Chess Denman on thu 30 nov 00
I cant give you the values you seek but tables for them do exist. When I got
my probe in England from Glendale controls ltd there was a little leaflet
and the Nernst equation and graphs of partial pressures and lots of advice
about what constituted medium low and high levels of reduction.
Stupidly I fired by the little graphs and immediately lost all my copper
reds! Six painful months later I found by trial and error (more error than
trial) three things.
First I needed a probe reading of 0.65-0.7 established at 800 and maintained
thereafter. for copper reduction to occur. Less and it disappears more and
everything melts or goes murky.
Second at this level of reduction cone 9 goes down at a low temperature by
my thermocouple (1225) which might mean all kinds of things e.g. that my
thermocouple is reading wrong or that the last two hours of rise are slow
+++
Third that I needed to overgass the kiln a bit partly for control (minimal
gas and all on the damper resulted in wild oscillations of reduction and
partly because over gassing seems more reducing than oxygen deprivation or
partial burning of propane.
Now I am not saying this in order to suggest you fire on my readings only to
point out that there are an enormous number of variables in play (consider
for example that reduction can occur in more than one way) and that
instrument calibration can vary a whole lot too.
So all in all my personal experience has been to abandon the nernst equation
and do a whole range of firing experiments ending eventually in a firing
regime that is reasonably reproducible but looks much more like Nils Lou's
suggested one than like the little leaflet I got with the probe.
Chess
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