What Does Chlorides Mean?
Chlorides are ions that are comprised of the element chlorine with a negative charge (Cl-). Chlorides are also defined as any compound that has chlorine in its chemical composition. These can be salts with chlorine in them or acids such as hydrochloric acid. Chlorides can cause corrosion on passive materials such as aluminum and stainless steel.
Corrosionpedia Explains Chlorides
Chlorides are abundant in nature. The ion form of chloride, in which a single, negatively charged chlorine ion exists, forms when chlorine gains an extra electron. Chlorides can also be found when a chloride salt is dissolved in an aqueous solution. For example, sodium chloride dissolved in water leaves a positive sodium ion and a negative chloride ion.
Chlorides create devastating corrosive effects on many materials. Some stainless steels, when exposed to high amounts of chlorides, will begin corroding in the form of pits. The negatively charged chloride ions are able to penetrate the passive oxide layer of stainless steel. Once this happens, the pit formation becomes the anode and the rest of the stainless steel surface becomes a cathode. As a result of this, a corrosive electrolytic reaction is created and can ultimately result in the failure of the stainless steel. To prevent this from happening, some stainless steels have higher amounts of molybdenum, which is able to more effectively combat the chloride ions.