This research studied the effects of several dispersants on the morphologies of cement hydrates and properties of refractory castables. The results showed that the cement hydrate morphologies were closely related to the types of dispersants used. With naphthalene sulfonate formaldehyde condensate (FDN) and sodium tripolyphosphate (STPP) as dispersants, the cement hydrate of C3AH6 obtained anomalistic shapes, and the AH3 particles showed a diameter of not more than 1 μm. When propionic acid (PA) was added, C3AH6 formed inerratic cubical grains, whereas AH3 changed from particles to long column agglomerates; the ratio of the long radius increased with increasing PA concentrations. The addition of PA as dispersant generated CaCH3CH2CO2+, which resulted in a decrease in Ca2+ concentration. Also, the relatively higher apparent porosity satisfied the space requirement for the growth of C3AH6, eventually resulting in larger inerratic cubical grains. The H+ hydrolyzed from PA accelerated the growth on the (100) and (110) crystal planes of AH3; thus, gibbsite stretched along the c-axis. The maximum values of CCS and CMOR for refractory castables prepared with PA as dispersant were 5.6 MPa and 46.6 MPa, respectively, which were higher than those for refractory castables with FDN and STPP. The observed excellent performance in strength might be related to the bridging effect resulting from the long-column AH3.

•The calcium aluminate cement with submicron MgAl2O4 (CMA) has been prepared.•MgAl2O4 is homogeneously distributed among CA and CA2 phases.•The first stage of hydration is dominated by NG and then dominated by diffusion.•The value of the exponent for CAC and CMA is 2.6353 and 3.1730, respectively.•The hydration rate of CMA cement is higher than that of CAC.Calcium aluminate cement with micro MgAl2O4 spinels (CMA) was prepared using a solid-state reaction. The results indicated that three mineral phases of CaAl2O4, CaAl4O7 and MgAl2O4 could be formed when the calcined temperature reaches 1300 °C. The submicron MgAl2O4 particles are homogeneously distributed among the phases of CaAl2O4 and CaAl4O7. Based on the Krstulovic–Dabic model, the hydration mechanism and kinetic parameters of calcium aluminate cement (CAC) and CMA were respectively studied by isothermal calorimetry. It was determined that the total hydration heats of CAC and CMA are, respectively, 309.756 J/g ± 15.5 and 275.496 J/g ± 13.8. The results showed that these two types of cement have the same hydration process. The nucleation and crystal growth process is the main reaction at the initial stage and then transforms into a diffusion controlled process.