Impact of Magnesia Grain Size on the In Situ Spinel Formation in Al2O3–MgO–C Refractories
Mehrgodaz Refractories Company, Sefid-Dasht, Chaharmahal & Bakhtiari 88751-16655/Iran
Revision 02.11.2017, 15.01.2018
Volume 10, Issue 2, Pages 80 - 85
In order to evaluate the effect of magnesia grain size on spinel formation process, four compositions with different dead burned magnesia grain sizes along with fused alumina and graphite were prepared. After pressing, samples were tempered at 220 °C and coked under reducing atmosphere at 1600 °C. Permanent Linear Change (PLC) and physical properties including Bulk Density (BD) and Apparent Porosity (AP) were measured. Phase analyses were investigated by X-Ray Diffraction (XRD) technique and flexural strength of samples at 1400 °C in Ar atmosphere were determined by HMOR test. In addition, the samples were coked once again under coke bed at 1600 °C in order to assess the spinel formation process. The results of the PLC have shown that the use of finer magnesia grain sizes in the composition would increase the available surface area for spinel formation reaction. In fact, the PLC value of the sample M4 was +4 % while this value for other samples M3, M2 and M1 was +3,27, +2,44 and +2,36 %, respectively. Moreover, spinel formation decreased by the increase of magnesia grain size to a certain level. Regarding the results of second coking process, although some unreacted magnesia were characterized by XRD in sample M1, only negligible expansion were recorded for samples which could be due to the formation of spinel phase in the magnesia and alumina interface acting as an ion diffusion barrier. Flexural strength of samples at 1400 °C increased by using finer fractions of magnesia in samples because of the formation of spinel phase in the matrix as a ceramic bond which has been revealed by SEM/EDS investigations.
alumina-magnesia-carbon, spinel, grain size, carbon containing refractories
 Muñoz, V.; et al.: Chemical wear of Al2O3–MgO–C bricks by air and basic slag. J. Europ. Ceram. Soc. 35 (2015)  1621–1635  Mukhopadhyay, S.; et al.: Effect of MgO Grain size on thermal expansion behavior of alumina-magnesia-carbon refractory. Int. J. Appl. Ceram. Technol. 1019 (2013) 1012–1019  Muñoz, V.; Martinez, A.G.T.: Thermal evolution of Al2O3–MgO–C refractories. Procedia Mater. Sci. 1 (2012) 410–417  Engineering, C.; Sahoo, S.: Study on the effect of the effect of different raw materials sources on spinelization and densification of MgO–Al2O3 spinel, 2014  Emmel, M.; et al.: In situ spinel formation in Al2O3-MgO–C filter materials for steel melt filtration. Ceram. Int. PART B 40 (2014)  13507–13513  Armijo, J.S.: The kinetics and mechanism of solid-state spinel formation – A review and critique. Oxid. Met. 1 (1969)  2, 171–198  Routschka, G.; Wuthnow, H.: Pocket manual refractory materials. Design, properties and testing. Essen 2008  Jin Fan, H.; et al.: Monocrystalline spinel nanotube fabrication based on the Kirkendall effect. Nat. Mater. 5 (2008)  627–631, 2006  Swain, M.V. (Ed.): Structure and properties of ceramics. Weinheim 1994  Baudín, C.: High temperature mechanical behavior of magnesia-graphite refractories. In: Fundamentals of refractory technology. Westerville, Ohio 2012
Göller Verlag GmbH