Design of an experimental case on material corrosion and protection
[Objective]In response to the teaching needs of students in the field of materials,an experimental teaching case of"enhancing the protective performance of the rust layer on weathering steels(WSs)through rare-earth(RE)alloying"was designed.The experiment aimed to improve the corrosion resistance of WSs in a marine atmospheric environment.The complete experimental process can strengthen students'research abilities and innovative thinking.[Methods]In this experiment,the corrosion resistance and mechanisms of RE WSs were studied using electrochemical and physical methods.Rusty WS samples were obtained through atmospheric exposure corrosion and laboratory accelerated corrosion simulation tests.Atmospheric corrosion tests were performed in Qingdao,a tropical coastal zone with high humidity,high Cl-1 concentration,and low industrial pollution.The accelerated corrosion test was performed using an LRHS-270-RY salt spray corrosion test chamber.The size of specimens was 50 mm×50 mm×3 mm.One test cycle was 60 min,i.e.,a 15 min spray stage and a 45 min drying stage,and the corrosion test times were 24,48,96,144,and 192 h.The phase composition of the corrosion products generated on all samples was characterized by X-ray diffraction(D/Max2500PC),and the surface morphology of the corrosion products was observed by scanning electron microscopy(Apreo S HiVac)equipped with an energy dispersive spectrometer.The electrochemical corrosion behavior of the RE WSs was studied and analyzed using a PARSTAT2273 electrochemical workstation using a conventional three-electrode system,with the WS samples as the working electrode,the saturated calomel electrode as the reference electrode,and the counter electrode as the platinum plate.The rusty samples of 10 mm×10 mm×2 mm were subjected to encapsulation treatment with acrylic resin to leave a working surface with an area of 1 cm2.The test solution was 3.5wt.%NaCl.[Results]The experimental results show that in a corrosive medium containing Cl-,significant pitting corrosion occurs on the surface of WSs during the initial stage of corrosion.The pitting pits on the surface of RE WSs are small,regular,and uniformly distributed,which is beneficial for inducing uniform corrosion on the steel surface and forming a dense rust layer in the later stage of corrosion.The RE elements in steels promote the generation of stable rust products such as α-FeOOH and the enrichment of copper in the rust layer.The addition of REs increases the corrosion potential and anodic polarization effect of the rusty WS samples during the electrochemical corrosion process.[Conclusions]REs can promote the formation of a dense,uniform,and stable rust layer on the surface of WS and improve its corrosion resistance.This experimental teaching case focuses on"Problem posing-Material preparation-Corrosion behavior analysis-Corrosion resistance evaluation,"covering multiple knowledge points such as alloy composition design,electrochemical corrosion mechanism,characterization technology,and electrochemical analysis.The experiment is conducive to the systematization and integration of professional knowledge and has a positive promoting effect on cultivating students'innovative awareness and research ability.
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