Synthesis,Corrosion and Bioactivity Evaluation of Gelatin/Silicon and Magnesium Co-Doped Fluorapatite Nanocomposite Coating Applied on AZ31 Mg Alloy

In this study, a nano-composite composed of gelatin as the matrix and Si-Mg-FA nano-particles as an additive was deposited on the AZ31 Mg alloy via dip coating method. In addition, a coating composed of MgO, MgSiO₃ and Mg₂SiO₄ phases was applied on the AZ31 Mg alloy by anodizing process. It was found that the Nano-composite coating with a uniform distribution of nano-particles within the gelatin matrix with the thickness of about 9 µm was dense, crack-free and uniform whereas the surface of anodized layer was relatively coarse due to the presence of flaws and micro-cracks. The surface morphology, EDS analysis and FTIR results revealed the ability of nano-composite coated specimen to form the bone-like apatite. Due to the presence of aforementioned phases and special surface features, the anodized specimen possessed higher and lower corrosion resistance than uncoated and nano-composite coated specimens, respectively. The passive coating resistances (R_CT) of nano-composite, anodized specimen and uncoated samples were 2164, 1449 and 1024 Ω cm², respectively.     

Microstructural Evolution During the Hot Deformation of Ti-55Ni (at. pct) Intermetallic Alloy

The hot deformation behavior of Ti-55Ni (at. pct) alloy was studied using compression testing at 1173 K (900 °C) to 1323 K (1050 °C) and at the strain rates of 0.001 to 0.35 s⁻¹. The microstructure evolution was characterized using optical and scanning electron microscopy (SEM). The influences of hot-working parameters on the flow stress and microstructural features of this alloy were then analyzed. The results indicate that, depending on the temperature and strain rate, the dynamic recrystallization (DRX) is the dominate mechanism. Besides, the particle-stimulated nucleation (PSN) mechanism could partially recrystallize the structure. The PSN phenomenon is of significant importance for the Ti-55Ni (at. pct) that suffers from insufficient workability because of its high content of intermetallic phases. It is of interest that the discontinuous yielding phenomenon has been observed when the specimens were deformed at 1173 K (900 °C). Finally, the optimum parameters for hot working of Ti-55Ni (at. pct) alloy are determined as well.     

Synthesis and Structural Characterization of New Lead(II) Discrete and Infinite Cage-Like Framework: A Precursor to Produce Pure Phase Nano-Sized Lead(II) Oxide

A novel Pb(II) complex, {[Pb₂(tpmba)₂(NO₃)₄]·MeOH} _n (1), was obtained by the reaction of a tripodal ligand, N,N′,N″-tris(pyrid-3-ylmethyl)-1,3,5-benzenetricarboxamide (tpmba), with Pb(NO₃)₂. The structure of complex was determined by X-ray crystallography. The results of structural analysis of the complex reveal that 1 is a M₂L₂ cage-like with a methanol molecule beside the cage. An entirely different structure and topology between 1 and similar complexes indicate that the nature of organic ligands affects the structure of assemblies. The results indicate that the framework of this complex is predominated by the nature of the organic ligand, anions, solvent and geometric need of the metal ions. It was found that the coordination number of Pb^II ions is eight, (PbN₃O₅) has a stereo-chemically active electron lone pair and the coordination sphere is hemi-directed. PbO nanoparticles are obtained by thermolysis of 1 at 180 °C with oleic acid as a surfactant. Scanning electron microscopy shows that the size of the PbO particles is ~30 nm.     

Green bio-synthesis of Ni/montmorillonite nanocomposite using extract of Allium jesdianum as the nano-catalyst for electrocatalytic oxidation of methanol

In this work, synthesis of Ni nanoparticles was carried out successfully by water extract of Allium jesdianum as a biochemical reducing agent in the presence of montmorillonite clay (MMT) as a natural solid support for the first time. Then the electrochemical activity of the synthesized nanocomposite was investigated in methanol electrocatalytic oxidation. MMT with high cation exchange capacity and nano layer structure was exposed to ion exchange conditions in nickel solution. Then Ni²⁺ ion exchanged form was used in this process as a source of ions and also capping agent. Water extract of Allium jesdianum used as a reducing agent due to abundant availability of phenolic and flavonoid contents. The synthesized Ni/MMT nanocomposite was characterized using UV–Vis spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX). The surface of prepared modified electrode has been characterized using SEM to evaluate the morphology, showing uniform dispersion of Ni nanoparticles with mean diameter of 12 to 20 nm. The modified carbon paste electrode was then used in methanol electrocatalytic oxidation reaction. Methanol oxidation on the proposed modified electrode surface occurs at 0.6 V and 0.3 V in alkaline and acidic medium respectively. Also, the results showed the better performance of modified electrode toward methanol electrocatalytic oxidation in comparison with carbon paste electrode that is modified by ion exchanged MMT. Charge transfer coefficients and apparent charge transfer rate constant for the modified electrode in the absence of methanol in alkaline medium were respectively found as: α_a = 0.53, α_c = 0.37 and k_s = 1.6 × 10⁻¹ s⁻¹. Also, the average value of catalytic rate constant for the electrocatalytic oxidation of methanol by the prepared nano-catalyst was estimated to be about 0.9 L·mol^-1·s^-1 by chronoamperometry technique. The prepared electrode was also effective for electrocatalytic oxidation of ethanol and formaldehyde in alkaline medium.     

Analytical approximate solution of competitive facilitated transport of acid gases through liquid membranes

An analytical approximate solution for the competitive facilitation factor of components A and E across a liquid membrane is developed in the case of instantaneous reactions inside the liquid membranes. This analytical solution solves the dimensionless, nonlinear diffusion-reaction transport problem governing the competitive facilitated transport of two gaseous components through liquid membranes. Prediction of the facilitation factors has been obtained for the equilibrium chemical reaction regime, considering the unequal complexes diffusivities and cases of zero and nonzero permeate side solute concentrations. This mathematical solution leads to analytical expressions for the concentration profiles of the species across the liquid membrane. In comparison with the present numerical solution and also numerical calculations and experimental data from the open literature, the difference between the analytical predictions and those obtained from the numerical solution were found to be in well agreement.     

Development of porous nanocomposite membranes for gas separation by identifying the effective fabrication parameters with Plackett–Burman experimental design

In this research, Plackett–Burman experimental design was used as a screening method to investigate seven processing factors in the preparation of new polyethersulfone based porous nanocomposite membrane. Polymer concentration, nanoparticle type, nanoparticle concentration, solvent type, solution mixing time, evaporation time, and annealing temperature are variables that were evaluated to fabricate mixed matrix membranes using the evaporation phase inversion method for gas separation. According to obtained results, polymer concentration, nanoparticle concentration, solution mixing time, and evaporation time processing factors had significant effects on gas permeation. In addition, the nanoparticle type, nanoparticle concentration, and polymer concentration had substantial effects on membrane selectivity. From analysis of variance, it was found that the model used for membrane gas permeability and membrane selectivity as response values were more reliable within spaced levels. Scanning electron microscope, gas permeation experiments and statistical analysis showed that polymer concentration, nanoparticle type, nanoparticle loading and evaporation time significantly affected the final membrane morphologies and performances. According to this study, trade-off limitation between gas permeability and membrane selectivity could be eliminated by identifying the effective fabrication parameters.     

Removal of methylene blue dye from aqueous solutions by a new chitosan/zeolite composite from shrimp waste: Kinetic and equilibrium study

The adsorption of methylene blue dye (MBD) from aqueous solutions was investigated using a new composite made up of shrimp waste chitosan and zeolite as adsorbent. Response surface methodology (RSM) was used to optimize the effects of process variables, such as contact time, pH, adsorbent dose and initial MBD concentration on dye removal. The results showed that optimum conditions for removal of MBD were adsorbent dose of 2.5 g/L and pH of 9.0, and initial MBD concentration of 43.75 mg/L and contact time of 138.65 min. The initial concentration of dye had the greatest influence on MBD adsorption among other variables. The experimental data were well fitted by the pseudo-second order kinetic model, while the Freundlich isotherm model indicated a good ability for describing equilibrium data. According to this isotherm model, maximum adsorption capacity of the composite was 24.5 mg/g. Desorption studies showed that the desorption process is favored at low pH under acidic conditions.     

Microstructure and mechanical properties of dual phase steels,with different martensite morphology,produced during TLP bonding of a low C-Mn steel

In this research, production of ferrite - martensite dual phase Steels with different martensite morphology was considered during transient liquid phase bonding of a low carbon steel. The steel was bonded using an iron base interlayer with melting point of 1443 K and 40 μm thickness. Bonding process carried out at 1473 K, under pressure of 0.5 MPa, at different holding time of 10, 20, 30 and 40 minutes. Microstructural studies of joint region showed that isothermal solidification completed at the bonding time of 40 minutes. Microstructure of joints made at the bonding time of 10, 20, and 30 minutes consists of two distinct region, athermal and isothermal solidified zones. Microstructure of these zones was studied and chemical composition of these zones was determined by EDS. Joints made with bonding time of 40 minutes were homogenized at 1008 K and then cooled into cold water to produce dual phase ferrite and martensite microstructure with different martensite morphology. According to shear test results, it was found that the shear strength of ferrite - fibrous martensite microstructure is greater than those with ferrite - continuous martensite and ferrite - blocky martensite microstructure.     

Electrochemically synthesized polypyrrole/MWCNTs-Al2O3 ternary nanocomposites supported Pt nanoparticles toward methanol oxidation

As known, a good support enhances the activity and durability of any catalyst. In the current study, polypyrrole (PPY)/nanocomposite (MWCNTs and Al₂O₃) films were fabricated by electrochemical polymerization of pyrrole solution with a certain amount of nanoparticles on titanium substrates and were used as new support materials for Pt catalyst. The modified electrodes were characterized by Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) techniques. High catalytic activity and long-time stability toward methanol oxidation of Pt/PPY–MWNTs-αAl₂O₃ catalyst have also been verified by cyclic voltammetry results and chronoamperometric response measurements. This catalyst exhibits a vehemently high current density (345.03 mA cm^?2) and low peak potential (0.74 v) for methanol oxidation. Other electrochemical measurements (electrochemical impedance spectroscopy (EIS), CO stripping voltammetry and Tafel test) clearly confirmed that Pt/PPY–MWNTs-αAl₂O₃/Ti electrode has a better performance toward methanol oxidation compared to the other electrodes and that can be used as a promising electrode material for application in direct methanol fuel cells (DMFCs).