Graphite

Tips and descriptions of materials you use

Graphite

Postby Doug Coulter » Mon Jul 19, 2010 1:26 pm

Although the jury is still out a little, I've gone to graphite and tungsten rod for cylinder fusor grids, using graphite as the endcaps.
Jerry once warned me -- and I'll repeat that here -- Things labeled "carbon" aren't pure graphite, they have clay binders and such like in them, and quickly ruin any cutting tool. Dont get mixed up with "carbon" be it battery rods, pencil leads and so on, they have graphite in them, but are very not pure and the additives are poison for both tooling and vacuum systems. Hit your scounged stuff with a torch and you'll see it either catch fire from wax in it, shatter, or something worse. Graphite just gets hot.

Pure graphite, from McMaster, is the other extreme -- machines like a dream to a mirror finish right off the mill or lathe, and you get some lube on your ways doing it. But you will blow black snot for awhile, as the "chip" is a very fine dust. I've been able to bore and then turn it quite thin, and it drills all too easily; start with smaller drill than the hole you need and pull it out to let the dust clear -- the dust rubbing will make the hole bigger than you wanted.

While graphite is a good lube in air, it isn't in a vacuum -- it loses the surface hydroxyls and sub-oxides that make it slippery in a vacuum and actually becomes sticky there.

Graphite is the king of elemental materials that take high heat and stay stiff doing it. It does not seem to sputter much in the fusor environment, but I have yet to check on the mass spectrometer if it's making hydrocarbons when hit with the ions -- it does roughen up in use a little bit, so some is going someplace. If I dared, and someday I might, I would make a whole grid out of it and try that -- it has great thermal conductivity too, so the feed-through can help suck heat out of it.

Next time I have my graphite grid out of the fusor, I'll put up a picture of it in this post. Right now, it's in use and working great!
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Graphite

Postby Jerry » Mon Jul 19, 2010 11:29 pm

A note about graphite.

Do NOT use it as a lubricant on things that are precise. So in other words sliding ways, precision tools, etc. Graphite is highly abrasive and will tear your machines apart over time. Graphite may seem to be slick but when you look at it on the microscopic level the graphite forms tiny plate like structures. As long as they are laying flat against each other they are slicker than snot, but if you get them on edge they will dig right into the metal they are supposed to be lubricating.

When machining be sure to protect the ways of your machine from the dust. Also make sure it does not get sucked into motor enclosures and electrical boxes!

Commercial machines that mill this stuff have special sealed way covers to keep it out of the machine. Buying a machine that had machined graphite is a real bad idea.

The best thing you can do in a home shop environment is use a shop vac with a hepa type filter and have it mounted right at the cutting tool. This will get almost all of the dust. Use this shop vac for graphite only so when it finally gets plugged up you can just throw the whole thing away. I would not want to open one!
Jerry
 
Posts: 573
Joined: Sun Jul 18, 2010 12:07 am
Location: Beaverton, OR

Re: Graphite

Postby Doug Coulter » Wed Aug 04, 2010 11:00 am

Jerry, I believe you are confusing graphite with other forms of carbon in this. For sure, your basic carbon is killer on tools. Graphite is not. The problem is, you really do have to know and trust your supplier so you get the one you want for sure, as if it's not pure graphite, everything you say is true in spades. The "high temperature pure graphite" at McMaster-Carr (expensive and only available in a few form factors) is the good stuff and wears bits and ways not at all that I can tell, and I've cut and machined a heck of a lot of it.

What kills you is anything labeled "carbon" or some low purity large crystal graphite, which tend to have other substances in them that are pure poison for tools and for any vacuum application as well.

Here I've used a pretty expensive (couple hundred bucks) HSS wide angle reamer to make concave cones inside 3" graphite rods, many of them, and the tool is still so sharp as to be dangerous to handle. This amounts to making a 45 degree cone in the stuff about 4" deep or more, and after about ten of them, the tool may as well still be brand new. That's a lot of cutting....not to mention the drilling and tapping and turning and other machining these need to get made. Zero tool damage -- even 6061 Al is much harder on them.

I chose this as an alternative to brass and such for making electrostatic lenses and cone traps/ion reflectors -- works great and is far easier when you have to hog out that much stuff.
(more on the cone traps later, probably under "other kinds of fusion")

BTW pure graphite isn't slippery anymore in vacuum, as NASA has found out when things jam in space. A thin layer of oxide and water/hydroxide is what makes it really slippery in air, in vacuum it becomes grabby stuff. So there you use MoS2 or teflon if you can handle their weaknesses (like it evaps or decomposes when hot).
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Graphite

Postby Jerry » Fri Aug 06, 2010 12:19 am

True, pure graphite is not so bad, its when it is alloyed with something so it is not as incredibly soft and fragile is when it rears its ugly head.
Jerry
 
Posts: 573
Joined: Sun Jul 18, 2010 12:07 am
Location: Beaverton, OR

Re: Graphite

Postby Doug Coulter » Fri Aug 06, 2010 10:34 am

Right, and the process it takes to get to pure but not too soft to work with is quite expensive -- so the good stuff is rare. It takes more time, temperature, and pressure to get there. Anathema to a producer, when most people don't care (or know) enough to pay more for the good stuff.

Imagine trying to put tens of thousands of psi on something nearly white hot and holding that for hours to get it hard while pure. Dunno how they do it without a lot of equipment failure.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Graphite

Postby Starfire » Mon Aug 23, 2010 4:22 pm

It has amazing properties - but it makes your hands black :lol:
Starfire
 
Posts: 143
Joined: Thu Aug 05, 2010 4:26 pm
Location: North Ireland

Re: Graphite

Postby Starfire » Mon Aug 23, 2010 4:37 pm

It has some interesting magnetic properties - it is diamagnetic. You can levitate a small magnet above it or levitate a small piece of graphite above a strong magnet - it floats in mid air without any visible support - cool.
Starfire
 
Posts: 143
Joined: Thu Aug 05, 2010 4:26 pm
Location: North Ireland

Re: Graphite

Postby Doug Coulter » Wed Aug 25, 2010 10:05 am

I have some pyrolytic graphite I got at scitoys.com that levitates nicely -- flies just like that bumblebee (there was once this theory you couldn't do mag levitation without feedback, just like the bumblebee couldn't fly). It's a lot of fun to play with, and I've made some interesting lab demo kludges with it. If you use 4 magnets (NeFeB) alternating poles as suggested by scitoys, and cut your graphite round -- it's a near perfect bearing, and has enough levitation to hold up a small mirror, like the ones I make by vacuum evaporation on microscope cover slips. At that point you can use this with a laser to measure tiny forces (sadly, haven't figured out a way to do that with anything involving magnetism in that big field that you need for the levitation). If someone could sort that out, you could really make a sensitive galvanometer or thermo-electric radiometer among other things.

The pyro stuff is a lot more diamagnetic than normal graphite, and also has non isotropic thermal conductivity. One of the nice lab demos for kids is to hand them a chip and let them slice up ice cubes with it -- till they drop it quick as their fingertips freeze.

I believe that some of us here could make our own pyrolytic graphite in our systems, if we were willing to have the mess it makes. I'm unsure of the details, but I believe you just heat a substrate really hot and let in some hydrocarbon gas to decompose on it to make the stuff. Anybody know the speeds and feeds used? I have some stuff on making buckyballs and diamonds in vacuum, but this is supposed to be a lot simpler IIRC.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Re: Graphite

Postby Doug Coulter » Sat Jan 08, 2011 7:25 pm

Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA


Return to Materials

Who is online

Users browsing this forum: No registered users and 3 guests

cron