"George E. Cawthon" wrote in message
...
Ok, Harold, you're right and I'm wrong. Hot iron dissolves
diamond. It doesn't say that in any of my chemistry books
and it doesn't say that in a chemical engineering book, it
doesn't say that in my CRC handbook, although it says
graphite is soluble in liquid iron. It says diamond melts
above 3550 degrees C, but a reference on the net indicates
that diamond breaks down at a much lower temperature. So
maybe it breaks down to graphite and then dissolves into the
steel.

Actually, I think that diamonds only sublime. I'm not convinced there's a
liquid phase of carbon, but I'm no chemist. This statement should open up
another round, yes?

In any case, there appear to be plenty of references in the
tooling industry that iron and diamond don't work together.

Yep. It's been long known that they don't.

As I already admitted in another reply, I was wrong about
the silicon carbide wheels on small grinders. To answer
your question, nope, I can't tell the composition of a wheel
at a glance. The dry ones mostly look gray and the water or
oil soaked ones just look dark. Although silicon carbide
ones come in black and green, mine are black, just like
silicon carbide wet/dry paper.

That, as far as I know, is how you identify silicon carbide wheels, aside
from reading the label.. In grinding wheels, I've never seen them in any
colors except for green and black. I've long wondered why, because you
can buy silicon carbide lapping compound in gray, as you've suggested.
I'll eventually check my reference books from Norton to see if they address
that issue.


I don't have a clue what the
red wheels are as they aren't marked.

They are usually aluminum oxide. Could be wrong, though.

I have sharpening
stones, but of the two that retain their packaging, one says
carborundum and the other says silicon carbide (unopened).
Both are the same (of course) and are essentially the same
color as my aluminum oxide grinding wheels. My packaged
grits are silicon carbide and they also have the same dark
grey color.

Well, it's been an interesting thread, and I learned
something.

That's the whole idea here. Share what we know. I commend you for your
polite post acknowledging all our comments.

Harold