The influence of disorder on magnetocaloric effect and the order of transition in ferromagnetic manganite (La1−x Nd x )2/3(Ca1−y Sr y )1/3MnO3

Magnetocaloric effect and order of transition in (La_1?x Nd _x )_2/3(Ca_1?y Sr _y )_1/3MnO₃, prepared by conventional solid-state reaction, have been investigated. Using Banerjee criterion, we demonstrate first-order transition for (J1) and (J2 ) as well as second-order transition for (J3 ), (J4 ), and (J5 ) samples. The ΔS _M ^max is ranging between 9.18 Jkg^?1 K^?1 and 4.87 when Nd and Sr content changes leading to relative cooling power (RCP) varying between 330 and 229.35 J/kg. Both ΔS _M ^max and the RCP are found sensitive to the disorder σ ². The universal behavior obtained from ΔS variation curves confirmed the first-order transition for (J1) and (J2 ) samples and second-order transition for (J3), (J4), and (J5 ) samples obtained by Banerjee criterion. All samples with second-order phase transition exhibit inhomogeneous character estimated from local exponent n.     

Kinetics of alkaline hydrolysis of p‐substituted benzylidenemalononitriles in 50% aqueous acetonitrile: substituent effects and quantification of the electrophilic reactivity

The rate constants of the reaction of p‐X‐substituted benzylidenemalononitriles 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h with hydroxide ion were measured in 50% water–50% acetonitrile at 20 °C. The experimental kinetic data reveal that the points pertaining to electron donating substituted compounds (X = Me, OMe and NMe₂) exhibit negative deviations from the Hammett plot. However, the Yukawa–Tsuno plot for the same rate constants resulted in a good straight line with an excellent correlation coefficient (r² = 0.9916) and an r value of 1.15. Possible ground‐state stabilization through resonance interactions has been suggested to explain the origin of the nonlinear Hammett plot. On the basis of the relationship between E and σ_p⁺, the electrophilicity parameter E of some benzylidenemalononitriles 1c and 1e , 1f , 1g , 1h has been evaluated. More importantly, the three compounds 1f (E = ?7.90), 1g (E = ?7.80) and 1h (E = ?7.55) exhibit high electrophilicities that compare well with that of 4,6‐dinitrobenzoselenadiazole (E = ?7.40), a compound which has a general behaviour representative for the superelectrophilic dimension. We have shown that the second‐order rate constants calculated from Mayr's approach for the reaction of 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h with hydroxide ion do not agree with the available experimental data. On the other hand, a good linear correlation between log k_exp and log k_calc has been observed and discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Critical behavior near the paramagnetic to ferromagnetic phase transition temperature in La0.7Pb0.05Na0.25MnO3

Critical behavior in La_0.7Pb_0.05Na_0.25MnO₃ has been investigated by dc magnetization measurements. Magnetic data indicate that the compound exhibits a continuous (second-order) paramagnetic (PM) to ferromagnetic (FM) phase transition. Estimates of critical exponents yield δ=4.80±0.01, γ=1.296±0.002 and β=0.344±0.007 (consistent with both the predictions for the three-dimensional-Heisenberg model and with those reported for materials when the FM transition is ascribed to the double exchange (DE) mechanism as a major origin) with T_C=334.54±0.08. The critical exponent γ is slightly inferior than predicted from the 3D Heisenberg model. Such a difference may be due, within the context of the quenched disorder, to the presence of some alterations of short-range magnetic order of FM clusters in the PM phase. The temperature variation in the effective exponent (γ_eff) is similar to those for disordered ferromagnets.     

Numerical Simulation of Drying of a Saturated Deformable Porous Media by the Lattice Boltzmann Method

A numerical study is reported here to investigate the drying of saturated deformable porous rectangular plate based on the Darcy–Brinkman extended model. All walls of the plate are maintained to a convective heat flux as well as the top and bottom faces are also subjected to a mass flux. The model for the energy transport is based on the local thermodynamic equilibrium between the fluid and the solid phases. The lattice Boltzmann method is used for solving the governing differential equations system. A comprehensive analysis of the influence of the Poisson’s coefficient, the Young’s modulus and the permeability on macroscopic fields is investigated throughout this work.     

Structural and magnetic characterisation of the perovskite oxides La0.7Ca0.3−x Na x MnO3

X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na⁺ ion substitution for Ca²⁺ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La_0.7Ca_0.3−x Na _x MnO₃ manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter σ ². The temperature dependence of magnetization of all samples obeys the Bloch T ^3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na⁺ ions causes a decrease in total exchange integral Aof the samples.      

Application of phenolic compounds as natural dye extracted from date-pits: dyeing studies of modified acrylic fibres

This research work involves the dyeing of acrylic fabric with natural dye extracted from date pits powders using Soxhlet extraction process. The effect of dye bath pH, salt concentration, dyeing time and temperature were studied. The optimal dyeing conditions where pH 4, 0 g/L salt, 60 min, and 80 °C. The COD and the BOD5 of the residual dye bath were measured and it was shown from the registered values that the residual dye bath presents an acceptable rate of organic discharge.     

Estimation of the magnetic entropy change by means of Landau theory and phenomenological model in La0.6Ca0.2 Sr0.2MnO3/Sb2O3 ceramic composites

In this paper, magnetocaloric properties of La_0.6Ca_0.2Sr_0.2MnO₃/Sb₂O₃ oxides have been investigated. The composite samples were prepared using the conventional solid-state reaction method. The second-order phase transition can be testified with the positive slope in Arrott plots. An excellent agreement has been found between the ?ΔS_M values estimated by Landau theory and those obtained using the classical Maxwell relation. The field dependence of the magnetic entropy change analysis shows a power law dependence,|ΔS_M|≈Hⁿ , with n(T_C) = 0.65. Moreover, the scaling analysis of magnetic entropy change exhibits that ΔS_M(T) curves collapse into a single universal curve, indicating that the observed paramagnetic to ferromagnetic phase transition is an authentic second-order phase transition. The maximum value of magnetic entropy change of composites is found to decrease slightly with the further increasing of Sb₂O₃ concentration. A phenomenological model was used to predict magnetocaloric properties of La_0.6Ca_0.2Sr_0.2MnO₃/Sb₂O₃ composites. The theoretical calculations are compared with the available experimental data.