Stripping AR coatings off glass substrates
bmar...@pacbell.net
I am manager of a small precision optical lab, making optics for the
laser/electronics industry, and am trying to find a way to remove a MgF
AR coating off fused silica and crystal quartz substrates, without
damaging the defect free, super flat surface. A coating company blew
the coating, and I would really like to be able to strip the coating,
as opposed to regrinding and polishing the surfaces.
Any comments would be greatly appreciated
Regards,
Bill Marriott
VA Optical Labs
415-459-2348
Salmon Egg
1167950939.9...@i15g2000cwa.googlegroups.com,
"bmar...@pacbell.net" <bmar...@pacbell.net> wrote:
Good Luck! You do not say how well you have to keep the surface figure or
quality. The problem with hot MgF2 is that it is very tenacious. Acids will
almost certainly generate HF which will etch underlying glass.
Bill
-- Fermez le Bush
wadex...@provide.net
Hi Bill,
You might find what you are looking for at
http://www.kolzer.com/files/WWII.pdf, on pdf page 88. However, you
might not. (I removed a MgF2 coating from an eyepiece using only my
eyelash, but it took 40 years.) Based on the long experience of an
optician I spoke to, I think a polisher is in your future.
"When coaters are good, they are very, very good. But when they are
bad, they are horrid."
Wade Kelman
Salmon Egg
1167966392.9...@i15g2000cwa.googlegroups.com,
"wadex...@provide.net" <wadex...@provide.net> wrote:
That reference looks interesting. I hope to live long enough to read it some
day.
My brief perusal indicated that hot deposition was in its infancy. Moreover,
the stripping methods just did not work on the hard mag fluoride. There was
a tongue in cheek complaint that now that they were getting the hard
coatings, they could not be stripped when stripping was wanted.
In your case, you may not have had a hard coating. Is it possible that your
AR coat was made with cryolite or other soft material rather than MgF2?
Kevin
of the substrate would may be affected, depending on how uniform the etching
process was.
<bmar...@pacbell.net> wrote in message
news:1167950939.9...@i15g2000cwa.googlegroups.com...
John McMillan
Salmon Egg <salm...@sbcglobal.net> wrote:
http://www.corning.com/docs/specialtymaterials/pisheets/H0607_MgF2_Produc
t_Sheet.pdf
says MgF2 "slowly dissolves in nitric acid". How slowly and whether
HF is released is not stated...
Salmon Egg
j.e.mcmillan-CB03...@no-reverse-defined.ja.net, "John
McMillan" <j.e.mc...@sheffielddot.acdot.uk> wrote:
> says MgF2 "slowly dissolves in nitric acid". How slowly and whether
> HF is released is not stated...
This is the reason everyone should have at least a modicum of chemical
knowledge.
Bill
-- Fermez le Bush--about two years to go.
John McMillan
Salmon Egg <salm...@sbcglobal.net> wrote:
> On 2/2/07 5:45 AM, in article
> j.e.mcmillan-CB03...@no-reverse-defined.ja.net, "John
> McMillan" <j.e.mc...@sheffielddot.acdot.uk> wrote:
>
> > says MgF2 "slowly dissolves in nitric acid". How slowly and whether
> > HF is released is not stated...
>
> This is the reason everyone should have at least a modicum of chemical
> knowledge.
>
I have a small modicum - but thats not enough apparently.
Looking at it I guessed that it wouldn't simply go to
magnesium nitrate and hydrofluoric acid because of the electrochemical
potentials of the ions. Is that right?
Helpful person
Unforunately your only resource is to repolish the surface.
Please visit my web site at www.richardfisher.com
Salmon Egg
j.e.mcmillan-12A4...@no-reverse-defined.ja.net, "John
McMillan" <j.e.mc...@sheffielddot.acdot.uk> wrote:
Well, HF dissolves silicate glass when in water solution. You get SiF4, and
your polish is gone.
GLS
We have removed MgF AR coatings and AlSiO coatings from optical
elements for astronomical applications, which require to maintain the
high surface accuracy quality. We made it by immersing the optics on a
warm bath of sulphuric acid and it works very good. It is very simple,
but you have to be very careful with the liquid.
Kind regards,
Ana.
Ana Manzanares, PhD
Optical System Design and Supply
GREENLIGHT SOLUTIONS
www.greenlightsl.com
Coater
Tablespoon of Boric Acid to a Quart of Sulfuric Acid. Raise temp to just
under boiling. This will remove MgF2 from optical glass. But, if the glass
cannot take acid, you're left with a lump of sand. CHECK THE BOOK!
The boric acid is used as a buffer to protect the surface of the glass, and
as I have been told, it helps prevent the formation of HF.
This is not for amateurs, and serious injury can occur. You'd most likely
be better off repolishing, or remaking the optics.
Regards
"GLS" <a.manz...@greenlightsl.com> wrote in message
news:1171023725.2...@a34g2000cwb.googlegroups.com...
Salmon Egg
"Coater" <nore...@nowhere.com> wrote:
> Tablespoon of Boric Acid to a Quart of Sulfuric Acid. Raise temp to just
> under boiling. This will remove MgF2 from optical glass. But, if the glass
> cannot take acid, you're left with a lump of sand. CHECK THE BOOK!
>
> The boric acid is used as a buffer to protect the surface of the glass, and
> as I have been told, it helps prevent the formation of HF.
>
> This is not for amateurs, and serious injury can occur. You'd most likely
> be better off repolishing, or remaking the optics.
What are the reactions that take place under these conditions? How does the
boric acid prevent the formation of HF?
I have removed MgF2 coatings using mineral acids, but high quality polished
surfaces are not maintained. A slight etch may be just fine for some
applications.
Salmon Egg
1171023725.2...@a34g2000cwb.googlegroups.com, "GLS"
<a.manz...@greenlightsl.com> wrote:
> We have removed MgF AR coatings and AlSiO coatings from optical
> elements for astronomical applications, which require to maintain the
> high surface accuracy quality. We made it by immersing the optics on a
> warm bath of sulphuric acid and it works very good. It is very simple,
> but you have to be very careful with the liquid.
Were these hot deposited MgF2 coatings? Those are not as tenacious as hot
deposited coatings and removal can be primarily mechanical as opposed to
chemical.
Coater
What I DO know, is that it has worked well for the last 40 years.
Acid resistant glass is left undamaged. But, as with any optical surfaces,
the more you handle it, the more it degrades.
So, take it, leave it, I don't care. Not going to debate this.
"Salmon Egg" <salm...@sbcglobal.net> wrote in message
news:C1F29AF1.60F93%salm...@sbcglobal.net...
John McMillan
Salmon Egg <salm...@sbcglobal.net> wrote:
> On 2/8/07 7:30 AM, in article
> j.e.mcmillan-12A4...@no-reverse-defined.ja.net, "John
> McMillan" <j.e.mc...@sheffielddot.acdot.uk> wrote:
>
> > In article <C1E90F7A.5F855%salm...@sbcglobal.net>,
> > Salmon Egg <salm...@sbcglobal.net> wrote:
> >
> >> On 2/2/07 5:45 AM, in article
> >> j.e.mcmillan-CB03...@no-reverse-defined.ja.net, "John
> >> McMillan" <j.e.mc...@sheffielddot.acdot.uk> wrote:
> >>
> >>> says MgF2 "slowly dissolves in nitric acid". How slowly and whether
> >>> HF is released is not stated...
> >>
> >> This is the reason everyone should have at least a modicum of chemical
> >> knowledge.
> >>
> >
> > I have a small modicum - but thats not enough apparently.
> > Looking at it I guessed that it wouldn't simply go to
> > magnesium nitrate and hydrofluoric acid because of the electrochemical
> > potentials of the ions. Is that right?
>
> Well, HF dissolves silicate glass when in water solution. You get SiF4, and
> your polish is gone.
>
>
yes, I know that. Thats why HF is used as a glass etchant.
I'm interested to know what the reaction is between
nitric (or sulphuric) acid and MgF2 that produces HF. Also, why does
boric acid prevent it. I'm attempting to obtain my modicum of chemical
knowledge.
Salmon Egg
j.e.mcmillan-47C1...@no-reverse-defined.ja.net, "John
McMillan" <j.e.mc...@sheffielddot.acdot.uk> wrote:
> I'm interested to know what the reaction is between
> nitric (or sulphuric) acid and MgF2 that produces HF. Also, why does
> boric acid prevent it. I'm attempting to obtain my modicum of chemical
> knowledge.
I would expect
2HNO3 + MgF2 --> Mg(NO3)2 + 2HF.
Don't complain about my equation writing if you would complain if I used
HTML.
I would also like to understand the effect of boric acid if it indeed
prevents formation of HF>
micky...@gmail.com
I just tested stripping.of ebeam deposited mgf2 using nitric acid 72 hours at room temp it only pitted the coating.
I also tested straight sulfuric after 2 hours the parent glass substrate that the mgf2 was deposited on etched (s-lah58) with no noticable effect on the coating.
Master Optician REO
Phil Hobbs
it for HF flow cell windows back in the day.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net