Friday, March 17, 2006


more on that unbreakable coffee cup. . .

and last week i got a nice letter from the students who made the wacky unbreakable coffee cup. altho' not strictly on-topic in the typical bccy vein, i found it really fascinating, maybe just because i'm a klutz who breaks a lot of stuff:

"The mugs are called a ceramic particulate composite since it contains zirconium dioxide particles dispersed in an aluminum oxide matrix. Think Jell-O mold. The fruit cocktail would be the zirconium dioxide particles and the Jell-O would be the aluminum oxide.

The mugs are as much a ceramic by definition as a 'regular' coffee mug. These mugs contain no metals whatsoever therefore do not fit the cermet category.

The aluminum oxide (called alumina by us engineers) is the main component of bauxite (aluminum ore) -- from bauxite aluminum metal can be produced by the Hall process. The Alumina used in our competition mugs is very pure and has excellent mechanical properties.

If processed correctly, alumina can have strength 10-20 times that of steel. Despite their strength, our ceramic mugs are not unbreakable as a steel one would be. Advanced ceramics are very strong (stronger than metals); however, they are very brittle. Because they are brittle, they are prone to cracking which will cause failure.

If a crack or chip in a ceramic occurs as you know, it is very easy for it to break catastrophically. Basically, our mugs won't break unless they are dropped in a way that would cause a chip or crack -- so dropping it repeatedly will probably eventually cause failure.

Dropping it onto a sharp edge could also cause failure because edges concentrate stress. The competition mugs are many, many times stronger than traditional mugs.

The other component in our mug is zirconium dioxide, or zirconia in the field. Zirconia is added to our mug to make it harder to a crack, if there is one, to move through the material. Like the alumina used, it is an advanced ceramic that is not seen in whitewares (plates, mugs, toilets, etc.)

Zirconia, in a different form can be made into a single crystal as a diamond knock-off. Zirconia is used in oxygen sensors in cars and there is much work in the ceramic engineering field to incorporate zirconia as the main material in solid oxide hydrogen fuel cells.

What a typical mug is made from:

Mugs that you drink from are what we refer to as traditional ceramics. The techniques and materials from which one makes mugs, toilets, plates, etc. have been around for centuries.

It's only recently (past 50 years) that work is being done with advanced ceramic materials as described above. Regular mugs are made from clay-based ceramics.

Different materials are incorporated with the clays (often china clays) such as feldspar and flint to make a porcelain. Bone china contains the above ingredients along with calcined bone ash -- the real stuff!!!

Traditional ceramics are also fired at lower temperatures compared to advanced ceramics. Regular mugs are typically fired to 1800 deg F whereas the mug we made was fired to almost 2900 deg F -- really hot!

The final product has a complex microstructure which causes it to have relatively poor mechanical properties (Bad for mug enthusiasts). The structure and material makeup of these ceramics on a microscopic level allows the strength as well as the thermal conductivity of the traditional mug to be poor.

This is why it's hard to get burned by a regular mug. The alumina mug we make for competition conducts heat almost as well as steel(!) making it really hard to enjoy hot coffee.

We really haven't talked to any companies that produce mugs for the public. Our mug really isn't suitable for consumers mainly because they would be so expensive.

Due to the processing hurdles and material costs, if mugs exactly like ours were commercially produced they would probably cost well over $100/ea!

I also hope that the above information will shed some light on ceramics in general for yourself and you fellow [coffee] mug-enthusiasts. Feel free to ask me anything.

Jeff Rhodelas
UM-Rolla, Keramos"

posted by fortune | 8:15 AM | top | link to this | email this: | links to this post | | 0 comments

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