Thursday, August 31, 2006

0 Interesting Materials

I encountered the following in my materials science class. However, not a lot was given about them in our textbook (Askeland, Phule : The Science & Engineering of Materials, 2006). So I did some reading on it. Here, I present them to you.

1. Zerodur (trademark name of Schott Glass Technology) - Zerodur is a type of glass-ceramic composite. A glass ceramic is obtained by nucleating small crystals (a quartz structure crystalline phase) , about the size of 50nm, within glass. The process its done by is called controlled volume crystallization (distribution of nano-crystals within a residual glass phase). Among its interesting properties is its stability in linear thermal coefficient of expansion over a wide range of temperatures, its homogenity and high operating temperatures compared to normal glass like pyrex or fused silica. Because of these properties, it is used to make mirror substrates for large telescopes like the Chandra and Hubble and for x-ray satellites and weather probes. More complete understanding of this material and how it is made can be obtained at Schott's webpage.

2. PZT (Lead Zirconium Titanate) - These class of compounds are the among the most extensively used materials for electro mechanical and electro acoustic transducers. It is, strictly speaking, a piezo-electic ceramic. Piezoelectric materials are those that have the capacity to generate a voltage on the action of a mechanical stress. Piezoelectrics were used even in earlier times, interestingly also by the Uncompahgre Ute Indians from Central Colorado, who used a cerimonial rattle filled with crystals of quartz (a piezoelectric) that threw out light when it was shaken in the dark. According to our text, it is used in gas grills. I belive it could also be applied in strain gage transducers. Well, absolutely anywhere concerned with the measurement of stress of strain. The best source of PZT manufacturing and educational information on piezo's I think is on the German Physik Instrumente website.

3. Magnetorheological fluid (MR Fluid) - Wow. I'm simply amazed at what these polymers can do. In the presence of a magnetic field (like from a magnet), these fluids change their viscosity (I think) to harden or change shape, and have a paste-like consistency. When the field is removed, the fluid becomes, well, fluid again. You'll understand and appreciate how this happens after watching this video. It is used in vibration and damping control. It is a superior material because it is more stronger and more insensitive to contaminants and extremes in temperature. Compared to? Compared to, say ER (Electrorheological liquids) , another interesting class that you'll find out about with a google search. Moreover, MR fluids require only low voltages for operation. This means a lot for areas such as the space industry, where "significant mechanical power wattages can be regulated with just a few wattages of electrical power". Its even used in your shock absorbers, if you own a Cadillac! Same principle : Reducing mechanical shocks with regulation through MR fluid ! Even though its applied in so many areas, researchers claim that more study of the inner working and physics of MR has to be done.

Intrestingly, a professor of chemical engineering at MIT, Alice Gast, thinks that these fluids could one day make its way to the viens of a robot, to make robot blood!!!


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