Hydrogen embrittlement metallic surface

It is clear from Eq. 62F that addition of materials that slow down (i.e., poison) the h.e.r. enhances the absorption of hydrogen into the metal, and vice versa. Thus, kinetic studies of the h.e.r. on iron and its alloys, in the presence of different additives, can be useful in the search for ways to decrease hydrogen embrittlement during surface treatment of the metal. 

Acids are substances that increase the hydrogen ion (H ) concentration of the solution they are dissolved in. This, in turn, reduces the pH of the solution, and the corrosion rate increases. Acids may also attack the metal by dissolving the protective film on the metal surface, Presence of acid aggravates the oxygen-influenced attack and also hydrogen sulfide-promoted hydrogen embrittlement [203]. 

General corrosion occurs in the weld metal and HAZ of welded Zr-2.25 Nb alloys in an environment of H2SO4 at temperatures greater than 343 K, the rate increasing with concentration. Above 70< oH2S04 both general corrosion and IGA occur, whilst above 80% hydrogen embrittlement was found also. Sulphides were found to be deposited on the metal surface . 

Features of the method This method has the advantage that sintered, carburised, nitrided and non-metallic articles can be plated, and that no involved surface preparation is required. Futhermore, the possibility of hydrogen embrittlement is avoided ... 

Owing to hydrogen embrittlement, the mechanical properties of metallic and nonmetal-lic materials of containment systems may degrade and fail resulting in leaks. Hydrogen embrittlement depends on many factors such as environmental temperature and pressure, purity of metal, concentration and exposure time to hydrogen, stress state, physical and mechanical properties, microstructure, surface conditions, and the nature of the crack front of material [23]. 

The main factors governing hydrogen embrittlement are the metal surface films that can restrict hydrogen absorption, the effect of electrical discharge machining that may... 

Glass that has been under stress for a period of time may fracture suddenly. Such delayed fracture is not common in metals (except in cases of hydrogen embrittlement of steels) but sometimes does occur in polymers. It is often called static fatigue. The phenomenon is sensitive to temperature and prior abrasion of the surface. Most important, it is very sensitive to environment. Cracking is much more rapid with exposure to water than if the glass is kept dry (Figure 15.11) because water breaks the Si-O-Si bonds by the reaction — Si-O-Si—H H2O -> Si-OH + HO-Si. 

Surface Instability and Internal Decay of Metals Hydrogen Embrittlement... 

What is the mechanism of this phenomenon Very early during investigations of this field, it was realized that metals become embrittled because at some stage of their career, their surface was the scene of a hydrogen-evolution reaction either because the metal was deliberately used as an electron-source electrode in a substance-producing cell or because parts of the metal became electron-source areas in a corrosion process. In fact, the phenomenon has come to be known as hydrogen embrittlement. 

Cathodic protection in the negative potential zone where reduction of oxygen or water commences, and where the rate of metal oxidation is low. In this case there has to be an inert auxiliary electrode close to the surface to be protected. The protection process consumes current, the quantity depending on solution resistance between the surface to be protected and the anode. This protection can be expensive in terms of energy consumption, and even more if there is hydrogen release and, consequently, hydrogen embrittlement. 

Let us begin with two common observations involving separated anodes and cathodes. The cathodic protection level obtained on metallic surfaces is often noted to vary with position. The metal is usually less well protected as the distance of the metal surface from the sacrificial or impressed current anode increases. Alternatively, the structure may be overprotected at positions close to the anode, leading to potentially embrittling hydrogen production. Similarly, it is well known that it is more difficult to plate metals electrolytically or throw current into corners or recesses, while exposed edges may receive a thicker plating deposit. The main explanation for this behavior is that the aqueous solution... 

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