Normal and anomalous electrodeposition of tin–copper alloys from methanesulphonic acid bath containing perfluorinated cationic surfactant

Abstract

Sn–Cu alloys were deposited from a 12˙5 vol.-% (1˙93 mol dm^–3) methanesulphonic acid bath containing a perfluorinated, cationic surfactant at 296 K. Electrodeposition was carried out under controlled flow conditions, using rotating disc, rotating cylinder and rotating cylinder Hull cell electrodes. The influences of deposition current and potential, rotation speed, cupric ion concentration, stannous ion level and surfactant concentration on the deposited alloy composition have been investigated. The presence of surfactant resulted in a shift in the Cu deposition potential compared to that of Sn deposition. Both 'normal' deposition (Cu deposited at a more positive potential than Sn) and 'anomalous' deposition (Sn deposited at a more positive potential than Cu) could be achieved. A series of Sn–Cu alloys was electrodeposited over a wide range of operating conditions to produce matte grey through golden yellow to light brown, surface finishes. Golden yellow coloured bronze deposits, containing 70–80 wt-% Cu and 20–30 wt-%Sn could be obtained. When Sn was deposited preferentially, the Cu content of the alloy was typically in the range 3–9 wt-% along the cathode of the rotating cylinder Hull cell.     

Performance of Low Output Impedance Composite pH Glass Electrodes

Low output impedance composite pH sensors were constructed by direct attachment of an impedance converter to laboratory purpose combined pH glass electrodes. The signal was transmitted in analog form by unshielded electric cable. The performance of new and aged composite pH sensors was determined by the multiple-point calibration method. In case of new electrodes, the slope and the response time, as well as the reproducibility, were insignificantly influenced by the converter attached (the mean slope values calculated for the six electrode group studied were 57.80 mV/pH for unmodified electrodes and 57.97 mV/pH for modified electrodes). The electrode response was not affected by the presence of various electromagnetic noise sources or by the input impedance value of the measuring instrument. The slope and the response time of aged sensors were considerably improved using the impedance converter. The response time decreased from about 150–180 sec to about 30 sec and the average slope value increased from 54.94 mV/pH, calculated for unmodified electrodes, to 56.96 mV/pH, for modified electrodes.     

Thermodynamic calculation and reference electrode calibration for high temperature molten salts

Abstract

Molten salts are important reaction media for chemical and electrochemical processing and have recently attracted attention for their potential in reprocessing and partitioning spent nuclear fuels. Electrochemical measurements are a convenient tool for exploring thermodynamic and kinetic properties of molten salts, but inconsistency in acquired data may arise from the use of inaccurate reference electrodes and differences in thermodynamic calculations. A thermodynamic approach to the calculation of half cell potentials for reactions in molten salts is proposed. As examples, chlorine/chloride and lithium ion/lithium half cell potentials in LiCl–KCl eutectic are thermodynamically analysed. The Ag/AgCl reference electrode is discussed as an example of a high temperature reference electrode. A technique involving in situ transient reduction of constitutive metal ions for the calibration of high temperature reference electrodes is developed which may enable the consistency of acquired data using different reference electrodes in a variety of molten salts. The thermodynamic approach and calibration technique may be extended to ionic liquid and other media at high and low temperatures.     

Developing and studying the properties of Pb–TiO2 alloy coated lead composite anodes for zinc electrowinning

Abstract

A new anodic material for zinc electrowinning from sulphate electrolytes has been developed. This is a lead–titanium alloy coated lead composite electrode containing titanium nanoparticles. The titanium is present in the lead matrix as n-type TiO₂. It has been established that the optimal content of the Ti in the composite coatings is about 0·5 wt-%. The behaviour of the lead–titanium anodes during the zinc electrowinning has been studied by means of galvanostatic polarisation investigations. The depolarising of the anodic reaction at lead–titanium composite electrodes is attributed to the increased anode area during continued polarisation. The processes occurring on the lead–titanium anodes during zinc electrowinning have been studied by cyclic voltammetry. The surface morphology of the composite lead–titanium electrodes was investigated by scanning electron microscopy.     

The wear characteristics of Ni-P-SiC composite coatings

The wear resistance of an electroless co-deposited Ni-8.73% P-SiC coating has been studied and the effects of microstructure and properties of the coating on wear have also been researched by comparing it with Ni-8.9% P, Ni-4.5% P-SiC and electroplated chromium coatings. It has been found that the high wear resistance of the Ni-8.73% P-SiC coating results from the SiC particle reducing the matrix grain size, increasing the coating hardness and resisting microcuts; and the Ni-P alloy matrix with high phosphorus content is hard and supports the SiC properly. The Ni-8.73% P-SiC coating is more wear resistance than the electroplated chromium coating as the latter surface is highly cracked and its high hardness will decrease quickly at high temperature.     

Back handspring of a multi-link gymnastic robot — reference model approach

This paper reports on the first gymnastic robot that can perform back handspring. The robot is a planar and serially connected four-link robot, with its joints actuated by electric servomotors. The paper describes the modeling of the robot and the control framework for a back handspring. The controller is derived from a task-specific reference model and its model matching. The use of a reference model described by global physical quantities such as center of mass or angular momentum allows the gymnastic motion planning of a multi-body system to be intuitive and the model matching controller can be applied directly to the experimental model without obtaining each joint trajectory. The controller effectiveness is confirmed via simulations and experiments of the back handspring. Although there remains the problem of how to systematically design the control parameters, the paper shows the strength of the model-based controller for fast gymnastic motions.     

Processing and performance of Cr2O3–Fe2O3 reference electrode powders prepared by oxide coprecipitation

Abstract

Cr₂O₃–Fe₂O₃ based oxide mixtures for reference electrode powders of oxygen sensors were processed using oxide coprecipitation route. A special method for preparing reference electrode powders has been developed by mixing coarse Cr particles with the oxide mixture in the form of Cr–Fe hydroxide. Morphology and size of the mixed oxide powders were characterised by means of scanning electron microscopy and laser diffraction method. With the coprecipitation process, chemically homogeneous and very fine powders with a mean particle size of 1.53 μm were prepared. This powder mixture adhered and loosely coated to Cr particles. The processed reference electrode powders were tested in low level oxygen concentration measurements of steelmaking process under industrial scale. The reference electrode powders showed excellent results in terms of electromotive force reproducibility, response time and accuracy in soluble aluminium predictions at the oxygen concentration measurements. Most of the particles of the reference electrode powder remained separated after dipping to molten steel.