Papers by Author: Cemail Aksel

Abstract: Corrosion resistance of MgO-Spinel (M-S) composite refractories containing various amounts of ZrSiO₄-Y₂O₃ constituents was investigated. Density and open porosity values were measured and evaluated. Corrosion tests of refractories were carried out statically under standard conditions using cylindrical shaped samples in terms of determining the interaction with cement clinker. Corrosion resistance was determined by measuring the values of penetration and depth of the corroded regions of refractories. The influence of corrosion resistance based on the microstructural changes occurred as a result of solubilities of constituents in the interface of clinker-refractory for various regions was examined using SEM and the results were evaluated using EDX analysis. It was observed that there was a significant increase in density values and decrease in porosity data for most of the compositions obtained from the additions of ZrSiO₄-Y₂O₃ to MgO-spinel. As a consequence of microstructural characterisation performed at the interface of clinker-refractory, the observations made were determined as follows: i) the formation of ZrO₂ and Mg₂SiO₄ phases among the MgO grains during sintering, ii) the formation of CaZrO₃ phase during penetration, iii) prevention of penetration by new phases formed that make a barrier effect against clinker with the improvement in densification, and iv) the decrease in the amount of CaO based on the EDX analysis made from clinker to refractory in a corroded region. The incorporation of ZrSiO₄-Y₂O₃ into MgO-spinel reduced the values of penetration and depth of the corroded regions of refractories and improved the corrosion resistance. The penetration of clinker to refractory showed a minimum level for the composition of M-20%S-20%(ZrSiO₄+Y₂O₃) and an improvement by a factor of 1.42 as compared to M-20%S. This development is also combined with a long service life of M-S-(ZrSiO₄+Y₂O₃) containing composite refractories for industrial uses.

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.