warthog Posted February 18, 2012 Posted February 18, 2012 (edited) I have a very quick question here... If I were going to make a fountain containing steel or iron filings and was gong to mix it and fire it the same day is it still necessary to coat the metal? How quickly does the oxidiser, in this case KNO3, begin to "rust" the metal anyway? I have always been curious about this one and all I can find is that you need to treat Iron & Steel used this way. I can also see where it will say "if stored for a time" and need to have some idea of what "a time" might be? (I doubt it is as long as the one in the Bible (See Daniel 7:25 to understand this reference)). Edited February 18, 2012 by warthog
dagabu Posted February 18, 2012 Posted February 18, 2012 No, I make rockets with iron in them and shoot them a week later with no ill effects. If you plan on storing them for a "time" greater then a week, if you are using water to bind, if you are building in a humid climate, if the iron is already showing signs of rust then yes, coat it with wax first. -dag
warthog Posted February 18, 2012 Author Posted February 18, 2012 (edited) Groovy! Then I am going to try at least to try out some of the stuff folks have sent me and see what sparkage I get from it. Thank you Edited February 18, 2012 by warthog
allrocketspsl Posted February 18, 2012 Posted February 18, 2012 Groovy! Then I am going to try at least to try out some of the stuff folks have sent me and see what sparkage I get from it. Thank you food processor keeps anything fresh in florida i ram rockets in the summer 95 percent humidity and can process them and a month later fire them and they are like brand new.No air no oxidation
warthog Posted February 18, 2012 Author Posted February 18, 2012 The air isn't where the oxidation comes from here, it is in the oxidiser itself. The steel becomes degraded as does the oxidiser making the whole thing worthless. Wasn't able to get to them today so if I can I will try tomorrow. I am still dubious about this one, I guess I will find out myself.
dagabu Posted February 18, 2012 Posted February 18, 2012 The air isn't where the oxidation comes from here, it is in the oxidiser itself. The steel becomes degraded as does the oxidiser making the whole thing worthless. Wasn't able to get to them today so if I can I will try tomorrow. I am still dubious about this one, I guess I will find out myself. The rust acts as protective layer... for a while. And no, its not necessarily true that the oxidizer itself is the culprit, as in fire, there has to be a rust triangle; anode, cathode and electrolyte (electrode). No water, no rust. -dag
Mumbles Posted February 20, 2012 Posted February 20, 2012 All you really need is oxygen for iron to oxidize. Very fine metals will light up in dry air just as fast as they do in moist air. Just air alone has trouble getting past the initial oxide layer. In the fountain case it's mostly moisture from the air that is the issue. If the iron is coarse and you kept them vacuum sealed or something they might be able to be stored for a little while. There is however a level where it's easier to just coat the turnings with wax or linseed oil or something. I'd put the storage limit around a few weeks to a month before I'd start worrying about oxidation. You can always make up a batch and fire them off once a month to see if there is any degradation. I've never heard it mentioned, but an additional problem could be the grain generating cracks. The metals should be much denser than the oxides, so they may expand and crack the grain or generate pockets if allowed to extensively oxidize.
dagabu Posted February 20, 2012 Posted February 20, 2012 Mum, I respectfully disagree with the statement that it only takes oxygen to oxidize iron, as in fire, three components must be present, in fire it is heat, oxygen and fuel. In rust it takes an anode, cathode and electrolyte (electrode). In fact you already have the necessary components in air to start the process as you have stated. Think also of the principal behind using a sacrificial anode inside a boat motor lower end (Mg) and in water heaters so that the steel (iron also applies) does not become the anode. Finely divided metals act differently than whole ingots and can be ignited easily due to its smaller mass (exothermic reaction) and because it has an enormous surface area available for oxidization.-dag
Mumbles Posted February 20, 2012 Posted February 20, 2012 I do believe we're talking about two different things. I was thinking more gas phase oxidation, where as it seems you're thinking of liquid phase. I completely agree that liquid phase will should require some sort of electrolyte, of which KNO3 is excellent at. I guess I was thinking of oxidation in general and that's not particularly applicable to the issue at hand. The issue here is very clearly liquid phase. If it was strictly gas phase, it'd be storage stable for decades most likely. My example with the fine metal was really just showing that oxidation will happen without the presence of water or any conventional electrolytes. 10 micron or 10 mm, there is still oxidation happening. It's just a matter of how much of the iron is consumed.
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