One-step synthesis of in-situ carbon-containing calcium aluminate cement as binders for refractory castables

In-situ carbon-containing calcium aluminate cement (CCAC) was synthesized through carbon-bed sintering with calcium citrate tetrahydrate and Al2O3 as raw materials. The synthesized product was characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and infrared carbon-sulfur analysis. The results show that after sintering at 1500 °C for 4 h, the phase compositions of the product approached that of the commercial cement Secar71. The in-situ carbons in the product had partially graphitized domains and porous structures, were uniformly embedded in calcium aluminate, and the carbon content of the product was 1.45%. The floating ratios and oxidation ratios of the CCAC were lower than those of carbon back/Secar71 (S71CB) composite powders, implying that the water dispersion and oxidation resistance of CCAC were improved. Furthermore, the cold crushing strength (CCS), and cold modulus of rupture (CMOR) of the corundum-based castables bonded with CCAC, and S71CB, respectively, were compared. The CCS and CMOR values of the castables bonded with CCAC after being fired at 1100 °C for 3 h are higher by 20% and 21%, respectively, than those of the castables bonded with S71CB, suggesting that CCAC can be applied as a promising binder for the refractory castables.