Water, properties thermal expansion coefficient

The vitreous B2O3 is colourless, transparent and hygroscopic. It can be prepared by dehydration of H3BO3 at 266 °C —270 C under a reduced pressure of 130 — 260 Pa. The removal of water by heating H3BO3 in air is quite difficult and even the melt contains considerable amounts of residual water.The final H2O content after fusion at 700,1100 and 1200 °C is 0.25, 0.17 and 0.14% respectively (Poch, 1964). As a result of the H2O content, the data on the basic properties (e.g. those on viscosity and thermal expansion coefficient) exhibit some differences. The viscosity curve shown in Fig. 7 should serve for rough orientation only. More detailed data are reported by Bruckner (1964), for example. 

Properties of water p = density, Cp = heat capacity, a = thermal expansion coefficient, A = thermal conductivity, t] = viscosity coefficient 402 Density />/kg m of water at different temperatures and pressures 404 Specific heat capacity Cp/kJ kg of water at different temperatures and pressures 405... 

Properties of water p = density, Cp = heat capacity, a = thermal expansion coefficient, X = thermal conductivity, t] = Viscosity coefficient. 

Thus, the unique temperature dependence of the volume of water is due to the unique packing of water molecules in such a way that an open local structure is correlated with large (negative) binding energy. This unique feature of the interaction has been built in the model of Sec. 2.5 to show a negative thermal expansion coefficient in a one-dimensional system. We shall also see in Chapter 3 that this unique property is also responsible for some outstanding properties of aqueous solutions of non-polar solutes. 

The presence of silica domains affects all the properties, with clear changes in the density, thermal expansion coefficient, thermal transitions, surface adhesion, water uptake, and mechanical resistance depending on the process and on the inorganic proportion incorporated [251-258]. 

The purpose of this section is to demonstrate, by a very simple model, one of the most outstanding properties of liquid water A negative thermal expansion coefficient at low temperatures. 

As will be discussed in Section V, spinel can be synthesized using different raw materials and via different processes therefore, the properties of synthesized spinels vary. Table 2, as an example, lists some typical properties of dense, sintered, stoichiometric spinel (4). Spinel has a higher melting temperature (2135°C) than AI2O3 (2054°C) but lower than MgO (2850°C). Its thermal expansion coefficient ( 8.4 X 10 /K) is close to that of alumina ( 8.8 x 10 Vi )> utmuch lower than MgO ( 13.5 x 10 /K). Furthermore, it has superior hydration resistance than periclase and thus can be used in water-based castable systems. 

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