Ranjani Siriwardane

Decomposition of the sulfates of copper, iron (II), iron (III), nickel, and zinc: XPS, SEM, DRIFTS, XRD, and TGA study

The bulk and surface characteristics during decomposition of the transition metal sulfates of copper, iron (II), iron (III), nickel, and zinc are investigated utilizing various spectroscopic techniques. An oxidized form of sulfur was detected on the surface during decomposition of all metal sulfate samples, except zinc sulfate. Surface characteristics were not necessarily representative of the bulk characteristics. Oxy-sulfate was observed with copper sulfate only. Lower decomposition temperatures were observed in vacuum as compared to those at atmospheric pressure. Uniform sulfur distribution was observed across sample cross sections. Analysis consisted of Scanning electron microscopy/X-ray microanalysis, X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetric analysis, and X-ray diffraction.

Thermal decomposition of the rare earth sulfates of cerium(III), cerium(IV), lanthanum(III) and samarium(III)

Surface and bulk chemical and elemental composition of the rare earth sulfates of cerium(III), cerium(IV), lanthanum(III) and samarium(III) were characterized during various stages of thermal decomposition. Decomposition was conducted under both vacuum and atmospheric conditions. In situ analysis was conducted on samples decomposed in vacuum. As identified by X-ray diffraction, the bulk decomposition of all the rare earth sulfate samples to their corresponding oxide, in atmosphere, proceeded via the formation of an oxysulfate. For the exception of cerium(III) sulfate, similar results were obtained in thermogravimetric analysis. The thermal decomposition profile, as determined by X-ray microanalysis was similar to that observed in thermogravimetric analysis and X-ray diffraction. Elemental maps revealed no observable concentration gradients of sulfur. Surface composition was not necessarily representative of the bulk composition. Thermal decomposition of sulfates to an oxide initiated at a lower temperature in vacuum than that observed at atmospheric pressure.

Characterization of copper oxides, iron oxides, and zinc copper ferrite desulfurization sorbents by X-ray photoelectron spectroscopy and scanning electron microscopy

Abstract Characterization of copper oxides, iron oxides, and zinc copper ferrite desulfurization sorbents was performed by X-ray photoelectron spectroscopy and scanning electron microscopy/energy-dispersive spectroscopy at temperatures of 298 to 823 K. Analysis of copper oxides indicated that the satellite structure of the Cu22p region was absent in the Cu(I) state but was present in the Cu(II) state. Reduction of CuO at room temperature was observed when the ion gauge was placed close to the sample. The satellite structure was absent in all the copper oxides at 823 K in vacuum. Differentiation of the oxidation state of copper utilizing both Cu(L 3 M 4,5 M 4,5 ) X-ray-induced Auger lines and Cu2p satellite structure, indicated that the copper in zinc copper ferrite was in the + 1 oxidation state at 823 K. This + 1 state of copper was not significantly changed after exposure to H 2 , CO, and H 2 O. There was an increase in Cu/Zn ratio and a decrease in Fe/Zn ratio on the surface of zinc copper ferrite at 823 K compared to that at room temperature. These conditions of copper offered the best sulfidation equilibrium for the zinc copper ferrite desulfurization sorbent. Analysis of iron oxides indicated that there was some reduction of both Fe 2 O 3 and FeO at 823K. The iron in zinc copper ferrite was similar to that of Fe 2 O 3 at room temperature but there was some reduction of this Fe(III) state to Fe(II) at 823 K. This reduction was more enhanced in the presence of H 2 and CO. Reduction to Fe(II) may not be desirable for the lifetime of the sorbent.

Interactions of NO and SO2 with iron deposited on silica

Abstract The interactions of NO and SO 2 with both clean and iron-deposited, single-crystal surfaces of SiO 2 at temperatures of 298, 473, and 673°K were studied using X-ray photoelectron spectroscopy. Neither NO nor SO 2 showed any reaction with clean SiO 2 at the three temperatures studied. The iron that was deposited onto the SiO 2 surface remained in the metallic state. Both NO and SO 2 interacted with this iron-covered silica (Fe/SiO 2 ). The total amount of adsorbed gas increased with increased iron coverage. Two forms of nitrogen, nitride and molecularly adsorbed NO, were observed when an Fe/SiO 2 surface at 298°K was exposed to NO. When the reaction was carried out at 473°K, the amount of nitride increased, but molecularly adsorbed NO was no longer observed. AT 673°K, neither form of nitrogen was observed. An adsorbed oxygen peak appeared at all three temperatures. The presence of both the nitride and the oxygen peaks indicated that dissociation of NO occurred on the Fe/SiO 2 surface. When the Fe/SiO 2 system at 298°K was exposed to SO 2 , two forms of sulfur, sulfate and sulfide, were observed. At 473°K the amount of sulfide increased slightly while the amount of sulfate decreased slightly. Neither form of sulfur was observed at 673°K.

Particle transfer from a continuous oil to a dispersed water phase: model particle study

The surface free energy of glass microbeads was controlled by varying the extent of reaction between t-butyldimethylchlorosilane with the surface silanols. This system was chosen so that the surface free energy of the particles could be varied without introducing an extraneous wetting agent. The wicking method was used to obtain the liquid-particle-air contact angles. Water-air contact angles on glass beads increased with increasing silanizing reaction. The dispersive and the nondispersive contributions of the surface free energy were calculated from the contact-angle data. Nondispersive contribution decreased with increasing silanizing reaction while dispersive component remained unchanged. These silanized glass beads were dispersed in the continuous oil phase and the extent of particle retention at the water-oil interface and distribution to the water phase were determined. The experimental data indicate that the surface free energy of particles is the controlling parameter determining the transfer of particles from the oil phase to the water phase. Particle size in the range 5–20 μm had no significant effect, either on the particles retained or distributed to the water droplets.

Interaction of H2S with zinc titanate in the presence of H2 and CO

Abstract The interactions of H2S and mixtures of H2S/H2 and H2S/CO with zinc titanate at temperatures of 943, 993, and 1073 K were studied using X-ray photoelectron spectroscopy. The initial sulfur products formed on the surface were sulfide and sulfate. Sulfate formation was due to the oxygen released from the sample in the presence of H2S, H2, and CO. The release of oxygen was faster in the presence of reducing gases H2 and CO than in pure H2S, although at higher exposures to H2 and CO, sulfate decomposed and was removed from the surface. Sulfide formation was not temperature dependent in the temperature range 943 to 1073 K, while sulfate formation was highly temperature dependent, with the maximum being at 993 K. The sulfide formation kinetics and the saturation coverage of sulfide on ZnO were similar to those of zinc titanate at 993 K but the saturation coverage of sulfide on TiO2 was considerably lower than that of zinc titanate. The saturation coverage of sulfide in the presence of CO on both zinc oxide at 993 K and zinc titanate at 1073 K was significantly higher as compared to that in the absence of CO. This was attributed to the formation of metallic zinc and subsequent reaction with H2S in the presence of CO. Based on the experimental results, a mechanism for the reaction of H2S with zinc titanate was proposed.

Control of surface energy of glass by surface reactions: Contact angle and stability

Abstract The surface energy of glass plates was modified by chemisorption of organochlorosilanes. Auger electron spectroscopy was used to measure the elemental composition of the surfaces of glass plates. Contact angles both water-air and xylene-water were measured as a function of reagent concentration in order to characterize the plate surface after reaction. An increase in both water-air and xylene-water contact angles was observed with increasing reagent concentration. An interesting behavior of the water-air contact angle hysteresis as a function of reagent concentration was observed. Based on contact angle hysteresis data regions of reagent concentrations corresponding to partial coverage, closepacked monolayer coverage and multilayer coverage on the glass surfaces were identified. The xylene-water contact angles were also measured as a function of time after placing the reacted plates in xylene, water, and air. Variations of xylene-water contact angles as a function of time were explained by effects due to rehydrolyzation, desorption of weakly adsorbed molecules and adsorption of hydrophobic impurities.

Characterization of ceramic hydrogen separation membranes with varying nickel concentrations

Abstract Ceramic hydrogen separation membranes in the stoichiometric form BaCe0.8Y0.2O3, doped with various concentrations of nickel, were characterized by utilizing X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and atomic-force microscopy (AFM). Characterization was performed at room temperature, 550°C and 650°C, and after exposure to hydrogen. Migration of nickel to the surface and changes in both elemental composition and oxidation states were observed at elevated temperatures. The concentration of nickel significantly affects surface morphology and roughness.

Liquid-impregnated Clay Solid Sorbents for CO2 Removal from Postcombustion Gas Streams

A novel liquid-impregnated clay sorbent [R. V. Siriwardane, U.S. Patent No. 6,908,497 B1 (2003)] was developed for carbon dioxide (C O2 ) removal in the temperature range of ambient to 60°C for both fixed-bed and fluidized-bed reactor applications. The sorbent is regenerable at 80–100°C . A 20-cycle test conducted in an atmospheric reactor with simulated flue gas with moisture demonstrated that the sorbent retains its C O2 sorption capacity with C O2 removal efficiency of about 99% during the cyclic tests. The sorbents suitable for fluidized-bed reactor operations showed required delta C O2 capacity requirements for sorption of C O2 at 40°C and regeneration at 100°C . The parameters such as rate of sorption, heat of sorption, minimum fluidization velocities, and attrition resistance data that are necessary for the design of a reactor suitable for capture and regeneration were also determined for the sorbent. A 20-cycle test conducted in the presence of flue-gas pollutant sulfur dioxide— S O2 (20 parts per...

Interaction of SO2 with iron deposited on CaO(100)

Abstract The interaction of SO2 with iron-covered CaO(100) at 373, 473, and 673 K was studied using X-ray photoelectron spectroscopy (XPS). Iron was deposited onto a CaO(100) surface in the metallic form; however, at lower iron coverages, other forms of iron relative to the metallic form were present. Scanning auger mapping analysis showed a random distribution of iron on CaO at both low iron coverage and high iron coverage. The adsorbed sulfur at 373 K on pure CaO and at low iron coverages was identified as sulfite. At high iron coverages, both sulfide and sulfite were identified. The sulfite formation was higher at low iron coverage than on pure CaO, but it decreased with increasing iron coverage. It was found that the iron sites at high iron coverage were blocking the active sites on the CaO surface; the reactivity at high coverage was similar to that of pure metallic iron. Sulfide formation increased with increasing iron coverage. Similar observations were made at 473 K, but the reactivity on iron at high coverage was considerably lower than that at 373 K. The total sulfur adsorbed was observed to be higher for all iron coverages at 373 K than for pure CaO. At 673 K, the reactivity on iron-covered surfaces was lower than that at either 373 or 473 K. However, the reactivity of iron-covered CaO was more than pure CaO at 673 K.