The effect of sodium on refractory phase formation in a model Calcium Aluminate Cement-bonded refractory was investigated from 700 degrees C to 1500 degrees C. Sodium reacts with -alumina to form sodium -alumina (-Al2O3) via the intermediate NaAlO2. Formation of -Al2O3 disrupts the reaction path of calcia with alumina, delaying crystallization of calcium hexaluminate, CaO6Al(2)O(3), from 1350 degrees C to 1500 degrees C. -Al2O3 is also shown to reduce Young's modulus and delay sintering. The presence of NaAlO2 and -Al2O3 result in an increase in internal friction. Increased linear expansion of up to 47% is observed when 1 wt% Na is added. The expansion is shown to scale with the amount of dopant with only 0.3 wt% Na leading to an additional 31% linear expansion. On cooling, the presence of -Al2O3 can be demonstrated by a peak in internal friction between 1200 degrees C and 1000 degrees C which could be caused by Na+ ion hopping along the spinel-like planes.