Effects of pretreatment on the structure and properties of electroless nickel coatings
The pretreatment process can significantly affect the corrosion resistance of electroless nickel (EN) coatings. One of the most important reasons is that different pretreatment processes can give different surface morphologies of the substrate. The scanning electron microscope (SEM) and the scanning tunneling microscope (STM) have been used to investigate the structure and properties of EN coatings in the as-plated condition for various deposition times, in relation to different mechanical/chemical pretreatment processes. The morphology of the substrate surface is found to be a key factor in control of the porosity of EN coatings. It can significantly affect the formation of EN deposits, not only in the early stage but also in the morphology/ structure during the continued growth of the deposit
A novel palladium-free surface activation process for electroless nickel deposition on micro-arc oxidation film of AZ91D Mg alloy
Abstract In this paper, a novel palladium-free and environmentally friendly surface activation process for electroless Ni plating on micro-arc oxidation (MAO) film of AZ91D Mg alloy was studied. A tight, dense and continuous structure of Ni–B/Ni–P coating was obtained on micro-arc oxidation film of AZ91D Mg alloy followed by an immersion into silver ion ink activation solution. Compared with bare AZ91D magnesium alloy, the corrosion potential of the composite coating increased by 1.2 V, while the corrosion current density decreased by two orders of magnitude. Electrochemical impedance spectroscopy (EIS) results showed that the corrosion resistance of AZ91D magnesium alloy was significantly improved by the composite coating. The MAO film as an intermediate layer could reduce the galvanic corrosion between Ni and Mg substrate in 3.5 wt.% NaCl solution. This novel method is a simple, acid-free and cost effective activation process for a replacement of Pd activation method in electroless plating Ni process.
Characterization and gene cloning of a maltotriose-forming exo-amylase from Kitasatospora sp. MK-1785
A maltotriose-forming amylase (G3Amy) from Kitasatospora sp. MK-1785 was successfully isolated from a soil sample by inhibiting typical extracellular α-amylases using a proteinaceous α-amylase inhibitor. G3Amy was purified from the MK-1785 culture supernatant and characterized. G3Amy produced maltotriose as the principal product from starch and was categorized as an exo-α-amylase. G3Amy could also transfer maltotriose to phenolic and alcoholic compounds. Therefore, G3Amy can be useful for not only maltotriose manufacture but also maltooligosaccharide-glycoside synthesis. Further, the G3Amy gene was cloned and expressed in Escherichia coli cells. Analysis of its deduced amino acid sequence revealed that G3Amy consisted of an N-terminal GH13 catalytic domain and two C-terminal repeat starch-binding domains belonging to CBM20. It is suggested that natural G3Amy was subjected to proteolysis at N-terminal region of the anterior CBM20 in the C-terminal region. As with natural G3Amy, recombinant G3Amy could produce and transfer maltotriose from starch.