Incomplete hydration

Still with the prebiotic scenario, the conditions developed by Limtrakul et al. (1985) are interesting as a consequence of evaporation, high local concentrations may have arisen, and under such conditions the incompletely hydrated metal ions may activate a dehydration leading to peptide condensation. From this, the technique of the salt induced peptide condensation (SIPC) has been developed (Oie et al, 1983 Suwannachst and Rode, 1999 Rode et al, 1999). 

Indeed, our analysis suggests that the H ions produced during the electrolysis reaction undergo removal from the photoanode surface region much less readily than would be expected for simple diffusion. A possible, more complete, explanation may be that the H+ ion is produced on the surface with an incomplete hydration sheath, facilitating a direct H " ion/electrode... 

There are many deficiencies associated with unmodified cement mortars, such as the potential for incomplete hydration (especially in thin sections), poor adhesion and the high water level needed for adequate workability. Above all, cement is a brittle product with low flexural strength, impact resistance and abrasion resistance (Rohm Haas, 1989). 

Type Bin. Although there is sufficient water to hydrate M completely, not only is there incomplete hydration of the cations but there are H2O molecules not attached to cations. 

ABSTRACT In the frame of calcium sulfate p-hcmihydratc hydration kinetical studies, a simple experimental set up has been developed to determine the rate of hydration for different species of incompletely hydrated plaster specimens. This apparatus may also be used to determine widi accuracy the amount of gypsum contained in plaster rocks, and acquire simultaneously quantitative analysis for six specimens. The apparatus is described, and the effect of vapor pressure is studied. 

Experimental results on incompletely hydrated plaster specimens show that either the weight loss or the integration curves allow the determination of the hydration ratio of the specimen with high accuracy. Il has been experimentally shown that the amount of heat involved in the hydration reaction is proportional all along the reaction to the conversion rate. 

Properties and reactivity of a calcium sulfate 3-hemihydrate are widely dependant on the preparation procedure. Although kinetical studies on the hydration reaction are done by a number of researchers, there is no standard procedure to elaborate a stable, reproducible calcium -hemihydrate specimen. This paper presents a very simple apparatus and an experimental procedure setup to elaborate a specimen that is stable and allows kinetical studies even after a long time of conservation. This apparatus also allows the simultaneous determination of the hydration rate for six different species of incompletely hydrated plasters and demonstrates experimentally that the amount of heat involved in the hydration... 

As gypsum dehydration is realized in quite reproducible conditions, the reactor may be used to determine with accuracy, the amount of gypsum contained in a plaster rock or an incompletely hydrated plaster. 

With a very simple apparatus and experimental procedure it is possible to elaborate a stable, reproducible standard specimen for kinetic studies. With this apparatus, the hydration ratio of incompletely hydrated plasters or plaster rocks can be determined with accuracy. Finally this apparatus demonstrates experi-... 

Karmazsin s paper describes a simple apparatus for measuring the degree of hydration of plaster and gypsum rock. The reactor consists of a vertical stainless steel cylinder capable of holding six small stainless steel sample tubes that are suspended from the removable roof of the cylinder by a stainless steel thermocouple well. The cylinder is fitted with a heater controlled by an external thermocouple, and a reservoir containing water vapor at 81% relative humidity is connected to the reactor. The reactor may be used to determine accurately the amount of dihydrate in either gypsum rock or incompletely hydrated plaster. 

It should be noted that the above definitions of pH are based on an assumption that the solution is behaving in an ideal nature meaning that the thermodynamic activity is equal to concentration (e.g., what happens when the dilution is infinite). However, as the concentration increases, ionic attraction and incomplete hydration results in a decrease in the effective concentration (or the activity). This activity is defined as the "apparent concentration" of an ionic species, which is due to the attraction that ions exert on one another, and the incomplete hydration of ions in solutions that are too concentrated. The lower the concentration, the less is the interaction. At infinite dilution, activity coefficients approach unity. 

Few studies have been made on transport processes involving concentrated solutions. In the concentrated solutions, in the range of dehydrated melt formation, incompletely hydrated melts and anhydrous salt melts, various structural models are described to define their properties, i.e. the free-volume model, the lattice-model and the quasi-crystalline model. Measured and calculated transport phenomena do not always represent simple ion migration of individual particles, but instead we sometimes find them to be complicated cooperative effects (27). 

A single and minute pectin particle will go into water solution readily, but when many such particles are added all at once to water, not all can dissolve instantly as single particles. Some of the incompletely hydrated, swollen but undissolved particles adhere to adjacent ones and usually entrap the less completely... 

The surface of the concrete substrate has to be prepared to provide sufficient bond of the repair material. Factors that may affect the bond are the strength and integrity of the substrate, the cleanliness of the surface, and the roughness. The surface should be rough and dust or incoherent residues should be removed (for instance by sandblasting or waterblasting). This operation is usually not necessary if hydro-demohtion has been used. If the cementitious repair material is appHed directly on the surface of the concrete, the surface should be saturated by water in order to avoid absorption of water from the substrate and subsequent plastic shrinkage and incomplete hydration of the repair material, which will result in loss of bond. 

Zjo corresponded to the number water molecules that could not contribute to the bulk water process due to hydration of the surfactant molecules. The Z o values for ChEOio and ChEOis were estimated as 40-45 and 55-65 molecules, respectively [33], Correspondingly, -4-4.5 water molecules were found to be hydrated per oxyethylene unit. Based on the analysis of Zgo, fuUy hydrated micelles were present with nearly no bulk water when Ws > -0.5, which was consistent with the boundaries of the h and Hi phases. A further reduction of the water content resulted in reduction of hydrated water and incomplete hydration of the oxyethylene chains. 

During the setting of a cement, a large amount of added water will be used to form hydrate phases such as C-S-H, portlandite, and AFt and AFm phases. Yet, even after complete hydration some free water will remain confined within the porous C-S-H gel and the capillary pore spaces. Notably, this occurs when surplus water is added so that the water/cement (W/C) ratio exceeds 0.6. A lack of water (W/C raho <0.2) results in an incomplete hydration of clinker minerals. The optimum W/C raho for Portland cement, leading to maximum strength, is 0.3 < W/C < 0.5. 

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