Random Interstratification in Organophilic Bentonites

Abstract--The exchange of Na, K, and Ca ions in vermiculite has been studied between 50 and 1500C at a total normality of 0.1. The free energy changes were negative in the Na ~ K, Ca ~ K, and Na ~ Ca exchange reactions, and the cation preference in the vermiculite was Na < Ca < K in the temperature range examined. The enthalpy changes, calculated by application of the van't Hoffequation to the relation between equilibrium constant and temperature, were positive. The cation preference in the vermiculite seems to have been largely controlled by the increase in entropy which was due to the positive values of the entropy change term in the solid for the Na-K and Ca-K exchanges and the positive values of the entropy change in the solution for the Na-Ca exchange. From a thermodynamic analysis of the cationmixing properties in vermiculite, the observed free energy change in the Na-K exchange was determined solely by the differences of the intrinsic electrostatic binding energy of the cations on the clay surface. That in the Na-Ca exchange was interpreted by taking into account an extra interaction energy of Ca-Ca pairs in addition to the intrinsic energy change. Furthermore, an additional interaction energy between K ions and the clay surface appears to have been added to the free energy change in the Ca-K exchange. In the Na ~ K and Ca ~ K exchange reactions a structural modification occurred in the K-equivalent fraction (RI0 range 0.05--0.6, and a regularly interstratified phase of 15-A and 10-A members was formed at 0.05 < Y(K < 0.4.

Section: Formation Of Interstratified Phasecontrasting

confidence: 97%

Section: Formation Of Interstratified Phasementioning

confidence: 80%

Thermodynamic Study of Na-K-Ca Exchange Reactions in Vermiculite

Inoue

1984

“…The interstratification phenomenon in the intermediate range of cationic composition has been reported for various cation pairs: Ca-Na (McAtee, 1956), Ca-K (Chaussidon, 1963), and Cu-Na (McBride, 1976).…”

Section: Introductionmentioning

confidence: 88%

Ca-K Exchange Reaction and Interstratification in Montmorillonite

Inoue

1979

Abstract--Cation-exchange equilibrium for Ca-K-montmorillonite was studied at 35 ~ 50 ~ and 90~ and at three total normalities of the equilibrium solution (0.1, 0.05, and 0.01 N). Changes of the standard free energy for the exchange from K-montmorillonite to Ca-montmorillonite were determined to be -53, -270, and -393 cal/eq at 35 ~ 50 ~ and 90~ respectively. Changes of the standard enthalpy and entropy were 1.7 kcal/eq and 5.6 cal/eq/degree at 35~ respectively. The sign of the change of the standard free energy was found to be determined mainly by the entropy change, in particular, by the hydration entropy of the cations.The calculation of the excess functions indicates that the mixing model of Ca-K-montmorillonite approximates that of a regular solution. Montmorillonite having potassium equivalent ion fraction of 0.1 to 0.7 consists of a random interstratification of Ca-montmorillonite (15.6 ]~) and K-montmorillonite (12.6/~).

“…For the silicate layer, the coordinates of muscovite (Radoslovich, 1960) were used. Since the influence of the interlayer material may also be important (McAtee, 1958), a 50 per cent occupancy of each layer by alkylammonium ions was adopted. The intensity function reveals that the apparent spacing d~ol varies between 13"6 and 17.6 & following the composition of the mixture.…”

Section: Methods Of Investigation (A) Relation Between Critical Chain mentioning

confidence: 99%

The Heterogeneity of the Charge Density in Montmorillonites

Stul¹

1974

Abstract--The heterogeneity of the interlayer cation density and the corresponding mean layer charge density due to isomorphous substitution have been determined for six montmorillonite samples. This has been achieved by considering the transition of a monolayer to a double layer complex with alkylammonium ions. The transition is related to the interlayer cation density, together with the variation of the apparent spacings, which in turn is related to the composition of this two-component mixture.All the samples showed a heterogeneous interlayer cation distribution and a differing mean charge density.