ABSTRACT
A detector with high dynamic range designed for combined small- and wide-angle x-ray scattering experiments has been developed. It allows measurements on single events and reactive systems, such as particle formation in flames and evaporation of levitating drops. The detector consists of 26 channels covering a region from 0.5° to 60° and it provides continuous monitoring of the sampled signal without readout dead time. The time resolution for fast single events is about 40 µs and for substances undergoing slower dynamics, the time resolution is set to 0.1 or 1 s with hours of continuous sampling. The detector has been used to measure soot particle formation in a flame, burning magnesium and evaporation of a toluene drop in a levitator. The results show that the detector can be used for many different applications with good outcomes and large potential.
Subject(s)
Scattering, Small Angle , Systems Integration , X-Ray Diffraction , Magnesium/chemistry , Signal Processing, Computer-Assisted , Time FactorsABSTRACT
The mean size of fluorescent nanoparticles produced in a propane flame has been measured with an in-situ technique employing a femtosecond laser to excite the sample and a streak camera for time-resolved detection of the fluorescence. The time profile of the fluorescence anisotropy showed a Gaussian behaviour, typical of free rotor reorientation. By measuring its width, we estimated an average carbon particle diameter of 3.3 nm, thus confirming the existence of combustion produced nanoparticles. The technique proves to be applicable to the study of gas-phase nanoparticles, both in combustion and environmental studies.
Subject(s)
Algorithms , Hot Temperature , Lasers , Models, Chemical , Propane/chemistry , Propane/radiation effects , Spectrometry, Fluorescence/methods , Anisotropy , Computer SimulationABSTRACT
A novel technique for measuring droplet temperatures has been demonstrated. Laser-induced phosphorescence from thermographic phosphors, seeded to distilled water and iso-octane, was used to measure temperatures of single falling droplets. The phosphors were excited by the fourth and third harmonics of a Nd:YAG laser. The subsequent emission was evaluated by spectral and temporal investigations of the thermographic phosphors Mg4FGeO6:Mn and La2O2S:Eu, respectively. The spectral and the temporal methods permitted temperature measurements of free-falling droplets up to 433 K. Results from both methods, which show an estimated accuracy of better than 1%, are presented.
ABSTRACT
Fluorescence lifetimes of formaldehyde excited by picosecond laser radiation with a wavelength of 355 nm were determined in nitrogen gas in a cell using time-resolved laser-induced fluorescence spectroscopy. The measurements were conducted at temperatures between 295 and 770 K and pressures up to 10 bar (1 MPa). Detection was broadband in most cases. Temperature and pressure were found to have a quenching effect on the fluorescence. At 295 K and pressures between 1 and 5 bar, decay rates between 0.03 and 0.04 ns(-1) were observed. At 770 K, the decay rates increased from 0.11 to 0.17 ns(-1) as the pressure was raised from 1 to 10 bar. The dependence on pressure was not linear at 1 bar. At 10 bar the linearity is unclear. The dependence on temperature appeared to be exponential.
Subject(s)
Formaldehyde/chemistry , Nitrogen/chemistry , Polymers/chemistry , Spectrometry, Fluorescence/methods , Spectrophotometry/instrumentation , Spectrophotometry/methods , Lasers , Pressure , Temperature , Time FactorsABSTRACT
The electronic A1A2 <-- X1A1 absorption spectra of formaldehyde vapour were studied at temperatures varying from 423 to 770 K with variable pressures from less than 0.1 to 1 MPa. Broadband vibronic and partially rotationally resolved 4(0)(1) rovibronic spectra of formaldehyde showed considerable sensitivity to temperature. The high resolution spectra showed collision-induced broadening as the pressure was increased. The results show that the absorption efficiency of the laser radiation from the third harmonic of Nd:YAG lasers is sensitive to the spectral properties of the laser, such as line position and shape. Promising results were obtained from the comparison between theoretical and measured absorption spectra.
