Science of … clay?

Here’s something you may not know about me: I’m a potter. No, I’m not related to Harry.

What I mean is I work with clay in the art known as ceramics. It’s been years since I’ve touched clay, but give me some time to brush up my rusty skills, and I probably can make you a mug, or two.

But I’m not here today to discuss my skills in clay-molding or to make you a mug. I want to talk to you about the science of ceramics. Just google “ceramics science” and you’ll get a vast amount of information describing the science behind this unassuming topic. There’s even a scientific journal containing papers dealing with research on ceramic materials.

In any case, here are some interesting basic facts you may not know about ceramics:

1. It’s old. 

And I mean really old. The earliest known object made of fired clay is almost 30,000 years old (it’s a small figurine of a woman, in case you’re wondering). The oldest pottery vessels came from East Asia, dating back some 20,000 years ago.

2. There are two major branches of ceramics: traditional and advanced.

Traditional ceramics are clay-based, and its applications include your typical dinnerware, ovenware and consumer products like tiles and sewer pipes. These have been in use for many years (see Point 1 above). Major categories of pottery encompass: i) earthenware, ii) stoneware and iii) porcelain. Their properties differ primarily due to the temperature the clay is fired at.

Advanced applications of ceramics enter the industry only in the last few decades or so. These include the precision manufacturing/engineering of products such as thermal insulations, space shuttle tiles, catalyst supports, biomedical implants and water purification membranes. Applications span across multiple industries: aerospace, chemical, environmental, homeland security, etc.

3. Clay minerals can be divided into three primary groups which differ in their structures:

a) Kaolinite

  • Formed by repeating layers of one silica and one alumina sheet
  • Known as 1:1 clay mineral
  • Each kaolinite unit (of one silica and one alumina sheet) are linked by strong hydrogen bonds

b) Illite

  • Formed by one alumina sheet sandwiched between two silica sheets
  • Known as 2:1 clay mineral
  • Each illite unit is linked by potassium (K+) ion and the bond is moderately strong

c) Montmorillonite

  • Formed by one alumina sheet sandwiched between two silica sheets
  • Known as 2:1 clay mineral
  • Each montmorillonite unit is bonded by weak Van der Waal’s forces
  • Montmorillonite can expand by several times its original volume when it encounters water

In case you find the description above too daunting to digest, here’s a diagram for illustration:

Screen Shot 2017-04-06 at 12.21.33 AM.png

4. Clay can be kneaded into different shape by applying a force to it.

I supposed this is a no-brainer: relatively wet clay can be molded easily, while dry clay is harder to do so. However, we need to understand this property from the structure of clay.

Wet clay layers are separated by a thin layer of water molecules which are linked to neighboring layers via hydrogen bonds. Even though I have mentioned above that hydrogen bond is a significant force, they are weak enough to allow the clay sheets to slide past each other when force is applied but strong enough to keep these sheets in position when the force is removed.

So, next time when you’re drinking from a ceramic mug, don’t forget the science behind it. Cheers!

– Ling Ling

References:

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