A.-M. Lafront

The use of electrochemical noise measurements to detect bad copper electrorefining conditions

Additives like thiourea, gelatin and chloride are used during copper electrorefining to promote a smooth deposit. However, additives can also facilitate nodule formation when their ratios and/or concentrations are inadequate. A preliminary investigation was conducted to determine if electrochemical noise (EN) measurements could be used to monitor and detect inefficient copper electrorefining conditions due to improper ratios and/or concentrations of additives. EN measurements were carried out in the laboratory under simulated industrial conditions. Galvanostatic experiments were conducted using a synthetic electrolyte containing different concentrations of additives. A 316L SS cathode and industrial copper anodes were used. The effects of three different data acquisition frequencies were also investigated. EN signals obtained as potential time record series were studied using statistical analyses and frequency domain transforms. The different calculated parameters gave similar results for all conditions studied except when additives present in the electrolyte led to nodule formation. Results also showed that the data acquisition frequency must be at least 10 Hz to detect improper ratios and/or concentrations of additives.

Influence of gelatin on deposit morphology during copper electrorefining using scaled industrial cells

Abstract This paper discusses the effect of Gelatin (G) on cathode quality during copper electrorefining. Binary system Gelatin-Chloride ions (G-Cl-) and ternary system Thiourea-Gelatin-Chloride ions (TU-G-Cl-) have been investigated using scaled industrial cells and laboratory cells. Concentration of Clwas 40 mg L-1 and temperature 65 °C. In the pilot plant, current densities ranged between 200 and 400 A m-2, Gelatin concentration from 50 to 300 grams per ton of copper produced (g t-1) and Thiourea from 20 to 60 g t-1. Gelatin influences the polarization curves, the deposit morphology (roughness and nodule formation), the crystal structure (columnar or pyramidal) and the copper grain type (round or field oriented). Addition of Gelatin increases cathodic polarization but does not always lead to nodule formation. For the binary system, the cathode surface smoothness is acceptable but edge quality deteriorates as current density increases. In the ternary TU-G-Cl- system, surface smoothness and edge quality are greatly improved while copper growth structure is modified to produce a dense cathodic deposit. However, nodules, dendrites and big porosities appear randomly if G/TU ratio is not appropriate. The best cathodes were obtained when this ratio was higher than 0.8 but lower than 1.7. Cet article traite de l’influence de la Gélatine (G) lors de l’électroraffinage du cuivre. Le système binaire Gelatin-ions chlore (G-Cl-) ainsi que le système ternaire Thiourée-Gélatine-ions chlore (TUG- Cl-) ont été étudiés en utilisant des cellules industrielles réduites et des cellules de laboratoire. La concentration des ions Cl- est 40 mg L-1 et la température 65 °C. Dans les cellules pilotes, la densité de courant varie de 200 à 400 A m-2. La concentration en Gélatine varie de 50 à 300 grammes par tonne de cuivre produite (g t-1) et celle de la Thiourée de 20 à 60 g t-1. La teneur en Gélatine influence la courbe de polarisation, la morphologie du dépôt (rugosité et nodulation), la structure des cristaux (colonnaire et pyramidale) et la structure des grains de cuivre (round ou orienté). L’addition de Gélatine augmente la polarisation cathodique mais ne conduit pas forcément à la nodulation. Pour le système binaire, la qualité de la surface des cathodes est acceptable quoique les bords se détériorent avec l’augmentation de la densité de courant. Dans le système ternaire, la finesse de la surface et la qualité des bords sont grandement améliorées. La structure de croissance du cuivre est également modifiée et assure un dépôt dense. Cependant, des nodules, des dendrites et de grosses porosités apparaissent lorsque le rapport G/TU n’est pas approprié. Les meilleures cathodes ont été obtenues lorsque ce rapport est plus grand que 0.8 mais inférieur à 1.7

Corrosion Resistance of the Skin and Bulk of Die Cast and Thixocast AZ91D Alloy in Cl- Solution Using Electrochemical Techniques

Abstract The corrosion resistance of die cast and freely solidified or electromagnetically stirred thixocast AZ91D alloy has been studied using electrochemical noise technique and electrochemical impedance spectroscopy in a 0.05 M NaCl solution. Specimens polished at different depths were immersed in the solution in order to assess the influence of the microstructure on corrosion kinetics and morphology. At depths between 10 and 50 μm (skin), all specimens showed general non-uniform corrosion with the lowest corrosion resistance. Between 100 and 200 μm (interior skin), the observed corrosion was accompanied by superficial undefined pits due to metastable pitting. The corrosion form in the interior skins gave the best corrosion resistance. Stable pitting corrosion was observed beyond 400 μm deep on the bulk specimens. The skin of all thixocast specimens prepared from both types of billets showed a more corroded surface than that of die cast. On the other hand, the interior skin as well as the bulk of thixocast specimens showed better corrosion performance than that of the die cast specimens.

Monitoring the Influence of Gelatin and Thiourea on Copper Electrodeposition Employing Electrochemical Noise Technique

Abstract The copper electrodeposition from sulphuric acid electrolytes in the presence of thiourea and gelatin as additives was investigated using Electrochemical Noise (EN) and Linear Sweep Voltammetry (LSV) in conjunction with the scanning electron microscopy technique. This study was oriented to examine the utility of using EN technique to characterize the electrowinning process and the deposit structure morphology was compared to LSV, an electrochemical method generally used industrially. Both EN and LSV techniques were successful in revealing the effect of different concentrations of thiourea and gelatin on the copper electrodeposition process. In this study, LSV detected an excess of thiourea leading to porous deposit; while the EN analysis in the time domain (skewness and kurtosis parameters) detected the presence of nodules and has provided useful information concerning the morphology of the deposit closely related to the macroscopic and microscopic studies.