Effect of Magnesium and Zinc Ions on the Hydration Kinetics of C3S

Impure tricalcium silicate (C3S) in portland cement may contain various foreign ions. These ions can stabilize different polymorphs of C3S at room temperature and may affect its reactivity. In this paper, the effects of magnesium and zinc on the polymorph type, hydration kinetics, and the hydrate morphology of C3S were investigated. The pure C3S has the T1 structure while magnesium and zinc stabilize polymorphs M3 and T2/T3, respectively. The two elements have distinct effects on the hydration kinetics. Zinc increases the maximum heat released. Magnesium increases the hydration peak width. The C-S-H morphology is modified, leading to longer needles in the presence of zinc and thicker needles in the presence of magnesium. Zinc is incorporated into C-S-H, while magnesium is only incorporated slightly, if at all, but rather seems to inhibit nucleation. Implementing experimentally measured parameters for C-S-H nucleation and growth in the ic hydration model captured well the observed changes in hydration kinetics. This supports C-S-H nucleation and growth to be rate controlling in the hydration of C3S.

HYDRATION OF TRICALCIUM ALUMINATE AND TETRACALCIUM ALUMINOFERRITE IN THE PRESENCE OF CALCIUM SULFATE

Karen Scrivener

It is the purpose of this report to summarize the state of knowledge regarding the hydration of C//3A and C//4AF in the presence of calcium sulfate at ordinary temperatures. These interstitial phases in combination with calcium sulfate may comprise up to 20 percent of portland cement and their hydration reactions affect rheological properties, early strength gain characteristics, and durability. Within limitations, reported results are related to the hydration of the interstitial phases in portland cement. Although C//3A and C//4AF are used as models for the interstitial phases in portland cement, two factors may lead to differences in the hydration behavior of the pure phases and the interstitial phases in cement paste. First, in the manufacture of cement, extensive substitution may occur resulting in the formation of anhydrous aluminate and ferrite solid solutions of variable composition. Second, the interstitial phases in commercial cements hydrate in the presence of other phases. These factors may result in significant variations in the rates, and possibly, in the mechanisms of interstitial phase hydration in commercial cements.

1986

Microhydration Effects on the Encapsulation of Potassium Ion by Dibenzo-18-Crown-6

Yoshiya Inokuchi, Thomas Rizzo

We have measured electronic and conformer-specific vibrational spectra of hydrated dibenzo-18-crown-6 (DB18C6) complexes with potassium ion, K+center dot DB18C6 center dot(H2O)(n) (n = 1-5), in a cold, 22-pole ion trap. We also present for comparison spectra of Rb+center dot DB18C6 center dot(H2O)(3) and Cs+center dot DB18C6 center dot(H2O)(3) complexes. We determine the number and the structure of conformers by analyzing the spectra with the aid of quantum chemical calculations. The K+center dot DB18C6 center dot(H2O)(1) complex has only one conformer under the conditions of our experiment. For K+center dot DB18C6 center dot(H2O)(n) with n = 2 and 3, there are at least two conformers even under the cold conditions, whereas Rb+center dot DB18C6 center dot(H2O)(3) and Cs+center dot DB18C6 center dot(H2O)(3) each exhibit only one isomer. The difference can be explained by the optimum matching in size between the K+ ion and the crown cavity; because the K+ ion can be deeply encapsulated by DB18C6 and the interaction between the K+ ion and the H2O molecules becomes weak, different kinds of hydration geometries can occur for the K+center dot DB18C6 complex, giving multiple conformations in the experiment. For K+center dot DB18C6 center dot(H2O)(n) (n = 4 and 5) complexes, only a single isomer is found. This is attributed to a cooperative effect of the H2O molecules on the hydration of K+center dot DB18C6; the H2O molecules form a ring, which is bound on top of the K+center dot DB18C6 complex. According to the stable structure determined in this study, the K+ ion in the K+center dot DB18C6 center dot(H2O)(n) complexes tends to be pulled largely out from the crown cavity by the H2O molecules with increasing n. Multiple conformations observed for the K+ complexes will have an advantage for the effective capture of the K+ ion over the other alkali metal ions by DB18C6 because of entropic effects on the formation of hydrated complexes.

American Chemical Society2014

Microhydration Effects on the Encapsulation of Potassium Ion by Dibenzo-18-Crown-6

Yoshiya Inokuchi, Thomas Rizzo

American Chemical Society2014