Let's Make Diamonds!

The WISE Women, Group 1, Spring '97

This project was part of URECA 187 for the spring 1997 semester at State University of New York at Stony Brook. The experiment was performed at the laboratories of the Center for High Pressure Research. Our mentors were Janet Niebling and Glenn Richard. From left to right in picture: Thien-Ly Doan, Suet Chan, Marta Soto, Jill Stafford, and Sabrina Khondaker

Goals

Our goal in this experiment was to convert graphite into diamonds by recreating the pressure and temperature of the earth’s mantle where this naturally occurs. In this part of the mantle the temperature is about 1350°C and the pressure is around 57 kbars.

Background

Diamonds form in the mantle of the earth at pressures of at least 57,000 atmospheres and a temperature about 1350°C. At this high pressure, diamond is a more stable form of carbon than graphite, which is not surprising, since it has higher density than graphite. At room pressure and temperature graphite is more stable than diamond. Although diamonds can exist under room conditions, the carbon-to-carbon bonds break over very long periods of time. It may take millions of years for natural diamonds to form, but with technological advances this process can be achieved in the laboratory within a matter of a few hours.

Methods and Materials

To replicate the mantle environment where diamonds can form, we needed the following materials: graphite, a catalyst, 8 tungsten carbide cubes, pyrophyllite gaskets, wooden spacers, an MgO octahedron containing a furnace, teflon gaskets, laminated plastic, and copper electrodes.

A good pressure medium for creating diamonds is an MgO octahedron. Since an octahedron is in the isometric crystal system, it is very symmetrical. This is beneficial, since it allows for a hydrostatic pressure, meaning equal pressure is applied from each direction. The tungsten blocks are cut at each corner and when gathered together to form a cube, an octahedron-shaped void is left in the center of the cube. This octahedral space in the center of the tungsten blocks is where the MgO octahedron resides during the experiment. Within a hole drilled inside the octahedron is the furnace. This is where we put the sample cup with the graphite disks and the Ni, Mn catalyst. TZM rings at each end of the furnace are electrical conductors that enable an electric current to pass from the electrodes located through the cubes numbered 3 and 8, and into the furnace. The electric current provides for the optimal temperature to create diamonds. The tungsten blocks were supported with pyrophyllite, teflon strips, and balsa wood. After the dressing of the cubes was complete, we glued the plastic lamination to secure the blocks together.

We used the Kennedy press to obtain a high pressure and high temperature environment.

Results

After many hours of waiting, we removed our sample from the Kennedy Press. Following, was the disassembling of the sample. Observations are listed below:

Laminated plastic is cracked, but no signs of heating.
One of the electrodes was split in half.
Spacers were flattened out, appearing to look longer and spread out.
Teflon gaskets were flattened to turn out curved and shorter.
Pyrophyllite was crushed to ashes.
MgO octahedron cracked into many pieces.
Graphite disk came out really fragile.
Both TZM rings is still in contact with their graphite rings.
No evidence of diamonds could be detected.

Discussion

Once we opened up our sample, we hypothesized that sufficient temperature was not created inside our sample. This insufficient temperature was evidenced by the

unmelted laminated plastic surrounding the six sides of the cube. We identified two possibilities for why the sample did not reach the adequate temperature. The first possibility may have been caused by problems with the circuitry of the Kennedy Press. We later concluded that the problem with our experiment was not caused by faults of the Kennedy Press, based upon computer data on the log sheet for other experiments.

The second possibility for the insufficient temperature in our sample may have been caused by an open circuit. Our sample contained two electrodes. After close examination, we noticed that one of them was broken. This could have occured any time during the experiment, but we suspect that the electrode broke during the initial stages of pressurization. As a result, the circuit was unable to carry electricity to the graphite furnace.

Another clue that led us to believe there was insufficient temperature in our sample was due to the nature of the contact between the TZM ring and the graphite ring. Initially, at room temperature, the TZM ring and the graphite ring were in direct contact with each other.

Although we did not successfully create diamonds in this experiment, our mentors reminded us that our results could be useful in figuring out how to create diamonds in the future.