Thermite

[knoba]

In the past, when I've been filing materials (mild steels & aluminium) in the bench vice. I had often not cleaned up the metal particles.

I was reading about thermite recently, and wondered if I had been in any danger from the risk of a reaction?

The bench stays clean now (good practice), but it still makes me wonder if there are any other possible dangers; eg. grinding m/s and aluminium composites...?

 

[fingers99]

Doubtful. Any dust -- almost -- is a potential explosion risk, but the heat required to set off a thermite reaction is pretty extreme. Isn't it iron oxide plus aluminium? And the two have to be pretty well mixed for anything to happen.

Apparently titanium filings are pretty dangerous and the fires from burning Ti very hard to extinguish. Magnesium is a more obvious one.

 

[knoba]

Isn't it iron oxide plus aluminium?

I think you're right.

Magnesium is a more obvious one.

I've certainly seen my share of flat-four burnouts in the past (mag ally), when the petrol hoses deteriorate; the heads can go next... unstoppable!

Thanks fingers! You've set my mind at rest.

 

[Archie]

I sometimes experiment with the filings covering my bench by pointing the oxy/propane at them. From this rigorous testing I can inform you that the grinding dust from the chop saw does pretty much sweet FA (except glow a bit and stick to the bench) whereas the iron filings from the metal hacksaw give a nice sparkler effect. Not really enough to blow the roof of, I'm afraid. All in all I've been distinctly disappointed.

 

[Hitch]

Doubtful. Any dust -- almost -- is a potential explosion risk

Quite right, even flour or custard powder.

 

[knoba]

archie.henderson

Not really enough to blow the roof of, I'm afraid. All in all I've been distinctly disappointed.

I honestly wouldn't know how you feel...

fingers99
Any dust -- almost -- is a potential explosion risk

Hitch

even flour or custard powder.

Hitch, ...you've been warned before about playing with other people's food!

Thanks guys!

 

[malcolm]

I've always thought mixing iron filings with aluminium was quite a big risk. Fear is the only thing that keeps my garage clean.

Might concentrated spray from an angle grinder put enough energy in to set things off?

 

[fingers99]

I suppose it's possible. But for the reaction to work it has to be iron oxide and aluminium, finely melded together and in the right proportions. (So iron filings won't do.) How it works (IIRC) is that the aluminium becomes aluminium oxide and the iron oxide iron. Generally they use slivers of magnesium to set it off.

 

[knoba]

Thing is... on my old wooden bench (...in the past) the iron filings had usually gone rusty anyway, sitting there for so long. But, as a guess, the proportions would probably require a greater amount of aluminium ...say 60:40 ..?

 

[knoba]

Could the process also be used, successfully, to weld 2 m/s surface plates together (with the compound between them)? ...say; 2 x 1/4" thick surfaces @ 6" x 4"?

 

[Hitch]

I think thats how railway tracks are welded isnt it? Thermite welding...?

 

[fingers99]

It welds railway lines together, so, in theory it's possible. I guess the issue would be some kind of hopper to distribute it all properly. Probably easier to use a stick!

 

[Hitch]

A bit from Wikipedia about thermite welding

 

[knoba]

Hitch is right. I think they use a ceramic cast.

youtube

 

[madkayaker]

Flour mills are highly regulated for electrical safety same level as fuel refineries!

 

[Paul.]

Back in the late 70s I did a course on the BOC / Murex Thermit welding, Ive just dug out some literature, Amazing what I keep in my attic!, This shows basically how it works

 

[Psymon]

I have made thermite before - several times in fact. You need almost powdered red iron oxide and aluminium powder around 200 mesh. Mix the 2 around 50/50 or 75/25 percent. The only way you are going to easily light the stuff is by using magnesium ribbon. Once it is alight there is little chance of putting it out. The reaction takes one oxygen atom from the metals to sustain the reaction.

I only tried it to see if I could weld something together a long time ago. It didn't work so never bothered trying it again...

 

[jimmy shoes]

i think my chemistry teacher lit thermite with a Bunsen burner before

 

[Robotstar5]

We had a stand-in chemistry teacher who used to mix all manner of chemicals etc. to produce impressive coloured flames and copious quantities of smoke, i think the thermite was lit with a magnesium ribbon fuse.
Class was really dull when the usual teacher got back!

 

[Gas mark 5]

we had fun in chemistry, i think it was 8 parts iron oxide to 3 parts aluminium powder we used, teacher mixed it up, put it in a bowl and held a match to it for a long time. after he got bored of that he found a bunsen burner, but still no joy. then it was time for the magnesium but that was too thin... in the end he found an oxy-accetalene torch and that was effective

when it finaly went he suddnly said 'oh crap!' and ran to the opposit side of the classroom...

very impressive flames and sparks etc, when it was over it had melted (turned to glass?) the sand it was in, gone straight through the metal bowel and halfway through the table
caretaker wasn't very happy

I think youd have difficulty lighting it by accident though...