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131.
Plasma sintering experiments in this laboratory at reduced pressures revealed efficient heating of the ceramic sample due to recombination of dissociated and/or ionized species on the surface. For establishing a model for this plasma sintering process, it is necessary to first consider the plasma itself. Therefore, a suitable model for an RF inductively coupled plasma has been developed considering reduced pressures. As the pressure decreases, the electron density also decreases at a fixed electron temperature, causing substantial deviations from chemical equilibrium. Due to the poor collisional coupling between electrons and heavy particles at reduced pressures, large deviations from kinetic equilibrium have also to be expected. The model is based on a rotationally symmetric plasma contained in a quartz tube. The power level ranges from 1.5 to 3 kW and the operating pressure is varied from 1 to 0.01 atm. Both deviations from chemical and kinetic equilibrium are included in this model. Thermodynamic and transport properties for two-temperature plasmas are used for this modeling work. The results indicate that for pressures below 0.1 atm, there is a strong ambipolar flux of charge carriers to the confining walls, leading to significant variations of the temperature across the tube. The electron temperature increases rapidly as the pressure decreases, whereas the heavy-particle temperature decreases. 相似文献
132.
Günter Block Dieter Hirschfeld Ilse-Marie Lichtenauer Annette Pohl 《Mikrochimica acta》1992,107(3-6):279-282
The aim of the first part of the paper is to give some advice for the faultless metallographic preparation of vacuum plasma sprayed coatings. Several coating/substrate combinations using metals, alloys and ceramics were investigated to derive some general rules. The second part deals with a preparation technique for cross-sections- of physical vapour deposition coatings. This technique was optimized for TiN and Ti(C, N) coatings on hardmetals which were examined in an analytical transmission electron microscope. 相似文献
133.
Oxidation of Styrene in a Silent Discharge Plasma 总被引:2,自引:0,他引:2
Anderson Graydon K. Snyder Hans Coogan John 《Plasma Chemistry and Plasma Processing》1999,19(1):131-151
A silent discharge plasma reactor has been developed to study the oxidation of styrene vapor in argon/oxygen mixtures. A number of analytical techniques were employed to determine the destruction efficiency and to characterize the intermediate products. The destruction efficiency was measured as a function of initial styrene concentration, temperature, and energy density of the plasma. The formation of solid products was observed in most experiments. At low temperature (100°C), the solid deposit was polymeric in nature, while at high temperature (300°C) the solid appeared to be amorphous carbon. A combination of high temperature and high energy density resulted in high destruction efficiency and minimal production of solid films. The destruction efficiency vs. energy density is shown to be more complex than a simple model predicting exponential behavior. Several reasons for the discrepancy are suggested. The e-folding energy density for the destruction of styrene is compared to literature values for other organic compounds, measured using similar types of plasma reactors. 相似文献
134.
Ogata Atsushi Mizuno Koichi Kushiyama Satoshi Yamamoto Toshiaki 《Plasma Chemistry and Plasma Processing》1998,18(3):363-373
The behavior of lattice oxygen species of the ferroelectric material during methane oxidation was investigated using a nonthermal plasma reactor packed with BaTiO
3
pellets. Lattice oxygen species in BaTiO
3
play an important role in the formation of N
2
O and the oxidation of CH
4
. The oxidation products such as CO and CO
2
were formed from independent reaction pathways. Lattice oxygen species were able to preferentially oxidize the carbon species deposited on the pellet surface into CO. Also, N
2
O and NO
x
were independently formed in the N
2–O
2
reaction, suggesting that different oxygen species give N
2
O and NO
x. N
2
O was produced by the oxidation of molecular nitrogen with lattice oxygen species. 相似文献
135.
A sensitive, simple, and accurate high-performance liquid chromatographic method has been developed for determination of valdecoxib and the internal standard rofecoxib in human plasma. Protein was precipitated from plasma samples by addition of perchloric acid (HClO4); the drug was then extracted with diethyl ether. Separation was performed on a Cosmosil C18 column (150 mm × 4.6 mm i.d., 5 m particles) with ammonium acetate buffer-acetonitrile, 60:40 (v/v), containing 0.1% TEA, pH 6.5, as mobile phase. Detection and quantification were performed by UV-visible detection at 239 nm. Detection and quantification limits were 3 and 5 ng mL–1, respectively. The linear concentration range for valdecoxib was 5–400 ng mL–1. The validated RP HPLC method was used for determination of the pharmacokinetic data for the drug in humans. 相似文献
136.
T. Vlase Gabriela Vlase N. Doca C. Bolcu 《Journal of Thermal Analysis and Calorimetry》2005,80(1):59-64
Decomposition of dichlorodifluoromethane in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixtures involving carbon, chlorine and fluorine in presence of argon (which is assumed to be the main plasma gas) and/or in addition of hydrogen and calcium together with hydrogen. The calculations were carried out for the temperature range between 500 and 6000 K and for the total pressure of the system of 1 bar. Use is made of the fact that a thermal plasma is a plasma in (local) thermal equilibrium, which makes possible the theoretical determination of its equilibrium composition at definite temperature by employing Gibbs free energy data for the compounds present in the system and assuming that the equilibrium of the system corresponds to its minimum energy state. The results of calculations show that toxic molecules and radicals can be, under convenient conditions (appropriate temperature and amount of added substances), converted into stable non-toxic species like CaF2 and CaCl2. 相似文献
137.
D. V. Khudyakov A. V. Mikhonin I. V. Rubtsov V. A. nadtochenko 《Russian Chemical Bulletin》1997,46(9):1531-1535
The kinetics of the formation and decay of photoexcited radical ion pairs of donoracceptor charge-transfer complexes between
C60 andN,N-diethylaniline (DEA) in chlorobenzene was studied by picosecond laser-induced diffraction gratings. It was established that
the anisotropy of polarization of the diffraction signal decreases as the concentration of DEA increases. The radical ion
states of the photoexcited C60
−...DEA+ complex have zero anisotropy. This effect is likely due to the isotropic intracomplex transfer of an electron from the local
excited state to the radical ion state. The rate constant of quenching of the singlet excited C60 byN,N-diethylaniline (1.4·1010 L mol−1 s−1) and the lifetimes of the solventseparated C60
−...DEA+ and tight [C60
−...DEA+] (95±7 and 31±4 ps, respectively) radical ion pairs were measured.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1605–1610, September, 1997. 相似文献
138.
139.
Inductively coupled plasma optical emission spectrometry (ICP-OES) was applied to the analysis of major and minor elements of Ni-Nb alloys obtained by aluminothermic reduction process. Digestion of samples was made using a mixture of HF+HNO3. Minor and trace elements were determined without matrix separation. The precision for all constituents was <3%. Recoveries for the analyte-spiked samples were 95%. 相似文献
140.
Modeling of plasma jets with superimposed vortex flow 总被引:1,自引:0,他引:1
This work is concerned with analytical studies of thermal plasma jets, which are finding increasing interest for thermal plasma processing. A two-dimensional model for turbulent plasma jets with superimposed vortex flow has been developed, incorporating multiple time scales for velocity and temperature fluctuations and a density-weighted averaging for the density fluctuation effect. Results show that adding swirl to the flow field for confined and free jets induces strong axial and radial pressure gradients near the nozzle exit, causing a rapid decay of the axial velocity with increasing distance from the nozzle. Comparisons with cold flow show similar trends close to the nozzle exit, but further downstream, the axial velocities increase again, especially for larges swirl numbers. Comparisons of theoretical predictions based on the present model with available experimental data are, in general, in reasonable agreement. 相似文献