What are the corrosion forms of titanium rods?

1. Crevice corrosion: Crevice corrosion is a local corrosion phenomenon that occurs in close gaps. The gaps can be caused by structures (such as flange connection surfaces or gasket surfaces, expansion joints between pipes and tube sheets, and bolts or rivets). joint surfaces, etc.), can also be caused by scale or sediment under the covering surface. In the early days, it was believed that titanium would not undergo crevice corrosion at all in seawater and salt spray. Later, in high-temperature chloride media (such as seawater heat exchangers), wet chlorine gas (such as wet chlorine gas tube condensers), oxidant-inhibited hydrochloric acid solutions , in media such as formic acid and oxalic acid solutions, crevice corrosion damage of equipment has occurred one after another.
The crevice corrosion of titanium rods is related to many factors such as ambient temperature, chloride type and concentration, pH value, and the size and geometry of the crevice. In addition, gaps composed of titanium and polytetrafluoroethylene, titanium and asbestos and other non-metallic materials are more sensitive to crevice corrosion than gaps composed of titanium and titanium.
2. Pointing corrosion: Pointing corrosion is a form of corrosion unique to passivated metals. Compared with stainless steel or aluminum alloy, the pitting corrosion resistance of titanium is very excellent. Due to the increasing use of titanium in high-temperature concentrated chloride solutions, pitting corrosion cases in titanium equipment are gradually increasing.
Examples of pitting corrosion damage have occurred in the titanium anode basket in electrolytic zinc, the titanium coil heated in zinc chloride solution, and the titanium ball valve in 175°C 72% calcium chloride solution. Generally speaking, pitting corrosion of titanium is more difficult than crevice corrosion. Crevice corrosion usually occurs in the form of pitting corrosion on the crevice surface.
3. Galvanic corrosion: Galvanic corrosion is a phenomenon in which dissimilar metals come into contact (including electrical contact) in an electrolyte solution. Due to the difference in the steady-state potential of the metals, one metal accelerates the corrosion of another metal (i.e., anodic dissolution). Titanium The oxide film of titanium is very stable and is generally always in the cathodic state. Galvanic corrosion will not accelerate the anodic dissolution of titanium.
However, attention must be paid to the hydrogen absorption of titanium in the cathode state, which will eventually lead to hydrogen embrittlement. At the same time, it is necessary to prevent the accelerated corrosion of coupled metals (such as aluminum, copper, zinc, etc.). The magnitude of galvanic corrosion of metals depends on the difference in galvanic sequence of the coupled metals in the medium.