Firing atmosphere

If we examine the oxidation states of the activators of 6.3.5., it is apparent that most require one of their lower valence states to function as an activator. Therefore, one needs to provide a neutral, or slightly reducing, atmosphere during firing, since the normal air atmosphere would promote the higher valence states. Suitable neutral atmospheres include N2, A, Ne, etc. A reducing atmosphere would usually consist of 95-98% N2 and 2-5% H2. 

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Thermal calculations suggest that the char barrier approach can be highly efficient if optimized. Funt and Magill (8) showed that a 1 mm layer would keep an underlying substrate from reaching ignition temperature when the external fire atmosphere was at 743 C, and a 2.7 mm layer would suffice when the fire atmosphere was at 1500 C (Table II). 

A large number of studies have also been done to investigate the lifetime of HC1 in a fire atmosphere [20-24]. These studies have shown that HC1 reacts very rapidly with most common construction surfaces (cement block, ceiling tile, gypsum board, etc.) so that the peak atmospheric concentration found in a fire is much less than would have been predicted from the chlorine content of the burning material. Furthermore, this peak concentration soon decreases and HC1 disappears completely from the atmosphere. 

Cicerone, R. J., Fires, Atmospheric Chemistry, and the Ozone Layer, Science, 263, 1243-1244 (1994). 

Debanne, S.M., Hirschler, M.M., and Nelson, G.L., The importance of carbon monoxide in the toxicity of fire atmospheres, in Fire Hazard and Fire Risk Assessment, Ed. M.M. Hirschler, ASTM STP 1150, American Society for Testing and Materials, Philadelphia, PA, pp. 9-23, 1992. 

Carbon monoxide Forest fires atmospheric combustion sources Incomplete combustion of... 

Burns and Roe. "Conceptual Design of a Gulf Coast Lignite-Fired Atmospherics Fluidized-Bed Power Plant" EPRI Report FP-1173, Palo Alto, California, September, 1979. 

Andreae, M. O., J. Fishman, and J. Lindesay. 1996. The Southern Tropical Atlantic Region Experiment (STARE) TRansport and Atmospheric Chemistry near the Equator-Atlantic (TRACE-A) and Southern African Fire/ Atmosphere Research Initiative (SAFARI) An introduction. Journal of Geophysical Research 101 23519-23520. 

Combustion toxicity research is the study of the adverse health effects caused by exposure to fire atmospheres. A fire atmosphere is defined as all of the effluents generated by the thermal decomposition of materials or products regardless of whether that effluent is produced under smoldering, nonflaming, or flaming conditions. The objectives of combustion toxicity research are to identify potentially harmful products from the thermal degradation of materials. 

An air fired, atmospheric pressure system suitable for small and medium scale energy producers such as industrial steam plants or hot gas generators,... 

Fig. 7.7. Influence of firing atmosphere on the evolution of crystallite size versus temperature in the case of a tetragonal zirconia membrane material [56].

An important practical feature of the inhalation toxicology of HCN is the development of incapacitating effects, since this may impede mobility and escape from a contaminated area. This could clearly be relevant to hazards from exposure to fire atmospheres, effectiveness of military operations and escape from enclosed areas where HCN has been deliberately released by terrorists. Over an HCN vapor concentration range of 102-156 ppm (114-175 mg-3), Purser et al. (1984) found a linear relationship between exposure concentration and the time to the development of hyperventilation and subsequent incapacitation. The slope on the relationship was such that a doubling of the HCN vapor concentration from 100 to 200 ppm (112-224 mg m-3) reduced the time to incapacitation from 25 to 2 min. Rat studies estimated that the HCN vapor concentrations producing incapacitating effects are about 65% of the lethal concentration (Levin et al, 1987). 

Morikawa, T. 1988. Toxic gases evolution from commercial building materials under fire atmosphere in a semi-full-scale room. J. Eire Sci. 6(2) 86-99. 

The fired colour of a clay is due principally to its content of iron oxide, but also depends on the firing-atmosphere (whether... 

Tsuchiya, Y. and Williams-Leir, G. Equilibrium composition of fire atmospheres. J. Fire and Flammability, 6, 5 (1975)... 

Considering the final part to be manufactured (the whole reason why the tape is cast), consideration must be given to the firing atmosphere. It would not serve to use an excellent air burnoff binder for casting silicon carbide if the SiC will be fired in a reducing atmosphere. This is an especially important consideration when casting metal powders or other nonoxide powders. 

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