Mahtab Assadian

Corrosion resistance of EPD nanohydroxyapatite coated 316L stainless steel

Abstract The effect of nanohydroxyapatite (HA) coating on corrosion resistance of 316L stainless steel was investigated. The stainless steel samples were pretreated in different volume concentrations of H2SO4 solution and were electrophoretically coated for various coating time spans and voltages. The coated samples were sintered in a vacuum furnace at different temperatures to modify the coating structure. The quality and morphology of the pretreated samples and the coating were microscopically characterised, and the compounds presented in the coatings were determined. The electrochemical corrosion test was performed in simulated body fluid to evaluate the coating impact on corrosion behaviour of the samples. The results showed that the deposition of nano-HA using moderate voltage and appropriate time span provides a smooth and almost cracked free coating, improving the corrosion resistance of the samples. Increasing the temperature of sintering modified the HA structure, resulting in the formation of denser coating and enhanced corrosion resistance of the samples.

Effect of solution treatment on corrosion characteristics of biodegradable Mg–6Zn alloy

A binary Mg–6Zn biodegradable alloy was solution treated to evaluate the effects of resulting microstructure changes on the alloys degradation rate and mechanisms in-vitro. The treatment was conducted at 350 °C for 6–48 h. Optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were used to analyze the as-cast and treated samples. Immersion and electrochemical tests were performed in simulated body fluid at 37 °C to assess the samples corrosion resistance. To confirm the results of the corrosion tests, pH measurement was carried out. It is found that over 24 h solution treatment dissolves intermetallic phases in matrix and produces an almost single phase microstructure. Decreasing the intermetallic phases results in lower cathode/anode region ratios and lowers corrosion rates. The results of the electrochemical and mass loss tests reveal that extended solution treatment improves the corrosion resistance of the alloy. The results also show that solution at 350 °C for 24 h enhances the corrosion resistance of the as-cast alloy more than 60%. In addition, decreasing intermetallic phases in the microstructure accompanied a lower pH rise reduced corrosion rate. Solution treatment is suggested as a corrosion improving process for the application of Mg–Zn alloys as biodegradable implant materials.

Hydroxyapatite and Fluoridated Hydroxyapatite Coatings and Their Effects on Commercially Pure Magnesium Corrosion Response

Dicalcium-phosphate dehydrate, converted to hydroxyapatite by post-treatment in sodium hydroxide, and fluoridated hydroxyapatite were electrodeposited on commercially pure magnesium substrates that were pretreated with sodium hydroxide. The coatings’ crystalline structure, thickness, scratch hardness, morphology and chemical composition were characterised by GIXRD, microscratch testing platform, SEM and EDS. The results showed that the apatite coatings had highly crystalline structure, acceptable scratch hardness, flake-like morphology and acceptable chemical composition. Corrosion behaviour of the uncoated and coated substrates was investigated by potentiodynamic polarization and immersion tests in simulated body fluid. The coated substrates, especially fluoridated hydroxyapatite coated substrates, showed significantly lower corrosion rates compared to uncoated substrates. The polarisation curves showed that the coatings hindered anodic reactions; the corrosion potentials were shifted toward less-negative. In general, this study concluded that the corrosion rate of commercially pure magnesium could be significantly decreased to be a candidate for future cost-effective biodegradable orthopaedic implants.

Green synthesis of silver nanoneedles using shallot and apricot tree gum

Abstract A green synthesis method to produce silver nanoneedles was described using shallot and apricot tree gum (ATG). A fast, simple, and low cost method was used to synthesize silver with nanoparticle and nanoneedle shape from the silver nitrate solution. Shallot as a reducing agent and apricot tree gum (ATG) as a stabilizer and a capping agent were utilized to reduce and form silver ions into silver atoms with needle and particle shape. Moreover, high crystalline structures of silver nanoparticles (AgNPs) with diameters of 8–20 nm and silver nanoneedles with average diameters of 50–60 nm and lengths of 5–10 μm were consequently synthesized by shallot and the mixture of shallot and ATG. A self-assembly mechanism was proposed to indicate the formation of needle-like structures of spherical AgNPs via carbon chains of ATG. The results indicate that the presence of ATG with shallot can transfer the reduced AgNPs into the silver nanoneedle. The findings were characterized using X-ray diffraction (XRD), ultra violet visible (UV-Vis) spectrometry, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) techniques.

Topography, wetting, and corrosion responses of electrodeposited hydroxyapatite and fluoridated hydroxyapatite on magnesium

In this study, different types of calcium-phosphate phases were coated on NaOH pre-treated pure magnesium. The coating was applied by electrodeposition method in order to provide higher corrosion resistance and improve biocompatibility for magnesium. Thickness, surface morphology and topography of the coatings were analyzed using optical, scanning electron and atomic-force microscopies, respectively. Composition and chemical bonding, crystalline structures and wettability of the coatings were characterized using energy-dispersive and attenuated total reflectance-Fourier transform infrared spectroscopies, grazing incidence X-ray diffraction and contact angle measurement, respectively. Degradation behavior of the coated specimens was also investigated by potentiodynamic polarization and immersion tests. The experiments proved the presence of a porous coating dominated by dicalcium-phosphate dehydrate on the specimens. It was also verified that the developed hydroxyapatite was crystallized by alkali post-treatment. Addition of supplemental fluoride to the coating electrolyte resulted in stable and highly crystallized structures of fluoridated hydroxyapatite. The coatings were found effective to improve biocompatibility combined with corrosion resistance of the specimens. Noticeably, the fluoride supplemented layer was efficient in lowering corrosion rate and increasing surface roughness of the specimens compared to hydroxyapatite and dicalcium-phosphate dehydrates layers.

Gold Recovery from WEEE by Chlorine System

This work compared the effect of nitric acid and chloride acid systems on dissolving precious metals of Electrical and Electronic Equipments (EEE). As a result of the revolution of informatics technology, the production of EEE is rapidly increasing in the world. Due to economic growth, technological innovation and market expansion of EEE there is a significant increase in waste of EEEs (WEEE) that presents a new environmental challenge.The results show that the best recovery of gold can be obtained via aqua regia (3HCl=HNO3), with concentration of 1/10 gr/L. The reaction temperature has little effect on the extent of extraction.

Effect of HF Concentration on Corrosion Resistance of Biomedical Implants

This work compared the variation of weight of Mg 1%Ca as cast in different concentrations of hydrofluoric acid (HF) such as 45% - 40% - 35% - 25% - 20 % - 13% - 7 % for 24 h at room temperature to be utilized in biomaterial application like hip, knee implants that have effect on corrosion resistance. By immersion Mg 1%Ca alloys in HF, the layer of MgF2 was constituted on the surface of alloy and this layer improves the corrosion and causes weight gain. The results show that in order to get a better corrosion resistance, surface treatment should be done in 40% of HF, because the weight gain is more than other HF concentrations.