Xem 1-5 trên 5 kết quả Solid sulfur
  • Sulfur is the element with the largest number of solid allotropes. Most of these consist of unbranched cyclic molecules with ring sizes ranging from 6 to 20. In addition, polymeric allotropes are known which are believed to consist of chains in a random coil or helical conformation. Furthermore, several high-pressure allotropes have been characterized. In this chapter the preparation, crystal structures, physical properties and analysis of these allotropes are discussed.

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  • Among halogens, fluorine is quite characteristic and specific since it has the largest electronegativity (4.0 vs 3.5 for oxygen) and the sterically second smallest van der Waals' radius (1.35 ~ vs. 1.20/~ for hydrogen). A carbon-fluorine bond is also stronger than a carbon-hydrogen bond (485 kJ/mol vs 414 kJ/mol). Therefore, fluoro organic compounds have unique chemical and physical properties.

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  • Gaseous injection of sulfur dioxide was beginning in 1993 and is a part of the quick-germ (QG) and quick-fiber (QF) techniques currently being devel- oped. There is revived interest in the use of special corn hybrids high in starch, though their use is still not widespread. Membrane filtration and yeast immobilization were being used in some plants in 1993, but their use, contrary to expectations, has not increased. Bacterial fermentation is still not used commercially, nor is cellulosic conversion of corn fiber.

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  • Pesticides are divided to insecticides, fungicides, herbicides, rodenticides, acaricides and nematocides according to the organisms that they affect. There are various forms of insecticides; most are repellants or insect growth regulators used in agriculture, public health, horticulture or food storage. It is evident that insecticides have been used to boost food production to a considerable extent and to control disease vectors.

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  • It is evident that insecticides have been used to boost food production to a considerable extent and to control vectors of disease. However, these advantages that are of great economic benefits sometimes come with disadvantages when subjected to critical environmental and human health considerations. Many insecticides are newly synthesized whose health and environmental implications are unknown.

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