halide conversion (was Re: Modifying bleaches)

While at this matter, I dug up my file to grab a few papers on this
topic.

Nishiyama, S. and Berg, W. F. 1973. Kinetic study of the conversion of
silver bromide sol to iodide. Photogr. Sci. Engr. 17, 299-305.

Zuckerman, B. 1976. Formation of mixed silver halides by a conversion
process, Photogr. Sci. Engr., 20, 111-116.

Calcines, Dolan, Falkenstern, Kelly, Murphy, Klinger, Kahn,
DiFrancesco, and Hailstone. 2002. Silver halide recrystalization:
I. quantitative kinetics for the conversion of AgCl to AgClBr.
J. Imaging Sci. and Tech., 46, 101-111.

Nishiyama and Berg used AgBr with and without gelatin, and converted
to AgBrI by addition of KI. Conversion was measured turbidimetrically.
Gelatin retarded the conversion, but addition of PEO accelerated the
conversion in presence of gelatin. The rate of conversion was
influenced by [KI] of halide jet, excess [Br-], and temperature.
Zuckerman used AgCl/AgICl and converted to AgBrCl/AgBrICl, and
observed the steps of the conversion process using electron microscope
and X-ray diffraction. Calcines et al's work is more along the line of
Nishiyama and Berg and others that I don't find right now., but they
used AgCl as the host crystal and used KBr and AgBr as the source of
bromide, while monitoring the conversion turbidimetrically. Their
paper is very rich of data and what is very nice is that they run an
experiment with added ripening agent 1,1,3,3-tetramethyl-2-thiourea,
3,6-dithia-1,8-octanediol and another with a stabilizing agent
4-hydroxy-6-methyl-1,3,3a,7-tetrazainedene. Addition of the former
accelerated the conversion, and the latter, retarded or completely
suppressed it. You'll find these papers interesting, as well as ones
by Sugimoto and Miyake.

Considering that stabilizers common in chloride emulsions, like
1-phenyl-5-mercaptotetrazole has much stronger adsorption and ripening
retarding effect than 4-hydroxy-6-methyl-1,3,3a,7-tetrazainedene even
in AgCl system, I don't see anything wrong or misleading in what I
said originally in light of Calcines et al's work, as well as based on
my own experience.

--
Ryuji Suzuki
"People seldom do what they believe in.  They do what is convenient,
then repent." (Bob Dylan, Brownsville Girl, 1986)
From: Ryuji Suzuki <rs@silvergrain.org>
Subject: Re: Modifying bleaches
Date: Tue, 30 Nov 2004 12:34:33 -0500 (EST)
> From: MARTINM <martinm@SoftHome.net>
> Subject: Re: Modifying bleaches
> Date: Tue, 30 Nov 2004 10:20:37 +0100
> 
> > It may depend on the specific stabilizer - since conversion to
> > silver iodide can be carried out routinely on commercial ultra-fine
> > grain (and supposedly stabilized) silver bromide emulsions.
> 
> I thought we were talking about printing paper
> emulsions. Chlorobromide emulsions usually use much more powerful
> stabilizer than iodobromide emulsions, especially in neutral to cold
> tone papers. I used 1-phenyl-5-mercaptotetrazole at 0.18 mmol/mole AgX
> in chloride emulsion and this halted ripening. And I can't seem to
> wash this stuff off once it's mixed in (as far as I know, fixing the
> emulsion is about the only practical way to get this stuff off the
> emulsion, but that's not useful anyway). This stabilizer reduces too
> much speed in bromide emulsions so I don't use it in them.
> 
> How do you measure the degree of conversion? What kind of time does it
> take for the conversion to take place?
> 
> --
> Ryuji Suzuki
> "People seldom do what they believe in.  They do what is convenient,
> then repent." (Bob Dylan, Brownsville Girl, 1986)
>