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.
Mercury porosimetry: state of the art
Mercury porosimetry is used extensively for the characterization of various aspects of porous media and powders. It is difficult to make a reliable estimate, but the order of magnitude of the total number of mercury porosimeters in use is something like 2000. There are a number of other techniques which provide a similar type of information, for example vapour sorption and sorption hysteresis (including the B.E.T. isotherm), micrography and E.M. micrography, flow and diffusion of gases through porous media, socalled suction c-es, and fluid evaporation velocity. The range of application of all these techniques overlaps at least partly with that of mercury porosimetry, and more often than not, mercury porosiinetry is used in combination with some other technique. Using one of the commercially available mercury porosimeters, this technique provides one of the most simple and rapid techniques to obtain a kind of ‘fingerprint’ of a porous medium. Of course, it does not follow that the tigerprint in all its aspects truly represents the porous medium, and it is even less certain that the interpretation of the fingerprint will make any sense. As early as 1842, Smelxna [l] mentioned the posibility of forcing mercury into wood to prove its porous stxucture. But it was not