I. Karakaya

Thermodynamic Properties of MgCl2 ‐ NaCl Melts from EMF Measurements

Thermodynamique de formation de MgCl 2 liquide pur et MgCl 2 dissous dans des masses fondues MgCl 2 -NaCl. Enthalpie et entropie de melange

Effects of current density, coating thickness, temperature, pH and particle concentration on internal stress during Ni–MoS2 electrocodeposition

Abstract Internal stress in plated deposits has been a common problem that may affect the functionality of coatings. Electrodeposition parameters and insoluble particles modify the characteristics and the level of internal stress of coatings. The influence of the electrocodeposition parameters and their interaction effects on the internal stress during the electrodeposition of Ni and Ni–MoS2 composite coatings were studied by fractional factorial design. The parameters studied and their ranges were: MoS2 particle concentration (0–10 g L−1), temperature (30–50°C), pH (2–4), current density (1·2–4·8 A dm−2), and coating thickness (25–50 μm). MoS2 addition into Watts bath resulted in the decrease in the tensile internal stress values or even changed the stress character from tensile to compressive. Moreover, low stress values were obtained when pH was 2 and coating thickness was 50 μm.

Electrolysis of MgCl2 with a top Inserted anode and an Mg-Pb cathode

High energy consumption in the production of magnesium by molten salt electrolysis is mainly due to the recombination of magnesium and chlorine. The large interelectrode distance used, in conventional techniques, to reduce the extent of ‘back reaction’, results in a significant potential drop. A laboratory cell that enables the operation with smaller interelectrode distance and easy separation of electrode products has been used to study electrolytic magnesium production. The cell features a top inserted graphite anode and a Mg-Pb alloy cathode at the bottom. Current efficiency and power consumption were determined at 690° C using a current density of 0.48 A cm−2. Experiments were performed to study the effects of MgCl2 concentration and anode-cathode distance (a.c.d.) on cell operation. Results indicated that an electrolyte containing 20% MgCl2 (equiweight NaCl:KCl and 1 % NaF) with a 3 cm a.c.d. reduced the cell voltage to 3.72 V. This value corresponds to an energy consumption of 11.3 kWh kg−1 including the refining of Mg-Pb alloy produced at the cathode. This cell performance is more energy efficient compared to conventional magnesium cells.

Alloy Corrosion Data Bases Combined with Thermochemical Analyses

ABSTRACT Experimental data and data analyses methods for high temperature alloy corrosion by gases have been incorporated into a computer-based information system. The system considers corrosion mechanisms that form mixtures of sulfides and oxides (sulfidation and mixed sulfidation/oxidation). Applications of the system can include equipment design, alloy selection, component failure analysis, and equipment corrosion studies. Corrosion rate data are correlated with temperature, alloy composition, exposure time, and gas composition. Data from a variety of sources are examined, archived, statistically analyzed, and then built into equations that have forms based upon theoretical expressions that are applicable to corrosion of simple alloys by gases. Interpolations and extrapolations of the conditions associated with the databases and the predictions by the system are obviously indicated. There is a large number of corrosion data observations for commercially available alloys in the growing databases. These alloys are a significant collection of those commonly incorporated into equipment used in high temperature processes.

The Ag-Re (Silver-Rhenium) System

Ag-Pd evaluation contributed by I, Karakaya, Middle East Technical University, Dept. of Metallurgical Engineering Ankara, Turkey 06531 and W.T. Thompson, Department of Chendstry and Chemical Engineering, Royal Military College of Canada, Kingston Ontario, K7L 2W 3 Canada. This system was analyzed usinga computer coupled phase diagrandthermodynaudc computational procedure. The calculations were performed with the F*A*C*T on-line computing system. The authors acknowledge the contribution of Dr. T. E1Kasabgy in the preliminm T stages of the evaluation. The work was partially supported by a grant fl~om the Canadian National Contmittee of the ASM/NBS Phase Diagram Project. Dr. Thompson is the ASM/NBS Data Program Co-Categol T Editor for binary silver alloys.

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.

Taguchi Design of Internal Stress and Friction Measurements duringElectrodeposition

The electroplating method is a promising alternative to produce composite plating by using dispersed fine particles in the metal plating bath. The process can be either called electro-deposition or composite deposition. The particles are trapped in the deposit during the process. Internal stress is a common problem in plated deposits that affect the performance of the coatings and may even result in adhesion problems. Hence, the amount and type (compressive or tensile) of the internal stress must be controlled. MoS2 particle – nickel coatings can be referred as self-lubricating coatings that satisfy the demand for decreased friction in severe applications. The internal stress during MoS2 particle – nickel electro-deposition was measured by deposit stress analyzer. The effects of electroplating parameters that are MoS2 particle concentration, temperature and coating thickness on the internal stress values were investigated by Taguchi design. It is found that increasing MoS2 particle concentration and coating thickness led to decrease in the internal stress developed during MoS2-nickel composite coatings. Interaction effects of these parameters were also revealed.

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.