Substrate effect on electrodeposited copper morphology and crystal shapes

Estimation of Zwitterionic Surfactant Response in Electroless Composite Coating and Properties of Ni–P–CuO (Nano)Coating

Abstract: Electroless Ni–P and Ni–P–CuO coating on mild steel was developed successfully with the addition of Zwitterionic surfactant. The usage of nano-CuO in electroless coating was intermittent though the cost is low with high catalytic activity. Zwitterionic surfactant was introduced into the composite coating for the first time to increase the suspension of nanoparticles effectively during the coating process. Surfactant helps to reduce the intermolecular attraction between the solid and liquid interfaces and hence binding of nanoparticles with the hydrogen gas bubbles was eliminated. Also agglomeration of nanoparticles was controlled by stirring the electrolyte continuously using magnetic stirrer. The characterization and tribological properties were tested for the newly developed composites. Scanning electron microscope micrograph reveals the deposits are produced without any defects and the presence of CuO nanoparticles in the deposit. Energy-dispersive spectroscopy measurement shows the changes of weight percentage of elements available in the substrate. The surface roughness of the deposit was improved with the addition of CuO, it packs the gap between two grains and offers smooth finish and as the result the surface properties are modified. Microhardness of the substrate was improved for the substrate added with nano-CuO. The corrosion resistance of the substrate was improved when compared to the substrate produced using electroless Ni–P binary coating. Zwitterionic surfactant reduces the agglomeration of nanoparticles during chemical reaction and allows the particles to coat only on the target. Similarly, this technique can be implemented in the production of other composites in electroless coatings.

Synthesis and characterization of novel Cu, Cu-SiC functionally graded coating by pulse reverse electrodeposition

Abstract: A Cu based functionally graded coating (FGC) has been deposited on an annealed Cu substrate by galvanostatic pulse reverse electrodeposition (PRED) route. The objective is to develop a hard surface with highly ductile and conductive interior. The cathodic current density (CCD) has been increased stepwise (from 50 to 200 mA/cm2) to synthesize Cu FGC on an annealed Cu substrate. It has three layers of Cu coating (20 μm each) with a gradual reduction in crystallite size along the thickness. Two layers of Cu-SiC nanocomposite coating with an increment in the amount of incorporated SiC nanoparticles (from 2 to 7 vol%) are electrodeposited on Cu FGC. This is done by introducing bath agitation (350 and 450 rpm) during deposition at CCD of 200 mA/cm2, which has resulted in Cu, Cu-SiC FGC with five layers (12 μm each). SiC nanoparticles are used to impart hardness to the coating through dispersion strengthening. The Cu, Cu-SiC FGC possesses higher hardness (∼3.8 GPa), lower residual compressive stress (∼291 MPa), and lower surface roughness (∼0.9 μm) as compared to electrodeposited single layer Cu-SiC nanocomposite coating. With such properties Cu, Cu-SiC FGC on annealed Cu substrate can serve as a novel prospective electrical contact material.

Machining characteristics of PCD by EDM with Cu-Ni composite electrode

Abstract: Polycrystalline diamond (PCD) is widely used for its excellent properties but difficult to be processed by traditional machining methods. Electrical discharge machining (EDM) is regarded as...

Reciprocating Sliding Wear of Cu, Cu-SiC Functionally Graded Coating on Electrical Contact

Abstract: The present work evaluates the coefficient of friction (CoF), electrical resistivity, and electrical contact resistance (ECR) of the electrodeposited single-layered Cu-SiC nanocomposite coating and five-layered Cu, Cu-SiC functionally graded coating (FGC). Both the coatings have a similar thickness (60 µm) and same composition at the top surface (7 vol.% reinforced SiC nanoparticles), while the FGC has a gradient of composition and microstructure throughout the thickness. The Cu, Cu-SiC FGC has two layers of Cu-SiC with a decrement in the content of SiC nanoparticles from 7 to 2 vol.% followed by three Cu layers with an increasing crystallite size towards the substrate. The electrical resistivity of the Cu, Cu-SiC FGC is measured by the four-wire resistance measurement method and the value is observed to be 50% less than the conventional nanocomposite coating. A linear reciprocating sliding wear test is carried out at 2, 5 and 8 N load at a constant frequency and stroke length of 10 Hz and 2 mm, respectively. The monitored value of CoF is significantly less for the Cu, Cu-SiC FGC than the single-layered coating at 2 and 5 N loads and is nearly equal at 8 N load. It is observed that before wear, the ECR values of both the coatings are higher than the uncoated Cu and after wear the ECR value of Cu, Cu-SiC FGC is the lowest.

Electrochemical approaches for selective recovery of critical elements in hydrometallurgical processes of complex feedstocks.

Abstract: Summary Critical minerals are essential for the ever-increasing urban and industrial activities in modern society. The shift to cost-efficient and ecofriendly urban mining can be an avenue to replace the traditional linear flow of virgin-mined materials. Electrochemical separation technologies provide a sustainable approach to metal recovery, through possible integration with renewable energy, the minimization of external chemical input, as well as reducing secondary pollution. In this review, recent advances in electrochemically mediated technologies for metal recovery are discussed, with a focus on rare earth elements and other key critical materials for the modern circular economy. Given the extreme heterogeneity of hydrometallurgically-derived media of complex feedstocks, we focus on the nature of molecular selectivity in various electrochemically assisted recovery techniques. Finally, we provide a perspective on the challenges and opportunities for process intensification in critical materials recycling, especially through combining electrochemical and hydrometallurgical separation steps.

The Growth of Crystals and the Equilibrium Structure of their Surfaces

Abstract: Parts I and II deal with the theory of crystal growth, parts III and IV with the form (on the atomic scale) of a crystal surface in equilibrium with the vapour. In part I we calculate the rate of advance of monomolecular steps (i.e. the edges of incomplete monomolecular layers of the crystal) as a function of supersaturation in the vapour and the mean concentration of kinks in the steps. We show that in most cases of growth from the vapour the rate of advance of monomolecular steps will be independent of their crystallographic orientation, so that a growing closed step will be circular. We also find the rate of advance for parallel sequences of steps. In part II we find the resulting rate of growth and the steepness of the growth cones or growth pyramids when the persistence of steps is due to the presence of dislocations. The cases in which several or many dislocations are involved are analysed in some detail; it is shown that they will commonly differ little from the case of a single dislocation. The rate of growth of a surface containing dislocations is shown to be proportional to the square of the supersaturation for low values and to the first power for high values of the latter. Volmer & Schultze’s (1931) observations on the rate of growth of iodine crystals from the vapour can be explained in this way. The application of the same ideas to growth of crystals from solution is briefly discussed. Part III deals with the equilibrium structure of steps, especially the statistics of kinks in steps, as dependent on temperature, binding energy parameters, and crystallographic orientation. The shape and size of a two-dimensional nucleus (i.e. an ‘island* of new monolayer of crystal on a completed layer) in unstable equilibrium with a given supersaturation at a given temperature is obtained, whence a corrected activation energy for two-dimensional nucleation is evaluated. At moderately low supersaturations this is so large that a crystal would have no observable growth rate. For a crystal face containing two screw dislocations of opposite sense, joined by a step, the activation energy is still very large when their distance apart is less than the diameter of the corresponding critical nucleus; but for any greater separation it is zero. Part IV treats as a ‘co-operative phenomenon’ the temperature dependence of the structure of the surface of a perfect crystal, free from steps at absolute zero. It is shown that such a surface remains practically flat (save for single adsorbed molecules and vacant surface sites) until a transition temperature is reached, at which the roughness of the surface increases very rapidly (‘ surface melting ’). Assuming that the molecules in the surface are all in one or other of two levels, the results of Onsager (1944) for two-dimensional ferromagnets can be applied with little change. The transition temperature is of the order of, or higher than, the melting-point for crystal faces with nearest neighbour interactions in both directions (e.g. (100) faces of simple cubic or (111) or (100) faces of face-centred cubic crystals). When the interactions are of second nearest neighbour type in one direction (e.g. (110) faces of s.c. or f.c.c. crystals), the transition temperature is lower and corresponds to a surface melting of second nearest neighbour bonds. The error introduced by the assumed restriction to two available levels is investigated by a generalization of Bethe’s method (1935) to larger numbers of levels. This method gives an anomalous result for the two-level problem. The calculated transition temperature decreases substantially on going from two to three levels, but remains practically the same for larger numbers.

Electrocrystallization: Nucleation and growth phenomena

Abstract: A review of the present status of the problem of metal deposition and electrochemical phase formation and growth is made. The historical background of the problem is given with an overview of the major contributions of different electrochemical schools. Phase formation is treated in classical and atomistic terms. Some of the basic consequences of the theory concerning the equilibrium form, the influence of the substrate, the size-overpotential dependence of low-dimensional systems, and the nucleation kinetics are discussed. The basic modes of crystal growth under electrochemical conditions are described. The influence of substrate surface modification in the UPD region concerning the formation of low dimensional phases and their stability ranges are discussed. The development of recent in situ techniques for nanostructuring and nanomodification of solid surfaces and their importance for electrochemical nanotechnologies are also shortly presented.

The effect of hydrogen codeposition on the morphology of copper electrodeposits. I. The concept of effective overpotential

Abstract: The effect of hydrogen codeposition on the morphology of copper electrodeposits was studied. The dependences of the overall current and the volume of evolved hydrogen on the quantity of electricity used were plotted and the average current efficiencies of the evolved hydrogen were derived from them. The morphologies of copper electrodeposits were correlated with the hydrogen evolution rates. It was shown that dendrites are the main characteristic of deposits obtained at overpotentials belonging to the limiting diffusion current density plateau, at which the hydrogen evolution rate is low. At larger overpotentials the dominant form become craters in the honeycomb-like electrodeposits due to the intensive hydrogen codeposition.

Morphologies of copper deposits obtained by the electrodeposition at high overpotentials

Abstract: Morphologies of copper deposits obtained at overpotentials belonging to the plateau of the limiting diffusion current density and at higher overpotentials were examined by the scanning electron microscopy (SEM) technique. Copper dendrites are formed at overpotentials belonging to the plateau of the limiting diffusion current density. The shape of copper dendrites depends on the electrodeposition overpotential. At higher overpotentials (800 and 1000 mV) and larger values of current densities, porous and very disperse copper deposits were obtained. These morphologies were a consequence of a very vigorous hydrogen evolution at these electrodeposition overpotentials. Also, the obtained copper structures consisted of agglomerates of copper grains. The size of copper grains is a function of the overpotential of electrodeposition, thus approaching to nano-sized dimensions is achieved when the electrodeposition overpotential is increased.

Mechanical and structural properties of electrodeposited copper and their relation with the electrodeposition parameters

Abstract: Thin copper-electrodeposited films have been prepared on steel substrates from an additive-free copper sulfate bath by applying different current signals such as rectangular and square wave pulses, triangular waveform and also by direct current with variation of its magnitude. Mechanical properties of these films have been studied by means of dynamic microindentation measurements known as the universal microhardness test. Values of the hardness, plastic component, Young's modulus and percent of elastic recovery have been measured. In order to obtain the preferential orientation and grain size of the electrodeposits, X-ray diffraction studies have been made as well as scanning electron microscopy to evaluate their morphology. All the deposits showed a preferential orientation but without a simple correlation with the mechanical features of the films. The influence of current density on microhardness through its effect on grain size has been found to obey the Hall–Petch relationship in the nanometer range. Finally, correlations between the mechanical properties of the electrodeposits and the electrodeposition parameters have been made. These kinds of studies raise the possibility of tailoring films with good mechanical performance for different technological applications just by selecting the appropriate electrodeposition conditions.