Abstract
Carbon deposition on alloys of iron with chromium and nickel has been investigated using acetone vapour in a carrier gas of carbon dioxide at atmospheric pressure. At 700°C, carbon deposition and oxidation were extensive on iron and an iron/nickel alloy. The carbon was invariably in filamentary form, and most profuse on the nickel-containing material. The oxide formed when carbon was deposited resembled that commonly referred to as "breakaway" type, whereas in the absence of carbon, normal crystalline magnetite was in evidence. Deposition at 500°C was negligible but could be detected using X-ray photo-electron spectroscopy for surface analysis. Adding a sulphur-bearing compound to the gas was effective in inhibiting carbon deposition, but carburisation of the underlying metal continued unchecked. From a review of the relevant literature and examination of the results, a mechanism is proposed concerning the initiation of carbon filament growth on ferrous materials. The way in which sulphur affects the growth of carbon filaments is considered together with its lack of effect on carburisation. The whole field of carbon deposition, carburisation and oxidation is brought together for discussion by considering attack by hydrocarbon gases at high pressure, commonly called "metal dusting", on steels used in the gas industry.