[ATM] Re Effect of pH on polishing fused silica & Zirconium Oxide

[Mark Cowan <toolontop@yahoo.com>]

Gary, Guy, all,

ZrO2:  I found it works at about 1/2-2/3 the rate of
my usual cerium oxide (sold as "1670" but also
designated C370-K ).  Randy sold me about a half-kilo
slurry (mud, more like) for some ridiculous price, and
it's my "goto" stuff for when I need slow predictable
action, but useful for that mostly on soft glass, not
helpful on fused silica. This bottle I've labeled
"super ZrO2" IIRC the particle size was .5 micron.  It
has an opalescent sheen in the slurry so that would
seem about right. 

I used it to get the final finish on a plate 10" f/7.7
that went to Florida, was run through Jame's robo and
pronounced by the club there to have "the best surface
they'd ever seen." ;)  It's now in South America in a
dedicated planetary equatorial, last I knew. :)


BTW all ZrO2's are not created equal!  I've used the
stuff W-B sells a long time back on plate and Pyrex,
and it was actually slightly more aggressive than CeO2
as I recall - but that was their CeO2 for comparison.

Salem has a wide spectrum of CeO2s intended for the
semiconductor industry, among others, and I've
discussed sub-micron products with them for the fused
silica application.  Bob Carter recently sent me a
free sample (a half-kilo in a pint bottle) of CR426-S,
this is Cerite 5200 with a .2-.6 micron particle size.
 I'd tried some SRS454/Cerite 4854 at .1-.2 micron
size earlier but found the lap drag prohibitive.  I
haven't yet tried it in a controlled experiment, it
takes a while to evaluate any new agent.  But where
I'm going with this is that as the average particle
size goes down, the lap contact improves and the
polishing drag goes up.

Here's the deal - the article (one request so far for
a copy - get your order in!) also gave measurements of
average particle size related to pH, and across the
board the particle size drops.  A summary

CeO2  Hastalite PO  .78  .58
CeO2  Opaline       .93  .82
ZrO2  TAM           .85  .74
Y2O3                2.0  1.2

All sizes in microns, starting pH compared to ph 4. 
Not a big effect, but there.  The effect on modern
suspension slurry components is an open question, of
course.  I don't believe CeO2 1670 is a suspension
product - this is what I was using in what I described
earlier.

I've had one (bad) experience with rouge years ago,
but if anybody has a known good supply and would be
willing to part with some, I'd be happy to run some
tests. I'm very happy with the surface I get with
highly dilute 1670 on fused silica (it won out in all
comparison work so far, trying various additives and
using high-resolution Foucault imaging), but if there
ever was a case of YMMV it's the use of various
polishing agents/particle size/suspension treatments
as they create different chemical environments on
different substrates.

To put that distinctly - what works great with one
glass may fail miserably on another...  

Best,
Mark

--- GARY FUCHS <gary@rcn.com> wrote:

> That Salem catalog sounds interesting. I hope I can
> understand it! 
> 
> Salem lists Zirconium Oxide - on their site - as
> being 0.6u and the old container I have is hand
> marked "slow polishing". Has anyone used this? 
> 
> Thank you,
> 
> Gary Fuchs
> 
> 
> 


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