Chlorine, atmospheric content

Wiedemann (143) determined the titanium content of a nonstoichiometric titanium carbide by a multistep, variable atmosphere, variable temperature program, TG method. The sample was first heated in a chlorine atmosphere to 975°C. This converted the titanium to volatile titanium chloride, leaving a residue of carbon in the sample container. The amount of carbon residue was then determined by heating from 475-600°C in an air atmosphere, resulting in the oxidation of carbon to carbon dioxide. These processes are illustrated in the TG curve in Figure 4.34. 

That fallout of trace elements from atmospheric pollution is widespread and far from confined to urban and industrial areas, is also borne out by data published by the UK Atomic Energy Authority, who determined, by neutron activation analysis, about 30 trace elements in airborne dust, rainwater and dry deposition, sampled at regular intervals in north-west England [188]. The highest concentrations measured in air were for chlorine, sodium, calcium, aluminium, iron, lead and zinc, and there were also measurable levels of antimony, arsenic and mercury, usually in the winter months, when there was a general increase in trace-element concentration. Further data were published on the atmospheric content and total deposition of a wide range of trace elements at seven non-urban sites (one in Shetland) in the UK in the years 1972 and 1973 [189]. Data have also been published for the North Sea and the Firth of Clyde [190]. 

Radiation-induced cross-linking of chlorinated and chlorosulfonated high-density PE has been reported by Korolev et al. [262]. It has been observed that the extent of cross-linking is strongly dependent on the chlorine content in the sample, chlorosulfonated PE is cross-linked more readily than the chlorinated sample in air and inert atmosphere. 

A large number of studies have also been done to investigate the lifetime of HC1 in a fire atmosphere [20-24]. These studies have shown that HC1 reacts very rapidly with most common construction surfaces (cement block, ceiling tile, gypsum board, etc.) so that the peak atmospheric concentration found in a fire is much less than would have been predicted from the chlorine content of the burning material. Furthermore, this peak concentration soon decreases and HC1 disappears completely from the atmosphere. 

Dehydrochlorination of poly vinylidene chloride and chlorinated polyvinyl chloride was carried out. High chlorine content in the polymers (more than 60%) provides the formation of chlorinated conjugated polymers, polychlorovinylenes. The reactivity of chlorinated polyvinylenes contributes to the sp carbon material formation during heat treatment. Synthesis of porous carbon has been carried out in three stages low-temperature dehydrohalogenation of the polymer precursor by strong bases, carbonization in the inert atmosphere at 400-600°C and activation up to 950°C. 

Chlorination. The titanium in the raw material is converted to titanium tetrachloride in a reducing atmosphere. Calcined petroleum coke is used as the reducing agent because it has an extremely low ash content and, due to its low volatiles content, very little HC1 is formed. The titanium dioxide reacts exothermically as follows ... 

Measuring Methods. Chlorine content was determined by the oxygen flask method (2) on a polymer purified by precipitation from the solution in cyclohexanone. Thermal stability, as HC1 evolution, was determined according to ASTM method D-793-49, determining the quantity of HC1 evolved by the polymer maintained at 180 °C in a nitrogen atmosphere. From the slope of the straight line for the amount of HC1 evolved with time, the constant K for the dehydrochlorination rate (DHC) is deduced. 

Because of evidence that BCME is carcinogenic even at very low levels in the atmosphere, current studies of its analysis are concentrating on extending the detection limit to even lower levels. Because of its chlorine content, BCME can be measured with extreme sensitivity by electron capture detection after gas chromatographic separation of this analyte. Efforts are underway by Dr. Robert Sievers (University of Colorado, Boulder) to improve collection methods that meet the criteria of (1) highly efficient collection of BCME at sub-ppb levels in air, (2) no loss of analyte from hydrolysis resulting from atmospheric humidity, and (3) rapid, efficient, nondestructive desorption of analyte from the collection medium. 

The best results are obtained if two thirds of the total hypochlorite content is present in the form of free acid, Avhieh corresponds to a concentration of hydrogen ions in the solution pH — 6 to 7 according to the sodium chloride concentration in the brine and according to temperature. Because, a small amount of chlorine escapes into the ambient atmosphere, hydrochloric acid must be gradually added in small quantities to the electrolyte during the process. 

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