Acceleratory effect

While it is generally true to state that reaction rates increase with temperature, such a qualitative statement is not specific enough to be useful and in some circumstances can be incorrect, e.g. at high a values when the deceleratory character of the reaction may be sufficiently great to offset the acceleratory effect of a slow temperature rise. 

Similar results have been found for the electron exchange between [Fe(CN)s]3 and [Fe(CN)6]4. In that case, the acceleratory effects are found to vary with the nature of the cation in the order... 

Ten years later Napper and Alexander, in studying the kinetics of vinyl acetate polymerization in the presence of anionic, cationic and nonionic emulsifiers arrived at the same conclusions as Priest s, although they did not cite his work (13). They also observed an acceleratory effect of added emulsifier like that found by Baxendale et al. (8), but they seemed unaware of that work as well. They showed that when the charge on primary particles (due to initiator fragments) was opposite to that of the emulsifier, the rate of polymerization was slower than that in the absence of emulsifier. This was presumably due to the greater instability of the colloid formed and the consequent production of fewer polymerizing centers. 

There is little information of the chemisorption of water on gold surfaces, although its presence has a marked acceleratory effect on the rate of carbon monoxide oxidation over Au/Si02 132 since the support is not expected to be involved in the reaction, it was considered that it might help the adsorption of oxygen on gold panicles. Water occupies oxygen vacancies on... 

Similar results have been found for the electron exchange between [Fe(CN)6]3 and [Fe(CN)e]4. In that case, the acceleratory effects are found to vary with the nature of the cation in the order Cs+ > Rb+ > K+ NH4+ > Na+ > Fi+, in accord with the size and solvation effects discussed earlier. For +2 ions, the order of effect on the rate is Sr2+ > Ca2+ > Mg2+, which is also in accord with the softness of these species. Exchange in these outer sphere cases is believed to involve the formation of bridged species containing cations that are probably only partially solvated. 

While the effect of the hydroxylic solvent on k2 cannot be quantified, it would be expected to accelerate it. The work of Hickey and Maitlis (19) involved the use of nonhydroxylic solvents, in which this accelerating effect is not available, and the assumption that k2 is fast under these conditions may not be justified. It is even possible that it may be slowed to the extent that it contributes to the rate-limiting step. If this is the case, the rate enhancements observed in their work might also be attributable to the acceleration of the k2 step by the Lewis acid countercations. Such effects of cations on migratory insertions are expected to be more important under their experimental conditions, where ion pairing was acknowledged to be significant. However, while this alternative explanation may appear to be consistent with the available data, we must emphasize that it is speculative. Certainly, more detailed studies are required to determine definitively the reason for this acceleratory effect. 

Urine from adult intact male mice accelerates puberty in young females (Vandenbergh, 1969 Kennedy and Brown, 1970 Colby and Vandenbergh, 1974). This acceleratory effect is even greater when the male is actually present with the young female mouse (Andervont, 1944 Vandenbergh, 1967) due to... 

The simultaneous treatment of young females with urine from females in estrus and either male urine or urine from pregnant or lactating females does not enhance the acceleratory effect. However, the simultaneous treatment of subjects with the urine of females in estrus and urine from grouped females results in delayed puberty (Drickamer, unpub.). 

Three of the four urinary chemosignals thus far explored in house mice have acceleratory effects on puberty and/or enhancing effects on the estrous cycles of adult females. It may be that these urinary... 

Hexamethylguandinium chlorides have been found to exhibit a pronounced acceleratory effect on the polymerization of both caprolactam and 2-pyrrolidone for systems initiated by alkali metal salts of these lactams. A series of papers have investigated the effect of reaction variables on the polymerization of 2-pyr-... 

The current if has been recently described as the one which controls the pacemaker activity of cardiac SA node cells and mediates the acceleratory effect of adrenaline (Brown, DiFrancesco Noble, 1979a). In this respect, i.e. in the voltage range of activation and in the response to adrenaline, i is similar to another current already described in the heart, the current i 2 Purkinje fibre... 

The rate of hydration of tricalcium silicate in the presence of different amounts of calcium formate (0.5%-6.0%) has been reported by Singh and Abha.i Calcium formate accelerates the tricalcium silicate hydration at 2% addition. It is speculated that in the presence of formate the protective layer on the silicate surface is ruptured, resulting in an acceleratory effect. 

The hydration of C2S is also accelerated by calcium formate. The increase in compressive strength of formate-treated dicalcium silicate samples in relation to the reference sample is evidence of an acceleratory effect (Fig. 

The relative acceleratory effects of calcium chloride, calcium nitrate, and sodium thiocyanate on cement have been studied.The total heat is higher in the presence of all accelerators. Calcium chloride addition results in the maximum amount of heat. Sodium thiocyanate accelerates better than calcium nitrate. Calcium nitrate works well at early stages, but sodium thiocyanate is more effective at later ages. Sodium molybdate and trioxide also have an acceleratory effect. 

Alkalis, such as NaOH, and Na salts of carbonate, aluminate, and silicate are known to accelerate the hydration of cement and cause early stiffening. In the hydration of tricalcium silicate with NaOH, there was an acceleratory effect even up to 28 days. After 7 days however, the strength of the reference was higher than that containing NaOH.[ l Evidence was also obtained for the incorporation of Na in the hydrated product. 

There has been continued interest in developing an organic-based accelerator. Ramachandran and coworkers studied the effect of o, m, and p-nitrobenzoic acids on the hydration of tricalcium silicate.The m and p nitrobenzoic acids acted as accelerators. The acceleratory effect was attributed to the complex formation between the organic compound and the C-S-H phase on the surface of the tricalcium silicate phase. 

Fig. 23).The peak occurs earlier and the amount of heat developed in the sample withNaOH is higher, even up to 28 days. The acceleratory effect does not reflect in increased strengths. The lower strengths inNaOH treated samples is attributable to the plate-like and reticular morphology of the hydration product with poor bonding characteristics. 

Portland cement is an accelerator for CAC and vice versa. The effect of proportions of each component on setting time is illustrated in Fig. 4. Ternary blends of portland blast-furnace cement and CAC also have an acceleratory effect. 

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