[ExI] Carbides (Was: hacked email)

[John Clark]

On Mon, Dec 1, 2014 Anders Sandberg <anders at aleph.se> wrote:

> I briefly looked at jewels, and found silicon carbide (moissanite) to be
> intriguing. Again, way cheaper than diamond, almost as hard,
>

Well,  moissanite has a Mohs rating of 9.5 with diamond being 10.0, but
that just tells you that it's softer than diamond and harder than corundum
(ruby), with its Mohs rating of 9.0, but Mohs is just a list of materials
from soft to hard and it doesn't say how much harder one is than another
only that if it has a larger number it is harder. On a absolute hardness
scale like the Knoop scale it turns out that diamond is much harder than
moissanite or of anything else; moissanite has a Knoop rating of 2480 but
for diamond its 7000.  On the other hand diamond is no good at cutting
steel, when it gets hot the carbon in the diamond reacts chemically with
the iron, so for that a moissanite or corundum coated blade would work
better.


[image: File:Knoop-and Mohs- scale.svg]


> > and with great optical properties.
>

Yes, moissanite has a even larger index of refraction than diamond.  And It
has more optical dispersion than glass or diamond too which makes it more
sparkly which is good for jewelry, but a lens made of it would have more
chromatic aberration

John K Clark
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