RESEARCH The effects of aluminum and aluminum borate addition on the properties of MgO-C refractories M. Heidari Bagherabadi 1 & R. Naghizadeh 1 & H. R. Rezaie 1 & M. Fallah Vostakola 1 Received: 14 February 2017 /Revised: 18 June 2018 /Accepted: 28 June 2018 # Australian Ceramic Society 2018 Abstract Aluminum and aluminum borate powders were used as antioxidants to increase oxidation resistance of magnesia-graphite refractories. Bulk density and cold crushing strength of bodies without additives and also containing 4 and 6 wt.% aluminum and aluminum borate were investigated. XRD results of the samples containing aluminum borate and aluminum after firing in coke bed and also oxidized atmosphere (in air) at 1200 and 1400 °C showed that spinel (MgAl 2 O 4 ) was formed. In addition to the high refractoriness, this phase can improve strength and fill the porosities of refractories. A liquid phase was formed in the bodies containing aluminum borate which developed a coating on the graphite surfaces, and can stimulate the formation of spinel. The results of oxidation resistance tests, which were measured according to weight percent of the samples, showed that the oxidation resistance of the bodies containing aluminum borate was better than that of the bodies containing aluminum. Keywords MgO-C refractories . Aluminum borate . Mechanical properties . Oxidation resistance Introduction The presence of carbon in refractories was reported to improve thermal shock resistance due to its low thermal expansion coefficient, high thermal conductivity, and low elasticity [1]. Furthermore, low wettability by melt caused by carbon makes refractories to show a better corrosion resistance [2]. Such properties in magnesia-carbon refractories make them a good choice in lining electric arc furnaces, steel ladles, and con- verters [3–5]. One of the main problems of these refractories is carbon oxidation. In fact, carbon oxidation may result in refractory deterioration. The presence of carbon in refractories would increase the oxidation and reduce the mechanical strength of the bricks. Previous investigations showed that the carbon oxidation in magnesia-carbon refractories can be divided into two main categories: direct oxidation and indirect oxidation. Carbon direct oxidation occurs at temperatures under 1400 °C. In this case, the oxidation agent is the oxygen in the atmosphere (reaction (1)). Carbon indirect oxidation oc- curs at temperatures above 1400 °C. In this case, the oxidation agent is the oxygen absorbed from magnesia and slag compo- sitions (reactions (2) and (3)) [6, 7]. 2C s ðÞþ O 2 g ðÞ¼ 2CO g ðÞ ð1Þ Cs ðÞþ MgO s ðÞ¼ Mg g ð Þþ CO g ðÞ ð2Þ Cs ðÞþ FeO l ðÞ¼ Fe l ðÞþ CO g ðÞ ð3Þ Graphite oxidation in magnesia-graphite refractories fol- lows diffusion mechanism. Oxidation agents, such as oxygen, can go through the decarburized layer and cause graphite ox- idation in refractories [8, 9]. In order to improve oxidation resistance, metal (Al, Si, etc.), alloy (Al-Mg, Al-Mg-Si, Si-Al, etc.), and ceramic (TiO 2 ,B 4 C, MgB 2 , SiC, CaB 6 , etc.) antioxidants are being used [4, 10–12]. Choosing the proper type of antioxidant (in terms of amount and type) depends on some parameters such as composition of the refractory, heat treatment conditions (temperature and atmo- sphere), slag composition, and thermal stress which may be applied during the process. Aluminum powders, as an antioxi- dant, are widely being used in industries [2]. Many studies clarified that boron-based antioxidants can lead to improve properties of MgO-C refractories. Boron- containing antioxidants, such as MgB 2 and Mg 2 B 2 O 5 , can create a coating on the surface of the graphite through the * R. Naghizadeh rnaghizadeh@iust.ac.ir 1 School of Metallurgy and Materials Engineering, Iran University of Science & Technology (IUST), Narmak, Tehran, Iran Journal of the Australian Ceramic Society https://doi.org/10.1007/s41779-018-0233-0