On Fri, Nov 20, 2009 at 05:10:18PM +0000, Leslie Newell wrote: > Carbon dioxide is 66% oxygen (CO2). As aluminum is very active it will > strip oxygen out of the CO2. That is also the reason why you should > never use a CO2 fire extinguisher on magnesium fires.
However, it is extensively used in fire extinguishers precisely because it does not give up its oxygen even at hundreds of degrees C. I'm not sure of how many thousand degrees magnesium burns at, but it is more than 1500, because thermite (magnesium and iron oxide) combustion melts the iron produced by the reduction of the iron oxide. If the cutting operation is hot enough to dissociate CO2, then there'd better not be any oil about, especially as mist, unless Gene has his detonation-deadening earmuffs on tight. ;-) Wikipedia appears to be self-contradicting: "Carbon dioxide also finds use as an atmosphere for welding, although in the welding arc, it reacts to oxidize most metals." The closest I've come in a quick search is: http://www.hitech-inst.co.uk/pdfs/technical/heat_treatment.pdf which says: "The graph shows cell output against carbon monoxide/carbon dioxide ratio. this is plotted at 634°C and 812°C, ..." i.e. CO2 is still so completely undissociated at 812°C that ratios can be measured for metallurgical analysis. So the aluminium would melt long before the CO2 dissociated to any measurable degree. Erik ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
