Monday, October 18, 2010

Chemistry Fun

As we continue National Chemistry Week at the Detroit Science Center, we are all about chemistry!

You Know You’re a Chemist When…
  1. All your shirts have holes.
  2. You know what saline water is composed of.
  3. You hear that someone had a bicycle crash and you think that he couldn’t handle working with Naphthalene.
  4. You stare at the bottle of water and begin to wonder how you would separate all those ions.
  5. You hear the word “Molar” and teeth are the last thing on your mind.
  6. The first thing you reach for in the morning are your prescription goggles

Chemistry makes up many of the everyday things that we use, but being in Detroit, we lean a little automotive. Courtesy of Gary Weaks, a Detroit Science Center docent and professional chemist, here are some fun chemistry facts about automotive paint:

1) Did you know that your car wears sunblock? It's true. Ultraviolet light is that part of the radiation coming from the sun that has a shorter wavelength than visible light (so we can't see it). However, just as it can damage our skin and cause sunburn, it can also damage the polymers that form the paint on your car. Paint manufacturers will add a family of polymers known as ultraviolet light absorbers (UVA's) to filter out the ultraviolet light while letting the brilliant, visible colors still shine through. Without UVA's your car's paint would crack and fall off in only a few months in the bright sunshine.

2) Did you know that white paint is white for the same reason that snow is white? Snow is frozen water, a colorless, clear material. However, when formed into crystals (snow flakes) it bends the light that travels though it. This bending is caused by the fact that light travels slower through water than it does though air. This difference in the speed of light is known as the refractive index. Pile up billions of crystals and bend the light billions times, and any image is lost, but the light is not. It just gets scattered and we see all colors at the same time, or white light! This is also why clouds are white. In paint, chemists will add Titanium Dioxide (TiO2) if it is to be white in color. Titanium Dioxide is also a colorless material. In a crystal form known as Rutile, it has the highest refractive index of any known material. Thus, the light entering it is returned completely scattered and it appears to us a white light.

3) How much paint does a car need? Your car's metal skin is protected by a very thin layer of paint. Typically, it is only about 5 to 8 microns, or the thickness of a couple sheets of notebook paper. A micron is 1/1000 of an inch! On average, it requires about 2 gallons of liquid paint to accomplish this thickness of coating. Some of the liquid paint is lost to inefficient transfer (it misses the car when being spray-painted) and some is lost through evaporation. The remaining material forms a protective and colorful coating.

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