Clinoptilolite: the distribution of potassium atoms and its role in thermal stability

Zeitschrift fur Kristallographie - Crystalline Materials - Tập 145 Số 3-4 - Trang 216-239 - 1977
Koyama, Takéuchi

Tóm tắt

Abstract The crystal structure of clinoptilolite has been worked out, based on C2/m, using two crystals from two different localities: one from Kuruma Pass, Japan, a = 17.660(4) Å, b = 17.963(5) Å, c = 7.400(3) Å, β = 116.47(3)°, and the other from Agoura, U. S. A., a = 17.662(4) Å, b = 17.911(5) Å, c = 7.407(3) Å, β = 116.40(3)°. In the tetrahedral framework of the heulandite type there are recognized four kinds of main cation positions, M(l), M(2), M(3), and M(4). At M(l) and M(2), which have so far been known as cation positions in the heulandite structure, Na and C'a are located ; M(l) tends to accommodate more Na than M(2). The new position, M(3), which is specific for K, is located almost at the center of the eight-membered ring of the channel parallel to a. This position is coordinated by six framework oxygen atoms and three water molecules. At M(4), which is octahedrally coordinated by six water molecules, Mg is located. It is very likely that these four positions are characteristic of all members of the heulandite-group zeolites. The difference between clinoptilolite and heulandite is primarily in the difference of site content: for clinoptilolite, M(l) and M(2) are rich in Na, while for heulandite, they are rich in Ca. The occupancy of K at M(3) in clinoptilolite is, in general, higher than that of heulandite. The location and coordination of K explain the evidence that the presence of K in the structure is one of the controlling factors of the thermal behaviour of the heulandite-group zeolites.

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Zeitschrift fur Kristallographie - Crystalline Materials

Tập 145 Số 3-4

216-239

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