Preparation of Al₂O₃@CaCO₃ aggregates and its effects on the thermal shock resistance of Al₂O₃‐MgO castables

Abstract

Al 2 O 3 @CaCO 3 aggregates were prepared by impregnating corundum aggregates (particle sizes with 3-1 and 5-3 mm) in precursor solutions (Calcium hydrogen citrate, CaHC 6 H 5 O 7 ) followed by heat treatment at 430°C. The phase composition and microstructure of the coatings were characterized via X-ray diffraction and scanning electron microscope, respectively. The novel aggregates were used in Al 2 O 3 -MgO castables. The effects of the Al 2 O 3 @CaCO 3 aggregates on the physical properties and thermal shock resistance (TSR) of castables were investigated. The results show that uniform CaCO 3 coating of aggregates (C15) with thickness about 10 µm can be attained when the concentration of Ca 2+ in solution was 0.15 mol L −1 . There was a strong bonding between the aggregates and coating that was constituted by particles with size about 0.2 µm. Both improving physical and TSR properties of the castables are related with the unique layer structure, calcium hexaluminate (CA 6 ) layer in-situ formed at the aggregate-matrix interface, of added Al 2 O 3 @CaCO 3 aggregates. There is a mass of multi-deflection of cracks along with the CA 6 layer which consumes more fracture surface energy. The castables with C15 exhibit optimal TSR and the residual strength ratio after the thermal shock test is 29.5%, which is 12.8% higher than the castables with corundum aggregates.

Convenient preparation of calcium hexaluminate based castables with low thermal conductivity and sufficient strength

“…[5][6][7] Platelet CA 6 grains exhibit anisotropic growth and can enhance toughness and thermal shock resistance of castables. 8,9 However, it is difficult to obtain full dense CA 6 due to plate-like grains with high aspect ratios. 10,11 Porous CA 6 with a small pore size presents low thermal conductivity (.4-.6 W/m•K).…”

“…Calcium hexaaluminate (CaAl 12 O 19 , abbreviated as CA 6 ) as the compound with the highest Al 2 O 3 content in the CaO–Al 2 O 3 binary system has a wide range of application prospects in the high‐temperature industry due to its low solubility and wettability for molten metal and slag, good stability under reducing atmosphere, and good resistance to alkaline corrosion 5–7 . Platelet CA 6 grains exhibit anisotropic growth and can enhance toughness and thermal shock resistance of castables 8,9 . However, it is difficult to obtain full dense CA 6 due to plate‐like grains with high aspect ratios 10,11 .…”

Particle grading effect on properties of reactive MgO‐bonded castables

“…Refractory castables encompass a broad range of materials that have undergone significant advancements, [1][2][3][4] leading to intricate and technically advanced formulations aimed at fulfilling highly demanding and rigorous industrial applications at elevated temperatures. [5][6][7][8][9][10] The primary features of castables consist of a well-chosen combination of raw materials, including aggregates, fillers, binders, and admixtures, [11][12][13][14][15][16][17][18] which leads to a deliberately designed particle gradation affecting the flowability and density of the mixture, [19][20][21][22][23][24][25] alongside the binder that influences both the green mechanical strength and the high-temperature properties, including phase evolutions.…”