Conductivity for Soot Sensing: Possibilities and Limitations

Abstract

In this study we summarize the possibilities and limitations of a conductometric measurement principle for soot sensing. The electrical conductivity of different carbon blacks (FW 200, lamp black 101, Printex 30, Printex U, Printex XE2, special black 4, and special black 6), spark discharge soot (GfG), and graphite powder was measured by a van der Pauw arrangement. Additionally the influence of inorganic admixtures on the conductivity of carbonaceous materials was proven to follow the percolation theory. Structural and oxidation characteristics obtained with Raman microspectroscopy and temperature programmed oxidation, respectively, were correlated with the electrical conductivity data. Moreover, a thermophoretic precipitator has been applied to deposit soot particles from the exhaust stream between interdigital electrodes. This combines a controlled and size independent particle collection method with the conductivity measurement principle. A test vehicle was equipped with the AVL Micro Soot Sensor (photoacoustic soot sensor) to prove the conductometric sensor principle with an independent and reliable technique. Our results demonstrate promising potential of the conductometric sensor for on-board particle diagnostic. Furthermore this sensor can be applied as a simple, rapid, and cheap analytical tool for characterization of soot structure.

Optical and electrical characterization of carbon nanoparticles produced in laminar premixed flames

“…The increase of conductivity from Flame 1 to Flame 4 sample follows the increase of I(D)/(IG) and can be therefore correlated to the increase of the in plane size of graphitic crystallites within the particles, L a , in agreement with the graphitization trajectory derived from Raman and optical band gap results. This trend is consistent to that observed by Grob et al [16], who measured the ratio of the two maxima in Raman the spectrum, I(D)/I(G), and the conductivity of a spark discharge generated soot and others disordered carbons, and observed that conductivity increased with I(D/I(G)). The same group also reported a larger amount of elemental carbon, and hence graphitization, in the samples with the larger conductivity [36].…”

“…4 left side. Similar trends are reported in literature [16,36]. It is unlikely that such inverse trend is due to uncertainties in the determination of the G band by the fitting procedure.…”

“…Although particulate matter as soot and carbon black derives from similar formation processes and possesses similar composition and properties, recent studies highlighted differences in both microstructure and electrical properties between soot particles and commercial carbon blacks [16].…”

Spectroscopic investigation of flame synthesized carbon nanoparticle/P3HT blends

“…These soot particles are composed of chain-like agglomerates of nearly spherical particles approximately 50 nm in diameter containing turbostratic graphite crystallites with an H/C ratio of approximately 0.01. These latter particles have a lower optical band gap than CNPs, fractions of eV, therefore absorbing light over a wide spectral range from the UV to IR and possessing a large electrical conductivity [23,24]. Therefore, it is evident that the particles produced in the various stages of the flame process have different electronic structures, characterized by the different positioning of the electronic bands, thus having different band gap values.…”

Electrodepositon of Dendritic Ni-Co onto High-Voltage Electrodes of Electrostatic Particulate Matter (PM) Sensors

“…4 In-situ sensor technologies are typically based on either resistive techniques that detect soot accumulation [5][6][7] or electrostatic methods that determine real-time particle concentrations. 10,11 A recently developed, low-cost electrostatic in-situ PM measurement approach has demonstrated both higher sensitivity and better durability compared to resistive techniques.…”