Sodium hydroxide, also known as caustic soda, is an important industrial product. It has a wide range of uses. It is a strong alkali. It does not corrode seriously at room temperature, but it will cause serious corrosion to many metals in the presence of high temperature and stress. Iron and steel can be used in dilute sodium hydroxide solution at room temperature, but it will corrode rapidly when the temperature or concentration increases. It is important to study the corrosivity of different alloys in sodium hydroxide solution for material selection.
NaOH 是一种强碱，在常温下腐蚀性不强，但在高温和有应力存在的情况下会对许多金属产生严重腐蚀。不同浓度的NaOH 溶液在不同温度下其设备和管道的选材如图１和表１所示。从图１和表１可以看出，氢氧化钠溶液的浓度为0～30％，若温度低于50℃的情况下，Ⅰ类材质的设备和管道通常是耐腐蚀的；而0％～30％氢氧化钠溶液在Ⅱ类材质的设备及管道中，在温度为50～100℃的情况下，耐腐蚀性能较好。
It is a kind of strong alkali. It is not very corrosive at room temperature, but it will cause serious corrosion to many metals at high temperature and in the presence of stress. The material selection of equipment and pipes for different concentration solutions at different temperatures is shown in Fig. 1 and Table 11. From Fig. 1 and Table 1, it can be seen that the concentration of NaOH solution is 0-30%. If the temperature is lower than 50 C, the equipment and pipes of Class I material are usually corrosion-resistant, while the corrosion resistance of 0%-30% NaOH solution is better in the equipment and pipes of Class II material at the temperature of 50-100 C.
It can also be seen from the material selection figures 1 and 1 that the corrosion resistance of silver pairs is the best, followed by nickel. Silver and nickel can withstand all concentrations and temperatures until they melt (480 C). For high temperature and high concentration alkali, nickel and its alloys (such as Inco nickel, Monel, etc.) are the best choice. Stainless steel can withstand 80-100 C for solutions below 40%-50%, but not high concentration and high temperature alkali solution. Carbon steel has good corrosion resistance in relatively low temperature NaOH solution and can form a solid oxide protective film on the surface. Because of its low cost, it is often the first choice of many users.
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