Modelling of the deposition of molybdenum on silicon from molybdenum hexafluoride and hydrogen

The deposition of molybdenum on silicon from MoF6 and H2 is studied using a microbalance setup. The deposition rate is time dependent, which is explained by the significant contribution of the reduction of MoF6 by Si. A model taking into account both deposition routes and in particular diffusion of Si through the growing layer allows to describe the observations quantitatively. The relative importance of two routes was assessed and the kinetics of the reduction by H2 could be distinguished from the overall growth kinetics. A partial reaction order of 1.4 in hydrogen was found for the reduction of MoF6 by H2. The order in MoF6 is negative

CFD based optimization of anionic polymerization in micro flow

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Micro structured reactors for synthesis/decomposition of hazardous chemicals. Challenging prospects for micro structured reaction architectures (4)

A review. This paper completes a series of four publications dealing with the different aspects of the applications of micro reactor technol. This article focuses on the application of micro structured reactors in the processes for synthesis/decompn. of hazardous chems., such as unsym. dimethylhydrazine (UDMH), a component of high-energy propellant for liq. fuel rockets. Several examples including highly exothermic reactions with a highly toxic component of high-energy propellant, unsym. dimethylhydrazine, are reviewed. [on SciFinder (R)

Analysis of the isothermal forced flow chemical vapour infiltration process. Part I: Theoretical aspects

In this paper the densification of a cylindrical pore due to a first order heterogeneous deposition reaction on the wall is described. The basic understanding of these mechanisms can aid in the prediction of the infiltration time and composite porosity after densification. The results of the modelling are compared with experimental results which are reported in an additional paper, i.e. Part 2 of this study. The main characteristic parameter that determines the infiltration behaviour is the gas velocity

The oxidative coupling of methane over MgO-based catalysts : a steady-state isotope transient kinetic analysis

To study the heterogeneous steps of the oxidative coupling of methane to ethane and ethene over MgO, Li/MgO and Sn/Li/MgO, oxygen and carbon dioxide isotope step experiments were carried out in the absence of reaction, and oxygen and methane isotope step experiments were carried out in a tubular reactor at 1023 K, atmospheric pressure, an inlet molar ratio of CH4/O2 equal to 4, a methane conversion of 24%, and an oxygen conversion of 85%. The steady-state axial total concentration profiles of the reactants, intermediates, and products have a significant influence on the shapes of the transient isotope responses under these conditions. Oxygen interacts strongly with all catalysts used by dissociative reversible adsorption, except for lined-out Li/MgO. Both surface and bulk lattice oxygen participate in the reaction. The promotion with lithium and even more with tin increases the mobility of oxygen in the bulk of the catalyst and the amount of exchangeable oxygen per unit BET surface area. Carbon in methane can either react to C2 products, without any significant interaction with the catalyst, or show a weak reversible interaction with the catalyst, which does not lead to C2 products. In the absence of reaction, carbon dioxide interacts with the catalyst only in the presence of lithium. Under reaction conditions, the experiments can be described satisfactorily by postulating a methoxy species as the only carbon-containing intermediate on the catalyst leading to carbon dioxide

Copiride : anionic polymerisation of 1,3-butadiene with low PDI in a continuous flow setup

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Model for NOx storage/reduction in the presence of CO2 on a Pt-Ba/γ-Al2O3 catalyst

We have constructed a global reaction kinetic model to better understand and describe the NOx storage/reduction process in the presence of CO2. Experiments were performed in a packed-bed reactor with a Pt–Ba/¿-Al2O3 powder catalyst (1 wt% Pt and 30 wt% Ba) with different lean/rich cycle timings. The model is based on a multiple storage sites mechanism and considers that fast NOx storage occurs at surface barium sites, as determined by the reaction kinetics. Slow NOx storage occurs at the semi-bulk and bulk barium sites, where diffusion plays a major role. It is assumed that surface, bulk, and semi-bulk sites differ not only in physical appearance, but also in chemical reactivity. The distribution of these sites is obtained from 9-h lean-phase and 15-h rich-phase cycling experiments and thermogravimetric analysis of fresh catalyst. The model adequately describes the NO and NO2 breakthrough profiles during 9 h of lean exposure, as well as the subsequent release and reduction of the stored NOx. Furthermore, the model is also capable of simulating transient reactor experiments with 240-s lean-cycle and 60-s rich-cycle timings

Pressure drop of gas-liquid Taylor flow in micro-capillaries for low to intermediate Reynolds numbers

In this paper, a model is presented that describes the pressure drop of gas–liquid Taylor flow in round capillaries with a channel diameter typically less than 1 mm. The analysis of Bretherton (J Fluid Mech 10:166–188, 1961) for the pressure drop over a single gas bubble for vanishing liquid film thickness is extended to include a non-negligible liquid film thickness using the analysis of Aussillous and Quéré (Phys Fluids 12(10):2367–2371, 2000). This result is combined with the Hagen–Poiseuille equation for liquid flow using a mass balance-based Taylor flow model previously developed by the authors (Warnier et al. in Chem Eng J 135S:S153–S158, 2007). The model presented in this paper includes the effect of the liquid slug length on the pressure drop similar to the model of Kreutzer et al. (AIChE J 51(9):2428–2440, 2005). Additionally, the gas bubble velocity is taken into account, thereby increasing the accuracy of the pressure drop predictions compared to those of the model of Kreutzer et al. Experimental data were obtained for nitrogen–water Taylor flow in a round glass channel with an inner diameter of 250 µm. The capillary number Ca gl varied between 2.3 × 10-3 and 8.8 × 10-3 and the Reynolds number Re gl varied between 41 and 159. The presented model describes the experimental results with an accuracy of ±4% of the measured value