Disilicate glasses

Utilizing this description of silicate glass formation, we suggest models to explain the incorporation of 4+ and 6+ actinide ions in sodium disilicate glass. During cooldown,... 

In contrast, disilicate glasses containing U 4+ showed much less leach resistance. The 4+ glass was only slightly more leach resistant than pure sodium disilicate glass which is water soluble. For 4+ glasses, the ph of the leach solution... 

Fuss T., Ray C.S., Lesher C.E., and Day D.E. (2006) In situ crystallization of lithium disilicate glass effort of pressure on crystal growth rate. /. Non-Cryst. Solids 352, 2073-2081. 

Neilson G.F. and Weinberg M.C. (1979) A test of classical nucleation theory crystal nu-cleation of lithium disilicate glass. /. Non-Cryst. Solids 34, 137-147. 

Lochhead and Bray (1995) studied Eu3+ doped sodium disilicate glass with a high-pressure fluorescence line-narrowing technique. This technique was used to characterize the local structure of the Eu3+ ions up to a pressure of 21 GPa. For the crystal-field analysis they assumed a C2v site symmetry which allowed for a complete splitting of the crystal-field components. The crystal-field strength was determined according to eq. (11). The effect of pressure... 

Figure 4.2. Opposing effects on the Si relaxation time and peak width of adding paramagnetic MnO to sodium disilicate glass, from the data of Mortuza (1989).

Figure 7.26. Changes in the P MAS NMR spectrum of sodium disilicate glass with increasing additions of P2O5. At the lower concentrations the orthophosphate resonance at 15 ppm is progressively replaced by pyrophosphate at 2.5 ppm. At higher P2O5 concentrations the metaphosphate chain units (-16 ppm) are replaced by SiP207 units (- 33 to — 40 ppm).

Figure 9.6. A. H CRAMPS-MAS correlation spectrum of hydrated sodium disilicate glass showing projections in both dimensions. B. Slices through the CRAMPS dimension of spectrum (A) showing the separate spectra from the H2O resonance at 4.0 ppm (upper) and the OH resonance at 14.0 ppm (lower). Note that the different sideband distributions from the 2 protonated groups are clearly distinguishable. From Schaller and Sebald (1995), by permission of the copyright owner.

Figure 10.4. A. Relationship between the Li isotropic chemical shift and the composition of lithium silicate glasses. B. Relationship between the Li and "Li isotropic chemical shift and the composition of a series of (Li.Na) disilicate glasses. The open circles denote the Li shifts, the filled squares denote the Li shifts. From Gee et al. (1997), by permission of Elsevier Science.

Farges F, Brown GE Jr (1996) An empirical model for the anharmonic analysis of high-temperature XAFS spectra of oxide compounds with applications to the coordination environment of Ni in NiO, y-Ni2Si04 and Ni-bearing Na-disilicate glass and melt. Chem Geol 128 93-106 Farges F, Brown GE Jr (1997) Coordination of actinides in silicate melts. J de Physique IV 7 (Colloque C2, X-Ray Absorption Fine Structure, Vol. 2) 1009-1010... 

M. Misawa, D. L. Price, and K. Suzuki,/. Non-Cryst. Solids, 37,85 (1980). The Short-Range Structure of Alkali Disilicate Glasses by Pulsed Neutron Total Scattering. 

G. N. Greaves, Solid State Ionics, 105, 243 (1998). Structural Studies of the Mixed Alkali Effect in Disilicate Glasses. 

Since 1959, however, the principle of heterogeneous nucleation with metals has been successfiilly applied in the development of only a few glass-ceramics. To produce lithium disilicate glass-ceramics, McCracken et al. 

As mentioned in the History section, lithium disilicate glass-ceramic was the first glass-ceramic that Stookey (1953, 1959) developed. The fimdamen-tal research conducted by Stookey provided a basis for the large-scale development of glass-ceramics in a variety of chemical systems. Furthermore, other materials systems based on lithium disilicate have been also developed according to his findings. 

Barret and Hench (1980) and Wu (1985) improved the chemical durability of lithium disilicate glass-ceramics to a significant extent by incorporating additions such as AiPj and K2O to the stoichiometric base glass. The objective of improving the chemical durability of this glass-ceramic was to render the material suitable for use as a biomaterial in human medicine and, in particular, as a restorative material in dentistry. 

It must be noted that a significant improvement of the chemical durability of lithium disilicate glass-ceramics was achieved later in the development of glass-ceramics with nonstoichiometric compositions. 

Lithium disilicate glass-ceramics demonstrate a relatively high linear coefficient of thermal expansion of approximately 105 x 10 K h This property is favorable for the fabrication of special composite materials, e.g., for sealing to metal substrates in the electrical industry (Beall 1993). 

Beall (1993) and Echeverrfa (1992) achieved notable results in the development of a new lithium disilicate glass-ceramic. The new material is distinguished by the following three characteristics ... 

Using a special hot-press procedure, Schweiger et al. (1998) and Frank et al. (1998) also developed a powder-processed lithium disilicate glass-ceramic. To optimize the viscous properties for the hot-press procedure at approximately 920°C, components such as La2 3 hlgO, and pigments were added to the main components Si02, ZnO. The fabrication... 

The preferential crystallization mechanism is that of volume crystallization. However, surface reactions cannot be neglected when considering crystallization and nucleation in powder compacting and subsequent sintering and crystallization. In these processes, water has a special effect on the production of lithium disilicate glass-ceramics, as demonstrated by Helis and Shelby (1983) and Davis (1997). 

In a study on the effects of oxidation on crystallization, Keding and Russel (1997) found that reduction produced the ion, which acted as a nucleating agent. Russel (1997) managed to control the orientation of the main crystal phases in a specific axial direction in various glass-ceramic systems. The fresnoite system as well as apatite glass-ceramics and lithium disilicate glass-ceramics were particularly suitable. 

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