S. de Persis

Rate constants of reactions involving SiH4 as an association product from quantum Rice–Ramsperger–Kassel calculations

Quantum Rice Ramsperger Kassel (QRRK) calculations are carried out to calculate the pressure-dependent rate constants of reactions involving SiH4 as an association product. It is shown that good estimates of pressure-dependent rate constants can be obtained from QRRK in spite of the very poor treatment of the activated complex in this simple theory. However, possible errors arising from energy truncation must be avoided and reliable kinetic data must be fitted in order to select the final value of the adducts mean vibrational frequency. The results obtained in this work are satisfactorily compared with the experimental data available and with previous RRKM calculations. Parameterized forms of the pressure-dependent rate constants are derived for several bath gases, which can be used over the whole pressure and temperature range of interest for chemical vapour deposition (CVD) and related processes.

The Influence of Carbon Precursors on the Gas-Phase Chemistry of Titanium Carbide CVD

The influence of carbon precursors, such as methane (CH 4 ), acetylene (C 2 H 2 ), and propane (C 3 H 8 ), on the gas-phase chemistry of the Ti-C-Cl-H system used to deposit titanium carbide (TiC) from titanium tetrachloride (TiCl 4 ) was investigated by calculating the thermodynamic equilibrium and modeling rate equations from a proposed kinetic model. Differences in the resultant gas-phase chemistries for reactions under reduced pressure at 1500 K are discussed. Initial mixtures of TiCl 4 , H 2 , and a hydrocarbon that produced identical equilibrium compositions were determined. Results for the Ti-C-Cl-H system for all three hydrocarbon precursors are compared to those of Ti-Cl-H and C-H in order to further illustrate the differences in thermal stability of key constituents, as well as the extent of conversion. Regardless of which carbon precursor is present, species belonging to the Ti-Cl-H subsystem are near equilibrium within 5 s. Conversely, species emanating from CH 4 decomposition in the Ti-C-Cl-H system are predicted to be far from equilibrium and unreactive with TiCl 4 . In contrast, the preponderant species under thermodynamic equilibrium, C 2 H 2 , provides a uniform source of carbon at any residence time. Finally, the stability of C 3 H 8 in the Ti-C-Cl-H system is significantly greater than in the C-H system. This greater stability is accompanied by a significant variation in the rate of by-product formation, suggesting that TiCl 4 and its subchlorides effectively compete with C 3 H 8 for important reactive intermediates. In the case of C 3 H 8 , a reaction flow analysis was carried out identifying the three main reaction paths that are responsible for propane decomposition, the further links that appear between these paths, and how the paths vary over time.

Combustion properties of a low-vulnerability propellant: an experimental and theoretical study using laser ignition

ABSTRACT Ignition and combustion characteristics of a low-vulnerability propellant based on RDX are studied experimentally. Ignition is obtained using a laser diode. Experiments are performed in a cylindrical closed-volume reactor for different initial pressures and initial propellant masses under nitrogen and argon surrounding atmospheres. Ignition delays, maximal overpressures, and propagation rates are obtained for different initial pressures and laser powers. Thermodynamic predictions of overpressures are also compared with experimental ones. Finally, ignition probabilities for different laser powers and gaseous atmospheres are investigated using a revised Langlie method.