Kinetics of hydration

The kinetics of setting of cement depends on the rate of hydration of the individual 

This situation has been nicknamed ... the fight for survival of the primary clinker phases.  

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A controversy exists regarding the early stages of formation of gas hydrates. The mechanism proposed by Sloan and Fleyfel [384,613,1637] for the kinetics of hydrate formation is composed of... 

R. L. Christiansen and E. D. Sloan, Jr. Mechanics and kinetics of hydrate formation. In Proceedings Volume, pages 283-305. New York... 

O. B. Kutergin, V. P. Melnikov, and A. N. Nesterov. Effect of surface-active agents on the mechanism and kinetics of hydrate formation of gases. Dokl Akad Nauk Sssr, 323(3) 549-553, 1992. 

The experiments were conducted at four different temperatures for each gas. At each temperature experiments were performed at different pressures. A total of 14 and 11 experiments were performed for methane and ethane respectively. Based on crystallization theory, and the two film theory for gas-liquid mass transfer Englezos et al. (1987) formulated five differential equations to describe the kinetics of hydrate formation in the vessel and the associate mass transfer rates. The governing ODEs are given next. 

However, this simple picture only applies to gases that do not undergo reactions in the boundary layers. For gases that do react, for example through hydration and acid-base reactions, the net flux depends on the simultaneous movement of all the solutes involved, and the flux will not be the simple function of concentration expressed in Equation (3.25). An example is CO2, which reacts with water to form carbonic acid and carbonate species-H2C03, HCOs and COs . The situation is complicated because the exchange of H+ ions in the carbonate equilibria results in a pH gradient across the still layer, and it is therefore necessary to account for the movement of H+ ions across the still layer as well as the movement of carbonate species. The situation is further complicated in the case of CO2 by the kinetics of hydration and dehydration, which may be slow in comparison with transport. 

If water will normally form ice in the absence of a solute molecule, the question arises about the mechanism for forming a clathrate with an exact structure, when the solubility of hydrocarbon molecules in liquid water is known to be small (or negligible in ice), relative to the amount of hydrocarbon needed for hydrates. Thus, along with the definition of what the hydrate structures are, comes the logical question of how these structures form. During the past two decades, sophisticated experimental and modeling tools have been applied to address this question. The microscopic mechanism and the macroscopic kinetics of hydrate formation are the major considerations of Chapter 3. 

The kinetics of nucleation of one-component gas hydrates in aqueous solution have been analyzed by Kashchiev and Firoozabadi (2002b). Expressions were derived for the stationary rate of hydrate nucleation,./, for heterogeneous nucleation at the solution-gas interface or on solid substrates, and also for the special case of homogeneous nucleation. Kashchiev and Firoozabadi s work on the kinetics of hydrate nucleation provides a detailed examination of the mechanisms and kinetic expressions for hydrate nucleation, which are based on classical nucleation theory. Kashchiev and Firoozabadi s (2002b) work is only briefly summarized here, and for more details the reader is referred to the original references. 

The inhibition of three-phase hydrate formation is discussed in Section 4.4. These predictions enable answers to such questions as, How much methanol (or other inhibitor) is required in the free water phase to prevent hydrates at the pressures and temperatures of operation Classical empirical techniques such as that of Hammerschmidt (1934) are suitable for hand calculation and provide a qualitative understanding of inhibitor effects. It should be noted that only thermodynamic inhibitors are considered here. The new low-dosage hydrate inhibitors [LDHIs, such as kinetic inhibitors (KIs) or antiagglomerants (AAs)] do not significantly affect the thermodynamics but the kinetics of hydrate formation LDHIs are considered in Chapter 8. 

This chapter deals with macro-, meso-, and molecular-level thermodynamic and transport hydrate properties of natural gas and condensate components, with and without solute. The feasibility of using these tools to measure the kinetics of hydrate formation and decomposition are also briefly discussed, while the results of these measurements have been discussed in Chapter 3. The results for insoluble substances such as porous media are discussed in Chapter 7. 

New, low dosage hydrate inhibitors (LDHIs) are being commonly used in the industry, based upon the kinetics of hydrate formation. 

It is this unpredictable and puzzling chemical reactivity which makes freshly formed silica dust a chemical poison that causes silicosis when it is inhaled. In many processes which deal with mineral products—e.g., the setting of cements, the milling of enamels and of pigments, the slaking of lime, etc.—solids with freshly formed surfaces are brought into contact with water. For understanding these phenomena the kinetics of hydration of incompletely screened surfaces has to be considered. 

R,8R)-dihydrodiol from the (+)-(7R,8S)-oxide at low conversion. A similar situation has been proposed to explain the kinetics of hydration of the enantiomers of styrene 7,8-oxide. 

Also the allylic exchange work indicated that nucleophiles do not like to attack the negatively charged monomeric it complex (Section III, B, 1). Furthermore, the kinetics of hydration of vinyl esters in wet acetic... 

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