Alkali ion mobility and exchange equilibriums in silica glass

Flinn, David R.; Stern, Kurt H.

doi:10.1021/j100651a021

Cited by 8 publications

(1 citation statement)

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“…In a first step, thermodynamic equilibrium constants * values for E from Kleppa and Hersh (1961) for nitrate mixtures at 310 and 350 ~ C, and from Kleppa et al (1963) for chloride mixtures at 800 ~ C AGI = (Xrnax--Xmin)'(AGBx--AGAx) from tabulated values (Flinn and Stern 1972) for the difference in the free enthalpies of formation (AGBx-AGAx) of the pure salts (BX and AX) at the temperature of interest K were evaluated from graphical integration of the Kielland (lnKc against XA) plots, which corresponds to the procedure of Gaines and Thomas (1953) using the simplified expression in K = ~ in Kc d2A (2) for uni-uni-valent exchange. The equilibrium coefficients Kc are given from the isotherms by…”

Section: Energy Balance Of Reactions and Relative Stability Of The Phmentioning

confidence: 99%

Ion exchange between tectosilicates with the nepheline-kalsilite framework and molten MNO3 or MO (M = Li, Na, K, Ag)

Sobrados

Gregorkiewitz

1993

Phys Chem Minerals

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Abstract. Natural nepheline, a synthetic Na-rich nepheline, and synthetic kalsilite were ion exchanged in molten MNO3 or MC1 (M=Li, Na, K, Ag) at 220-800 ~ C. Crystalline products were characterized by wet chemical and electron microprobe analysis, single crystal and powder X-ray diffraction, and transmission electron microscopy and diffraction. Two new compounds were obtained: Li-exchanged nepheline with a formula near (Li,Ko.3,D)Li~[A13(A1,Si)Si~O16] and a monoclinic unit cell with a=951.0(6) b=976.1(6) c=822.9(5) pm 7= 119.15 ~ and Ag-exchanged nepheline with a formula near (K,Na, D)Ag3[At3(A1,Si)Si40~6] and a hexagonal unit cell with a = 1007.4(8) c = 838.2(1.0) pm. Both compounds apparently retain the framework topology of the starting material. Ion exchange isotherms and structural data show that immiscibility between the end members is a general feature in the systems Na-Li, Na-Ag, and Na-K. For the system Na-K, a stepwise exchange is observed with (K,D)Na3[A13(AI,Si)Si40~6] as an intermediate composition which has the nepheline structure and is miscible with the sodian end member (Na,D)Na3[A13-(A1,Si)Si40~6], but not with the potassian end member (K,D)4[A13(A1,Si)Si4Oa6] which shows the kalsilite structure; there was no indication for the formation of trior tetrakalsilite (K/(K + Na) ~ 0.7) at the temperatures studied (350 and 800 ~ C). The exact amount of vacancies [] on the alkali site depends upon the starting material and was found to be conserved during exchange, with ca 0-0.2 and 0.3-0.4 vacancies per 16 oxygen atoms for the synthetic and natural precursors, respectively. Thermodynamic interpretation of the Na-K exchange isotherms shows, as one important result, that the sodian end member is unstable with respect to the intermediate at K/(K +Na)~ 0.25 by an amount of ca 45 kJ/mol Na in the large cavity at 800 ~ C (52 kJ/mol at 350 ~ C).

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