Charring

About: Charring is a research topic. Over the lifetime, 1765 publications have been published within this topic receiving 34948 citations.

Determination of atmospheric soot carbon with a simple thermal method

Abstract: The dark component of carbonaceous aerosols is often referred to as “soot carbon”. Soot consists of pure elemental carbon along with highly polymerized organic matter. An accurate discrimination between the soot carbon and the other components of carbonaceous aerosols is difficult to obtain by thermal analytical processes. Here, we report an optimization of a 2-step thermal method focused on the soot carbon determination of atmospheric particles. The organic material which does not absorb visible light is removed from the collection substrate under a pure oxygen flow during a precombustion step which has been carefully optimized in terms of temperature (340°C) and duration (2 h). The remaining carbon content is determined by coulometric titration of the CO 2 evolved from the combustion of the samples. The method has been tested quantitatively for analytical artefacts (e.g., “soot” production due to the charring of organics; soot losses during the preheating step) by using various standards such as pure graphite, pure organic and natural biogenic compounds and replicates of ambient air samples collected in urban, rural and forested areas in France. The results obtained so far indicate that this approach satisfactorily distinguishes between organic and soot carbon and allows reliable soot carbon determination at the μg level in atmospheric samples from a wide variety of environments. This study confirms that soot carbon is not composed primarily of elemental carbon. It appears to be a variable mixture of highly condensed organic compounds. These compounds may be either combustion-derived material or the result of low-temperature gas-to-particle conversion processes. DOI: 10.1111/j.1600-0889.1989.tb00316.x

A Generalized Pyrolysis Model for Combustible Solids

Abstract: This dissertation presents the derivation, numerical implementation, and verification/validation of a generalized model that can be used to simulate the pyrolysis, gasification, and burning of a wide range of solid fuels encountered in fires. The model can be applied to noncharring and charring solids, composites, intumescent coatings, and smolder in porous media. Care is taken to make the model as general as possible, allowing the user to determine the appropriate level of complexity to include in a simulation. The model considers a user–specified number of gas phase and condensed phase species, each having its own temperature–dependent thermophysical properties. Any number of heterogeneous (gas–solid) or homogeneous (solid–solid or gas-gas) reactions can be specified. Both in–depth radiation transfer through semi–transparent media and radiation transport across pores are considered. Volume change (surface regression or swelling/intumescence) is handled by allowing the size of grid points to change as dictated by mass conservation. All volatiles generated inside the solid escape to the ambient with no resistance to mass transfer unless a pressure solver is invoked; the resultant flow of volatiles is then calculated according to Darcy’s law. A gas phase convective–diffusive solver can be invoked to determine the composition of the volatiles. Oxidative pyrolysis is simulated by modeling diffusion of oxygen from the ambient into the pyrolyzing solid where it may participate in reactions. Consequently, the mass flux and composition of volatiles escaping from the solid can be calculated. To aid in determining the required input parameters, the model is coupled to a genetic algorithm that can be used to estimate the required input parameters from bench–scale fire tests or thermogravimetric analysis. Standalone model predictions are compared to experimental data for the thermo– oxidative decomposition of non–charring and charring solids, as well as the gasification and swelling of an intumescent coating and forward smolder propagation in polyurethane foam. Genetic algorithm optimization is used to extract the required input parameters from the experimental data, and the optimized model calculations agree well with the experimental data. Blind simulations indicate that the predictive capabilities of the model are generally good, particularly considering the complexity of the problems simulated.

PA-6 clay nanocomposite hybrid as char forming agent in intumescent formulations

Abstract: This work deals with new flame retardant (FR) intumescent formulations for ethylene-vinyl acetate copolymers (EVA) using charring polymers polyamide-6 (PA-6) and polyamide-6 clay nanocomposite hybrid (PA-6-nano) as carbonization agents. Use of PA-6 nano improved both the mechanical and fire properties of FR EVA-based materials. The part played by the clay in the improvement of the FR performance was studied using FTIR and solid state NMR. It is shown that the clay allowed the thermal stabilization of a phosphorocarbonaceous structure in the intumescent char which increased the efficiency of the shield and, in addition, the formation of a ‘ceramic’ which can act as a protective barrier. Copyright © 2000 John Wiley & Sons, Ltd.