The kinetics of the gas-phase thermal decomposition of chlorodifluoromethane

Barnes, George R.; Cox, R. A.; Simmons, Robert F.

doi:10.1039/j29710001176

Cited by 28 publications

(10 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(3) Dissociation (rate constant k 1) is rate determining, with a limiting high-pressure activation energy of 234 kJ/mol.8 As HC1 accumulates, reaction of CF2 with HC1 (rate constant kf) competes effectively with (3), and the net reaction rate decreases. 8 For the laser-induced reaction of CFICIF2, we find similarly that the amount of product per flash decreases as HC1 accumulates. Thus, because of the identical products and the similar kinetic effect of HC1, we shall assume that the laserinduced reaction also proceeds by the two-step mechanism (2) and (3).…”

supporting

confidence: 56%

Megawatt infrared laser chemistry of chlorodifluoromethane. Photochemistry, photophysics, and molecular dynamics of excitation

Grunwald¹,

Olszyna²,

Dever³

et al. 1977

J. Am. Chem. Soc.

View full text Add to dashboard Cite

Pulsed laser-irradiation of gaseous CHCIF2 at 1088 cm-1 causes decomposition to C2F4 and HC1, the same products as in homogeneous gas-phase thermolysis. Conversions per flash are as high as 50% with unfocused beams. Changing the surface/volume ratio or the irradiated fraction, in an attempt to change the cooling rate of the laser-heated gas, does not affect the conversion per flash if). Relations between/and the absorbed energy per mole_(£abs), and between £abs (or its equivalent, uabs, the number of 1088 cm-1 einsteins absorbed per mole) and average dose (D) are determined as functions of pressure, pulse duration, and added inert gas. For neat CHCIF2 in the pressure range 5.8-100 Torr, the photophysics is well described by cabsID = 1.50 + 30.64P/(P + 22.06) when cabs 5 2. The same relation applies in the presence of an inert gas X, except that £eff = P + KP\ takes the place of P\ K = 0.21 for He, 0.38 for N2, and 0.7 for S1F4. For neat CHCIF2, at pressures ranging from 1.6 to 100 Torr, uabs ranging from 2 to 8.5, and pulse durations of 270 and 800 ns, the relation off to £abs is independent of pressure and pulse duration and is described in fair approximation by f = A exp(-£act/£abs), where £act is the known thermal activation energy of the primary process. Addition of inert gas reduces /below the value observed at the same £abs in neat CHC1F2. The reduction can be formally described in terms of a spoil factor, s. For a given mole ratio of CHC1F2/X, s is independent of total pressure when X = SiF4 and decreases with increasing pressure when X = He, so that there is no loss in photochemical efficiency as the total pressure is increased.

show abstract

supporting

confidence: 56%

Megawatt infrared laser chemistry of chlorodifluoromethane. Photochemistry, photophysics, and molecular dynamics of excitation

Grunwald¹,

Olszyna²,

Dever³

et al. 1977

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…These final frequencies and the moments of inertia from the computed geometries are listed in Table 3. [32][33][34][35][36][37] All of these data are closer to the highpressure limit than any of the high-temperature shock tube data. 43 Including the 4.0 kcal mol -1 zero point energy correction, the best theoretical value for the reaction barrier is 56.3 kcal mol -1 (Table 3) obtained at the QCISD(T)/CC level.…”

Section: Discussionmentioning

confidence: 78%

“…10,[32][33][34][35][36][37] The lower temperature studies [32][33][34][35][36][37] were carried out in slow-flow systems and/or static vessels using either 100% CF 2 HCl or in dilution with N 2 or He. 10,[32][33][34][35][36][37] The lower temperature studies [32][33][34][35][36][37] were carried out in slow-flow systems and/or static vessels using either 100% CF 2 HCl or in dilution with N 2 or He.…”

Section: Discussionmentioning

confidence: 99%

Thermal Decomposition of CF₂HCl

Su¹,

Kumaran²,

Lim³

et al. 1996

J. Phys. Chem.

View full text Add to dashboard Cite

The development of a multipass optical absorption (MPA) technique for detecting CF 2 radicals behind reflected shock waves and its application for studying the thermal dissociation of CF 2 HCl in Kr are reported. In an earlier work, a Cl atom atomic resonance absorption spectrometric (ARAS) study on the thermal decomposition of CF 2 Cl 2 gave the stoichiometric yield of two Cl atoms per dissociating CF 2 Cl 2 , indicating the overall process is CF 2 Cl 2 ) 2Cl + CF 2 . CF 2 yields with CF 2 Cl 2 as the thermal source were then used to obtain the CF 2 curve of growth. The effective absorption cross section is 2.86 × 10 -18 cm 2 at 249.8 nm. In the CF 2 HCl experiments, the yield was measured to be 1.01 ( 0.06, confirming that the thermal decomposition pathway is molecular HCl elimination; i.e., CF 2 HCl (+ M) f CF 2 + HCl (+ M). Above 1900 K, C-Cl bond fission was measured to be <1%. Rate constants for the title reaction were measured by observing the temporal formation of CF 2 radicals. Also, rate constants were measured and the overall enthalpy change was determined in incident shock waves using the laser schlieren (LS) technique. Over 1047 e T e 1731 K and 113 e P e 589 Torr, both the magnitude and the T dependence of the measured rate constants from the two techniques are in good agreement. A fit to combined sets of data is expressed to within (54% by the Arrhenius equation: k ) 2.42 × 10 -9 exp(-20180K/T) cm 3 molecule -1 s -1 . With an E 0 ) 54.85 kcal mol -1 that is fixed by the low-temperature data, ab initio transition state properties, determined at the MP4(SDTQ) and QCISD(T) levels, were used in RRKM modeling of the rate constants. Excellent agreement with the present and previous high-temperature density-dependent data was obtained with constant 〈∆E〉 down ) (265 ( 20) cm -1 . From the LS experiments, ∆H 0 0 ) 52.1 kcal mol -1 , implying ∆ f H 0,CF 2 0 ) -39.5 kcal mol -1 if the JANAF value for ∆ f H 0,CF 2 HCl 0 is accepted. For the reverse insertion process this suggests a barrier of 2.8 kcal mol -1 .

show abstract

“…For CHClF 2 it was demonstrated that the thermal decomposition starts with the elimination of HCl. 26 Based on the above mentioned results, in this study CCl 2 F 2 was used as thermochemical modifier, as it contains both Cl and F and as the molar concentration of Cl is higher than with CHClF 2 . Ren and Salin 27 systematically investigated the effect of Freon R12 as a gaseous halogenation reagent on the evaporation of refractory oxides and carbides such as aluminium oxide, silicon dioxide, zirconium dioxide and tantalum carbide (with maximum particle diameters <74 mm).…”

Section: Optimization Of the Temperature Programmentioning

confidence: 99%

Direct multielement determination of trace elements in boron carbide powders by slurry sampling ETV-ICP-OES

Amberger

Broekaert

2010

J. Anal. At. Spectrom.

View full text Add to dashboard Cite

The use of slurry sampling electrothermal evaporation inductively coupled plasma optical emission spectrometry (SlS-ETV-ICP-OES) for the direct determination of trace elements in boron carbide powders with different particle size distributions was investigated. It was found that the addition of 6 mL min À1 of Freon R12 (Cl 2 F 2 C) to the 500 mL min À1 Ar carrier gas flow as a thermochemical reagent resulted in an increase of the net line intensity for Ti by a factor of 25 in SlS-ETV-ICP-OES, when analyzing 20 mL of a slurry containing 1% of the boron carbide powder BC-1. After heating the dry residue of 20 mL of a slurry of 1% of boron carbide for 12 s to 2600 C on a L'vov platform the residues on the platforms were analyzed by total reflection X-ray fluorescence spectrometry (TXRF). The evaporation efficiency for Ti was found to have increased from 12 to 97% by the addition of 6 mL min À1 of R12 as compared to evaporation in Ar only. When heating dry residues of boron carbide slurries on L'vov platforms to temperatures ranging from 2000 to 2600 C without adding R12 to the Ar, it could be observed visually that only a small fraction of the boron carbide matrix is evaporated. However, when heating at 2600 C under the addition of R12 almost no residues were found on the platform after the evaporation step. For the analysis of boron carbide powders with SlS-ETV-ICP-OES the limits of detection were found to be between 0.002 and 2 mg g À1 for the elements Al, Ca, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni and Ti. For Fe a wide variety of samples could be analyzed by SlS-ETV-ICP-OES with one calibration under the use of R12. This was shown for different samples, namely three boron carbide powders, three boron nitride powders, an aluminium oxide powder (NIST 699), silicon carbide powder (BAM S-003), powdered apple leaves (NIST 1515), a reference sample for trace elements in natural water (NIST 1643d) and an aqueous standard solution. When plotting the net line intensities versus the accepted concentrations a coefficient of determination of 0.990 is obtained. By SlS-ETV-ICP-OES under the addition of R12 the values obtained were found to be between 78 to 128% of the mean of the results of slurry sampling-TXRF and of ICP-OES subsequent to wet chemical digestion. 11 trace elements with concentrations ranging from 0.7 to 370 mg g À1 for Co and Fe, respectively, could be determined in two boron carbide powders with particle size distributions of d 90 ¼ 3.5 mm and d 90 ¼ 9.2 mm, respectively.

show abstract

The kinetics of the gas-phase thermal decomposition of chlorodifluoromethane

Cited by 28 publications

References 0 publications

Megawatt infrared laser chemistry of chlorodifluoromethane. Photochemistry, photophysics, and molecular dynamics of excitation

Megawatt infrared laser chemistry of chlorodifluoromethane. Photochemistry, photophysics, and molecular dynamics of excitation

Thermal Decomposition of CF₂HCl

Direct multielement determination of trace elements in boron carbide powders by slurry sampling ETV-ICP-OES

Contact Info

Product

Resources

About

The kinetics of the gas-phase thermal decomposition of chlorodifluoromethane

Cited by 28 publications

References 0 publications

Megawatt infrared laser chemistry of chlorodifluoromethane. Photochemistry, photophysics, and molecular dynamics of excitation

Megawatt infrared laser chemistry of chlorodifluoromethane. Photochemistry, photophysics, and molecular dynamics of excitation

Thermal Decomposition of CF2HCl

Direct multielement determination of trace elements in boron carbide powders by slurry sampling ETV-ICP-OES

Contact Info

Product

Resources

About

Thermal Decomposition of CF₂HCl