Chemical Composition: The grey firebricks are composed of various oxides, including Na2O (0.5%), MgO (1.2%), Al2O3 (11.7%), SiO2 (45.4%), SO3 (1.8%), K2O (2.9%), CaO (18.0%), TiO2 (0.7%), MnO (8.8%), Fe2O3 (8.1%), NiO (0.6%), and CuO (0.5%).

Physical & Mechanical Properties: The apparent density of the firebricks is 2.03 g/cm³, while the real density is 2.82 g/cm³. They have an open porosity of 27.82% and a water absorption rate of 13.67%. The cold crushing strength is measured at 38.29 MPa, and the flexural strength (M.O.R) is 9.45 MPa.

Thermal Properties: The refractoriness of the firebricks is greater than 1100°C, with a permanent linear change of less than 1%. Thermal conductivity is 1.16 W/m·K at 200°C and 1.05 W/m·K at 400°C. The heat capacity is 0.75 J/g·K. Thermal diffusivity is 7.6·10^-7 m/s at 200°C and 6.9·10^-7 m/s at 300°C.