Sulfur ageing study

Short-term studies indicate that Thermopave mixes generally attain their ultimate stability after a curing time between one to five days, depending upon the sulfur/asphalt ratio and sand type. The results of a long-term aging study of Marshall briquettes stored at room temperature are presented in Table V. The data indicate a random variation in stability values but no significant change in stability over a five-year period. 

As previously mentioned, past studies used non-filtered air with unknown concentrations of trace gases at unknown relative humidities. Also, many of the studies used plastic aging chambers that may have introduced volatile monomers into the air. These unknown factors are important to determine in order to fully understand the nature of the ultrafine particle mode. According to the classical thermodynamic theory of ion cluster formation (Coghlan and Scott, 1983), the relative humidity and trace gases will affect the existence of condensation nuclei. Megaw and Wiffen (1961) observed an increase in nuclei formation with the presence of sulfur dioxide. 

Fig. 23. Significant coarsening of the domain structure did not occur, at least for the time scale investigated. Thus, charge-induced reconstruction in sulfuric acid results in a much smaller domain size than that associated with a freshly flame-annealed crystal. The domain boundaries act as preferred nucleation sites for subsequent (hex) (1 X 1) transformation, which occurs much more rapidly than for a freshly flame-annealed sample. Studies of this nature have provided keen insight into aging effects that would be difficult to assess by other means.

When the metals were studied, the release of gases and vapors was observed. For example, Paracelsus reported that when iron was dissolved in sulfuric acid air comes out like a wind. The differentiation of these kinds of air took more than two centuries. Research on the analysis of gases was extremely productive in developing the basic methods to handle and study gases and even paved the way to design techniques for elementary analysis of the constituents of organisms. Thus the study of gases became the second epoch of analytical chemistry it is called the pneumatic age. ... 

Raman and IR spectroscopic studies dealing with the qualitative and/or quantitative determination of rubber compounding ingredients, i.e., the elastomer itself [22, 26-31], fillers [32, 33], vulcanisation chemicals and other additives [34-37], are not included here. The same applies to studies dealing with the crosslinking of elastomers by means of chemicals other than sulfur or peroxide [38-41], self-crosslinking of elastomers blends [42-44], crystallisation (strain-induced) [45-48] and oxidation/ageing [49-53]. 

Another study used 13C NMR to examine the thermal ageing of NR with both peroxide and conventional and EV sulfur vulcanised samples [59]. The samples were heat aged at 70 °C in air with 13C NMR recorded after 3 and 21 days. The vulcanisate structures vulcanised by peroxide and the EV sulfur system showed low sensitivity to ageing effects while peaks in the conventional sulfur system almost disappeared after 21 days of ageing. In addition, the main chain isoprene carbon peaks showed considerable broadening due to increasing stiffness of the network. 

Similar results were obtained in an activity testing experiment which lasted for over 600 hours. Sulfur was added to the zirconia catalyst using a SOJN2 mixture and impregnated with chloroplatinic acid to achieve a concentration of 0.6 wt. percent. The feedstocks were n-C16, n-C1Q and mixtures of n-C10 and n C16. A number of different process variables were studied at 150°C. Catalyst aging was monitored by returning... 

The pilot plant-scale extract used in this study was made from bark obtained from old trees decked at a plywood plant. When 4.0% sodium sulfite and 0.4% sodium carbonate (on dry bark weight basis) were used to extract this finely ground bark for 2 hours at 100 °C, extract yields were only 18% of dry bark weight. The extract had a Stiasny polyphenol number of only 0.52 it gave a total of 18% sugars after hydrolysis, and contained 5.8% sodium and 3.8% sulfur. When bark from pulpwood-aged trees is extracted under similar conditions, extract yields typically vary between 20 and 24% and Stiasny polyphenol numbers are typically 0.60 to 0.75. The extract used for this work was also dried by a hot-pan evaporation method rather than being spray dried. So, the extract used represented a near worst-case example. 

Finally, some of the most powerful wine aroma compounds take part in reversible interactions which evolve during wine aging and that can be reversed, at least in part, when the wine takes contact with air. These aspects have not yet been studied in depth, but it is well known that carbonyls form reversible associations with sulfur dioxide and that mercaptans take part in complex redox equilibria. These molecules involved in interactions or in redox equilibria are the most likely cause of the aromatic changes noted during the aging of wine or after the bottle is opened. 

The NAC/AEGL Committee estimates the range in variability of response to specific chemical exposures primarily on the basis of quantitative human data. Acceptable experimental data are more likely to be available for AEGL-1 and AEGL-2 endpoints than for AEGL-3 endpoints. For example, numerous studies have considered induction of bronchospasm after controlled exposmes to sulfur dioxide (SO2) in asthmatic and nonasthmatic individuals (see references below). There is marked individual variability in the severity of reaction to inhalation of low concentrations of SO2. Asthmatics, individuals with hyper-reactive airways, smokers, and those with chronic respiratory or cardiac disease respond at relatively lower concentrations (Aleksieva 1983 Simon 1986). Susceptibility may also be increased in people over 60 years of age, but reports have not been consistent (Rondinelli et al. 1987 Koenig et al. 1993). By contrast, comparable human data for AEGL-3 tier concentrations are limited to anecdotal case reports. 

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