Chain reactions inhibition

It may be stated as a conclusion that the problem of chain reaction inhibition may not be brought only to the reaction of the inhibitor with the chain carriers. Surely, the problem requires the comprehensive consideration of the complex inhibited reactions. A similar situation should be expected for the inhibitors that have the action of a different nature. 

The basic requirements of a reactor are 1) fissionable material in a geometry that inhibits the escape of neutrons, 2) a high likelihood that neutron capture causes fission, 3) control of the neutron production to prevent a runaway reaction, and 4) removal of the heat generated in operation and after shutdown. The inability to completely turnoff the heat evolution when the chain reaction stops is a safety problem that distinguishes a nuclear reactor from a fossil-fuel burning power plant. 

Removal of one of the corners of the fire triangle normally results in extinguishment of a fire. Propagation of a flame can also be stopped by inhibition of the chain reactions, e.g. using dry powders or organo—halogen vaporizing liquids. 

Steady-state treatment for the transients (H02- and UO2 ) leads to the observed rate law. The chain reaction is indicated by (/) strong catalysis by Cu " ions and ill) partial and complete inhibition respectively by added Cl" and Ag" ions. The inhibition by Ag" is not indefinite, however, and takes the form of an induction period, during which time metallic silver is deposited. 

The processes by which unsaturated monomers are converted to polymers of high molecular weight exhibit the characteristics of typical chain reactions. They are readily susceptible to catalysis, photoactivation, and inhibition. The quantum yield in a photoactivated polymerization in the liquid phase may be of the order of 10 or more, expressed as the number of monomer molecules polymerized per quantum absorbed. The efficiency of certain inhibitors is of a similar magnitude, thousands of monomer molecules being prevented from polymerizing by a single molecule of the inhibitor. ... 

Lipid peroxidation (see Fig. 17.2) is a chain reaction that can be attacked in many ways. The chain reaction can be inhibited by use of radical scavengers (chain termination). Initiation of the chain reaction can be blocked by either inhibiting synthesis. of reactive oxygen species (ROS) or by use of antioxidant enzymes like superoxide dismutase (SOD), complexes of SOD and catalase. Finally, agents that chelate iron can remove free iron and thus reduce Flaber-Weiss-mediated iron/oxygen injury. 

Molecular methods used to uncover mutations are subject to several variables. The anticoagulants used for blood collection can affect digestion with restriction enzymes and amplification reactions. The type of detergent used in cell lysis can affect amplification of DNA by inhibiting the DNA-amplifying enzyme such as the taq polymerase used in the polymerase chain reaction (116). The control of contamination is crucial in ensuring the quality of results obtained by molecular analysis (117). 

G(-CO) is about 8. In the absence of oxygen, the main products are C02 (G = 2), a suboxide of carbon that is solid, and various gaseous compounds. In the presence of oxygen, the suboxide is inhibited but a chain reaction occurs, ultimately giving C02, probably through an ionic mechanism. 

Although there seems little doubt that antimony trihalides play a chemical role in inhibition of free radical chain reactions in the flame zone, a comparison... 

ET Denisov, YY Azatyan. Inhibition of Chain Reactions. London Gordon and Breach, 2000. 

As already noted (see Chapter 4), autoxidation is a degenerate branching chain reaction with a positive feedback via hydroperoxide the oxidation of RH produces ROOH that acts as an initiator of oxidation. The characteristic features of inhibited autoxidation, which are primarily due to this feedback, are the following [18,21,23,26,31-33] ... 

The duration of the inhibition period of a chain-breaking inhibitor of autoxidation is proportional to its efficiency. Indeed, with an increasing rate of chain termination, the rates of hydroperoxide formation and, hence, chain initiation decrease, which results in the lengthening of the induction period (this problem will be considered in a more detailed manner later). It should be noted that when initiated oxidation occurs as a straight chain reaction, the induction period depends on the concentration of the inhibitor, its inhibitory capacity, and the rate of initiation, but does not depend on the inhibitor efficiency. 

As shown above (see earlier) for straight chain reactions, the inhibitor is consumed at a constant rate v-Jf Similarly, during the inhibited autoxidation of RH, the inhibitor is initially consumed at a constant rate vi0/f, but then the rate of inhibitor consumption drastically increases [57,58], which leads to a rapid accumulation of hydroperoxide and the enhancement of initiation (see Figure 14.1). 

This problem was first approached in the work of Denisov [59] dealing with the autoxidation of hydrocarbon in the presence of an inhibitor, which was able to break chains in reactions with peroxyl radicals, while the radicals produced failed to contribute to chain propagation (see Chapter 5). The kinetics of inhibitor consumption and hydroperoxide accumulation were elucidated by a computer-aided numerical solution of a set of differential equations. In full agreement with the experiment, the induction period increased with the efficiency of the inhibitor characterized by the ratio of rate constants [59], An initiated inhibited reaction (vi = vi0 = const.) transforms into the autoinitiated chain reaction (vi = vio + k3[ROOH] > vi0) if the following condition is satisfied. 

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