Forms of carbon

Adsorption. Adsorption involves the transfer of a component onto a solid surface. An example is the adsorption of organic vapors by activated carbon. Activated carbon is a highly porous form of carbon manufactured from a variety of carbonaceous raw materials such as coal or wood. The adsorbent may need to be... 

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

Dilute acids have no effect on any form of carbon, and diamond is resistant to attack by concentrated acids at room temperature, but is oxidised by both concentrated sulphuric and concentrated nitric acid at about 500 K, when an additional oxidising agent is present. Carbon dioxide is produced and the acids are reduced to gaseous oxides ... 

Amorphous carbon, having a far greater effective surface area than either diamond or graphite, is the most reactive form of carbon. It reacts with both hot concentrated sulphuric and hot concentrated nitric acids in the absence of additional oxidising agents but is not attacked by hydrochloric acid. 

All forms of carbon, if heated to a sufficiently high temperature, give carbon dioxide in a plentiful supply of air, and carbon monoxide if the supply is limited (p. 178) ... 

In combination, carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters. It is a component of great rock masses in the form of carbonates of calcium (limestone), magnesium, and iron. Coal, petroleum, and natural gas are chiefly hydrocarbons. 

The use of accurate isotope ratio measurement is exemplified here by a method used to determine the temperature of the Mediterranean Sea 10,000 years ago. It is known that the relative solubility of the two isotopic forms of carbon dioxide COj) in sea water depends on temperature... 

One method for measuring the temperature of the sea is to measure this ratio. Of course, if you were to do it now, you would take a thermometer and not a mass spectrometer. But how do you determine the temperature of the sea as it was 10,000 years ago The answer lies with tiny sea creatures called diatoms. These have shells made from calcium carbonate, itself derived from carbon dioxide in sea water. As the diatoms die, they fall to the sea floor and build a sediment of calcium carbonate. If a sample is taken from a layer of sediment 10,000 years old, the carbon dioxide can be released by addition of acid. If this carbon dioxide is put into a suitable mass spectrometer, the ratio of carbon isotopes can be measured accurately. From this value and the graph of solubilities of isotopic forms of carbon dioxide with temperature (Figure 46.5), a temperature can be extrapolated. This is the temperature of the sea during the time the diatoms were alive. To conduct such experiments in a significant manner, it is essential that the isotope abundance ratios be measured very accurately. 

CARBON - CARBON AND ARTIFICIALGRAPHIPE - OPHER FORMS OF CARBON AND GRAPHIPE] (Vol 4)... 

Other forms of carbon-carbon composites have been or are being developed for space shutde leading edges, nuclear fuel containers for sateUites, aircraft engine adjustable exhaust nozzles, and the main stmcture for the proposed National Aerospace plane (34). For reusable appHcations, a siHcon carbide [409-21 -2] based coating is added to retard oxidation (35,36), with a boron [7440-42-8] h Lsed sublayer to seal any cracks that may form in the coating. 

Carbon and Graphite. Fluorine reacts with amorphous forms of carbon, such as wood charcoal, to form carbon tetrafluoride [75-73-0], CF, and small amounts of other perfluorocarbons. The reaction initiates at ambient conditions, but proceeds to elevated temperatures as the charcoal bums ia fluoriae. 

Renewable carbon resources is a misnomer the earth s carbon is in a perpetual state of flux. Carbon is not consumed such that it is no longer available in any form. Reversible and irreversible chemical reactions occur in such a manner that the carbon cycle makes all forms of carbon, including fossil resources, renewable. It is simply a matter of time that makes one carbon from more renewable than another. If it is presumed that replacement does in fact occur, natural processes eventually will replenish depleted petroleum or natural gas deposits in several million years. Eixed carbon-containing materials that renew themselves often enough to make them continuously available in large quantities are needed to maintain and supplement energy suppHes biomass is a principal source of such carbon. 

Synthetic manganese carbonate is made from a water-soluble Mn (IT) salt, usually the sulfate, by precipitation with an alkafl or ammonium carbonate. The desired degree of product purity determines the quaUty of manganese sulfate and the form of carbonate to be used. For electronic-grade material, where the content of K O and Na20 cannot exceed 0.1% each, the MnSO is specially prepared from manganese metal, and ammonium bicarbonate is used (26) (see Electronic materials). After precipitation, the MnCO is filtered, washed free of excess carbonate, and then, to avoid undesirable oxidation by O2, dried carefljlly at a maximum temperature of 120°C. 

Food-grade specifications requite further purification in the form of carbon treatments and recrysta11i2ation from aqueous or other solvent systems. The illustrated flow scheme for sorbic acid production in Figure 1 has been greatly simplified. 

In ancient India, a steel called wootz was made by placing very pure kon ore and wood or other carbonaceous material in a tightly sealed pot or cmcible heated to high temperature for a considerable time. Some of the carbon in the cmcible reduced the kon ore to metallic kon, which absorbed any excess carbon. The resulting kon—carbon alloy was an excellent grade of steel. In a similar way, pieces of low carbon wrought kon were placed in a pot along with a form of carbon and melted to make a fine steel. A variation of this method, in which bars that had been carburized by the cementation process were melted in a sealed pot to make steel of the best quaUty, became known as the cmcible process. 

Fermentation is an anaerobic cataboHc process that uses organics as electron receptors. Since fermentation produces organic products that have lower free energy than their precursors, it is usefijl in remediation. The lowest free energy form of carbon produced is methane [74-82-8]. 

Processing of baked and graphitized carbon. Properties of manufactured graphite, Appbcations of baked and graphitized carbon. Other forms of carbon and graphite. 

Various forms of carbon, semigraphite, and graphite materials have found wide apphcation ia the metals iadustry, particularly ia connection with the productioa of iroa, alumiaum, and ferroalloys. Carbon has been used as a refractory material siace 1850, though full commercial acceptance and subsequent rapid iacrease ia use has occurred only siace 1945. 

Of the many forms of carbon and graphite produced commercially, only pyrolytic graphite (8,9) is produced from the gas phase via the pyrolysis of hydrocarbons. The process for making pyrolytic graphite is referred to as the chemical vapor deposition (CVD) process. Deposition occurs on some suitable substrate, usually graphite, that is heated at high temperatures, usually in excess of 1000°C, in the presence of a hydrocarbon, eg, methane, propane, acetjiene, or benzene. 

Baked and Graphitized Products, Uses" under "Carbon" in ECT2nd ed., VoL 4, pp. 202—243, by W. M. Gaylord, Union Carbide Corp. "Other Forms of Carbon and Graphite Carbon" under "Carbon (Carbon and Artificial Graphite)" in ECT 3rd ed., Vol. 4, pp. 628—631, by R. M. Bushong, Union Carbide Corp. 

In 1955, a team of research workers at General Electric developed the necessary high pressure equipment and discovered solvent—catalytic processes by which ordinary forms of carbon could be changed into diamond. 

AH graphite has crystal stmcture but only certain kinds and sizes of natural graphites are commercially classified as crystalline, a term used for import duty purposes. Throughout this article reference is made separately to dake, vein (lump or high crystalline), and amorphous forms, all of which are essentially the same crystalline form of carbon. However, fine stmctured graphites (cryptocrystalline (2)) have been classified as amorphous. 

The composition varies with the heat treatment and the end point according to x-ray diffraction studies it is a form of carbon that reconverts to weU-ordered graphite on heating to 1800°C. Before the use of x-rays, chemists used the Brodie reaction to differentiate between graphitic carbons and turbostratic carbons. Turbostratic carbons yield a brown solution of humic acids, whereas further oxidation of graphite oxide produces mellitic acid (benzenehexacarboxyhc acid) [517-60-2] ... 

Under extremely high pressures of about 5.5 GPa (5.4 x lO" atm) and temperatures up to 175°C, a black, soHd form of carbon disulfide has been observed (17). 

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