Welcome Address: Ulf Frohneberg - President of the German Refractories Association: "The Talent Challenge"
Keynote: Simon Schnetzer - Expert for Generation Y and Generation Z: "The Talent Challenge - attracting and retaining the next generation in refractories"

Generally, the physical characteristics, namely the density, of refractory aggregates used in refractory castables are to be adapted to achieve high thermo-mechanical performances, thermal and chemical stabilities. An example is given with the comparison between tabular alumina (TA) and white fused alumina (WFA) for which a different strength performance after thermal treatment is generally observed. This difference could be attributed to the thermal mismatch between WFA aggregates and the matrix or/and a difference in their bonding linkage. Nevertheless, the generation of a microcrack network is also believed to adapt the thermal stresses during thermo-cycling operations and then positively contributes to the service life of the refractory lining. Thus, along with a specific chemistry, the microstructure of a refractory castable can be designed according to the physical and morphology characteristics of the aggregates for the improvement of its mechanical properties, in particular the thermal shock resistance.

The results presented in this paper discuss the evaluation of different types of refractory aggregates and their effect upon thermo-mechanical properties of their corresponding refractory castables, with a specific approach on thermal shock resistance assessment.

Magnesia-spinel refractory bricks are widely used in rotary kilns since they offer a desirable combination of mechanical, chemical and thermal properties at elevated temperatures. Recent trends in energy-efficiency and reduction of carbon footprint have led refractory manufacturers to develop energy-saving refractory bricks. One possible way to decrease energy consumption is using an energy-saving brick in which the thermal conductivity is reduced by increased porosity. However, mechanical, chemical and thermal limitations of the rotary kilns should be considered in brick design since porosity will degrade relevant properties. In this study, novel basic refractory bricks with reduced thermal conductivity were developed to reduce kiln shell temperature and hence reduce energy consumption. Substances forming different pore structures and their influence on microstructure as well as physical, mechanical and thermal properties were investigated. A novel energy-saving basic refractory brick with reduced thermal conductivity by optimum porosity structure is developed without compromising the refractoriness as well as mechanical and thermal properties.

Recently, with the growing demand for reduction of kiln heat loss, lightweight monolithic working lining with low thermal conductivity and low bulk density were proposed and developed. These refractories were expected to decrease the kiln heat loss and specific refractory consumption per ton of products. To improve the energy-saving capacity of aluminosilicate refractory castables for working lining of high-temperature kilns, this study presents the researches on structure, microstructure and properties of lightweight aluminosilicate refractory aggregates and castables. Firstly, the lightweight aggregates were produced using the high-quality kaolin and the porogenous material using high temperature processing and investigated in terms of XRD-mineralogy, pore structure and chemical composition. Secondly, the lightweight castables with different particle size distribution, as per Dinger and Funk model, were designed to attain different flow consistency. Both calcium aluminate cement (CAC)-containing and cement-free monolithics were processed conventionally and heat treated at temperatures between 110-1200°C. The samples of precast refractory shapes were investigated in terms of physicomechanical and thermal properties, XRD-mineralogy, microstructure-SEM/EDS and corrosion resistance. Moreover, a comparative study on lightweight and dense aluminosilicate castables was done. In conclusions, the lightweight specimens exhibited high strength, excellent thermal shock resistance, low thermal conductivity and good corrosion resistance, which can meet the requirements for furnaces for thermal treatment of steel.

Creep strain recovery after unloading has been well studied for metals and certain ceramic composites; however, it has not yet been investigated for ordinary ceramic refractories applied in industrial furnaces. The present study explores the question whether creep strain recovery can be observed in ordinary ceramic refractories to justify its consideration in the design of such refractories and refractory linings. To this end, the dependence of creep strain recovery on different loading conditions was investigated for a high-alumina in situ spinel-forming castable, which is commonly used as refractory lining of steel ladles in secondary steel metallurgy. Several loading/unloading compressive creep tests were performed at 1300 °C for different loading histories. Creep strain recovery was observed to occur and it was significantly affected by the holding time and degree of unloading. A longer holding time for the loading period was found to increase the internal stress, which is the driving force for creep strain recovery. In addition, the findings indicate that a higher excess of internal stress over external stress after unloading induces higher strain recovery.

Low-cement-bonded alumina-chromia castables are used in the ferroalloy industry. However, the presence of Cr2O3 in these refractories can lead to the formation of water-soluble hexavalent chromium-containing alkali chromate salts, which are carcinogenic and pose environmental and health hazards.
Alumina-spinel castables, which combine alumina and spinel/MgO, offer a balance of properties including good thermal shock resistance, corrosion resistance, and mechanical strength. These materials are widely used for steel ladles.
Four alumina spinel castables were developed and tested in the laboratory, including three low-cement-bonded castables and one non-cement-bonded castable.
The low-cement-bonded castables had higher compressive strength and porosity compared to the non-cement castable.
This study demonstrates that alumina spinel castables are a viable alternative to alumina-chromia castables.
Subsequently, both low-cement and non-cement castables were field-tested.
The results showed that the non-cement castable did not exhibit the expected service life, whereas the low-cement-bonded castable with calcium magnesium aluminate cement showed promise as a replacement for the alumina-chromia castable.

RHI Magnesita is dedicated to advancing sustainability and fostering a circular economy within the refractory industry. However, the diverse range of products used in custom linings presents significant challenges. Notably, we are focusing on increasing the recycling rate of magnesia carbon (MgO-C) bricks, which are extensively used in the steel industry. One well known challenge for this type of refractory product is the reuse of magnesia carbon recycling containing antioxidants, especially aluminium metal, due to the formation of aluminium carbide. This article will provide a comprehensive understanding of the existing issues regarding its detection and treatment, and will introduce innovative, custom-made solutions to overcome these obstacles. Furthermore, it will discuss how the automated sensor-based sorting solution developed within the EU-funded project ReSoURCE project is contributing to strengthening the circular economy of magnesia carbon and innovating the entire process chain of refractory recycling.

The automotive industry is changing to attain the global aim of emission-free mobility. In the last few years, the ratio of electric driven vehicles is constantly growing, which results in a booming battery industry. The most used battery technology for electric vehicles is the lithium-ion battery (LIB).
Ternary materials such as NMC (Lim-n(NixMnyCo1-x-y)O2) and NCA (Lim-n(NixCoyAl1-x-y)O2) are commonly used for the cathode of LIBs for electric vehicles. These materials are usually prepared through solid-state reactions at temperatures between 500 and 1000 °C [1, 2]. Refractory saggars are necessary for this calcination process. Due to the low thermal expansion coefficient, good hot modulus of rupture, and low cost, saggars are commonly manufactured from cordierite-mullite materials. These show severe damage in consequences of corrosion after a few sintering cycles, which results in periodic replacing of the saggars and contamination of the cathode materials. To avoid these disadvantages, a high corrosion resistance against battery materials is a key property of new saggar materials.
The corrosion resistance of common saggar materials and other interesting refractory materials of STEULER were investigated. For ranking the materials in relation to their corrosion resistance a modified and repeated crucible test, also called cup test, was implemented, which reflects the requirements during the calcination. In addition to the crucible test, the reaction products between the potential saggar materials and the lithium carbonate containing precursor were discovered by X-ray diffraction analysis.

Refractory materials are exposed to thermal, mechanical and chemical stress, which can lead to wear and destruction. They behave in a brittle-elastic manner up to high temperatures. One-sided heating during use creates a temperature gradient in the material, which can cause thermally induced stress cracks. These cracks can lead to failure of the material. At high temperatures, the material softens and its fracture behaviour changes to plastic behaviour. This softening can contribute to melt phase formation and reduce the thermally induced stresses.
In this study, field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) were used to investigate the controlled formation of melting phases in refractory castables and to draw conclusions about the influence of the melting phase on softening behaviour, erosion and corrosion resistance.

The world is becoming increasingly aware of the importance of sustainable development, and the refractory industry is no exception. As the demand for environmentally friendly products increases, and regulatory requirements become more stringent, the sector is undergoing significant changes. However, it is difficult to assess the actual sustainability of the industry’s transition due to the lack of reliable data on the environmental performance of refractories.
This study offers solutions to improve the quality of life cycle assessment (LCA) of refractories by analysing the production routes of raw materials. The LCAs of alumina, magnesia, and mullite, allow to identify the most critical environmental domains and impacting processes, searching for underlying trends typical of the sector. Scenarios and sensitivity analyses are used to quantify inconsistencies and to discuss the quality, reliability and comparability of inventory data and results in terms of technological, geographical and temporal coverage.
Strategies are identified for enhancing data quality to improve the robustness of the assessment and calculate comprehensive and accurate results. Emphasis is put on modelling energy consumption, which is demonstrated to be an environmental hotspot. Indeed, most of the results variations generated by regionalization, technological options and eco-design can be attributed to differences in energy mix or energy demand. Such considerations guide the dataset improvement and pave the way for the harmonization of refractories’ LCA.
Overall, the project supports the transition of refractory industry by orienting stakeholders’ effort in data collection and implementation of efficiency solutions towards the current criticalities and environmental hotspots.

Practical experience shows that the particle size distribution (PSD) and the specific surface area (SSA) of their ceramic matrix significantly influence the processing, setting and sintering properties of refractory castables. However, there is a lack of knowledge about the extent to which the properties of refractory castables are influenced by changes in the SSA and the PSA of the matrix of refractory castables. A better understanding of this influence promises considerable new potential for innovative refractory castables.
The zeta-potential of suspensions of matrix particles (< 45 µm) was measured, depending on the matrix’ SSA and the dispersing system used. Castables based on the analysed matrices were mixed and investigated. Two dispersing systems were used in the refractory castables with different amounts of the dispersing agent.
Results reveal the influence on deflocculation and the first stiffening of the corresponding castables. Using polycarboxylate ether (PCE) as dispersing agent, with increasing amount of the PCE the time until stiffening is elongated distinctly. The same effect occurs when the SSA of the matrix is being decreased while the amount of dispersing agent remains constant. A correlation between the moment of stiffening and the amount of dispersing agent per surface area can be shown.
Using a polymethacrylate (PMA) in combination with citric acid as dispersing agent, both an increase in the amounts of PMA and citric acid lead to a longer time until stiffening. The role of the SSA of the matrix is not completely clear here.

Alternative Cr-free refractory materials are still sought to substitute magnesia-chrome refractories, as the latter negatively influences environment and labor conditions due to the release of carcinogenic Cr6+ compounds.

Spinel (MgAl2O4), hercynite (FeAl2O4) and galaxite (MnAl2O4) successfully substituted picrochromite (MgCr2O4) in magnesia-chrome refractories in burning zones in cement rotary kilns. In this work, we propose a new multicomponent spinel (Mg,Zn)[Fe,Al]2O4 as a matrix or aggregate used in magnesia-based refractories for high-temperature furnaces in the copper industry. Besides the thermomechanical advantage of using spinel in the composition of the refractory via microcrack formation, which dissipates energy, spinel may accept multiple ions from slag like Fe2+/3+, Zn2+, Cu2+, which are deleterious for refractory materials. Pre-saturation of the refractory spinel matrix with slag elements may hinder the further dissolution of the refractory by reducing the concentration gradient of elements between slag and refractory, thus lowering the driving force (chemical potential) for diffusion-induced corrosion, as well as the formation of a protective layer at slag/refractory interface.

This work presents the production route of new Cr-free aggregate from the system (Mg-Zn-Fe-Al-O) with different compositions. We reveal the phase composition (XRD), iron valency and site occupancy (Mosbauer spectroscopy), microstructure (SEM/EDS), physical properties, penetration depth by copper slag, variation of slag contact angle with temperature, and sintering characteristics by dilatometry.
This work relates to the European patent submission no: EP24153408.0 (Inventor: I. Jastrzębska).

The idea of a circular economy, incorporating industrial waste, is now being extended to refractories as well but enough importance was not given in recent past how to recycle spent refractories. As a result, a significant portion of spent refractories were used for landfilling or repurposed for road maintenance. However, recent initiatives aim to start using different spent refractories through proper processing techniques and to maximize the utilization to achieve several advantages. Recycling of spent refractories not only reduces the consumption of prime raw materials but also controls the carbon emissions associated with their high-temperature processing. Since substantial portion of refractories are utilized in high-temperature applications and many a times come in direct contact with molten metals or steel and therefore the quality of spent refractories is very crucial to prevent operational failures. Challenges in recycling include the lack of established technologies for sorting spent refractories based on their characteristics after collecting from muck or debris. In most of the times manual sorting has been employed in numerous instances. In that case, effective methodologies and highly skilled labor are essential for transforming spent refractories into an acceptable and consistent manner. Common recycling processes are cleaning, crushing, grinding, sorting, segregation, calcination etc. but chemical treatment is also another process to remove slags or other impurities in specific cases.

This study discusses a systematic industrial approach to obtain different grades of refractory raw materials from spent refractories and incorporating them into various formulations, followed by performance monitoring.

In spinel-forming castables, additive additions can promote the development of the spinel phase at elevated temperatures. Here we study the effect of small additions of titania and carbon with respect to the amount of in-situ formed spinel. The samples used for the investigation were casted from an aqueous model mass containing beside fine-grained alumina and magnesia also a certain amount of the additive. The phase compositions of the burned samples were determined in quantitative phase analyses employing measured X-ray powder diffraction data. Further investigations were carried out to scrutinize the effect of the additives on changes in the microstructure and some crucial key properties of the castables.
Compared to additive-free reference samples, the castables containing titania were found to exhibit an improved sinterability and a higher cold crushing strength after burning. In parallel, the TiO2-containing samples formed significantly higher amounts of spinel during the heat-treatment.
For the carbon-containing samples, the grain size of the carbon source proved to be an important parameter controlling the influence on the spinelization. While the addition of carbon black (particle size d90 < 1 µm) clearly facilitated the spinel formation, the influence of fine-grained graphite (particle size d90 ~ 75 µm) was less pronounced. The use of coarse-grained graphite (particle size d90 ~ 180 µm) finally even hampered the spinelization. This latter effect is attributed to the presence of large graphite flakes which presumably inhibit the chemical reaction by blocking the direct contact between alumina and magnesia grains.

The refractory, metallurgical and high temperature processs industry are in a change. The trend to a fossil free and sustainable economy is accompanied with challenges and efforts. The younger generation is highly involved in this process in all parts of the world. But how does the younger generation see and chooses its career decsions in this changing industrial environment? How can the field of refractories, metallurgy and high temperature process be reimaged.? The need for well educated and prepared engineers for this area is due to time pressure very high.
This talk gives an overview about different worldwide student, education and research programmes. Academic as well as industrial, single and cooperative campaigns are highlighted to give a comprehensive view on this important field of education in a changing industrial area.

Beside the coarse and medium grain size distribution, the matrix components play a pivotal role in the performance of refractory castables. Based on practical experience, it is evident that the PSD and the resulting specific surface area of the ceramic matrix exert a significant influence on the processing, setting and sintering properties of refractory castables, which in turn influence each other. However, there is a paucity of knowledge regarding the extent to which the properties of refractory castables are influenced by changes in PSD or specific surface area of the raw materials in the matrix. The objective is to gain a general understanding of this.
To shed more light on this issue, the ceramic matrices were varied, resulting in model castables with gradations in the specific surface area of the matrix. The refractory castables were dispersed using two disparate dispersing agents with different mechanisms of action (electrosteric and steric) at graded concentrations.
This contribution demonstrates that matrices with lower specific surface areas require less mixing energy than coarser ones. A higher specific surface area leads to a lower slump-flow. A shear-thinning behaviour was observed for matrix compositions with higher specific surface areas and a dilatant behaviour for matrix compositions with lower specific surface areas. Higher specific surface areas of the matrix result in an earlier first rise of the US signal, while the addition of more dispersing agent leads to a delayed first stiffening. However, there are clear differences in the setting behaviour of the various dispersing agents.

Every year, approximately 28 million tons of used refractories are generated worldwide. The majority of the consumed refractories are used for foreign applications, such as aggregates for road construction (downcycling), or deposited in landfills, while their recycling played a rather subordinate role until now. For ecological and economic reasons, an increased research potential to deal with the application of refractory recyclates was identified in the last few years.

The objective is to research and develop new sophisticated recycling options for used MgO-C refractories allowing both the recycling (re-utilization in similar high-temperature materials) and the upcycling (material upgrading) of refractories in metallurgical processes.

The development of a new generation of coarse-grained high-temperature materials based on MgO-C refractory recyclates with particular functional properties for high-temperature processes in the metallurgy covers two concepts: 1) MgO-C refractories based on recyclates and a pitch- and resin-free environmentally-friendly lignin-collagen binder system with an application as lining material for steel ladles, and 2) Novel metal-ceramic composites based on MgO-C recyclates with an application as electrode material for aluminium fused-salt electrolysis.

The presentation will provide insights into the latest technical results of this long-term project, such as physical (bulk density, open porosity, Brazilian-test) and thermo-mechanical properties (CCS, oxidation resistance, RuL) of MgO-C with the new binder system as well as microstructure (SEM/EBSD), electrical conductivity electrochemical potential, and appliance tests of the MgO-steel anode materials.

Cement is made by heating a mixture of limestone and clay, or other materials of similar bulk composition and sufficient reactivity, to a temperature in the neighbourhood of 1450 °C. Alternate raw materials and alternate fuels are used in cement kilns to reduce production costs. Alkali compounds, Sulphur and Chlorine are introduced in the system by the raw meal constituents. As a result, the OPC chemistry cannot simply be defined by CaO - Al2O3 - Fe2O3 - SiO2 system. Rather the impact of minor constituents like MgO, TiO2, K2O, Na2O, SO3, Chloride etc. need to be considered for cement production process as well as their influence on the refractory performance. “Build Up” is one of the major issues in this unit and the situation is likely to worsen with the increase of Alternate Fuel usage. The volatile compounds, i. e. alkali Sulfates and chlorides, once formed by virtue of reaction between the Alternate Fuel (AF) combustion yield, travel with the flue gas. Sulphur compounds have relatively higher melting points and as a result travel towards the kiln outlet and get recirculated. Chloride compounds, on the other hand, have lower melting points and they are primarily in the inlet area of the kiln. During this study, samples, from different sections of the kiln system, were collected and analysed to understand the root cause of coating build up and refractory failure in various sections of the kiln. Based on these results compatible refractories have been recommended.

Female Talents – Innovation Through Diversity

Keynote by Dr. Stevie Schmiedel, Panel Discussion, and Networking

The event will kick off with a keynote by the esteemed Dr. Stevie Schmiedel, followed by a dynamic panel discussion on "Female Talents - Innovation Through Diversity. The future of the refractory industry relies on attracting and promoting talented women. By showcasing various perspectives from decision-makers, managing directors, and young talents, we aim to highlight the potential benefits of fostering a diverse and inclusive workplace. This event is a unique opportunity to:

Gain Insights: Hear from leaders in the industry about the importance of gender diversity.
Network: Connect with forward-thinking professionals dedicated to shaping a sustainable and innovative future.
Be Inspired: Learn how diverse teams can enhance creativity, problem-solving, and overall workplace satisfaction.

This event is organized by Women@Refractories, a network founded to support and connect women in the refractory, raw materials, and process industries. We believe that by empowering women and increasing their visibility, we can create an industry that appeals to new talents and addresses the current talent shortage.

3d printing has evolved enormously within the last years. New areas of technical ceramics in aerospace, energy generation and construction are being opened up, but refractories are actually not part of that emerging business. But technically, 3d printing is not a single method, but a summarizing term for a variety of different manufacturing processes. These technologies vary across a broad spectrum to fulfill several needs, from fine-grained to coarse-grained particles , dense or porous bodies, as well as small to comparably large parts. So, every technique has its own pros and cons. Additionally, all this is limited by the application and needs for refractories.
This presentation gives an systematic overview of 3d printing methods suitable for the manufacturing of refractories . We show the limitations and possibilities with several technologies and materials and why it’s not “plug and play” with refractories but how the methods can be adapted to the challenges. Solutions are presented for applications which work and which are already in use today. We give examples what can be expected form a 3d printed refractory body nowadays compared to conventionally manufactured refractory materials.

The steelmaking industry generates several by-products and wastes during the whole steel production process. Producing one ton of steel in a steel plant generates half a ton of by-products such as slags, dusts, and sludges. To meet the goal of achieving net-zero greenhouse gas emissions by 2050, handling such massive quantities of by-products is a major concern. As part of the CESAREF European network dedicated to developing sustainable applications of refractory materials, this project aims to transfer vanadium-bearing slags into high-alumina refractory castables. By implementing advanced mineral processing techniques for alternative calcium aluminate cement and grog aggregates, the project seeks to reduce reliance on natural virgin raw materials, thus promoting a circular economy. Reducing the usage of natural virgin raw materials minimizes costs related to their extraction and processing. The present work investigates the impact of vanadium-bearing residues introduced in self-flow castables formulation both as a typical bonding phase and as typical aggregates. Vanadium-bearing slag exhibits promising properties to be used as a secondary raw material in castable applications. Beyond its structure and chemical composition, its microstructure offers significant advantages for castables, particularly in terms of maintaining mechanical strength under high temperatures. This study evaluates the mechanical properties and microstructural analysis of both conventional castables and those incorporating slag, providing insights into their comparative performance.

Hydrogen will play a key role in the decarbonization of steel manufacturing and other high temperature processes in the industry replacing carbon as reactant for reduction processes and fossil fuels. Hydrogen can attack oxide based refractories by creating volatile phases through reduction and weakening and destroying refractory linings over time. The resistance of oxides against such attack depends on their thermodynamic stability and the process conditions in the application. Temperature, process gas composition and pressure, and gas velocity are important factors. Synthetic alumina based materials are known for their higher resistance against hydrogen attack and therefore are applied for example as refractory linings in petrochemical processes. However, new hydrogen applications such as reducing agent for direct reduced iron or as fuel in industrial combustion processes will involve higher hydrogen concentrations and process temperatures when compared to existing applications in the petrochemical industry. Therefore research is needed on resistance of alumina-based refractories under these new conditions. The paper discusses new results for hydrogen resistance of synthetic alumina based castables with different cement contents, hydratable alumina and matrix approaches including reactive alumina and silica fume. Testing was done with pure hydrogen at 1150 and 1400 °C for 200 hours and measuring weight and strength loss.

In order to develop Steel Ceramic Composites able to withstand the contact with liquid aluminum and aluminum alloys the understanding of the interaction mechanisms within the heterogenous metal melt/solid material system is indispensable. The crucial and most sophisticated aspect of the composite corrosion process is the corrosion initiation caused by the contact with the liquid metal. This urged comprehensive investigations of all factors contributing to the corrosion, including the electrochemical as well as chemical driving forces. For the analysis of the initial corrosion stage novel DSC-aided corrosion tests, high temperature electrochemical investigations and wettability measurements were developed and adapted.
The evaluation of composites applicability lead to in-depth analysis of their structures, its transformation during the surface treatment as well as its degradation after the corrosion tests. The determination of phases resistant to molten aluminum alloy and necessity of understanding of corrosion mechanisms between the materials resulted in very comprehensive series of experiments, including evaluation of the pre-oxidation process on the structural transformation of the composites as well as numerous in-depth short- and long-term corrosion tests. All of presented investigations have been extensively supported by various thermal and electrochemical analyses, numerous CLSM and SEM micrographs with EDS/EBSD analyses and comprehensive phase analyses using X-Ray Diffraction.

The usual objective of light weight refractory raw materials is to insulate furnaces in high temperature processes to allow a safe operation, with as little energy consumption at a maximum furnace capacity. A range of raw materials that are frequently used to formulate insulating bricks and castables are discussed in the first part of this review. In the second part, some special technical features of recently developed lightweight and weight-reduced refractory raw materials will be highlighted. They allow a valorisation in specific application areas beyond insulation and energy saving effects.

Poster Slam

A new mineral binder for No Cement Castable (NCC) and its adaptability to specific working and hardening times will be discussed in this paper. Commonly, setting behavior of refractory castables can vary in different ambient temperatures, depending on the binding type used due to the different reactions involved (hydraulic, chemical, gelling-coagulating, polymerization,...). Also, at a given temperature, levers are needed to adjust the working and hardening time to specific applications and formulations. Due to different reaction kinetics at different ambient temperatures for a given castable binder system, usually one experiences an excessively long setting time at low temperatures, while inversely, having a very short workability and setting at high temperatures. This article will first show the impact of curing temperature in the range of 5-35°C on a castables bonded with the new NCC-mineral powder binder prototype, in comparison with other binders like colloidal silica by measuring rheology, ultrasonic profile and green/dried mechanical strength of a bauxite reference castable. In the second part it will be investigated how the usage of common accelerators/retardants interact with this new binder system. Solutions will be explored that could be used as a lever to create sufficient robustness to curing conditions and to help formulators to adjust their recipes to specific working and demolding time requirements.

The rheological behaviour of vibratable castables is of great importance for their performance and practical application. This study assesses the reproducibility and accuracy of the conventional slump test in evaluating castable flowability. Three model vibratable castable formulations with q-values of 0.28, 0.31, and 0.34 were analysed. Key variables such as varying oil amounts on the vibration table and the influence of different operators on measuring spread dimensions were examined. Furthermore, the efficacy of 3D spread flow measurements using an integrated 3D camera was investigated as an advanced alternative to the conventional slump test. The system demonstrated sensitivity to oil quantity, with increased oil on the vibration table augmenting spread flow but also increasing measurement deviation. The findings also revealed a robust correlation between spread flow measurements obtained with calipers and those recorded using a 3D camera, thereby enhancing measurement precision. The 3D spread flow technique demonstrated superiority in capturing complex rheological behaviours, enabling the quantification and comparison of flow velocity and shear rate during vibration across different formulations. Each formulation displays distinct shear rates and flow profiles, underscoring variations attributable to differing q-values.
This study highlights the potential of incorporating 3D spread flow techniques into standard testing protocols, providing refined insights into the rheological properties and overall performance of castables. The advanced method enables the optimisation of castable formulations for industrial applications.

The use of microsilica-gel bonding in no-cement (NCC) shotcreting has gained interest in the last decade with the aim of increasing the lifetime of the refractory material. Consequently, the accelerators that are conventionally used for low-cement and ultra-low cement shotcreting are not suitable. Alternatives that are currently being used for NCC shotcreting either have cost implications for installation or maintenance of equipment or performance limitations of the refractory product. This study investigates the use of different hydrogels as accelerators in NCC shotcreting, together with a binder system, SioxX®-Flow, with the aim of improving the shotcrete applying process, high temperature refractory properties, and limitations associated with current alkali-free accelerators. The evaluation consisted of two parts: 1) characterization of the hydrogels through rheology measurements, 2) evaluation of hydrogels in refractory shotcrete. The characterization of the hydrogel consisted of rheology evaluation of refractory slurry suspension that contained the hydrogel and oscillatory rheology for the pure hydrogels to determine gel strength. The evaluation of the hydrogel in the refractory shotcrete included non-destructive resonance frequency and damping analysis of samples after demoulding, drying, and firing at 1500°C. A preferred hydrogel was proposed based on the requirements for application of refractory shotcrete and results from this evaluation.

Plastic storable masses are essential materials in refractory applications due to their convenient storage and handling characteristics. They can be shaped without a casting formwork which makes them ideal for custom applications and repairs.
Plastic mixes frequently contain a phosphate source like mono aluminium phosphate solution as a binder instead of water. This enhances the refractoriness under load, gives good abrasion resistance, higher slag resistance and better adherence to spent refractories.
One of the issues with phosphate bonded plastic refractories is their limited shelf life of around three (3) months. We present a newly developed phosphate binder, which increases the shelf life for plastic mixes significantly.
This study compares the plasticity over time and analyses the typical physical properties like density and cold crushing strength at different ranges of temperature.

Historically, improving refractory castables' high-temperature performance involved reducing calcium aluminate cement (CAC) content. However, even small amounts of CaO caused issues and CAC-bonded castables require careful drying to avoid damage. Cement-free castables with sol-gel binders, like colloidal silica (CS), emerged as alternatives, but CS-bonded castables still face structural stabilities at high temperatures. Given the limitations of CS-based binders, research has shifted to alternative sols like spinel and mullite. Castables bonded with them offer better high-temperature performance but suffer from extended setting times and low green strength due to lower solid content in initial sols (5-10 wt.% vs. 30 wt.% in commercial CS).
In this context, spinel suspensions with 30 - 50 wt.% solid content were developed. Then, the impact of the solid content on setting and green mechanical properties, as well as thermomechanical properties (elastic modulus and HMOR) was analysed. The findings demonstrate that higher solid content enhances green mechanical properties of spinel-bonded castables, though demoulding time is longer than for CS-bonded castables. However, thermomechanical properties are improved notably during initial heating, surpassing those of CS-bonded castables, especially above 1000 °C, where viscous or liquid phases start to form in CS-bonded materials.

Elastic properties of materials are essential for the description of the material behaviour due to external stresses. Young’s modulus values are of high importance for technical application with refractories. Precise determination of this material parameter is crucial for a reliable and cost effective construction and simulation of high temperature vessels and processes.
This study compares different methods for the determination of static and dynamic Young’s Modulus at low and high temperatures. For the acievement of static Young’s Modulus data usually stress strain curves of three point bending tests are used. Nevertheless the high stiffness of the testing samples often leads to compression of the testing device itself resulting in too high deformation values as well as less precise Young’s Modulus values. Due to the use of a stiff bending bar quantification of the bending device deformation is possible and therefore a modified and realistic achievement of the Young’s Modulus data is generated. Furthermore the deflection of testing bars was measured by means of digital image correlation (DIC). The applied DIC device ignores typical spring-back and setting effects, reveals a direct measurement of local strains on the sample surface and due to a stochastic pattern the deflection and area analysis is possible. High temperature results of this static measurements are compared and discussed to other methods such as the dynamic resonance frequency damping analysis (RFDA).

The main purpose of this work is to evaluate the thermal stability performance of different aggregates such as; fireclay, bauxite, granite, calcium aluminate clinker, silica sand, furnace slag with calcium aluminate cement(CAC) containing 35%, 40% and 50% alumina under high temperatures. 20 cubic samples are prepared to observe every aggregate with every CAC individually. In fresh concrete, water cement ratio gradient develops around aggregate particles during casting, resulting in an altered microstructure of the surrounding hydrated cement paste. This zone around the aggregate is called interfacial transition zone (ITZ). The quality of ITZ defines the thermal stability performance of the sample. A traditional CAC based castable form ceramic bond between 900-1200°C and then becomes stronger in terms of bond strength. This work is supported with the SEM images of ITZs. Eventually, the bonds are broken and melting is observed at different temperatures for every sample. After 1250°C, the melting point is differentiated according to alumina content and aggregate type. All in all; performance of fireclay samples are the most durable ones with a melting point above 1550°C while the CAC aggregate show the best performance by filling the pores since the partial reaction at the surface of this aggregate also improves the bond between aggregate and cement.

Al2O3-C refractories are extensively used as functional components in continuous casting of steel. These high-duty Al2O3-C products -like submerged entry nozzles, ladle shrouds and monoblock stoppers- contain up to 30 wt.-% carbon and present excellent mechanical, thermal and chemical properties, enabling the cost- and quality effective implementation of the continuous casting process.
Ceramic glazes are externally applied on Al2O3-C flow control refractory products to protect carbon from oxidation. These glazes are typically boron-containing. However, the increasing requirements for clean steel technology along to environmetal- and health issues associated with boron compounds will make the utilization of boron-free glazes a necessity in the upcoming years.
New boron-free self-glazing Al2O3-C formulations with wollastonite, magnesia, sodium carbonate and/or calcium magnesium aluminate additives were developed with the assistance of the FactSage software tool. These compositions presented a softening point in the range of 1000 – 1100 °C for self-glaze formation, which is the typical preheating temperature range for Al2O3-C functional refractory products. In addition, the influence of particle packing on their oxidation resistance was investigated, based on established and newly developed particle size distribution models with distribution moduli in the range of 0,28 – 0,8.

The way of processing of vibrating refractory castables is largely responsible for the properties and durability of the final products and is fundamentally determined by their rheological character. However, it has not been possible to quantify the shear rate-dependent rheological properties, such as dynamic viscosity and shear stress, of vibrating refractory castables until now. A lifting sphere rheometer for measurements on vibrating refractory castables was developed and validated. Results from measurements under vibration show that the shear rate-dependent rheology can be well quantified.

The bonding phases of refractory castables play a central role in their performance. Especially their behaviour at high temperature is decisively responsible for the performance of a refractory lining. While calcium aluminate cements have established themselves as "workhorse" for refractory castables (reliable and cost-effective), they nonetheless have some drawbacks (high risk of explosive spalling during drying, limited resistance to acidic slags and ashes) and, after years of optimization, only limited potential left for further improvements. By contrast, sols bonded castables experience a growing use in the industry (silica sols) and, despite their current limitations (low green strength, limited refractoriness), have much to offer. Especially alternative sols such mullite and spinel sols are starting to draw attention in order to improve the refractoriness and resistance to corrosion of sols bonded castables, but studies regarding their performance at high temperature are extremely sparse.
The thermomechanical and thermochemical behaviour of silica and spinel sols bonded high alumina refractory castables was investigated using wedge splitting measurements, high temperature thermal shocks and induction furnace tests. Silica sol bonded high alumina refractory castables are rather weak when compared to cement bonded high alumina refractory castables, but displayed an improved resistance to high temperature thermal shocks. The use of spinel sols improved greatly the high temperature mechanical and fracture resistance of the sol bonded high alumina refractory castables without degrading their resistance to thermal shocks and even slightly improving their resistance to corrosion.

Currently, the main purpose for obtaining alternative binders for use in taphole clay is to reduce the exposure to harmful polycyclic aromatic hydrocarbons (PAH) associated with conventional coal tar (CTht) binders. Some advances have been made such as using lower-PAH alternative binder or phenolic resole resin (resin-bonded) in taphole clays. The use of non-toxic binders has become exceedingly difficult due to the versatility of CTht in taphole clay. This study investigated a combination binder system that consisted of a sugar alcohol (research-grade glycerine) and phenolic resole resin as a potential non-toxic binder for use in platinum smelting taphole clay. The binder system was characterized according to its composition through Fourier-transform infrared spectroscopy and the PAH content (16-EPA-PAH) was determine using targeted gas chromatography mass spectroscopy. Flow behaviour of the binder was determined through rotational rheology, and the volatilization and rheological thermal stability of the binders were assessed through thermogravimetric analysis and thermorheology, respectively. The effect of mixing these binder constituents on the cross-linking behaviour of the phenolic resin was evaluated using differential scanning calorimetry. The combination binder had a higher average mass loss and lower carbon yield compared to conventional CTht, but with a lower total PAH content, making it a more health-friendly alternative.

Calcium hexaluminate (CaAl12O19 or CA6) formation has been found to occur via solid and liquid state reactions at high temperatures in calcium and alumina containing compositions of refractory castables. In this research, focus is given to the solid-state reaction predicted for the silica-free refractory systems.
Pure alumina aggregates tend to have different morphologies (surface roughness, pore structures, grain sizes and shape) due to the varying processing routes. This affects the interaction or bonding between the matrix and the aggregates. For the formation of CA6, the diffusion of calcium into the alumina aggregates and segregation at the borders or surface at high temperatures has been reported. However, the extent of this transport mechanism due to a chemical potential gradient (Ca2+ concentration difference) is not very clear. In this paper, the influence of the type of aggregate, grain anisotropy and impurities on CA6 crystal location has been investigated and discussed. Furthermore, the expansion effects of CA6 on inducing microcracks into the aggregates and refractory castables has been analysed.

In the last decades, X-ray computer tomography (XRT) has become an important examination technique in the materials science with a wide range of applications. XRT is a non-destructive and noncontact testing method that provides the investigation of external structures as well as three-dimensional insights into the volume of objects. Due to this benefits, XRT application still exhibits increasing importance and expansion of its research field.
This work presents the opportunities and advantages of XRT technology in the characterization and determination of material specifics of refractory materials. Based on several examples, it is demonstrated how different types of X-ray tubes enable measurements from nano to micro scale. The use of the high-resolution nanofocus tube allows the observation of small samples with a resolution down to 0.5 µm, while the high-power microfocus tube permits the penetration of large and dense samples.
In addition to the well-known function of XRT to determine the quality of prototypes or components with regard to geometrical correctness or defects such as pores and cracks, it is demonstrated, how the view into the volume helps to answer scientific questions in the field of refractories. The ability to perform non-destructive testing combined with extensive graphical analysis allows the examination of multi-step test series with a single specimen. This enables the observation of the progression in damaging or corrosion processes, which in turn leads to a better understanding of the relationship between materials properties and structural phenomena.

Alumina-carbon-based refractories, due to their unique physical and mechanical properties, are widely used as sliding gates, shroud nozzles, monoblock stoppers, and sub-entry nozzles in the steelmaking industry. In this study, the effect of modified surface of nano alumina additives and their composites with multi-walled carbon nanotubes with silane group in alumina-carbon refractories was investigated.
In this regard, nano alumina was added to functionalized carbon nanotubes to prepare the nanocomposite. To achieve better distribution of the nano additives, the particles were first functionalized with APTES silane groups. Then, 1% by weight of the additive was added to the fine grain part and subsequently mixed with the coarse particles of the alumina-carbon body. For the physical and mechanical property assessments, the samples were shaped under uniaxial pressing at a pressure of 150 MPa, tempered at 200°C for 6 hours, and fired at 1450°C for 2 hours in a reducing atmosphere under a coke bed.
Apparent density, apparent porosity, and cold crushing strength (CCS) were determined according to the standards. For microstructural phenomena and phase analysis, SEM and XRD were used. The results showed that the sample containing 1% by weight of the alumina-MWCNT nanocomposite exhibited the highest cold crushing strength of approximately 156 MPa. Additionally, the Weibull modulus results confirmed this finding. According to the SEM results, the improvement in mechanical properties can be associated with the increased formation of SiC in the presence of Al2O3-MWCNT by the vapor-solid mechanism.

In recent years, cement-free binders have been of interest due to their fast dryout behavior and improved high-temperature performance properties compared to low-cement castables. However, the mechanical strength of conventional no-cement castables (NCCs) at intermediate temperatures is limited. This study aims to develop innovative binder systems specifically for NCCs that are primarily targeted at intermediate temperature applications but can also be used at high temperatures. The flowability, setting behaviour, and mechanical strength of NCCs containing different types of cement-free binders were initially evaluated. Subsequently, the hot properties, including hot modulus of rupture (HMOR) and refractoriness under load (RUL) were evaluated. The results demonstrated that a novel binder incorporating a speciality additive, either SioxX®-Ten or SioxX®-Ten PLUS, exhibited superior mechanical strength and improved hot properties across various temperatures. Notably, the RUL results indicated that the NCCs with the novel binder contributed to mullite formation at lower temperature than the conventional NCC, and with less shrinkage after maximum expansion. Scanning electron microscopy (SEM) analysis confirmed that the introduction of the novel binder influenced both the temperature of mullite formation and the morphology of the formed mullite, contributing to the observed improvements. Overall, this study highlights the significant potential of the novel binder in enhancing the performance and durability of NCC and ultra-low cement alumina based (ULCC) castables for intermediate temperature applications in various industrial sectors, including but not limited to aluminum, petrochemicals, and power plants.

H.-J. Klischat, G. Urbanek and R. Gaebel

Steelmaking is a high-temperature process, making it one of the industries that use refractories the most, especially for constructing steel ladles. Ladles are vessels used for transporting and refining molten steel in secondary metallurgy. Proper thermal management for the ladle is essential to reduce the risk of thermal shock to the refractory linings caused by steel tapping, which can lead to ladle breakouts. Additionally, the steel temperature is influenced by refractory linings’ temperature, particularly the ladle’s hot face. Therefore, tracking the temperature profile of ladles is necessary to achieve safe and cost-effective operations. Direct measurement with thermocouples of the refractory linings' temperature in each cycle is expensive, leading steel plants to use mathematical models, such as Computational Fluid Dynamics models, to monitor the temperature of the ladle’s refractory linings. However, these models often provide temperature data for every layer of the ladle, complicating interpretation and slowing subsequent calculations. This research project considers a finite volume model for predicting the temperature of refractory layers, developed at ArcelorMittal R&D. In this model, the temperature is simulated for 108 layers across the wall, bottom, and cover, highlighting the problem's high dimensionality. We present two model reduction methods, Proper Orthogonal Decomposition as a traditional and AutoEncoders as a machine learning approach, to obtain a reduced temperature profile of the ladle and compare these approaches. These methods can be used in further applications, online temperature prediction and heating estimation to manage refractories’ lifetime and reduce CO2 emissions.

The global initiative to significantly reduce greenhouse gas emissions drives industry towards the use of hydrogen both as reducing agent and as fuel for high temperature processes.
Some knowledge on the impact of reducing gas environment with hydrogen on refractory linings is available from established industrial processes, namely glass manufacturing, ammonia or syngas syntheses or natural gas based DRI (direct reduced iron).
The use of hydrogen as a reductant for iron production is considered the main solution for the steel industry on its path to net-zero. Hydrogen can be added in small percentages as coal replacement in the blast furnace and to a much larger extend (up to 100%) instead of natural gas in the DRI process. Also, the increased demand for fossil free fuels worldwide has triggered the development of novel and optimized hydrogen and syngas generation.
The detailed conditions in new and known processes might deviate largely. In literature is few information about the impact of extended exposure of refractories to H2 rich atmospheres. Recent studies show contradicting results and differences to earlier reported ones.
It is hence challenging to distinguish between myths and facts and therefore assess the refractory performance and expected lifetime of the lining in hydrogen rich atmospheres. In this presentation we will present fact-based results of ongoing research and our experience in different industries to create insight on the impact of hydrogen on refractory linings as a function of process and testing parameters.

Alumina-magnesia-carbon (AMC) bricks are essential in steelmaking due to their exceptional resistance to thermal, mechanical, and chemical stresses. This study investigated the impact of different alumina sources, particle size distributions, and raw material modifications on AMC brick performance, focusing on optimizing their use in the ladle bottom impact zone. Results demonstrate that replacing white fused alumina (WFA) with tabular alumina significantly improves the brick's cold-crushing strength (CCS) after coking due to increased spinel formation. While WFA offers superior initial strength, the enhanced reactivity of tabular alumina results in superior hot CCS and overall high-temperature performance. This study further explored the coking behavior of AMC bricks under different conditions, revealing the importance of considering potential chemical interactions when selecting materials. These findings highlight the potential of alternative alumina sources like tabular alumina in AMC bricks to enhance performance in the demanding ladle bottom impact zone, offering valuable insights for refractory material design and optimization in steelmaking. Notably, the CCS of the reference brick decreased after coking, while an alternative recipe using tabular alumina demonstrated increased CCS after coking.

The steel sector is the highest consumer of refractory materials worldwide, accounting for more than the 70% of the overall production. In parallel, for each ton of steel produced roughly 10 kg of refractories are used of which, on average, 40% are consumed during the production process and the remaining become waste. Although recycling practices are pivotal to accomplish EU Green Deal circularity targets, improvement of operative lifetime and re-use of refractory products are at a higher priority level. Reliable investigations to improve refractory operativity require the combination of experimental analysis, on site recording, post-mortem investigation, and numerical methods. Among the different analytical approaches, Finite Element Analysis (FEA) has been considered. From FEA simulation of tundish continuous casting steps conditions, the resulting key parameters for an effective prediction of refractory linings energetic performance has been extrapolated. Furthermore, supported by experimental measurements on new and post-mortem refractories, the impact of different anchoring arrangements has been evaluated. Transient thermal analysis at each time step of the casting has been computed, and the results compared over different steps may allow an estimation of the remaining useful life of the refractories considering operational guidelines and thermal efficiency standards.

Carbon-bonded magnesia (MgO-C) is an established lining material in converters, steel casting ladles and electric arc furnaces. With regard to the increasingly desired recycling of refractory materials, the comparison of the thermo-mechanical behavior between MgO-C batches with fresh MgO and with partially recycled MgO-C agglomerates is of high economic relevance. The Refratechnik Steel GmbH provided the MgO-C material used in this study, which is applied in industry. Two batches were provided to evaluate the influence of MgO already used in practice in MgO-C materials: MgO-C consisting of only fresh MgO, as well as MgO-C with recyclates with a proportion of recyclate:fresh material of 1:1.

In this study, the thermo-mechanical properties of the MgO-C materials were determined at temperatures of up to 1300 °C. The focus was on determining the compressive strength, which provided the basis for the subsequent creep and stress relaxation tests. The thermo-mechanical tests were carried out on an electromechanical high-temperature testing machine with an integrated protective gas chamber. This enables testing at temperatures of up to 1500 °C in an inert gas atmosphere.

It was shown that the introduction of recyclates influences the microstructure of the composite material and therefore also its properties. In addition to a change in porosity, density and dynamic Young’s modulus, the use of recyclates also has an effect on compressive strength, stress relaxation and creep behavior. SEM images provide insights into the deformation and damage behavior.

Our modern industrialised society is facing a new challenge with regard to our own living environment. A change of mindset and a change of economy are therefore indispensable. We can call this a global green deal as the basis for a sustainable economy.
To achieve this goal, greenhouse gas emissions must be reduced. This is only one part, but it is very important. This will require a major transformation of industrial processes. The steel industry is in focus of this transformation because it has an alternative process that has a high potential for reducing emissions. The direct reduction process will be one of the main production routes for iron and steel in the future.
This presentation will explain the main process and compare the benchmark standard with the new developments (HIRON series) based on STEULER REFRACTORY LININGS more than 15 years of experience in direct reduction.

Until recently, the refractory wear lining of the converter vessels of the BOS2 steel plant of Tata Steel in the Netherlands was mainly originated from our own refractory plant. Due to the green, clean and circular future plans of the steel plant in IJmuiden our dedicated brick plant has closed.
Alternative suppliers had to be selected and therefore several suppliers were approached for a proposal for a refractory wear lining of the converters.
To select the most suitable refractory lining, a transparent, verifiable and logical selection method was developed based on the experiences in wear of the converter lining in BOS2 with the in house produced materials. For the different parts of the lining, the contributions of different wear mechanisms have been assigned. Per wear mechanism, the test results of all materials offered are put in order and ranked. Thereafter, based on these rankings and the significance of the different mechanisms, a ranking of bricks was made for the different parts of the lining, followed by a final ranking of each supplier for the bricks of a full lining.
This method was used for the selection of the current refractory wear lining of the BOS2 converter vessels. The results out of plant trials will be used to finetune the selection method.

Thermal shock tests have been investigated on a fused mullite refractory brick, the DURITAL from RHI Magnesita, according to the EN 993-11 standard. The co-simulations heat transfer - stress show a full convergence for all the investigated mesh sizes and seem to be independent of the cohesive element thickness. The crack modelling with a mesh size of 0,0005 m is characterised by a flexural frequency close to the experimental one (3959 Hz vs. 3415 Hz).

Stopper clogging is a significant issue that significantly affects the process parameter and quality of steel produced in continuous casting processes. The goal of this work is to predict stopper clogging by concentrating on anomaly detection and clogging prediction. For this purpose, we implement AI, and in particular machine learning algorithms to find trends and abnormalities in the operational data so as to capture temporal and spatial relationships in operational data.

This study aims to evaluate the methodologies based on deep learning neural networks to detect the occurrence of clogging based on historical data of process variables. For the evaluation of model, the performance metrics, such as precision, recall, F1-score, and area under the receiver operating characteristic curve (AUC-ROC), will be used to evaluate the proposed models' effectiveness. The study will help to develop a new algorithm model for real-time prediction and anomaly detection for stopper region of CC Systems.

According to preliminary findings, it is possible to predict the evolution of several parameters, such as casting speed, stopper position and mold parameters that can help to anticipate potential clogging, which therefore enables prompt treatments and preventive measures. The predictive model will show an immense potential for predicting clogging events in the future, which will increase operational effectiveness and decrease downtime. This study tackles a persistent industrial difficulty by combining modern data-driven methodologies to solve the problem which occurs during continuous casting process.

This work investigates the effect of hydrogen on the microstructure of phosphate-bonded high-alumina refractories applied in the working lining of direct reduction reactors (DRR). These types of refractories are mainly composed of alumina, andalusite, mullite, and a glassy phase. Samples were exposed to a 100% hydrogen atmosphere at 900°C for a period of 16 and 48 h. The as-received refractory microstructure was composed of a matrix of needle-shaped mullite grains embedded in a minor glassy phase and agglomerates of corundum and andalusite. Under the exposure conditions, mullite transformed to corundum, which is the major microstructural transformation representing a considerable alteration of the refractory matrix and results in a gradual increase in the glassy-phase content. Besides, a low mass loss of about 0.075% has been observed, although the hydrogen caused some effects on the microstructure such as reduction of the mullite. Moreover, energy-dispersive X-ray spectroscopy of the postexposure material showed higher silicon content in the glassy phase, due to the reoxidation of silicon monoxide. Thermodynamic calculations confirmed the reduction of mullite and the formation of corundum under hydrogen.

The steel industry is undergoing a major transformation process to focus on low carbon emissions at the moment. Beside the development of completely new process routes, the effect of the already used refractory material is significant. On the one hand, the refractory material does have an intense carbon footprint, coming from the raw materials used and the pre-firing, in case of bricks. On the other hand, the refractory materials cause emissions when applied to aggregates in steel industry. With focus on refractory castables, an energy intensive dry-out process needs to be completed. Another main point is the lifetime of the refractory lining. The longer the lifetime is, the lower the impact on total carbon emissions will be. To contribute to all of these goals, cement free castables were developed to reach high heating up rates to safe energy and reach the maximum possible lifetime. In addition, a special product range was put into the market, which combines fast heating up and high strength over the complete temperature range to ensure a significant reduction in emission for the steel plants. In this study the realistic impact on emissions and lifetime with using tailored refractory solutions is shown. Focusing on the goal to be as efficient as possible, examples from industrial applications of cement free castables is shown for steel ladles and tundish linings.

This study examined the influence of a hydrogen-containing atmosphere on cement-bonded refractory castables. Four series of tests were conducted using different materials, including fireclay, high-alumina bricks with SiC, and sol-gel bonded phases such as mullite and anorthite. Each test series consisted of three samples, which were subjected to aging in a tube furnace at temperatures of 1100 °C and 1500 °C and holding times of 24 and 72 hours, respectively. The temperature of 1100 °C represents the upper temperature limit of a direct reduction plant, while the temperature of 1500 °C represents a temperature range in which corrosion is accelerated. An optical examination of the samples revealed a change in colour, indicative of the formation of oxygen vacancies. At 1100 °C, there were only minor changes, with no significant loss of mass or change in porosity. At 1500 °C, however, a greater loss of mass was observed, particularly at the gas inlet, as well as an increase in porosity. The chemical composition of thretee high-alumina material undergoes a transformation, with the loss of SiO2, MgO, and alkalis. Depending on the temperature and holding time, non-oxide agglomerates, primarily composed of iron and phosphorus, form on the surface of the samples. Similarly, agglomeration occurs in the castable with a high alumina content and SiC. In contrast to the other test series, however, these agglomerates do not consist of iron and phosphorus, but of iron and silicon.

Dry Vibrating mix is a product range commonly used as refractory lining of core induction furnaces in foundries. As indicated in their name, these products are installed dried, and the initial strength is only due to the densification by vibration. In this type of product, the shape of the grain, the granulometry curve and the type of vibration used have an impact on the densification. To determine the optimised parameters of our solutions, the Discrete Element Method seems the easier way to validate or optimise our products and is an alternative to the classic experimental process.

The first part of the study consists in the characterisation of two different DVM to define as precisely as possible the parameters of the model. This is the more complex part of the study. The granulometry curves, bulk density, E modulus, shapes of the grain are the simplest initial parameters. Some more tricky parameters like static response angle, dynamic response angle, rolling resistance or adherence need also to be characterised. These parameters are defined by simulating two different flow tests coming from Granutools.

When the model is defined, it is easy to simulate the densification process, and analyse the impact of several parameters in the densification of our products like type of vibration, initial loading, or shape of the grain.
This new method offers a new way to optimise our products and seems a promising way to improve several types of manufacturing processes in the refractories field.

MgO-C refractories are widely used in steel industry especially in steel ladles, BOF and EAF. They are exposed to mechanical and thermal stresses as well as interaction with corrosive media. In contact with slag or metal most severe wear can be observed, that’s why high purity raw materials must be used to withstand those conditions. Usually, in order to strengthen the thermo-mechanical properties of MgO-C materials, they are achieved by introducing antioxidant additives, which at high temperatures create ceramic forms that strengthen their structure. However, other additions may be considered in this area. Aggregates containing CaO and MgO-bearing aluminates improve selected slag resistance but also are one of the most promising solutions for stabilization for steel ladle lining.
Application in the laboratory test different grain sizes of aluminate aggregate to MgO-C refractories improved the slag resistance by contact layer formation, but also allowed to control the secondary dimensions change after heating end thermal expansion. Research included tests of the possibility of using recycled raw materials in combination with aluminates. Obtained results enabled to design a complete ladle lining construction optimal for ladles with silicon-killed steel process and high thermomechanical stress in advanced secondary metallurgy. Laboratory samples and post mortem samples observation of microstructure by SEM/EDS method allow to explain influence aluminates on slag attack and thermal stress resistance especially by joints enforcement.

Drying and dehydrating cement bonded refractory castables are crucial steps prior to their industrial application. In dense refractories, steam transfer to the surface is hindered, leading to increased vapor pressure within the material and the potential risk of spalling. Elevated pressure results in higher evaporation temperature, creating hydrothermal conditions that likely impact the hydration process and drying behavior of CAC bonded castables. The objective of this study is to provide a better insight into the development of hydrate phases in CAC-bonded refractory castables under these conditions. Autoclave treatments are employed to generate hydrothermal conditions on a laboratory scale, emulating the circumstances during the initial heating of the castable in industrial application.
As part of this study mineral phase analysis using X-ray diffraction spectroscopy is conducted on alumina-based, CAC-bonded matrix mixes spiked with two different types of liquefier after autoclave treatment at various temperatures. The findings are correlated with additional research presented at the same conference, which focuses on Raman spectroscopy of the matrix mixes and determining the pore size distribution of fully fledged castables using mercury intrusion porosimetry.

In the face of ever more pressing environmental challenges, hydrogen is anticipated to play an important role in the decarbonization of the steel industry. Importantly, there is a number of different ways it can be introduced in steelmaking processes: it can reduce iron oxide in the blast furnace or in the direct reduction of iron (DRI) in the place of more traditional reductants such as coke or natural gas; hydrogen in its plasma form could also be used to reduce iron oxide in the hydrogen plasma smelting reduction (HPSR) process; H2 can be used as a combustible in industrial furnaces to substitute fossil fuels or natural gas. Each new use of hydrogen will, however, bring about new challenges to refractory materials. When used as reducing agent for iron ores, H2 could also reduce and volatilize components of the refractory lining, leading to weight loss, a decrease in density, and the deterioration of the mechanical properties. The hydrogen flame will present a higher temperature and volumetric flow rate, which will affect the heat transfer inside the furnace. It will also produce a flue gas with a high water content, potentially causing the corrosion of the refractory lining with the formation of volatile hydroxides. The implications of hydrogen use for refractory materials are, however, not fully understood, and this presentation will show, based on a comprehensive literature review, what is currently known as well as the open questions that need to be addressed to ensure a reliable performance of the refractory lining.

Cold start ladle shrouds (without preheating) are widely used now-a-days and require very good thermal spalling resistance mainly where fluctuation of casting temperature is very severe. Considering high thermal spalling behavior cold start ladle shrouds are prepared with Al2O3-Carbon or Al2O3-SiO2-Carbon (here written as AG) systems. One of the most important parameters is to optimize the mix granulometry to improve the thermal spalling resistance.
In this study, by enhancing finer grain sizes of AG mixes, the modulus of elasticity (MOE) of the product is reduced and one new ladle shroud has been developed having better thermal spalling resistance. The improved ladle shrouds are used at several customers end with trouble free casting operations.

Drying and dehydration of calcium aluminate cement (CAC)-bonded castables is critical to their industrial performance. However, internal pressure build-up during heating can impede vapor removal, affecting mass transport. This preferentially drives steam towards cooler areas, increasing internal vapor pressure and potentially causing spalling under severe hydrothermal conditions.

We investigated hydrate evolution in CAC-bonded castables under simulated conditions using autoclave treatments. These treatments replicate the hydrothermal environments experienced during industrial heating on a laboratory scale.

We are using Raman spectroscopy, a non-destructive technique for analyzing mineral and amorphous phases as well as liquids, to analyze alumina-based CAC matrix castables containing two different liquefiers after autoclave treatment at different temperatures. Complementary research focuses on X-ray diffraction (XRD) of the matrix compositions and the pore size distribution of the finished castables using mercury intrusion porosimetry.

In production of clean steel or special grades of steel, calcium is injected during ladle furnace process in order to remove inclusions. However, normal Alumina-ZrO2-carbon slide gate plates suffer from calcium vapor attack leading to chemical corrosion and shortening the life of the plates. In this research, a new MgO-spinel-carbon slide gate plate was developed to overcome the drawback of Al2O3-ZrO2-C ones. The result was also compared to a commercially available MgO-C slide gate. In this regard, the chemical analysis, physical and mechanical properties as well as mineralogical composition of all the plates were investigated. The different corrosion mechanisms of each plate were discussed. The result showed that although the commercial imported MgO-C carbon plate had the best performance in practice, the domestically developed MgO-Spinel-carbon plates also showed much better performance than Alumina-Zirconia Carbon and can be used safely for flow control of Ca-Treated steel.

Drying and dehydrating of cement-bonded refractory castables are critical steps before industrial implementation. During the heat-up the steam transfer to the hot side can be interrupted due to the internal pressure build-up. As a result, the steam mass transport shifts towards the cold side because of the lower internal pressure on that side. Thus, the vapor pressure within the material increases even more, creating hydrothermal conditions and leading, in the worst case, to the feared spalling. These conditions in the material can be reproduced on a laboratory scale by using autoclave treatments.
The study, conducted at CAC, utilized two liquefiers and varied water content to achieve a deeper insight into the development of hydrate phases under hydrothermal conditions. It is expected that hydrothermal treatment at different temperature levels will induce varied crystal growth, thereby affecting pore size distribution within each material batch. The pore size distribution of the samples was determined using mercury intrusion porosimetry. This paper is part of a broader investigation, and its findings are correlated with additional research presented at the same conference, focusing on hydrate phase characterization through X-ray diffraction spectroscopy and Raman spectroscopy.