Troels Dyhr Pedersen.indd - Solid Mechanics

Figure 12: Termination of the low temperature reactions
- 40 - -
Formaldehyde is the intermediate radical with the highest concentration in the interval
between the LTR and HTR processes. Formaldehyde appears to have a constant
concentration, but it is produced and consumed continuously. Production is mainly
through dissociation of the methoxy-methyl radical. Consumption is by reaction 32 that
produces HCO, which dissociates by reaction 12, to form CO:
# 12 :
HCO + M → CO + H + M
The continuous production of CO consumes the majority of the available OH radicals and
keeps the other possible reactions at low levels. With a limited amount of OH radicals
available, the reaction path consisting of reactions 274, 282, 32 and 12 dominate the
interval between the LTR and HTR processes.
The non-carbon radicals interact in a simple way during the LTR process. First the
hydrogen produced mainly by reaction 12 combines with O2 to form HO2. The HO2 then
combines with itself, H or OH. Roughly half reacts to form H2O2 which accumulates.
About half of the remaining HO2 produces new OH radicals, and the rest is used in the
chain terminating reaction.