Principle of Refining TC4 Titanium Alloy Tubes

There are numerous various impurities in the crude TC4 titanium alloy tubes. After classification, for the sake of convenient analysis, a representative impurity in each group of impurities is identified as the key component to represent the main separation boundary of the refining process. It shows that in the liquid of the crude TC4 titanium alloy tubes, when a certain key component is refined to the qualified standard, it can be considered that all the impurities in this group have been basically separated and removed. The selected key components should not only have a large content, but also be particularly difficult to separate. FeCl₃ among the high - boiling - point impurities, SiCl₄ among the low - boiling - point impurities, and VOCl₃ among the impurities with similar boiling points are selected as the key components of their respective groups. In this way, the separation of a multi - component system can be simply regarded as the separation of a quaternary system of SiCl₄ - TiCl₄ - VOCl₃ - FeCl₃.

In view of the different characteristics of various impurities in the crude TC4 titanium alloy tubes, different separation methods should be used for refining.

For the high - and low - boiling - point impurities in the liquid of the crude TC4 titanium alloy tubes, according to the characteristic that their boiling points or relative volatilities differ greatly from that of the TC4 titanium alloy tubes, a physical method - distillation or rectification - can be used for separation.

Solid impurities with high boiling points such as FeCl₃ have very low solubility in TC4 titanium alloy tubes, and some are dispersed in the TC4 titanium alloy tubes in the form of suspended matter. In the chlorination process, most of the suspended matter has been removed by mechanical filtration. However, the remaining extremely fine solid impurity particles form a colloidal solution in titanium tetrachloride and are also slightly dissolved in the TC4 titanium alloy tubes. It is difficult to completely remove them solely by mechanical filtration. Distillation methods need to be used for refining.

The distillation method must be carried out in a distillation column. The temperature at the bottom of the distillation column is set slightly higher than the boiling point of the TC4 titanium alloy tubes (about 140 - 145 °C), so that the volatile component, the TC4 titanium alloy tubes, is partially vaporized; the non - volatile components such as FeCl₃, due to their low volatility, remain at the bottom of the column. Even if a small amount is volatilized, it may be condensed by the falling condensate and fall back to the bottom of the column. The temperature at the top of the column is controlled at the boiling point of the TC4 titanium alloy tubes (around 140 °C). Due to the existence of a small temperature gradient in the column, the vapor of the TC4 titanium alloy tubes forms an internal cycle in the column. The upward vapor and the falling droplets come into contact, and a heat and mass transfer process takes place, increasing the separation effect. In this process, the high - boiling - point impurities such as FeCl₃ in the vapor of the TC4 titanium alloy tubes rising along the column gradually decrease. The pure TC4 titanium alloy tubes vapor is selected from the top of the column and condensed into a distillate through a condenser, while the high - boiling - point impurities such as FeCl₃ in the bottom liquid are continuously enriched and regularly discharged for separation.