S. A. Salman

Preparation and Characterization of Hydroxyapatite Coating on AZ31 Mg Alloy for Implant Applications.

Magnesium alloys as biodegradable metal implants in orthopaedic research received a lot of interest in recent years. They have attractive biological properties including being essential to human metabolism, biocompatibility, and biodegradability. However, magnesium can corrode too rapidly in the high-chloride environment of the physiological system, loosing mechanical integrity before the tissue has sufficiently healed. Hydroxyapatite (HAp) coating was proposed to decrease the corrosion rate and improve the bioactivity of magnesium alloy. Apatite has been cathodically deposited on the surface of Mg alloy from solution that composed of 3 mM Ca(H2PO4)2 and 7 mM CaCl2 at various applied potentials. The growing of HAp was confirmed on the surface of the coatings after immersion in SBF solution for 7 days. The coating obtained at −1.4 V showed higher corrosion resistance with bioactive behaviors.

Improvement of corrosion resistance of AZ31 Mg alloy by anodizing with co-precipitation of cerium oxide

Anodizing of AZ31 Mg alloy in NaOH solution by co-precipitation of cerium oxide was investigated. The chemical composition and phase structure of the coating film were determined via optical microscopy, SEM and XRD. The corrosion properties of the anodic film were characterized by using potentiodynamic polarization curves in 17 mmol/L NaCl and 0.1 mol/L Na2SO4 solution at 298 K. The corrosion resistance of AZ31 magnesium alloy is significantly improved by adding cerium oxide to alkaline solution. In addition, the surface properties are enhanced and the film contains no crack.

A Comparative Electrochemical Study of AZ31 and AZ91 Magnesium Alloy

A comparative study has been carried out on AZ31 and AZ91 magnesium alloys in order to understand the electrochemical behavior in both alkaline and chloride containing solutions. The open circuit potential (OCP) was examined in 1 M NaOH and 3.5 mass % NaCl solutions. AZ31 magnesium alloy shows several potential drops throughout the immersion in 1 M NaOH solution, though AZ91 does not show this phenomenon. The specimens were anodized at a constant potential of 3 V for 30 minutes at 298 K in 1 M NaOH solution. The anticorrosion behavior of the anodized specimens was better than those of nonanodized specimens. The anodized AZ91 has better corrosion resistance compared to nonanodized specimen and anodized AZ31 magnesium alloy.

Synthesis and Characterization of Cobalt Nanoparticles Using Hydrazine and Citric Acid

Cobalt nanoparticles were produced by employing the liquid-phase reduction method and hydrazine. The effect of citric acid additives on the formation and growth mechanism of cobalt nanoparticles was investigated using polarization methods. The cobalt nanoparticles produced in 0.2 M cobalt sulfate and 5 M hydrazine at 298 K had a spherical shape with a diameter of 400 nm. The dendritic nanoparticles formed with the decreasing of hydrazine concentration at 298 K. On the other hand, dendritic large particles are confirmed at 353 K. It was confirmed that the reduction reaction progressed with the addition of citric acid, and a hexagonal close-packed (eCo) phase was formed.

Influence of calcium hydroxide and anodic solution temperature on corrosion property of anodising coatings formed on AZ31 Mg alloys

Abstract Anodisation of AZ31 Mg alloy (3 mass%Al, 1 mass%Zn) was performed in 1M NaOH solution, with and without adding 35 mM of calcium hydroxide at various temperatures. The anodising process was carried out at constant potential 3 V; the change in current density during the first period of anodising revealed the mechanisms of anodic film formation. Adding 35 mM Ca(OH)2 to the solution improved the corrosion resistance, e.g. in 17 mM NaCl and 0·1M Na2SO4 solution at 298 K from anodic polarisation measurements. The anodic layer thickness increases with the amount of Ca(OH)2 added. The temperature of the solution also affects the anodising process; i.e. increasing the solution temperature improved the corrosion resistance of the anodised film.

Deposition of Self-Assembled Monolayer on Vanadate Conversion Coated AZ31 Mg Alloy

Self-assembled monolayer (SAM) was adsorbed on the surface of vanadate conversion coated AZ31 magnesium alloy. The SAM thin film was deposited using (Tridecafluoro-1, 1, 2, 2-tetrahydrooctyl) trimethoxysilane (FAS13) and Tetrakis (trimethylsiloxy) titanium as a catalyst. Contact angles measurement, SEM, XRD, EDS and XPS were employed to analyze the surface morphologies, molecular composition, phase structure and wettability of the coatings formed on Mg alloy substrate. Corrosion resistance property of the coatings was also examined using the anodic polarization method and salt spray test. The anticorrosion property was improved with SAM post treatment. Furthermore, the contact angle increases from 12 deg. to 165 deg. indicating to production of super hydrophobic surface with SAM post treatment.

Formation of Vanadate Conversion Coating on AZ31 Magnesium Alloy

Magnesium alloys have high strength-to-weight ratios, excellent castability, machinability, weldability, and thermal stability, and good damping capacity. Therefore, Magnesium alloys are recognized as alternatives to Al alloys and steel to reduce the weight of structural materials. However, a major obstacle to the widespread use of magnesium alloys is its poor corrosion resistance, particularly in wet environments. Therefore, further surface treatment of magnesium and its alloy is important in meeting several industrial specifications. In the present investigation, a chromate-free, corrosion-resistant conversion coating using vanadium based solution was applied to AZ31 magnesium alloy. Conversion coating was carried out in vanadium based solution. The effect of vanadium concentration and treatment time on the coating film was characterized by SEM, EDX and XRD. The corrosion characteristics of anodic films were evaluated using potentiodynamic polarization test in deaerated NaCl solution. Corrosion resistance property was improved with conversion coating treatment.

Formation of Self-Assembled Monolayer on Cerium Conversion Coated AZ31 Mg Alloy

Magnesium alloys are recognized as alternatives to Al alloys and steel to reduce the weight of structural materials. However, a major obstacle to the widespread use of magnesium alloys is its poor corrosion resistance. Therefore, further surface treatment of magnesium and its alloy is important in meeting several industrial specifications. In a previous research, we investigated the surface treatment of AZ31 magnesium alloy using cerium conversion coating. The anticorrosion properties could be improved with the cerium treatment. In this present research, self-assembled monolayer (SAM) was adsorbed on the surface of cerium conversion coated AZ31 magnesium alloy. The SAM thin film was deposited using (Tridecafluoro-1, 1, 2, 2-tetrahydrooctyl) trimethoxysilane (FAS13) and Tetrakis(trimethylsiloxy)titanium (TTMS) as a catalyst. The corrosion resistance of cerium conversion coated AZ31 Mg alloy was improved with SAM post treatment. Furthermore, the contact angle increases from 13 deg. to 169 deg. indicating to production of super hydrophobic surface with SAM post treatment.

Effect of Sn4+ Additives on the Microstructure and Corrosion Resistance of Anodic Coating Formed on AZ31 Magnesium Alloy in Alkaline Solution

Magnesium is the lightest structural metal with high specific strength and good mechanical properties. However, poor corrosion resistance limits its widespread use in many applications. Magnesium is usually treated with Chromate conversion coatings. However, due to changing environmental regulations and pollution prevention requirements, a significant push exists to find new, alternative for poisonous Cr6+. Therefore, we aim to improve corrosion resistance of anodic coatings on AZ31 alloys using low cost non-chromate electrolyte. Anodizing was carried out in alkaline solutions with tin additives. The effect of tin additives on the coating film was characterized by SEM and XRD. The corrosion resistance was evaluated using anodic and cathodic polarizations and electrochemical impedance spectroscopy (EIS). Corrosion resistance property was improved with tin additives and the best anti-corrosion property was obtained with addition of 0.03 M Na2SnO3.3H2O to anodizing solution.

The Effect of Reaction Driving Force on Copper Nanoparticle Preparation by Liquid Phase Reduction Method

Copper nanoparticle was prepared by liquid phase reduction technique. Cu 2+ was reduced to copper particle by adopting different types of reductants. Ascorbic acid (C 6 H 8 O 6 ), phosphinic acid (H 3 PO 2 ), titanium sulfate (Ti 2 (SO 4 ) 3 ) and sodium borohydride (NaBH 4 ) were chosen as reductant, respectively. The effect of reaction driving force upon the average size of copper particle was investigated in the paper. It can be concluded that there is a firm relationship between the reaction driving force and the average size of copper particle. The average size of copper particle decreases with the increasing of reaction driving force.