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排序方式: 共有93条查询结果,搜索用时 15 毫秒
1.
G. Bruno P. Capezzuto G. Cicala F. Cramarossa 《Plasma Chemistry and Plasma Processing》1986,6(2):109-125
Plasma-chemical reduction of SiCl4 in mixtures with H2 and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H2 ratio strongly affects the plasma composition as well as the deposition (r
D) and etch (r
E) rates of Si: H, Cl films and that the electron impact dissociation is the most important channel for the production of SiClx species, which are the precursors of the film growth. Chemisorption of SiClx and the reactive surface reaction SiClx+H–SiCl(x–1)0+HCl are important steps in the deposition process. The suggested deposition model givesr
D [SiClx][H], in agreement with the experimental data. Etching of Si: H, Cl films occurs at high Ar: H2 ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step. 相似文献
2.
Denis A. Knyazkov Artëm M. Dmitriev Oleg P. Korobeinichev Ksenia N. Osipova Gianmaria Pio Andrey G. Shmakov Ernesto Salzano 《Proceedings of the Combustion Institute》2021,38(2):2467-2475
The knowledge of the combustion chemistry of oxygenated fuels is essential for the development of detailed kinetic mechanisms suitable for the combustion processes involving biofuels. Moreover, epoxidized olefins, are increasingly used as chemical intermediates or as bulk chemicals. Nevertheless, a dearth of data for their reactivity in the oxidative environment can be observed in the current literature. This study reports the experimental and the model characterization of the flame structure of propylene oxide at stoichiometric and fuel-rich conditions at atmospheric pressure. To this aim, the species mole fractions in three premixed flames stabilized on a flat-flame burner have been quantitatively measured by using the flame sampling molecular beam mass spectrometry. Three chemical kinetic mechanisms retrieved from the current literature involving propylene oxide chemistry have been validated against the novel experimental data. In general, the predictions appeared to be in satisfactory agreement with measurements except for acetaldehyde and ketene. The rate of production analysis in the flame has shown that the discrepancies observed for these species are related basically to the incorrect ratio between the rates of primary reaction pathways of propylene oxide destruction. 相似文献
3.
Denise Tofanello Gimenes Wallans Torres Pio dos Santos Rodrigo Alejandro Abarza Munoz Eduardo Mathias Richter 《Electrochemistry communications》2010,12(2):216-218
In this work, we describe for the first time the use of the internal standard method in flow injection analysis (FIA) with amperometric detection. The method is based on the application of sequential potential pulses to the working electrode in an electrochemical flow cell. The sequence of potential pulses is selected in such a way that the analyte and internal standard compound are detected and monitored individually and independently at the same working electrode. This approach compensates for random errors associated with variations of flow rate, injection volume, ionic strength difference between standards and samples, and accidental insertion or formation of air bubbles in the carrier stream. In addition, this method can overcome the major drawback of amperometric detection using solid electrodes, which is gradual electrode passivation. To illustrate the potential of this method, the flow-injection amperometric detection of uric acid using [Fe(CN)6]3? as an internal standard (IS) is presented as an example. 相似文献
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6.
S. M. Almeida M. C. Freitas C. A. Pio 《Journal of Radioanalytical and Nuclear Chemistry》2008,276(1):161-165
A Gent stacked filter unit sampler was used to collect air particulate matter (APM) in separate coarse (PM2.5–10) and fine (PM2.5) size fractions, at a sub-urban site in Lisbon, Portugal. The sampling was done during the year 2001 and two daily samples
were taken per week. The filters were analyzed for particulate mass by instrumental neutron activation analysis (INAA). The
chemical analysis of APM levels and the study of the atmospheric dynamics by back-trajectories showed that most of the PM2.5 and PM2.5–10 peaks events were associated with air masses transport from the Saharan desert. High mineral load in ambient particulate
matter levels were registered during the Saharan dust outbreaks. The accuracy of INAA to measure Fe, Sc and Sm was evaluated
by NIST filter standards, revealing results with an agreement of ± 10%. This method constituted an important tool to identify
these events. 相似文献
7.
A family of linear copolymers, characterized by the presence along the polymer chain of variable amounts of two atomic groups of different mesogenic potentiality, has been studied by differential scanning calorimetry and X-ray diffraction methods. The range of composition that allows enantiotropic mesophasic behaviour is defined for four homologous sets of copolymers. The experimental phase diagram gives, by extrapolation, indications about the potential mesophasic properties of that extreme composition (corresponding to a homopolymer) that shows no direct mesophasic properties. 相似文献
8.
Guaratini T Lopes NP Pinto E Colepicolo P Gates PJ 《Chemical communications (Cambridge, England)》2006,(39):4110-4112
We report here a general mechanism for the elimination of aromatic molecules from polyene containing natural products of several compound classes in tandem mass spectrometry. 相似文献
9.
Wallans Torres Pio dos Santos Edimar Gledison Nascimento de Almeida Humberto Eustáquio Alves Ferreira Denise Tofanello Gimenes Eduardo Mathias Richter 《Electroanalysis》2008,20(17):1878-1883
The present work reports a simple and quick strategy for simultaneous determination of paracetamol (PC) and ascorbic acid (AA) in pharmaceutical formulations using flow injection method with multiple pulse amperometric detection. The method allows the resolution of the mixture without chemical pretreatment of the sample or electrode modification or the use of chemometric techniques for data analysis. The compounds are detected by applying four sequential pulses (waveform) in function of time to a three‐electrode amperometric system that uses a wall‐jet cell with gold as working electrode. AA is direct detected at +0.40 V and PC is indirectly detected at 0.0 V by the reduction (desorption) of the oxidation product (N‐acetyl‐p‐benzoquinoneimine) electrochemically generated at +0.65 V. The fourth potential pulse (?0.05 V) is applied for the complete regeneration (cleaning) of the gold electrode surface. The linear response range was optimized between 5 and 24 mg L?1 for AA and 50 and 240 mg L?1 for PC. The difference between the two responses ranges (10‐fold) present correlation with the concentration of these compounds in two different pharmaceutical formulations available in the Brazilian market. The analytical frequency was calculated in 60 injections per hour. The use of the proposed methodology for PC quantification in the presence of higher AA concentrations was also carried out. Using the standard addition method, it was possible to detect PC in trace levels (LD=0.2 mg L?1) in the presence of 880‐fold more of AA (176 mg L?1). 相似文献
10.
Valence excitation spectra for the linear isomers of He-, Ne-, and Ar-Br2 are reported and compared to a two-dimensional simulation using the currently available potential energy surfaces. Excitation spectra from the ground electronic state to the region of the inner turning point of the Rg-Br2 (B,nu') stretching coordinate are recorded while probing the asymptotic Br2 (B,nu') state. Each spectrum is a broad continuum extending over hundreds of wavenumbers, becoming broader and more blueshifted as the rare gas atom is changed from He to Ne to Ar. In the case of Ne-Br2, the threshold for producing the asymptotic product state reveals the X-state linear isomer bond energy to be 71+/-3 cm(-1). The qualitative agreement between experiment and theory shows that the spectra can be correctly regarded as revealing the one-atom solvent shifts and also provides new insight into the one-atom cage effect on the halogen vibrational relaxation. The measured spectra provide data to test future ab initio potential energy surfaces in the interaction of rare gas atoms with the halogen valence excited state. 相似文献