[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]
Re: [ATM] Fwd: [Fwd: [atm_free] Effect of pH on polishing fused silicawas Re. Session 24...]
Interesting stuff here, guys; thanks for posting the link to the Applied
Optics paper. Does anyone here have a low-cost way to monitor surface
micro-roughness in a quasi-quantitative way? My own thoughts on this
subject:
1. you have a friend that has access to an AFM or optical profilometer.
2. you implement some form of the Zernike phase-contrast method, and
benchmark the patterns against some known reference standard.
3. you obtain a short-wave laser (wavelength < 450 nm), focus the output
through a spatial filter to clean up the speckle, place the filtered output
focal point approximately at the focal point of whatever mirror you are
interested in, and in a dark room, observed the expanded,r eflected bean
projected onto a white, matte background (white painted wall for instance).
Rougher mirrors will show more distinct speckle pattern in the far field
(try it, it really works if you can find all of the pieces).
Scott Milligan
-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Guy Brandenburg
Sent: Thursday, August 30, 2007 10:04 PM
To: atm@atmlist.net
Subject: [ATM] Fwd: [Fwd: [atm_free] Effect of pH on polishing fused
silicawas Re. Session 24...]
Interesting comments on pH levels and polishing with CeO2
Alan Bromborsky <brombo@comcast.net> wrote: Date: Thu, 30 Aug 2007 17:37:14
-0400
From: Alan Bromborsky <brombo@comcast.net>
To: Guy Brandenburg <gfbrandenburg@yahoo.com>
Subject: [Fwd: [atm_free] Effect of pH on polishing fused silica was Re.
Session 24...]
To: atm_free@yahoogroups.com
From: "Mark Cowan" <toolontop@yahoo.com>
Date: Thu, 30 Aug 2007 19:47:54 -0000
Subject: [atm_free] Effect of pH on polishing fused silica was Re. Session
24...
I was looking through the paper I cited in
the last post and noted the following about hydration layers and silicate
redeposition:
Buffering the CeO2 slurry to pH 4 increased the drag greatly, but
according to the paper and the assorted micrographic and AFM imagery the
resulting surface is much smoother - /because/ (they say) the redeposition
from the slurry is greatly reduced. Thus the polishing action is surface
removal primarily. They also say the lap lasts much longer because the
"ceria particles are suspended in the slurry rather than embedded in the
lap." The lack of the redeposited layer means that the final surface is
made from the pure substrate, and so might bond to the coating better,
improving coating life.
Perhaps you need to start with a fresh lap for this experiment. I plan to
test some of this with the robotic figuring machine, which is much more
capable than I am of maintaining constant lap speed against high
resistance.
Best,
Mark
> Here's an interesting experiment that demonstrates that.
>
> H. Highstone set me a copy of an Applied Optics paper from '92 (pp >
7164-7172, Vol 31, no 34) that explored the use of various agents > (CeO2,
ZrO2, Al2O3, Y2O3, YF3) on fused silica at varying pH ratios.
> Al2O3 has by far the highest roughness of any of these compounds.
> Anyway, lowering the pH from 7 to 4 with CeO2 on fused silica lowers >
the roughness by a factor of almost 4x under controlled conditions.
> You can use citric acid to buffer the pH of a slurry down to these >
levels. I've tried it. The lap drag immediately becomes /enormous/, > to
the point that the lap can't be moved smoothly. Although it may > result
in lower roughness under machine control, by hand the result > was
horrible, with roughness quite visible under Foucault testing.
__._,_.___
Messages in this topic (0)
Reply (via web post) | Start a new
topic
Messages | Files
| Photos | Links | Database
| Polls | Calendar
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch
format to Traditional
Visit Your Group | Yahoo! Groups
Terms of Use | Unsubscribe
Recent Activity
5
New Members
16
New Files
Visit Your Group
Yahoo! News
Kevin Sites
Get coverage of
world crises.
Yahoo! Finance
It's Now Personal
Guides, news,
advice & more.
Yahoo! Groups
Beauty & Fashion
Connect & share
tips and advice.
.
__,_._,___
Guy Brandenburg, Washington, DC
My home page on astronomy, mathematics, education:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
or else
http://tinyurl.com/r6fh2
=============================
"Thus, from the war of nature, from famine and death, the most exalted
object which we are capable of conceiving, namely, the production of the
higher animals, directly follows. There is grandeur in this view of life,
with its several powers, having been breathed into a few forms or into one;
and that, whilst this planet has gone cycling on according to the fixed law
of gravity, from so simple a beginning endless forms most beautiful and most
wonderful have been, and
are being, evolved." --- wrote Charles Darwin, ending The Origin of
Species
=============================
_______________________________________________
ATM mailing list http://www.atmlist.net/
_______________________________________________
ATM mailing list http://www.atmlist.net/