Thermite

[lacrima97]

I know that a main source for a lot of us is wikipedia. I am a bit puzzled by something stated in the thermite article at wikipedia.

 

It states that thermite is most commonly prepared with Fe3O4, and that Fe2O3 yields a less energetic reaction than the former.

 

I may be way off, and I may not, because I haven't learned to much on this subj. yet, but if this relates then good:

 

I know the standard enthalpy of iron III oxide is around -825, and iron II,III oxide is around -1118.4 I believe. Would these enthalpy's have any relation to the energy produced from the reaction?

 

Sorry if i'm way off or something.

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I seem to have found a correction.

 

Fe2O3 + 2Al --> 2Fe + Al2O3 + /_\H

change in H = 851.5 kJ

 

3Fe3O4 + 8Al --> 9Fe + 4Al2O3 + /_\H

change in H = -3347.6 kJ

 

http://www.ilpi.com/genchem/demo/thermite/ for enthaply formula

 

rust reaction=(-1669.8)-(-822)=-847

magnetite reaction=(4)(-1669.8)-(3)(-667)=-3347

 

In the end Fe3O4 thermite releases alot more energy than Fe2O3 thermite... I hope this becomes more known. I wish people would refer to thermite as primarily not consisting of rust anymore.

 

I don't guess this is really a post anymore, just a review of my findings. Tell me if it needs to be deleted.

[EP.]

Not related to the thermite issue, but as a general rule I would suggest avoiding sources like Wikipedia and sticking to pyro-specific sources. I like Wikipedia just as much as the next guy, but when dealing with dangerous things like pyrotechnics, I'd look for better sources.

[Mumbles]

I figure I'll put some of my inorganic chemsitry class to use.

 

Fe3O4 is not just Fe2O3 and FeO together as it might seem. It is actually a complex crystal structure known as a spinel. The spinel structure is what gives it it's magnetic properties while neither Fe2O3, nor FeO are very magnetic. The structure creates more lone electrons, and coordinates their spins. I suspect this structure has to do with the much higher enthalpy than of Fe2O3.

 

Yes, I agree with EP. Wikipedia might be good for general info, but ALWAYS do more research. I can go in and change stuff no problem and cause some serious injuries for people.

[lacrima97]

When the Fe3O4 thermite reaction takes place, does the -3000+ enthalpy mean that more energy, heat, awesomeness is actually released, as opposed to the -800+ enthalpy of the Fe2O3 reaction? Thats what i'm really wanting to know at this point. Sadly, I can't say that I know for 100% exactly what those numbers mean. Hopefully, If I am thinking correctly though, the first reaction releases more energy than the second. Can anyone confirm?

[Mumbles]

Yes, more energy, and thus heat will be released. Other factors would indicate rate, and that is directly related with awesomeness. Fe3O4 thermite will release more energy than Fe2O3. The negative number is the enthalpy of formation. Meaning to form it, a -3347 kJ/mol change in energy of the system takes place, that can be released at a latter date.

[lacrima97]

Thanks Mumbles, my question has finally been put to rest.

[FrKoNaLeaSh1010]

If your really interested in learning about thermites I would suggest the exotic thermite thread at the science madness forum for a little extra reading. It is rather long but I know I learned a lot from it.

 

http://www.sciencemadness.org/talk/viewthread.php?tid=127

[Dr Boom]

Just a thought to pass along-

 

With all the thermite compositions out there to choose from I thought i'd put my 2 cents in about them.

 

I've tried many good formulas that work efficently and depending on the application (whether or not you need a lot of heat to destroy something -or- put things together) the Fe3O4/ Fe2O3 may not be the best choice for a job.

 

Example: If you want to melt hinges off a steel object or burn through armor plating- yeah, the high output stuff will work fine. But what if you need thermite to do more than just turn things into molten slag, say- welding things together.

 

I ran into a problem a few years back when I was helping my little brother build a race cart to enter in the county fair. The engine mount had broken away from the aluminum tubing conecting it to the frame and we didn't have time to take it to a welding shop that was in the next town over. I did, however, have enough material in my Lab at the time to do some experiments with variations of thermite. An aluminum mixture with carbon dust worked surprisingly well and kept the temperature down to avoid burn throughs.

 

The added carbon took on the excess oxygen molecule forming the much need 'shielding gas' carbon dioxide and leaving very nice filler slag. I'll try to dig up some pictures of the hap-hazard welding job but the kart was able to finish the races without further mishap.

 

A friend of mine that helped with the comp asked if I could make thermite in a stable- stick form that could have a strike ignitor on one end. Being out in the woods, a couple thermite sticks in glove box that won't deteriorate and can be used to weld a broke CV shaft, deer stand, or hole in an aluminum boat- would be very useful. Granted the individual knows how to use it and doesn't make matters worse.

 

I'm sure that having a "stick welder" in your pocket isn't something everyone would like to carry around but the MacGyver in me thinks that a couple sticks the size of No.2 pencils that can fix metal work problems- wouldn't be that bad.