Hydrogen embrittlement chemical processes

MSTMF519, Std. Methodfor Mechanical Hydrogen Embrittlement Testing of Plating Processes and Mircraft Maintenance Chemicals, American Society for Testing and Materials, Philadelphia, Pa., 1977. 

Ion Vapour Deposition A variant of the process is ion vapour deposition, in which a high negative potential is applied to the workpiece during chemical vapour deposition. The process has been employed on a commercial scale chiefly for depositing aluminium on to steel and titanium in the aerospace industry as an alternative to cadmium plating, which is liable to cause hydrogen embrittlement, especially of high tensile steel components. The aluminium is evaporated from a wire-fed resistance-heated boat . 

Hydrogen has a low solubility in solvents for example, at ambient conditions, only 0.018 and 0.078 mL of gaseous H2 dissolves into each milliliter of water and ethanol, respectively. However, the solubility is much more pronounced in metals. Palladium is particularly notable in this respect, which dissolves about 1000 times its volume of the gas. The adsorption of hydrogen in steel may cause "hydrogen embrittlement," which sometimes leads to the failure of chemical processing equipment [4],... 

In processes using certain chemicals stresses have been shown to make the parts prone to corrosive attack which can reduce their strength. Similarly failures have occurred where a chemical in contact with the part has affected its ability to carry stresses through causing embrittlement such as zinc embrittlement of stainless steel and hydrogen embrittlement of grade T chain. ... 

So far, reactions between the corrosion products themselves and between the metal and the corrosion products have been ignored. It will be seen later that the formation of metal oxides and hydroxides via chemical reaction may be critical in determining the thermodynamics (section 10.2 and kinetics (section 10.3) of corrosion processes. Additionally, in the case of acid electrolytes, hydrogen evolution (reaction (10.9)) may result in the blistering of paint films or hydrogen embrittlement. 

Hydrogen embrittlement has also been observed in steel structural components exposed to aqueous environments (Sheinker and Wood 1971). Termed stress corrosion cracking, this natural process can result in the failure of a component from the combined action of stress and chemical attack. It is now fairly well established that stress corrosion cracking of steels in aqueous solutions is governed, at least to some extent, by a series of electrochemical reactions at the surface which permit the entry of hydrogen into the metal (Parkins 1964). 

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