Sustainable Approaches to Monolithics
Innovative ideas and technologies represent, on a more holistic level, a contribution to a self-sufficient, resource-efficient implementation of the company’s own raw materials with reference to new applications of the Eisenberger Luting Sand with its fractionable and defined finest grain fractions in micrometre and sub-micrometre scales. Above all, mineral raw materials such as Eisenberger Luting Sand enhance the applications and properties of synthetic high-temperature ceramics such as refractory materials. The inherent bonding capacity, especially the Al–Si gel-enriched fine grain fractions and the technologically advanced interaction of fine particles of Eisenberger Luting Sand with different hydraulic, pozzolanic, organic and inorganic binders, “hide” market-oriented refractory applications and qualify Eisenberger Luting Sand excellently as a sustainable raw material. The company pursues the goal of sustainable and environmentally friendly refractory production. Novel material solutions will be presented and discussed, which can incidentally also be applied in a growing market segment within large-volume applications. All the more important is the overall deposit of Luting Sand in the Eisenberg Basin located in Palatinate, Germany. Its geological significance has a positive impact not least on specific energy considerations and common logistics.
1 Preface A technically and scientifically profound as well as no less humorous position on the nature of ceramic materials should be made memorable, which can almost certainly be applied to all refractory ceramics: „Minerals of variable composition and questionable purity are exposed to an unmeasurable thermal treatment that remains long enough to allow unknown reactions to proceed incompletely, forming heterogeneous, non-stoichiometric compounds known as ceramics.” [1] 2 Motivation Raw material costs are of particular importance for unshaped refractory products, which underline shares of up to 80 % of the product price. For some years now, there have been signs of a steady increase in raw material costs. Currently, the general international supply situation, for example, for aluminosilicate or high-alumina raw materials and also binders can be described as being difficult due to the extraordinarily high demand within the ceramic industry in general and the refractory industry in particular. But also on a national level, sometimes restrictions in the continuous supply of specific refractory raw materials have to be accepted (i.e. supply chain resilience), which ultimately call for alternative solutions with a focus on the essentials. The new supply chain act, on the other hand, opens up opportunities within a clearly defined and transparent mode of production. The economic pressure caused by volatile raw material costs also makes the search for inexpensive and technically comparable products inevitable. The earlier a company can offer convincing solutions here, the more its competitive situation improves. The aim is to use the knowledge gained so far about the properties and functions of the available products and product derivatives of Eisenberger Luting Sand to make an effective contribution to optimising the common demand for selected imported raw materials by means of targeted development and production processes while maintaining progressive production capacity utilisation. It is imperative that economic aspects are taken into account in addition to the fulfilment of technological solutions. 3 Characterisation of Eisenberger Luting Sand as a functional raw material The Eisenberger Luting Sand is formally a kaolinised quartz sand and represents a sedimentary deposit as a loose rock that was formed by weathering, deconsolidation and rearrangement of layers of the variegated sandstone in the Tertiary period about 30 million years ago. Mineralogically simplified, it is characterised by about 80 mass-% quartz and 20 mass-% clay minerals. Thus, even in its untreated state and in a wide temperature range between room temperature and about 1700 °C, Eisenberger Luting Sand combines high mechanical strength with outstanding bonding properties. Predestined as a refractory raw material and component, Eisenberger Luting Sand with its joined μm- and nanoscaled Al–Si crystalline and gel phases per se supports a wide range of applications [2]. Interconnected deposits of Luting Sands are very rarely found. The well-known classical applications of the Eisenberger Luting Sand as refractory ceramics represent the foundation of the EKW Company. Recent investigations on the Eisenberger Luting Sand provided findings, especially in relation to carbonaceous binders, to apply selected and extracted fine and ultra-fine fractions for the functionalization of modern refractory materials [3]. It should be emphasised that ultra-fine fractions in particular are said to have an intrinsic binder effect even at room temperature due to their specific reactivity. An existing raw material such as quartz sand or any ceramic matrix system should be positively influenced by the outstanding binder effect of ultrafine fractions of the Eisenberger Luting Sand and contribute to an optimisation of the properties of general ceramic raw materials or components and their application. In view of the remarkable chemical purity of the different grain size fractions of the Eisenberger Luting Sand, especially the finer quartz sand fractions intergrown with species-typical binder can also be described as pure quartz sand, but already characterised by binder. The findings on moist, granular fractions, which are only produced by mixing two substances, namely the granulate and a liquid, have per se a technological and thus industrial relevance. It is evident that the capillary bridges that form between neighbouring grains when the liquid is distributed in the granulate also play a significant role in the mechanical stability of the material and its further processing in downstream production processes [4]. 4 Approach to the production of innovative refractory ceramics A refractory material system is defined in simplified form by primarily synthetic raw materials from German, European, but often Asian origin (South Africa and South America, however, also represent a noteworthy provenance). In view of the associated raw material costs, irrespective of any exchange rate corrections, dependencies on the raw material market are productionrelevant variables that have a significant impact on medium-sized companies. R&D activities, which not least obey defined targets, have led to a systemic consideration of the raw material situation, taking into account the company’s own resources, which include not only raw material deposits but also personnel and plant availability. A major focus here is on the integrity of development and production as essential to realising the specified targets in a resultsoriented and relatively speedy manner. Based on the Eisenberger Luting Sand, approximately ideal raw material combinations were to be found for applications primarily in the already existing and secondarily in a novel product portfolio to support and optimise the operational production processes. A cost-intensive proportion of synthetic raw materials was thus to be replaced by the company’s own raw material resources in a functionally adequate way, which meant that the performance and quality of the technological properties of the refractory ceramics had to be achieved at the very least. It was vital not to lose sight of the quality of the expected installation techniques attributed to the refractory ceramics. Open pit mining, classification and fractionation are followed by further processing steps on the especially smaller grain fractions of the Eisenberger Luting Sand, which have a “true” maximum particle size of 0,5 mm. In a combined drying and grinding plant, taking into account energetic boundary conditions, a process technology was developed that enables the physical separation of so-called alumosilicate fine particles in a targeted manner and with a high yield. Due to the characteristic reactivity and phase purity, the dry ultra-fine fractions should in principle be functionally comparable to synthetic raw materials of similar particle sizes, which also appeared evident from a mineralogical point of view. The quasi “in-house”, and thus exclusive, novel standard fractions, exemplarily shown in Fig. 1 and Fig. 2, were contrasted with product lines with different mineral raw material compositions, which, depending on the total alumina content of the ceramic matrices, fulfilled their function in the temperature range from room temperature up to 1600 °C (unidirectional), which was also confirmed by tests close to the application. Obviously, mechanisms are in place that certify the suitability of the refractory ceramics for identical requirements and thus contribute decisively to guaranteeing the availability of refractory ceramics at customer companies. The market thus opens up the prerequisite for a positive technology assessment. Irrespective of the type of application of the refractory ceramics, the dry fine fractions function well with carbonaceous (typical suitability and property improvements: binding contribution at low and high temperatures, thermomechanical stabilisation, in situ coking and carbon oxidation protection) and carbon-free refractories (typical suitability and property improvements: Binding contribution at medium and high temperatures, creep resistance, strength profile). So-called “black” material variants are high-alumina or aluminosilicate-based, mostly SiC-containing, carbon-bonded refractory ceramics (mixes or shaped bodies) taking into account defined granulates and particle fractions of the Eisenberger Luting Sand. “White” material variants, on the other hand, are free of carbon sources but follow similar design characteristics. It is worth noting that the demand for new standard fractions is steadily increasing. As early as six years ago, a respectable 1100 t of the fractions of Al–Si crystalline and gel phases isolated via air separation were transferred to production for the functionalization of the existing different product lines as part of a resource-saving internal raw material supply. The proportion of finished products is considerable. And of all things, a traditional raw material provided the key achieving that goal and was the milestone of an intelligent use of indigenous raw materials. With a glance at production areas such as the above-mentioned drying and grinding plant, which are subject to intensive use and high energy consumption at the same time, it is also important to determine whether and where opportunities for improving energyrelated performance can be identified. As part of the implemented energy management system in accordance with DIN EN ISO 50001 (supervisory audit five years ago by the company Kiwa Deutschland GmbH), measurements of specific energy consumption are evaluated constantly to monitor and measure energy-related performance and to determine system-internal Energy Performance Indicators (EnPI). The indicators represent a quantitative metric. From September 2017, optimisation measures on the processes for drying and fractionating the technologically relevant particles of Eisenberger Luting Sand led to an effective improvement in energy-related performance and thus to a cost-optimised discharge of the company’s own aluminosilicate raw materials. The optimisation measures additionally brought about the quantitative fracimprovement of the material flow by currently 1000 kg per day of the technologically most important fraction, the Al-Si gel phase-enriched, highly reactive key raw material. The improvements in the EnPI compared to the initial period in 2017 is mapped today in a larger two-digit range. 5 Corrosion – a brief excursus: impacts on refractory ceramics This compact excursus, which is based on the presentations in [5], is intended to illustrate an important factor of extrinsically induced effects by means of selected examples. In the present context, the frequently observed corrosion of refractory materials is considered. Using a simple parameter representation of reaction versus infiltration, six typical cases of corrosion are outlined (Figs. 3 a–f). Case A – no reaction/infiltration None of the parameters deviates from its zero point. Both a potentially corrosive medium and the refractory ceramic do not interact in a macroscopically visible way (Fig. 3 a). Case B – infiltration, but no degrading reaction Almost the only parameter that deviates from its zero point is infiltration. A potentially corrosive medium enters into macroscopically visible interaction with the refractory ceramic, but without causing any damage to it. The infiltration shown remains in principle without effects, which ideally also extends to the thermal stress states of the refractory ceramic. This assumes that both the thermal expansion coefficient and the density of the infiltrated corrosion medium and the refractory ceramic are very similar (Fig. 3 b). Case C – reaction to dense, protective layer Almost exclusively the reaction parameter deviates from its zero point. A potentially corrosive medium enters into macroscopically visible interaction with the refractory ceramic, but without damaging it. The reaction shown causes a protective layer to form on the near-surface area of the refractory ceramic, which protects it from further corrosive effects. Prominent examples of the phenomenon known as passivation are also aluminium oxide on aluminium or silicon dioxide on silicon carbide (passive oxidation). If the coefficient of thermal expansion of the reaction layer is similar to that of the refractory ceramic, induced spalling of the reaction layer is to be expected (Fig. 3 c). Case D – melt solidification in the refractory material Both reaction and infiltration deviate from their zero point. A potentially corrosive medium enters into macroscopically visible interaction with the refractory ceramic and damages it. The infiltration shown does not remain without effects and, as is to be expected, will initially degenerate matrix constituents of the refractory ceramic. If the viscosity of the molten corrosion medium is increased, the corrosion process can be stopped (Fig. 3 d). Case E – infiltration and reaction to new phases Both reaction and infiltration deviate intensively from their zero point. A potentially corrosive medium interacts with the refractory ceramic in a macroscopically visible way and damages it. The infiltration shown does not remain without effects and, as is to be expected, will initially degenerate matrix constituents of the refractory ceramic. New phases are formed from the reactants corrosion medium and refractory ceramic. The similarity of the values of the thermal expansion coefficient and density of a respective reaction phase with those of the refractory ceramic is questionable. This can lead to a general reduction in the thermodynamic stability of the refractory ceramic, accompanied by a deterioration in thermal shock behaviour and structural fatigue (weakening of the microstructure; Fig. 3 e). Case F – disintegration/destruction Both reaction and infiltration deviate maximally from their zero point. A potentially corrosive medium occurs in macroscopically visible interaction with the refractory ceramic and damages it noticeably. The infiltration shown does not remain without effects and integrally disintegrates the refractory ceramic via its components. New phases are formed from the reactants corrosion medium and refractory ceramic both in the material volume and on its surface of the refractory ceramic, which is manifested by the build-up shown. The complete destruction of the refractory ceramic is initiated (Fig. 3 f). Between refractory ceramics and the environmental impact there are interacting relationships and effects that should be individually adjustable, exemplified in Fig. 4. 6 Case studies of functionalised refractory ceramics: examples from everyday life in industry The adaptive application of the Eisenberger Luting Sand within the systems of black ceramics is impressively demonstrated in Fig. 5 by the example of macroscopically appearing corrosion effects. The impact of corrosive media is inhibited by the mechanism of in situ carbonisation. Despite the oxygen partial pressure of the air atmosphere, this is made possible by “aluminosilicate barrier layers”, which are generated by essential gel phases of the Eisenberger Luting Sand steadily with increasing temperature and assist in preventing oxidation of the carbon contained [8]. The integration of jelly phases of the Eisenberger Luting Sand is not limited to black ceramics. Primarily, the realisation of aluminosilicate phase components has increasingly prevailed within a recent time interval. At medium and high temperatures, the socalled stimulated mullitisation supports the matrices of white refractory ceramics. The aim and result are generally improved thermomechanical properties, which are also associated with a mineralisation of softening or plastic fine grained particles. Some example scenarios considering the abovementioned insights, which have their own implications, from the typical customer industry of innovative refractory materials are shown in Figs. 6–9. In 2021, EKW received an honourable mention for its innovative ideas and solutions that are becoming increasingly established in everyday industrial life. More about the award winner in the category Special Price Industry in moving pictures: https://www.ekw-refractories.com/en/ news/ 7 Sustainability and progress It is to be expected that the contribution to a viable, resource-saving implementation of the company’s own raw materials will develop into success with regard to new applications of the Eisenberger Luting Sand with its fractionable and defined fine grain fractions in micrometre and sub-micrometre scales. A consideration on the subject of “efficiency”: discussions about the so-called Carbon Leakage Regulation implies an enormous financial burden, especially for small and medium-sized enterprises. The trend towards rising CO2 costs is also getting to the substance of historically grown companies, which often look back on centuries-old local traditions and have accordingly provided jobs and are still responsible for them today. In this context, the terms “resource protection” and “transport efficiency” may possibly inspire and positively influence the discussion about CO2 pollution. By using sustainably and regionally produced consumables, and these consist of refractory ceramics, for the operation of, for example, combustion or to stimulate the discussion of sustainably and regionally produced refractory ceramics. 8 From history to today Following the idea of the resource-efficient use of Eisenberger Luting Sand, the need for cost-intensive, synthetic raw materials in refractory products can be completely avoided or significantly reduced and, in principle, the demands of industry can be met. In this way, EKW contributes to the self-sufficient and progressive use of regional raw materials and, last but not least, supports customer companies in reducing their use-specific carbon footprint. Acknowledgements Selected studies and projects were gratefully financially supported by the Federal Ministry of Economics and Climate Protection (BMWK) via the German Federation of Industrial Research Associations Otto von Guericke e. V. (AiF), supported by the Central Innovation Programme for SMEs (ZIM).
References
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