Knudsen cell reactor

Caloz, F F. F. Fenter, K. D. Tabor, and M. J. Rossi, I Design and Construction of a Knudsen-Cell Reactor for the Study of Heterogeneous Reactions over the Temperature Range 130-750 K, Performances and Limitations, Rev. Sci. Instrum., 68, 3172-3179 (1997). 

Mass spectromeliy was recently used to identify the technctium-rhenium mixed oxides TcReOy and TcReOs by heating a combination of TcO. and ReOy at 700-800 °C in a gaseous mixture of oxygen and iodine in a Knudsen cell reactor [53],... 

We have studied the interactions of HNO3, HCl and HBr with liquid sulfuric acid surfaces using both time dependent uptake and equilibrium vapor pressure methods in a Knudsen cell reactor equipped with mass spectrometric detection. Measured solubilities will be presented as Henry s law coefficients along with thermochemical parameters. 

Figure 1 Knudsen cell reactor with low temperature bath.

The Knudsen cell reactor is a versatile tool in the study of heterogeneous atmospheric chemistry. The rate of interaction with the surface is measured relative to a physical process, escape through an aperture, which is straightforward to calibrate. This puts the gas-surface rate measurement on an absolute basis. In addition, the low operating pressure means that complicated corrections for gas-phase diffusion do not need to be made. 

The Knudsen cell reactor has been used successfully to measure reaction and uptake rates on solid and liquid surfaces, including ice, nitric acid trihydrate, soot and concentrated sulfuric acid [8,9,16,26,27]. Recent measurements of uptake and reactivity on soot surfaces are particularly intriguing. In these experiments, funded by NASA s Subsonic Assessment Program, we are investigating the impact of solid particles found in the exhaust of aircraft, i.e., soot, on stratospheric chemistry. 

Recent laboratory work has shown that the uptake and photooxidatirm of organics on Ti02-containing mineral dust proxies can be an efficient process [190]. n-Propyl and isopropyl alcohols were efficiently oxidized to propionalde-hyde and acetone, respectively, after uptake to photoactive dust in a Knudsen cell reactor when the dust substrate was exposed to actinic radiatirm. The presence of trace amounts of O2 in the reactor enhanced the production of oxidized product. These observations are consistent with the general mechanism for Ti02 photoactivity, as shown below for isopropanol ... 

A variety of experimental techniques have been used for the determination of uptake coefficients and especially Knudsen cells and flow tubes have found most application [42]. Knudsen cells are low-pressure reactors in which the rate of interaction with the surface (solid or liquid) is measured relative to the escape through an aperture, which can readily be calibrated, thus putting the gas-surface rate measurement on an absolute basis. Usually, a mass spectrometer detection system monitors the disappearance of reactant species, as well as the appearance of gas-phase products. The timescale of Knudsen cell experiments ranges from a few seconds to h lindens of seconds. A description of Knudsen cell applied to low temperature studies is given [66,67]. 

L MX undergoes unimolecular decomposition by collision with the walls of a Knudsen cell flow reactor maintained at constant temperature ... 

The measurements of uptake coefficients of N2O5 on ice particles at 188 K by Leu (1988), and Hanson and Ravishankara (1991b, 1993a) using a coated wall fiow reactor, and by Quinlan et al. (1990) and Seisel et al. (1998) using a Knudsen cell agreed well. The NASA/JPL panel (Sander et al. 2011) and the lUPAC subcommittee (WaUington et al. 2012) both recommend y = 0.02. 

In an MOVPE reactor, these capping layers can be deposited by photodecomposition of PH3 or ASH3 [48] after sample growth. In the case of MBE, such layers can be grown using the Knudsen cells for the single elements (As, P, Sb, etc..). 

Simpler methods of generation of intermediates in the gas phase are the thermal ones. The thermal reactions are carried out either in Knudsen effusion cells under equilibrium conditions or in flow reactors at very low pressure. Effusion cells are widely applied for the evaporation of monomeric... 

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