Faraday's Laws of Electrolysis

Abstract

Electrodeposition of nickel based tertiary Al₂O₃/Y₂O₃/CNT nanocomposites by using pulsed current has been studied in this investigation. The coating process has been performed in a nickel sulphate bath and the nanostructure of the obtained compound layer was examined with high precision figure analysis of SEM nanographs. The effects of process variables, i.e. Y₂O₃ concentration, treatment time, current density and temperature of electrolyte have been experimentally studied. Statistical methods were used to achieve the minimum corrosion rate and average size of nanoparticles. Finally the contribution percentage of different effective factors was revealed and a confirmation experiment has shown the validity of the obtained results. In addition, it has been revealed that by changing the size of nanoparticles, the corrosion properties of coatings will change significantly with this trend. Atomic force microscopy and transmission electron microscopy analyses have confirmed the smooth surface and average size of nanoparticles in the optimal coating.     

Effect of bonding time on joint properties of vacuum brazed WC – Co hard metal/carbon steel using stacked Cu and Ni alloy as insert metal

Abstract

Hard metal WC – Co and carbon steel were successfully joined using double layered Cu alloy and amorphous Ni alloy as inert metal and an oil cooling method after brazing. Defects such as cracks and voids were not formed near the bonded zone. This result means that double layered insert metals and oil cooling minimised the residual stress near the bonded zone after brazing. The shear strength of the joints decreased with increasing bond time. The reasons why the shear strength decreased as bond time increased could be many, including shape of the interface, formation and growth of brittle intermetallic compounds, and coarsening of WC particles near the bond zone. The maximum shear strength of the joints was 310 MPa under conditions 0·6 ks bond time and 8 wt-%Co content in the WC hard alloy.     

Molecular level investigation into selective permeability of silicon based membranes with potential use in gas separation processes

Abstract

The effect of the modification of the molecular structure on the permeability coefficients of typical rubbery and glassy silane and siloxane polymers at different temperatures was experimentally investigated. It was shown that carbon dioxide had higher permeability coefficients than those of nitrogen and oxygen due to the higher affinity of the various polymers toward the gas molecules. In order to provide a detailed understanding into the effect of the molecular structure on the gas diffusion behaviour in polymers, molecular modelling of carbon dioxide diffusion in silicon based membranes was used. The polymer molecules were shown to have lower self-diffusion coefficients than the gas ones related to the small size of the gas molecules as compared to the large size of the polymeric segments, thus allowing the gas molecules to jump from one unoccupied site to another through a series of connected pores or channels within the polymeric matrix. Increasing the temperature was shown to have a proportional effect on the mean square displacement, possibly due to the increase in the kinetic energy available to the systems. At high temperatures, the glassy siloxane molecules had similar values for the mean square displacement to those of the gas molecules since the polymer in this case is in close proximity to its glass transition temperature. The presence of the alternating oxygen atoms in the main backbone of the polymeric chains led to higher values for the selfdiffusion coefficients for the siloxane polymers as compared to those of the silane polymers as a result of the change in the bond angle about the oxygen atom (~ 144°) as compared to the tetrahedral angle (~ 110°) about the silicon atoms.     

Preparation of electrically conductive fibres by new surface coating method

Abstract

In the present research, a new surface coating method (dissolving-coating method) that is on the basis of dissolution mechanism was designed. Substantially transparent antimony doped tin oxide (ATO) particles were used instead of carbon black as conductive particles. ATO coated polyester (PET) fibres and ATO coated polycaprolactam (PA6) fibres were prepared by the traditional coating method and the dissolving–coating method respectively. The electrical conductivity, mechanical property and launderability of the coated fibres were discussed. For the characterisation, a laser particle size distribution analyser was used to analyse the size distribution of ATO. Scanning electron microscopy (SEM) and transmittance electron microscopy (TEM) were used for the observation of ATO particles and fibre surface. Electron probe was carried out to make an elemental analysis of the fibre.     

Effect of grain size on grain boundary strengthening of copper bicrystals under cyclic loading

Abstract

To clarify the strengthening effect of grain boundaries (GB), cyclic deformation behaviour of really grown [4¯79] ∥ [1¯25] copper bicrystals with different widths (4, 6, and 8 mm, denoted RB-4, RB-6, and RB-8) of com-ponent crystals and a combined copper bicrystal (denoted CB-6), obtained by sticking component single crystals G1 [4¯79] and G2 [1¯25] together, was investigated. The results showed that the cyclic saturation stresses increased in the order of bicrystals of CB-6 < RB-8 < RB-6 < RB-4. It is indicated that the GB effect caused different degrees of strengthening, which increased with the decreasing width of the RB bicrystals. By surface observation, it was found that only the primary slip system was activated in the combined bicrystal during cyclic deformation. However, an additional slip system appeared near the GB within the crystal G2 [1¯25] in the RB bicrystals (except in the primary slip system), and formed a GB affected zone (GBAZ). The width of the GBAZ was about 400 and 600 μm at plastic strain amplitudes of 0·1% and 0·2% respectively. Meanwhile, using an electron channelling contrast (ECC) technique in the SEM, the dislocation patterns near the GB and within the component crystals were observed. It was found that a two phase structure of persistent slip bands (PSBs) and matrix (or veins) can form in these bicrystals, similar to that in copper single crystals. But these PSBs cannot transfer through the GB during cyclic deformation. Based on the results above, the effect of grain size on GB strengthening of copper bicrystals was discussed.     

New method for preparing composite containing nanometre diamond particles

Abstract

Different powder mixing methods were used to prepare Al-5Cu and Cu-10Sn wt- based composites containing nanometre diamond. A new method for obtaining ultrafine Cu, Sn particles and a good distribution of nanometre diamond aggregates was developed. The nanometre diamond aggregates were well dispersed in the Cu-10Sn matrix. However, the distribution of nanometre diamond in the Al-5Cu based composite was unacceptable. Owing to the dispersion of nanometre diamond, Cu-10Sn based composite possessed higher hardness and lower bend strength than Cu-10Sn alloy.     

Dimensional change in high carbon steel wire owing to heavy reduction by tandem cold drawing

Abstract

Curious behaviour has been found in a heavily reduced high carbon steel AISI 1070. A wire of 1˙5 mm in diameter manufactured through tandem cold die drawing with total elongation of 13˙4 was subjected to heating. When it was heated above 473 K, remarkably, the length of specimen slightly increased after cooling. The ratio of increase in length was about 0˙1%. The decrease in diameter was slightly larger than the expected value to ensure the volume constancy condition owing to plastic metal working. This change in dimensions did not occur in the parent wire of 5˙5 mm in diameter, and it was concluded that this change was induced by heavy reduction by cold tandem drawing. SEM observation showed the occurrence of new isolated cementite when the heating temperature exceeded 473 K and it was assumed that it might be closely related to the mechanism through which increase in length occurs.     

Effect of post-weld heat treatment on joint properties of friction welded joint between brass and low carbon steel

Abstract

This paper describes the effect of post-weld heat treatment (PWHT) on joint properties of copper–zinc alloy (brass) and low carbon steel friction welded joints. The as-welded joint obtained 100% joint efficiency and the brass base metal fracture without cracking at the weld interface, and had no intermetallic compound layer. The joint efficiency with PWHT decreased with increasing heating temperature and its holding time, and its scatter increased with those increasing parameters. When the joint was heat treated at 823 K for 360 ks, it did not achieve 100% joint efficiency and fractured between the weld interface and the brass base metal although it had no intermetallic compound. The cracking at the peripheral portion of the weld interface was generated through PWHT. The cracking was due to the dezincification and the embrittlement of the brass side during PWHT.