Project WISE - Spring 1997

Let's Make Diamonds!

The group, spring, 1997

Back row: Laurie McMillen (teacher), Kerri Brady, Kristen Moore, Brittany Larkin, Lisa Basso

Front row: Brigid Cody, Kim Kessler

During the spring semester of 1997, six young women from five different high schools in Suffolk County, Long Island are engaging in an experiment designed to convert graphite to diamond, using high pressures and temperatures. During the first session we sampled the wide variety of minerals and their physical properties.

Optical Effects

	Birefringent Iceland spar splits light to create a double image.
Fluorescent calcite from Franklin, New Jersey appears white in visible light.
	Fluorescent calcite from Franklin, New Jersey appears red under ultraviolet light.

Aragonite has the same composition as calcite, but a different atomic structure.
Mass of aragonite crystals

Native Elements

Native elements are minerals that contain only one kind of atom. Diamonds and graphite are composed solely of carbon atoms.
	Arborescent native Gold from California
Native wire silver from Honduras
	Native sulfur crystals from Sicily
Beads of liquid native mercury from California

Symmetrically Arranged Chocolate Chip Cookies

These piles of cookies exemplify two forms of close packing that are characteristic of minerals.
	Hexagonally close-packed cookies
Cubically close-packed cookies

Let's Make Diamonds: Final Report

Abstract

In this experiment we learned how diamonds are created deep in the earth, by high temperatures and pressures. We sought to recreate these conditions in a lab setting, hoping to make our own diamonds. To begin we learned about the shape, both molecular (internal) and external. We learned that the strength of a material such as a diamond was determined by strong internal bonds. Following this we needed to make the proper settings in the laboratory. A "furnace" was filled with graphite (the main component of diamonds) and a Ni and Mn catalyst. This furnace was put into Tungsten Carbide cubes fitted with pyrophllite gaskets and Teflon tape. This whole set up was placed in a machine which would exert the necessary temperatures and pressures. Later we concluded that we had a diamond by testing it's hardness as compared to other materials. The diamond was able to put a scratch in Silicon Carbide, another very hard material. In addition to the scratch test we used an X-ray diffractometer to determine if the proper d-spaces were present.

Background

A diamond is nothing more then a piece of graphite with its structure transformed by heat and pressure. Yes, diamonds can be made from the same materials that you use in your pencils. However making diamonds from graphite takes some work.

Using heat and pressure, one may turn a piece of graphite into diamond. The effects that pressure has on solids, like graphite, are instrumental in creating the desired substance. Pressurization compresses bonds, and changes in atomic packing take place. These changes, added to the changes brought on by heat, change the structure of graphite into what we call diamonds.

Methods

In this experiment, we utilize pressure and temperature to transform graphite disks into diamond. The phase change is facilitated by a nickle-manganese powder catalyst that we put between the graphite disks. The disks and catalyst are put into a sample cup composed of magnesium-oxide (MgO).

Procedure

We inserted the sample cup into a cylindrical graphite furnace. The furnace is encased in a zirconia cylinder, which is placed in a hole drilled into an MgO octahedron. We cap off the ends of the zirconia cylinder with two zirconia disks. These disks have small holes in them for TZM rings that contact two graphite rings that sit in the ends of the furnace. The TZM rings, as well as the graphite components, are electical conductors. This enables us to pass an electric current through the furnace, which brings the sample to the desired temperature.

The TZM rings are in contact with the second stage anvils composed of tungsten carbide. These cubic anvils provide pressure to the sample assembly, and two of them are part of the electrical circuit. The force is supplied by the hydraulic pumps that apply pressure to oil.

We take the magnesium oxide octahedron and place it within eight tungsten carbide cubes. Placing the octahedron within the cube in essence completes a circuit to the furnace in which our sample heats up to the necessary temperature. When the tungsten carbide cubes are put together, the space for the octahedron is not big enough, so spacers are needed. In this experiment teflon and pyrophyllite were used. These spacers are also used as lubricants for when the block is pressurized and the cubes are pressed close to each other. We then cover three sides of each tungsten carbide cube with teflon tape. The teflon tape acts as a electrical insulator. This allows the electrical current to flow where we want, which is through the sample. The teflon tape lets us control that. We then proceeded to glue laminated plastic on the outside faces of the assembled tungsten carbide cubes. This held all the cubes together and prevented shifting. We glued copper electrodes on opposite ends of the cube to conduct the electricity through the cube and our sample. We were then ready to place it in the Kennedy press.

We placed the tungsten-carbide cubes into the Kennedy press. First, we bring the pressure to about 60 kilobars, and then turn on the electric current that heats the sample. Throughout the duration of the experiment, we monitor the temperature.

Findings

Our first reaction upon opening the cube was to attempt to scratch test. Silicon carbide is a man-made material that is close to diamond on the Woodell Abrasion scale. Diamond is the only substance that can scratch it. Our sample scratched it – we then ground up our sample in preparation to undergo another test. After grinding the substance, which we suspected contained diamond, we placed it in an x-ray diffractometer. The x-ray diffractometer generates a graph which can be viewed via computer.

The d-spacing for many materials is known; using the data, we could determine if what we had was in fact diamond. Looking at the graph, we could zoom in on areas with high peaks. Diamond has d-spacing of 1.075 and 1.261. Near 1.261 we found a large peak – could this be diamond? Well, we found that MgO has a d-spacing of 1.27, and since we used MgO as a sample cup, we concluded that the peak was most likely a product of that. We did however find a small peak at 1.075, this leads us to believe that there was a small amount of diamond present.

All in all, we came to the conclusion that there was so much contamination on our sample which accounts for the fluctuation on our graph numbers. These discrepancies may also have occurred due to lack of proper orientation of the crystals. Orientation is obtained by carefully and finely crushing your sample. Due to lack of time and smallness of our sample, proper grinding was not possible.

Discussion

From the data collected in this experiment, we can conclude that we did in fact succeed in creating diamonds:

• Through a visual inspection, there were distinct differences in the pre-pressurized graphite and the pressurized substance. The product had a definite luster. When inspected under the microscope, we found that the pressurized substance contained crystal-like structures that we have inferred to be diamond crystals after performing various other tests.
• After visually testing our substance, we tested its hardness. SiC is one of the hardest substances besides diamond. Since our substance was successful in scratching the SiC, we can consider our substance diamond.
• After determining the hardness of our substance, we continued to identify it by using a x-ray machine to find the d-spacing of our substance. If the peaks on the graph match the peaks produced by a diamond then we could infer that our substance did in fact contain diamonds. Our sample contained very few crystals that we believe to be diamonds. To get an accurate graph from the x-rayed material, the substance must be x-rayed on many different planes. When working with a small amount of a substance, extracting the wanted crystals is very difficult and often debris is incorporated into the sample. This leads to a less accurate graph of the d-spacing of the wanted material. In addition, if the substance is not x-rayed on all necessary planes, not all of the expected peaks will be present. The expected d-spacings of diamonds are 1.075, 1.261, and 2.06. We found that our graph contained peaks with approximate corresponding numbers. The numbers only differ by the amount of significant figures used. These peaks correspond with diamond peaks, although they are not the prominent peaks on the graphs. The most prominent peaks on the graph correspond with the d-spacing of MgO, which should have peaks at 2.106, 1.49, 1.22, and 2.43. Our graphs contained prominent peaks at 1.49, 1.22 and 2.43. The possible explanation for the presence of these peaks is that debris from the sample cup and octahedron was incorporated into our sample. The crystals may have also been attached to the MgO. ZrO2 is what the Zirconia ring was made of. Its d-spacings appeared at 2.96, 1.826, and 1.538. This again could be due to debris that was contained in the sample. Some of the graphite was not properly pressurized. A peak was present at 3.34, which is a d-spacing of graphite. Although those peaks were present, the diamond peaks corresponded to all of the expected d-spacing.

Last modified: May 29, 1997