What materials is NaOH corrosive to?
Thread Content
I would like to ask: Which materials are corroded by NaOH? For example, does it cause corrosion to materials such as fiberglass, rubber, and plastics? What kind of materials are generally used for storage containers? What gasket should be used for the seal?
Sodium hydroxide can corrode carbon steel pipes, and the degree of corrosion varies depending on the concentration and temperature. The corrosion mentioned refers mainly to alkali embrittlement
I’m currently dealing with a 20% NaOH storage tank; the tank is made of carbon steel, and its interior has been coated with glass flake material for corrosion protection. However, some people argue that such corrosion protection is not necessary, claiming that NaOH can corrode glass flakes, glass cloth, as well as rubber gaskets and plastics. I would appreciate it if experts could provide a definitive explanation on this matter
I would like to ask fellow sailors: what type of containers are commonly used in factories to store 20% NaOH at room temperature?
Use PE tanks or steel with a PE lining
Under specific conditions of higher temperatures and sodium hydroxide solutions at certain concentrations, hot alkaline solutions can cause stress corrosion in carbon steel or alloy steel; this phenomenon is commonly known as alkali embrittlement or caustic alkali embrittlement. There is currently no unified understanding of the mechanism of steel alkaline embrittlement. Generally, carbon steel undergoes the following chemical reaction with water vapor at high temperatures: In this reaction, sodium hydroxide acts as a catalyst. The Fe3O4 produced as a result of this reaction covers the surface of the steel, forming a protective layer. However, excessive local tensile stress may cause the protective film in that area to be damaged ； It may also be due to the enrichment of sodium hydroxide on the surface, which causes Fe3O4 to dissolve ； Or due to the combined effect of these two factors, initial corrosion cracks form on the metal surface; sodium hydroxide accumulates in these cracks, leading to electrochemical corrosion. The tip region of the crack acts as the anode, while the protective layer surrounding the crack functions as the cathode; combined with the effect of tensile stress, this causes the crack to expand rapidly, ultimately leading to fracture. Alkali embrittlement of steel generally requires three conditions to occur simultaneously: high temperature, high concentration of alkali, and tensile stress. Tests have shown that a sodium hydroxide solution with a concentration of 10% can cause alkali embrittlement, whereas a 5% concentration does not. The above information is what I found on Baidu. Now, let me talk about the actual situation here: the containers used to hold the alkaline solution are made of ordinary carbon steel, without any lining inside; the concentration of the alkaline solution is 30%. There is also an alkali washing tower, where the concentration of the alkaline solution ranges from 2% to 15%. That tower is also made of ordinary carbon steel, and so far there has been no sign of corrosion. Alkaline corrosion mainly occurs at high temperatures when the concentration of the alkaline solution reaches a certain level; further research is needed by scientists to determine the specifics.
NaOH is corrosive to glass
NaOH certainly causes corrosion to fiberglass-reinforced plastic, but the temperature also plays a role; generally, bisphenol A vinyl can withstand temperatures around 80°
A 20% concentration has quite strong corrosivity. NaOH is special in that its corrosivity at concentrations of 5-25% is greater than that of a 40% concentration