William Felder

HTFFR kinetics studies of Al+CO2→AlO+CO from 300 to 1900 K, a non‐Arrhenius reaction

High‐temperature fast‐flow reactors (HTFFR) were used to obtain the rate coefficients k1 (and their accuracies) for the reaction Al +CO2→AlO+CO. At 310, 490, 750, 1500, and 1880 K, k1 is found to be (1.5±0.6) ×10−13, (6.9±2.7) ×10−13, (1.6±0.7) ×10−12, (9.0±3.8) ×10−12, and (3.8±1.5) ×10−11, respectively (all in ml molecule−1 s−1 units). For this temperature range k1(T) may be expressed by the curve fitting equation k1(T) =2.5 ×10−13 T1/2 exp(−1030/T)+1.4×10−9 T1/2 exp(−14 000/T). The data also indicate a wall‐oxidation process of zeroth order in [CO2] with γAl of 10−3 to 10−2, not measurably dependent on T. Factors affecting the accuracy of the measurements are discussed. Over the 310–750 K range k1(T) obeys an Arrhenius expression, with an activation energy of 2.6±1.3 kcal mole−1, which implies D(Al–O) ?122 kcal mole−1. Above 750 K, k1(T) increases much more rapidly with T. This behavior cannot be described on the basis of simple transition state theory alone; the most probable additional factors involv...

HTFFR kinetics studies of Sn/N2O, a highly efficient chemiluminescent reaction

High temperature fast‐flow reactors (HTFFR) were used to study the Sn/N2O reaction from 300–950 K at pressures from 4 to 110 Torr. The observed emissions are SnO[a 3Σ+(1) –X 1Σ+] and (b 3Π–X 1Σ+). The photon yield of the former system is 0.53±0.26 independent of T, that of the latter (5.9±2.9) ×10−1 exp[−(1200±200)/T]. Comparison of the photon yields of N2O‐ in‐excess experiments, where [Sn] is measured in absorption, to experiments where Sn is in excess allows determination of oscillator strengths for the ground electronic states of Sn: f[Sn(3P0) (286.4 nm)]=0.20±0.10 and f[Sn(3P1) (300.9 nm)]=0.052±0.026, in good agreement with literature values. At T≳950 K, emission from SnO(c–X 1Σ+) and (A 1Π–X 1Σ+) is observed, apparently due to N2O decomposition followed by Sn/O2 reaction. Quenching rate coefficients at ≈900 K for SnO (a) are determined to be kQN2(a)⩽2.3×10−16; kQAr(a)⩽4.0×10−16; kQN2O(a)⩽4.0×10−14; kQSn(a)⩽4.0×10−12 ml molecule−1 s−1 based on τrad(a)⩾2.5×10−4 s. For SnO (b) the data yield τbkQN2(b)...

High-temperature fast-flow reactor study of Sn/N2O chemiluminescence

Abstract The Sn/N 2 O reaction at 1000 K produces intense chemiluminescence belonging to the A, B, C, D-X systems of SnO. The number of photons emitted per Sn atom reacted is on the order of 0.5. New A-X bands at λ ≫ 550 nm have been identified. The overall reaction proceeds with a rate coefficient of ≈ 5 × 10 −13 ml molecule −1 s −1 .

High‐temperature fast‐flow reactor kinetic studies. The AlO/O2 reaction near 1400 K

A high‐temperature fast‐flow reactor (HTFFR) has been adapted to the study of the kinetics of diatomic radicals via laser induced fluorescence. In this work, the homogeneous gas‐phase reaction of AlO with O2 has been investigated near 1400 K. The reaction proceeds via AlO(v)+O2→AlO2 +O; k (v) = (3.1±1.7) ×10−13 ml molecule−1⋅sec−1, with no discernible difference between AlO in the v=0 and 1 vibrational levels.

High temperature photochemistry, a new technique for rate coefficient measurements over wide temperature ranges: initial measurements on the O + CH4 reaction from 525–1250 K

Abstract High temperature photochemistry (HTP) is being developed to study elementary kinetics from approximately 300 to 1900 K. A summary description of HTP and first results on O + CH 4 → OH + CH 3 are reported, which compare well with those obtained previously by techniques suitable for either the T 1200 K regimes.

HTFFR kinetic studies of the fate of excited BaO formed in the Ba/N2O chemiluminescent reaction

Rate coefficients for quenching kQ and intersystem conversion kT of excited BaO formed in the reaction Ba+N2O(1)→BaO+N2 have been measured for several collision partners. Methods are developed and applied here for obtaining quenching rate coefficients in chemiluminescent reactions involving a reservoir state. Experiments were performed between 450 and 1000 K at 1–120 Torr in a modified high‐temperature fast‐flow reactor (HTFFR). The rate coefficients (or their upper limits) are, in ml molecule−1 s−1 units: kArQ (600–1000 K) ?3×10−13; kHeQ (460 K) <3×10−13; kN2Q (600 K) = (4.8±2.0) ×10−12; kN2OQ (600 K) = (4.2±1.0) ×10−10; 2.5×10−10?kO2Q (600 K) ?7.0×10−10; kArT (600 K) ?1.5×10−11. Incidental data at ?1000 K indicate that k1?5×10−11, and that the Ba/O2 reaction has about the same rate coefficient. In addition to BaO emission, strong Ba atomic emission arising from energy transfer processes was observed for [Ba]≳1×1013 ml−1 at T?1000 K. Measurements of the spectral distributions of the Ba/N2O chemiluminesce...

A new gas-phase combustion synthesis process for pure metals, alloys, and ceramics

Many high purity materials can be synthesized by a self-sustaining gas-phase flame for example: photovoltaic silicon; advanced fuels (e.g., boron); refractory metals (e.g., titanium, tantalum, zirconium, hafnium and niobium); and ceramics (e.g., silicon carbide, silicon nitride, tantalum carbide, titanium boride, and zirconium boride). Reactive metals, e.g., sodium or magnesium, combined with metal halides or mixtures of halides react hypergolically to produce the desired product as an aerosol and the by-product, reactive metal halide, in the gas phase. The key to the success of the process is the separation of the product from the by-product. This has been achieved by a novel supersonic impaction technique. The reaction products are expanded through a nozzle to produce a supersonic stream which is caused to impact a surface to produce a shock wave. The particles, unable to make the sharp turn behind the shock wave along with the gas, impact the surface where they are collected either as a solid, liquid, or powder, depending upon the surface configuration and temperature. The process has been examined thermodynamically for a large number of systems, and it has been demonstrated experimentally for silicon at 1.5 kg/h and yields exceeding 90%. Product purity is very high because of self-purification mechanisms inherent in the process.

Hiffr kinetics studies. Temperature dependence of Al/O2 and AlO/O2 kinetics from 300 to 1700/1400 K

A high-temperature fast-flow reactor (HTFFR) has been adapted for the near room temperature study of the kinetics of atoms and free radicals of refractory species. The rate coefficients of the reactions A l + O 2 → ( 1 ) A l O + O and A l + O 2 → ( 2 ) A l O 2 + O have been found to be (3.4±2.3)×10 −11 and (7.2±3.6)×10 −13 ml molecule −1 sec −1 , respectively at 310 K. Combining these results with high temperature HTFFR measurements leads to the recommended values k 1 (300–1700 K)=(3.4±2.2)×10 −11 and k 2 (300–1400 K)=(4.8±3.1)×10 −13 ml molecule −1 sec −1 . The remarkable absence of a positive temperature dependence for these rate coefficients over such large temperature ranges is discussed. In the case of Reaction (2) this absence indicates D (O−AlO)>- D (O−O)=118 kcal mole −1 , consistent with the re-interpreted previous determination of this bond energy of 121.5±2 kcal mole −1 (508±8 kJ mole −1 ).

High‐temperature photochemistry reactor for kinetic studies of isolated elementary gas‐phase reactions

A reactor suitable for kinetic measurements on photolytically initiated elementary free‐radical reactions over approximately the 300–1900 K temperature range is described. Performance data are given for the O+CH4→OH+CH3 reaction.

High Temperature Photochemistry (HTP): Kinetics and mechanism studies of elementary combustion reactions over 300-1700 K

Abstract The HTP technique makes it possible to study the kinetics and mechanisms of elementary reactions of important combustion-related free radicals over wide temperature ranges. It utilizes standard flash photolysis methods to generate the radicals and resonance fluorescence diagnostics to follow their time-dependent concentrations, from which kinetic and mechanistic information is derived. The use of a single technique to explore the kinetics of reactions over wide temperature ranges gives high confidence in the experimentally determined temperature dependences and provides a precise data base for both theoretical and empirical extrapolation of kinetic parameters to other temperatures of interest. Results obtained in HTP studies of the reactions O+CH3, H+H2O, OH+CH4, and OH+C6H6 are discussed.