Reducing Silicon to powder

[otto]

Not sure where this belongs, it crosses a few lines but pertinent folks will find it here.

 

Got a local business at auction with some curious metals on the block. Of interest to me are the "high purity" silicon, some FeSi, lots of aluminum ingots and lead pellets. I know what to do with the Al and Pb. The FeSi appears to be easily reducible to powder but I'm not sure if I want that much (200#).

 

There is also nickle, cobalt, chromium, niobium(?) and, well I can't recall the rest right now. Presses, high temp lab ovens, slicers, grinders, vac pumps, geez, I don't what all they were doing there

 

The silicon appeals on a number of levels but it would still be a lot (150#). If I have the capability to reduce to a usable powder I could share/trade right here. The raw product looks like this:

I have plenty of milling options with some zirc-M media I could use with a dedicated jar. My finest screen is only 200 mesh so that's as far as I could "guarantee" without purchasing an additional screen.

So questions;

1. Is silicon in this state brittle enough to mill with the methods I have at hand?

2. Is 200 mesh fine enough for pyro purposes or do I need to classify finer?

3. Any safety/health issues I should be aware of should I undertake this enterprise?

Thanks for any input and I greatly appreciate this venue as a resource and "advisory board".

 

[lloyd]

'Chip' silicon is very pure, and VERY frangible material. Steel or ceramic media will grind it, although due to its lower density, the ceramic might take a bit longer.

 

When we were home-schooling our kids, we set up a lab and shop to make (just for a fun experiment) silicon solar cells. (Yeah. really.. kiln, plating baths, doping goo, the whole shebang!) The wafers were so brittle, we never received a box of them without some being broken when they arrived.

 

Lloyd

[otto]

Thanks Lloyd, I appreciate the input. I take it there are minimal safety issues or you'd have mentioned them. For finely dusty stuff I always wear standard respirator just because and gloves (they're cheap).

 

So how fine do I have to go with this for, say, pooping up some primes? There doesn't appear to be any other uses that I have uncovered unless there are other suggestions that pop up here. I'll buy into a screen if necessary but if 200 will get it done....

[Mumbles]

I bet a "grind your own" and pre-ground material would both me attractive. -200 mesh is definitely good for primes.

 

I agree that silicon wafers or pure silicon is pretty fragile. It's like a fancy tortilla shell in terms of breakability.

 

I honestly don't know about health issues. Silicosis is mostly amorhphous silica (the oxide), but am not sure about elemental product.

[lloyd]

Otto,

There's a 'cheat' you can use to get a particular fineness of grind without having to resort to extremely fine screens. It's used all the time in industries where the exact mesh size isn't so important as if it all passes a certain mesh.

 

Grind everything ONLY as long as to pass your finest screen (say 100-mesh). Do numerous 'sizing checks' during that first run, so that you do not grind much of it excessively fine.

 

Now you'll be left with a mass that is finer than 100-mesh, but only-just. Next, grind the whole mass at once for a certain fixed time (for you to determine by microscopy) that will be 'enough' to get the average mesh size below 200-mesh.

 

Although very fine screens are used in industry, often methods such as 'air column separation' are used, too. A controllable jet of air is introduced into the bottom of a funneled cylinder full of the dust to be characterized. At an initial slow air velocity, what dust escapes the top is 'finer than selected', and what stays suspended or falls back is correct size (or coarser).

 

After the super-fines have been removed thus, the jet is increased in velocity so that only the 'chosen' material is ejected from the top, and the coarser material that requires re-grinding stays behind.

 

Lloyd

[otto]

Interesting method, it shouldn't be too difficult to standardize a procedure. Once determined, consistency in time and load should get me there. I'm all about working smarter.

 

I don't know where this will go. There's 200# and lackluster bidding. Auction closes Feb. 9th. If it lands in my lap I'd offer it both ways here like Mumbles suggested. Lots of interesting stuff at this one.