Single layered polysilicate kanemite (NaHSi2O5·3H2O) was allowed to react with alkyltrimethylammonium chloride solutions to form alkyltrimethylammonium–kanemite complexes. During the organic intercalation, the SiO2 layers in the complexes were condensed to form three-dimensional SiO2 networks. The calcined products of the complexes had micro pores 2–4 nm in diameter, and the surface areas were ca. 900 m2g−1. The pore size of the calcined products was altered with the variation in the alkyl-chain length of the alkyltrimethylammonium ions employed.

The preparation of alkyltrimethylammonium-kanemite complexes and their conversion to microporous materials.

The relevance of EXAFS for studying the structure of glass is reviewed. Examples are taken from recent work on SiOx films, soda silica glasses, calcium and iron containing mineral glasses and amorphous biogenic phosphates. The sensitivity of the environment of modifiers to the morphology of the glass network is stressed. The concepts underlying a modified random network (MRN) are introduced and are discussed in relation to the rheological and diffusion properties of glasses.

EXAFS and the structure of glass

The Raman scattering intensity of the 1100 cm−1 polarized band, which appears on the addition of Na2O to SiO2 glass, reaches a maximum at the disilicate composition. The intensity of the polarized band at 950 cm−1 increases sharply as the Na2O concentration increases above 30 mole %. These data were interpreted by normal mode calculations and by IR and Raman intensity calculations for the silicate anion structural units: SiO4 isolated tetrahedra, Si2O7 dimers, Si2O6 chain links, Si2O5 sheet units, and Si2O4 framework units. According to these simplified models, the polarized high frequency band is due to symmetric stretching of Si–O− nonbridging bonds and the frequency increases with degree of polymerization of the tetrahedra. The previous assignments of the 1100 cm−1 band to the symmetric stretch of tetrahedra containing one nonbridging oxygen and of the 950 cm−1 band to the symmetric stretch of tetrahedra containing two nonbridging oxygens were confirmed. The other main feature of the alkali silicate gl...

Raman spectroscopic investigation of the structure of silicate glasses. III. Raman intensities and structural units in sodium silicate glasses

Normal Raman spectra of xM2O · (100 − x)SiO2 glasses (M = Li, Na, K, Rb, Cs and x = 0, 5, 10, 15, 20, 25, 30) and differential Raman spectra of the 5, 10, and 15% M2O glasses are presented. The Raman spectra reflect distinct structural differences in the silicate networks of these glasses caused by the presence of different alkali cation types. The structural origin and localization of vibrational modes producing characteristic spectral bands of these glasses are discussed. Bands in the 900–1200 cm−1 region of the spectra of the alkali-silicated glasses result from highly localized Si-nonbridging oxygen stretching modes and relative intensities of these bands may be used to determine alkali distributions around SiO4 tetrahedra. Comparison of the Raman Spectra of the alkali-silicate glasses has shown that smaller alkali cations exhibit a greater tendency than their larger counterparts to cluster in pairs around SiO4 tetrahedra in these glasses, even at low alkali contents. The high frequency spectral features at 1100 and 1150 cm−1 also indicate the presence of two distinct structural environments in which an SiO4 tetrahedron contains one nonbridging oxygen in all alkali-silicate glasses containing ⩽ 25% M2M except those containing lithium. Intensity of the low frequency spectral band at 440 cm−1 indicates that regional alkali clustering such as that required for phase separation is also more prevalent in glasses containing smaller alkali cations. It is proposed that modeling of the silicate structure in alkali-silicate glasses must account for both long-range and localized alkali cation distribution.

The structure of high-silica alkali-silicate glasses. A Raman spectroscopic investigation

Extended X-ray absorption fine structure is used to study local order in silicate glasses around sodium and silicon atoms. It is demonstrated that modifying cations like sodium have well-defined short range order that is complementary rather than incidental to the glass forming silicate network.

D. W. J. Cruickshank

Papers

The crystal structure of α-Na2Si2O5