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.
Porosity in plasma electrolytic oxide coatings
Abstract Plasma electrolytic oxide coatings are generally assumed to be almost fully dense. However, evidence is presented here for the presence of sub-micrometre, surface-connected porosity in such coatings, on aluminium alloys, at levels of the order of 20%. This evidence comes from densitometry, mercury porosimetry, helium pycnometry, BET adsorption measurements and high-resolution scanning electron microscopy. The very fine scale of the porosity (pore diameter ∼10 to 100 nm), coupled with severe difficulties in making unambiguous microstructural observations, may account for the failure to detect this feature previously. It is pointed out that various measured properties, such as Young’s modulus and thermal conductivity, are consistent with the presence of these relatively high porosity levels. Various other observed characteristics can also be explained on this basis. Finally, a possible mechanistic origin for the porosity is proposed.
Electrophysiological Studies of Penticainide (CM 7857), a New Antiarrhythmic Agent, in Mammalian Myocardium
The intracellular electrophysiologic properties of a new antiarrhythmic substance, penticainide, were studied in isolated rabbit, dog, and guinea pig myocardial preparations superfused or perfused with oxygenated Tyrode's solution. “Therapeutic” concentrations of penticainide (1.5 to 3 x 10-5 M) had little effect on sinus node automaticity; sinoatrial conduction was slightly delayed. In atrial, Purkinje and ventricular fibers, amplitude, and maximal rate of rise of phase 0 (dV/dtmax) were decreased by penticainide; Purkinje-ventricle conduction velocity was depressed. Penticainide did not significantly modify action potential duration (APD) of rabbit atria and dog ventricle and reduced APD and effective refractory period (ERP) of dog Purkinje and guinea pig ventricular fibers. Penticainide reduced APD heterogeneity of Purkinje-ventricle junction with a preferential effect at the gate and decreased tension amplitude of perfused papillary muscle in dog heart. The effect of penticainide on dV/dtmax was voltage and rate dependent; the resting block was weak. Thus, penticainide is a class 1 antiarrhythmic agent with properties of class 1B agents such as APD reduction and properties of class 1C agents such as slow recovery kinetic of rate-dependent block.