Silicates thermal contraction

In framework silicates, the apparent thermal contraction of the T-0 bonds has been related to a transverse vibration of the oxygen atoms normal to the T-O-T bonding plane [2.34,35]. Increased amplitudes of this mode, on time average, would increase the bond distance, which is compensated for by a movement of the Si atoms towards the oxygen. Consequently, if bond lengths... 

When colloidal silica is embedded in a matrix of sodium silicate it tends to crystallize and form cristobalite at the temperatures the cores reach when metals are cast. Due to the difference in thermal expansion coefficient, the expansions and contractions of the cristobalite crystals embedded in the glass matrix tend to crack the binder film surrounding the sand grains therefore weakening the mold or core. This weakening effect has to be added to the... 

The neutron diffraction studies confirmed earlier X-ray results about other important structural changes with temperature [2.5] the mean Si-0 and Al-0 tetrahedral distances were found to decrease continuously with temperature, whereas the Li-0 distances increased see Table 2.2. The decrease in the Si-O and Al-0 distances is comparable to the decrease in the Si-0 distance measured in quartz, also listed in Table 2.2. In fact, zero expansion or slight apparent contraction of T-O bond lengths with temperature has been found in high-temperature structural analyses of many silicates. Hazen and Finger compiled data for silicates and other compounds and evaluated them statistically [2.33]. The large positive thermal expansion of the Li-0 bonds in /3-eucryptite is also in line with their findings for electrostatically weak M-0 bonds. 

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