Diffusion Of Tin Atoms Research Articles

Electrochemical aspects of tin electrodeposition on copper in acid solutions

The electrodeposition of tin on copper electrodes was studied in sulphuric acid solutions in the 283–338 K range by employing electrochemical techniques, including electrochemical quartz crystal microbalance, and scanning electron microscopy imaging. The voltammetric profiles show the presence of both, underpotential and overpotential electrodeposition of tin. While the first process (upd) involves surface controlled reactions, the latter (opd) is under mass transport control. SEM imaging shows the formation of nanoparticles under upd conditions and larger ones in the opd potential region. Analysis of chronoamperometric response indicates an instantaneous nucleation and 2D growth coupled to an adsorption process during the early stages of underpotential deposition. Conversely, data obtained in the overpotential deposition range is consistent with the occurrence of a progressive nucleation and 3D growth under diffusion control. Electrochemical impedance experiments are characterised by Nyquist plots that exhibit two capacitive time constants and a single capacitive time constant followed by a Warburg contribution in the upd and opd potential ranges, respectively. Rotating ring-disc voltammograms display current peaks in the corresponding ring profiles associated with the formation of adsorbates on the disc during the underpotential deposition. From rotating disc data the diffusion coefficient of Sn(II) ions at the different temperatures and the corresponding diffusion activation energy were determined. A reaction scheme for the electrochemical behaviour of tin on copper electrodes in the range between the threshold potentials for the copper electrodissolution and the hydrogen evolution reactions is proposed. Mass transport of soluble species, formation of weakly and strongly adsorbed species on copper and the diffusion of tin atoms into the copper lattice are considered.

Dilatometric investigations of the processes of liquid-phase sintering of materials of the Cu-Sn system

The shrinkage of Cu-Sn powder compacts during liquid-phase sintering, which is due to dissolution of copper particles in molten metal and their regrouping, is preceded by growth caused by preferential diffusion of tin atoms from the liquid phase to the solid. The process of regrouping of solid-phase particles as a result of the destruction of the rigid skeleton of a compact at a high tin content at the instant of appearance of molten metal fails to manifest itself explicitly. The possibility cannot be ruled out that regrouping takes place at the instant of diffusional growth of compacts and, superimposing itself on the latter process, is responsible for the extent of relative growth being dependent on starting porosity.

すずめっき被覆したＣｕ‐Ｓｎ合金の加熱拡散処理について

The heat-treatment of tin-electrodeposited bronze has been studied to improve the surface hardness and corrosion resistance by the formation of Cu-Sn alloy layers. The formation of the alloy layers proceeds by the diffusion of tin atoms from the deposited layer inwards and of cupper atoms in the substrate outwards. Cu-Sn alloys with 0, 6, and 12wt% of tin content were coated by an electrodeposited tin layer of 10μm thickness, prior to the heat-treatment of the specimens at different temperatures of 400, 450, and 500°C for 1, 2, and 3 hours. The vertical cross sections of the heat-treated specimens were analysed by EPMA and micro hardness measurements. By the heattreatment at 400°C, the surface layer on all specimens consists of an η-phase (Cu6Sn5) at the outer part, and an ε-phase (Cu3Sn) at the inner part. The η-phase transforms to ε-phase during the treatment, and the transformation occurs more easily with Cu-Sn alloy substrates than with Cu substrate. After 3 hours of the treatment the surface layer of all specimens consists of only the ε-phase with a hardness of 360-420Hmv. By the treatment at 450°C, all the specimens shows the existence of the ε-phase at the outer part and a δ-phase (Cu4Sn) at the inner part of the surface layer. The hardness of the δ-phase changes from 370-405Hmv after a 1 hour treatment, through 400-410Hmv after 2 hours, to 430-440 Hmv after 3 hours. The hardness of the δ-phase could not be measured after the 1 hour treatment because of the thinness of the δ-phase, but it is measured to be 420-500 Hmv after 3 hours. The change in the hardness of the two phases is due to the relatively thin surface layer. At 500°C, both ε-and δ-phase are found after 1 hour treatment and only δ-phase after 2 or more hours treatment. The hardness of the δ-phase after 2 hours treatment is 500-530 Hmv. The activation energy for the formation of δ-phase is obtained to be 81.7KJ/mol.

Effect of Phosphorus on the Friction and Wear Characteristics of Cu-Sn-P Alloys

The effects of phosphorus on the friction and wear characteristics of Cu-5 at. percent Sn-P alloys containing 1–5 at. percent P were studied using a pin on disc apparatus. The results showed that the decrease in both the coefficient of friction and the rate of wear became conspicuous with the increase in quantity of Cu3P coexisting in the matrix; its amount increases with the content of phosphorus. The structural changes in the surface of the specimen due to heating in a vacuum were observed by using Auger electron spectroscopy and X-ray photoelectron spectroscopy. It was seen that the surface concentration of phosphorus strongly increased after heating at 573K, whereas the diffusion of tin atoms was markedly retarded. It was concluded from these results that the behavior of phosphorus atoms in the surface during sliding played an important role in the friction and wear characteristics of Cu-Sn-P alloys.