Ozone Also Group

This section on ozone is included under oxygen in group 16 because of its importance today in the lives of citizens and its effect on the environment. It is treated as another element with its own properties and characteristics, uses, and hazards. 

Ozone has a very distinctive pungent odor. It exists in our lower atmosphere in very small trace amounts. In higher concentrations it is irritating and even poisonous. Ozone is in relatively low concentrations at sea level. In the upper atmosphere, where it is more concentrated, it absorbs ultraviolet radiation, which protects the Earth and us from excessive exposure to ultraviolet radiation. 

FoUowing are the chemical reactions for the production of ozone at ground level. Ozone can be formed when a mixture of and NO is exposed to sunhght. Given that this reaction is very slow at normal temperatures, it is not a problem until hot gases in the cylinders of automobiles internal combustion engines cause the foUowing more rapid reactions. 

It was once believed that air was a single element, but by the fifteenth century ce, scientists began to question whether it was possibly at least two separate gases. Leonardo da Vinci was one of the first to suggest the air consisted of at least two gases. He even determined that one of them would support hfe and fire. 

Ozone produced by electrical discharge is used to purify drinking water and to treat industrial wastes and sewage. It is also use to deodorize air and kill bacteria by passing dry air through special ozone-producing electronic devices. 

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Ozone diffuses readily into amorphous region of the polyethylene (32) and oxidation probably occurs much deeper in the solid sample. Ozone also attacks the crystalline part of polyethylene but it has a slow initiation stage followed by more rapid oxidation (13). Because ozone does not diffuse into the crystalline regions (13.32). oxidation is restricted to the surface. The resulting oxidized functional groups on the crystalline regions will remain at the surface, whereas those formed in the amorphous region can diffuse into the bulk. 

The gas finally obtained had a density of 19.086, and Ramsay and Rayleigh still believed it to be a modification of nitrogen, similar to ozone. However, when Ramsay examined its spectrum, he saw not only the bands of nitrogen but also groups of red and green lines which had never before been observed in the spectrum of any gas. Sir William Crookes made a very thorough study of the spectrum and observed nearly two hundred lines (28). 

The formation of oxygen anion radicals and molecules of ozone also should be counted with at the ionization initiation of oxidation [26]. Initiation reaction caused by oxygen anion radicals may play an important role within the polymer bulk while the effect of ozone forming in the surrounding air atmosphere will include only the formation of radicals on the polymer surface. The latent effect of ionization initiation on polymer oxidation which is very distinct may be documented on a relatively fast increase of concentration of carbonyl groups, observed over 1 year after irradiation crosslinking of polyethylene [27]. 

Like NR, SBR is an unsaturated hydrocarbon polymer. Hence unvulcanised compounds will dissolve in most hydrocarbon solvents and other liquids of similar solubility parameter, whilst vulcanised stocks will swell extensively. Both materials will also undergo many olefinic-type reactions such as oxidation, ozone attack, halogenation, hydrohalogenation and so on, although the activity and detailed reactions differ because of the presence of the adjacent methyl group to the double bond in the natural rubber molecule. Both rubbers may be reinforced by carbon black and neither can be classed as heat-resisting rubbers. 

The close structural similarities between polychloroprene and the natural rubber molecule will be noted. However, whilst the methyl group activates the double bond in the polyisoprene molecule the chlorine atom has the opposite effect in polychloroprene. Thus the polymer is less liable to oxygen and ozone attack. At the same time the a-methylene groups are also deactivated so that accelerated sulphur vulcanisation is not a feasible proposition and alternative curing systems, often involving the pendant vinyl groups arising from 1,2-polymerisation modes, are necessary. 

Ozone cracking is a physicochemical phenomenon. Ozone attack on olefinic double bonds causes chain scission and the formation of decomposition products. The first step in the reaction is the formation of a relatively unstable primary ozonide, which cleaves to an aldehyde or ketone and a carbonyl. Subsequent recombination of the aldehyde and the carbonyl groups produces a second ozonide [58]. Cross-linking products may also be formed, especially with rubbers containing disubstituted carbon-carbon double bonds (e.g. butyl rubber, styrene-butadiene rubber), due to the attack of the carbonyl groups (produced by cleavage of primary ozonides) on the rubber carbon-carbon double bonds. 

The fluorocarbons have the best heat stability of all rubbers, being capable of giving extended service life at over 250 °C. As a group, fluorocarbons resist aliphatic, aromatic and chlorinated hydrocarbons, and most oils and mineral acids. They are also highly resistant to oxygen, ozone and UV light. 

Nitric acid synthesis, platinum-group metal catalysts in, 19 621 Nitric acid wet spinning process, 11 189 Nitric oxide (NO), 13 791-792. See also Nitrogen oxides (NOJ affinity for ruthenium, 19 638—639 air pollutant, 1 789, 796 cardioprotection role, 5 188 catalyst poison, 5 257t chemistry of, 13 443—444 control of, 26 691—692 effect on ozone depletion, 17 785 mechanism of action in muscle cells, 5 109, 112-113 oxidation of, 17 181 in photochemical smog, 1 789, 790 reduction with catalytic aerogels, l 763t, 764... 

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