Modern levitation furnaces are enabling melting and freezing of refractory materials like Al2O3 to be studied in depth with synchrotron radiation techniques. Whilst α-Al2O3 is a close packed Debye-like solid, liquid Al2O3 has smaller co-ordination numbers and the structure has networklike characteristics. Under contactless conditions, substantial under cooling can be achieved. Melting involves a significant decrease in density which is approximately recovered on recrystallisation, both of which can be followed with high speed video imaging. Freezing occurs with a burst of energy – recalescence – which substantially raises the temperature momentarily. Using Rietveld refinement the density of α-Al2O3 and the mean square displacement of the average atom can be followed up to the melting point and upon freezing using in situ X-ray diffraction. As melting is approached for α-Al2O3 exceeds the harmonic approximation of the Lindemann-Galvarry law and for liquid Al2O3 above the melting point appears to be greater still. On freezing from the undercooled state α-Al2O3 is initially decompressed with the TP point falling on the melting curve extrapolated to negative pressures.