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21.
Chengcheng Hu Lei Chen Ruxi Gu Junrong Yu Jing Zhu Zuming Hu 《Journal of Macromolecular Science: Physics》2013,52(5):726-737
Heterocyclic aramid fibers are one of the high-performance fibers with excellent mechanical and thermal properties. In this article, the thermal decomposition behaviors of a type of the fibers were studied in nitrogen and air by pyrolysis/gas chromatography–mass spectrometry (Py/GC-MS), thermal gravimetric analysis–differential thermal analysis/Fourier transform infrared spectroscopy (TGA-DTA/FTIR), and thermal gravimetric analysis–differential thermal analysis/mass spectrometry (TGA-DTA/MS). The results showed that under nitrogen atmosphere, the thermal decomposition mainly happened between 520°C and 580°C, the temperature of the maximum weight loss rate was 550°C, and the weight remaining at 800°C was 58%. HCN, NH3, NO2, NO, CO2, CO, H2O, and some other compounds containing benzene rings were detected by the TGA-DTA/FTIR. Among these released chemicals, the intensity of the absorption peak assigned to CO2 was the strongest. These chemicals were also identified by the TGA-DTA/MS. The Py-GC/MS analysis revealed that the number of chromatographic peaks increased with the increase of temperature. Most of the pyrolysis products were produced between 550°C and 600°C, which represented the major pyrolysis process. Moreover, the detection of benzene ring containing compound fragments reflected the process of the molecular chain scission. In air atmosphere, the thermal decomposition mainly happened between 500°C and 680°C. The maximum weight loss rate was observed at 600°C, and almost 100% weight was lost at 900°C. NH3, NO2, CO2, and H2O were detected by the TGA-DTA/MS, and the ion current intensity of CO2 was again the strongest with a strong oxidation reaction at around 670°C. It was speculated that the thermal decomposition began with the breaking of the bonds between PPTA (poly-p-phenylene terephthalamide) blocks and heterocyclic blocks at high temperature. Then, with the increase of temperature, the chemical bonds inside the PPTA blocks and heterocyclic blocks were broken. In this process, free radicals that led to restructuring and new breakages to produce micromolecular products were introduced. 相似文献
22.
G.R. Sonnemann V.E. Semenov 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):481-489
Stable auto-solitary solutions were found on the basis of three-dimensional numerical simulations within the simplest model
under global constraint. The model involves a diffusion equation with a nonlinear source term containing both local and non-local
nonlinearity. The source term was chosen so as to describe qualitatively the most fundamental peculiarities of discharge physics,
namely local nonlinear increase in heating and ionization rate and non-local attenuation of electric field strength with plasma
density growth. The properties of the autosolitons created by the model have been investigated employing the different parameters
as control parameter. Therefore the results of calculations can be used to construct a process of plasma contraction in gas
discharge.
Received 26 July 1999 and Received in final form 5 February 2000 相似文献
23.
A weakly nonlinear model is proposed for multimode Kelvin-Helmholtz instability. The second-order mode coupling formula for Kelvin-Helmholtz instability in two-dimensional incompressible fluid is presented by expanding the perturbation velocity potential to second order. It is found that there is an important resonance in the course of the sum frequency mode coupling but the difference frequency mode coupling does not have. This resonance makes the sum frequency mode coupling process relatively complex. The sum frequency mode coupling is strongly dependent on time especially when the density of the two fluids is adjacent and the difference frequency mode coupling is not. 相似文献
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This paper presents experimental evidence that using the KrF excimer laser for quantitative laser-induced fluorescence (LIF)
studies of the OH A-X (3,0) system is highly problematic if the effects of both photobleaching and photochemistry are not included for laser spectral irradiances greater than 20 MW/cm2 cm-1. Pump-probe and time-resolved measurements of the OH LIF signal in an atmospheric pressure, premixed CH4-air flame at low- and high-laser-spectral-irradiance conditions show that a significant amount of OH is produced from photofragments
resulting from the simultaneous 2-photon predissociation of H2O molecules in the C-X system. A 5+2-level rate-equation model that includes the effects of both photobleaching and photochemical
OH production is shown to satisfactorily predict the data using a single adjustable parameter given by the effective, spectrally
integrated 2-photon cross-section of H2O near 248 nm. The time-integrated OH LIF signal was found to depend on both the laser spectral irradiance and the local concentration of H2O. Additionally, use of the KrF excimer laser for 2-line rotational thermometry can produce temperature errors as great as
+550 K at high laser-pulse energies.
Received: 21 August 2000 / Revised version: 30 October 2000 / Published online: 21 February 2001 相似文献
26.
B. A. Mann S. V. O'Leary A. G. Astill D. A. Greenhalgh 《Applied physics. B, Lasers and optics》1992,54(4):271-277
Single shot degenerate four wave mixing (DFWM) images of the distribution of nitrogen dioxide (NO2) doped into a propane/air flame at concentrations of the order of 7000 ppm have been obtained. These images indicate the relative concentration of NO2 in different parts of the flame with an estimated spatial resolution of 150 m.Initial experiments were performed using NO2 in a glass cell with nitrogen buffer gas. DFWM signals were generated using both the frequency doubled output of a pulsed ND:YAG laser and the tunable blue output of an excimer pumped dye laser. The signal was investigated as a function of laser power, NO2 concentration and buffer gas pressure. In addition, spectra of NO2 in the region 450 to 480 nm were obtained.Signals were then sought in both a cold air/NO2 gas flow and an ignited mixture of propane and air seeded with NO2, using a DFWM imaging geometry. The resulting images from the flame demonstrate the disappearance of the NO2 molecules in the flame interaction zone.This work was done when previously employed by AEA Technology at Harwell 相似文献
27.
Josefina Prez-Arantegui Gemma Cepri Erika Ribechini Ilaria Degano Maria Perla Colombini Juan Paz-Peralta Esperanza Ortiz-Palomar 《Trends in analytical chemistry : TRAC》2009,28(8):1019-1028
Archaeological cosmetics, as well as revealing ancient knowledge, contain a complex mixture of very different organic and inorganic components with diverse properties. Most information on the preparation of ancient cosmetics comes from classical texts. However, although analysis of products contained in archaeological objects has recently identified some ingredients, there is still little known about how the cosmetics were prepared.Using a multi-analytical approach, we studied the chemical composition of two Roman pink make-ups that were preserved on the surface of a Roman bronze cosmetic tool and in a glass unguentarium. The results revealed that both make-ups were colored by madder lake but prepared in two different ways and with two completely different matrices (i.e. scented oils in the first case and gypsum in the second) highlighting that the make-ups had been prepared thoroughly, the ingredients carefully selected and their properties and possibilities for good cosmetic use had been understood. 相似文献
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