Date: Wed Sep 22 13:41:53 1999
Posted By: Martin Thomas, Post-doc/Fellow, Phyiscal Chemistry, Quantachrome Corporation
Area of science: Chemistry
ID: 937293777.Ch
Message:
I'm sure that you did not first want me to teach you on the chemistry
of ceramics, but rather what to teach.
The following subjects should be introduced to your students (click on a
question for a brief answer) :
Briefly: A
mixture of minerals (produced as a result of the weathering of rocks) and
water. In the correct ratio
the clay is plastic and can be formed by a variety of processes. The
minerals are mainly alumina (aluminium oxide)
and silica (silicon oxide) based plus a variety of other elements such as
iron and magnesium.
Briefly: The
water must be removed by drying. The "green" piece is fragile since no
chemical changes have taken place.
Add water and all you get back is the original plastic mass.
Briefly:
High temperatures are used to promote changes in the clay. The particles
collapse and start to bond together.
Continue heating and the minerals sinter. Some components might even melt
to form glassy or vitreous components.
The higher the temperature, the less porous the piece will be. The piece
cannot be returned to its original clay state
(except by thousands of years of weathering). Don't forget about the
effects of the kiln atmosphere!
Briefly:
All due to coefficients of thermal expansion (on heating) and
contraction (on cooling).
Briefly:
Materials applied to the piece to make it waterproof, durable and for
decoration. These materials are melted
during firing and produce a glass-like or vitreous finish. They may be
clear or opaque and/or colored depending on the exact consituents.
There is quite a lot out on the web. Gentle introductions can be found
at:
http://potteryguide.com/index.htm<
/a> (newsletter style) and
http:/
/cator.hsc.edu/~kmd/caveman/projects/pottery/index.html
An excellent introduction can be gleaned from http://www.amug.org/~mishlowe/FAQs/clayfaq.html
and for glazes at http://users.lmi.net/~dr
ewid/Glaze_FAQ.html
If you want a real indepth websource for the ceramicist , look at http://www.digitalfire.com/
magic/toc.htm
Give http://ceramics.miningco.com/
index.htm(ABOUT.com) a visit too.
Finally, there is a beautiful not-to-be-missed slide show at
http://www.uiowa.e
du/~intl/links/rft/pottery.html
Or you can go straight for their science page at http://www.uiowa.ed
u/~intl/links/rft/science.htm
For a practical investigation, you could do the following...
- Fire various similar pieces (small tiles might work best)at different
temperatures to investigate the sintering effect. Does the piece shrink ,
grow or stay the same?
- How does clay fired in an electric oven, gas oven or firepit differ?
- Try to determine which chemicals produce specific colours. Are the
colours the same before and after firing?
- Maybe you could organize a field trip to visit University
of Birmingham's School of Metallurgy and Materials
for a look at high-tech ceramics?
Thanks for thinking of MadSci.org.
Good luck.
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