On Tue, 2002-10-29 at 00:23, Sean R. Lynch wrote: > What if, in general, it's *only* the oxides of these metals that are > catalytic and not the metals themselves at all? What if silver is only > so good because its oxide is so tenacious? If this is the case, then the > process would be clear: find a transition metal with a tenacious oxide > that can stand high temperature... this would be what you call > "convenent properties." Even if they don't *form* their oxides easily, > they probably will form oxides at high temperatures in highly oxidizing > environments. Even stainless will, but from what you're saying it sounds > like it would probably be sacrificial. Of course, the damned chamber is > stainless, but clearly it doesn't have the kind of surface area we need.
Nickel, beryllium, aluminum, and chromium apparently all form tenacious oxides, and I think they in fact oxidize very easily, but since the oxides are tenacious and end up protecting the metal, they're not really like rust so it tends to be a good property (except when you're welding). Silver melts at 961.93C. Aluminum melts at 660.37C, so it's clearly out. Nickel melts at 1453C, so it's a definite candidate assuming it will form an oxide and the oxide is catalytic at temperatures we can reasonably heat it to electrically. Chromium melts at 1857C, so we have another candidate. Beryllium melts at 1278C, but it's not a transition metal. Apparently, it's chromium oxide that forms on the surface of stainless steel and makes it stainless. A stainless catalyst would probably really be a chromium oxide catalyst, not an iron oxide catalyst as I was originally thinking. Since stainless has both nickel and chromium in it but it's chromium oxide that protects it, I'm thinking that chromium maybe forms its oxide more easily than nickel? Nichrome wire anyone? We could make a catpack out of used model rocket ignitors :) Is it aluminum oxide that we're making inside our tanks when we passivate them? Clearly both of these are pretty compatible with peroxide at reasonable temperatures, but heat them up and who knows? In any case, it would seem that the actual metals are in fact *reactive* with peroxide. It is probably this reaction that causes the nice gunshot effect when we start a fresh catpack. The "burning" of the metal in addition to the breakdown of the peroxide probably releases a lot of energy very quickly. I guess it's just a matter of semantics, because a catalyst that reacts with the byproducts of the reaction it catalyses is just as well called a reactant. We passivate the tank because aluminum reacts with peroxide. In passivating we create an oxide layer that may or may not be catalytic, but it's not catalytic at temperatures at which a sane person would store peroxide.
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