Let me first start by saying that I'm approaching this from the perspective of a chemistry student, not a welder.
Magnesium may burn at high temp, but the heat is quite localized and may be recorded as much lower if you were, say, to take at thermometer to it.
Also, powdered and thin strips of magnesium burn readily, but good luck igniting a solid block; i would expect the see different temps listed for
different forms. Also, magnesium will also burn in water. The only way to put it out is to remove it from a reactive atmosphere, which usually means
smothering it in dry sand. I imagine that if you bury it in the thermite mix, it may go out before you reach ignition.
The easiest way to ignite thermite is, shocker, with thermite. Get a tiny bit ignited and it will set off the rest.
If your aluminum has formed an aluminum oxide layer, it will increase the temp needed for ignition since you'll need to melt through to the aluminum
(mp is over 3x that of elemental aluminum) Note that aluminum oxide is a product, and therefore it will slow the reaction.
There are ways to make this reaction occur more easily, depending on the intended use. Sulfur is a good additive because it lowers the melting point
of surrounding Fe and leads to superior welds. Oh, yeah. Don't forget that the molten Fe you make is well past the melting point. It will melt into
and through a lot. I personally love the scene in Burn Notice where Michael bores through the engine block of a car using a coffee can of a thermite
mixture.
Thermate is a mixture of iron thermite (yes, you can have copper, chromium, ect thermites; thermite is actually any mixture of reactants that undergo
a thermite reaction) and several other additives like sulfur, barium nitrate, and a binder (which allows you to shape it and avoid losing reactants to
the slightest breeze). Red gum should work. It's often used in fireworks and the like, though I've heard that synthetic polymer resins like PBAN are
used by the military in thermate anti-material grenades.
Thermate is nice because it's easier to ignite and interacts more with the surrounding metal. Now, before you point and say, "Hey, I want to weld, not
melt through heavy artillery", I will point out that thermite is also used for welding (didn't mean to get you excited by all that "anti-material"
stuff).
@4s2: This is pure conjecture, but I would assume that thermate is the thing you heard about the marines using for quick welds.
I
Oh, one final note. Sparklers are often cited as a good tool for igniting thermite because they are a cheap, readily available source of magnesium,
though they do contain a mix of metals. You can smother them just as easily as magnesium. "Burning" is simply an exothermic redox reaction. If you
remove the reactants, you terminate the reaction. |
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