Jon Singer on sat 9 oct 99
Lowell Baker asked a set of questions about water on
Thursday. I'm behind in my reading (see forlorn plea
at end of msg), so I don't know whether anyone else
has said anything. I'm going to jump in anyway
because it's a subject that really intrigues me; I hope
that's okay. I haven't seen earlier postings on this
subject, and I hope I'm not going over territory that
has already been covered.
I will quote bits of what Lowell said in his posting, and
respond to them. If it starts with ">", it's Lowell. (If it
starts with "<", it's me summarizing the subject because
I've left some stuff out; I think I only do that once.)
========
>My understanding of physical science, which is growing
>more and more limited, is that matter is neither destroyed or
>created (under normal conditions)
Quite right.
>My belief
>is that it takes just as much energy to break those raskels apart
>as they produce to get wet. I told you this would be low-brow
>science.
1) This is precisely correct. This has to do with a Law
of Nature called "Conservation of Energy". If you
got more out than you had put in, you could build a
perpetual motion machine that ran on the excess...
...and if you got less out we'd all be very frozen & very
dead.
2) This is not low-brow at all; it's Thermodynamics.
3) That's "rascals", actually, but let's not worry about it.
>So, we throw some water in the kiln at very high temperatures
>and something happens. That something may be steam or
>a mutually agreeable divorce of the former fluid state into
>the elemental individual.
This one is a bit tricky. Steam _by_itself_ does not come
apart into hydrogen and oxygen very much without a
catalyst (or electricity, or strong ultraviolet light) until
it gets quite hot. I think you get something like 1%
dissociation near 2,000 degrees celsius, and I think that's
about cone 38. (It is possible to detect water even in the
atmosphere of a coolish star!)
BUT: Steam itself may not be the issue here.
There are many things running around in the kiln,
especially during reduction. In the presence of carbon,
for example, water comes apart very happily. In fact,
if there's _enough_ carbon around, 99% of the steam
goes away at less than 1150 celsius.
...But it _doesn't_ become H2 and O2. Instead, it turns
into something called "water gas", which is a mixture
of CO and H2. Both of these are flammable, and
both of them are good reducers for pottery. (Though
I think wet hydrogen is better than dry hydrogen,
for some reason.)
Note that the carbon is _not_ a catalyst -- it gets turned
into CO (carbon monoxide) in the reaction.
The reaction takes some heat out of the kiln gases --
if I may quote Robert Heinlein and various other
people, "There Ain't No Such Thing as a Free Lunch!"
In other words, even though both reaction products
are flammable, this won't make your kiln any hotter,
....though there's a fair chance it helps you reduce by
providing hydrogen and extra CO.
Now, this depends a whole lot on various conditions,
and I don't know how much carbon is present in any
particular kiln at any particular time. Also, CO and
steam, in the presence of some catalysts and under
some conditions, will turn into CO2 and H2.
It turns out that some of the oxides we use in pottery
(in particular, some coloring oxides) can be catalysts for
this reaction. I don't really think we want to get into
the specifics of that here, though. There are limits!
>Therefore no real heat gain from burning all those little
>Hs and Os. Am I right or stupid?
Entirely correct. Not stupid at all. No free lunch.
>If there is a temperature increase in the kiln where does
>it come from?
You got me. I have no idea. My friend Scott Scidmore
suggests that maybe hydrogen diffuses through the
mullite protector tube around the temperature sensor
& changes the reading, either by carrying some heat in
or by some weird interaction with the thermocouple.
This sounds slightly hoky to me, but I'm no expert.
Scott also points out that steam could react with
alkali metals (lithium, sodium, potassium) in pots
and glazes and even in the surfaces of kiln furniture,
pulling some of them out. This _could_ possibly have
an effect like that of salting the kiln, and it might
cause cones to slump sooner.
(Remember, I haven't done this myself, and I don't
know whether people are going by cones or pyrometers.
I _do_ seem to recall that cones don't work very well
in salt kilns... but again, this is just a suggestion from
a friend, and needs to be tested.)
>If I am stupid and adding water does really increase the heat in the
>kiln, then we wood firers have solved the worlds energy problems.
>We should just burn water.
You are not stupid, and we can't burn water.
On the other hand, because some things react
differently when there's steam around, and also because
hydrogen diffuses into things much quicker and
farther than CO does, it's entirely possible that some
reactions in the glazes are happening quicker or more
thoroughly when you add water, even if the kiln stays
at the _same_ temperature. (Barium carbonate, for
example, is fairly stable even at cone 11 if it is sitting
all by itself ...but not in the presence of steam.) Also,
if there isn't enough carbon or CO to decompose all
of the steam, there's a good chance that steam itself
does things to glazes. I'm not sure what, but it might
be possible to research this at some point.
>It is my understanding that water was added to piston engines to
>dramatically increase horsepower, ie WWII fighter planes, but this
>water did not burn, it turned to steam which drastically increased
>the compression in the engine, hence more power. It also
>drastically shortened the life expectancy of the engine while
>increasing the life expectancy of the pilot in a jam.
I have also heard this, or something like it. Another
reason why this drastically shortened the lifespan of the
engine (in addition to the increased pressure) is that
steam at 600 celsius or higher is a really amazing solvent.
Dissolves things like quartz and steel fairly rapidly,
for example. No surprise that water injection would
cause aircraft (or car) engines to fail rapidly!
Anyway, while I can understand how water would do
_something_ to a pottery firing, I still don't really
have any idea how it could change the temperature
much.
One other thing -- I seriously hope that nobody here
tries pouring water into an electric kiln. Even if they
didn't get electrocuted (and I don't really think they
would -- the water would evaporate too fast), I bet the
steam would wreck the elements.
Cheers --
jon
========================
PS, A forlorn plea:
About 3/4 of the traffic on this list is stuff we've already
seen, some of it several times. Much of that is unnecessary
to the discussion, and I'm drowning in it!
I saw a posting recently where one member asked where
somebody was, and another member answered; the
name of the missing person was in the subject of the
message, so there was really no need to quote the original,
but in fact it _was_ quoted. All of it. _Including_the_
_headers_. I've also seen people quote an entire 400-line
msg, and then give, as their entire response "I agree
with what so-and-so said about this."
I don't know about the rest of you, but I can't deal. It
takes me a couple hours just to read through one day's
worth of Clayart Digest, and I don't have that kind of
time. I'd like to be more active on this list, but as things
now stand I can only read it about once every two weeks.
(That may be a good thing, I dunno -- maybe my overly-
technoid approach is just a pain in the butt for people.)
This is _not_ to say that all repetition is unnecessary --
many times it is very important to be able to refer to
what the original poster said. This is especially true
(just for example) when there's a glaze recipe in the
original question. If someone like Ron gives a revised
recipe, I _definitely_ want to be able to compare! ...And
that's just one example.
Anyway, if everyone could please try to leave out any
_unnecessary_ repetition, I would be eternally grateful.
(I can't believe that I'm the only one with this problem,
so it would also help anyone else who finds it impossible
to slog through 4,000+ lines a day.)
And now, because _this_ message is huge, I think I
should offer my apologies to all of you -- I'm sorry
I take so long to say things, and I hope that this has
been helpful to at least a few of you.
===============
PPS, standups: When I built my wheel, I built it as a standup
for no particular reason -- just seemed like a cool idea.
Then I started hearing from other people about how bad
their backs are... My wheel is fairly lousy (too rickety),
and I've never centered more than 9 lbs of clay on it;
but eventually I will rebuild it, and it will be a lot
more steady & stable.
I find standing up while throwing fairly comfortable,
but I tend to make small porcelain shapes. If I were
throwing large stoneware objects, I suspect it would
probably be much different.
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