Silicate glasses, alkali

A more quantitative model for these glasses can be obtained if we calculate the concentrations of bridging and non-bridging oxygens per 

Once we know how Q4 and Q3 vary with the concentration of alkali oxide, we can calculate several other useful numbers. First, we can determine the concentration of alkali oxide needed to completely 

If we wish to know the fraction of oxygens which are non-bridging, we simply divide the number of Q3 units (2x), which each contain one NBO, by the total number of oxygens, i.e., the number of NBO plus the number of bridging oxygens, BO, as given by Eq. 5.2, or  

We might also wish to know the average number of NBO per tetrahedron, which, since there are no NBO in a Q4 tetrahedron, and one NBO in a Q3 tetrahedron, is given by  

The connectivity of the structure might be discussed in terms of the average number of bridging comers per tetrahedron, which would be given by the contributions from the Q4 (4 bridging comers) units, plus those from the Q3 (3 bridging comers) units, divided by the number of tetrahedra, or  

---

Alkali silicate glasses, 12 571-572, 584, 585 studies of, 12 577 Alkali silicates, 22 452... 

Nath P. and Douglas R. W. (1965). Cr /Cr equilibrium in binary alkali silicate glasses. Phys. Chem. Glasses, 6 197-202. 

Dran, J.-C., Della Mea, G., Paccagnella, A., Petit, J.-C. Trotignon, L. 1988. The aqueous dissolution of alkali silicate glasses Reappraisal of mechanisms by H and Na depth profiling with high energy ion beams. Physics and Chemistry of Glasses, 29, 249-255. 

In the alkali silicate glasses, the decay time appears to increase with increasing ionic radius of the alkali metal modifier. The decay time also increases with increasing silica content, and apparently reaches a saturation value of 1.03 msec at a silica content of about 85 mole per cent. Figure 37 shows this result. 

There are a number of papers which report the use of Si NMR in studies of the structures of various soluble silicates and alkali silicate glasses. (93, 97-103) Early workers concluded that in soluble sodium metasilicate solutions only simple monomeric silicate structures are present. (104) The presence of polymeric structures was subsequently identified using Raman spectroscopy (105-107) and trimethylsilylation experiments. (108) Marsmann (97) first reported the existence of dimer, linear trimer, tricyclic, and polymeric structures based on Si NMR... 

Mortuza, M.G. (1989) A Nuclear Magnetic Resonance Investigation of the Structure of Some Alkali Silicate Glasses. PhD thesis. University of Warwick. 

The refractive indices of alkali silicate glasses (Na20-Si02) vary linearly with modifier concentration. Where change of coordination occurs such as with B2O3, AI2O3, or Geo2 °, maxima and minima of refractive index vs. composition are observed. 

The variations of the conductivity ratios as a function of the activity ratios found in such measurements, are shown in Figure 6.03 for a variety of alkali silicate glasses. It is evident from the figure that... 

The first two terms arise from alkalis 1 and 2 unassociated by electrodynamic coupling in the structure and the last term is due to those associated by such effect, a is the total number of alkali ions. and can be evaluated statistically assuming a priori probabilities of their distribution. When p and are known, conductivity behaviour may be examined with three adjustable parameters, namely A, and. An example of sodium-potassium silicate conductivities where excellent fits were obtained is shown in Figure 6.09. In the figure, conductivities normalised with respect to the maximum conductivity in the single alkali silicate glasses (at 150 °C), have been plotted. 

It has been shown that a plot of Si chemical shifts (Figure 12.03 (a), (b) and (c)) in a variety of alkali-silicate glasses, crystalline silicates and gels... 

Figure 12.03. chemical shifts versus the parameter P for (a) alkali silicate glasses, (b) other complex silicate glasses and (c) combined glasses, gels and crystalline silicates. Best fits are indicated by dashed lines (After Prabakar et al., 1991)... 

Two reactions can convert alkali silicate glass into a solid mass with which contaminated sludges can be bound (1) by adding acid to form silica gel, whereby the evaporation of water does not occur (alternative to vaporization ) and (2) reaction with multi-valent metal ions (e.g., calcium chloride) while forming aqueous metal silica gel, where heavy metals are precipitated and are mechanically bonded into the gel structure. The CHEM-FIX-Process is primarily used in the United States for inorganic contaminants the Belgian SOLIROC-Process contains additives to make it usable for the solidification of organic wastes. 

This describes the specific curing behavior of fly ash, cement dusts, and certain steel works byproducts, is based on the reaction of silicate and aluminous materials with quick lime. Here too, as with the above-mentioned additives, a higher pH causes the precipitation of metal hydroxides and carbonates. The British SEALOSAFE-Process uses fly-ash plus Portland cement, or alkali silicate glass and Fe/Al hydroxides to solidify a broad spectrum of wastes. In the POZ-O-TEC-Process, the wastes from flue gas scrubbers are solidified together with grate ash and fly-ash. The pozzolanic processes have the advantage of excellent longterm stability however, the products solidify rather slowly and are susceptible to acids. 

The alkali silicate glasses are easily corroded by aqueous acids and the main reaction is an exchange between H3O+ of the solution with the alkali M+ of the glass the corrosion rate increaseswith the ionic radii ofM+, that is, K > Na" " > Li" ". The chemical durability is greatly increased by addition of divalent CaO or trivalent AI2O3 oxides, leading to commercial soda-lime-silica compositions. 

---