Disilicate Melt Research Articles

The microstructure of silicate varying with crystal and melt properties under the same cooling condition

Diopside dendrites and plagioclase spherulites were formed from Ab–An–Di silicate melts under exactly the same cooling conditions. The effects of crystal and melt structure on the microstructure of silicate were studied by optical microscopy and Raman spectroscopy . The results show that the anisotropy is truly an important factor in the growth pattern evolution. The phenomena can be described by the morphology diagram. In spite of the dendritic shape, diopside dendrite behaves like a single crystal, while the plagioclase spherulite is polycrystalline. The silicates crystallized from a fast-cooling silicate melt can reflect the structural characteristics of the melts, as is apparent from the Raman spectra. The growth units for silicate crystals are mainly the segments of SiO polymers with different polymerization degree other than simple ions. The structural units in the silicate melt interact strongly with the crystal at the solid and melt interface; this acts as a buffer layer for structural transform from disordered or less ordered short-range structure to long-range ordered structure. The results imply that the phase-field approach to modelling the growth patterns has a realistic basis at the atomistic scale.

The microstructure of silicate varying with crystal and melt properties under the same cooling condition

Diopside dendrites and plagioclase spherulites were formed from Ab–An–Di silicate melts under exactly the same cooling conditions. The effects of crystal and melt structure on the microstructure of silicate were studied by optical microscopy and Raman spectroscopy. The results show that the anisotropy is truly an important factor in the growth pattern evolution. The phenomena can be described by the morphology diagram. In spite of the dendritic shape, diopside dendrite behaves like a single crystal, while the plagioclase spherulite is polycrystalline. The silicates crystallized from a fast-cooling silicate melt can reflect the structural characteristics of the melts, as is apparent from the Raman spectra. The growth units for silicate crystals are mainly the segments of SiO polymers with different polymerization degree other than simple ions. The structural units in the silicate melt interact strongly with the crystal at the solid and melt interface; this acts as a buffer layer for structural transform from disordered or less ordered short-range structure to long-range ordered structure. The results imply that the phase-field approach to modelling the growth patterns has a realistic basis at the atomistic scale.

The Effect of Fe3+ Ions on the Anionic Structure of Iron-bearing Sodium Silicate Melts.

The effects of the coordination of iron ions on the anionic structure of molten iron bearing sodium silicate slags at 1 273 K have been investigated by Raman spectroscopy. The Raman spectra of Na 2 O-SiO 2 -FeO-Fe 2 O 3 system equilibrated with various oxygen pressures (pO 2 ) have been measured. The effect of the concentration of iron oxide on the Raman spectra of these systems has also been studied. Under low pO 2 conditions (CO 2 /CO 54), a new Raman band of around 900 cm -1 appears and its intensity increases with increase of pO 2 and iron oxide content. The scattering intensity at low frequency region (<550 cm -1 ) also becomes intense with increase of the iron oxide content. It is confirmed that the near 900 cm -1 band can be attributable to the network structure involving Fe 3+ ions. Fe 3+ ions in the metasilicate melts is found to conjugate the chain units and produce the sheet and monomer units. In the disilicate melts, it will conjugate the sheet units and produce the chain and three-cimensional network units.

Compressibility of titanosilicate melts

The effect of composition on the relaxed adiabatic bulk modulus (K0) of a range of alkali- and alkaline earth-titanosilicate [X 2 n/n+ TiSiO5 (X=Li, Na, K, Rb, Cs, Ca, Sr, Ba)] melts has been investigated. The relaxed bulk moduli of these melts have been measured using ultrasonic interferometric methods at frequencies of 3, 5 and 7 MHz in the temperature range of 950 to 1600°C (0.02 Pa s < s < 5 Pa s). The bulk moduli of these melts decrease with increasing cation size from Li to Cs and Ca to Ba, and with increasing temperature. The bulk moduli of the Li-, Na-, Ca- and Ba-bearing metasilicate melts decrease with the addition of both TiO2 and SiO2 whereas those of the K-, Rb- and Cs-bearing melts increase. Linear fits to the bulk modulus versus volume fraction of TiO2 do not converge to a common compressibility of the TiO2 component, indicating that the structural role of TiO2 in these melts is dependent on the identity of the cation. This proposition is supported by a number of other property data for these and related melt compositions including heat capacity and density, as well as structural inferences from X-ray absorption spectroscopy (XANES). The compositional dependence of the compressibility of the TiO2 component in these melts explains the difficulty incurred in previous attempts to incorporate TiO2 in calculation schemes for melt compressibility. The empirical relationship KV-4/3 for isostructural materials has been used to evaluate the compressibility-related structural changes occurring in these melts. The alkali metasilicate and disilicate melts are isostructural, independent of the cation. The addition of Ti to the metasilicate composition (i.e. X2TiSiO5), however, results in a series of melts which are not isostructural. The alkaline-earth metasilicate and disilicate compositions are not isostructural, but the addition of Ti to the metasilicate compositions (i.e. XTiSiO5) would appear, on the basis of modulus-volume systematics, to result in the melts becoming isostructural with respect to compressibility.