提高NaNO_2法钝化效果的途径

Way to Raise Efficiency of NaNO_2 Passivation

ＮａＮＯ_２属于氧化型钝化剂，它通过产生局部活性电流使金属阳极极化到金属钝化区而使金属钝化。氯离子和铁离子的存在对ＮａＮＯ_２的钝化效果有影响。氯离子浓度的增加能缩小钝化的范围；铁离子浓度高时在碱性条件下生成氢氧化物沉淀。另外，温度和钝化液的浓度也对钝化效果有影响。使用ＮａＮＯ_２钝化时，如果加热温度达不到要求，将降低ＮａＮＯ_２与铁反应的活性；而钝化液浓度过高会导致过钝化，反到加剧了金属的腐蚀。钝化液的ｐＨ值过大，会导致腐蚀的加剧；设备管道死角处残留的酸洗液也影响钝化效果。钝化过程中考虑上述因素，即可以提高钝化效果。

The effect of passivation can be influenced the existance of Cl- and Fe-, When Cl- concentration increasing, the passivation range decreases. When Fe- concentration is high, under alkalinity, sediment of hydrnxide formed. moreover the effect of passivation can be influenced by temperature and by the concentration of passivation liquid. Using NaNO_2, to passivation if temperature can' t get to the requirement then the activation of reaction of NaNo_3, with Fe will .be decreased, but if the concentration of passivation liquid is excessively high it will lead to overpassivation and speed up the corrosion of metal. If the pH of passivation liquid is excessively large, it will lead to speed up the corrosion of metal.