I am looking for a reliable, very long (order of 24 hours) clock
reaction. Ideally, I would want an oxidation or evaporation reaction,
where a single chemical compound is exposed to the atmosphere and the
reaction proceeds with a rate strongly dependent on the ambient
temperature, changing colour, or opacity, rapidly at the end of the
time period.

I would want the reaction to virtually be stopped at around -20C and
take 24 hours at 0 deg C and halve every rise of 15 deg C or so, but
that's not too critical. It may be a combination of chemical and
phyical processes (i.e. a material that has a specific permeability,
slowing the evaporation rate) might be required.

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Request for Question Clarification by synarchy-ga on 08 Jun 2003 20:55 PDT

Hello -

If a chemical hardening event (cements appear to meet the timeframe)
would be of interest, I have found the following:

A very long thesis on modeling the reaction rate of chemical clocks
(which also advocates the hydration of cements as a clock reaction):
http://www.cs.bham.ac.uk/~sjp/publications/thesis.pdf

And by the same authors, a long treatise on the kinetics of such
reactions:
http://www.mat.bham.ac.uk/J.Billingham/clock.pdf

Otherwise, the best I've found involves the BZ reaction, which is on
the timeframe of minutes, not hours...

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Clarification of Question by barryn56-ga on 09 Jun 2003 05:44 PDT

Unfortunately, I need a visible reaction, so I don't think hardening
will be useful in this context. Another thought that occured would be
some form of osmosis or diffusion, but I don't think this would have
the temperature sensitivity. Ideally I would be able to have the
reaction taking place in a small (say 2.5 by 0.5 cm) panel.