The Effect of Nitrate on the Corrosion Resistance of Carbon Steel

• Main Authors: Fang,Yow Shing, 方又興
• Other Authors: Hsu,Chung Jen
• Format: Others
• Language: zh-TW
• Published: 1993
• Online Access: http://ndltd.ncl.edu.tw/handle/96934498729403187679

碩士 === 逢甲大學 === 化學工程研究所 === 81 === The study was executed by potentiodynamic polarization method to investigate : (1)the effect of sodium nitrate on the corrosion of carbon steel in sodium chloride aqueous solutions; (2) the in- hibition effect of chromate on the corrosion of carbon steel in sodium nitrate aqueous solution at pH.dbond.3; (3) the effect of organic solvent of isopropyl alcohol on the corrosion of carbon steel in a similar system described above. The results are summarized as follows : 1.The corrosion rate increases with the increasing concentration of chloride ion,at pH.dbond.3 and the concentration of sodium nitrate .gtoreq.0.2M ,it decreases with the increasing concentra- tion of chloride ion. That may be caused by that the concentra- tion of nitrate ion(powerful corrosive) on iron metal surface is decreased by the competitive adsorption of chloride ion. 2.At pH.dbond.3, the corrosion rate increases with the increasing concentration of nitrate ion. This may attribute to that iron is oxydized to ferrous ion by nitrate ion, and which is reduced to nitrogen monoxide . At pH.dbond.5 and 11, the corrosion rate decreases with the increasing concentration of nitrate ion, which may be caused by nitrate ion was adsorbed and formed a passive film on the surface of iron. At pH.dbond.7 and 9, if the con- centration of sodium nitrate .gtoreq. 0.2M the corrosion rate is increased by the additional crevice corrosion, which is caused by the defects of passive film and decreasing oxygen concentration in the crevice between the iron specimen and the rubber cushion. 3.Chromate acts as an inhibitor in sodium nitrate solution, probably due to the formation of a protective filmof ferrous dichromate. 4.The effects of isopropyl alcohol on the corrosion system are : (1) to decrease the conductivity and oxygen concentration in solution; and (2) to reduce the concentrations of nitrate ion and hydroxyl ion on the surface of iron.