involving the use of a contactless technique of recording the superheat temperature of a specimen. The solution of the heat equation for a cylinder with due regard for the Gaussian distribution of energy over the laser beam cross section forms the basis of the measurement method. The structural scheme of the experimental facility is described using an IBM PC and a GOR-100M type laser. The results of measuring the thermal diffusivity of Co–Si and Co–Ge systems in the temperature range of 300–1650 K are presented. The polytherms of the thermal diffusivity in the vicinity of the Curie point and in structural transitions exhibit anomalies. These anomalies are smoothed out as the concentrations of Si and Ge increase, and are not observed at a concentration of admixtures higher than 10 at. %. The obtained results are in satisfactory agreement with the diagrams of state for Co–Si and Co–Ge alloys.     

Measurements of Microstructural, Mechanical, Electrical, and Thermal Properties of an Al–Ni Alloy

The Al–7.5 wt% Ni alloy was directionally solidified upwards with different temperature gradients, $G$ ( $0.86\,\text{ K}~{\cdot }~ \text{ mm}^{-1}$ to $4.24\,\text{ K}~{\cdot }~\text{ mm}^{-1})$ at a constant growth rate, $V$ ( $8.34\,\upmu \text{ m}~{\cdot }~\text{ s}^{-1})$ . The dependence of dendritic microstructures such as the primary dendrite arm spacing ( $\lambda _{1}$ ), the secondary dendrite arm spacing ( $\lambda _{2}$ ), the dendrite tip radius ( $R$ ), and the mushy zone depth ( $d$ ) on the temperature gradient were analyzed. The dendritic microstructures in this study were also compared with current theoretical models, and similar previous experimental results. Measurements of the microhardness (HV) and electrical resistivity ( $\rho $ ) of the directionally solidified samples were carried out. Variations of the electrical resistivity ( $\rho $ ) with temperature ( $T$ ) were also measured by using a standard dc four-point probe technique. And also, the dependence of the microhardness and electrical resistivity on the temperature gradient was analyzed. According to these results, it has been found that the values of HV and $\rho $ increase with increasing values of $G$ . But, the values of HV and $\rho $ decrease with increasing values of dendritic microstructures ( $\lambda _{1}, \lambda _{2}, R,$ and $d$ ). It has been also found that, on increasing the values of temperature, the values of $\rho $ increase. The enthalpy of fusion ( $\Delta {H}$ ) for the Al–7.5 wt%Ni alloy was determined by a differential scanning calorimeter from a heating trace during the transformation from solid to liquid.     

Volumetric Properties of Binary Mixtures of 2,4,6-Trimethylpyridine with 1,2-Ethanediol,Methanol, and Water,and the Association Energies of the O–H· · ·N Bonded Complexes

2,4,6-Trimethylpyridine forms 1:1 complexes with methanol, 1,2-ethanediol, and water due to the O–H· · ·N bonds. The association energy of the complexes was calculated using MP2 and DFT methods. The complexes with 1,2-ethanediol and water aggregate in the liquid phase as a result of the O–H· · ·O bonds. In spite of the higher O–H· · ·N bond energy, the aggregation of the ethanediolic complexes is less pronounced than that of the aqueous ones. That is probably caused by the weaker induction effect due to the C–C chain separating the hydroxyl groups in the diol molecule. Aggregation is impossible in the methanolic system, because of the lack of proton-donating functional groups. Differences in the hydrogen bond energy and in the ability to aggregate are manifested in the volumetric properties of the mixtures.     

Measurement of Binary Diffusion Coefficients for Neon–Argon Gas Mixtures Using a Loschmidt Cell Combined with Holographic Interferometry

The paper reports on experimental binary diffusion coefficient data of neon–argon gas mixtures. Measurements were performed in the temperature range between 293.15 K and 333.15 K and for pressures between 1 bar and 10 bar over almost the whole composition range using a Loschmidt diffusion cell combined with holographic interferometry. The thermostated Loschmidt cell is divided into two half-cells, which can be separated and connected by a sliding plate. Prior to the measurements, two different pure gases are filled into the two half-cells. After starting the diffusion process, the temporal change of the partial molar densities, or rather of the refractive index of the gases, is detected in both half-cells using two holographic interferometers. With this apparatus, the temperature, pressure, and concentration dependence of the binary diffusion coefficient can be determined. The relative uncertainty of a diffusion measurement is between 0.4 % and 1.4 % depending on the pressure. The experimental data are compared with data from the literature and with new theoretical data based on quantum-mechanical ab initio calculations combined with the kinetic theory of gases. Due to a systematic error, the concentration dependence determined in the upper half-cell shows deviations from the theoretical values and from most of the literature data. The concentration, temperature, and pressure dependence obtained from the data from the lower half-cell, however, are in very good agreement with available data. The product of the binary gas diffusion coefficient and the molar density of the gas mixture shows no significant dependence on pressure for the studied neon–argon noble gas system.     

Characterization of the Mechanical Stress–Strain Performance of Aerospace Alloy Materials Using Frequency-Domain Photoacoustic Ultrasound and Photothermal Methods: An FEM Approach

Determining and keeping track of a material’s mechanical performance is very important for safety in the aerospace industry. The mechanical strength of alloy materials is precisely quantified in terms of its stress–strain relation. It has been proven that frequency-domain photothermoacoustic (FD-PTA) techniques are effective methods for characterizing the stress–strain relation of metallic alloys. PTA methodologies include photothermal (PT) diffusion and laser thermoelastic photoacoustic ultrasound (PAUS) generation which must be separately discussed because the relevant frequency ranges and signal detection principles are widely different. In this paper, a detailed theoretical analysis of the connection between thermoelastic parameters and stress/strain tensor is presented with respect to FD-PTA nondestructive testing. Based on the theoretical model, a finite element method (FEM) was further implemented to simulate the PT and PAUS signals at very different frequency ranges as an important analysis tool of experimental data. The change in the stress–strain relation has an impact on both thermal and elastic properties, verified by FEM and results/signals from both PT and PAUS experiments.     

Thermal Conductivity of Carbon Dioxide–Methane Mixtures at Temperatures Between 300 and 425 K and at Pressures up to 12 MPa

The thermal conductivities of carbon dioxide and three mixtures of carbon dioxide and methane at six nominal temperatures between 300 and 425 K have been measured as a function of pressure up to 12 MPa. The measurements were made with a transient hot-wire apparatus. The relative uncertainty of the reported thermal conductivities at a 95% confidence level is estimated to be ±1.2%. Results of the low-density analysis of the obtained data were used to test expressions for predicting the thermal conductivity of nonpolar mixtures in a dilute-gas limit developed by Schreiber, Vesovic, and Wakeham. The scheme was found to underestimate the experimental thermal conductivity with deviations not exceeding 5%. The dependence of the thermal conductivity on density was used to test the predictive scheme for the thermal conductivity of gas mixtures under pressure suggested by Mason et al. and improved by Vesovic and Wakeham. Comparisons reveal a pronounced critical enhancement on isotherms at 300 and 325 K for mixtures with methane mole fractions of 0.25 and 0.50. For other states, comparisons of the experimental and predicted excess thermal conductivity contributions showed a smaller increase of the experimental data with deviations approaching 3% within the examined range of densities.     

Galvanic Corrosion of Steel–Brass Couple in Petroleum Waste Water in Presence of a Green Corrosion Inhibitor: Electrochemical,Kinetics, and Mathematical View

Journal of Failure Analysis and Prevention - Control of galvanic corrosion of steel–brass couples in petroleum waste water solution by Curcuma longa was studied at different temperatures,...     

Mapping of nanoscience and nanotechnology research in India: a scientometric analysis, 1990–2009

This paper analyses the growth pattern of Nanoscience and Nanotechnology literature in India during 1990–2009 (20 years). The Scopus international multidisciplinary bibliographical database has been used to identify the Indian contributions on the field of nanoscience and nanotechnology. The study measures the performance based on several parameters, country annual growth rate, authorship pattern, collaborative index, collaborative coefficient, modified collaborative coefficient, subject profile, etc. Further the study examines national publication output and impact in terms of average citations per paper, international collaboration output and share, contribution and impact of Indian Institutions and impact of Indian journals.     

Current–Voltage Measurements and Vortex Dynamics in a Bi2Sr2CaCu2O x Whisker: Observation of the Peak Effect and Calculation of the Critical Current in the Flux Flow Regime with and Without Applied Field

In this article, we report current–voltage measurements carried out on a Bi₂Sr₂CaCu₂O _x whisker in a large temperature range below the critical temperature with and without applied magnetic field. We examine the critical current peak effect and the vortex dynamics at low field. The critical current peak effect consists of the initial increase of the critical current that subsequently decreases as the applied field is increased. For current–voltage measurements, this effect is associated with a change in the current–voltage curves that are typical of the flux flow regime at low fields and resemble flux creep characteristics for higher fields. As a general rule, our observations are consistent with the models that link the peak effect to vortex phase transitions. We calculate the critical current in self-field in the flux flow regime taking into account intervortex forces. We suppose that most vortices are pinned by defects while mobile vortices move through plastic channels between the strongly pinned vortex regions. When an external field is applied, we suggest that the increase in the critical current that is observed is linked to oscillations of the pinned vortices.     

Using a statistical model for the analysis of the influence of the type of matrix carbon–epoxy composites on the fatigue delamination under modes I and II of fracture

This paper analyzes delamination processes under modes I and II fracture and fatigue loading for two types of composite materials. The studied materials were manufactured with the same unidirectional carbon reinforcement though with two types of epoxy matrix. Experimental data were treated with a probabilistic model based on a Weibull distribution allowing the identification of relevant aspects of the fatigue behavior of the materials, such as the estimation of the fatigue strength for periods greater than the tested values and the analysis of the reliability of the results.This study suggests a variable behavior depending on the type of fracture loading: modes I and II, and the type of matrix used.     

Entropy Generation Analysis of Al2O3–Water Nanofluid Flow Past a Permeable Cone Under the Effect of Suction/Injection and Viscous Ohmic Dissipations

Journal of Engineering Physics and Thermophysics - A hydromagnetic nanofluid flow past a permeable cone with heat and mass transfer has been investigated. An incompressible, steady, laminar flow...     

Influence of material and process parameters on microstructure evolution during the fabrication of carbon–carbon composites: a review

Journal of Materials Science - Carbon–carbon composites (CCCs) are a unique form of carbon fiber-reinforced materials that exhibit excellent thermomechanical properties under extreme...     

Extruder scale-up assessment in the process of extrusion–spheronization: comparison of radial and axial systems by a design of experiments approach

Scaling-up the extrusion–spheronization process involves the separate scale-up of each of the five process steps: dry mixing, granulation, extrusion, spheronization, and drying. The aim of the study was to compare two screw extrusion systems regarding their suitability for scaling-up. Two drug substances of high- and low-solubility in water were retained at different concentrations as formulation variables. Different spheronization times were tested. The productivity of the process was followed up using the extrusion rate and yield. Pellets were characterized by their size and shape, and by their structural and mechanical properties. A response surface design of experiments was built to evaluate the influence of the different variables and their interactions on each response, and to select the type of extrusion which provides the best results in terms of product quality, the one which shows less influence on the product after scale-up (“scalability”) and when the formula used changes (“robustness”), and the one which allows the possibility to adjust pellet properties with spheronization variables (“flexibility”). Axial system showed the best characteristics in terms of product quality at lab and industrial scales, the best robustness at industrial scale, and the best scalability, by comparison with radial system. Axial system thus appeared as the easiest scaled-up system. Compared to lab scale, the conclusions observed at industrial scale were the same in terms of product quality, but different for robustness and flexibility, which confirmed the importance to test the systems at industrial scale before acquiring the equipment.     

Internal melting and coarsening of liquid droplets in an Al–Cu alloy: a 4-D experimental study

In conventional melting experiments of pure monocrystalline metals, the phase transformation starts at the sample surface and progresses inwards according to thermal gradients. In solutionized alloys, traces of internal melting are usually observed after reheating and quenching from the semi-solid state. The formation and development of these liquid pockets are not fully understood despite their significance in semi-solid processing, where the formability is greatly influenced by the distribution of liquid within the feedstock material. In situ X-ray microtomography was performed in this study to shed light on this phenomenon. We report in detail the melting and isothermal holding of a model binary alloy where a remarkable number of liquid droplets were observed to develop and coalesce. Various computational tools have been used to study their statistical evolution as well as the local ripening mechanisms involved. We analysed an interesting case of particle coarsening which differs from classical case studies by the fact that the fast-diffusing liquid phase is entrapped within the slow-diffusing solid medium.