Characteristics of nickel sulphide reduction in Ni2+ free background and Watts nickel plating electrolytes

Abstract

The electrochemical behaviour and composition of nickel sulphide coatings deposited on glassy carbon (GC) electrode by the successive ionic layer adsorption and reaction (SILAR) method using a nickel(II) ammonia complex and Na₂S solutions have been studied in Ni²⁺ free background, Watts nickel plating and 0·05 M H₂SO₄ electrolytes by the cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) methods. Analysis of XPS data suggests that the coating is a mixture of two sulphides where NiS dominates. In the Ni²⁺ free background solution at first the electrochemical reduction of the sulphur rich nickel sulphide to NiS occurs. After that the NiS to metallic Ni is reduced in the potential range of H₂ evolution. During the cathodic reduction of the coating in Watts nickel plating electrolyte the sulphur is reduced in the potential range from 0·0 to ?0·4 V, while at the potential values <?0·5 V the sulphur rich nickel sulphide and NiS reduction in the H₂ evolution range and Ni plating occur.     

A study of zinc phosphate coatings on 12·5Cr–21·0Ni stainless steel

Abstract

12·5Cr–21·0Ni stainless steel was chemically treated with zinc phosphate in order to find the most suitable phosphate solution and its operating parameters. The phosphate coatings were tested for their corrosion protection of stainless steel using three methods: the salt spray test, the humidity cabinet test and the brine immersion test. The phosphate coatings were also mechanically tested using a tensile test for determining their mechanical properties. Results clearly show that phosphate coatings with a uniform appearance and full coverage can give high corrosion protection to 12·5Cr–21·0Ni stainless steel by forming a physical barrier against the corrosive environment. The 12·5Cr–21·0Ni stainless steel after coating with zinc phosphate still retains reliable mechanical properties, thereby providing valuable applications in the engineering field.     

Gold soldering in microelectronic products with tin–indium solder

Abstract

The results of research into the interaction of 0.04 mm diameter gold microwire with STI50 solder have been presented when soldering hybrid integrated circuits and microassemblies on printed boards. The dependence of dissolving of gold wire on the temperature and duration of soldering has been established as well as on holding time at a seam temperature of 100 ° C; the interaction of STI50 solder with gold coating on UHF and HIC boards has been considered when soldering on metallic substrates.     

Evaluation,degradation and life assessment of coatings for land based combustion turbines

Abstract

Use of metallic and thermal barrier coatings to protect hot section blades and vanes of combustion turbines for power generation has been common practice for the past three and one decades respectively. Because these coatings must be optimised with respect to both different forms of corrosion and modes of operation (base load versus peak load), their performance may be machine specific. Industrial end users generally do not have detailed knowledge of the failure mechanisms of the coatings and the basis for selecting coatings to suit specific requirements, topics the present review seeks to address. The evolution of protective coatings, coating failure mechanisms and a methodology for selecting machine specific coatings are described. The methodology, which can be used to rank and optimise coating systems and to predict the remaining life of coatings, forms the basis of a computer code known as COATLIFE. The ingredients of this methodology, i.e. degradation modelling and thermomechanical fatigue life prediction, are reviewed.     

Improved approach for predicting weld creep strength factors of ferritic steels

Abstract

The cross-weld (CW) creep strength of ferritic steels is typically lower than that for parent metal (PM), and in the past the ratio of CW to PM creep strength (weld strength factor – WSF) was assumed to be limited to ～80%. For newer Cr steels WSF can be significantly lower for a typical design life of 100 000 h or more. The possibility of low WSF is also accommodated in the current design codes such as EN 13445, but no suggested WSF values are given for guidance. Assuming a too high WSF for such welds obviously results in an unsafe (too long) predicted creep life. Unfortunately, as a further complication the WSF of the newer Cr steels can decrease when the operating temperatures are increased for improved efficiency of future power plants. It is hence important that reliable and sufficiently high values of WSF can be guaranteed. However, there is often much less extensive data on the creep strength of welds than on parent steel, and also the extrapolation to long term values of WSF can add more relative uncertainty than what is expected in extrapolating the long term creep strength of parent steel. Here an improved approach is proposed to predict WSF using the Wilshire creep model to obtain the relationship between the CW creep strength and the corresponding parent material (PM) strength. The Wilshire model directly provides the WSF value for each CW data point, when the expected normalised stress is based on the CW time to rupture at stress and temperature. The corresponding master curve parameters are those for PM, when the PM hot tensile strength is also known. The WSF data points for each CW test can then be fitted for temperature and stress dependence. This approach avoids fitting distortion in WSF, unlike the traditional assessment where a master curve is first obtained for the CW creep strength. As an example, WSF of welded P91 steel at 100 000 h is here predicted in the temperature range of 550–650°C.     

Corrosion resistance of Ni/Al2O3 coatings in NaCl solution

Abstract

This paper presents results of a research on the corrosion resistance of composite Ni/Al₂O₃ coatings electrochemically deposited from Watts baths containing different amounts (0, 20, 100 g dm^?3) of Al₂O₃ particles. Potentiodynamic tests and electrochemical impedance spectroscopy (EIS) measurements were carried out in a 3% solution of NaCl. The coatings with about 6 wt-% of corundum, deposited from a bath with 100 g dm^?3 of a powder, showed the best protective properties. The rate of corrosion of such coatings after 7 days of exposure in the NaCl solution was over two times slower than that of coatings containing 2 wt-% of Al₂O₃ and six times slower than that of a standard nickel coating. Two equivalent circuits: one consisting of two RC circuits and the other one made up of three RC circuits were used for the analysis of the impedance spectra. Regardless of the presence and amount of the Al₂O₃ particles in the nickel coating, during first day of exposure in the NaCl solution a layer of nickel oxides and hydroxides forms on the surface of the coatings increasing their corrosion resistance. In the case of coatings with 6 wt-% of Al₂O₃, the passive layer is least vulnerable to the aggressive action of Cl^? ions.     

Management Issues of a Mobile Agent-Based Service Environment

This paper introduces the concepts of a servicemanagement system for mobile agent-based services. Incontrast to several other approaches in whichagent-based applications are used to handletraditional network or service managementaspects, this paper describes a way to manage thedistributed agent environment itself. The proposedapproach was designed and developed by using OSI SystemsManagement concepts as a starting point, which are modified andadjusted in order to fulfill the new requirementsassociated with the mobile agent paradigm. However, thispaper does not cover integration or co-existence of the introduced agent management system (AMS)and traditional OSI management systems. Instead, theentire AMS environment is based on mobile agenttechnology. At present, this approach is validated inthe context of the European research project MobileAgent Environments in Intelligent Networks(MARINE).     

Influence of Yttrium on the Oxidation of Pure Iron at 973 K; Comparison Between Ion Implantation and Sol-Gel Coatings

The influence of yttrium introduced by ionimplantation or by sol-gel coatings on the oxidation ofpure iron has been studied at 973 K underp(O₂) = 0.04 Pa. The oxide scales wereexamined using a wide range of analytical techniques. The addition ofyttrium by ion implantation or by sol-gel coatingssignificantly improved the oxidation resistance of pureiron. This effect depends upon the introduction mode of yttrium on the surface.     

Study on Design Techniques of a Long Life Hot Forging Die with Multi-Materials

A new design technique for the long life hot forging die has been proposed. By finite element analysis, the reason for the failure of hot forging die was analyzed and it was concluded that thermal stress is the main reason for the failure of hot forging die. Based on this conclusion, the whole hot forging die was divided into the substrate part and the heat-resistant part according to the thermal stress distribution. Moreover, the heat-resistant part was further subdivided into more zones and the material of each zone was reasonably selected to ensure that the hot forging die can work in an elastic state. When compared with the existing techniques, this design can greatly increase the service life because the use of multi-materials can alleviate the thermal stress in hot forging die.     

Effects of different metals on adhesive wear behaviour of alloy surface produced by TIG process

Abstract

Low carbon steel surfaces were alloyed with composite powders using the tungsten inert gas welding method. After the alloying process, the effects of cladding surface on the microstructural characteristics and adhesive wear of the alloyed samples were examined. The sliding wear behavior of samples was investigated in a block on ring apparatus under the loads of 20, 40, 60 and 80 N respectively. In the experimental investigation, a low carbon steel surface was alloyed with austenitic stainless steel powder and austenitic stainless steel powder mixed with 4·5% Co, Mo and Ti particles respectively. Following surface alloying, conventional characterisation techniques, such as optical microscopy, scanning electron microscopy, energy dispersive spectrograph and X-ray diffraction, were used to study the microstructure of the alloyed zone. Examination of the microstructure revealed the presence of M₂₃C₆ carbides, solid melt phases and intermetallic phases, such as Ni₃Ti, depending on the alloying element in the composite. As the amount of the reinforcing material increased, the saturation rates for the samples decreased, while their hardness increased. The adhesive abrasion tests conducted revealed that temperature input plays a significant role on the microstructure characteristics, which positively affected the adhesive abrasion values of the samples. Consequently, the tungsten inert gas welding method was successfully used for the surface alloying of low carbon steels.