Viscosity of liquid silicates

The viscosity of liquid silicates such as drose containing barium oxide and silica show a rapid fall between pure silica and 20 mole per cent of metal oxide of nearly an order of magnitude at 2000 K, followed by a slower decrease as more metal oxide is added. The viscosity then decreases by a factor of two between 20 and 40 mole per cent. The activation energy for viscous flow decreases from 560 kJ in pure silica to 160-180kJmol as the network is broken up by metal oxide addition. The introduction of CaFa into a silicate melt reduces the viscosity markedly, typically by about a factor of drree. There is a rapid increase in the thermal expansivity coefficient as the network is dispersed, from practically zero in solid silica to around 40 cm moP in a typical soda-lime glass. 

As in die case of die diffusion properties, die viscous properties of die molten salts and slags, which play an important role in die movement of bulk phases, are also very stiiicture-seiisitive, and will be refeiTed to in specific examples. For example, die viscosity of liquid silicates are in die range 1-100 poise. The viscosities of molten metals are very similar from one metal to anodier, but die numerical value is usually in die range 1-10 centipoise. This range should be compared widi die familiar case of water at room temperature, which has a viscosity of one centipoise. An empirical relationship which has been proposed for die temperature dependence of die viscosity of liquids as an AiTlienius expression is... 

G. Urhain and M. Boiret, Viscosities of liquid silicates Ironmaking and Steelmaking, 17(1990), 255-260... 

It follows that since the addition of metal oxides has such a profound effect on the properties of liquid silicates such as the viscosity, that the Reynolds number of liquid silicates in metal-silicate liquid two-phase systems will influence the boundary layer thickness to a greater extent than in the liquid metals and alloys, mainly because of the higher viscosity of the silicate. 

Shaw, H. R. 1972. Viscosities of magmatic silicate liquids an empirical method of prediction. American Journal of Science, 272, 870-893. 

Most spectroscopic techniques (e.g. infrared and Raman spectroscopy) provide a snapshot view of the structure of a liquid because the timescale of the techniques is of the order of lattice vibration. However, NMR can probe much lower frequency motions, motions which are important in the glass transition and the viscosity of a silicate liquid. In addition, the timescale of the NMR experiment may be varied (by changing the magnetic field, or the type of experiment, T or T fJ, or observing quadrupolar effects) from a few hertz to several hundred megahertz. 

Urbain, G., Bottinga, Y., and Richet, P. (1982) Viscosity of liquid silica, silicates and alumino-silicates. Geochimica et Cosmochimica Acta, 46 (6), 1061-1072. 

Figures 10.9S(a,b) show isopleths calculated between (a) corium and siliceous concrete and (b) corium and limestone concrete. Comparison between experimental (Roche et al. 1993) and calculated values for the solidus are in reasonable agreement, but two of the calculated liquidus values are substantially different. However, as the solidus temperature is more critical in the process, the calculations can clearly provide quite good-quality data for use in subsequent process simulations. Solidus values are critical factors in controlling the extent of crust formation between the melt-concrete and melt-atmosphere interface, which can lead to thermal insulation and so produce higher melt temperatures. Also the solidus, and proportions of liquid and solid as a function of temperature, are important input parameters into other software codes which model thermal hydraulic progression and viscosity of the melt (Cole et al. 1984).

Fig. 3. Effects of metal oxides on the viscosity of binary liquid silicates 37).

Polycomponcnt systems of liquid oxides studied have mostly been silicates. Detailed discussions of these systems are beyond the scope of the present review. Perhaps the most important feature regarding polycomponcnt liquid silicates is their ionic nature. This may be conveniently illustrated by recent studies on the viscosity of some of these melts. 

The Joosten process, properly used, results in a strong gel that can give unconfined compressive strengths above 500 psi. However, the utility of the process is limited by the high viscosity of the solutions and the need for many closely spaced grout holes. Also, the nature of the reaction prohibits complete reaction of the two liquids. For many years research and development were aimed at a silicate-based grout with gel time control to eliminate the inherent disadvantages of the two-shot system. As those research efforts met with success, the Joosten system was phased out as a construction tool. Today it is virtually a method of the past. 

The viscosity of a sodium aluminate/sodium silicate grout solution increased gradually with time and a mix with an initial viscosity of 3.6cP and gel times 73 minutes at 20°C remains below S.OcP for 50% of its life and below lOcP for 75% of its liquid life. 

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