The Effects of Content of Zr(NO3)4 on Formation and Characteristics of Micro-arc Oxidation Coatings Formed on ZAlSi12Cu2Mg1 Surface
The aims of this work are to prepare micro-arc oxidation coatings on the surface of ZAlSi12Cu2Mg1 aluminum alloy in Na2SiO3+NaOH+Na2EDTA electrolytes with and without Zr(NO3)4 and study their formation and characteristics. The phase constituent, surface microscopic morphology and cross-sectional morphology of the ceramic coatings were analyzed by XRD(X-ray diffraction), SEM(scanning electron microscope) and optical microscope. The thickness of the ceramic layer were measured by eddy current thickness gauge. The results show that the micro-arc oxidation films are mainly composed of mullite, α-Al2O3 and γ-Al2O3, it provides excellent adhesion with the substrate. With the content of Zr(NO3)4 in electrolyte varies from 0g/L to 1.0g/L, the thickness of the ceramic coating increases sharply at first, but afterwards reduces slowly, and the maximum of thickness up to 202μm when content of Zr(NO3)4 is 0.5g/L. The addition of Zr(NO3)4 into the base electrolyte solution is helpful in coatings formation and the coating formed in the solution containing 0.5g/L Zr(NO3)4 exhibits the best comprehensive features.
Influence of silicon on growth process of plasma electrolytic oxidation coating on Al–Si alloy
Abstract Ceramic coating was formed on the surface of Al–Si alloy via plasma electrolytic oxidation (PEO) technique. The influence of silicon on the growth process, morphology and composition of the PEO coating was investigated. It was observed that the coating was simultaneously formed on the surface of primary α phase and eutectic (α + β) in the initial stage of PEO process. No plasma discharge occurred on the surface of eutectic Si phase. But the silicon would be oxidized and mixed with Al 2 O 3 in coating melted at high temperature. The PEO coating on primary α phase was mainly composed of Al 2 O 3 . By contrast, the content of SiO 2 in coating formed on eutectic (α + β) was higher than that of Al 2 O 3 . With the time increasing, the amount of α-Al 2 O 3 in the PEO coating increased because of the transformation from γ-Al 2 O 3 to α-Al 2 O 3 at high temperature.
Effect of Aeration and Agitation Regimes on Lipase Production by Newly Isolated Rhodotorula mucilaginosa–MTCC 8737 in Stirred Tank Reactor Using Molasses as Sole Production Medium
The influence of media and process parameters (aeration and agitation) on fermentation broth rheology and biomass formation has been studied in 1.5-l stirred tank reactor for lipase production using Rhodotorula mucilaginosa MTCC 8737. Molasses, as sole production medium, is used for lipase production by varying aeration (1, 2, and 3 vvm) and agitation speeds (100, 200, and 300 rpm). Maximum lipase activity of 72 U/ml was obtained during 96 h of fermentation at 2 vvm, 200 rpm, pH 7, and 25 ± 2°C temperature. Lipase production kinetics with respect to dry cell weight of biomass showed YP/S of 25.71 U/mg, specific product formation of 10.9 U/mg DC, and YX/S 2.35 mg/mg. Maximum lipase activity (MC 2) of 56 U/ml was observed at 1% molasses, and a further increase in the molasses concentration of (%) 1.5 and 2 inhibited the product formation of lipase with 15 and 8.5 U/ml, respectively. The production kinetics of molasses media showed YP/X was 14 U/mg DC, YP/S 16 U/mg, and YX/S 1.14 mg/mg during 96 h of bioreactor operation. The kLa values for all batches (MC 1–MC 4) at 96 h of fermentation were 32, 28, 21, and 19/h, and the |oxygen transfer rate were 54.4, 56, 35.7, and 17.29 mg/l h, respectively. Increase in molasses concentration resulted in decreased lipase activity by increase in viscosity of the fermentation broth.