Tuesday, July 28, 2020

Introduction to the corrosion resistance of titanium tubes

Everyone knows that titanium tube is a new type of metal that we have formed in recent years. The performance of titanium is mainly related to its proportion of carbon, nitrogen, hydrogen, etc. It has been widely used. Now let us popularize the corrosion resistance of titanium tubes in neutral or weakly acidic oxide solutions.
The corrosion resistance of the titanium tube is highly stable in neutral or weakly acidic oxide solutions. For example, titanium and titanium alloys are in CuC12 at 100 ℃ FeCl at 100 ℃, HgC1 at 100 ℃: (all concentrations), 60 % AlCl2 and all concentrations of NaCl at 100°C are stable. Many other metal oxides of titanium are also stable in 100% monooxyacetic acid and 100% peroxyacetic acid. Therefore, titanium and titanium alloys are It has been widely used in the solution. Titanium and titanium alloys are also highly stable to ion-containing oxidant solutions, such as 100qC sodium hypochlorite solution, oxygen water, gas (up to 75°C), sodium oxide solution containing hydrogen peroxide, etc.
The corrosion resistance of titanium pipes in wet chlorine gas exceeds that of other commonly used metals. This is because chlorine has a strong oxidizing effect. Titanium and titanium alloys can be in a stable passive state in wet chlorine. In order to maintain the passivity of titanium in chlorine, A certain water content is required. The critical water content is related to oxygen pressure, flow rate, temperature and other factors, as well as the shape and size of titanium equipment or parts and the degree of mechanical damage to the titanium surface. Therefore, the critical water content of titanium passivation in oxygen in the titanium tube literature is Inconsistent, it is generally believed that the mass fraction of 0.01% to 0.05% can be used as the critical water content of titanium in oxygen, but actual experience has pointed out that in order to ensure the safe use of titanium equipment in oxygen, sometimes the water mass fraction is 0.6 % Is not enough, it needs to be as high as 1.5%. The critical water content also increases with the increase of chlorine temperature and the decrease of airflow velocity. Actual operating experience also shows that after the surface oxide film of titanium and titanium alloy is destroyed, higher water content is required to passivate titanium and titanium alloy again.
Titanium and titanium alloys will react violently in dry chlorine even below 0°C to form titanium tetrachloride. Titanium tubes pose a fire hazard. Once the destruction of titanium and titanium alloys in dry chlorine gas begins, the reaction is collapsible, and the addition of water cannot prevent the reaction from proceeding. The behaviour of titanium in the dry and wet zone of chlorine gas has not been fully understood. Based on the thermodynamic analysis, titanium and chlorine cannot exist in equilibrium at room temperature. According to the thermodynamic free energy, a stable compound titanium tetrachloride is formed in this reaction system. If it does not coexist with water, it will react further, namely TiC14+4H20.
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