Measurements of the structures of nanoparticles in flames by in situ detection of scattered x-ray radiation

Abstract

The angular pattern of scattered synchrotron x-ray radiation has been used to measure the composition of molecules and nanometer-sized particles in flames. The measured patterns were compared with patterns obtained from calculations for different species compositions. After ensuring that the calculations could reproduce the experiments for air and for ethylene flames under two different combustion conditions flames under special particle producing conditions were studied. In one case, the patterns showed a strong presence of spherical or fullerenelike structures with very little presence of graphitelike particles and little soot production on a cooling plate. In the other case, under soot producing conditions, the scattering showed a clear presence of nanometer-sized graphite particles. The results show that high concentrations of particles with the size around 1 nm can be produced in flames. These particles either remain free or condense into larger particles, depending on the combustion conditions. This technique opens up for experimental studies of molecular and particle dynamics in combustion processes and other processes where nucleation and structural transformations of particles occur.

Synchrotron radiation studies of additives in combustion I: Water

“…We and others have recently used Small Angle X-ray Scattering (SAXS) [14][15][16][17][18][19][20][21][22][23] and Small Angle Neutron Scattering (SANS) [24,25] techniques to study in situ the size and distribution of soot particles in diffusion flames. In an extension of our work, we have investigated the change in the size and number of soot particles that occurs when water is injected into an ethylene flame.…”

In-situ neutron imaging of hydrogenous fuels in combustion generated porous carbons under dynamic and steady state pressure conditions

“…Since X-ray attenuation is weaker for hydrogen than for carbon (for 10 keV radiation it as about 73 times), hydrogen detection can thus be three orders of magnitude more sensitive utilizing cold neutrons instead of hard X-rays. In practice, neutrons would be able to detect pressurized gaseous hydrogen surrounding carbon nanoparticles and thus be well-suited for the study of the interaction hydrogen and methane with carbon nanoparticle assemblies such as soot, the structure of which can be characterized by X-ray scattering techniques (see [5][6][7]9,11] and references therein).…”

“…Different carbon structures can be produced from combustion-like processes, such as fullerenes, nanotubes, and graphite. These may be found as components [2][3][4][5] in carbon soot, one of the most common unwanted by-products from incomplete combustion, which normally has a negative effect on health and the environment. It can also have positive aspects in that it may play an important role for clean energy conversion in combustion due to its material properties such as low density and fractal structure.…”

A combined small- and wide-angle x-ray scattering detector for measurements on reactive systems

“…The computer (NI PXI-1042) had a dual core processor enabling programs to be executed in parallel, meaning that data acquisition and processing could be run at the same time on each processor and that data were sampled continuously without processing dead time. The scattered intensity I i at channel i can be described by the following equations, based on previous works: 23,33 …”

“…[8][9][10][11] One of the most promising tools for particle dynamics studies is based on synchrotron x-ray scattering, [12][13][14] which has demonstrated the ability to study soot formation in flames in situ: small-angle x-ray scattering (SAXS) to characterize the size distribution of soot particles, [15][16][17][18][19][20][21] and wide-angle x-ray scattering (WAXS) to study the subnanometer structure. 22,23 These scattering techniques measure the intensity of scattered photons as a function of the exchanged momentum, q, according to…”