Metehan Erdogan

Electrochemical Formation of Alloys of Scandium in Molten Salts

The Al–Sc alloy formation by the reduction of Sc containing compounds in a molten salt containing CaCl2 was investigated in this study. The preliminary tests revealed that Al3Sc intermetallic, which gives the superior properties to this alloy, was successfully formed and distributed homogeneously throughout the Al matrix. XRD, SEM-EDS and optical microscopy analyses were used to confirm the results.

An Electrochemical Procedure for Copper Removal from Regenerated Pickling Solutions of Steel Plants

Pickling is the treatment of metal surfaces by removing oxide layer, rust, scale, inorganic contaminants or other impurities from ferrous metals, copper or precious metals. A strong inorganic acid such as hydrochloric acid is used for plain carbon or low alloy steel pickling. When the concentration of copper in the pickling solution exceeds about 100 mg/L, reversion may take place and randomly plating of copper onto the steel strips which causes visual incompatibility occur. Furthermore, efficiency of pickling decreases with the increase of copper content. The reversion may be delayed to higher Cu concentrations by adding fresh acid to the line. Increased acid consumption only delays the time to discard the solution but increases the cost and hazardous nature effect on the environment. An experimental electrochemical procedure has been conducted to remove copper from pickling solution to reduce the concentration below 100 mg/L. Within this scope, effects of applied current density, copper concentration and electrolysis duration on copper deposition were studied. Current density was determined as the most effective parameter to remove copper from the regenerated pickling solutions of steel plants.

Formation and Characterization of Sub-Micron Inert Particle Embedded Nickel Composite Coatings

Composite coatings have a wide range of application areas requiring improved mechanical and tribological properties. Due to its enhanced properties, Ni-Al2O3 electro-co-deposition rather than pure Ni electrodeposition was investigated. A typical sulfamate bath was used to evaluate the effects of current density on hardness and the amount of deposited Al2O3. It was found that increase in current density increases the hardness and deposited wt.% Al2O3 particles within the parameter ranges covered in this study. The linear sweep voltammetry results were used to support outcome.

Production of Tungsten by Pulse Current Reduction of CaWO4

Tungsten is mainly produced by H2 reduction of WO3 which makes its production difficult and costly. A promising method was recently reported for direct electrochemical production of tungsten from CaWO4 (scheelite) which is estimated as the seventy percent of the all tungsten reserves of the world. This paper investigates the application of pulse current in the electrochemical reduction of CaWO4 pellets attached to a current collector. The electrolyte was composed of calcium chloride and sodium chloride salts at eutectic composition (48 pct mol NaCl at 873 K). The reduced samples were cleaned with dilute hydrochloric acid solutions and characterized by X-ray diffraction and scanning electron microscopy. Examination of the results revealed that metallic tungsten was obtained by pulse current reduction.

A Pulse Voltage Application in Electrochemical Reduction of Solid CaWO4 Powder

Scheelite is the most abundant mineral of tungsten, but wolframite is used more than scheelite due to easier dissolution in alkaline solutions used in present processing methods. An alternative method based on electrochemical reduction of CaWO4 by direct current applications in molten salt solutions was recently reported. Pulse voltage and constant voltage reduction mechanisms were compared and an optimization of reduction kinetics was achieved in this study. The results have shown that faster reduction rates could be achieved during pulse voltage applications compared to constant voltage applications, when average value of pulse voltage application was the same as its constant counterpart. Furthermore, analysis of charge, energy and theoretical reduction graphs showed that reduction of calcium tungstate occurs at higher potential differences than 2.2 V, between calcium tungstate and graphite.

Formation of gold-plated electroformed copper structures

Abstract Gold-plated electroformed copper structures are used to protect sensors from stray radiation and improve the image quality in infrared cameras, imaging systems, missile guidance systems and several other devices. These multilayer electroformed objects have tight dimensional and weight tolerances. Furthermore, their internal and external surfaces often exhibit low and high emissivity, respectively. Reflectivity at the outer surface was achieved by gold electrodeposition. Moreover, inner copper layer was converted to copper oxides to obtain high absorption. Characterisation of the coatings were done in terms of microstructure, roughness, infrared specular reflectivity of layers, texture and stress formation by SEM, profilometer, FTIR, parallel beam XRD and deposit stress analyzer, respectively.

Reduction of Porous Silica Pellets by Electrodeoxidation in Molten Salts

Direct electrochemical reduction of porous SiO 2 pellets in molten CaCl 2 salt and CaCl 2 -NaCl salt mixture were investigated by applying 2.8 V potential. The study focused on the effects of temperature, powder size and cathode contacting materials. Starting materials and electrolysis products were characterized by X-ray diffraction analysis and scanning electron microscopy. Due to reactive nature of silicon, different cathode contacting materials were used to test the extent of reactions between silicon produced at the cathode and the contacting materials. X-ray diffraction patterns showed that silicon produced at the cathode reacted with nickel, and iron in stainless steel to form Ni-Si and Fe-Si compounds respectively. Besides, studies revealed that higher temperature and smaller particle size had positive effects in increasing reduction rate. The results were interpreted from variation of current versus time graphs under different conditions, microstructures and compositions of the reduced pellets.