When the tin bronze is hot processed, it will be found that there is an oxidation mold on the surface. So, how exactly is the oxide film formed? In fact, this surface oxide is a mixture of various copper oxides of beryllium oxide (BeO). The composition and thickness of this oxide film depend on the temperature of the heat treatment and the atmosphere in the furnace. It is important to remember that tin has a strong affinity for oxygen, and because beryllium oxide cannot be reduced by hydrogen, there is no heat treatment atmosphere that can guarantee the absence of beryllium oxide on the surface of tin bronze. How many oxides, what form of oxides, and how easy it is to clean depend on the conditions and steps of the heat treatment. Heat treatment of a clean surface without oil stains and other stains will simplify the cleaning work after heat treatment. In any case, the operation should be standardized.
The oxide film formed on the surface of different tin bronze alloys is also different, especially the thickness and structure composition will vary with the tin content, and the characteristics of alloy 25 (C17200) are typical. The degree of BeO formed during the heat treatment of Alloy 25 in a conventional nitrogen atmosphere (with or without hydrogen) depends on the temperature, as is the total thickness of tin. At 700F and above, the outermost layer is basically beryllium oxide (BeO). When lower than this temperature (600F and 500F), the outer layer is a mixture of BeO and copper oxide. The typical situation is that at 600F, 30% BeO; 20% BeO at 500F. From a cleaning point of view, these phenomena are very important because BeO is not easily cleaned by acid. Not only does the oxide form a thinner at low temperature, but the composition of the oxide at this time also makes it easy to clean in the pickling tank. The holding time at a certain temperature and the type of inert atmosphere also affect the oxide film The composition factor of thickness.
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