[ATM] Will Alum Oxide fine grind quartz blank?

[Mark Cowan]

Anthony,

Aluminum oxide (corundum, Al2O3, AlOx) is definitely NOT harder than silicon carbide (SiC, carborundum, "ouch damn it").  If it were I'd use it exclusively for grinding fused silica and pyrex, as it gives a nicer finish than SiC due to planing over fracturing.

Sources I find list SiC as 9-10 on Mohs scale, AlOx as 9, quartz as 7.  More linear measures show AlOx as 1100-1440 kg/mm^2 (depends on purity) and SiC as 2800 kg/mm^2, fused silica as 600 kg/mm^2, hence AlOx is harder than fused silica but not nearly as much harder as SiC is.

See:

http://www.accuratus.com/silicar.html
http://www.accuratus.com/alumox.html 

Anybody who's interested - I still have about 100 lbs of roughly 120 grit AlOx you're welcome to for the shipping...  It was free and it works well for softer glasses! 

Best,
Mark

--- On Thu, 10/8/09, Anthony Stillman <atmer at flash.net> wrote:

> From: Anthony Stillman <atmer at flash.net>
> Subject: Re: [ATM] Will Alum Oxide fine grind quartz blank?
> To: atm at atmlist.net
> Date: Thursday, October 8, 2009, 3:43 PM
> >Will Alum Oxide fine grind quartz
> blank?
> 
> My experience with quartz, and by quartz I mean fused
> silica, is that grits behave on it compared to pyrex
> (borosilicate) as if they are one and half to two grits
> finer.  60 grit behaves like 100, 80 like 220, 600 like 9
> micron and so on. Also the grit breaks down much more
> quickly.  What would be a one minute wet on pyrex might be
> only 10 seconds on quartz. Since mostly alpha corundum is
> used for fine grinding it can seem like it isn't doing
> anything.  Incidentally di-aluminum tri-oxide is harder
> than silicon carbide.  It's a 9 as opposed to 8 to 8.5 on
> the mohs hardness scale.  Fused silica is nearly a 7.  The
> mohs hardness scale is pretty linear except for diamond (10)
> which is 50 to 100 times harder than saphire(9) depending on
> the diamond's origin.
> 
> I've tried mirror grinding with fine diamond powder,
> scratch city.
> 
> Anthony
> 
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