Chemical Vapour Deposition of Pure Titanium Using a Heated Wire Reactor and TiI4

Abstract

An experimental reactor system has been optimized throughout a series of experiments for making titanium tubes from an electrically heated titanium coil filament by a chemical vapour deposition method, based on the original van Arkel-de Boer -process. The titanium is thermally decomposed on the filament from vapourized titanium tetraiodide in a method not seen in similar experiments. The small-scale reactor is built for this purpose, and the associated systems and methods are developed to maintain the optimal conditions for a continuous metal deposition. A filament current control system is made of an Arduino micro-controller, utilizing a photo-resistor to measure thermal radiation from the filament, working for maintaining a constant filament temperature. Five experiments are conducted with the small-scale reactor and presented in this thesis, where different procedures, materials, duration and amount of starting material is tested. By the use of copper electrodes, it was quickly found that the metal could easily be contaminated from other metal sources. The most important precautions necessary to achieve a good deposition of high purity is to keep air out of the system, and a purpose-built glove box is made to fulfill this. In the first two experiments, titanium was deposited on a platinum wire and tungsten wire, respectively. In the three following experiments, a titanium coil filament was used, whereas experiment 5 was considered the most successful, by the purity of the deposited titanium and the growth on the coil filament, forming a solid tube. Index Terms: Chemical vapour deposition, thermal decomposition, titanium, titanium tetraiodide