Essential condition for hydrogen embrittlement of titanium rod in electrolyte solution!

Release time：2022-07-13 15:18:25 丨 Number of visits：

In chemical plant, the environmental conditions for hydrogen embrittlement can be roughly divided into: non-oxidizing acid with pH below 3; A strong alkaline solution with a pH higher than 12; Organic acids with pH = 3; Salt solution containing F-, I-, neutral solution containing H2S. Under the above conditions, some cases are due to homogeneous corrosion and some are related to local corrosion, but in all cases hydrogen is produced by electrochemical reaction. Of course, there are other types of environments where hydrogen is already present.

For seawater cooled titanium condensers or condensers, when titanium metal and aluminum brass tube are mixed or titanium metal tube and Muntz copper alloy tube plate are used at the same time, cathodic protection is usually used to reduce the corrosion of copper alloy. When the protection potential is too low, hydrogen absorption of the effect tube will be caused. Based on the analysis of these hydrogenation cases, the hydrogenation of titanium rods in electrolyte solution must meet the following three conditions:

(1) The pH of the solution (which may also be local) must be below 3 or above 12.

(2) There must be some mechanism for hydrogen generation, such as uniform corrosion, local corrosion, surface mechanical scratches or pollution to make the corrosion potential (overall or local) of titanium metal in the electrofresh substance below the hydrogen evolution potential, or because the cathodic protection potential is too negative directly on the titanium surface hydrogen evolution.

(3) The ambient temperature must be higher than 80℃, otherwise, although there is a mechanism of hydrogen evolution and hydrogen absorption by titanium, hydrogen diffusion is slow and hydrogen kneel is difficult to occur at lower than 80℃, unless severe tensile stress promotes low temperature diffusion of hydrogen or hydrogen produced by electrochemical reaction sometimes causes high chamber partial pressure.

The electromotive force of hydrogen evolution corrosion is much lower than that of oxygen reduction corrosion, but oxidizes with titanium. The reaction potential of Ti -- Ti++ NE is close. When oxygen supplementation (including oxidants) is too slow to compete with hydrogen evolution, hydrogenation corrosion often prevails. Hydrogen evolution usually occurs under the following circumstances.

(1) The standard potential of metal is very negative, such as titanium in the case of continuous film removal.

(2) The corrosion potential of metal is lower than the hydrogen evolution potential of electrolyte. At high concentrations, as in strongly reducing acids.

(3) Due to the formation of complex ions, the concentration of titanium ions in the solution is always kept at a very low point.