IM #02: Fused Quartz

So, last week, we talked about normal Quartz, and its surprising properties of piezoelectricity and triboluminescence. We talked about how it had several crystaline forms, including some which were not macrocrystalline, but only microcrystalline (the agate, tiger's eye, etc). However this week we're discussing something that ALSO has the same chemicals, but is not crystalline. At the molecular level, the bits of silicon and oxygen don't form repeating patterns, but instead exist in an amorphous glass arrangement.

Fused Quartz Glass (amorphous SiO2)	Quartz (crystalline SiO2)

This means, in part, that fused quartz (also called fused silica) does not have the piezoelectric or the triboluminescent properties of the crystal quartz. It does, however, have its own set of very interesting properties and uses.

Its three primary properties are its transparency across IR, UV and visible light, its very low thermal expansion coefficient, and its very high softening temperature. Combined with reasonable toughness, these properties make it very useful for many many applications.

The high softening point combined with the infrared (heat-waves) transparency make it a common material for encasing the heating elements in electric heaters. The quartz tubing protects the heating elements from oxidation, and allows infrared radiation out (which can be directed and absorbed by people and objects) while limiting the conduction and convection, which would heat the air instead of the people.

The low thermal expansion coefficient combined with its glass structure make it very useful for telescope mirrors which are less sensitive to thermal stresses. It's generally great for nearly any optical situation where you might use normal glass. The low thermal expansion also means it's been used for pendulums in clocks to prevent them from being as sensitive to time variation from a thermally lengthening pendulum slowing down the clock.

And, one last particularly interesting use of fused quartz is in the Gravity Probe B. Fused quartz was crafted into the smoothest man made sphere known to exist. If it were scaled up to the size of the earth, the highest mountain peak would be about 8 feet! I would highly recommend reading more about the Gravity Probe B experiment, which in May 2011 helped validate previously untested parts of Einstein's General Relativity. The experiment was first suggested in 1960, but only in 2011 was accurate enough technology developed to provide the level of accuracy needed.

Fused quartz is manufactured using laser cutting, grinding, polishing and glassblowing techniques.

IM #01: Quartz

IM = Interesting Material

I'm going to try to do 52 materials this year. Some of these might be longer than others, but I hope all of them are at least somewhat interesting.

The first interesting material post is about quartz. It's a material that most people have heard of, since in the modern world it is actually quite commonly used in quartz watches.

Quartz, chemically, is SiO2, Silicon Dioxide. This same ratio of atoms can be arranged in a variety of slightly different arrangements, the most common of which are α-quartz and β-quartz. They are very slightly different in how the tetrahedrons are arranged, and in general will look the same macroscopically.

However, this clear, six-sided "superman" crystal is fairly rare to see; about the closest that is common is the crystals in geodes, available wherever tourist trinkets are sold.

Chemically pure quartz is clear, but if there are bubbles of gas or liquid, it can be smoky white. If there are other impurities, the color can vary widely. In fact, several "different" gemstones are just different colors of the same mineral, and quartz is no exception.

Citrine,
amethyst,

and rose quartz are all the same underlying material. Even further, Chalcedony, Agate, Onyx, Jasper, Tiger's Eye, and Carnelian are all essentially quartz, with different sets of impurities and a lack of macrocrystaline form.

But the name quartz is probably most famous for being used in clocks, and this is due to one of its unique properties: piezoelectricity. When a voltage is applied to the crystal, it deforms, and when it deforms, it produces a voltage. Because of this, if a piece of quartz is made to "ring" or vibrate at its natural frequency, it produces regular electronic output that can be used to regulate a digital watch. Inside every cheap digital watch is a tiny tuning fork of quartz.

The use of quartz oscillators is a foundational technology to our modern world. Precise timing is at the heart of most of the advances in science, and cheap quartz resonators allowed reliable radios and computer timing circuits to proliferate.

As practical as quartz's piezoelectric property is, there's a much less practical, but far more awesome property that quartz has: triboluminescence. Triboluminescence is the awesome and not particularly well-understood process where mechanical stress produces light directly, not from incandescence due to friction heating. Although several common crystals have this property, the effects are often unnoticed because the light produced is very dim. As noted in the wikipedia article on triboluminescence, some American Indians used the triboluminescence of quartz to make flashing rattles used in nighttime dances. Triboluminescence is also behind the very interesting story of the x-rays from scotch tape in a vacuum story.

So, simple quartz is able to produce both light and electricity by being smashed. How cool is that?