Реферат: From Graphite To Diamond Essay Research Paper
From Graphite To Diamond Essay, Research Paper
From Graphite to Diamond
The Whole Journey
It is a long journey for a piece of graphite to transform into a beautiful diamond. It only takes a little energy ( 1.9 K/j mole ) but it is a very difficult process. To create a diamond you must have temperatures ranging from room temperature to four thousand degrees Celsius, but the big factor is that you must have at least one-hundred thousand and upwards of a million pounds of pressure per square inch (Sass). Diamonds are born 50 miles below Earth’s surface, in the hot mantle, where a pressure of 55,000 atmospheres and a temperature near 2,700 degrees Fahrenheit pound away at the graphite to turn it into a beautiful diamond (Preiser 22).
Diamonds were formed millions of years ago in molten lava. As the lava flowed to the Earth’s surface through vents known as pipes, it cooled and solidified into kimberlite, a blue rock. Kimberlite contains the diamonds and is known to diamond miners as blue ground (Comptons).
Diamonds have been found on all continents. India was once a chief source. In about AD 600 diamonds were found in Borneo and are still mined there. The rich fields of Brazil were discovered in the 1700s. In the 19th century even richer diamond fields were found in South Africa. Most of the world’s diamonds are mined in African countries. Zaire produces mostly industrial diamonds. South Africa is the major source of gem-quality diamonds. Congo, Ghana, Namibia, and Angola are other major suppliers. Russia has diamond-mining operations in northeastern Siberia. Since the late 1970s many diamonds have been found in Australia (Comptons).
About 20 percent of the world’s output is used for industrial purposes, with the United States importing some 60 percent of the industrial diamonds mined. A few diamonds are found in Pike County, Ark., and diamonds have also been found in the Upper Peninsula of Michigan. (Comptons)
The diamond is one of the world’s most important mineral resources, it is made of pure, natural carbon with the atoms organized in a close-packed cubic arrangement that gives the stones their hardness. In fact the diamond is four times harder than the next hardest natural mineral, which is corundum.(3) But as hard as the diamond is, there is one small weakness. The diamond has four directions of cleavage. So if it receives a sharp blow to any of these four points it will break. The common crystal form is the octahedron, which looks like two four- sided pyramids placed base to base. Since diamond is so much harder than any other natural or artificial substance known, it is ideal for both gem and industrial purposes. Special optical properties guarantee its superiority among gems. First, its high light-bending ability enables it to throw back almost all the light that enters a well-cut gem. This gives rise to the gem’s brilliant luster. Second, it exhibits the ability to separate the various colors of the spectrum. This causes the gem to throw back the bright flashes of separated colors for which it is particularly noted. Also the diamond is the world s be heat conductor (Diamond Comments).
Diamond is composed of the single element carbon, and it is the arrangement of the carbon atoms in the lattice that give diamond its amazing properties. Compare the structure of diamond and graphite, both composed of just carbon. In diamond we have the hardest known material, in graphite we have one of the softest, simply by rearranging the way the atoms are bonded together (May).
Graphite Lattice Diamond Lattice
The relationship between diamond and graphite is a thermodynamic and kinetic one. At normal temperatures and pressures, graphite is only a little more stable than diamond, and the fact that diamond exists at all is due to the very large activation barrier for conversion between the two. There is no easy mechanism to convert between the two and so interconversion requires almost as much energy as destroying the entire lattice and rebuilding it (Field 54). Once diamond is formed, therefore, it cannot convert back to graphite because the barrier is too high. So diamond is said to be metastable, or relatively unstable. Diamond is created deep underground under conditions of extreme pressure and temperature. Under these conditions diamond is actually the more stable of the two forms of carbon ( graphite and diamond ), and so over a period of millions of years carbonaceous deposits slowly crystallize into single crystal diamond gemstones (Bundy 15,16).
Here are some of the physical characteristics of the diamond:
h Color- is variable and tends toward pale yellows, browns, grays, and also white, blue, black, reddish, greenish and colorless.
h Luster- is adamantine to waxy.
h Transparency- crystals are transparent to translucent in rough crystals.
h Crystal System- is isometric; 4/m bar 3 2/m
h Crystal Habits- include isometric forms such as cubes and octahedrons, twinning is also seen.
h Hardness- is 10
h Specific Gravity- is 3.5 (above average)
h Cleavage- is perfect in 4 directions forming octahedrons.
h Fracture- is conchoidal.
h Streak- is white.
h Associated Minerals- are limited to those found in kimberlite rock, an ultramafic igneous rock composed mostly of olivine.
h Other Characteristics- refractive index is 2.4 ( very high), dispersion is 0.044, fluorescent.
h Notable Occurrences- include South Africa and other localities throughout Africa, India, Brazil, Russia, Australia, and Arkansas.
h Best Field Indicator- is extreme hardness (The Mineral Diamond).
In the best gem-producing areas only about 25 per cent of the diamonds mined are of gem quality. The remaining diamonds are poor gem quality because of color or faults, so they are used in industry. In the diamond industry you need a diamond to be able to cut a diamond. So diamonds are employed by gem cutters to shape and polish diamonds and other gems (Gait 182-185).
The stones also are used to true the surfaces of precision grinding wheels. In machine shops tools tipped with diamonds cut grooves around automobile pistons and perform other precision-cutting tasks. Needles tipped with diamond dust drill holes through diamonds. A new process does this electrically. Diamonds with holes are used as feeder nozzles for oil furnaces and as wire-drawing dies. Some 400 tons of copper can be drawn through a diamond die into a wire fine enough to circle the world 20 times before the die shows signs of wear. Geologists and engineers use diamond-tipped hollow steel bits for drilling into the earth to obtain samples of rock deep underground. (Weidner 419)
A number of individual diamonds have become famous, primarily because of their size. The largest of all known diamonds is the Cullinan, which was discovered in the Premier mine in South Africa in 1905 and was presented to Edward VII, king of Great Britain, by the government of the Transvaal. The Cullinan weighed 3106 carats before cutting and is said to be a cleavage fragment of a considerably larger stone. When the stone was cut, a total of 105 gems were produced, weighing 1063 carats in all. The largest of these was the stone called the Star of Africa, 530.2 carats (shown on the coverpage on left), the largest cut diamond in existence, and now set in the British royal scepter. The Vargas diamond, found in Brazil in 1938, weighed 726.6 carats in its uncut state. When cut in 1945, it produced 29 stones with a total weight of 411 carats. In 1934 a diamond of almost the same weight, the Jonker diamond, was discovered in an alluvial deposit near the Premier mine. The Jonker is the finest large diamond ever found. It was cut into 12 gems ranging from 125.35 to 5.3 carats in weight. In 1967 the Lesotho diamond was discovered. It weighed 601.25 carats uncut (Gait182-185).
The Great Mogul diamond, said to have weighed 240 carats when cut, disappeared after it was described by the French traveler Jean Baptiste Tavernier in India in 1665. Some authorities believe that the Koh-i-noor diamond, which now weighs 106.1 carats and is one of the British crown jewels, is a part of the Great Mogul (Gait 182-185).
To bring out the beauty of a gem diamond, a number of processes are necessary. These processes, which include cleaving, sawing, cutting, and polishing, are usually known as diamond cutting. The primary object of diamond cutting is to bring out the beauty of the stone. But also very important is the cutting of the stone according to a plan that will get rid imperfections, such as cracks, flaws, and cloudiness, and will produce a gem of the biggest size, best appearance, and the maximum value (Gait 182-185).
The first step in cutting a diamond is the careful examination of the stone. During the course of this examination the expert cutter determines the cleavage planes of the diamond and decides how the stone can be divided by cleaving and sawing. The rough diamond is marked with lines of india ink as a guide for the operations. The stone is then firmly cemented into a wooden holder and the holder firmly mounted in a vise. The cutter holds a cleaving iron, an instrument like a heavy, dull knife, on the line and parallel to the cleavage plane of the diamond. The stone is cleft by striking the iron with a light blow of a hammer. The tools used for cleaving are simple, but skill is needed in their use because too hard a blow applied in the wrong direction may ruin the stone. In present-day practice, diamonds are sawed more often than they are cleaved. The saw is a thin metal disk the edge is inserted with a mixture of diamond dust and oil (Comptons).
The final step in the cutting of a diamond is called polishing. Polishing consists of forming the facets of the finished stone. For the polishing process the gem is held firmly in a mount called a dop. Diamonds are most often cut in the form of brilliants with a total of 58 facets. Facets are formed on a flat, revolving cast-iron wheel that is charged with a mixture of diamond dust and oil. The stone in its dop is held against the surface until the facet is formed. In the course of polishing, the stone is moved many times in its dop to present new surfaces to be polished (Comptons).
In conclusion the diamond is a mineral that has captured the essence of wealth, beauty, and love for another individual all in one stone. It is incredible that a soft piece of graphite with a lot of work and time can turn into the hardest and most beautiful natural occurrence on Earth. It was incredibly interesting to research, learn and discover a small piece of what the diamond has to offer.