Radiative gasification

To further explore the influence of silica material properties (morphology, surface area, silanol concentration, and surface treatment) on the silica flame-retardant properties, various types of silicas (silica gel, fumed silicas, and fused silica) were investigated.50 51 Material properties of the various silicas are summarized in Table 8.6. These different types of silicas were added to polypropylene and polyethylene oxide to determine their flame-retardant effectiveness and mechanisms. Polypropylene was chosen as a non-char-forming thermoplastic, and polyethylene oxide was chosen as a polar slightly char-forming thermoplastic. Flammability properties were measured in the cone calorimeter and the mass loss rate was measured in the radiative gasification device in nitrogen to exclude any gas phase oxidation reactions. 

The observed reduced flammability in the nanocomposites may not be attributed to an additional retention of carbon alone since the residue yields are not markedly increased. Some key insights are provided by radiative gasification experiments which enable to follow pyrolysis either in a nitrogen or in a nitrogen-oxygen atmosphere. The example of PA6 nanocomposites is revealing... 

A detailed study of the char formation process in PA 6/clay nanocomposites was performed by Kashiwagi et al, using a NIST radiative gasification apparatus [60]. 

XRD pattern TEM (Figure 3.13) confirms the disordered structure of clay layers in the char. The charring process associated with PP-clay nanocomposites was also studied using the radiative gasification apparatus in the same way as the PS nanocomposite described previously in this chapter. This research was also part of the same NIST consortium work mentioned with the PS nanocomposite... 

Gilman, J.W. Kashiwagi, T. Giannelis, E.P. Manias, E. Lomakin, S. Lichtenham, J.D. Jones, P. Nanocomposites radiative gasification and vinyl polyma flammability, in M. Le Bras, G. Camino, S. Bourbigot, and R. Delobel, Eds., Fire Retardancy of Polymers The Use of Intumescence. Royal Society of Chemistry, London, 1998, pp. 203-221. 

Heat of combustion = 12.0 kJ/g Heat of gasification = 6.0 kJ/g Effective vaporization temperature = 380 °C Radiative loss fraction = 0.35 Conversion constants ... 

Radiative heat transfer plays an important part in many fluidized bed processes operated at high temperatures, such as coal combustion and gasification. When treating a fluidized bed as a whole solid gray body, the radiative heat transfer coefficient ht between the fluidized bed at temperature 7), and a heating surface at temperature Ts is defined as... 

The values of the heat of gasification and surface reradiation loss determined in pyrolysis are used. The flame heat flux is determined from the flame radiation scaling technique [2,3,13]. This technique utilizes the knowledge that in small-scale fires, flame radiative heat flux increases with increase in the oxygen mass fraction (To) [2,3,13]. For ToS0.30, the flame radiative heat flux reaches an asymptotic limit comparable to the limit for large-scale fires burning in the open [2,3,13]. 

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