Mechanism of Activation of Polymer Surfaces by Mixed Stannous Chloride/Palladium Chloride Catalysts

Mixed stannous chloride/palladium chloride catalysts are often used to activate etched ABS surfaces prior to electroless nickel or copper deposition. Little is known of the nature or activation mechanism of the catalyst. The nature of the catalyst was investigated using nephelometry and electron diffraction. No evidence for the existence of colloidal metallic palladium was found. The active component of the catalyst is thought to be a complex chloride of tin (II) and palladium (II). The major species present on the ABS surface at each step of the pretreatment cycle were identified using electron diffraction. A mechanism of activation was proposed involving hydrolysis of an adsorbed chloride complex within the ABS surface. On subsequent treatment with ammonium bifluoride accelerator, a surface redox reaction is presumed to occur between the hydrolised species forming active palladium nuclei: Sn (II) + Pd (II) = Sn(IV) + Pd (0). The process variables were also investigated. It was found that immersion times in all pretreatment solutions including rinses had a direct influence on induction period.     

Plasticity induced transformation in a metastable β Ti-1023 alloy by controlled heat treatments

Abstract

Investigations into the possibility of improving the strength–ductility relation in a metastable β-titanium alloy (Ti–10V–2Fe–3Al) through plasticity induced transformation (PiTTi) have been carried out. Various heat treatments in the β and/or α+β condition were performed to study their influence on both the microstructure and solute partitioning, which eventually control the PiTTi effect. Stress induced martensite formation promoting such effect has been observed upon compression testing for β and β+(α+β) microstructures. The stress–strain curves exhibiting stress induced martensite show a ～20% increase in strength, while still retaining a reasonable ductility level. Microstructural parameters such as grain size and solute concentration (especially V) in β have been related to the alloy's ability to exhibit PiTTi.     

Examination of HA230 turbine transition duct

Abstract

The present paper reports the results of an examination of a service run transition duct from one of Siemens' industrial gas turbines and the correlation between the findings for this, and those from the studies undertaken on laboratory exposed Haynes alloy 230 material. The studies have shown that there are changes in the microstructure and hardness of the material that can be related to temperature and time of exposure, and the information gained can lead to estimations of the average component operating temperature. Metallographic studies revealed a high level of heterogeneity of the grains in this transition duct.     

Interfacial reaction mode and its influence on tensile strength in laser joining Al alloy to Ti alloy

Abstract

In order to obtain a robust dissimilar joint of Al/Ti alloys, a filler wire of Al–12 wt-%Si and 45° V shape groove on the base metal were used during CO₂ laser welding. Heat input had evident influence on the interfacial reaction mode. It was found that a dissolution mode for low heat input and a melting mode for high heat input exist at the joint interface, which was analysed from thermodynamic point of view. Tensile strength of the joints in the dissolution mode reached as high as 296 MPa, which was significantly higher than that in the melting mode.     

Synthesis of hydrophobic aerogels for transparent window insulation applications

Abstract

The present paper deals with the synthesis of hydrophobic aerogels using methyltrimethoxysilane (MTMS) as a hydrophobic agent for transparent window insulation applications. The molar ratio of methanol (solvent), water, and ammonia (catalyst) to the tetramethoxysilane (precursor) MeOH/H₂O/NH₄OH/TMOS was fixed at 12/4&/3·6×10^-3/1 throughout the experiments and the MTMS/TMOS molar ratio M was varied from 0 to 1·55. After gelation, the alcogels were dried supercritically using the high temperature alcohol method. It has been found that lower (<0·26) M values resulted in highly transparent (optical transmission >90% for a 10 mm thick sample at 800 mm wavelength) and negligible volume shrinkage (<2%) but less hydrophobic aerogels whereas higher (>1·03) M values resulted in semitransparent (<20% optical transmission of 800 nm for a 1 cm thick sample) aerogels with >10% volume shrinkage but excellent hydrophobicity. A good compromise of acceptable optical transmittance (～85% optical transmission at 800 nm for a 1 cm thick sample), hydrophobicity with 42 kg m^-3 bulk density, and negligible volume shrinkage were obtained at M≈0·70. Hydrophobicity of the aerogels was tested by measuring the contact angle between a water droplet and the aerogel surface. The aerogels were characterised by infrared spectroscopy, bulk density, optical transmittance, and thermal conductivity measurements.     

Effect of powder size on microstructure and mechanical properties of Ti(C,N) based cermets

Abstract

Effect of the particle size of TiC and TiN on the microstructure and mechanical properties of Ti(C,N) based cermets has been evaluated. Ti(C,N)–WC–Co cermets made from four groups of mixed raw powders of different sizes were manufactured by vacuum sintering. The microstructure and composition were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDX). The result shows that the four samples have the typical microstructures of 'black core/grey rim'. The mechanical properties of the cermet manufactured from submicron TiC and nano TiN are the best among the four samples.     

Stress corrosion cracking behaviour of 2091 Al—Li alloy in sulphate and chloride containing solutions

Abstract

The stress corrosion cracking resistance of 2091 Al—Li alloy in underaged, and in peak aged condition was investigated in chloride solutions with or without sulphate addition using both the static load technique and the slow strain rate technique. It is shown that the underaged material is more resistant than peak aged material. Sulphate additions to chloride solutions increase the stress corrosion cracking susceptibility. Metallographic cross-section observations show the simultaneous occurrence of other kinds of corrosion: generalised. corrosion, pitting corrosion, intergranular corrosion, and exfoliation corrosion. It appears that stress corrosion cracking susceptibility increases as the extent of intergranular corrosion decreases.     

Investigation of microstructure,surface and subsurface characteristics in titanium alloy friction stir welds of varied thicknesses

Abstract

Friction stir welding of titanium alloy (Ti–6Al–4V) was demonstrated on 3, 6, 9 and 12 mm thickness square groove butt joints. Complete microstructural and microhardness evaluations were conducted in addition to surface and subsurface examinations for each case. The 3 mm welds exhibited an extremely fine grained microstructure with evidence of processing temperatures below the beta transus temperature of the alloy. The 6, 9 and 12 mm samples possessed larger grains formed by a slower cooling rate from above the beta transus temperatures. The thick section weld exhibited a nearly uniform microhardness, while the thinner welds showed a slight, 6%, increase in hardness compared with the parent material.     

Risk assessment in pressure equipment inspection: review of recent applications in Jiangsu

Abstract

The application of risk based inspection (RBI) technology in five typical cases in Jiangsu Province, China was summarised and reviewed. Based on 10 year experiences of risk assessment, some key problems, which require special attention in the process of publicising and applying RBI technology in China, were put forward, and the integrity management of pressurised equipment and the qualification requirement for organisation undertaking the RBI projects were emphasised as well. Responses to RBI demands from Chinese petrochemical enterprises were analysed and recommended to be categorised into three groups. To conduct RBI successfully in China, the importance of combining a first rank RBI software and a well organised RBI team is proposed. A sinicised database of materials and chemicals owing to Chinese intellectual property is suggested to be built gradually as well.     

Gas tungsten arc welding of titanium using flux cored wire with magnesium fluoride

Abstract

Grade 2 Ti–CP was gas tungsten arc welded using flux cored (FC) wires and flux pastes that contained various MgF₂ contents. The effects of MgF₂ on bead morphology, chemical composition and hardness of weld bead were investigated and interpreted. With an increase of MgF₂ content in the flux paste, depth/width ratio of weld bead increased gradually with little variation in interstitial element contents and hardness. Weld bead made with cold FC wire feed showed even deeper and narrower bead, indicating the greater effectiveness of wire feed than flux paste on weld penetration. While the 50% MgF₂ FC wire produced complete slag coverage and smooth weld bead surface, 85% MgF₂ wire resulted in incomplete slag coverage and rough weld surface. Arc spectroscopy revealed that the 50% MgF₂ FC wire produced plasma spectrum with atomic and ionised titanium peaks, which is an indication of a high temperature arc and a larger amount of flux vapours in the arc. Therefore, it is believed that deep weld penetration associated with high MgF₂ fluxes in this experiment is caused by arc constriction, resulting from the greater amount of flux vapours owing to high arc temperature.