Stages propagation

Effects of compounds observable at lower concentrations ai e probably connected with the effect on the initiation/termination stages (transition metals in TMB-0, reaction with photoinitiation, UDMH in the same reaction with chemical initiation), while the compounds influencing only at higher concentrations may affect chain propagation stages. 

Since pp of the metal within the crevice is raised by the decrease in pH, the metal is active whereas the outer surface is passive, and this represents the active propagation stage of crevice corrosion there is a significant IR drop between the two zones. 

EM). The initiation is a nucleophilic attack of water, which is probably contained in the enzyme, onto the acyl carbon of the intermediate to produce m-hy-droxycarboxylic acid (n= 1), the shortest propagating species. In the propagation stage, the intermediate is nucleophilically attacked by the terminal hydroxyl group of a propagating polymer to produce a one-unit-more elongated polymer chain. 

A mathematical program developed and checked for this purpose (35) has been used to determine the three parameters rA, rB, and which determine the shapes of the curves. Table IV uses as examples the values obtained (6) for rA, rB, and in a homogeneous family such as ethers which are treated in co-oxidation with cumene, Tetralin, cyclohexene, and among themselves. The reactivity in the propagation stage depends much more on the substrate attacked than on the attacking radical. This hypothesis, moreover, is confirmed by the values of the product of rA X t b, values which are and have to be quite close to 1 (18,19). 

Relatively large molecules are transformed by chain reactions, in which product distribution is defined by the limiting chain propagation stages. For example, Benson [12] presents the following version of -butane cracking ... 

The propagation stages of the cationic polymerization are not well understood. Egusa et al. have claimed that the long-lived absorption at 340 nm observed from the styrene solution in n-butyl chloride might be due to the bonded-trimer radical cation St St St4 which was formed by the reaction of a bonded dimer cation with a styrene monomer [24]. 

When some critical crack length (between 200 pm and 400 pm, i.e. about 15% of the contact diameter) is reached, a brittle propagation stage is observed which is associated with a sudden and drastic drop in the lateral stiffness, K. The measured crack width in the plane of the contact is then of the order of magnitude of the contact diameter. Post-mortem microscope observation of specimen cross sections in the contact zone (Fig. 8) indicates that the depth of the cracks is of the order of magnitude of the contact radius (i.e. about 900 pm). The two deep cracks induced at the edge of the contact may thus be viewed as some kind of half-penny cracks whose radii are approximately equal to the radius of the contact. In the subsequent part of this paper, the two deep cracks will be referred to as primary cracks . 

The second part of the investigation was directed toward the understanding of the crack propagation stages. Two questions were especially addressed (i) the determination of the transition from fatigue to brittle fracture (ii) the determination of the crack arrest conditions. Within the frame of linear elastic fracture mechanics, such an analysis requires the... 

Fig.s 9 and 10 show results obtained for the propagation stage on HDPE-1 and HDPE-2 respectively. 

Note, that in both the EXCEL equations only absolute notation is used to distinguish cells containing fixed values, from those which changes during the propagation stages. 

The beginning of the polymerization requires an activation of the monomers, whether it is thermal, photochemical, by free radicals, or ionic, which allows the binding of the activated monomer in the propagation stage this way, lineal or branched polymeric chains are produced, depending on the chemical characteristics of the monomer used. 

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