Carbon dioxide amorphous solid form

Even before alchemy became a subject of study, many chemical reactions were used and the products applied to daily life. For example, the first metals used were probably gold and copper, which can be found in the metallic state. Copper can also be readily formed by the reduction of malachite—basic copper carbonate, Cu2(C03)(0H)2—in charcoal fires. Silver, tin, antimony, and lead were also known as early as 3000 BC. Iron appeared in classical Greece and in other areas around the Mediterranean Sea by 1500 BC. At about the same time, colored glasses and ceramic glazes, largely composed of silicon dioxide (Si02, the major component of sand) and other metallic oxides, which had been melted and allowed to cool to amorphous solids, were introduced. 

Silicon dioxide (silica) exists in two familiar forms in nature quartz, small chips of which occur in sand and flint (Latin fe), an uncrystallized amorphous type of silica. Silica is properly represented as (Si02) because it is a polymeric solid of SiO tetrahedra sharing all oxygens among surrounding tetrahedra (Eigure 13-32c). Eor comparison, solid carbon dioxide (dry ice) consists of discrete 0=C=0 molecules, as does gaseous CO2. 

Although it constimtes only about 0.09 percent by mass of Earth s crust, carbon is an essential element of living matter. It is found free in the form of diamond and graphite (see Figure 8.17), and it is also a component of natural gas, petroleum, and coal. (Coal is a natural dark-brown to black solid used as a fuel it is formed from fossilized plants and consists of amorphous carbon with various organic and some inorganic compounds.) Carbon combines with oxygen to form carbon dioxide in the atmosphere and occurs as carbonate in limestone and chalk. 

We note here that the ordinary condensed solid phase of CO2 is a molecular solid. At variance with silica and germania, a nonmolecular CO2 crystalline form of carbon dioxide in which carbon atoms are tetrahedrally coordinated to oxygen atoms only exists at high pressure [16,17], In addition, an amorphous phase of CO2, formed by a disordered arrangement of CO4 tetrahedra, has recently been obtained at very high pressure [18]. 

Abstract Supercritical antisolvent technology can precipitate polyvinylpyrrolidone (PVP) particles and crystallize paracetamol (PCM) crystals first separately and then together in the form of a solid dispersion. Supercritical carbon dioxide (SCCO2) is used as an antisolvent. For PVP particle generation, ethanol, acetone, and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5 and 5 wt%, the operation pressure between 10 and 30 MPa, and the composition of ethanol/acetone solvent mixtures between 100 and 0 wt% of ethanol at a constant temperature of 313 K. An increase in the content of the poor solvent acetone in the initial solution leads to a significant decrease in mean particle size. Fully amorphous PVP powder always precipitates for all the parameters investigated. 

Carbon also is produced and used in other forms namely, activated carbon, carbon black, and coke, that have many commercial applications. Structurally they are amorphous forms of carbon belonging to the graphites. Activated carbon or activated charcoal has a highly porous honeycomb-like internal structure and adsorbs many gases, vapors, and colloidal solids over its very large internal surface area. Some of its major applications include purification of water and air, air analysis, waste treatment, removal of subur dioxide from stack gases, and decolorization of sugar. 

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