Refractory ceramics for the aluminium foundries: Novel perspectives for greater process and product sustainability

Since the beginning of time creativity, intelligence, and consciousness have helped mankind developing a more convenient World. The mastery of metallurgy was a transformative leap for humanity which promoted the production of revolutionized tools and weapons. In the simplest terms, humans developed the first metallurgical techniques around 6000 B.C. by putting a start on the timeline of metallurgical advancements which spans several millennia. One of the metals that has the potential to change the global metallurgical industry is aluminium (Al). The exponential evolution of aluminium production over the past decades reflects its increasing importance, and future projections anticipate an 80% increase in demand by the year 2050[1]. Indeed, infinite recyclability, reduction of production costs, and eco-compatibility combined with extreme versatility of the metal make aluminium foundries sustainability-conscious and cutting-edge. Castable refractory ceramics play a crucial role in the aluminium production process, allowing the transportation of molten Al from the furnace to the casting station. The key aspects of this ceramics involve high-temperature, thermal shock, chemical, and mechanical resistance as well as shape adaptability, durability and insulating properties. In order to test the materials, several analysis techniques are usually employed. Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) allow the study of the thermal profile of materials which is a key element because of the contact between the ceramic and molten Al. Strength testing is also crucial as ceramics are subjected to high mechanical stresses. Finally, extensive studies of both surface and bulk chemical composition allow the determination of erosion/corrosion resistance. In this work, BN-doped ternary SiO2-Al2O3-CaO ceramics were synthetized and characterized to evaluate the physicochemical properties of the materials. SiO2-Al2O3-CaO composite is a well-known system which is able to meet many demands[2]. Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) analysis allowed an insight into the chemical composition confirming the theoretical values of the major elements derived from calculations on raw materials, i.e., 33.4 ± 0.5 % Si (vs theoretical 35.0%), 7.2 ± 1.8 % Al (vs theoretical 9.0%) and 5.0 ± 1.2 % Ca (vs theoretical 5.1%). Scanning Electron Microscopy (SEM) analysis provided morphological and structural information of the samples showing the heterogeneity of the synthetized ceramics which consisted of a calcium aluminosilicate matrix in which fragments of silica and BN were dispersed. Moreover, porosity of materials as a function of calcination was highlighted. X-Ray Diffraction (XRD) technique revealed the presence of both amorphous and crystalline phases. Interestingly, XRD analyses before and after a heat treatment were similar, although the calcinated material showed a loss of water-related phases, i.e., aluminium hydroxide (nordstrandite) and calcium aluminium hydroxide hydrate. This phenomenon has already been observed[3] and ascribed to water loss which changes crystalline lattice. Finally, a MatLab project for calculating heat losses during the effective utilization of the ceramics was created to meet the need for improved product sustainability combined with the possibility of creating uniqueness, whose purpose is to lead to products and processes customization. References [1] Circular Aluminium Action plan. Available online on http://www.european-aluminium.eu/. [2] H. Mao et al. J. Am. Ceram. Soc. 89 (2006) 298. [3] N. M. Reza et al. Iran J. Chem. Chem. Eng. 26 (2007) 19.