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Crystal Trivia Time!

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November 19, 2009 10:29PM
I figure I need to live up to my name a little, and since I just took a materials science class, I might as well share some stuff I learned that's applicable to WISes!

First off: sapphires and rubies? Two names for nearly the same thing. Both are aluminum oxide crystals (Al2O3). What causes them to be different colors is other elements that fit in the empty spaces between aluminum and oxygen atoms in the crystal lattice. A ruby is "contaminated" with chromium, which gives it its characteristic red color. Any other color aluminum oxide crystal is called a sapphire (they're not just blue!), and can contain any number of elements including iron that give them their many different colors. They find their places in watches because they are VERY hard--they are a 9 on the Mohs scale, which is used to measure hardness (diamonds are a 10, though this scale is misleading... diamonds are 4 times as hard as sapphires and rubies).

Now, onto the big boy: quartz. Quartz is silicon dioxide (SiO2), which is also the chemical formula for sand. Silicon dioxide is the most common substance in Earth's crust (quartz is the second most common). Quartz comes in many different varieties and colors, just like sapphires and rubies, depending on the impurities and crystal structure: citrine, amethyst, and onyx.

Quartz is fairly strong (about a quarter as strong as sapphires and rubies, or a sixteenth as hard as diamonds), and it gets used in a lot of places, like in fiber optic telecommunications fibers, but the real reason we love quartz is due to another of its physical properties: piezoelectricity. The atomic basis for piezoelectricity could be a post unto itself (and deals a lot with atomic structures, crystalline structures, induced dipoles, etc.), but the long story short is that applying a mechanical force (say, squeezing) causes little charges inside the crystal to shift and generate new, temporary charges, which generates a (measurable) electrical field. Here's where it applies to watches: the reverse is also true, meaning that if you apply an electric field to a piece of quartz (which has to be cut very precisely), it will actually vibrate at a very, very predictable rate, and the change in the electric field caused by this vibration can be measured with fairly simple electronics. In this case, the magic number is around 32,768 Hz (cycles per second), a number which seems random but isn't. I've since read that it was selected because it strikes the best balance between high accuracy--the greater the vibration, the more accurate the clock--and low power consumption.

Anyway, the real reason that it's magic is because it's also 2^15, or two to the fifteenth power. Why does this matter? Because using only very simple circuitry (again, simple is the key--simple usually means cheaper and lower power consumption), you can divide by two fifteen times to get 1 Hz--one cycle per second! Then you just use this frequency to drive a stepper motor that causes the second hand to tick once per second, or once every 32,768 vibrations of the quartz crystal, and step the hour and minute hands down accordingly.

Quartz crystal clocks are everywhere. Open up the side of your computer one of these days (note, I assume no responsibility for anything that happens to you or your computer by doing so! Rolling on the floor laughing my a.. off) and look for a small, silver, pill-shaped component near where the CPU is. It will look like this:



The thing on the left is a quartz resonator! That one generates a frequency of 14,300 Hz (you can see a 14.3 stamped on it). These clocks are essential for synchronizing the transmission of data between different components on the motherboard of your computer.

Okay, that's all for now! Next time, maybe something off-topic, like bananas! laughing



Edited 1 time(s). Last edit at 11/19/2009 10:29PM by Lukipedia.
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Crystal Trivia Time! Jpeg Attachments

Lukipedia1017November 19, 2009 10:29PM

Wow! That was some interesting reading, thanks for posting!Thumbs up! (n/t)

Wycombe405November 19, 2009 10:40PM

I love this stuff!! Piezoelectrics are really fascinating...I learned a little about it repairing a humidifier (n/t)

jinxed520November 20, 2009 02:07AM

Who are you really? Where did you come from? Eek!LaughingPMWF Museum please! (n/t)

JohnnyT450November 20, 2009 02:10AM

I will archive it (n/t)

Reto424November 20, 2009 05:33AM

Interesting read! I worked with piezoelectric crystals years ago. (n/t)

Mark C.479November 20, 2009 03:13AM

That's Cool insight! Thanks!Thumbs up! (n/t)

Nuvolari431November 20, 2009 03:45AM



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