Science Under Pressure
Applying very high pressure to a material is one of the most useful methods of learning about its properties and behavior. Why?
High pressure causes materials to take on forms they otherwise would not, allowing new properties or behaviors to emerge. High-pressure devices can simulate the hot, dense conditions deep within the Earth, providing a glimpse of what happens to metals, rocks, and minerals in those extreme environments.
Additionally, high pressure forces materials to mix in interesting ways, such as forcing molecules of one material between layers or into open spaces of another, or causing chemical bonds to break and new ones to form.
Using high-pressure devices, scientists can study these processes in a controlled way. One device commonly used to apply high pressure is the diamond anvil cell (DAC), which uses the polished faces of two diamonds to squeeze a small sample. This setup, enclosed in tiny chamber, is surrounded with water or another liquid, which evenly transmits the applied pressure to all sides of the sample.
A DAC can apply pressures equal to millions of pounds per square inch. Samples are also often simultaneously heated to very high temperatures, up to thousands of degrees, using lasers. To follow the effects of pressure and/or temperature on the sample, such as chemical bond changes or the shifting of atoms, scientists bombard it with a beam of highly focused x-rays, such as those produced at the National Synchrotron Light Source (NSLS). The x-rays scatter and bounce off the atoms, emerging from the sample in a particular pattern. Using computers, scientists analyze the patterns to model the sample’s changing structure as pressure increases.
The NSLS high-pressure research, which draw scientists from all over the world. Some of the materials studied there are:
- Glasses made from metals, such as zirconium, which are often stronger and more resilient than traditional glasses, and may have applications as materials in medical and sports equipment
- Minerals, crystalline metal oxides called zeolites, ceramics, and other materials similar to those within inner Earth
- Metals, such as sodium, which can yield information about how free electrons behave under high pressure
- Gases, such as hydrogen, which take on new, ordered structures when compressed.