HCl Partial Pressure Research Articles

The influence of charge-mode operation of a XeCl laser on the beam profile

The shape of the beam profile of a discharge excited XeCl excimer laser using a spiker-sustainer electrical circuit has been varied from a ‘bell’-, through a ‘top-hat’-, to a ‘camel-back’-profile by varying the delay between the spiker pulse and the main-current with the circuit operating in the charge-mode. Fine-tuning of the beam profile can be done by varying the charging voltage of the main pulse forming network or the temperature of a gas purifier regulating the Xe and HCl partial pressures.

Erosion-corrosion modelling of gas turbine materials for coal-fired combined cycle power generation

The development of coal-fired combined cycle power generation systems is receiving considerable worldwide interest. The successful development and commercialisation of these new systems require that all the component parts are manufactured from appropriate materials and that these materials give predictable in-service performance. Corrosion and erosion-corrosion, resulting from coal derived particulates, deposition and gaseous species, have been identified as potential life limiting factors for these systems. Models to predict these modes of materials degradation are under active development. This paper outlines the development and testing of models suitable for use in gas turbine environments. The complexity of the corrosion processes means that an empirical approach to model development is required whereas a more mechanistic approach can be applied to erosion processes. For hot corrosion conditions, statistically based corrosion models have been produced using laboratory tests for two coatings and a base alloy at typical type I and type II hot corrosion temperatures (900 and 700°C). These models use the parameters of alkali sulphate deposition flux and SO x partial pressure (at each temperature and for set HCl partial pressures), to predict the rate of the most likely localised damage associated with hot corrosion reactions. For erosion-corrosion modelling, a series of laboratory tests have been carried out to investigate erosion behaviour in corrosive conditions appropriate to coal-fired gas turbines. Materials performance data have been obtained from samples located in the hot gas path of the Grimethorpe PFBC pilot plant, under well characterised conditions, for testing the corrosion and erosion-corrosion models. The models successfully predict the materials damage observed in the pilot plant environments.

Determining past atmospheric HCl mixing ratios from ice core analyses

Laboratory and field measurements have been performed in order to improve our understanding of the HCl air-snow transfer function. The solubility and diffusion of HCl in laboratory grown single crystals of ice have been measured as a function of HCl partial pressure,P HCl, between −8 and −25 °C. Measurements ofP HCl and of the mole fraction of HCl in snow,X'HCl, have been measured at Summit, Greenland. Comparison of the field and laboratory measurements show that theX'HCl values are well below equilibrium values. The major processes involved in the formation of snow crystals and in their evolution after deposition are discussed in order to attempt to understand theX'HCl values and their variations. The discussion is focussed on a few well identified snow layers. It is concluded that sublimation and recrystallization of snow probably play a major role in the evolution ofX'HCl, but that our understanding of the HCl transfer function is very incomplete. Laboratory and field measurements are suggested to improve this situation.

Transmission properties of spark preionization radiation in rare-gas halide laser gas mixes

A charge collection apparatus was used to measure photocharge yields and transmission properties of light emitted from a spark preionizer discharge through various rare-gas halide laser gas mixes as well as through their component gas mixes. The data indicates that for HCl partial pressure (p) and photon path length (d) pd products /spl ges/100 Torr-cm, a narrow transmission window (114-124 nm) for preionization of XeCl and KrCl lasers occurs. In contrast, fluorine based rare-gas halide laser gas mixes were largely transparent over a critical 100-150 nm spectral window responsible for preionization. The role of gaseous impurities, two photon ionization processes, the photoelectric effect, passivation and air contamination on the photocharge signal and light transmission are described.

Diffusion and solubility of HCl in ice: preliminary results

The diffusion and solubility of HCl in ice have been measured between −5 and −15°C by exposing large single crystals of ice to low vapor pressures of HCl for several days. The solubility is found to be (1.0±0.15) × 10−4 mol/1 at −15°C under a 5.6×10−4 Pa HCl partial pressure. The diffusion coefficient is of the order of 10−12 cm2s−1 at −8°C, but the determination of the value is affected by small angle boundaries, where HCl motion is much faster. Extrapolation of these results suggests that HCl is not incorporated into stratospheric ice crystals.

Rate of SiC Deposition from Methyltrichlorosilane and Influence of HCL Addition

AbstractSuitable feedgas compositions for monophase SiC deposition were determined starting from methyltrichlorosilane-hydrogen-argon mixtures at 1 bar total pressure and H2/MTS ratios between 50 and zero. At temperatures from 900 to 1400°C, only a ratio of 1 at PMTS = 18 mbar gave the desired result. The deposition rate of SiC was determined as a function of MTS and HCl partial pressures, of gas flow rate, and of temperature at a H2/MTS ratio of 1. Two different rate equations were found at [MTS]/[HCI] ≥ 5.8 (region I) and < 5.8 (region II), respectively:where brackets denote gas concentrations. The apparent activation energy was 380 kJ/mol common to both rate equations. A mathematical model taking into account temperature fields at reactor wall and substrate, heat and mass transport in the flowing gas, and heterogeneous reaction rates jSiC(I) and (II) was developed and found to be in very good agreement with the experimental results.

Simulation of Growth Rate of Chemical-Vapour-Deposited TiN Film along the Axial Direction in a Tubular Reactor

A model was proposed to simulate the growth rates of chemical-vapour deposited TiN films obtained in the previous study. In this model, flow and mass transfers are taken into account. The chemical reaction rate which expresses the effects of TiCl 4 and HCl partial pressures is used. The calculated distributions of film growth rate almost agreed with the experimental results, and the effects of gas flow rate, deposition temperature and partial pressure of TiCl 4 on the growth rates of film were explained by the proposed model. From a comparison between the calculated and experimental growth rates of the films, it was shown that the deposition occurred under the reaction controlled conditions at 1223 K, and that the effect of mass transfer resistance was larger at low partial pressures of TiCl 4 and at temperatures higher than 1273 K

Heterogeneous reactions of hypochlorous acid + hydrogen chloride .fwdarw. Cl2 + H2O and chlorosyl nitrite + HCl .fwdarw. Cl2 + HNO3 on ice surfaces at polar stratospheric conditions

Heterogeneous reactions of HOCl + HCl → Cl 2 + H 2 O (1) and ClONO 2 + HCl → Cl 2 + HNO 3 (2) on ice surfaces at a temperature of 188 K have been investigated in a flow reactor interfaced with a differentially pumped quadrupole mass spectrometer. Partial pressures for HOCl and ClONO 2 in the range of 6.5×10 -8 -2.0×10 -6 Torr, which mimic conditions in the polar stratosphere, have been used. Uptake of HCl on ice surfaces using partial pressures of HCl in the range of 1.8×10 -7 -8.0×10 -6 Torr has been measured prior to contact with HOCl or ClONO 2

Uptake of hydrochloric acid and hypochlorous acid onto sulfuric acid: solubilities, diffusivities, and reaction

The interaction of HOCl and HCl vapors with liquid sulfuric acid surfaces was studied in a flow tube equipped with chemical ionization mass spectrometry detection. Time-dependent uptake of HCl and HOCl was measured. A methodology for deriving the value of the quantity H[radical]D[sub 1], (the product of the Henry's law coefficient and the square root of the liquid-phase diffusion coefficient) is discussed. The partial pressures of HCl over HCl-doped sulfuric acid solutions were also measured to directly determine H for HCl (H[sub HCl]*). Using the measured values of H[sub HCl]* and H[sub HCl]*[radical]D[sub 1], the value of D[sub 1] for HCl in 50 wt % sulfuric acid was extracted. Values for H[sub HOCl] and for the second-order rate coefficient for the reaction between dissolved HOCl and HCl were also obtained. The application of these results to modeling stratospheric heterogeneous processes in sulfuric acid aerosols is discussed. 31 refs., 14 refs., 3 tabs.

Role of HCl ionization by metastable neon atoms in XeCl laser kinetics

Using recent information on the reactions of metastable neon atoms with HCl, the role of HCl ionization by metastable neon atoms in self-sustained discharge pumped XeCl laser kinetics was studied by means of kinetic codes. A detailed comparison of the modeled results by the codes with and without these reactions for a XeCl laser is presented. The comparison shows that the higher the HCl partial pressure, and/or the higher the total pressure, and/or the lower the charge voltage, the more important the influence of these reactions on the laser performance.

Interaction of HCl vapor with water‐ice: Implications for the stratosphere

The nature of the interaction of HCl vapor with ice has been investigated, using thermal analysis and FTIR spectroscopy to characterize the ice substrate, and mass spectrometry to measure the concentration of HCl and H2O vapors in the gas phase. The results indicate that a liquid layer is formed rapidly at the ice surface for ice exposed to HCl vapor at partial pressures above those characteristic of the ice‐liquid (aqueous HCl solution) equilibrium system. This liquid layer also forms below the eutectic temperature (186 K); that is, it forms even at temperatures at which the liquid is metastable with respect to the formation of HCl trihydrate. For smaller HCl partial pressures such as those prevailing in the stratosphere, the HCl is taken up by the ice surface in amounts corresponding to a large fraction of a monolayer. The chemical reactivity of this surface HCl is very large: Chlorine activation by type II polar stratospheric clouds (consisting of ice particles) should occur efficiently by reaction of the HCl with ClONO2.

The heterogeneous reaction of HOCl + HCl → Cl2 + H2O on ice and nitric acid trihydrate: Reaction probabilities and stratospheric implications

The heterogeneous reaction HOCl + HCl → Cl2(g) + H2O(s) has been observed to proceed readily on cold water‐ice and nitric acid trihydrate (NAT) surfaces. For reactant partial pressures in the 10−7–10−5 torr range, the reaction probability (γ) on water‐ice is found to be 0.16 ± 0.10 at 202 K, and 0.24 +0.5/−0.15 at 195 K, as measured by the decay of HOCl vapor when the HCl partial pressure is above that of HOCl. On NAT, γ is found to have a strong dependence on the H2O vapor pressure of the NAT crystals: at 202 K, reaction probabilities of 0.17 are measured for H2O vapor pressures approaching those of ice (H2O‐rich NAT), whereas γ drops to 0.002 if the H2O pressure is lower by a factor of five (HNO3‐rich NAT). The yield of Cl2(g) relative to HOCl(g) loss is measured to be 0.87 ± 0.20. These results suggest that the heterogeneous process ClONO2 + HCl → Cl2(g) + HNO3(s), which occurs on polar stratospheric cloud surfaces, may be comprised of two steps: ClONO2 + H2O(s) → HOCl + HNO3(s), followed by HOCl + HCl → Cl2(g) + H2O(s). Also, the HOCl + HCl reaction may be directly of importance in the polar stratosphere providing an additional path for chlorine activation.

Non-equilibrium vibrational, dissociation and dissociative attachment kinetics of HCl under high electron density conditions typical of XeCl laser discharges

The non-equilibrium vibrational kinetics of pure HCl is studied for typical conditions of a discharge sustained xenon-chloride laser, namely: HCl partial pressure range 1 to 15 Torr, electron density from 1014 to 1016 cm-3 and reduced electric field from 2*10-17 to 5*10-17 V cm2. This work emphasizes the role of processes which are not usually included in the kinetic models for this laser. Particular attention is devoted to V-V (vibration-vibration) energy exchanges, direct dissociation by electron impact and deactivation of vibrational quanta by V-T (vibration-vibration) collisions. The role of the various vibrational levels on the formation of Cl- is also considered.

Selective epitaxial growth of silicon

We have studied selective epitaxial growth of silicon in the SiCl2H2/HCl/H2 system. Our results on growth rate and selectivity are reported here. We found that the growth rate and selectivity are strong functions of the partial pressures of HCl, SiCl2H2, H2, exposed Si area, and wafer position. We propose that growth and selectivity are controlled by surface reactions between SiCl2H2 and HCl and the SiO2 and Si surfaces. Higher HCl flow rates decrease the adsorption coefficients and/or incorporation rates of the reactive SiCl2H2(g) species on both SiO2 and Si. When either is zero for SiO2 and both are greater than zero on Si, selective depositions occur. Finally, we present data on the effect various SiO2 surface treatments have on the density and distribution of Si nuclei on this surface.

Interferometric measurement of two-dimensional Xe and electron density distributions in XeCl laser discharges

A near-infrared, interferometric measurement of the density distribution of the electrons and excited xenon atoms has been performed at two discharge pumped, X-ray preionized XeCl lasers. The experimental results of one of these lasers are in good agreement with model calculations for the homogeneous phase. The electrons and excited states of xenon show a different behaviour in their spatial distributions at both lasers. In addition a region of inhomogeneities, which is identified as the hot-spot region, is been found near the cathode. Filamentation of the discharge can occur after a short time. The dimension of the hot-spot region depends on the preionization delay time. The same holds for the filamentation process, which in addition depends on the HCl partial pressure.

Output characteristics and electron-HCl kinetics of a XeCl laser at very high current density

Output characteristics of a XeCl laser at very high discharge current density (j=14 kA cm-2) were studied experimentally. At an estimated electron number density of about 1*1016 cm-3, electron quenching did not dominate over XeCl* (B or C) formation. The XeCl active medium exhibits very high gain characteristics at high current density. High power laser output was extracted from the active volume and a volatile dependence on HCl partial pressure was observed. The rapid build-up of gain was attributed to fast excimer formation resulting from increased number of densities of ionic precursors (Xe+ and Cl-). Electron-HCl kinetics processes that contribute to the enhancement of the formation of atomic ions were also discussed.

Silicon selective epitaxial growth at reduced pressure and temperature

In a rapid thermal process (RTP) system working at a total pressure of a few Torr, we have obtained selective epitaxial growth (SEG) of silicon at temperatures as low as 650°C. When using SiH 2Cl 2(DCS) as the reactive gas no addition of HCI is needed. Nevertheless, using SiH 4 below 950°C a small amount of HCl should be added. The kinetic aspects of the two systems, DCS/HCl/H 2 and SiH 4/HCl/H 2, are presented and discussed. For the DCS system we show that the rate-limiting reactions are slightly different from those commonly accepted in the literature, where results are from systems working at atmospheric pressure or in the 20–100 Torr range. The growth rate for our system is found to be a linear function of the partial pressure of hydrogen, as well as the partial pressure of HCl, mainly in the gas phase diffusion-controlled regime. The saturation in growth rate as a function of the DCS input pressure can be explained by our model, as can the non-hydrogen partial pressure dependence in the kinetically-controlled regime. This model is based on the main decomposition of DCS, SiH 2Cl 2 → SiHCl + HCl, instead of the widely accepted reaction SiH 2Cl 2 → SiCl 2 + H 2. This is the main reason why no extra HCl is required in the DCS/H 2 system to obtain full selectivity from above 1000°C down to 650°C.

Broensted superacidity of hydrochloric acid in a liquid chloroaluminate. Aluminum chloride - 1-ethyl-3-methyl-1H-imidazolium chloride (55.O m/o AlCl3)

The system HCl (0.1-1 atm)/AlCl{sub 3}-EMIC (55.0 mol % AlCl{sub 3}) (EMIC = 1-ethyl-3-methyl-1H-imidazolium chloride) at 23{degree}C is a Broensted superacid capable of protonating arenes to a degree similar to that of liquid HF at 0{degree}C (H{sub 0} = {minus}15.1). Arenes used in this investigation were biphenyl (I), naphthalene (II), 9H-fluorene (III), chrysene (IV), 2-methylnaphthalene (V), mesitylene (VI), pentamethylbenzene (VII), hexamethylbenzene (VIII), anthracene (IX), and 9,10-dimethylanthracene (X). In both the chloroaluminate melt and HF I is a weak base while VIII-X are strong bases. In between these extremes the order of basicities in both media is II < III and IV < V < VI < VII < VIII. A study of the effect of HCl partial pressure showed, for example that V is 50% protonated at 0.3 atm HCl. The overall reaction is arene + HCl + Al{sub 2}Cl{sub 7}{sup {minus}} {r reversible} arene {times} H{sup +} + 2AlCl{sub 4}{sup {minus}} and is reversible. The degree of protonation was measured by optical absorption spectrophotometry. The arenes are stable in the liquid chloroaluminate for many hours, and their protonated forms (arenium ions) are stable for 1 h or more. A new procedure for the preparation of EMIC was developed thatmore » yields exceptionally clean AlCl{sub 3}-EMIC melts with very low concentrations of protic and oxidizing impurities. 17 refs., 6 figs., 2 tabs.« less

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

The thermodynamic study of the different compounds of the system MgCl2, H2O, HCl allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H2O partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCl2.

Halogen VPE of AlGaAs for optoelectronic device applications

We report on the growth of the ternary AlxGa1−x As in a specially designed halide transport reactor. High quality layers with background doping levels in the 1016 cm−3 range have been achieved. Furthermore, the small FWHM (for example, 4 meV measured on an Al0 17Ga0.83 As film) obtained from low temperature photoluminescence demonstrates the excellent optical quality of the films By varying the growth temperature between 700 and 800°C, the Al concentration of the layers can be changed between < 1 and 70% whereas the AsH3, HCl and HCl-bypass partial pressures have hardly any effect on the composition of the films. These results are in accordance with a thermodynamic model which takes into account a diffusion step from the bulk gas phase to the substrate surface The doping behaviour with DEZn and H2S as sources for n and p-type doping respectively leads to similar results as have been reported for MOCVD, MBE or LPE layers. The fabrication of a light emitting diode with satisfactory efficiency demonstrates the suitability of this method for growing device quality films.