OPTIMIZATION OF LEACHING OF COPPER FROM OXIDIZED COPPER ORE IN NH3-(NH4)2SO4 MEDIUM

Studies were carried out for selective leaching of Cu with simultaneous avoidance of iron dissolution during leaching of oxidized copper ore in an aqueous NH₃-(NH₄)₂SO₄ system. The effects of leaching parameters, such as ammonia concentration, ammonium sulphate concentration, leaching time, and solid-to-liquid ratio, were investigated on leaching of copper. A 2ⁿ factorial experimental design method in the dissolution experiments was used. In addition, the “Steepest Ascent” method was also applied to determine the optimum leaching conditions. It was observed that the most effective parameters on the leaching of copper were ammonia concentration and leaching time. Only 0.17% of iron in ore was dissolved in ammonia and ammonium sulphate medium. The optimum conditions established for maximum copper recovery were: ammonia concentration 2.824 mol L^?1, ammonium sulphate concentration 0.236 mol L^?1, solid-to-liquid ratio 0.167 g mL^?1, leaching time 2 h. Fixed parameters chosen in the experiments were: room temperature, average particle size 2.8 mm, stirring speed 500 rpm. Under the optimum conditions established for maximum copper recovery, the percentage of leached copper was 98.87.     

Effect of post-restoration on stresses in premolars with endodontic–periodontal lesion: an FEA study

Aim: This finite elemental stress analysis (FEA) study was aimed to test the effect of fiber and metal posts on stress distribution in premolar teeth with endodontic–periodontal (EP) lesion. Methodology: Three FEA models representing different EP lesions (primary endodontic disease (PED), PED with periodontal involvement and true-combined) were created. Tooth-model without EP lesion was used as control. The root-canals were assumed as root-filled, restored using glass-fiber or metal posts, resin composite build-up, and ceramic crown. A 300 N load was applied from the palatal surface of the crown with a 135° angle. The SolidWorks/Cosmosworks structural analysis program was used for FEA analysis. Results were presented by considering von Mises criteria. Results: Maximum stress values for PED, PED with periodontal-involvement and true-combined lesions were 2.26, 1.25, 0.74 MPa for glass-fiber post; 2.08, 1.51, 1.18 MPa for metal post, respectively. If there is PED, fiber-post gave an advantage to the tooth at core structure and coronal third of the root. Metal post kept the stress inside its body however caused small, high stress concentrated areas at cervical. When there is PED with periodontal-involvement, metal post forwarded less stress toward the apical while fiber-post saved the coronal structure. In true-combined lesion model, metal post kept the stresses within its body and forwarded less stress toward the remaining root structure and periodontium. Conclusion: EP lesions have an effect on stress distribution therefore the post material selection should be done based on the severity of the lesion. Metal posts might be preferrable since it forwards less stress toward the surrounding periodontal tissues during wound healing.     

RAFT-mediated synthesis of poly(N-(2-hydroxypropyl)methacrylamide-b-4-vinylpyridine) by conventional and microwave heating

We report the synthesis of N-(2-hydroxypropyl)methacrylamide (HPMA) macroCTA and HPMA-b-4-Vinylpyridine block copolymers via reversible addition-fragmentation chain transfer (RAFT) reaction. Polymerization was carried out in dimethylformamide (DMF) at 70 °C using 4-Cyano-4(thiobenzoylthio) pentanoic acid as chain transfer agent and AIBN as an initiator. Control over molecular weight and composition was achieved by altering the CTA, monomer and initiator feed ratio. The controlled living character of the polymerization was verified with pseudo-first-order kinetic plots, a linear increase of the molecular weight with conversion, and low polydispersities (PDIs ≤ 1.2). Effect of microwave heating on the homo- and copolymer formation was investigated and the rates were significantly higher than those observed under conventional heating conditions. These polymerization reactions were in controlled fashion resulting in polymers with low PDIs, too. These polymers have a great potential to be used in developing delivery vehicles and conjugates for further drug or gene delivery applications.     

Structural and spectroscopic properties of Nd:Y2Si2O7 phosphors

Phosphors of α-Y₂Si₂O₇ doped with Nd³⁺ ions were prepared using the sol–gel technique. Nano-sized crystalline phosphor powders were obtained by annealing the dried gels at 960 °C. The crystallization properties of the phosphor powders were determined from their XRD patterns. The α-Y₂Si₂O₇ phase was the only phase observed in all compositions. As the amount of amorphous SiO₂ in the composition was increased, the crystalline sizes and the widths of the size distribution curves were found to decrease from 17.8 nm to 10.6 nm and from 15.6 nm to 12.2 nm, respectively. The spectroscopic properties of the powders were studied by measuring the luminescence and the decay patterns of the ⁴F_3/2→ ⁴I_9/2 and ⁴F_3/2→ ⁴I_11/2 transitions between 50 K and 310 K. No appreciable effect of the crystallite sizes on the average lifetime of the ⁴F_3/2 level was observed at temperatures below 100 K. The effect of temperature, however, becomes relevant above 100 K as the size of α-Y₂Si₂O₇ nano-crystal becomes smaller.     

Micro-Capacitor Behavior of Poly(3-Hexyl Thiophene)/Carbon Fiber/Electrolyte System and Equivalent Circuit Model

In this article, 3-Hexyl thiophene (3HTh) monomer was electrocoated on carbon fiber micro electrode (CFME) to study electrochemical impedance spectroscopic (EIS) analysis. Poly(3HTh)/CFME is characterized by Cyclic voltammetry (CV), Fourier transform infrared reflectance-attenuated total reflection spectroscopy (FTIR-ATR), Scanning electron microscopy-Energy Dispersive X-ray analysis (SEM-EDX), and electrochemical impedance spectroscopy (EIS). The effects of different monomer concentrations (0.5, 1.0 and 1.5 mM) on polymer were reported in 0.1 M tetraethyl ammonium tetrafluoroborate (TEABF₄)/acetonitrile (ACN) solution. The highest low frequency capacitance (C_LF = 1.394 mF cm^?2) was obtained for [3HTh]₀ = 0.5 mM. The equivalent circuit model of R(QR(CR)(RW))(CR) was examined for polymer/electrolyte system.     

Effect of Initial Baking and Storage Time on Pasting Properties and Aging of Par-Baked and Rebaked Rye Bread

Part-baked rye bread with and without Ca-propionate (0.2 g/100 flour) were baked for 10, 15, 20 minutes at 230°C and stored at refrigerator temperature (4°C) for 10, 20, 30 days then second-baked for 5, 10, 15 minutes at the same temperature to give an oven-fresh end product. The effect of antimicrobial additive (Ca-propionate), part-baking, storage in refrigerator and rebaking on quality parameters such as yield of volume and crumb softness, water activity and pasting properties of rye bread crumb was evaluated. Addition of Ca-propionate increased bump area, while yield of volume and softness values of rye bread crumb decreased. The increase in initial baking time caused a decrease in the pasting temperature, water activity, and softness value and an increase in the bump area and viscosity of the rebaked bread crumb. Bump area and pasting temperature of rebaked rye bread crumb increased with longer (intermediate storage) time, while viscosity, yield of volume, water activity, and softness values decreased. A strong negative correlation was observed between pasting temperature and other parameters, which are bump area, peak viscosity, holding end viscosity, cooling end viscosity, and softness value for rye bread that was rebaked after part-baked and storing at refrigerator temperature. The re-baking rye bread after part-baking for 10 and 15 minutes and storage for 7, 14, and 21 days at refrigerator temperature gave softer crumb than the control group.     

Effect of Baking Procedure and Storage on the Pasting Properties and Staling of Part-Baked and Rebaked White Pan Bread Crumb

In this investigation, the white pan breads were part-baked for 10, 15, 20 minutes at 230°C with and without calcium propionate (0.2%), were stored at room temperature (20°C) for 3, 5, 7 days wrapped with two polyethylene bags. After storage, baking time of part-baked breads was completed to the baking time of control breads (25 minutes). Breads were subjected to softness analysis and pasting properties of bread crumb were determined using the Brabender Amylograph. Addition of Ca-propionate decreased softness value of crumb of bread rebaked after part-baked, while the peak, holding end and cooling end viscosities increased. The increase in initial baking time resulted in a decrease in the pasting temperature and softness value and an increase in the bump area and viscosity of the rebaked bread crumb. Bump area, water activity, softness value and peak, holding end and cooling end viscosities of crumb of the rebaked bread after part-baking decreased with longer (intermediate storage) time. Peak viscosity and water activity significantly correlated with softness of bread crumb rebaked following part-baking and storage at room temperature. Rebaking bread for 10 and 15 minutes after storage of 3 and 7 days at room temperature resulted in softer crumb than the control group.     

甲基丙烯酸三丁基锡酯的辐射聚合

本文介绍了用~(60)Coγ辐射引发聚合合成纯度较高的聚甲基丙烯酸三丁基锡酯(PTBTM),并对它的辐射聚合反应动力学进行了研究。结果表明TBTM浓度与聚合反应速率R_P之间的关系为R_P=K_P[TBTM]~2;辐射剂量率I与反应速率之间的关系为R_P=K_PI~(0.66);辐射聚合反应的表观活化能E_n为3.12J/mol。本文还对聚合反应的机制进行了探讨。     

Mode II fracture testing method for highly orthotropic materials like wood

In this paper a mode II fracture testing method has been developed for wood from analytical, experimental and numerical investigations. Analytical results obtained by other researchers showed that the specimen geometry and loading type used for the proposed mode II testing method results in only mode II stress intensity and no mode I stress intensity at the crack tip. Experiments have been carried out to determine mode II fracture toughness K _IIC and fracture energy G _IIF from the test data collected from both spruce (pice abies) and poplar (populus nigra) specimens. It was found that there existed a very good relation between fracture toughness K_IIC and fracture energy G _IIF when the influence of orthotropic stiffness E _II ^* in mode II was taken into account. It verified that for this mode II testing method the formula of LEFM can be employed for calculating mode II fracture toughness even for highly orthotropic materials like wood. In the numerical studies for the tested spruce specimen, the crack propagation process, stress and strain fields in front of crack tips and the stress distributions along the ligament have been investigated in detail. It can be seen that the simulated crack propagating process along the ligament is a typical shear cracking pattern and the development of cracks along the ligament is due to shear stress concentrations at the crack tips of the specimen. It has been shown that this mode II fracture testing method is suitable for measuring mode II fracture toughness K _IIC for highly orthotropic materials like wood.