Ulf Jäglid

Detection of sodium and potassium salt particles using surface ionization at atmospheric pressure

Abstract The surface ionization of sodium and potassium salt particles with diameters of 1–100 nm is studied at atmospheric pressure. Particles impact on a resistively heated and positively biased Pt filament. The particles melt and dissociate at the filament and alkali ions are emitted, giving rise to a positive current at a closely situated collector. Salt particles with diameters below 5 nm are concluded to melt and ionize completely at the filament. Larger particles melt and ionize partially, yielding an ion signal that is proportional to the particle surface area. The ionization efficiency decreases with increasing particle size and reaches values around 1% for 0.1 μm particles, with small variations depending on the stability of the alkali salt.

Desorption kinetics at atmospheric pressure: alkali interactions with rhodium and steel surfaces

Abstract The kinetics for alkali ion emission from rhodium and stainless steel surfaces are studied with field reversal (FR) technique under atmospheric conditions. Rapid electric FR outside the surface disturbs the surface population of alkali metal atoms by retarding or accelerating the desorbing ions, and the flux of ions from the surface is monitored to determine the rate constants for desorption. The rhodium surface is oxidized at surface temperatures below 1373 K, and the oxides decompose at higher temperatures. This phase transition is clearly observed as a change in the desorption kinetics for alkali ions, with a higher alkali stability on the oxidized surface compared to the metallic surface. The kinetics for Na + , K + and Cs + desorption from Rh in air are characterized, and rate constants in the range 10 −2 –10 3 s −1 are obtained at surface temperatures of 990–1710 K. Rate constants for Na + and K + desorption from stainless steel are determined in the temperature range 920–1450 K. The heterogeneous character of the Rh and steel surfaces is reflected in the observed desorption kinetics that show effects of combined desorption and diffusion steps on the surfaces. The results confirm that the FR technique can be used as an in situ probe, capable of monitoring phase transitions and kinetics on hot surfaces at elevated pressure.

Reaction rates of the consecutive transesterification of tetraethoxysilane with methoxide ions and distribution reaction rates of ethoxytrimethylsilane and methoxytrimethylsilane in alkaline alcohol solutions

Abstract The reaction kinetics of Si(OC2H5)4 and methoxide ions, Si(OC2H5)4+4CH3O− → Si(OCH3)4 + 4C2H5O−, were investigated in methanol solutions with Fourier transform infrared spectroscopy. The net reaction was assumed to consist of four consecutive reaction steps. The formation of ethanol was followed and the rate constants were established as κ1 = 0.43±0.09 M−1 s−1, κ2 = 0.39±0.10 M−1 s−1, κ3 = 0.29±0.05 M−1 s−1 and κ4 = 0.17±0.06 M−1 s−1 at 295 K. The reverse of the reaction sequence was neglected since the concentration of produced ethoxide ions was assumed to be low in methanol solution compared with methoxide due to the fast equilibrium reaction, C2H5O− + CH3OH ⇌ C2H5OH + CH3O−, for which the equlibrium constant was estimated to 1.52±0.35. The reaction kinetics of the equilibrium reaction, (CH3)SiOC2H5+CH3O− ⇌ (CH3)3SiOCH3 + C2H5O−, were also studied with FTIR spectroscopy. The changes in concentrations of (CH3)3SiOC2H5 and (CH3)3SiOCH3 were measured in solvents with different molar ratios of ethanol and methanol. The rate constants for the forward and reverse reactions were graphically established as 2.49±0.26 M−1 s−1 and 3.08±0.47 M−1 s−1 at 295 K. The equilibrium constant for the reaction, (CH3)3SiOC2H5 + CH3OH=(CH3)3SiOCH3 + C2OH5OH, was determined to 1.37±0.31 at 295 K.