①The occurrence of crevice corrosion has a gestation period, and the size of the gestation period is related to many elements, corresponding to ambient temperature, chloride sort and focus, oxidant focus, materials involved with Pickling Titanium Alloy Wire, pH value of the answer, and the scale and geometry of the crevice, and many others. . In the sodium chloride answer of titanium, the upper the chloride ion focus, the higher the temperature, and the lower the pH value, the shorter the incubation interval of crevice corrosion, that is, the stronger the sensitivity of crevice corrosion.
②The composition and pH worth of the solution within the gap is totally different from the bulk resolution. Generally speaking, the oxygen concentration in the hole is decrease, the chloride ion and hydrogen ion concentration are increased (the pH value is decrease than the bulk answer), the pH value in the hole can drop to <1, and the electrode potential in the gap becomes more negative, Thus, the titanium in the gap is in an active state. Laboratory electrochemical measurements show that the order of crevice corrosion potential of various halide ions is: CI- < Br- < I-, that is, the crevice corrosion sensitivity of titanium in chloride is the largest, which is exactly the same as the pitting corrosion sensitivity of titanium. on the contrary.
③ The crevice corrosion of titanium is usually localized on the crevice surface, and usually does not corrode on all the crevice floor. After the incubation period of crevice corrosion is over, that’s, as soon as “nucleated”, the corrosion develops quickly due to the autocatalytic mechanism, eventually leading to local perforation and destruction.
④The prevalence of titanium crevice corrosion is usually accompanied by hydrogen absorption, and even the existence of needle-like hydrides in titanium will be observed by metallographic microscope. With the rise of hydrogen absorption, the hydrides on the floor proceed to increase, which accelerates the corrosion in an all-round manner. At the same time, hydrogen repeatedly penetrates into the metallic, and the internal hydride precipitation could develop into the crack supply of stress corrosion cracking, resulting in cracking underneath the action of exterior stress.
⑤ After years of research, the bodily picture of the crevice corrosion process of titanium welded tubing has been comparatively clear. Briefly, it is divided into two phases: the incubation interval and the energetic dissolution period.
Firstly of the gestation interval, the identical response takes place inside and out of doors the crevice. The cathodic reaction consumes the oxygen in the crevice solution. When the oxygen in the crevice is depleted, the cathodic reaction only proceeds exterior the crevice, and the anodic response is mainly carried out in the crevice – the anodic dissolution of titanium. With the continuous improve of titanium rod ions within the gap, in order to take care of the charge stability of positive and negative ions within the hole, titanium sheet chloride ions proceed to migrate into the hole. At the same time, titanium ions accumulate in the crevices and endure a hydrolysis response to generate a white corrosion product, specifically titanium hydroxide. The white corrosion product after the dehydration of titanium hydroxide is identified as TiO2. The hydrolysis response reduces the pH value within the crevice, which additional destroys the passivation of titanium forging. Therefore, once the incubation period of crevice corrosion is over, its development is very fast, which is the so-known as “autocatalysis”.
⑥ In the “geometric factor” of crevice corrosion of titanium, components such because the size of the crevice, the width of the crevice and the ratio of the area inside and out of doors the crevice are included. These values usually have to be decided experimentally for a selected system, titanium tubing and cannot be obtained by theoretical prediction. The check tells us that the crevice corrosion tendency of narrow seam is much bigger than that of broad seam, and the width of normal seam is lower than 0.5mm.