Etude de l'èquilibre de dissociation du carbamate d'ammonium à l'aide d'un appareil nouveau

Janjic, D.

doi:10.1002/hlca.19640470726

Cited by 11 publications

(8 citation statements)

References 3 publications

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“…Kp ϭ 4P diss 3 /27 (7) Similar experiments were also performed by Janjic 26 and equilibrium constants and calculated free energies were comparable. From these data, the maximum concentration of free CO 2 C CO2 (in ppmv) in a cylinder containing liquid NH 3 and an excess of solid NH 4 COONH 2 can be estimated with Eq.…”

Section: Thermodynamic Predictionssupporting

confidence: 67%

Impurities in hydride gases part 2: Investigation of trace CO2 in the liquid and vapor phases of ultra-pure ammonia

Funke¹,

Welchhans²,

Watanabe³

et al. 2004

Journal of Elec Materi

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Ammonia (NH 3 ) as a precursor for epitaxial nitride films is required to be free of trace oxygenated impurities, such as CO 2 , that have been shown to negatively affect growth processes and device performance. Carbon dioxide can react reversibly with the NH 3 gas to form ammonium carbamate, NH 4 COONH 2 (a solid with low solubility in liquid NH 3 ) and, therefore, can be present in cylinder sources both in the free and chemically bound form. A gas chromatograph (GC)-based method has been developed to accurately quantify the total CO 2 content in both vapor-and liquid-phase NH 3 streams. A heated GC-sampling manifold is used to thermally decompose any NH 4 COONH 2 present in the sample or calibration standard so that all CO 2 is analyzed in its free form. Several commercial cylinder sources maintained at room temperature were analyzed by this method, and in all cases, equilibrium concentrations of Ͻ75 parts-per-billion by volume (ppbv) CO 2 were present in the gas phase as long as residual liquid was present. Slightly higher concentrations were found in the liquid phase, and upon exhaustion of the liquid phase and heating, CO 2 levels strongly increased to parts-per-million by volume (ppmv) levels. The excess CO 2 is likely adsorbed on the cylinder walls or dispersed in the liquid as solid NH 4 COONH 2 . These results are consistent with thermodynamic calculations based on equilibrium data for the carbamate system available in the literature. To meet the purity requirements of organo-metallic vapor-phase epitaxy processes, the performance of an adsorbent-based purifier that is capable of removing residual CO 2 in both free and chemically bound forms from NH 3 streams is discussed.

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Section: Thermodynamic Predictionssupporting

confidence: 67%

Impurities in hydride gases part 2: Investigation of trace CO2 in the liquid and vapor phases of ultra-pure ammonia

Funke¹,

Welchhans²,

Watanabe³

et al. 2004

Journal of Elec Materi

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“…The NH 3 /CO 2 system, see eq 11, has been studied by measuring the dissociation pressure of solid ammonium carbamate at different temperatures, , and the values Δ H 0 ≅ +160 kJ mol -1 and Δ S 0 ≅ +460 J mol -1 K -1 have been reported …”

Section: 23 Thermodynamic Considerationsmentioning

confidence: 99%

Converting Carbon Dioxide into Carbamato Derivatives

et al. 2003

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“…For example, the equilibrium dissociation pressure, P eq , above solid AC is 85 Torr at 298 K, and it reaches 1 atm at 332 K. Furthermore, as these data imply, the dissociation pressure of AC is strongly temperature dependent, with a temperature coefficient of about 12.8 kcal/mol, which is one-third of the enthalpy of reaction. The equilibrium properties of the AC system have been well characterized, and there are several reports in the literature concerning the temperature dependence of the vapor pressure of AC. − …”

Section: Introductionmentioning

confidence: 99%

Kinetics and Mechanism of the Reversible Dissociation of Ammonium Carbamate: Involvement of Carbamic Acid

1998

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The kinetics of the reversible decomposition of ammonium carbamate, NH 4 CO 2 NH 2 (AC), into NH 3 (A) and CO 2 (C) has been studied between 278 and 312 K by recording the time dependence of the total pressure above an AC sample that, after being previously evacuated, is exposed to the headspace of an isoteniscope. At early times (<1 s), the data show an inflection, which is enhanced in first derivative transformations. Three mechanisms are discussed, each containing six rate constants. Two assume the presence of gas phase carbamic acid (CA) as an intermediate. These mechanisms are explored further through ab initio computational studies of CA. These results indicate that gas phase CA is a very stable species. No evidence could be found for its presence from Fourier transform IR spectra of the equilibrium vapor above AC. The mechanism that we suggest involves the reversible decomposition of AC into surface-bound CA, A, and C molecules, with the latter two reversibly desorbing from the surface. The experimental kinetic data are consistent with all three mechanisms. The rate data do not contain sufficient information to allow all rate constants to be uniquely determined. Simulation studies are used to demonstrate consistency of the mechanisms with the data.

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Etude de l'èquilibre de dissociation du carbamate d'ammonium à l'aide d'un appareil nouveau

Abstract: The author describes a simple apparatus for study of heterogenous equilibria.

Cited by 11 publications

References 3 publications

Impurities in hydride gases part 2: Investigation of trace CO2 in the liquid and vapor phases of ultra-pure ammonia

Impurities in hydride gases part 2: Investigation of trace CO2 in the liquid and vapor phases of ultra-pure ammonia

Converting Carbon Dioxide into Carbamato Derivatives

Kinetics and Mechanism of the Reversible Dissociation of Ammonium Carbamate: Involvement of Carbamic Acid

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