Investigation of the Improvements on Mechanical Properties and Thermal Performance of MgO-MgAl2O4 Composite Refractories by Additions of ZnO-Al2O3 to MgO

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doi:10.4028/www.scientific.net/AMR.445.530

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HomeAdvanced Materials ResearchAdvanced Materials Research Vol. 445Investigation of the Improvements on Mechanical...

Investigation of the Improvements on Mechanical Properties and Thermal Performance of MgO-MgAl₂O₄ Composite Refractories by Additions of ZnO-Al₂O₃ to MgO

Abstract:

The variations and developments with the reasons on the mechanical properties of MgO-MgAl₂O₄ and MgO-ZnO-Al₂O₃ composite refractories were examined and thermal parameters affecting the durability of composites at high temperatures were investigated. The density, porosity, strength, modulus of elasticity, fracture toughness, fracture surface energy, critical defect size and mean MgO grain size values of composites were measured/calculated and evaluated. In addition, microstructural changes using XRD measurements and SEM analysis were examined. Thermal stress/shock parameters R and R_st that are used for determining high temperature performance of composites were calculated. The relationships between mechanical properties and structural variations for different compositions and the factors affecting this connection were investigated. With the additions of various amounts of ZnO-Al₂O₃ to MgO, significant improvements were achieved on both mechanical properties and R-R_st parameters of in-situ formed M-S-ZnAl₂O₄ composite refractories, compared to MgO-MgAl₂O₄ materials containing preformed spinel, by factors of up to 3.6 and 2.0, respectively. The important parameters increasing mechanical properties and thermal performance of M-S-ZnAl₂O₄ composites were determined as follows: i) formation of ZnAl₂O₄ phase leading to a high resistance to crack initiation and propagation, ii) propagation of microcracks formed in the structure for a short distance by interlinking to each other, iii) arresting or deviation of microcracks when reaching pores or ZnAl₂O₄ particles, and additionally iv) co-presence of both intergranular and transgranular types of cracks on fracture surfaces, and with the incorporations of ZnO-Al₂O₃, v) increase in density, vi) rise in critical defect size, and vii) a significant reduction in MgO grain size. The optimisation of M-S-ZnAl₂O₄ composite refractories that could be used for obtaining longer service life in industrial applications was performed.