APPLICATION NOTE Characterization of complex refractories for steel production using the Axia ChemiSEM Introduction Refractories are composite materials employed in the manufacturing industry in many fields due to their high temperature and corrosion resistance. One of their main applications is in steel production as protection in heating furnaces, refining vessels, and to contain the flow of molten metal. Refractory oxides experience extreme working conditions, including corrosive environments and high temperatures (liquid metal temperatures exceed 1,650°C). Corrosion and erosion processes occur by contact with molten metal, liquid oxide slag, and abrasive surfaces, having a notable impact on the stability of the refractories during their service and, possibly, leading to a reduced service life. For this reason, the physical and chemical properties of the materials employed are very important for the stability and wear resistance of the refractory product during use, hence making proper material selection crucial. Most of the refractories are fabricated by combining many different material types, such as ceramic (oxide) powders, reactive metals, or carbides, and sometimes carbon/graphite flakes to form the final product. Figure 1. Refractories are used to contain the molten steel. Large-scale overview of complex refractories The materials characterized in this application note may be employed in pressed bricks, monolithic linings, or carbonbonded products such as the stopper rod and submerged entry nozzle for continuous casting of steel. The refractory mixture contains zirconia mullite (ZM), brown fused alumina (BFA), and fine-grained fused silica. For the purpose of this study, the different grains have been mounted in epoxy and polished. A large area of the polished section has been characterized to provide an overview of the distribution of the different materials. A conventional approach would provide either a backscattered electron (BSE) image or a secondary electron (SE) image, but these would not disclose the composition of the grains. In fact, the information provided by the BSE contrast, where the grayscale levels change according to the average atomic number of the material, is not enough to distinguish the different phases and possible contaminations within this mixture of complex refractories. In this application note, we present a new approach to elemental analysis, which, in a scanning electron microscope (SEM), is commonly provided using energy dispersive X-ray spectroscopy (EDS). The new approach using the Thermo Scientific™ Axia™ ChemiSEM is no longer guided by the information retrieved from the SEM image. Instead it is based on the elemental information that, with the new ChemiSEM workflow, comes in combination with the SEM image (either BSE or SE image) and is displayed instantaneousl

500 μm C O Al Si Zr Ti Fe Na Ca S Figure 2. A modern refractory system often contains a range of different grain materials to achieve the desired properties. Being able to easily unravel the different materials distribution is important. The three boxes highlight the ZM, BFA, and fine-grained silica grains (acc voltage 15 keV, beam current 0.85 nA). Figure 2 shows a ChemiSEM large-area overview with a field of view of more than 2 mm. The overview has been acquired by combining neighboring frames while collecting the EDS signal for each of the single frames, which has then been processed in order...

The distribution of the different elements can be made more evident by selectively visualizing them. The ChemiSEM images in Figure 4 that show Zr, Al, and Si distribution have been saved after the first SEM image acquisition with no need to re-acquire or further process the EDS data. Point analyses and linescan confirm the presence of three phases: the zirconia, a silicate phase, and the mullite. The results of the point quantifications are presented in Table 1. 30-second point analyses have been acquired in the points marked in Figure 3 as 1, 2, and 3. The linescan in Figure 5 has been acquired...

By selecting the elements of interest, you can immediately find the presence of at least three phases: the first phase is a Si-Al and Na-rich material (distribution shown in the first row of Figure 8), the second phase, intertwined with the first, can be identified as titanium oxide (TiO2), while the smaller grain contains Fe and S. Given the speed of the analysis, and as no post-processing is required to obtain quantitative information, another unique impurity has been imaged and characterized. The distribution of the carbon and oxygen are hidden to avoid possible confusion with the overlay...