Dear Bill,


A laudable endeavour for which I wish you all the best.

Seriously though, one of my favourite adages is "too much is not a problem,
not enough usually is". So, if you can a high temp oven going the can
sustain 1600-1800 C for prolonged periods without suffering from HTOB at a
reasonable, if not to say realisitic cost, I certainly would like to join
the queue.

Thankfully, my TC/EA oven doesn't suffer from HTOB at present but it
showing signs of HTOF (high temp oven fatigue), which means I will need to
move cable B sooner or later.

On the subject of control temp more acurately, I am wondering if 2
thermocouples, 2-3" apart, and corresponding temp control (differential?)
could provide the solution for HTOB prevention? I reckon this would also
help cure the issue of ceramic tubes going pearshaped and the crystal
growth on the outside of the glassy carbon tube. I am not happy with the
single thermocouple solution chiefly because of the expensive consequences
a thermocouple can cause when it hasn't been positioned properly.

I lost my first furnace because of this (I suspect). In my first furnace,
the ceramic tubes developed a paunch over time (much like their owner) that
eventually one tube got stuck and wedged itself so tightly into the heating
element that extraction of the tube caused the heating element to fracture.
In fairness to a certain manufacturer, I received a replacement heating
element under warranty. Still, the instrument was down for weeks, which
didn't impress me much (I'm sure Shania Twain will forgive me).

Coming back to the temp control issue, I am not convinced that only 1
thermo couple will be the answer even if one could seat it 'inside' the
ceramic tube (without compromising wall integrity). One would still be left
with a bell shaped T-profile rather than the Table Moutain kind of profile
we'd like to have. In other words, one would still have to "overheat" in
order to get a wider "plateau" within which T is at least T(min required).

I always come back to the question do we really need ceramic for high temp
applications? By doing so, we still rely essentially on heat transfer by
convection, which is really not that efficient. Can't we use a
ferromagnetic metal, which would lend itself to being heated by induction?
This might not be the cheapest way in terms of purchase price but it may be
more cost efficient to run long-term.

Just a few thoughts.


Cheers,

Wolfram

P.S.: With regards to your precipitation, I'd love to receive a few ml's
plus another few ml's of your local tap water. If could spring for a lock
of your hair, too, one of my PhD students would be very happy.


On May 27 2005, Bill Buhay wrote:

> Dear list members,
>
> We are currently suffering from a fairly common ailment known as "high
> temp oven burnout" (HTOB). Once we picked ourselves up off the floor
> after receiving the rebuild quote from a certain manufacturer we took
> the whole thing apart and decided we could rebuild it ourselves. In the
> spirit of Oscar Goldman from the "6 million dollar man" we would like to
> build it more durable, accurate and capable of higher temps. One problem
> related to us from others in the same situation, which became apparent
> when we took our oven apart, is since the thermocouple is mounted
> adjacent to the ceramic tube, the temperature setting on the EA may
> actually be significantly lower than the actual temp in the reaction
> tube, resulting in premature-HTOB.
>
> Our vision is to build an easily replicable high temp oven with the
> thermocouple built right into an oven (ceramic tube) capable of even
> higher temps. My question (since we would like to do this right the
> first time and make the instructions available for all HTOB sufferers)
> is what is the maximum temp necessary for the various
> methods/applications practiced? My initial thought is make an oven that
> can sustain 1600oC over long periods without burning out. Is 2000oC
> necessary for certain applications (which in our estimation is certainly
> attainable)?
>
> Thoughts?
>
> Bill
>
> PS does anyone require precipitation? We have more than we need here in
> Winnipeg!
>
>
> Dr. William Mark Buhay, P. Geo.
> Assistant Professor
> Department of Geography
> Center for Forest Interdisciplinary Research
> University of Winnipeg
> Winnipeg, Manitoba
> Canada R3B 2E9
> Tel: 204 786 9481
> Fax: 204 774 4134
>