[alt-photo] Re: fumed silica

[Richard Sullivan]

I've been playing with this for a couple of years now but mostly trying to make microporous paper for various processes. In the last year we've started using it by itself and not trying to make a "precoat." First off dry coating our machine coated Stonehenge albumen paper before rolling the silver mattes it up quite nicely so we don't have to stock two types.

First off it does not cause silicosis. Apparently it is too fine for that. 

Wiki:
"Health issues

Fumed silica is not listed as a carcinogen by OSHA, IARC, or NTP. Due to its fineness and thinness, fumed silica can easily become airborne, making it an inhalation risk, capable of causing irritation."

http://www.tomps.com/pdf_vault/MSDS/CABOSIL_MSDS.pdf

It is not silica flour, it is fumed silica another animal altogether. 

It can, according to the MSDS it can be irritating but is not carcinogenic or very dangerous in normal handling situations. It's widely used in industry from dairy desserts, cough syrup (as a thickener) to face powder (to keep it flowing) and it makes microporous inkjet paper microporous.

It is in the size range of cigarette smoke. 150 sq M of surface area per gm.

How it acts is largely by observation and conjecture at this point.

It traps light in a similar manner that velvet does. Light enters the traps and does not come out. Thus it mattes the surface. It traps coating solution, more is needed, but it is transparent so there is more black.

We suspect it acidifies buffered paper through the Lewis pH effect, thus making bad papers good for pt/pd. Howard Efner who has worked on this with us says the silicon as soon as it hits air grabs on to a double bond of O2. I think I got this right.

Wiki again: Chew on this!

"The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms.[1] Thus, H+ is a Lewis acid, since it can accept a lone pair, completing its stable form, which requires two electrons.

The modern-day definition of Lewis acid, as given by IUPAC is a molecular entity (and the corresponding chemical species) that is an electron-pair acceptor and therefore able to react with a Lewis base to form a Lewis adduct, by sharing the electron pair furnished by the Lewis base.[2] This definition is both more general and more specific—the electron pair need not be a lone pair (it could be the pair of electrons in a π bond, for example), but the reaction should give an adduct (and not just be a displacement reaction).

A Lewis base, then, is any species that donates a pair of electrons to a Lewis acid to form a Lewis adduct. For example, OH− and NH3 are Lewis bases, because they can donate a lone pair of electrons.

Some compounds, such as H2O, are both Lewis acids and Lewis bases, because they can both accept a pair of electrons and donate a pair of electrons, depending upon the reaction.

Usually the terms Lewis acid and Lewis base are defined within the context of a specific chemical reaction. For example, in the reaction of Me3B and NH3 to give Me3BNH3, Me3B acts as a Lewis acid, and NH3 acts as a Lewis base. Me3BNH3 is the Lewis adduct.


Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR3 where R can be an organic substituent or a halide. For the purposes of discussion, even complex compounds such as Et3Al2Cl3 and "AlCl3" are treated as trigonal planar Lewis acids. Metal ions such as Na+, Mg2+, and Ce3+, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base. Other reactions might simply be referred to as "acid-catalyzed" reactions."

More:

http://thecarbonworks.com/blog/wp-admin/post.php?post=16&action=edit

--Dick Sullivan


-----Original Message-----
From: alt-photo-process-list-bounces at lists.altphotolist.org [mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On Behalf Of Loris Medici
Sent: Friday, December 16, 2011 1:25 PM
To: The alternative photographic processes mailing list
Subject: [alt-photo] Re: fumed silica

Thanks much for sharing this Richard,

I would like to ask something: How does silica fume (or fumed silica)
physically act? I mean, does it have a tendency to get airborne
easily? Reading this page, I think we definitely wouldn't want to
inhale silica: http://en.wikipedia.org/wiki/Silicosis.

>From the page:
"...Silica flour is nearly pure SiO2 finely ground. Silica flour has
been used as a polisher or buffer, as well as paint extender,
abrasive, and filler for cosmetics. Silica flour has been associated
with all types of silicosis, including acute silicosis.
Silicosis is due to deposition of fine respirable dust (less than 10
micrometers in diameter) containing crystalline silicon dioxide in the
form of alpha-quartz, cristobalite, or tridymite..."
(In my understanding, silica fume / fumed silica is a more finely
ground / synthesized form of - the above mentioned - silica flour,
right?)

Thanks again & regards,
Loris.


2011/12/16 Richard Sullivan <richsul at earthlink.net>:
> We've gotten some very positive reports on this from the field. At least one
> atelier printer is using it for their platinum work.
>
> It's still in its experimental stage. There are numerous ways it can be used
> so the permutations are virtually endless.
>
> The best way to start may be using it dry. The Athenatype video on Vimeo is
> a good tutorial The first part is dry coating:
>        http://thecarbonworks.com/blog/?cat=38
>
>
> Compiled notes:
>        http://thecarbonworks.com/blog/?p=16
>
>
> Used on Cyanotype:
>        http://thecarbonworks.com/blog/?cat=4
>
> We have done one test that indicates that it makes Pt/Pd work well on
> buffered papers and several reports from the field that confirm this. Howard
> Efner thinks this could be due to the Lewis pH effect.
>
> --Dick Sullivan
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