Si active oxidation

[siegenerbuerger]

Hello engineering fellows,

does anyone have an idea about critical factors for the formation of volatile SiO instead of SiO2, e.g. temperature and oxygen partial pressure?

I have an alloy which forms a silica scale at 1200°C under vacuum conditions. The silica appears as small droplets upon the metal which is quite uncommon compared to the conditions in air. My first idea was these droplets form due to some evaporation occured (such as SiO formation).

Any kind of discussion about this question is highly appreciated. Thanks to everyone.

 

[Compositepro]

Some of the information you are looking for is in this article that I just happened to read yesterday. Look at figure 4.

http://www.industrialheating.com/Articles/Online_Exclusives/BNP_GUID_9-5-2006_A_10000000000000768124

 

[Ceramicguy]

At reduced oxygen pressures, i.e. below 1 torr and at temperatures above 1422K, the oxidation mechanism of SiC changes from passive to active mode. A volatile SiO film is formed. ...rate increases with temperature.

Engineering Property Data on Selected Ceramics v. 2, Carbides, Metals and Ceramics Information Center Battelle Columbus Laboratories, Report MCIC-HB-07-Vol. II, 1979.

There was also a significant amount of work done in the 1980's for the Dept. of Defense adiabatic heat engine programs. I believe much of this information is in the public domain. Many papers were presented at the American Ceramic Society Cocoa Beach meetings.

Bruce

http://www.accuratus.com