Initiator “burnout

The solution of eqns [8] and [9] provides the conversion achieved in adiabatic polymerization. Figure 23 shows the results for methyl methacrylate with an initial temperature of 25 °C, using thermodynamic data from Odian." The conversion is 0.93, which means that independent of initiator burnout, complete conversion can never be achieved because of the high front temperature. This value is very sensitive to the exact values of the thermodynamic parameters so the calculated value may not correspond precisely to experiment. Nonetheless, thermodynamics must be considered when selecting candidates for FP. Similar monomers may exhibit very different conversions at the same temperature. For example, zero conversion will be obtained at 310 °C with styrene but a-methylstyrene will not react above 61 °C." ... 

Burning times for coal particles are obtained from integrated reaction rates. For larger particles (>100 fim) and at practical combustion temperatures, there is a good correlation between theory and experiment for char burnout. Experimental data are found to obey the Nusselt "square law" which states that the burning time varies with the square of the initial particle diameter (t ). However, for particle sizes smaller than 100 p.m, the Nusselt... 

G3. Grace, T. M., The mechanism of burnout in initially subcooled forced convection systems, TID-19845 (1963). 

A typical transition to behavior of a ventilation-controlled fire begins with excess air as the fire feeds on the initial compartment air, but then is limited by air flow at the vent. As a consequence the fire can move to the vent and withdraw as the fuel is consumed. This might lead to two areas of deep burning if the fire is extinguished before complete burnout. 

The combustion time from the initial particle size to burnout is... 

As an example of thermolysis, consider the burnout of polyvinyl alcohol from a barium titanate compact in air. Initially, there is loss of hydroxyl and hydrogen side groups, leaving a conjugated hydrocarbon ... 

X 10 sec or 7.25 hr. As the bulk temperature is increased, the surface reaction curve moves to lower temperatures compared to the other curves, eventually causing a three-curve intersection (R, HTBL, PTC). This gives a new set of rate determining steps, where we have a mixed resistance for the transfer of heat. In addition, sufficiently high surface temperatures, for example, initially, can cause a runaway of the surface temperature to near 2000 C. These carbon burnout condi-... 

In view of the known rapid chemisorption by tungsten, it must be concluded that the film is contaminated. Enough gas has been desorbed from the glass so that the film after filament burnout is saturated to such an extent that it cannot reduce the pressure below the initial value. On the other hand, if evaporation is carried out in short bursts, the initial low pressure drops steadily, showing that tungsten acts as a getter under these conditions and that cleaner films may be prepared by slight modification of the conventional techniques. 

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