Activation of non-metallic substrates for metal deposition using organic solutions

Non-metallic substrates, such as plastics or oxides, need to be activated before electroless metal deposition. In this paper, a novel process of using metal Pd and Pd-Cu ion loaded organic solutions for surface activation of non-metallic substrates is described. The organic media used are strong polarizing and low ionic conducting solutions of the type commonly used in the solvent extraction industry. Different types of non-metallic substrates, including polyester, alumina and carbon nanotubes, have been evaluated, and it was shown that a uniform and complete Cu coating can be electrolessly deposited after activation in metal ion loaded organic solutions.     

Performance evaluation of laser surface alloyed hard nanostructured Al2O3-TiB2-TiN composite coatings with in-situ and ex-situ reinforcements

Hard and wear resistant Al₂O₃-TiB₂-TiN composite coatings have been developed on low carbon steel (AISI 1025) substrate by following two different routes involving laser surface treatment. In the first (termed ‘in-situ’ process), reinforcing phases TiB₂ and TiN, as well as the matrix Al₂O₃ of the composite are synthesized in-situ by laser-triggered self-propagating high temperature synthesis (SHS) from a mixture of Al, TiO₂ and h-BN and coated onto the substrate surface by laser surface alloying (LSA). In the second (termed ‘ex-situ’ process), the constituents Al₂O₃, TiB₂ and TiN of the coating are provided directly as a pre-placed precursor powder mix and laser surface alloyed onto the substrate. Of these two laser assisted manufacturing procedures, it is of interest to determine the one that is more appropriate for the development of a hard, wear resistant coating. In the present work, investigation of the comparative merits and demerits of Al₂O₃-TiB₂-TiN coatings produced by in-situ and ex-situ processes is attempted through analysis of microstructure and evaluation of mechanical and tribological properties.     

Bioleaching of pyrite by A. ferrooxidans and L. ferriphilum

Pyrite oxidation rates were examined under various conditions in the presence of A. ferrooxidans and L. ferriphilum, in which different pulp concentration, inoculation amount, external addition of Fe^3＋ and initial pH value were performed. It is found that A. ferrooxidans and L. ferriphilum show similar behaviors in the bioleaching process. The increasing pulp concentration decreases the leaching rate of iron, and external addition of high concentration Fe^3＋ is also adverse to leaching pyrite. The increased inoculation amount and high initial pH value are beneficial to leaching pyrite, and these changed conditions bring more obvious effects on leaching pyrite by L. ferriphilum than by A. ferrooxidans. The results also show that adjusting the pH values in leaching process baffles leaching pyrite due to the formed jarosite. Jarosite formed in leaching process was observed using XRD, SEM and energy spectrum analysis, and a considerable amount of debris with a crystalline morphology is present on the surface of pyrite. The results imply that the indirect action is more important for bioleaching pyrite.     

A survey of bio-corrosion rates of magnesium alloys

The dissolution rates of a number of experimental magnesium (Mg) alloys in simulated body fluid are surveyed in this work. Degradation conditions approximating the human physiological environment were examined using Minimum Essential Medium (MEM) and exposure in a CO₂ incubator at 37 °C. The results herein provide a timely baseline for the assessment of the role of alloying elements in dictating dissolution rates of Mg alloys in vitro, together with some important considerations in the assessment of Mg alloys as possible candidates for biomedical implants with customisable dissolution rates.     

激光金属沉积Ti-Zr-Ta合金的制备及其冲击释能特性研究

难熔金属型含能结构材料（ESMs）具有良好的力学性能和优异的冲击释能特性,但由于组元熔点高,利用传统的熔炼铸造法难以制备出大尺寸无缺陷铸件。本研究利用等离子旋转电极雾化制粉技术制备出Ti-Zr-Ta难熔合金粉末,结合激光金属沉积（LMD）技术制备了Ti-Zr-Ta难熔金属型ESMs,并对其组织结构、力学性能和冲击释能特性进行研究。结果表明,利用LMD技术可实现Ti-Zr-Ta难熔金属型ESMs的致密化成型,合金致密度达到98.75%,具有良好的力学性能,其准静态抗拉强度达到1202MPa。弹道枪试验结果表明,在1202m/s的冲击速度下,激光金属沉积Ti-Zr-Ta合金在27 L密闭靶箱内可产生0.144 MPa的准静态压力,释能特性优良。     

Corrosion characterisation of alumina-magnesium metal matrix composites

Alumina magnesium metal matrix composites are a precious alternative for aerospace and automotive applications because of their high stiffness-to-weight ratio. A considerable deal of investigations had been devoted to their processing and mechanical properties, while the corrosion behaviour is still uncertain. In this study, the corrosion behaviour of Al₂O₃ fibres strengthened magnesium AS41 composite, in aqueous solutions containing various concentrations of NaCl at different pH values, was studied and compared with the behaviour of pure AS41 magnesium matrix alloy using electrochemical techniques, hydrogen evolution test, optical microscopy, and scanning electron microscopy (SEM) coupled with EDX and WDX capabilities. The results showed that the corrosion behaviour of the composite was comparable to its pure matrix alloy, yet a reduction in the corrosion resistance was observed in the composite at higher chloride concentrations. The corrosion mechanism involved, as well as the corrosion characteristics, was extensively discussed in terms of the effect of Al₂O₃ fibres. Also, an appropriate model describing the corrosion mechanism was proposed.     

Microstructure and wear performance of gradient Ti/TiN metal matrix composite coating synthesized using a gas nitriding technology

Surface modification is an attractive method to enhance the surface hardness and wear resistance of titanium. In this paper, a continuous wave 2 kW Nd:YAG laser was used to synthesize Ti/TiN metal matrix composite coating on the surface of commercial pure titanium. The microstructure and the wear resistance of the synthesized metal matrix composite coating were investigated. The synthesized surface Ti/TiN metal matrix composite coating had a pronounced gradient microstructure through the melt depth. Good metallurgical bonding between the reinforcing phase of the metal matrix composite and the titanium matrix was observed. The hardness and wear resistance under block-on-ring dry sliding wear testing conditions of the synthesized Ti/TiN metal matrix composite coating were markedly enhanced.     

Inhibition of aluminum corrosion using Opuntia extract

The inhibitive action of the mucilage extracted from the modified stems of prickly pears, toward acid corrosion of aluminum, is tested using weight loss, thermometry, hydrogen evolution and polarization techniques. It was found that the extract acts as a good corrosion inhibitor for aluminum corrosion in 2.0 M HCl solution. The inhibition action of the extract was discussed in view of Langmuir adsorption isotherm. It was found that the adsorption of the extract on aluminum surface is a spontaneous process. The inhibition efficiency (IE) increases as the extract concentration is increased. The effect of temperature on the IE was studied. It was found that the presence of extract increases the activation energy of the corrosion reaction. Moreover, the thermodynamic parameters of the adsorption process were calculated. It was found also that the Opuntia extract provides a good protection to aluminum against pitting corrosion in chloride ion containing solutions.