China's Refractories

The movement of the Iron & Steelmaking (I&S) industry towards Net-Zero emissions and digitalized processes through disruptive, breakthrough technologies will be achieved through the use of Hydrogen. The biggest challenge for the refractory industry is to continue to meet the performance expectations while, at the same time, moving to a more sustainable production direction. The complexity and urgency of these technological changes, highlighted by the European Green Deal, requires ambitious, international, interdisciplinary and intersectoral projects, bringing together institutes from across the global value chain, to carry out cutting edge research. The European Union, through its flagship doctoral training program, MSCA, has, and continues to support research and development as well as the promotion of the refractory industry in Europe. An introduction to two MSCA projects and some of the results achieved are highlighted within this article.

The CALPHAD thermodynamic databases are very useful to analyze the complex chemical reactions happening in high temperature material process. The FactSage thermodynamic database can be used to calculate complex phase diagrams and equilibrium phases involving refractories in industrial process. In this study, the FactSage thermodynamic database relevant to ZrO₂-based refractories was reviewed and the application of the database to understanding the corrosion of continuous casting nozzle refractories in steelmaking was presented.

Clean steel encompasses a multitude of concepts that are based on fulfilling customer requirements and can be produced in many ways depending on the existing equipment and detailed customer demands. A common feature of all clean steel production is tight process control along with continuous monitoring. To meet an increasing demand for cold-rolled (CR) steel sheets of improved mechanical properties, and to cope with the change of the annealing process from a batch-type to a continuous process, it is necessary to establish a technique for making ultralow carbon (ULC) steel with a C-concentration lower than 20 ppm for the steelmaking process associated with a major challenge to guarantee the competitiveness with observance of environmental requirements. Steel ladle lining plays an important role on the energy consumption during the production and the refractory lining design contributes to minimize thermal bath loss, carbon pick up and shell temperature. A new generation of unfired zero carbon refractories was developed with two specific approaches: (1) replacement of firing bricks reducing CO₂ footprint and (2) replacement of carbon containing with performance increasing. Bricks can be used in working and safety linings with a unique microstructure with better heat scattering and similar thermomechanical properties. This work presents customers’performance compared to traditional products highlighting energy savings.

This study aims to provide the basic knowledge for furnace refractory design by investigating refractory property changes occurred in a hydrogen atmosphere. Since refractory bricks are thermodynamically stable in a hydrogen atmosphere at 1 100 °C, we tried to find out the minute changes. In this experiment, a refractory brick was prepared by andalusite, mullite chamotte, and clay as raw materials and heated to 1 100 °C in a 100% hydrogen atmosphere for 72 h. It was found that the strength of the brick was decreased and the color was changed to black by the reduction of impurities. And in addition, this study covered research on the slaking risk of MgO raw materials because the minimum temperature is expected to 400 °C in fluidized reduction furnaces unlike shaft furnaces.

Alumina is one of the crucial and extensively utilized refractory components. As the refractory wear due to dissolution at elevated temperatures during operation is a major threat to refractory lifespan, quantifying dissolution is important for developing cost-effective and resource-efficient refractories. This study investigated the dissolution of alumina particles in two silicate and one calcium aluminate slags at 1 450, 1 500, and 1 550 °C using high-temperature confocal laser scanning microscopy (HT-CLSM). Dissolution was quantified in terms of diffusivity, with all influencing factors, including Stefan flow and bath movement, incorporated into the determination process. The trends observed in total dissolution time and diffusivity in three slags at three experimental temperatures could not be explained solely on the basis of slag basicity. Two parameters, considering the influencing factors, were introduced to explain these trends. Furthermore, the linear trend observed in Arrhenius plots of diffusivities supports the diffusivity results. Additionally, good agreement between the diffusivities of alumina in one silicate slag obtained via CLSM and rotating finger test investigations verified the reliability of the results.

Refractories have unique capabilities such as sustaining their shape and properties at extreme conditions such as the combination of high temperatures and thermal shock, contact with molten metals and slags and in some circumstances resistance to erosion from abrasive particles. Given the large processing output of the heavy industries such as the cement and steel ones which both require high temperature processes, the refractories structures span various meters and weight of several tons. As the water removal stage of hydraulic bonded castables in industrial sites takes hours (10-60 h) due to the risk of explosive spalling, efforts to mitigate it are commonly studied. This has provided theoretical understanding of the general aspects of drying and important tools, such as the thermogravimetry analysis (TGA), for the design of refractory compositions with higher explosive spalling resistance. However, the optimization of this process is still far from the industrial reality especially because the actual linings that require the drying are orders of magnitude larger than the samples considered in the laboratory tests. Therefore, this study proposed the analysis of the sample volume effect on the water removal dynamics through TGA of high alumina castables with calcium aluminate cement. Conventional φ5 cm×5 cm cylindrical samples were assessed in a laboratory scale equipment whereas macro TGA were carried out considering 20 cm×20 cm×20 cm and 30 cm×30 cm×30 cm cubic samples. Additionally, the effect of polymeric fibers was also considered. It was found out that the different thermal gradients within the macro TGA samples resulted in an inflection on the sample’s heating rate and that the mass loss was affected by the volume considered, especially for the composition without additives. These findings highlight the requirement of carefully taking into consideration the different dimensional sizes and thermal gradients in the samples when analyzing and interpreting the laboratory studies, and especially when trying to extrapolate such results to the industrial reality.

Purging plug refractories in China typically contain around 3 mass% of super-fine chromium oxide in the matrix in order to improve the performance of the purging plugs, primarily, slag corrosion and wear resistance. Alternatives to chromium oxide containing refractories have gained interest due to health concerns related to the formation of soluble chromium compounds over long storage periods of refractory wastes. Super-ground reactive alumina can replace chromium oxide in purging plug refractories and this paper discussed the new reactive alumina E-SY 88 in comparison to chromium oxide in a typical purging plug castable. The mixing behaviour, wet castable properties, as well as cured, dried, and fired properties at different temperatures up to 1 600 ℃ were compared. In addition, the hot modulus of rupture, creep behaviour, thermal shock resistance and slag corrosion resistance were tested. The microstructure after slag corrosion was investigated by SEM. The results prove that E-SY 88 is an economically viable technical alternative to chromium oxide in purging plug refractories.