Materials Science Forum Vol. 985

Abstract: Surface wettability is thought to influence the osteoconductivity of bone-substituting materials; however, the effects of surface wettability on osteoblast behavior are not well understood. In this study, we prepared both an as-polished pure titanium with a water contact angle (WCA) of 57° and heat-treated pure titanium with more hydrophobic surface and WCAs of 68°-98°. The effects of the surface wettability of pure titanium on osteoblast behaviors were evaluated by in vitro assays. Compared with the as-polished titanium, the proliferation rate of osteoblast increased on heat-treated titanium. This suggested that surface wettability affects osteoblast behaviors, meaning osteoconductivity is influenced by surface wettability.

Abstract: Surface morphology and composition of anodized Ti-15Zr-4Nb-4Ta alloys with nanotube were examined by using X-ray diffractometry and analytical scanning electron microscopy. The Ti alloy consisted of α and β phases. Anodizing to form nanotube on the Ti alloy was carried out using electrolyte of 0.2 wt.% NH₄F and 2 Vol.% H₂O in ethylene glycol under different potential at from 30 to 60V. SEM observation showed that nanotubes were vertically aligned on surface of the Ti alloy. Inner diameter of these nanotubes varied from 45 to 127 nm with increasing applied potential to the specimen from 30 to 60 V. Surface of the Ti alloy with nanotube was ragged due to the difference in dissolution rate of the internal structure of α and β phases.

Abstract: The possibilities of removing impurities in molten iron by oxidation and evaporation, which are usual methods in metal refining, are firstly investigated. Of all the elements which are dissolved in molten iron, Cu, Sn Ni, Co, Mo and W are found to be difficult to be removed by such usual methods as oxidation and evaporation. The elements which are difficult to be removed in steel making when they are once dissolved into molten iron are called “tramp elements”. In recycling ferrous scraps, to begin with, it is important to keep iron from being mixed with tramp elements. But, it is necessary to develop a method to remove tramp elements, because it is impossible to avoid the contamination of these elements completely. In this work, several prospective methods to remove such tramp elements are discussed. Copper, which is one of the most important tramp elements in iron, can be removed by evaporation or by sulfurization, although it is not enough to apply them in practical use. As other methods, in this work, the possibilities to remove copper in molten iron by oxidation and by the use of calcium are proposed. It is found that copper and tin in iron can be decreased at the content of 0.2 to 0.4mass% and under 0.001mass%, respectively by oxidation. If pure calcium is equilibrated with iron directly at 1823K, the high distribution ratios, L_Sn(mass) (=(mass%Sn)_{in Ca-Pb}/[mass%Sn]_{in Fe}) = 3400 and L_Cu(mass) (=(mass%Cu)_{in Ca-Pb}/[mass%Cu]_{in Fe}) = 200 are expected.

Abstract: The addition of oxygen or nitrogen in titanium alloys increases the hardness by the solid solution strengthening. Spinodal decomposition in titanium alloys is also the way to increase the hardness. This study aimed to reveal the effect of oxygen or nitrogen addition on spinodal decomposition in Ti-10at%V. Ti-10at%V-(0, 1, 3)at%O or N alloys were prepared by arc-melting. They were solution-treated at 1200 or 1300 °C for 0.6 ks and then quenched in iced brine. The solution treated specimens were aged at 375 °C. The increase of hardness was decreased by the oxygen or nitrogen addition in the alloys. The addition of nitrogen more suppressed the age-hardening than the case of oxygen addition. The modulated structure caused by spinodal decomposition in the laths was observed in all the aged specimens. The wavelength of spinodal decomposition of the aged specimens increased with the addition of oxygen or nitrogen, leading to a decrease in age-hardening by spinodal decomposition.

Abstract: The surface wettability of biomaterials influences on osteoblast behavior and bone formation. In this research, the variation of wettability of nacre by heat treatments was examined. Plates of the nacre were fabricated from shells of the Akoya pearl oyster. The specimens were heated at 100, 200, 300, 400, 500, and 600 °C. Characterizations of the specimens during and after heat treatments were carried out using scanning electron microscopy, X-ray diffractometry, and thermogravimetry-differential thermal analysis. The water contact angle (WCA) of the specimen was measured to evaluate wettability. The color of nacre changed from iridescent color to brownish weak-iridescence by the heating at and over 300 °C. The nacre heated at and over 300 °C became brittle because organic substances in nacre, which acts as the glue between the aragonite platelets were evaporated by the heating. The WCA of the specimen was decreased with increasing heating temperature, which should be related to the decrease in the number of organic substances in nacre by the heating.

Abstract: Inconel 625 is a nickel superalloy, characterized by high fatigue strength. The alloy is resistant to a wide range of corrosive environments, including high-temperature oxidation. For this reason, it is an attractive material for the chemical, shipbuilding and aviation industries. Inconel 625 alloy is designed for plastic working. However, the significant difficulty is the appropriate process design, due to the high deformation resistance. In order to improve the plastic properties of the alloy, processing at elevated temperatures is practiced. In this work, attempts were made to implement rotary forming process of Inconel 625 superalloy. For this purpose, an experiment was designed, investigating the impact of three variables on the process – feed rate, spinning rate and heating. For the tests were used Inconel 625 metal plates in the shape of discs. Axial-symmetrical products were formed, using a spinning machine. The geometry of the products according to selected quality factors was investigated. Optimal process parameters were chosen using multivariate statistical optimization. These parameters will be used to set up processes to obtain product that meets quality requirements.

Abstract: This study aims to investigate the effect of processing routes (A and Bc) and temperature on microstructure, texture and mechanical properties of pure magnesium was studied in this research. An extruded pure magnesium (~99,9 %) was subjected to severe plastic deformation (SPD) by ECAP. Deformation was conducted at 523K and 473K and two different processing routes (A and Bc) were used to control the texture. The microstructure and texture characterization of the pressed materials were carried out. It was found that the microstructure displayed a bimodal grain structure after two passes and then became homogeneous after four passes following both routes A and Bc. The misorientation distribution was examined and the results revealed that the fraction of high angle grain boundaries (HAGB) was higher at temperature 473K. The texture was randomized following route Bc whereas it became strengthened in route A after four passes. According to the Hall-Petch (HP) relationship, the yield stress of polycrystalline metals increases with a decrease in grain size. In this study, a positive slope k was achieved in the strengthened texture while a negative one was obtained in the softened texture. The ductility of ECAP processed material was considerably improved (from 23% to 38%) without sacrificing the yield stress by route Bc at 423K.

Abstract: The Al₆₅Cu₂₀Fe₁₅ (in at.%) rapidly solidified ribbon in the form of brittle flakes was produced by melt-spinning technique. It consists the cell or dendrites of the icosahedral quasicrystalline I-phase surrounded by copper rich cubic τ-Al(Cu, Fe). The pulverized ribbon (fraction <32 μm) was subjected to NaBH₄ or 20% aqueous NaOH treatment, which led to the formation of oxide in the form of thin flakes at the outer layer of the powder particles. Test of the catalytic properties of the as spun ribbon and powder before and after treatment was made in the reaction of phenylacetylene hydrogenation. It was shown that for as received ribbon, even at very mild conditions (60 °C, H₂ pressure of 5 bar), 40% of phenylacetylene was converted to hydrogenation products with 0.7 styrene/ethylbenzene ratio. The use of pulverized ribbon resulted in improvement of activity, with the same ratio of reaction products. The effect of treatment with NaBH₄ led to improvement of the catalyst activity, while strongly alkaline solution of NaOH worsened significantly the catalytic activity, but improved selectivity to styrene (styrene/ethylbenzene=1.2).

Abstract: Becher process was applied for upgrading Ha Tinh ilmenite concentrate (54-55% TiO₂) to synthetic rutile. The process includes reduction of ilmenite concentrate using anthracite coal as reductant, followed by aeration of reduced ilmenite in ammonium chloride solution (NH₄Cl). The controlled parameters were temperature and NH₄Cl concentration. The results showed that the degree of iron metallization was 83% after 4 hours of reduction at 1150 °C. Most of the metallic iron (98%) was successfully rust after 9 hours of aeration at 70°C, 7/1 of liquid/solid ratio (L/R), 4 liter/minutes (L/min) of air flow rate and 0.5% of NH₄Cl concentration. The addition of acetic acid or citric acid in to the aeration solution has facilitated the aeration process. The aeration time could be vastly reduced when ammonium chloride solution used in aeration was replaced by the mixture of CH₃COOH 0.075M and CH₃COONa. Leaching with H₂SO₄ 15% has improved TiO₂ content from 82% in the aerated ilmenite to approximately 89% in synthetic rutile. The research work has proved that Becher process is applicable for the beneficiation of Ha Tinh ilmenite concentrate.

Abstract: In nature, kaolin clay is referred to a readily available cheap source of silicon and used in various fields such as the paper, ceramic, paint, plastic, rubber, and cracking catalyst industries. This paper introduces utilization of natural kaolin clay for a new application. In particular, the kaolin clay is used as a new raw material for synthesis of ordered mesoporous carbon (OMC) materials, which serve as electrode active materials for supercapacitors. Kaoline used in the present work is originated from Yen Bai province (Vietnam). After subjected several steps of the treatment process, silica present in the kaolin clay is converted to sodium silicate and used directly as a source of silicon for the synthesis process of mesoporous porous silica (SBA-15). The synthesized SBA-15 mesoporous silicas exhibit rod-like nanostructure with the specific area of 432.7 m2 g^-1 and the mean pore size of 7-8 nm. Subsequently, SBA-15 silica serves as hard template for preparation of OMCs by using nanocasting method. The OMCs carbonized at different temperatures in the absence and presence of boric acid reveal highly ordered mesoporous structure with the highest specific area of 1039.2 m2 g^-1 and the mean pore size ranging from 6 to 7 nm. As used as electrode active material in 6 M KOH aqueous solution, the resultant OMCs exhibit excellent capacitive performance with a specific capacitance higher than 80 F g^-1 at a scan rate of 5 mV s^-1. The obtained results show that, in addition to the high specific area, the electrical conductivity also plays an important role in enhancing energy storage ability of the OMC electrodes. At the same carbonization temperature, the high surface area plays crucial role. However, at the higher carbonization temperatures, effect of the electrical conductivity of the materials prevails over the high surface area. This study illustrates highly application feasibility of Vietnam natural kaolin clay as available and cheap raw material source for synthesis of electrode active materials with the high supercapacitive performance for electrochemical double layer capacitors.