Sulfur controlled-atmosphere studies

The choice of materials of construction for controlled-atmosphere studies is also crucial. Most metals adsorb, desorb, and react with sulfur-containing compounds depending upon the experimental conditions. For experiments at very low h2s /Ph2 values (<1-10 ppm), adsorption, desorption, and even generation of H2S from metal- and glass-containing systems result in serious problems, particularly at reaction temperatures 196). Quartz and teflon are the preferred materials of construction for studies at low H2S concentrations 99, 100, 114, 140, 196, 197). 

Gracia FJ, Guerrero S, Wolf EE, Miller JT, Kropf A. 2005. Kinetics, operando ETIR, and controlled atmosphere EXAFS study of the effect of sulfur on Pt-supported catalysts during CO oxidation. J Catal 233 372-387. 

Although there have only been a few studies to date, it has been suggested that coastal plumes (Turner et al., 1996 Simo et al., 1997) and estuaries (Iverson et al., 1989 Cerqueira and Pio, 1999) may be important atmospheric sources of DMS. DMS, a compound produced by certain phytoplankton, has been shown to have possible implications for climate control once released into the atmosphere (Charlson et al., 1987). DMS is formed by cleavage of dimethylsulfoniopropionate (DMSP) (Kiene, 1990). In fact, DMSP, shown to be correlated with bacterial activity, may provide as much as 100% of the sulfur and 3.4% of the carbon required for bacterial growth in oceanic waters (Kiene and Linn, 2000). Other sulfur compounds such as COS and carbon disulfide (CS2) have also been shown to be possible sources of S in estuaries. For example, significant concentrations of COS and CS2 were found in four European estuaries, 220 150 and 25 6 pM (Sciare et al., 2002). COS is the most abundant sulfur compound in the... 

Table 9-2 summarizes exposure studies that used controlled exposures to sulfur dioxide. Mild irritation, bronchoconstriction, and decreased lung function, as assessed by measurements of specific airway resistance or decreases in forced expiratory volume or expiratory flow, are produced after exposure of healthy individuals to low concentrations of sulfur dioxide. People with asthma are more susceptible. Exercise, cold air, and airborne participates appear to exacerbate the toxic effects (Gong et al. 1995 Roger et al. 1985 Schachter et al. 1984 Stacy et al. 1981). Concentration seems to be more important than duration as a determinant of health effects. Initial atmospheric exposure to sulfur dioxide can result in immediate discomfort, irritation, and coughing that abate after gradual acclimation to increasing concentrations (Andersen et al. 1974). Health effects reported by healthy volunteers are summarized in Table 9-3. 

A Study of Leaching of the Infiltrated Concrete. The distilled water experiments provided the most information for examining the reactions involved in the leaching of sulfur-infiltrated concrete in aqueous media. Products selected from the specimens were analyzed, and the experiment was continued in a controlled environment. One specimen was partly immersed in distilled water under a nitrogen atmosphere. Fragments of the concrete were also sealed in a test tube. 

Although most reactivity studies have been conducted with a controlled background air or a clean background air, other parameters, especially sulfur dioxide and relative humidity in the atmosphere, influence the atmospheric process. In Table VI and Figures 12, 13, and 14 the influence of S0.2 is shown on some solvent systems (5, 22, 23). In Table VI the eye irritation, with and without S02, is shown for five solvents one cannot state a priori that S02 reduces or increases the eye-irritation factor. Adding S02 to the mineral spirit systems increased eye irritation whereas adding S02 to methyl isobutyl ketone reduced irritation. For the other three solvents shown, there is no significant difference between the clean air or the S02 clean air system. 

Fall R, Albritton DL, Fehsenfeld C, et al. 1988. Laboratory studies of some environmental variables controlling sulfur emissions from plants. Journal of Atmospheric Chemistry 6 341-362. 

After the flame annealing of the noble metal surface at the main chamber, the sample must be transferred to the pre-chamber covered with a droplet of pure water. This reduced the surface contamination by residual atmospheric contaminants. Then, by using the dipping technique [83] that avoids new risks of contamination by the elimination of nitrogen, sulfur, carbon, etc., the surface is put in contact with the solution by careful dipping to avoid water from the lateral side of the hemispherical crystal. The contact of the electrode with the solution is performed potentiostatically at a select potential, where a negligible transient current is observed. This overall experimental process allows the control of surface purity in the system for the electrochemical experiment. This special technique, adopted for the studies on platinum surfaces, provided the novel observations on the behavior of platinum electrodes reported previously [1]. 

As already mentioned, the distinctive property of polyacid-modified composite resins is that, once the polymerization reaction has occurred, the set material is able to take up traces of moisture. This activates the acidic character of the carboxylic functional monomer and triggers an acid-base reaction with the glass [1,2]. The water uptake behaviour of these materials has been studied in detail [15], along with the corresponding water desorption processes. Three commercial polyacid-modified composite resins were used in a study of water uptake and loss, and cured samples were prepared as small discs of size 6 mm diameter x 2 mm thickness. Water uptake was allowed to take place in a controlled humidity environment at 93% relative humidity. Following the initial water uptake, there was an intervening desorption cycle in which specimens were stored in a dry atmosphere over concentrated sulfuric acid. 

Hvgrometry related evolution. We have studied the samples of o.33[Cu-Cr-S04] at 21 C in relation to the relative humidity (%RH) of the ambient atmosphere. The hygrometry was controlled via sulfuric acid solutions or phosphor pentoxide as a drying agent. Figure 7-24 shows the evolution of interlamellar spacings for the IH and 3R polytypes. The samples are biphased, at least between 30%RH and 50%RH, and in this hygrometry domain the ratio of the two polytypes evolves. Even in a dry... 

The influence of dimethyl disulfide on flavor quality of modified atmosphere stored broccoli florets was further demonstrated by data shown in Table VI which revealed that aroma assessments of undesirable sulfurous aromas in broccoli florets more closely corresponded with concentrations of dimethyl disulfide than with methanethiol. In this experiment broccoli florets were treated by dipping in various solutions containing either ascorbic acid (500 ppm), sodium hy oxide (0.01 M), or phosphoric acid (0.1 M). Broccoli florets dipp in distilled water were used as the control samples. Samples held in sealed Curlon 850 pouches were analyzed after storage for 4 days at 10°C. Ascorbic acid was included in this study because it acts as a reducing agent for methanethiol under anaerobic conditions in model systems (25). 

The growing demand for environmental protective actions has led to lower atmospherie sulfur levels, at least in developed countries, as a result of the use of eleaner eoals and sophisticated gas emission controls [29-31]. This has raised the relative signifieanee of other atmospheric compounds and the interest in studying their effects on zinc and galvanized steel, including CO2 [32, 33], ozone [19,34], NaNOs [35] and NO2 [19,34,36-38]. 

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