Preparation of the Sb-containing purple conversion coating on brass

A new chemical method for preparing a purple conversion coating on brass was developed. The effect of antimonous oxide concentration and temperature on color and corrosion resistance of the conversion coating, and the change of electric potential with time on coating forming process were studied. The optimum technological conditions were 10?g/L antimonous oxide, 20?g/L copper acetate, 200?mL/L hydrochloric acid at 65°C for 3?min. Results of electrochemical and dropping experiments showed that the brass with purple conversion coating presents better corrosion resistance than bare brass. The scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) results showed that the conversion coating mainly comprising copper and antimony was uniform and compact.     

Effects of environmental factors on corrosion behavior of aluminum

Aluminum, used as a material for heat exchangers in air conditioners, often has problems of leakage of refrigerant on the Al surface due to corrosion. The problems originate from pitting corrosion of the Al in an external environment. To understand corrosion problems, it is necessary to study the corrosion behavior of Al in various environments. In this study, the effects of environmental factors on the corrosion behavior of Al were studied by the surface analysis and electrochemical testing in 3.5 wt% NaCl solutions, with changes of dissolved oxygen, temperature, and concentration of Cl⁻ and S ions. Among the external environmental factors, the presence of oxygen and the increase of Cl⁻ ion concentration do not significantly affect the corrosion potential of Al, leading to an increase of only 1.1 and 6 times, respectively. There was a significant decrease in the corrosion resistance of Al, approximately 40 and 800 times, respectively, with the increase of concentration of S and temperature.     

Changes of porcine pancreas α‐amylase in activity and secondary conformations under inhibition of tea polyphenols

To investigate two‐sided functions of tea polyphenols (TP) in antinutrition and energy balance modulation, TP were extracted from Chinese green tea and used to complex porcine pancreas α‐amylase (PPA). Changes of PPA in activity and secondary conformations were analysed. Porcine pancreas α‐amylase was found sensitive to TP treatment. Tea polyphenols exhibited IC₅₀ at 0.41 mg mL^?1 against PPA and maximum inhibitory rate (98.17%) at 3.0 mg mL^?1. Tea polyphenols inhibition was concluded as noncompetitive pattern based on its unchanged Km value (0.98 mg mL^?1) for soluble starch substrate. Tea polyphenols inhibition arose from pH 1.5 to 10.14, covering gastric and intestinal environments inside body. Circular dichroism spectra analysis revealed regular changes of PPA in secondary conformations (increased proportions of α‐helix and β‐sheet) prior to its inactivation at low TP concentrations. Tea polyphenols‐inhibited PPA had distinct double‐negative peaks at 204 nm and 208 nm. Porcine pancreas α‐amylase was inactivated by TP in ways of complexation and modification of secondary conformations.     

Microstructure,microhardness and corrosion susceptibility of friction stir welded AlMgSiCu alloy

Microstructure, microhardness and corrosion susceptibility of friction stir welded joint in an AlMgSiCu alloy were investigated. It was found that the joint exhibits different corrosion susceptibility among the microstructural zones. The base material is the most susceptible to intergranular corrosion because of the presence of continuous cathodic precipitates (Si and Q phases) at grain boundaries and the precipitate free zone along the grain boundaries. The coarsening of intergranular precipitates and the precipitation of Q′ phases in the grain bodies reduce intergranular corrosion susceptibility but introduce pitting corrosion in the heat-affected zone. The significant elimination of intergranular corrosion both in nugget zone and thermo-mechanically affected zone is related to the low volume fraction of intergranular precipitate. Microhardness variations depend on the evolution of intragranular precipitates. The dissolution and/or coarsening of the strengthening precipitates result in the softening within the welded zone.     

Influence of microalloying additions on Al-Mg alloy. Part 2: Phase analysis and sensitisation behaviour

A range of alloys based on the Al-4Mg-0·4Mn system were produced with selected quaternary microalloying additions. In Part 1 of this study, the electrochemical and corrosion response was studied. To characterise the sensitisation behaviour of these alloys, where sensitisation is the major mode of degradation of 5xxx alloys, heat treatment at 150°C was carried out and followed by the Nitric Acid Mass Loss Test (NAMLT) according to ASTM G67-04. Herein the alloying elements studied include silicon, zinc, titanium, zirconium and strontium. The results indicate that strontium (Sr), silicon (Si) and titanium (Ti) have a significant influence in reducing intergranular corrosion (IGC) susceptibility.     

Electrochemical study of the corrosion of different alloys exposed to deaerated 80 °C geothermal brines containing CO2

Corrosion of metallic engineering materials accounts for problems during geothermal operation in the Upper Rhine Graben (URG). Herein, we study the electrochemical behaviour of various metal alloys in an 80 °C simulated geothermal environment by using potentiodynamic polarisation and open-circuit potential measurements. Two different natural geothermal waters from URG geothermal sites were used for the experiments. The measurements reveal spontaneous passivation to be a key process for all alloys. This ennoblement protects more noble alloys from significant corrosion (e.g. titanium gr. 2, alloy 625) and brings less noble alloys to failure, mostly due to pitting corrosion (e.g. 316L).