Initial hydration rate

The initial hydration rate v and the equilibrium hydration amount were obtained as parameters reflecting the hydration behavior of LB films (see Figure 8). Temperature dependencies of the hydration behavior (v0and W ) of 10 layers of DMPE (Tc = 49 °C) LB films are shown in Figure 9. Large W and v0 values were observed only around the phase transition temperature (7C) of DMPE membranes. Thus, DMPE LB films were hydrated only near the Tc, but not in the solid state below the Tc and in the fluid state above the Tc. This indicates that the... 

Figure 9 Effect of temperatures on the hydration amount (O) and the initial hydration rate v0 (Z of 10 layers of DMPE LB films...

In concrete mixes made with Portland cement, the addition of microsilica increases the initial hydration rate of the cement and especially that of the alite and belite phases (Wu and Young, 1984 Huang and Feldman, 1985a, 1985b Durekovic, 1986 Lilkov et al.,... 

The reactions in the regulated-set cements containing Cjj A3CF2 (note mixed notation) as a principal phase resemble those in ordinary Portiand cements. Initial reaction rates are controlled by ettringite formation. Setting occurs with formation of the monosulfate, along with some transitory lower-limed calcium aluminate hydrates that convert to the monosulfate within a few hours. 

The rates of hydration of alkenes increase dramatically with increasing alkyl substitution (see table at left). This is usually attributed to the relative stabilities of carbocations formed as intermediates in the initial (and rate-hmiting) step of the reaction, e.g., for hydration of propene. 

Uddin et al. (2008b) conducted several depressurization simulations for the Mallik 5L-38 well. Their results showed that the Mallik gas hydrate layer with its underlying aquifer could yield significant amounts of gas originating entirely from gas hydrates, the volumes of which increased with the production rate. However, large amounts of water were also produced. Sensitivity studies indicated that the methane release from the hydrate accumulations increased with the decomposition surface area, the initial hydrate stability field (P-T conditions), and the thermal conductivity of the formation. Methane production appears to be less sensitive to the specific heat of the rock and of the gas hydrate. 

The several attempts, published in the literature, to describe the kinetics of vapour phase olefin (mostly ethylene) hydration can be classified into two groups according to the basic model used. One model, for reactions catalysed by phosphoric acid supported on solids, treats the kinetics as if the process were homogeneous acid catalysis and takes into account the acid strength of the supported acid. Thus, a semiempirical equation for the initial reaction rate [288]... 

A more likely assumption would be that the nitric oxide is not hydrated until it is released by the ferrous chelate. Since the hydration rate is so slow (18) (k 0.14 at 25 °C), the rate of reaction of Fe2+(L)(N0) + S03 no longer depends on k i, but on Keq and the hydration rate constant. Using this methodology, the calculated rates agree well with the observed rates for both Fe +(EDTA)(NO) and (NTA) (NO). For example, with initial concentrations of... 

Complexes of Fe(II), Cu(II) and Zn(II) with 1,10-phenanthroline (phen) and its hydrophobic derivatives exhibited remarkable interfacial adsorptivities, although the ligands themselves could be hardly adsorbed at the interface [40-42]. The extraction rate profiles of Fe(II) with phen and its dimethyl (DMP) and diphenyl (DPP) derivatives into chloroform were investigated using the HSS method [43]. Both the formation rate of the phen-derivative complex and the interfacial adsorptivity of the complex were remarkably dependent on the hydrophobicity of the ligand and the hydration tendency of anions. The initial extraction rate of the iron(II) complex is described by the following equation ... 

First of all, it shonld be noted that the regime of these reactions is not uniform within reaction time. As the initial hydrated oxides are solids, the reaction starts via the sohd phase mechanism. The solid phase mechanism is confirmed by the observed inflnence of initial disperse state on the interaction rate, the participation of surface acid-base centers in the reactions, the existence of concentration gradient in the surface layers of the reagents, etc. [1-8]. 

For both substrates, a-pinene and camphene, initial activity (taken as the initial reaction rate, to) shows a strong dependence on Nai (figure 3). In both hydration reactions, ro achieves a maximum value at values of Nai around 22. 

Figure 2 shows the initial activity of the catalytic composites for camphene hydration (A), expressed as the initial reaction rate calculated finm the slope of the camphene kinetic curve and the initial activity for isobomeol oxidation (B), expressed as the initial reaction rate calculated from the slope of the isobomeol kinetic curve. It was observed that the initial activity regarding camphene hydration, decreases when the crosslinking degree increases, for the catalysts Co(acac)2/PVAx (fig. 2 bar Cl > bar C2), in spite of the increase in the number of acid sites. This result, which is also in contradiction with those observed for the oxidation of isobomeol, is likely to be due to the expectable decrease in the sorption coefficient of camphene caused by the increase of the number of sulfonic groups. The same explanation may be given for the decrease in activity observed when the load of Co(acac)2trien NaY in the polymeric matrix... 

Rates of solution of calcium oxide increase rapidly with increasing temperature. Thus raising the temperature of the water used for slaking a given quicklime, results in increased primary nucleation. Moreover, as the reaction is highly exothermic, the initial hydration raises the temperature and accelerates the hydration of the coarser/less reactive particles. Reducing the water to lime ratio reduces the thermal capacity of the mix, increases the rate of temperature rise and accelerates the rate of slaking. 

Polymorphs generally dissolve more rapidly than their hydrates, but there have been reports of drug pseudopolymorphs containing, e.g., ethyl acetate or n-pentanol, which display enhanced solubilities, both in vitro and in vivo, when compared with their nonsolvated forms [25]. Figiue 12 shows powder dissolution rate curves for two polymorphs of nitrofurantoin. The significance of the curves for this system is that the retarded initial dissolution rate for the a-poly-morph may render it more favourable for pharmaceutical formulation since there is evidence that adverse side effects may be associated with rapid absorption of the -polymorph [61]. 

CO2 hydration catalyzed by 1 was followed by production at 25°C. which was detected by using a pH-indicator in buffer solution (pH 6-10). The kinetics demonstrated the catalytic nature of the zinc(II) complex 1 at various pHs. A plot of the initial rates against total zinc(II) complex concentrations (=[l]totai) indicated that the CO2 hydration rate varied linearly with [1]total and [CO2] to give an observed second-order rate constant ( at)obs- Shown in Fig. la is a plot of (kcat)obs data as a function of pH. The sigmoidal curve is characteristic of a... 

These advantageous properties do not show calciirm and magnesium oxides, which hydration rate depends primarily on the reactivity of initial substrates phases towards water. Their reactivity is primarily the fimction of burning temperature... 

Equation 14 can be solved analytically for the initial reaction rate of a metal ion catalyzed reaction between phenol and methanal. This yields an equation for both methanal and phenol consumption that is only dependent on one conversion variable. Figure 4 shows the dependence of the rate constants on the ionic radius of the hydrated cation, based on equation 14. The formation of the chelate complex between methanal, phenol and the metal ion is the slowest reaction step (see Scheme 3). Therefore, one can observe a second order kinetic law analyzing the kinetic data. 

This short initial period of rapid hydration is followed by the induction period (also called the dormant period), in which the hydration rate slows down significantly. It usually lasts several hours. 

Table 10.4 shows the effect of temperature on the rate of conversion of CAHjq and C2AHg in a humid enviromnent. The rate of conversion is temperature dependent, and increases steeply as the temperature increases. It also increases with increasing water/cement ratio. An increased temperature during the initial hydration may also accelerate the subsequent rate of conversion. The process takes place only under humid... 

Finally, team checks the gas gathering and gas sales pipeline composition, temperature and pressure to initiate hydrate prevention measures. In parallel, the team checks the pressure drop versus flow rate in inlet gas gathering pipeline to detect/predict potential hydrate problem. This is important to prevent wet-gas or off-spec gas accidental releases in related processes. 

The competitive experiments were carried out with a series of terminal al-kynes characterized by similar electronic properties but differing in portions of the molecule remote from the reaction site. For aliphatic alkyne, the three substrates ethynyl cyclohexane, 1-octyne (which represents an acyclic isomer of the former substrate), and 1-dodecyne were tested, with the free catalyst compared to the encapsulated catalyst. In the former case, after a short induction time, the initial reaction rate for the three substrates showed similar behavior for 1-dodecyne and 1-octyne, while the cyclic isomer, being slightly more electron rich, reacted 1.5 times faster (Fig. 7.8a). Encapsulation of the catalyst led to a magnification of the favorable hydration of the cyclic substrate that reacted more than twice as rapidly as the longer substrate. It is likely that extended linear substrates, that in their extended conformation are approximately 1.4 and 2.1 times longer than ethynyl cyclohexane, have to fold to better complement the residual space left available within Ihe cavity occupied by the catalyst. 

When concretes with the same moisture content are compared, resistivity is higher for the lower wIc ratio, for higher levels of hydration and for the use of additional components like fly ash, SF, etc. Resistivity increases with age and hardening of concrete because the pore system becomes less permeable there is an inverse correlation between concrete resistivity and the chloride diffusion rate. This fact is exploited for the measurement of concrete resistivity in view of assessing its susceptibility to chloride penetration and, consequently, to corrosion of reinforcement for both its initiation and rate of progress. The resistivity of external concrete cover is the most important and is expressed by the formula ... 

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