Diffusion Of Sulfide Research Articles

Surface diffusion of hydrogen sulfide and sulfur dioxide in alumina membranes in the continuum regime

Surface diffusion of H2S and SO2 in alumina membranes with an average pore diameter of ca. 350 mm, impregnated with γ-Al2O3, is studied as a function of pressure at temperatures between 446 and 557 K. Diffusion through the gas phase in the pores of the membrane almost entirely takes place in the continuum regime. The pressure dependence of transport by diffusion through the gas phase and by surface diffusion is different, a fact which is used for the interpretation of the steady-state diffusion measurements. It is observed that the contribution of surface diffusion to the total diffusion through the membrane can be as high as about 40%. The surface diffusion data obtained are interpreted by a theoretical surface diffusion model using two parameters to be fitted, the product of the effective surface diffusion coefficient, the concentration of the adsorption sites and the adsorption parameter as well as the adsorption parameter itself. The parameters fitted for SO2 show a remarkable change between 498 and 525 K. This probably maybe attributed to a change in the adsorbed species also reported in literature. The parameters fitted for H2S at different temperatures show a maximum; however, the product of the effective surface diffusion coefficient and the concentration of the adsorption sites increases with temperature.

2D monomolecular inorganic semi-conductors, inserted in a Langmuir-Blodgett matrix

The present work describes the realization of inorganic semi conducting compounds in the form of a monomolecular plane, generated from an L.B. matrix. Mercury and cadmium sulfides are obtained by a two step, in situ synthesis, from the organic molecules of an L.B. film: multilayers of behenic acid are transformed into cadmium or mercury behenate by an aqueous diffusion of each ion. Next, a gaseous diffusion of hydrogen sulfide precipitates the HgS or CdS in the polar plane with regeneration of the behenic acid matrix. These chemical reactions are followed by infrared spectroscopy. The observed photoelectric properties in the near U.V. range argues in favour of a) a monomolecular plane of a semiconducting sulfide. b) a 2D structure of the sulfides, different from the known 3D crystals of HgS and CdS which absorb in the visible and infrared range. Hence it can be assumed that the 2D sulfide synthesis is matrix controlled, since the physical properties are different. This opens the field for new monomolecular materials because this experiment can be enlarged to other compounds.

On the sulphur chemistry of a super-anoxic fjord, Framvaren, South Norway

Abstract The concentrations of total carbonate (C t ), sulphate, sulphide, thiols and oxygen, the ratio between the stable sulphur isotopes 34 S and 32 S in sulphate and sulphide, and the density (used to calculate salinity) were determined on samples from the water column of Framvaren, a superanoxic fjord in southern Norway. From a depth of 18m (the oxic-anoxic boundary) the initial sulphate concentration, ([SO 4 ] init ), as calculated from salinity, is significantly higher than the sum of the measured sulphur species. This is attributed to a loss of sulphur from the water column. The amount of total carbonate produced, corrected for the initial concentration (C t - 2.4 Sal/35) is found to be proportional to the amount of sulphate consumed, ([SO 4 ] init - [SO 4 ]), according to the following relation C t - 2.4 Sal/35 = 1.84 ([SO 4 ] init - [SO 4 ]). Isotopic fractionation caused by bacterial sulphate reduction in the anoxic part of the water column produces sulphide with a δ 34 S ∼ 40‰ lower than the δ 34 S for sulphate at corresponding depths. The isotopic fractionation also results in δ 34 S value for the remaining sulphate at depths below 80 m being considerably higher than the mean value for ocean water, which is close to + 20‰. The δ 34 S values for sulphate at depths between 10 and 50 m were lower than + 20‰ which indicates oxidation of sulphide, which follows upon diffusion of sulphide from deeper parts of the water column and inflow of oxygenated seawater over the sill into the anoxic water of the fjord. A conclusive scenario of the Framvaren sulphur chemistry is presented.

Alteration of Alluvium by Natural Gas in the Pyramid Lake Area, Nevada

Some of the chemical and physical processes associated with the migration of natural gas and their impact on engineering properties of soils are not well known. In the vicinity of the Truckee River Delta, gas (mostly methane with some hydrogen sulfide) was noted in natural seeps and in shallow test holes in sandy Holocene deltaic alluvium and in ancient Lake Lahontan clays and silts. Shiny black cores of Lahontan silt, after exposure to air, become buff from the surface inward. The black color is caused by iron sulfide pigmentation which disappears upon oxidation. Seasonal color changes from black (when submerged) to buff (when air-exposed) were observed in outcrops of Lahontan silts in the riverbed. They indicate periodic oxidation and reduction of the pigment by diffusion of either oxygen or hydrogen sulfide. Iron sulfides change the plasticity, shear strength, and other engineering properties of sediments and, together with gas pressure, may be partially responsible for underwater landslides in the delta. Oxidation of iron sulfides in ground water near the ground-water table probably caused development of a limonitic “rusty” stain on pebbles and sand near the top of deltaic alluvium. Isotopic composition of carbon in the methane seems to indicate its “marsh” origin. Hydrogen sulfide is probably created by bacterial ( Desulfovibrio desulfuricans ) reactions with methane and sulfates.

Interrelationships between sulfate reducing and methane producing bacteria in coastal sediments with intense sulfide production

Coastal sediments receiving different amounts of organic carbon through sedimentation were investigated with respect to sulfate reduction and methanogenic activity. Sampling was carried out at sediment temperatures of 7° and 15°C. Sulfate-reducing and methanogenic bacteria were found at all depths. Sulfate reduction decreased with depth and the highest sulfide concentrations were found a few centimeters below the sediment surface, up to 15 mM at 15°C and pH 7.1. In the same segments a maximum in the methane concentration was also found, 0.91 mM. The high sulfide concentration inhibited the methane formation from acetate but not from carbon dioxide. In the organic rich sediment sulfate reduction was limited by the diffusion of SO 4 + into the sediment and methane production from acetate by sulfide diffusion out of the sediment. When electron acceptor concentration limits sulfate reduction, thermodynamic calculations show that the utilization of electron donors more reduced than acetate is favored. In the sediment with the high carbon-input, acetate predominated at 15°C whereas in the low carbon-input sediment hardly any short chain organic acids were detected. The possibility of a shift in sulfate reduction from acetate oxidation to acetate production is discussed.

硫化鉛の揮発速度について

Using a thin disk made of the powder of galena single crystals from several mines or synthetic lead sulfide, the sublimation rate of lead sulfide has been measured thermogravimetrically at atmospheric and reduced pressures in a stream of inert gas. The limiting gas velocity for the rate of sublimation respectively appeared as the velocity was elevated.The apparent activation energy for the sublimation was found to be independent of pressure and was determined to be about 54 kcal/mol. This value is nearly equal to the enthalpy of sublimation of lead sulfide.The experimental results indicated that the sublimation rate was controlled by diffusion of gaseous lead sulfide through the gas boundary layer.The rate of sublimation under argon was nearly equal to that under nitrogen, but was only half the rate under helium. Decrease in the sublimation with increasing pressure of inert gas was also observed. These two results can be rationalized as reflecting the change in diffusion coefficient of inert gas.Decrease in the sublimation area may be expected by mixing lead sulfide with a nonvolatile substance or by changing grain size of the lead sulfide particles in a disk. Therefore, a disk containing 13 wt-% alumina was tested. The rate curve showed good agreement with that obtained from the specimen of pure lead sulfide in the incipient sublimation. Moreover, it was found that grain size of lead sulfide particles in a disk had no effect upon the sublimation rate. It may, therefore, be concluded that the section area for diffusion of gaseous lead sulfide correspond to the area, not of the lead sulfide on the disk_ but of the surface of the disk.

Does the bowel prevent the outward diffusion of gas from within the balloon of intestinal tubes?: An experimental study

Abstract The effect of submersion of balloons of intestinal decompression tubes inflated with different gases in water was studied and compared with similar studies in which the inflated balloons were exposed to air. The experiment indicated that there was very little or no difference in the speed of diffusion of the gases from within the balloons exposed to air or submerged in water. In reproducing in vivo conditions the inflated balloons were inserted within the intestinal tract of an hour-old autopsy specimen. The inflated balloon caused the bowel wall to be stretched tightly over it. We noted that the speed of diffusion of the gases out of the balloons was the same whether the bowel was empty or filled with intestinal secretions. There appeared to be very little difference between the speed of diffusion of gases out of the balloons within the bowel or those submerged in liquid or exposed to air. This experimental study clearly shows that if an intestinal decompression tube balloon becomes inflated as a result of carbon dioxide or hydrogen sulfide, the passage of a second intestinal tube to decompress the circumjacent bowel would rapidly result in the diffusion of the hydrogen sulfide or the carbon dioxide from within the balloon into the bowel. The speed of diffusion of the hydrogen sulfide is so fast that it is extremely doubtful whether this gas enters into the problem at all. The only possible influence this gas might have is suggested by our observations that balloons filled with hydrogen sulfide rapidly lost this gas in less than four hours. If then these balloons were permitted to lie exposed to the air, they took up some of the air. This diffusion of air into balloons formerly filled with hydrogen sulfide might constitute a real problem in intubation, or the presence of an air-filled Miller-Abbott balloon which could not be evacuated as a result of a knot in the tube might be quite serious for the patient. The reason for this is obvious from our observations that the air-filled balloons showed very little or no change in twenty-four hours. Some balloons filled with air were observed for four days and were then noted to show very little if any loss of air. When we recall that approximately 80 per cent of the air consists of nitrogen, a gas which is extremely slowly diffusible through a rubber membrane, it becomes obvious why this should be so. Once air has accumulated within the intestinal tube balloons many days of bowel decompression are required before any appreciable loss of air occurs from the balloon. The best treatment for this unusual accident is to prevent it by the use of a No. 18 French lumen tube and a safety valve vent as described in an earlier publication.1