Volume 113, Issue 2

Magnesium and its alloys are excellent implant material candidates with their biodegradable structure and mechanical properties close to human bone. In order to provide the desired strength in implant applications, the corrosion resistance of the materials is expected to be high. In this study, to improve the corrosion resistance of AZ31 and AZ91 magnesium alloys, an electrostatic hydroxyapatite coating process was applied, and optimum conditions were determined. The samples were structurally characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy and stereo microscopy methods, and their corrosion behavior was determined by the weight loss method. As a result of the coating, the corrosion resistance of the samples increased up to 250 %.

Diverse wet adhesives were prepared from oleic acid (OA), polyvinyl pyrrolidone (PVP), and cis -1,4-polyisoprene (PI) at different ratios for attracting and trapping insects. The ratios of (PVP-PI)/OA were 1:2, 1:1 and 2:1 (g/g). The ratio between PVP and PI was 9 to 1 (g/g). The blends were irradiated with doses from 10 to 50 kGy. Adhesion properties, water sorption, Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy were conducted. The results show that the adhesion of all wet adhesives was augmented by increasing the irradiation dose up to 20 kGy. The best wet adhesive composition was 2:1, which contained a high concentration of oleic acid. The wet adhesives of (PVP-PI)/OA were tested to attract and trap flies and mosquitoes.

New lacunary Keggin type polyoxometalate salts (Ni 2.5 PMo 11 M (H 2 O)O 39 / M = Co, Fe, Cu, Zn), were synthesized using the inorganic condensation method. X-ray diffraction and infrared spectroscopy results showed that the Keggin structure of the salts was preserved. The thermal stability was checked by differential scanning calorimetry coupled with thermogravimetric analysis showing that the thermal resistance was significantly improved by the incorporation of the metals into polyoxometalates. Proton and molybdenum substitution respectively by nickel and cobalt, iron, copper and zinc metals induced a positive effect on the crystallographic configuration of the prepared salts allowing them a better thermal resistance (up to 580 °C). Cyclic voltammetry revealed an interesting electrochemical property of synthesized samples, especially for Ni 2.5 PMo 11 Zn(H 2 O)O 39 sample in which the presence of zinc greatly boosted the redox behavior.

This paper presents the results of a study of the effect of energy conditions (additional heating of the walls of the reaction chamber and subsequent action of an electron beam on the synthesized powder) of pulsed plasma-chemical synthesis on the morphology, average geometric size, phase and chemical composition of copper-containing silica-based nanocomposites. The nanocomposites were synthesized using a TEA-500 pulsed electron accelerator. It was the first time that copper-containing silica-based nanocomposites had been prepared using the pulsed plasma-chemical synthesis. The values of the band gap for the as-prepared nanocomposites were calculated. The nanocomposites were characterized by means of transmission electron microscopy and X-ray diffraction. The analysis revealed the changes in the morphology and phase composition of the nanocomposites upon energy conditions.

The superior physical and chemical properties of holmium hexaborides enable their use in high-tech industrial applications. It is vital to examine these structure types on the atomic scale to elucidate the details of their structure and improve their functional properties. For this reason, holmium hexaboride, cobalt–holmium hexaboride and magnesium oxide–holmium hexaboride crystal structures were investigated systematically employing ab initio material modeling, including the dispersion corrected density functional theory approach, using an interface to the PWscf code of Quantum Espresso and Vienna Ab initio Simulation Package software. The effects of cobalt (∼4 wt.%) and MgO (∼2.8 wt.%) doping on holmium hexaboride structures are discussed in terms of optical, magnetic, and electronic properties including the charge transform, scanning tunneling microscopy, density of states, and K-edge X-ray absorption spectra analyses. Scanning tunneling microscopy and K-edge X-ray absorption spectra analyses were conducted to enable correlation with future experiments. Results indicate that cobalt doping does not provide enough driving magnetic force to alter the magnetic properties of the HoB 6 . Furthermore, MgO addition leads to significant distortions in the structure of the HoB 6 . The properties of HoB 6 were affected adversely, especially due to the distorsion of the octahedral boron unit.

A group of orthogonal experiments were conducted to investigate the effects of alloying elements on the microstructure and mechanical properties of as-cast Cr12MoV cold-working die steel. The results indicate that the solidification structures are mainly composed of equiaxed grains with reticular eutectic carbides precipitated at grain boundaries. While Mo has little effect on grain size, the structures could be effectively refined by V and Ce, and Ce addition is beneficial for breaking up the grain boundary eutectic networks. The compressive yield strength and micro-hardness increase with increasing V content and decreasing Ce content. For Mo, the yield strength and micro-hardness reach their maximum values at 0.5 wt.% and 0.9 wt.% respectively. Overall, considering the grain size number, micro-hardness and yield strength, the optimal contents of Mo, V and Ce are given.

In this paper, the effect of variations in the traverse and rotational speeds of the welding tool on mechanical properties of friction stir welding of AA 5052 plates have been investigated. For this purpose, variations of microstructure, tensile properties and hardness of metals joined at rotational speeds of 500, 800 and 1000 rpm and traverse speeds of 41.5, 80 and 125 mm min −1 have been studied. The results showed that the average grain size of the welded joint reduced with increasing rotational and traverse speeds, because of more intensive dynamic recrystallization. Micro-hardness and ultimate tensile strength increased with increasing rotational speed. The effects of adding of SiC particles on the microstructure and mechanical properties at optimum rotational and traverse speeds were examined.

The influence of hot extrusion on the microstructure and mechanical properties of Al 2 O 3 /7075 aluminum matrix composites was investigated via optical microscopy, scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, transmission electron microscopy and tensile testing. The results indicate that the yield strength, tensile strength, and elongation of the as-extruded composites respectively reached 244.4 MPa, 360.3 MPa, 11.0 %, which increased by 20.24, 33.28 and 507.73 %, compared to those of the as-cast composites. The hot extrusion process grants the composites fine compactness and significantly improves the distribution of Al 2 O 3 particles in the composite. The eutectic phase at the grain boundaries was crushed into small fragments under shear force after hot deformation. Moreover, high dislocation density near the Al 2 O 3 particles and grain boundaries was observed in the extruded composite. The failure mode of the as-cast material was quasi-cleavage fracture, while the failure mode of the as-extruded material was primarily ductile fracture.

Highly-ordered Fe nanowires (NWs) were successfully electrodeposited in a laboratory made anodic aluminum oxide template with a diameter of 30 nm. The as prepared Fe NWs were used as a substrate to prepare core–shell Fe@Fe 3 O 4 NWs after annealing and hydrogen reduction at high temperature. The phase transformation of the oxide shell of electrodeposited Fe NWs took the form Fe 2 O 3 → α-Fe 2 O 3 → Fe 3 O 4 . Transmission electron microscopy images revealed that the surface of Fe@Fe x −1 O x NWs was smooth and orderly, and the oxide layer was dense and uniform. The magnetic analysis of Fe@Fe x −1 O x nanowires was carried out using a vibrating sample magnetometer. It was found that Fe@Fe 3 O 4 nanowires manifested the characteristics of super-paramagnetism in the direction perpendicular to the nanowires due to smaller coercive force, and they can be suitable material for future biomedical applications.