Determination of mechanical, electrical and thermal properties of the Sn―Bi―Zn ternary alloy

The development of lead-free solders has emerged as one of the key issues in the electronics packaging industries. Sn―Zn―Bi eutectic alloy has been considered as one of the lead-free solder materials that can replace the toxic Pb―Sn eutectic solder without increasing soldering temperature. This study investigates the effect of temperature gradient and growth rate on the mechanical, electrical and thermal properties of the Sn―Zn―Bi eutectic alloy. Sn-23 wt.% Bi-5 wt.% Zn alloy was directionally solidified upward with different growth rates (V = 8.3-478.6 μm/s) at a constant temperature gradient (G = 3.99 K/mm) and with different temperature gradients (G = 1.78-3.99 K/mm) at a constant growth rate (V = 8.3 μm/s) in the Bridgman-type growth apparatus. The microhardness (HV), tensile stress (σ_t) and compressive stress (σ_c) were measured from directionally solidified samples. The dependency of the HV, σ_t and σ_c for directionally solidified Sn-23 wt.% Bi-5 wt.% Zn alloy on the solidification parameters (G, V) were investigated and the relationships between them were obtained by using regression analysis. According to present results, HV, σ_t and σ_c of directionally solidified Sn-23 wt.% Bi-5 wt.% Zn alloy increase with increasing G and V. Variations of electrical resistivity (ρ) for cast samples with the temperature in the range of 300-420 K were also measured by using a standard dc four-point probe technique. The enthalpy of fusion (ΔH) and specific heat (C_p) for same alloy was also determined by means of differential scanning calorimeter (DSC) from heating trace during the transformation from eutectic liquid to eutectic solid.     

Dispersive liquid–liquid microextraction based on the solidification of floating organic drop followed by inductively coupled plasma-optical emission spectrometry as a fast technique for the simultaneous determination of heavy metals

A simple, rapid and efficient dispersive liquid–liquid microextraction based on the solidification of floating organic drop (DLLME–SFO) method, followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for the simultaneous preconcentration and determination of heavy metals in water samples. One variable at a time method was applied to select the type of extraction and disperser solvents. Then, an orthogonal array design (OAD) with OA₁₆ (4⁵) matrix was employed to study the effects of different parameters on the extraction efficiency. Under the best experimental conditions (extraction solvent: 140 μL of 1-undecanol; disperser solvent: 2.0 mL of acetone; ligand to metal mole ratio: 20; pH: 6 and without salt addition), the enhancement factor ranged from 57 to 96. The calibration graphs were linear in the range of 0.5–250 μg L⁻¹ for Mn, 1.25–250 μg L⁻¹ for Cr, Co and Cu with correlation coefficient (r) better than 0.990. The detection limits were between 0.1 and 0.3 μg L⁻¹. Finally, the developed method was successfully applied to extraction and determination of the mentioned metal ions in the tap, sea and mineral water samples and satisfactory results were obtained.     

Modeling dendritic solidification of Al–3%Cu using cellular automaton and phase-field methods

We compared a cellular automaton (CA)–finite element (FE) model and a phase-field (PF)–FE model to simulate equiaxed dendritic growth during the solidification of cubic crystals. The equations of mass and heat transports were solved in the CA–FE model to calculate the temperature field, solute concentration, and the dendritic growth morphology. In the PF–FE model, a PF variable was used to identify solid and liquid phases and another PF variable was considered to determine the evolution of solute concentration. Application to Al–3.0 wt.% Cu alloy illustrates the capability of both CA–FE and PF–FE models in modeling multiple arbitrarily-oriented dendrites in growth of cubic crystals. Simulation results from both models showed quantitatively good agreement with the analytical model developed by Lipton–Glicksman–Kurz (LGK) in the tip growth velocity and the tip equilibrium liquid concentration at a given melt undercooling. The dendrite morphology and computational time obtained from the CA–FE model are compared to those of the PF–FE model and the distinct advantages of both methods are discussed.     

A volume of fluid approach for crystal growth simulation

A new approach to simulating the dendritic growth of pure metals, based on a recent volume of fluid (VOF) method with PLIC (piecewise linear interface calculation) reconstruction of the interface, is presented. The energy equation is solved using a diffuse-interface method, which avoids the need to apply the thermal boundary conditions directly at the solid front. The thermal gradients at both sides of the interface, which are needed to obtain the front velocity, are calculated with the aid of a distance function to the reconstructed interface. The advection equation of a discretized solid fraction function is solved using the unsplit VOF advection method proposed by López et al. [J. Comput. Phys. 195 (2004) 718–742] (extended to three dimensions by Hernández et al. [Int. J. Numer. Methods Fluids 58 (2008) 897–921]), and the interface curvature is computed using an improved height function technique, which provides second-order accuracy. The proposed methodology is assessed by comparing the numerical results with analytical solutions and with results obtained by different authors for the formation of complex dendritic structures in two and three dimensions.     

Optimization of dispersive liquid–liquid microextraction based on the solidification of floating organic droplets using an orthogonal array design and its application for the determination of fungicide concentrations in environmental water samples

A dispersive liquid–liquid microextraction method based on the solidification of floating organic droplets was developed as a simple and sensitive method for the simultaneous determination of the concentrations of multiple fungicides (triazolone, chlorothalonil, cyprodinil, and trifloxystrobin) in water by high‐performance liquid chromatography with variable‐wavelength detection. After an approach varying one factor at a time was used, an orthogonal array design [L₂₅ (5⁵)] was employed to optimize the method and to determine the interactions between the parameters. The significance of the effects of the different factors was determined using analysis of variance. The results indicated that the extraction solvent volume significantly affects the efficiency of the extraction. Under optimal conditions, the relative standard deviation (n = 5) varied from 2.3 to 5.5% at 0.1 μg/mL for each analyte. Low limits of detection were obtained and ranged from 0.02 to 0.2 ng/mL. In addition, the proposed method was applied to the analysis of fungicides in real water samples. The results show that the dispersive liquid–liquid microextraction based on the solidification of floating organic droplets is a potential method for detecting fungicides in environmental water samples, with recoveries of the target analytes ranging from 70.1 to 102.5%.     

Capabilities and limitations of dispersive liquid–liquid microextraction with solidification of floating organic drop for the extraction of organic pollutants from water samples

Dispersive liquid–liquid microextraction with solidification of floating organic drop (DLLME-SFO) is one of the most interesting sample preparation techniques developed in recent years. Although several applications have been reported, the potentiality and limitations of this simple and rapid extraction technique have not been made sufficiently explicit. In this work, the extraction efficiency of DLLME-SFO for pollutants from different chemical families was determined. Studied compounds include: 10 polycyclic aromatic hydrocarbons, 5 pesticides (chlorophenoxy herbicides and DDT), 8 phenols and 6 sulfonamides, thus, covering a large range of polarity and hydrophobicity (Log K_ow 0–7, overall). After optimization of extraction conditions using 1-dodecanol as extractant, the procedure was applied for extraction of each family from 10-mL spiked water samples, only adjusting sample pH as required. Absolute recoveries for pollutants with Log K_ow 3–7 were >70% and recovery values within this group (18 compounds) were independent of structure or hydrophobicity; the precision of recovery was very acceptable (RSD < 12%) and linear behavior was observed in the studied concentration range (r² > 0.995). Extraction recoveries for pollutants with Log K_ow 1.46–2.8 were in the range 13–62%, directly depending on individual Log K_ow values; however, good linearity (r² > 0.993) and precision (RSD < 6.5%) were also demonstrated for these polar solutes, despite recovery level. DLLME-SFO with 1-dodecanol completely failed for extraction of compounds with Log K_ow ≤ 1 (sulfa drugs), other more polar extraction solvents (ionic liquids) should be explored for highly hydrophilic pollutants.     

Some physicochemical studies on organic eutectics

The phase diagrams of phenothiazine with each of m-nitrobenzoic acid (m-NBA) and m-dinitrobenzene (m-DNB) have been studied by thaw-melt method. These materials have been characterized by X-ray diffraction. Growth behavior of the parent components, eutectic and charge transfer complex (CTC) studied by measuring the rate of movement of the growth front in a capillary suggests the applicability of Hillig–Turnbull equation for the system. Microstructure and electrical conductivities of congruent melting complexes and eutectics have been determined. The low electrical conductivities of these materials have been due to weak interaction and mixed stacking of donor and acceptor. Excess thermodynamics functions of the charge-transfer (CT) materials and eutectics have been determined.     

Lattice Boltzmann model for thermal free surface flows with liquid-solid phase transition

Purpose

The main objective of this work is to develop an algorithm to use the Lattice Boltzmann method for solving free surface thermal flow problems with solid/liquid phase changes.

Approach

A multi-distribution function model is applied to simulate hydrodynamic flow and the coupled thermal diffusion-convection problem.

Findings

The free surface problem, i.e. the reconstruction of the missing distribution functions at the interface, can be solved by applying a physical transparent momentum and heat flux based methodology. The developed method is subsequently applied to some test cases in order to assess its computational potentials.

Practical implications

Many industrial processes involve problems where non-isothermal motion and simultaneous solidification of fluids with free surface is important. Examples are all castings processes and especially foaming processes which are characterized by a huge and strongly changing surface.

Value

A reconstruction algorithm to treat a thermal hydrodynamic problem with free surfaces is presented which is physically transparent and easy to implement.     

One-dimensional solidification of pure materials with a time periodically oscillating temperature boundary condition

A finite difference method is used to solve a one-dimensional solidification problem with a periodic boundary condition prescribed at the bottom of the mold of finite thickness. The temperature distributions in the solidified shell and mold, the position of the moving freezing front, and its velocity are evaluated. Analytical results are obtained for the limiting cases and then compared with the numerical predictions to establish the validity of the model and the numerical approach. Interactive effects of the process parameters such as Stefan number of the solidified shell material, the mold thickness, the thermal conductivity and thermal diffusivity between the shell and mold materials on the evolution of the freezing front and its velocity are investigated in detail. The results show that the solidified materials with larger Stefan number grow slower than those with relatively smaller Stefan number. The impact of oscillating mold temperature boundary on the growth of shell thickness is particularly significant at earlier stages of the process and more pronounced for smaller Stefan numbers. Increasing mold thickness or thermal conductivity ratio between the shell and mold materials slows down the evolution of the shell thickness.     

Morphology of cells at the grain boundaries of an anisotropic material

We have studied the formation of ridges on the grain boundaries of an anisotropic crystal known as pivalic acid. These results are compared with very well studied another isotropic material succinonitrile to understand the formation of defects in anisotropic crystals. Preliminary results show that along with anisotropy, orientation has a large influence on the morphology of solid-liquid interface formed after planar interface becomes unstable. The formation of ridges and hence the defects at the interfaces are more favoured in highly anisotropic materials.