A catalyst

[arm]

Does anyone know a good catalyst for the decompostion of Potassium Nitrate. I know Vanadium Pentoxide and Potassium Dichromate can do it but the trouble is, one is damn toxic and the other is damn toxic and a known carcinogen. I need something a little friendlier.

Whats the effect of Iron Oxide? I know this works in candy rocket propellant and whistle mixes but what about its effect when using inorganic fuels or charcoal?

Any thoughts/knowledge?

[Arkangel]

Iron Oxide is a well known catalyst, as you mention. The current archive rocket fuel thread discusses it I believe.

I would be interested in people's ideas as to how to get this stuff. I can probably gather large amounts of "rust" from ships near me, plus loads of scrap metal with flakes of rust all over them. Is this ok to use - how would it be powdered (ball mill?) - has anyone done it. I know red AND black Iron Oxide are available from Skylighter

[arm]

Yeah its brittle stuff so its easy to powder. Rust is Ok but its really a mixture of oxides and hydroxide. Its the red and black oxides (Fe3O4 and Fe2O3) in it that are the catalysts. The FeO and the hydroxide dont do much.

You can also buy it at pottery suppliers in the form of red and black iron oxides.

[Mr Cool]

I was going to recommend pottery suppliers. Otherwise, iron (II) sulphate fertiliser + sodium hydroxide + air --> Fe(OH)3, a brown ppte. Then roast this, 2 Fe(OH)3 --> Fe2O3 + 3 H2O, to form iron (III) oxide.
Have you seen in one of the rocket threads a link to a place with a video comparing uncatalysed, and 1% Fe2O3 catalysed candy propellants? It's quite effective!
As I understand it, iron oxides are catalysts for the breakdown of potassium nitrate, and thus their effects should be independant on the fuel used, so they can be used with candy propellant, BP, sulphurless BP, and any other nitrate mixture.
Does anyone actually know the mechanism of the catalysts action? I'm wondering about other uses, such as sensitising AN perhaps...

[arm]

Cant help you with a reaction mechanism there Mr.C. The only reason I asked about the use of Iron Oxide was because ive only seen it used with organic compounds (sugar, Sodium Benzoate, Sodium Salicylate etc) and assumed that it catalysed only their breakdown. It would seem logical that it would catalyse KNO3 decomposition though. The Net has been pretty unhelpful so far, i might consider a trip to the Uni library.

[blindreeper]

I belive this http://www.jamesyawn.com/fe2o3/index.html is the link you are reffering to Mr Cool

[arm]

Heres an interesting one...

Apparently Iron(II)Sulfate Catalyses the combustion of Black powder. This appently occurs partly because it prevents the formation of H2S (which inhibits the decompostion of KNO3). It also has the added benefit of being a high temperature oxidizer and forms the catalyst Iron(III)Oxide when it decomposes.

Ive been trying to find more info to back this up.................so far, no luck.

Iron compounds seem work best as catalysts when the iron is in a +2 oxidation (ferrous) state rather than the +3 (ferric) state.

[Mr Cool]

Yes, that is the link Blindreeper, thanks.

"Iron compounds seem work best as catalysts when the iron is in a +2 oxidation (ferrous) state rather than the +3 (ferric) state."

Most transition metal compound catalysts work by having the metal ion switch from one oxidation state to another, and back again. Thus I find it surprising that one state works better than another. If FeO is indeed better, that makes things a little harder. The method I proposed probably couldn't be used easily, since Fe2+ is easily oxidised to Fe3+ in alkaline conditions. Maybe roasting FeSO4 without oxygen present could work (don't waste the SO3 made!), although this requires a higher temperature and wouldn't be quite as easy, but it would still be easy.

I have also heard about catalysts that prevent H2S formation in BP combustion arm, it would be interesting to try. Maybe add an additional 1% of FeSO4 (hydrate) to the BP ingredietns and mill it for a while. Dan William's site has a burn-rate tester, something like this could be used to compare catalysed and normal BP.

I think it would be interesting to try catalysts in low explosive mixtures. It could give significantly more performance with very little extra effort. Unfortunately, there does not seem to be much information on the subject at all :(.

[arm]

Sorry Mr Cool, i retract the statement about iron working best in a +2 oxidation state. After a little reading it seems i was infact talking utter bollocks. Thinking about it, iron is in a +3 state for Fe2O3 and this is the most desired catalyst for rocket propellants.

My temporary insanity was most likely caused by the freak spell of good british weather we're having right now.:D Better make the most of it, its probably all were gonna get as a summer.

But yeah, it would be a nice experiment to try by testing burn rates. I think there are a couple of US patents on catalysing BP but i cant find them.

At what temperature do the Iron(II) and Iron(III) Hydroxides decompose into the oxides???

[kingspaz]

arkangel, you have mail regarding the Fe2O3.

[static_firefly]

Iron Oxides can be bought at hardwear stores as concreat colouring. I bought black and red inro oxide for $5 each for 1L bucket. Im not sure if its useful stuff tho

[arm]

Theres a small bit on Richard Nakkas Rocketry site about catalysts.

He mentions Iron Sulfate as a catalyst for Nitrate comps. He also references an experiment that showed that adding 1% Iron Oxide to a Nitrate composition gave a burn rate improvement of around 60%. A pretty impressive improvement. Another point however, is that adding a catalyst also increases the sensitivity of a composition as well, especially if a lot is present.

[Desmikes]

You could just get some fine steelwool (every hardware store) put it in the container with Vinegar for a few min and then let it sit in the open air for some time. I've never done this myself but I believe the rusting time will be about 1hr. However, I have had steelwool sit outside for weeks and turn into finely powdered rust. The rocked fuel made with this rust did burn about 20-30% faster.

[Tuatara]

Since iron seems oft quoted as a catalyst, perhaps FeCl3 would be useful. Providing both catalysis and chlorine, esp. for pyrotechnics. Commonly available in electronics hobby shops for etching printed circuit boards. Mucky stuff though, stains everything yellow...

[vulture]

IIRC, FeCl3 will quickly convert to Fe(OH)3 when exposed to air. Fe(OH)3 can easily be converted to Fe2O3.

[arm]

At what temperature does Fe(OH)3 convert to Fe2O3 if doing so by heating?

[arm]

Well,

From what i can tell, Iron Oxide is probably a fuel decomposition catalyst rather than an oxidiser decomposition catalyst. I've seen experiments where two samples of paper are burnt, one is a control sample and another is doped with iron oxide. The doped sample burns in about a third of the time the control sample does. Also theres the sugar lump experiment, where a sugar lump doped with Fe2O3 catches fire from a match whereas an untreated one does not. Furthermore, ive read that to allow the complete combustion of soot (mainly carbon), Fe2O3 is again used as a catalyst.

So with from this info it would be best to add 1-2% of iron oxide to the charcoal when it is being milled. If Iron Sulfate is to be used as an H2S inhibitor then i imagine this would be best added to the Sulfur when that is milled.

[vulture]

Fe(OH)3 is so unstable in solution that it will immediatly decompose to Fe2O3.xH2O, which is brown.