Lithium nitrate salt-assisted CO2 absorption for the formation of corrosion barrier layer on AZ91D magnesium alloy.

Mg alloy corrosion susceptibility is a major issue that limits its wide industrial application in transport, energy and medical sectors. A corrosion-resistant layer containing crystalline MgCO3 was formed on the surface of AZ91D Mg alloy by Li salt loading and thermal CO2 treatment. Compared to the uncoated AZ91D surface, the surface layer exhibited up to a ∼15-fold increase in corrosion resistance according to the electrochemical results in 3.5 wt% NaCl solution and ∼32% decrease in wear rate compared to untreated AZ91D. The improved corrosion resistance is attributed to the formation of a <10 µm thick dense layer containing Mg, O, C and Li with crystalline MgCO3 phases. The initial step was to form a porous MgO layer on the surface of AZ91D Mg alloy, followed by loading an alkali metal salt (i.e., LiNO3) onto the MgO surface. The porous MgO surface was then reconstructed into a dense insulation layer containing Mg carbonate through CO2 absorption facilitated by molten Li salt during thermal CO2 treatment at 350 °C. As a potential method to utilize excessive CO2 for beneficial outcomes, the formation of the carbonate-containing film introduced in this study opens a new pathway for protecting various existing Mg alloys for diverse industrial applications.

Charging of radioactive and environmental airborne particles.

The charging of various airborne particles was investigated using single-particle levitation and charge-balance equations. Though radioactive decay and triboelectrification can induce charging, it is typically assumed that the aerosols in a radioactive plume will not carry significant charge at steady state since atmospheric particles can have their charge neutralized through the capture of adjacent counter-ions (i.e., diffusion charging). To assess this assumption, we directly measured the surface charge and charge density of various triboelectrically charged aerosols including radioactive uranium oxide (<1 µm), urban dust, Arizona desert dust, hydrophilic and hydrophobic silica nanoparticles, and graphene oxide powders using an electric field-assisted particle levitator in air. Of these particles, uranium oxide aerosols exhibited the highest surface charge density. Charge balance equations were employed to predict the average charge gained from radioactive decay as a function of time and to evaluate the effects of diffusion charging on triboelectrically charged radioactive and non-radioactive particles in the atmosphere. Simulation results show that particles, initially charged through triboelectrification, can be quickly discharged by diffusion charging in the absence of radioactive decay. Nevertheless, simulation results also indicate that particles can be strongly charged when they carry radionuclides. These experimental and simulation results suggest that radioactive decay can induce strong particle charging that may potentially affect atmospheric transport of airborne radionuclides.