Vacuum characteristics of TiN film coated on the interior surface of a vacuum duct

Abstract

Titanium has been proposed as a material for chambers designed for UHV and XHV. As the pumping characteristics of a titanium chamber at room temperature had not been investigated yet, test ducts of 1 m in length and 150 mm in diameter were made by titanium and pumped down at room temperature. A chemically polished titanium duct showed a higher outgassing rate than an electropolished stainless steel duct. We then coated the interior surface of another titanium duct with TiN by hollow cathode discharge ion plating. The outgassing rate of the TiN coated titanium duct was half of that of the chemically polished titanium duct after 65 h pumping at room temperature. The pumping time to obtain 5 × 10 −7 Pa was also reduced to half by TiN coating. In the evacuation at room temperature, water was the dominant outgas. The ion current curve of the water of the TiN coated titanium duct was lower in one order of magnitude than that of chemically polished one and it resembled that of TiN coated stainless steel duct. It was thought that either the amount of water absorbed on TiN film was strongly reduced or water was desorbed from TiN film more easily.