June 2024 | On the 5. Freiberg Refractory Symposium, Rath presented groundbreaking study results on the effects of hydrogen on refractory materials in steel production and provided exciting insights into the development of continuous oxide ceramic fibers.
The 5th Freiberg Refractories Symposium focused on the latest findings as well as on practical experiences relating to the new and ongoing development of refractory materials and the opportunities and challenges the energy transition poses for the refractory industry. The problem of hydrogen corrosion on refractory materials was a special focus: Refractories manufacturer RATH presented a study that has delivered groundbreaking results on the effects on refractory material when using hydrogen in steel production. And in a presentation on the status quo in the development of continuous oxide ceramic fibers, RATH provided some fascinating insights into another future-oriented topic.
Around 160 experts from industrial furnace and plant construction, application technology, assembly companies, representatives from research and development, and refractory manufacturers attended the 5th Freiberg Refractory Symposium, which was organized in cooperation with the German Ceramic Society (DKG), the German Society for Refractory and Chimney Construction (DGFS) and RATH AG. More than 20 specialist presentations were on the agenda.
Effects on refractory material when using hydrogen in steel production
In the refractory industry, the sustainable use of resources and associated efforts to reduce the carbon footprint have become increasingly relevant, and this was reflected in the symposium’s presentation topics.
A topic that was discussed intensively was “green steel” – because global steel production contributes significantly to global warming and climate change. However, there are promising approaches towards decarbonization in the steel industry and therefore more sustainable steel production: Hydrogen-based direct reduction plants are going to play an important role in the future.
“We recently studied the effects of using hydrogen on the refractory materials used in these plants, and investigated which are particularly resistant to these changed stresses as part of a broadbased, comparative corrosion study – and we gained groundbreaking insights,” says Jürgen Puhl, Head of Group Research & Development at RATH.
The focus was on questions such as: How do these new operating conditions affect corrosion behavior and corrosion dynamics? How strong is the influence of temperature? And how do refractory materials need to be formulated to meet the individual requirements of a customer, thereby enabling optimal and cost-effective performance in direct-reduction systems?
Investigations into aluminosilicate and high-alumina refractory materials
In the course of the study, RATH’s extensive non-basic product portfolio with a composition of 40– 99 % Al2O3 was exposed to an H2 atmosphere. Samples of lightweight refractory bricks, dense bricks, monolithic products, mats made of high-temperature wool, and vacuum-formed parts were evaluated. The corrosion tests were carried out at the German Institute for Refractories and Ceramics (DIFK).
The temperature exposure was 1250 °C and 1400 °C in a 100-% H2 atmosphere, with an exposure time of 200 hours. In addition, aging at 1100 °C under a typical mixed gas atmosphere was performed specifically for use in direct reduction plants.
Corrosion was assessed by determining the mass loss in order to be able to make statements about temperature dependency and corrosion rate. In addition to determining the physical properties, further chemical analyses and X-ray diffractometry measurements were carried out before and after exposure to provide further information on phase stability and new mineral formation.
Important findings from the study
- High-corundum materials show very good corrosion resistance in all products.
- Under certain conditions (selected raw material usage and production parameters), mullite also proves a suitable material in an atmosphere containing hydrogen.
- Glass phases and SiO2 phases are significantly reduced in the presence of high hydrogen contents.
- Foreign oxides and impurities in the overall system play a significant role with regard to stability in a hydrogen atmosphere.
- The porosity of refractory materials has only a minor influence on corrosion.
- In the temperature range of 1250 °C – 1400 °C, a significant increase in the corrosion rate was recorded.
- Phosphate-bonded fired bricks are only slightly more resistant to corrosion than phosphatefree products.
In summary, RATH’s study results are highly relevant for future material selection in the respective application. The targeted further development of refractory materials and systems is particularly important for the transition to direct-reduction plants with additional hydrogen admixture and the goal of producing steel in a completely climate-neutral way in the future.
Innovative continuous oxide ceramic fibers for industrial applications
“Continuous oxide ceramic fibers made in the EU” was another future-oriented Rath presentation topic: Based on 35 years experience in the development and production of high-temperature ceramic fibers, Rath is always exploring innovative ways to offer new product solutions to the industry.
Continuous oxide ceramic fibers are widely used, especially as reinforcing fibers in various matrices (CMC, MMC). Due to their high tensile strength and stiffness as well as their excellent chemical and thermal resistance, continuous filaments can, for example, provide ceramic matrices with quasiductile, damage-tolerant fracture behavior.
“These continuous fibers are an important raw material for the production of oxide ceramic matrix composites. However, the manufacturing process for such fibers is complex and there are very few suppliers worldwide, which makes it even more difficult to establish secure supply chains,” says Christopher Kluthe, Senior R&D Manager, Rath.
Rath has been developing such continuous fibers for several years as part of the Horizon Europe project InVECOF (Innovative Value Chains for European Ceramic Oxide Fibers).
“After thermal treatment, these fibers, which are produced using the sol-gel process in a dry spinning process, have a mullite or corundum microstructure,” adds Christopher Kluthe, whose presentation included information on the current state of development at Rath.
For example, Rath has developed the mullite fiber M75 (with a tensile strength of up to 1,500 MPa and a modulus of elasticity of over 200 GPa) and the corundum fiber K99 (with a tensile strength of up to 3,000 MPa and a modulus of elasticity of over 350 GPa). Production processes for all the relevant manufacturing steps were developed in collaboration with specialist companies.
The goal
Christopher Kluthe highlighted the challenge of transferring the excellent results from the pilot plant to production scale as the current priority in fiber development and took a look at the near and longer-term future: The plan is to construct a fiber production plant by summer 2024. “The current focus is the production of larger quantities of K99 and M75 fibers for the manufacture of fabrics and composites, as well as the development of further grades, especially those with higher creep resistance. The long-term goal is to become the first European supplier of oxide ceramic fibers and to produce up to 10 tons per year as a first step,” says Christopher Kluthe.
About the Freiberg Refractory Symposium
What began as a seminar for a small circle of experts and initially consisted of around 90 participants has continually grown in popularity since then: The three-day event, which stands for intensive discussions on technological process engineering and high-caliber professional exchange has become a fixed institution in the industry and is held every two years.
About Rath
Rath is a specialist in refractory technology with a comprehensive product portfolio of refractory materials for application temperatures of up to 1800 ℃. With around 600 employees and sales representatives in numerous countries, Rath AG, based in Vienna, has become internationally established as a competence leader in the refractory sector.
