Midterm Project (Exploring the Vacuum)
a joint project with Johnny Lu
Our project focused on a less structured approach to materials exploration. We set out with a very general thesis… build a specialized environment, a vacuum chamber, and see what kind of interesting results could be achieved with unique materials and material states within it.
The Chamber
We fabricated our chamber using a 9 inch stainless steel vessel obtained from a restaurant supply, an air-driven vacuum pump, high-pressure ball valves, negative pressure gauge, silicone gasket, .7 inch acrylic, and plywood. The air-driven pump was rated at -28.3″ Hg (95 kPa).
Our initial tests achieved about -15″ Hg (50 kPa), later we were able to bring the reading down to nearly -28″ Hg (93 kPa) after we increased the drive compressor from 90 psi to around 120 psi. The chamber was able to hold a vacuum for an extended period without and signs of leaking, -a lucky first success!
A short video of initial testing:
We decided that our first experiments would focus on the effects of a vacuum on super-saturated solutions, namely: sugar in water and plaster of paris mixed with CO2 saturated water. The idea was that super-saturated solutions are stabilized by specific atmospheric and thermal conditions and that we could potentially alter those conditions within a vacuum -particularly while the solutions were undergoing transitional phases such as the cooling of a sugar solution or the exothermic reaction of plaster into a solid.
Sugar
We prepared a heated solution of 300ml of distilled water with about 1.3 Kg of sugar (C12H22O11) which was the maximum amount that would dissolve.
We transferred the mixture to the vacuum chamber and began decompressing the chamber to 90 kPa. The reaction was nearly instantaneous… the solution bubbled over releasing a large amount of the water as vapor after which the remaining sugar seemed to instantly crystalize and harden. The water vapor released so quickly that it obscured our viewing window:
After reaching maximum vacuum we let the mixture cool for 15 minutes in the vacuum then opening the chamber to reveal a super hardened cavitied mass of solid sugar:
After drilling a sample core of the hardened sugar we could clearly see that the violent release of the mixture’s water had left a structure of cavities in the sugar.
We partially disolved the hardened sugar with hot water to see it more clearly, the structure was very hard and resembled coral or lava rock:
Plaster
Next we prepared two mixtures of plaster (calcium sulphate hemihydrate, CaSO4·1/2H2O), one with distilled water and another with CO2 saturated water.
We expected little to happen with the distilled water mixture, but were not entirely sure what to expect from the super-saturated water.
As we evacuate the chamber both solutions began to bubble but as the vacuum increased the CO2 saturated mixture began to expand rapidly:
We maintained the pressure and allowed the mixtures to set. After removing them from the chamber the CO2 mixture revealed a cavatied structure similar to the sugar.
While it is often standard to de-gas casting materials prior to casting in a vacuum chamber we thought the resulting in-vacuum cast to be very interesting -essentially creating a lighter weight equivalent volume of cast material.
Ulterior Motives (X-rays)
The fabrication of the vacuum chamber was motivated in part by the possibility that it might facilitate an inexpensive X-ray source using scotch tape a phenomenon researched at the University of California, Los Angeles in 2008.
If we are able to produce X-rays with the chamber we hope to use it too effect mutation rates in different plant seeds.
Another possibility would be to make a cloud chamber.