how fine is too fine (grit wise)

[pcm81]

Good evening all.

I found this forum b/c i am interested in thermite welding. Since fuels discussed here are also in some cases single redox reactions like thermite, I figured i'll ask questions here...

 

I've read that nano-thermite (not interested in 911 conspiracies) is a very useful mixture, b/c burn rates, and with it the reaction temperatures, can be better tailored to a particular application.

 

I am trying to make a list of sorts for grit vs reaction rate for various thermite mixtures (mostly iron and copper oxides reduced by aluminum). In other words, if i want a fizz rather than a bang, should i stick with grit that is larger than X micrometers. Or the other end of the spectrum: if i want to attain reaction temperature greater than X degrees i need A/B ratio of nano-meter powder to certain size micrometer powder, etc.

 

At what grit level does a fizz become a bang?

How about nan-scale aluminum and large size Iron-Oxide grit?

 

I've read some place that if shock-wave can not trigger unreacted elements to react, then it is not an explosive, but rather just burning fuel. Does grit size have an effect on this property or is it mostly dependent on composition.

 

I am mostly interested in controlled reactions that yield some useful byproduct. For example molten iron from Fe2O3 +Al or a molter copper from copper thermite. May be molten steel if some carbon is added to Fe2O3+Al mixture. What if I use Al powder milled with charcoal (I think it's called Eckart German Blackhead); will i make steel instead of iron or do i need to add extra carbon? Will graphite milled to micro level work or i need nano-scale graphite particles?

 

Thanks all.

Stay safe.

 

[Arthur]

First remember that coper thermites can go high order regardless. Second, it's usually a factor of scale that matters. a 100g of thermite should work at 50 mesh, but 100kilos of thermite will work with baseball size lumps.

[pcm81]

First remember that coper thermites can go high order regardless. Second, it's usually a factor of scale that matters. a 100g of thermite should work at 50 mesh, but 100kilos of thermite will work with baseball size lumps.

I am interested in welding applications, so say 10grams to 150 grams scale (1/3oz to 5oz). Looking online i found a paper on nano-scale aluminum as reducer for thermites. The conclusion was that Aluminum Oxide layer that forms on aluminum can actually negatively affect the reaction rate for nano-scale size particles, b/c larger surface area means more AlOx and less usable Al before the reaction starts...

[mikeee]

You can look up the MSDS sheets on Cadweld shots and several other companies that make the thermal weld shots.

The MSDS sheet usually lists the materials in the compounds. If you take one of their shots and run it through some screens you will soon discover the mesh of the materials they use.