Defect and Diffusion Forum Vol. 416

Abstract: Current aspects of the developing of modern self-shielding flux-cored wires composition for arc welding of low-alloyed steels are considered. Advantages and disadvantages of flux-cored wires of carbonate-fluorite, oxide and oxide-fluoride types of are shown in comparison. The effectiveness of gas shielding of molten metal at welding with self-shielding flux-cored wires of carbonate-fluorite type is analyzed considering the thermal properties of their cores. It is shown that to improve reliability of gas shielding at welding using the wires of this type it is important not only to ensure generation of sufficiently large volume of shielding gases at thermal destruction of the wire core, but also to control this process, providing gas evolution at all stages of heating and melting of the wire. The results of complex thermal analysis of the wire core mixtures containing, for example, lithium carbonate show substantially large heat losses for heating and melting of the wire core, which are accompanied by the development of energy-intensive processes of thermal destruction of core components. It is shown that the limitation of lithium carbonate content in the wire at the level of not more than 2 wt. % allows not only to preserve welding arc burning stability at the acceptable level but also to provide effective gas shielding of molten metal and easy separation of slag crust. The control of thermochemical reactions in the core is achieved by selection of its proper composition to ensure favorable melting of flux-cored wire and electrode metal transfer to the welding pool. Results of metallographic examinations of distribution and composition of non-metallic inclusions in metal of the welds made with wires of the oxide and oxide-fluoride types are presented. Main properties of the developed self-shielding flux-cored wires and recommendations on welding are given in conjunction with prospective fields of their application.

Abstract: The process of wire electrical discharge machining (WEDM) of welded joints applied to stainless steel parts has raised important questions due to the effects on the machined surface and even the deep substrates. The paper proposes the possibility of improving working conditions by multiple activation of the effective processing space. The experimental research was performed under the conditions of simultaneous activation, both ultrasonic of the wire electrode and by magnetic activation of the dielectric liquid. The selection of the optimal parameters of magnetic activation was made using an experimental statistical modeling method, with a statistical analysis of the objective functions, using specialized software. The additional introduction of ultrasonic energy into the workspace has led to the rapid refresh of the dielectric fluid and the accelerated evacuation of eroded particles.

Abstract: Electronic components soldered with tin base alloys are subject to whiskers formations after an operation period, which produced failures by short circuits. The main factors which determine formation of whiskers are soldering alloy characteristics, substrate alloys which is placed on the surface of the PCB boards and not the least the working environment. Soldering alloy has a major influence on germination and growing whiskers process, by its nature and grain form, dimensions and orientation. Given the preliminary research carried out to diminish the formation of these defects, was proposed to realize these soldered joints using new soldering alloys obtained by melt-spinning method, which have a nanocrystalline, quasi-crystalline or even amorphous structure. In this paper are presented some results obtained on following the influence of soldering alloy structure over whiskers germination and growing process, by simulating the operation conditions according to applicable standards. Were obtained soldered joints on copper plates using a commercial soldering alloy as well as soldering alloys base on Sn-Cu-Ga, Sn-Cu-Ni, Sn-Cu-CO families, obtained by melt-spinning method. Soldering was performed using a soldering iron and after this process, the soldered joints were placed in an incubator under controlled temperature and humidity conditions. Performing SEM analyzes on soldered joints subject to the above treatment, was observed that formation and growing of whiskers diminished with decrease of the grain size.

Abstract: Resistance spot welding has significant role in the joining technologies of automotive industry. In the recent period there were some rival technologies, but resistance spot welding remains important. This has numerous reasons however mass production is one of the main motivations. The applied base materials both steel and aluminium develop rapidly. The dual-phase (DP) steels with different strength are typical in the automotive chassis, and the high strength aluminium alloys also continuously spread. These special material combinations mean new challenges for joining technologies, sometimes hybrid aluminium - steel joints should be prepared. In this paper hybrid joints between DP800 steel and 5754-H22/6082-T6 sheets were prepared. The microstructural and strength properties of the joints were investigated and compared. An intermetallic compound was formed between the dissimilar sheets during welding which is basically determine the joint properties.

Abstract: The paper presents some general aspects of adhesives used in the automotive industry, the method used to determine mechanical properties, and the advantages compared to the traditional technology used. Adhesives are substances capable of permanently bonding to surfaces by an adhesive process. This process implies that two different bodies are in contact so that the mechanical forces or work can be transferred across the interface region. Since their discovery, researchers have made great efforts to obtain more ecological and high-performance adhesives. Substances such as bitumen or beeswax have been replaced by synthetic types of adhesives. Today, adhesives have two purposes: to join two different bodies, in creating a permanent assembly, and to seal. In this paper, the type of adhesive used to fix the windshield directly to the car body which is made of metal is presented. Compared to traditional technology that involves a rubber gasket attached to the body of the car and the windshield that is fixed on it, adhesives have the role of sealing and bonding directly to the metal surface. The first part of the paper focuses on the determination of the mechanical properties of adhesives used in the automotive industry. The next step was to realize the bonding between glass and steel using windshield adhesive with different drying times.

Abstract: Future EU policies on the dynamics of the food industry impose increasingly stringent hygiene principles. The principles of hygienic design are becoming more and more extensive, with the chapter on hygienic welding occupying a priority position. Surfaces that come into contact with food must be free of imperfections. In order to achieve these goals, research is being undertaken aimed at the continuous improvement of manufacturing technologies. This paper covers some aspects of a critical analysis of welded joints in stainless steel pipes used in the food industry. Some correlations of surface imperfections from the interior areas of the pipes jointed, with a big level of contamination, based on sanitation tests and visual analyses are presented. The conclusions contain some express technological recommendations for the designers of manufacturing and maintenance technologies, especially for welding specialists.

Abstract: A new biopolymer based on chitosan and k-carrageenan with the addition of mesoporous phosphoric acid (mPTA) filler was used as an electrolyte membrane for Direct Methanol Fuel Cell (DMFC) applications. Electrolyte membranes of pure solution of chitosan, k-carrageenan, and various compositions of chitosan/k-carrageenan (Cs/k-Car) (80/40, 90/30, 100/20 mL) were carried out to determine the composition of chitosan/k-carrageenan optimal. The optimum chitosan/k-carrageenan membrane is Cs/k-Car 80/40 which has a tensile strength of 22.00 MPa and a methanol permeability of 14.33 x 10^-6 cm²/s. Membrane Cs/k-Car 80/40 was then added with variations of mesoporous phosphotungstic acid (mPTA) filler (0.05, 0.1, 0.15, 0.2 and 0.25 %) to determine the optimum membrane electrolyte. The chitosan/k-carrageenan/mPTA 0,2% (Cs/k-Car/mPTA 0.2%) electrolyte membrane is the most optimum electrolyte membrane which has a proton conductivity of 12 x 10^-3 S/cm and a methanol permeability of 7.64 x 10^-6 cm²/s so it is expected to be the most suitable electrolyte membrane for DMFC application. Key words : Electrolyte membrane, chitosan, k-carrageenan, mesoporous phosphoric acid (mPTA), DMFC

Abstract: This work aims to prepare BiOI films via simple heating of BiI₃ materials and study their characters from structural, optical, and morphology perspectives. In the heating process, we varied the heating treatment time. In addition, the solar cell performance of prepared BiOI films was tested. In BiOI preparation, we deposited BiI₃ films first onto FTO substrates via BiI₃ heating in the air using a closed chamber at the temperature of 360 °C for 30, 45, and 120 minutes. The deposited BiI₃ films were then rinsed with water/ethanol and re-heated at 350 °C for 30 minutes. As a result, by increasing the heating treatment time, it could form thicker BiOI films. All the resulting films confirmed the BiOI characters. A longer BiI₃ heating time could direct the growth of BiOI crystal, wavelength red-shift, and flake structure. In the electrochemical solar cell study, it was known that BiOI films had a lower performance compared to the reported results. After a certain thickness (~1.3 μm), the device's open-circuit voltage and current decreased.

Abstract: In this study, chitosan (Chi), alginate (Alg), and mesoporous phosphotungstic acid (mPTA) were used as electrolyte membrane materials for DMFC. Chi and Alg will be crosslinked with mPTA filler to improve the performance of the electrolyte membrane. Characterizations carried out include tensile tests, methanol permeability, and proton conductivity. The results of the tensile test showed that the Chi-Alg(3:1) membrane had a higher tensile strength value (26.64 N/mm²) than the pure chitosan membrane (11.97 N/mm²). The results of methanol permeability show that the Chi-Alg(3:1)/mPTA(2.0%) membrane has a lower methanol permeability value (8.17 × 10^-6 cm² s^-1) and a relatively high proton conductivity value, (45.8 × 10^-3 S cm^-1). Chi-Alg/mPTA membrane, simplicity of the used simple preparation method and the cost reduction can be applied as an electrolyte membrane for DMFC.

Abstract: Chitosan (CS) was successfully extracted from the shrimp shell of Litopenaeus vanamei and used as a biopolymer for the fuel cells. The composite membranes containing chitosan blended poly ether-ether ketone (PEEK) and graphene oxide (GO) as filler were fabricated using solvent evaporation method and its physicochemical studies were also investigated. The sulfonation degree of sulfonated poly ether-ether ketone (SPEEK) was 60.61%. Among the fabricated membranes, the CS/SPEEK/SGO membrane was the best membrane to achieve high ion exchange capacity (IEC) which is 5.94 mmol.g^-1. Moreover, its methanol uptake and permeability were 6.21% and 6.34×10^-6 cm².s^-1, respectively. The highest water uptake was also obtained by CS/SPEEK/SGO membrane which is 61.54% followed by other membranes CS/SGO, CS/GO, CS/SPEEK, CS/SPEEK/GO, and CS. In a comparison, the lowest water uptake was obtained by pristine CS membrane which is 52.17%.