Lucapa Diamond

The Perth-based Lucapa Diamond Company found a 404 carat diamond at its mine in Angola, a republic in southern Africa. It is the biggest diamond found to date in Angola and has been valued at about $20 million.

The mass of gemstones such as diamonds is measured in carats. 1 carat equals 200 mg.
1 carat is subdivided into 100 points, so a point is equal to a mass of 2mg.

Diamonds form at depths of 150 - 200 km in the upper mantle where temperatures range from 900 to 1300^oC and the pressure is about 50,000 times atmospheric pressure. Under these extreme conditions, carbon atoms come together to form the diamond structure in which each carbon atom makes 4 covalent bonds to other carbon atoms. In the diagram shown, each black ball represents a carbon atom and each line represents a covalent bond.

Diamonds are brought to the earth's surface from the upper mantle  in a dyke which geologists refer to as a kimberlite pipe.

 The density of naturally occurring diamonds varies between 3.15 and 3.53 g cm^-3, with the purest diamonds having a density closer to 3.52 g cm^-3.
Type I diamonds include diamonds in which nitrogen is present as an impurity. A colourless Type 1 diamond has very little nitrogen impurity. As the amount of nitrogen present increases, the diamond becomes more yellow.
Type II diamonds have  no measurable nitrogen impurity. The Lucapa diamond is a Type II diamond and is colourless because it contains no measurable nitrogen or other impurity, and, the structure has not been changed significantly from the "pure" diamond structure shown above during formation.
Some Type II diamonds are coloured pink, red or brown as a result of changes to the structure of the diamond during formation so that light is scattered in such a way as to produce these colours.
The presence of boron as an impurity results in a light blue coloured diamond, whereas the presence of black impurities such as graphite or sulfides produces a black diamond.
The presence of measurable quantities of hydrogen as well as structural changes during formation can result in purple diamonds.


Reference:
http://www.abc.net.au/news/2016-02-15/giant-diamond-found-in-angola-by-wa-company-lucapa/7168974


Further Reading:
Mass Conversions
Density
Allotropes


Suggested Study Questions:

1. Convert 200 mg to a mass in
   • grams
   • kilograms
   • micrograms
2. The diamond found at Lucapa is reported to be a 404 carat diamond. What is the mass of this diamond in
   • grams
   • kilograms
   • micrograms
3.  The value of the Lucapa diamond is estimated to be $20 million. What is the value of the diamond:
   • per carat
   • per point
   • per milligram
   • per gram
4. Assuming the Lucapa diamond to be a pure diamond, its density is 3.52 g cm^-3 . What is the volume of this diamond? 
5. Imagine pouring 500 mL of water in a 1000 mL measuring cylinder at 101.3 kPa and 25 ^oC, then dropping the Lucapa diamond into the water. What would the new volume of water be in the measuring cylinder? (assume the density of water is 1 g cm^-3)
6. Coal is also made up largely of carbon atoms, with tiny amounts of oxygen and impurities such as sulfur.  It is usually found as a vein or seam of coal within sedimentary rocks. Coal has an average density of about 1.2 g cm^-3. If a lump of coal had the same volume as the Lucapa diamond, what would its mass in grams be?
7. Given the difference in the density of diamond and the density of coal, what does this tell you about the structure of diamond and coal?
8. If you were given 5 grams of coal and 5 grams of diamond, which would have the greatest volume?
9. Draw a diagram to represent the 3-dimensional structure of diamond. On your diagram:
• draw a red line to indicate a covalent bond
• use a blue pencil to show a carbon tetrahedron
• use a black pencil to show one carbon-carbon bond angle
10. What is the angle between two adjacent carbon atoms in the diamond structure?

Packing Density

In the particle theory of matter, all matter is made up of tiny particles. You've probably drawn circles in boxes to represent solids, liquids and gases. Each of those circles is a 2-dimensional representation on the paper of a 3-dimensional sphere. So, your representation of the particle theory of matter also implies that all matter is made up of particles which are spherical in shape.

If you draw the circles so close to each other that they are touching, you label the drawing "solid".
If the circles are little bit further apart, you label the diagram "liquid".
If the circles are much further apart, you label the drawing "gas".
But, have you ever wondered just how close you can pack those spheres together?

The study of soot is becoming very important because soot in the air relates to the balance of climate: heating from light absorption versus cooling from light reflection.
Soot is made up of small round particles of carbon about 10 or 20 nanometres across. The particles stick together randomly in short chains and clumps of a half dozen or more spheres. These, in turn, clump loosely together to form larger, loose aggregates of 10 or more which over a few hours will compact into a somewhat tighter ball which is atmospheric soot.
The closer you pack the soot spheres together, then the more dense the soot becomes. That is, since all the atoms have the same mass, if you pack them more tightly together then they will occupy a smaller volume, and, since density is mass per unit volume, the density of the soot will increase.

Mathematicians have been looking at sphere packing problems for more than a hundred years. In 1831, Carl Friedrich Gauss (one of the greatest mathematicians the world has known), determined that a close-packed arrangement in which 1 sphere is surrounded by 12 other identical spheres has an average density of π/√18 ≈ 0.74
The assumed density of soot in models of atmospheric soot has, until now, been 0.74.

A research group at the National Institute of Standards and Technology (NIST), have made measurements of actual soot particles and found the density of soot to be 0.36 not 0.74
So, the researchers set out to model soot particles using 6 mm plastic spheres glued together in thousands of random combinations forming clumps of from 1 to 12 spheres which were then used to fill every available size of graduated cylinder. When they graphed their results as a function of clump size,  they got a curve which levelled off at 0.36, the same as the density of soot particles they measured, but not the same as that predicted by the close-packing of spheres according to Gauss.

It now appears that, under normal conditions (not extreme temperature or pressure), the density of close-packed particles of any size, from nanometres to tens of metres is 0.36

Reference:
C. D. Zangmeister, J. G. Radney, L. T. Dockery, J. T. Young, X. Ma, R. You, M. R. Zachariah. Packing density of rigid aggregates is independent of scale. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1403768111


Further Reading
http://ausetute.com.au/density.html
http://ausetute.com.au/massconv.html
http://www.ausetute.com.au/voluconv.html

Suggested Study Questions

1. Draw a diagram to represent each of the following states of matter using the particle theory of matter:
   • solid
   • liquid
   • gas
2. Calculate the volume of a spherical carbon particle that is 20 nanometres in diameter.
3. Calculate the volume of a cube in which the length of each side is 20 nanometres.
4. Calculate the ratio of the volume of the sphere to the volume of cube.
5. Why is this ratio NOT 0.74?
6. Draw a diagram showing the close-packing of just 2 carbon particles each with a diameter of 20 nanometres.
7. Draw a square around each sphere to represent the volume of space occupied by the close-packed spheres and label the total volume occupied and the volume of carbon particles.
8. For the close-packing of 2 carbon particles as drawn above, calculate the ratio of the volume occupied by the spheres to the total volume of the rectangular prism.
9. Consider placing 1 more sphere above the 2 spheres you have already drawn. Draw a diagram of an arrangement that will occupy the
   • maximum total space
   • minimum total space
10. Research the difference between hexagonal close packing and cubic close packing.

Graphene Capillary

Graphene is made up of carbon atoms, it is an allotrope of carbon.
 Each carbon atoms bonds to 3 other carbon atoms forming hexagons. Each hexagon shares each side with another hexagon. So this lattice of hexagons extends indefinitely, but it is only 1 carbon atom high! For this reason graphene is referred to as a two-dimensioal lattice or array.

Graphene is strong, light, nearly transparent and an excellent conductor of heat and electricity. Graphene is also hydrophobic, it repels water. However, narrow capillaries made out of graphene actually suck in water, if the water layer is only one atom thick.

Two years ago, researchers at the University of Manchester found that graphene capillaries could be made by stacking layers of graphene oxide on top of each to form a laminate. One-atom wide graphene capillaries are produced between these layers. These laminates are impermeable to all gases and vapours, except for water. This means that no gas or vapour, except for water, can pass through the laminate. Even helium, the smallest of the Nobel Gases cannot pass through the laminate.

These results suggest that graphene capillaries could be used to filter water. Researchers at the University of Manchester having been studying the use of graphene for water filtration and have found that ions less than 9 angstroms can quickly flow through with the water, but larger ions are blocked. With further research it is hoped to control the graphene mesh size to reduce it below 9 angstroms so that even the smallest ions like those found in seawater could be filtered out of water.

Reference:
R. K. Joshi, P. Carbone, F. C. Wang, V. G. Kravets, Y. Su, I. V. Grigorieva, H. A. Wu, A. K. Geim, R. R. Nair. Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes. Science, February 14, 2014 DOI: 10.1126/science.1245711

Further Reading
Allotropes
Metric Conversions

Suggested Study Questions:

1. What is meant by the term "graphene is an allotrope of carbon?"
2. Name, and describe the structure of, two other allotropes of carbon.
3. Explain how the structure of graphene is different to the structure of graphite.
4. Why is graphene considered to be a good electrical conductor? 
5. Which other allotrope of carbon is considered to be good electrical conductor? Explain how this allotrope conducts electricity.
6. 1 angstrom = 1 Å = 10^-10 metres. Convert 9 Å to:
   • metres
   • millimetres
   • microns (micrometres)
   • nanometres
7. 1 picometre = 1 pm = 10^-12 metres. Convert 900 pm to :
   • metres
   • millimetres
   • microns (micrometres)
   • nanometres
   • angstroms
8. Consider the crystal ionic radius for each of the following ions commonly found in seawater:
   • Na⁺ : 116 pm
   • Mg²⁺: 86 pm
   • Cl^- : 167 pm
   • F^- : 119 pm
   • What is the diameter of each of these ions in angstroms?
   • Which, if any, of these ions would pass through a graphene capillary? Explain your answer.
9. A nitrate ion has a diameter of about 0.33nm and a sulfate ion has a diameter of about 0.49 nm. Which of these ions, if any, could pass through a graphene capillary? Explain your answer.

Diamond Planet Discovered

Scientists from Australia, Germany, Italy, the UK and the USA, have detected a companion planet for Pulsar J1719-1438 in our Milky Way, and they believe that this companion planet could be made of diamond. The planet is thought to be small, less than 60,000km in diameter, with a mass slightly greater than that of Jupiter, about 2 x 10²⁷kg.
P1719-1438 and its planet are so close together that the planet is most likely to be a 'stripped-down' white dwarf, that is, one that has lost its outer layers and over 99.9% of its original mass. Based on the planet's orbiting times, the scientists think that this remnant is likely to be made up mostly of carbon and oxygen, while its high density suggests that the material present is crystalline, which leads them to believe that the planet could contain a sizable proportion of diamond.

Graphite can be transformed into diamond under pressures of more than about 4GPa, as is shown in the simplified phase diagram on the right. On Earth, diamonds can be formed in the mantle where the pressure is great enough to transform carbon sources into diamonds. Diamonds can also form when a meteorite impacts on the Earth because the impact creates a zone of high pressure and temperature in which carbon can be transformed into diamond.

Reference
M. Bailes, S. D. Bates, V. Bhalerao, N. D. R. Bhat, M. Burgay, S. Burke-Spolaor, N. D'Amico, S. Johnston, M. J. Keith, M. Kramer, S. R. Kulkarni, L. Levin, A. G. Lyne, S. Milia, A. Possenti, L. Spitler, B. Stappers, W. van Straten. Transformation of a Star into a Planet in a Millisecond Pulsar Binary. Science, 2011; DOI: 10.1126/science.1208890

Further Reading
Mass Conversions
Density Calculations
Allotropes

Study Questions

1. Convert 60,000km to a distance in:
   • meters
   • centimeters
     
   • millimeters
     
2. Convert 2 x 10²⁷kg to a mass in
   • grams
   • megagrams
   • gigagrams
     
3. What is the approximate radius of of the planet in cm?
4. What is the volume of the planet in cm³ (assuming the planet is spherical)?
5. Calculate the approximate density of the newly discovered planet (in g/cm³).
6. Convert 4GPa to a pressure in:
   • kilopascals
   • pascals
   • megapascals
   • atmospheres
     
   
   
7. Using the phase diagram for carbon in the article above:
   • What is the minimum temperature and pressure required to produce liquid carbon from gaseous carbon?
   • What is the maximum pressure at which graphite can exist?
   • What is the maximum temperature at which graphite can exist?
     
   • How many phases of carbon are present at 4500K and 0.01GPa?
   • What is the triple point for diamond?
     
   
   

Graphene: AUS-e-NEWS December 2010

Excitement is growing in the scientific community about the possible uses for graphene.
This simple, naturally occurring allotrope of carbon could revolutionize our world.
The December 2010 issue of AUS-e-NEWS, AUS-e-TUTE's quarterly newsletter, takes a look at the chemistry of graphene, and at its possible future uses.

To subscribe to AUS-e-TUTE's free newsletter email:


and type subscribe as the subject.

Nobel Prize for Work on Graphene

The 2010 Nobel Prize in Physics has been awarded to Andre Geim and Konstantin Novoselov for their "groundbreaking experiments regarding the two-dimensional material graphene".

Graphene is an allotrope of carbon, it is the thinnest and strongest material known. It conducts electricity as well as copper and outperforms all other materials as a conductor of heat. It is almost completely transparent, yet it is so dense that not even helium, the smallest known gas atom, can pass through it.

Geim and Novoselov extracted graphene from a piece of graphite such as is found in "lead" pencils. Using a piece of adhesive tape they obtained a flake of carbon that was just one atom thick, which is the allotrope known as graphene.

Reference:
http://static.nobelprize.org/nobel_prizes/physics/laureates/2010/info_publ_phy_10_en.pdf

Further Reading
Allotropes
Elements

Study Questions:

1. What is meant by the term allotrope?
2. Name two other naturally occurring allotropes of carbon.
3. Draw a table listing the physical properties of both of these allotropes and graphene.
4. Discuss the similarities and differences between these allotropes.
5. Draw a possible structure for graphene.
6. Describe the similarities and differences between the structure for graphene that you have drawn and the structures for the other two allotropes in your table.
7. Using your structure for graphene, explain the similarities and differences between the physical properties of graphene and the other two allotropes.
   

Hexagonal Boron Nitride

Graphene, a single-atom thick allotrope of carbon and an electrical conductor, is considered to be a possible successor to silicon in microelectronics applications.
Hexagonal boron nitride (h-BN) is an insulator. It is highly elastic and nearly as strong as graphene. Rice University scientists have found a way to implant sheets of h-BN into sheets of graphene, which controls the sheet's electronic character.
They have also found a way to deposit sheets of pure h-BN, 1 to 5 atoms thick, onto a copper substrate using a chemical vapour deposition process at about 1,000^oC. The h-BN material can then be transferred to other substrates. The size of h-BN sheets is limited only be the size of the copper foil and furnace used to grow it.
It should be possible to draw microscopic patterns of graphene and h-BN, useful in creating nanoscale field-effect transistors, quantum capacitors or biosensors.

Reference:
Li Song, Lijie Ci, Hao Lu, Pavel B. Sorokin, Chuanhong Jin, Jie Ni, Alexander G. Kvashnin, Dmitry G. Kvashnin, Jun Lou, Boris I. Yakobson and Pulickel M. Ajayan. Large Scale Growth and Characterization of Atomic Hexagonal Boron Nitride Layers. Nano Letters, 2010; 100722142755098 DOI: 10.1021/nl1022139

Study Questions

1. What is meant by the term allotrope?
2. What are the naturally occurring allotropes of carbon?
3. In what ways are these allotropes of carbon the same?
4. In what ways are these allotropes of carbon different?
5. If the formula for boron nitride is BN, what is the oxidation state (number) of boron?
6. Given the name hexagonal boron nitride, draw a possible Lewis Structure (electron dot diagram) for hexagonal boron nitride.
7. In what ways are graphite and hexagonal boron nitride the same?
8. In what ways are graphite and hexagonal boron nitride different?
9. Why is graphite a conductor while hexagonal boron nitride is an insulator?
   

Buckyballs in Space

In 1970, Japanese professor Eiji Osawa predicted the existence of buckyballs.
In 1985, Buckminster Fullerenes were first observed in the laboratory.
In 1996, Sir Harry Kroto, Bob Curl and Rick Smalley shared the Nobel Prize in chemistry for the discovery of buckyballs.
They were named after the architect Buckminster Fuller because they resemble his geodesic domes which have interlocking circles on the surface of a partial sphere. Buckyballs, 60 carbon atoms arranged into a three-dimensional spherical structure resembling a soccer ball, are allotropes of carbon.
Buckyballs have been found on Earth in candle soot, layers of rock and meteorites.

Astronomers using NASA's Spitzer Space Telescope have now discovered buckyballs in space, in a planetary nebula named Tc 1. Planetary nebula are the remains of stars that shed their outer layers of gas and dust as they age. A compact, hot star, or white dwarf, at the centre of the nebula illuminates and heats these clouds of discarded material. The buckyballs were found in these clouds when the astronomers used Spitzer's spectroscopy instrument to analyze infrared light from the planetary nebula and see the spectral signatures of the buckyballs. The data from Spitzer were compared with data from laboratory measurements of the same molecules and showed a perfect match.

Reference:
Jan Cami, Jeronimo Bernard-Salas, Els Peeters, and Sarah Elizabeth Malek. Detection of C₆₀ and C₇₀ in a Young Planetary Nebula. Science, 2010; DOI: 10.1126/science.1192035

Study Questions:

1. What is an allotrope?
2. Name two naturally occurring allotropes of carbon other than buckminster fullerenes.
3. In what ways are these allotropes above the same?
4. In what ways are these allotropes above different?
5. It has been suggested that buckyballs could be used in armour, drug delivery, and, superconductors. What do you think the physical and chemical properties of buckyballs are likely to be?
   
6. Name the other allotrope of oxygen besides (bi)molecular oxygen.
   
7. In what ways are the two allotropes of oxygen the same?
8. In what ways are the two allotropes of oxygen different?
9. There are several allotropes of phosphorus. Discuss the similarities and differences of these allotropes.
   

Lunar Graphite

Scientists have been analyzing 3.8 billion year old Mare Serenitatis lunar samples brought back to Earth by astronauts in 1972. Raman spectroscopy of the sample allowed scientists to create an image of the minerals it contained. The scientists were surprised to find graphite and graphite whiskers, formed under very hot conditions between 1273K and 3900K. The graphite whiskers appeared to be a few microns in diameter and up to 10 microns long.
The scientists believe that the carbon they detected came either from the object that made the impact crater, or, that it condensed from the carbon-rich gas that was released during the impact.

Reference:
A. Steele, F. M. McCubbin, M. Fries, M. Glamoclija, L. Kater, and H. Nekvasil. Graphite in an Apollo 17 Impact Melt Breccia. Science, 2010; 329 (5987): 51 DOI: 10.1126/science.1190541

Study Questions:

1. Carbon is present on Earth in different forms. What is the term given to these different forms?
2. Name two different natural forms of carbon found on Earth.
3. In what ways are the two different forms of carbon named above similar?
4. In what ways are the two different forms of carbon named above different?
   
5. Name two different synthetic forms of carbon.
6. Give a use for each synthetic form of carbon named above.
7. Why do you think the scientists were surprised to find graphite in these lunar samples?
   

Graphane and Quantum Dots

Graphene is a honeycomb-like form of carbon that is just one atom thick. Graphane is produced when hydrogen atoms are added to both sides of the graphene matrix, making graphane an insulator.

Rice University scientists have discovered that the strategic extraction of hydrogen atoms from a two-dimensional sheet of graphane opens up hexagonal spaces of pure graphene that look and act like quantum dots. Quantum dots interact with light and magnetic fields in unique ways and can be used for chemical sensors, solar cells, medical imaging and nanoscale circuitry.

Reference:
Abhishek K. Singh, Evgeni S. Penev, Boris I. Yakobson. Vacancy Clusters in Graphane as Quantum Dots. ACS Nano, 2010; : 100513111745088 DOI: 10.1021/nn1006072