High temperature processes consume large amounts of energy, which comes mostly from burning fossil fuels. The firing step in refractory production releases a large amount of carbon oxide, making the search for cleaner processes a priority for this industry.

RH degassers are used in the secondary refining of steel, and it is responsible for decarburization or nitrogen reduction, heating, alloy addition and the deoxidizing of molten steel.  A typical RH degasser consists of hot-of-take, upper vessel, lower vessel, and two snorkels. The complex reactions that take place in the equipment create a critical operational environment. In this context, various parts of RH vessels are lined with different grades of magnesia-chrome brick, as they have excellent corrosion resistance, high thermo-mechanical properties and volume stability.  Most of these materials are rebonded bricks, and they are known for their ability to develop ceramic bonds due to a high firing temperature above 1700°C.
The production of steel with ultra-low carbon content has increased the demand for refractories with superior physical and chemical properties. Aligned with that, an unfired magnesia-chrome brick with a zero-carbon binder has been developed to replace the traditional fired material, which has been used in RH degassers since the 1960s. The novel MgO-Cr2O3 is delivered to customers just tempered at 200°C. It has a similar composition to a standard grade fired at 1760°C and is differentiated only by the binder system and production process. Withdrawing the firing process from MgO-Cr2O3 brick production implies a reduction of 700 kg of CO2 emitted per ton of refractory produced, as well as a shorter lead time.
The developed binder system allows an early secondary spinel formation, which ends at 1400°C. These phases lead to an effective direct bonding between aggregates and matrix. In this context, the aim of this work is to compare the physical and thermo-mechanical properties of fired and unfired bricks. Also, the comparative microstructure is highlighted. Tempered brick presents similar bulk density, apparent porosity, cold crushing strength, corrosion, and erosion resistance to the standard material. Although crystallographic phases are common to both compositions as observed by XRD (X-ray diffraction), SEM (scanning electron microscopy) and EDS (energy dispersive X-ray spectroscopy) show a greater diffusion rate of ions for the unfired material, attesting the high reactivity of the system due to the binder presence, which leads to a fast-sintering capability. Besides that, well distributed small pores in the microstructure are observed for the unfired brick, which induces a lower elasticity modulus and higher thermal shock resistance. Field trials were conducted and the novel MgO-Cr2O3 presented at least a similar performance compared to the fired material, and it was already approved for a regular customer supply.