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Acid Embrittlement

Definition - What does Acid Embrittlement mean?

Acid embrittlement is a process in which brittleness is induced in metals, especially steel, when immersed in acidic solutions. Acids contain hydrogen, and when these metals are immersed in acids, they absorb hydrogen, becoming brittle, and can readily fracture when subjected to stress.

The presence of hydrogen in the metal structure increases cracks and should be avoided as it decreases the strength of materials as well as service life. Hydrogen embrittlement compromises the strength of the materials and it can only happen in some manufacturing processes such as electroplating, zinc plating and exposure of hot metals to the atmosphere, especially after welding processes.

Corrosionpedia explains Acid Embrittlement

The process usually starts by exposing the metal to hydrogen, such as during the electroplating process when the metal is passed through an acid bath for cleansing. Acids contain hydrogen and through such a process hydrogen molecules may find their way into the metal structure.

The current used during the process of electroplating and the pickling provides molecules with energy for a hydrolysis reaction to commence. Water molecules are broken down into hydrogen and oxygen atoms. Hydrogen can also be produced by corrosive reactions. Other manufacturing processes that can expose a metal to embrittlement include welding processes and phosphate-plating. One method of purging the absorbed hydrogen is by baking the components.

The susceptibility of a material to hydrogen embrittlement is related directly to the physical structure of the material (the material's microstructure, dislocations present and carbides, among others). Hydrogen concentration will lower the critical stress of the component, at which the material is susceptible to fail. Hence, great care should be taken to reduce this phenomenon, especially during the plating process as well as welding. Heat treatment processes such as annealing should also be used to relieve residual stress, which forms on the metal structure. Materials such as those that are used to make steel bridges should be thoroughly checked for embrittlement—this can cause tragic accidents in the case of failures due to the induced embrittlement.

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