| 1. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Carbon dioxide interactions with crystalline and amorphous ice surfaces
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:21, s. 4627-4631
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide interactions with crystalline and amorphous water ice have been studied by time-resolved molecular beam techniques. CO2 collisions at thermal kinetic energies with ice in the temperature range 100-160 K result in efficient trapping on the ice surface followed by desorption. The desorption kinetics on crystalline ice at 100-125 K are well described by the Arrhenius equation with an activation energy of 0.22 +/- 0.02 eV and a preexponential factor of 10(13.32+/-0.57) s(-1). Below 120 K, CO2 populates strongly bonded sites on amorphous ice, resulting in surface residence times on the order of minutes at 100 K, and the desorption data can in this case not be explained by a simple first-order process. The results are compared to previous studies of gas-ice interactions, and the implications for heterogeneous processes in the terrestrial atmosphere are discussed.
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| 2. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of NH4+ and ND4+ ions : Storage ring experiments and ab initio molecular dynamics
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:16, s. 7391-7399
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Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.
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| 3. |
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| 4. |
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| 5. |
- Kotarba, A., et al.
(författare)
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High pressure desorption of K+ from iron ammonia catalyst migration of the promoter towards Fe active planes
- 2004
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Ingår i: Catalysis Letters. ; 95:1-2, s. 93-97
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Tidskriftsartikel (refereegranskat)abstract
- The thermal desorption of potassium ions from industrial iron catalysts was studied in situ in the wide pressure range of 10(-8)-10 bar of Ar, N-2 and synthesis gas mixture of N-2:3H(2). While high activation energy of 284 +/- 1 kJ/mol, for K (+) was determined for the catalyst precursor, in the reaction conditions it drops down to 231 +/- 5 kJ/mol, corresponding well to that found for iron single crystals in UHV studies. The results are rationalized in terms of potassium migration from oxide storage phases towards the iron facets developed during the catalyst activation.
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| 6. |
- Suter, Martina, 1966, et al.
(författare)
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Molecular Beam studies of Carbon Monoxide Interactions with Water Ice.
- 2004
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Ingår i: Physica Scripta. ; T110:doi:10.1238/Physica.Topical.110a00350, s. 350-354
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of CO interactions with water ice surfaces are studied using molecular beam techniques. The experimental method allows for detailed investigations of interaction between molecules and ice surfaces under single collision conditions, and collision dynamics and energy transfer are characterized. An ice surface is prepared by deposition of water vapor on a cold substrate and the surface is maintained in a vacuum chamber with a partial water vapor pressure up to 10-4 mbar, which allows for experiments with ice surfaces in the temperature range 100–190 K. A molecular beam is directed towards the ice surface, and the molecular flux from the surface is detected by mass spectrometry. Angular-resolved intensity and time-of-flight distributions are measured, and the effects of surface temperature, incident translational energy and incident angle are investigated. The surface collisions are highly inelastic with large energy loss observed for the directly scattered flux, similar to the results for the previously studied Ar-ice and HCl-ice systems. The data for the energy loss as a function of scattering angle show that energy transfer is substantial both parallel and perpendicular to the surface plane. The trapping of CO on the surface is found to be very effective under typical thermal conditions. The molecules accommodate to the temperature of the ice, but rapidly leave the surface by desorption because of the low binding energy to the surface.
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| 7. |
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| 8. |
- Svane, Maria, 1957, et al.
(författare)
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Chemical analysis of individual alkali-containing aerosol particles: Design and performance of a surface ionization particle beam mass spectrometer
- 2004
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 38:7, s. 655-663
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Tidskriftsartikel (refereegranskat)abstract
- A mobile particle beam mass spectrometer has been developed to measure the alkali metal content in individual submicron aerosol particles. The instrument employs an aerodynamic inlet system for efficient sampling of particles into vacuum, and the detection of individual particles is based on decomposition and surface ionization on a hot platinum surface. A boxlike design of the hot ionizing surface is shown to limit problems associated with particle bounce effects and incomplete ionization, and the decomposition/ionization process is not sensitive to detailed particle properties. High transmission efficiencies and quantitative determination of the alkali metal content in individual particles with diameters down to 14 nm are demonstrated. Experiments with particles doped with alkali salt show that the size range may be extended down to a few nanometers after further improvements of the inlet system. High size resolution can be achieved with the instrument for particle sizes down to tens of nanometers, as illustrated by the detection of multiply charged particles passing through a DMA. The robustness of the instrument makes it suitable for field measurement applications, and the technique is demonstrated at a 12 MW biomass combustion facility. The performance of the instrument and further refinements of the technique are discussed, and potential applications in field and laboratory studies are outlined.
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| 9. |
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| 10. |
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| 11. |
- Svenson, Jenny, 1975, et al.
(författare)
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Fast pyrolysis of the main components of birch wood
- 2004
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Ingår i: Combustion Science and Technology. - : Informa UK Limited. - 0010-2202 .- 1563-521X. ; 176:5-6, s. 977-990
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Tidskriftsartikel (refereegranskat)abstract
- The pyrolysis kinetics of cellulose, birch hemicellulose, and birch lignin are studied in a single particle reactor under inert atmosphere. Experiments are carried out with samples of 1-5 mg and mass loss data are measured at constant reactor temperature in the range 225-650degreesC. Arrhenius parameters are determined and are comparable with previous studies. The char yield for cellulose, hemicellulose, and lignin is about 5, 10, and 15%, respectively, at temperatures above 400degreesC. Calculations, where the results for the three independent materials are added together in the proportions of birch wood, give good agreement with birch wood data. This supports the assumption that the three materials act independently during pyrolysis. The results also indicate that above 400degreesC 70% of the char formed during birch wood pyrolysis originates from hemicellulose. visual observations show that lignin melts and boils at high temperatures, whereas hemicellulose expands considerably during the pyrolysis process.
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| 12. |
- Tran, K. Q., et al.
(författare)
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A novel particle trap impactor for use with the gas-quenching probe sampling system
- 2004
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 38:10, s. 955-962
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Tidskriftsartikel (refereegranskat)abstract
- A novel particle trap impactor has been developed for use with the gas-quenching probe in order to exclude solid particles from entering into the probe during sampling of gaseous metallic species in fluidized bed combustion conditions. The impactor must be small in size (empty set(impactor)less than or equal toempty set(probe) = 45 mm) but capable of collecting a relatively large amount of particles at elevated temperatures. As the first step, the impactor was designed, constructed, and tested at room temperature for KCl aerosol particles. The impactor with a nozzle of 0.95 mm in diameter, in combination with the orifice-to-jet diameter ratio of 1.5 and the ratio of the jet-to-plate spacing to jet diameter at 1.4 yielded a sharp cutoff curve with a maximum collection efficiency of about 0.9 and a rootStk(50) value of about 0.22. In addition, the collection efficiency of the impactor was compared with the particle removal efficiency of a filter of the same type as the filter previously used with the gas-quenching probe. The difference from the comparison is very small, indicating that the impactor can be used to replace the filter to prevent fly ash particles from entering the gas-quenching probe in fluidized bed combustion conditions.
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| 13. |
- Tran, K. Q., et al.
(författare)
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On the application of surface ionization detector for the study of alkali capture by kaolin in a fixed bed reactor
- 2004
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Ingår i: Fuel. ; 83:7-8, s. 807-812
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metals, mainly potassium, together with other ash forming inorganic components in biomass are believed to be responsible for bed agglomeration in fluidized bed boilers burning biomass. A solution to the problem is to capture alkali vapor released from the fuel during combustion by inorganic solid additives such as kaolin. In this study, the capture of vaporous potassium chloride was investigated in a fixed bed reactor equipped with an on-line alkali detector. The detector, which is based on surface ionization, is capable of operating at alkali metal concentrations as low as those encountered after reaction with kaolin during biomass combustion (of the order of 1 ppb). Various experiments of KCl capture by kaolin powder were made at a reactor temperature of 850 degreesC. Kaolin removed up to 99% of alkali species in gas phase. The efficiency slightly decreased when KCl concentration decreased. The effect of kaolin addition on the release of alkali metals during wood combustion was studied at 650 degreesC in air. During pyrolysis, the alkali metal release increased slightly when kaolin was mixed with the wood due to the release of alkali metal impurities in the kaolin additive. The alkali metal release during char combustion was reduced to approximately 50% of the original value. The reduction increased as the amount of kaolin addition increased. Overall, the addition of kaolin suppressed the alkali metal release from the wood by approximately 20%. (C) 2004 Elsevier Ltd. All rights reserved.
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