CINDY M. MOON

1997 SUMMER TEACHER ENRICHMENT PROGRAM

SUMMARY OF LABORATORY EXPERIENCE

HOSTS: DR. ROGER KROES AND DR. DON REISS

LABORATORY: SPACE SCIENCES

DIVISION: MICROGRAVITY EXPERIMENTS

BRANCH: CRYSTAL GROWTH

After talking to Dr. Kroes and Dr. Reiss about the basic physics and chemistry of growing crystals, we decided that the best way for me to take back as much applicable experience as I could was to grow crystals in the laboratory using the same types of equipment that I would have access to in the school in which I teach. Also, we decided that I should also use some equipment that I did not have access to at school so that I could make some measurements and so that I could tell my students about the types of equipment that one would use to conduct experiments in crystal growth.

One of the first crystals that I worked with was TGS, triglycine sulfate. TGS is a crystal that they have studied extensively. It has optical properties that detect infrared light sources. It is used in infrared detectors. It also dissolves readily in water, making handling the crystals for long periods of time impossible. In infrared detectors they use a dessicant like silica gel to control the moisture. Sometimes the infrared detectors do not work well in periods or areas with high humidity. The TGS is fairly expensive. Only one company makes it. Now they make their own when conducting flight experiments due to the amount of debris and contaminants in the usual batches sent from the company.

The next type of crystals I worked with were less expensive. Their shape is completely different from the TGS. These crystals are alum crystals. They consist of a metal in an aluminum sulfate compound. The alum crystals do not dissolve as readily as the TGS. They also require a higher concentration in order to nucleate or produce seed crystals.

One neat thing about the alum crystals is the colors that are produced by the different metals. Potassium aluminum sulfate dodecahydrate is clear. Chromium aluminum sulfate is light to deep purple. Both types of crystals can grow on top of the other. It is possible to grow the clear potassium on top of the purple chromium one, but since the chromium is so dark, one cannot grow the chromium on top of the potassium for it will not show the potassium through the chromium .

I also got to observe an undergraduate summer student working on a project for the space shuttle crystal experiments. Natalie worked on L-histidine tetrafluoroborate crystals in the same lab I was working. She ran into several problems on the way which is typical of a pure research project. We observed polymorphism in her crystals due to differing concentrations as well as pH differences. I also observed equilibrium of growth using a laser to produce a shadowgraph.

There were several types of equipment to which I was exposed. First, I used the laser to observe growth plumes of a crystal on a shadowgraph. Next, I used two different types of refractometers to measure the index of refraction for both solids and liquids. I also used the magnetic stirrer/ hot plate to mix solutions.

I hope to take back this experience to my students by letting them grow crystals in our laboratory. I plan to stress the importance of studying crystals to improve medicines since the shape of the protein crystals are important to the lock and key enzyme reactions. Growing crystals in space allows larger crystals which are necessary to take X-ray diffraction pictures which in turn, are necessary to derive the sequence of the amino acids that compose these proteins.