Corrosion Degradation Of Tinplate/Coating System Under Different Temperature And Deformation

Tinplate is important raw material of seal pot for food and beverage.Different levels of corrosion is inevitable for tinplate and coated tinplate with the influence of environment and other factors so that the quality and taste of food is destroyed.The corrosion degradation of tinplate and coated tinplate in citric acid and NaCl solution under different temperatures and deformations has been studied.Three temperatures of 5 oC(cold storage),20 oC(room temperature)and 37 oC(high temperature in summer)are chosen to explore the corrosion behavior of tinplate and coated tinplate in 0.1 mol/L citric acid solution and 0.1 mol/L NaCl solution and the influence of temperature on the corrosion process.The electrochemical characteristic of samples with immersion time is analyzed by electrochemical methods that mainly is electrochemical impedance spectroscopy(EIS).The variation of morphology during immersion is observed by scanning electron microscope(SEM).And the metallic dissolved amounts for different corrosion period are measured by inductively coupled plasma source mass spectrometer(ICP).The results show that the corrosion of tinplate in citric acid started from the dissolution of Sn and then the substrate steel was reacted with electrolyte and passivated.The corrosion rate increased with temperature rising.The coating of coated tinplate in citric acid absorpted water firstly and then reacted with Sn.The protective effect of coating at 5 oC was still well during experimental time while those at 20 oC and 37 oC had been lost in advance.The degradation of tinplate in NaCl solution could be divided into four steps which was leaded by the corrosion of steel,and the corrosion reacted fast in the first immersion day.The coating of coated tinplate cracked finally because of the accumulation of corrosion products.And the coating had been fail around 100 days at 37 oC,while that was about to be fail at 20 oC and still had good protective function at 5 oC when immersed for 200 days.So the protective effect of coating was worse with temperature rising.The degradation process of tinplate and coated tinplate in 0.1 mol/L citric acid solution under different deformation amounts of 3%,10%,17% for tinplate and 2%,4%,7% for coated tinplate,which is chosen from stress-strain curve of samples,is studied.The experimental method is same with that of temperature tests.The results show that when the samples were immersed for 30 days,the order of corrosion resistance rate for tinplate was 17% >10% >3% and that for coated tinplate was 2% >4% >7%.