ABSTRACT
This study evaluated the effect of solvent acids on the structure and corrosion resistance performance of chitosan (CS) film on MAO-treated AZ31B magnesium (Mg) alloy. Initially, CS solutions were prepared in four solvent acids: acetic acid (HAc), lactic acid (LA), hydrochloric acid (HCl), and citric acid (CA). The CS films were subsequently deposited on MAO-treated AZ31B Mg alloy via a dip-coating technique. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FT-IR), contact angle measurement, and atomic force microscopy (AFM) were employed to characterize the surface and cross-sectional morphology as well as chemical composition. Furthermore, the samples were subjected to potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests to assess their resistance against corrosion in simulated body fluid (SBF). These results indicated that the CS film prepared with LA exhibited the lowest surface roughness (Ra = 31.2 nm), the largest contact angle (CA = 98.50°), and the thickest coating (36 µm). Additionally, it demonstrated superior corrosion protection performance, with the lowest corrosion current density (Icorr = 3.343 × 10-7 A/cm2), highest corrosion potential (Ecorr = -1.49 V), and highest polarization resistance (Rp = 5.914 × 104 Ω·cm2) in SBF. These results indicated that solvent acid types significantly influenced their interactions with CS. Thus, the structure and corrosion protection performance of CS films can be optimized by selecting an appropriate solvent acid.
Subject(s)
Alloys , Chitosan , Solvents , Chitosan/chemistry , Corrosion , Alloys/chemistry , Solvents/chemistry , Magnesium/chemistry , Spectroscopy, Fourier Transform Infrared , Acids/chemistry , Surface Properties , X-Ray DiffractionABSTRACT
In this work, the propagation of CH4/air deflagration flames in three semi-confined ducts with different obstacles was numerically investigated using large eddy simulation (LES). The shape of the premixed flame, flow field structure, and overpressure characteristics of the interaction between the flame and the obstacle are simulated accurately in three ducts with obstacles of different heights. The results show that the structure of the flame is changed by the presence of obstacles, and a change in the shape of the hemispherical conical brush appears, and a flame vortex is generated by the entrapment of unburned premixed gas on the left side of the obstacles. In the process of CH4/air deflagration, the existence of obstacles would lead to the change in combustion velocity and overpressure relief velocity and then have a certain influence on the peak of overpressure and the shape of the premixed flame.
ABSTRACT
In this work, the influence of different N2/CO2 contents (up to 60% in fuel volume) on combustion features of laminar-premixed CO/CH4/H2 flame with various equivalence ratios (0.6-1.6) at standard conditions was numerically calculated using ANSYS CHEMKIN-PRO with the GRI-Mech 3.0 mechanism. The mole fraction profiles of the major species and the rate of production of dominant elementary reactions in the flames of CO/CH4/H2/N2/CO2/air were obtained. The effect of inert gas addition on the formation of NO X , H, O, and OH was analyzed, and the sensitivity coefficient of the active radical mole fraction was obtained. The results suggest that the addition of inert gas of the fuel mixture with various equivalence ratios reduces laminar burning velocity and adiabatic temperature, which have always had a good positive correlation and the maximum peak point shifted left. CO2 has obvious inhibitory effect on the formation of NO by reducing the amount of O radicals and obstructing the conduct of the reaction of NNH + O â NH + NO, but it promotes the formation of NO2 mainly through the reaction HO2 + NO â NO2 + OH. The reactions H + O2 + H2O â HO2 + H2O, H + O2 â O + OH, and OH + CO â H + CO2 are three very important reactions for the molar fractions of H, O, and OH that decrease significantly with an increase of inert gas concentration.