Mineral Transform and Specific Heat Capacity Characterization of Blast Furnace Slag with High Al 2 O 3 in Heating Process

The specific heat capacity ( C p ) of blast furnace (BF) slag critically impacts BF smelting and reports on the C p of BF slag with high Al 2 O 3 are rare. Mineral transform and C p characterization of synthesized BF slag (CaO–SiO 2 –MgO–Al 2 O 3 ) with high Al 2 O 3 in the heating process are herein discussed. Differential scanning calorimetry curves show a major exothermic peak at a low temperature and multiple endothermic peaks at elevated temperatures. The exothermic peak at approximately 920 °C appears when amorphous SiO 2 (or SiO 2 in silicate) becomes crystal SiO 2 (or SiO 2 in silicate). The endothermic peak between 1224–1254 °C is attributed to the reverse eutectic reaction, CaO·Al 2 O 3 ·2SiO 2  + 2CaO·0.5MgO·0.5Al 2 O 3 ·1.5SiO 2  → Liquid, along a eutectic line. CaO·Al 2 O 3 ·2SiO 2  + MgO·SiO 2  → Liquid + 2MgO·SiO 2 (reverse peritectic reaction) or CaO·Al 2 O 3 ·2SiO 2  + 2MgO·SiO 2  → Liquid (reverse eutectic reaction) at approximately 1268 °C will occur with an endothermic reaction in some cases. The sharp endothermic peak between 1282 and 1303 °C is the reverse eutectic reaction, CaO·SiO 2  + 2CaO·Al 2 O 3 ·SiO 2  → Liquid. The blunt endothermic peak between 1388 and 1447 °C is the residual slag melting, Solid → Liquid. The relationships of C p with temperatures and compositions ( R , ratio of w (MgO)/ w (Al 2 O 3 ), and w (Al 2 O 3 )) are established with a good fit.