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Open-cell ceramic foams are widely used as filters for the purification of molten metals due to their high permeability and high efficiency for capturing non-metallic inclusions. With the consideration of manufacture and filtration behaviour, most filters are produced by replica methods. The intrinsic multiscale porous structure requires the ceramic foams to have sufficient strength. As a consequence, different processing approaches, material compositions and characterizations are investigated. Meanwhile, to further enhance the filtration performance, the functionalization of ceramic foam filters is often conducted with surface coating. This review summarizes the processing and characteristics of ceramic foam filters (CFFs), the nature and formation of non-metallic inclusions (NMIs), the filtration mechanism and applications of CFFs. The characterization of mechanical and filtration performance, as well as the corresponding strengthening and functionalization methods are also presented.

In this work, refractory components based on alumina were produced by binder jetting using a large-scale 3D printer. The formulation contained several particle fractions up to a grain size of 3 mm, equal to the printer resolution. The binder system contained fine dead burnt magnesia, milled citric acid and reactive alumina, which were added to the aggregate mixture to create the powder bed. Deionized water was deposited from the printer's nozzles and triggered the binding reaction between the magnesia and citric acid. After 24 h, the printed samples were removed from the powder bed, dried and sintered at 1600 °C for 5 h. Reactive alumina contributed to the in situ creation of magnesium aluminate spinel at high temperature. The samples were characterized in terms of Young's modulus of elasticity, bending and compressive strength in 2 directions (parallel and perpendicular to the printing direction). The broken parts were used to investigate physical properties such as the open porosity and bulk density. The microstructure was studied by means of computed tomography. Finally, powder samples were used to determine the phase composition at different stages of production by means of XRD.

In the steel industry, a large amount of diverse waste is generated, including carbon-bonded magnesia-rich waste originating from refractories. This study focused on the development and characterization of composite material based on magnesium oxychloride cement (MOC), with an emphasis on incorporating MgO–C-based refractory waste (CBMW) as a sustainable filler. To reach the best possible material properties, two different size fractions were applied in various ratios, completely replacing quartz sand. A comprehensive analysis of all composite material samples was conducted utilizing various analytical techniques, XRD, SEM, EDS or STA-MS. Mechanical properties such as compressive strength, flexural strength, and Young's modulus of elasticity were evaluated. Even though even the best sample did not surpass the mechanical properties for the reference, compressive strength 78.1 MPa was achieved, which is a more than sufficient value for most indoor applications.

A main challenge for materials in steel melt filtration is to provide an open pore structure enabling constant melt flow while simultaneously withstanding the high thermo-mechanical stresses involved in the casting process. In the present study, alumina-based extrusion materials were investigated for the purpose of manufacturing cellular filter structures for continuous casting and filter sample holders for ingot casting. The impact of adding a coarser alumina fraction and/or monoclinic zirconia, and/or carbonaceous material on the structural and mechanical properties of the material was analyzed. The extrusion capability, linear shrinkage, density, porosity, mechanical strength, Weibull modulus and thermal shock resistance were tested in detail. The results showed that coarse alumina-zirconia materials, either carbon-bonded or sintered, delivered the best compromise in terms of these properties. These materials were successfully used to extrude filter sample holders and cellular hollow-ware prototypes.

The flame spraying of refractory ceramics such as alumina is a promising technique for the modification of manifold substrate materials for high-temperature application. Its high potential for automation and feedstock design allows for swift adaption to variable demands. Consequentially, a tailoring of flame-sprayed barrier coatings can be realised in terms of the phase composition and the mechanical performance. In order to isolate the effects of the addition of zirconia and titania, as well as the coating thickness, the present study focused the biaxial flexure of self-supporting flame-sprayed alumina bodies, produced by a fully automated and robot-aided flame spray station (on the lab-scale).

Alkali-Metal-Thermal-Electric-Converter systems (AMTEC-systems) pose a promising approach for energy conversion, e.g. from waste heat. Central components are a gas-tight ion-conductive solid membrane and an enclosed porous electrode. The presented study covers an adapted synthesis routine for single-phase sodium-tritanate (Na2Ti3O7) and its assessment as an alternative AMTEC-membrane-material. In contrast to the conventional stoichiometric solid state reaction between sodium carbonate and titania, the adapted synthesis reaction was performed with sodium excess. Up to 900 °C, the as-synthesised material evinced both, a constant thermal expansion behaviour over various thermal cycles and an expected electric conductivity. More important, phase stability either in pure state as well as in contact with a potential electrode material (La0.8Sr0.2)0.98MnO3 was demonstrated by long term exposure at 900 °C over 240 h. According to those findings the synthesised Na2Ti3O7 is considered to be an alternative membrane-material for AMTEC-application.

To widen the understanding of tensile failure of reticulated ceramic foams and expand the available mechanical method, a cylindrical splitting test is developed in the present study based on alumina open-cell foams of three different pore densities. The biaxial method is validated by characterization of mechanical parameters, and the in-situ fracture process is validated by a digital image correlation, followed by a formula correction for effective tensile strength with consideration of discrete crack paths. For experimental setup curved loading platens, compliant pad and intermediate quasi-static loading rate are proposed for guaranteeing tensile failure under a radial compressive load. Tensile strength, fracture energy, and brittleness increase with the foam pore density, and the fracture behavior is a balanced result of materials and foam structural support strength. An analytical model of splitting tensile strength with structural parameters is derived, which implies its dependence on cell size and critical stress intensity factor of strut materials.

This study extensively investigated characteristic non-metallic inclusions in oxidized and deoxidized 42CrMo4 steel after contact to MgO–C refractories, proposing possible formation and modification mechanisms of non-metallic inclusions. The structures and compositions of different inclusion species were analyzed, revealing various types: crystalline, amorphous, and complex inclusions containing both crystalline and amorphous phases. The latter always consisted of an amorphous Mn–Si–Al–O matrix containing various crystalline phases such as Al2O3, MnAl2O4 and/or MnTiO3. The formation of amorphous Mn–Si–Al–O inclusions was attributed to steel melt oxidation, while pure crystalline corundum inclusions resulted from both the steel melt oxidation and deoxidation. Alumina inclusions exhibited different shapes, likely because of variations in aluminum and oxygen supersaturation in the steel melt during their formation. Complex inclusions were suggested to form through precipitation on existing inclusions and mutual collision of pre-existing inclusions, facilitated by the non-wetting behavior of solid alumina inclusions in the steel melt.

This study focused on the development of an environmentally friendly binder system based on lignin and collagen for uniaxial pressed MgO–C refractories as an alternative to commonly used resin or pitch binders. Additionally, recycled MgO–C refractories from steel plants were partially utilized as raw material, investigating their influence on the resulting physical and mechanical properties. The binder system showed reliable binding properties, although the recyclate-containing MgO–C exhibited higher porosity, slightly lower density, and lower strength compared to the reference batches without recyclates. However, antioxidants significantly improved the properties of the recyclate-containing MgO–C samples. Scanning electron microscopy analysis with energy-dispersive X-ray spectroscopy revealed the formation of whiskers, as well as oxidation and nitridation of aluminum particles. This research highlights the potential of environmentally friendly binders and the utilization of recycled materials in MgO–C refractories to mitigate their environmental impact and enhances the environmental performance of carbon containing refractory materials.

In the recent years, the demand for clean steel in critical applications e.g. in construction or transportation industry has increased. In view of the research and developments in the steel production and refinement it seems logical to pursue new approaches on the refractories and to evaluate the existing ones. Within this study zirconia castables stabilized by yttria or magnesia with additions of an alumina or an alumina-magnesia based binder were developed. The influence stabilizer and binder type on the phase evolution of the zirconia castables was investigated. The physical, mechanical and thermomechanical properties were evaluated. Subsequently, the zirconia castables were tested in a steel casting simulator under industry-oriented conditions. Alterations in surface chemistry and morphology were studied via optical light and scanning electron microscopy. Using an automated feature analysis, the solidified steel was investigated regarding the formation of non-metallic inclusions during steel casting experiments to identify their type and frequency.

For ceramic foams, there is no thermal shock resistance testing standard available at the moment. This work aims to investigate the influence of the different test conditions. Among the descending thermal shock test conditions, heating mode, thermal shock temperature, and quench medium, the latter has the highest impact on the residual mechanical properties. Reference alumina (Al2O3) foams and commercially-available ceramic foam filters (ZrO2, Al2O3–ZrO2, Al2O3–P, and SiC) were subjected to thermal shock with water and air as quenching medium. Due to the low thermal expansion coefficients, SiC and ZrO2 possess the highest calculated thermal shock resistance Rfoam. SiC and ZrO2 foams also had the highest experimentally evaluated residual strength after being quenched in water. An immersion thermal shock procedure with molten metal was tested on Al2O3 reference test pieces. The residual elastic moduli and strengths decrease with increasing temperature which is a function of immersion duration and depends on the usage of an interlayer between the foams and the melt. In order to evaluate the temperature gradient and its development over time, temperature measurements were conducted using a thermocouple inserted and fixed in the midplane of the foams and bulk test pieces.

Zirconia is one of the most promising functional refractory materials in continuous steel casting and is employed in areas with high thermal and chemical stresses such as the slag line, the nose of monoblock stoppers or the inlet area of submerged entry nozzles. The key for the application of zirconia in this application areas is a profound understanding of its thermomechanical and thermochemical properties that are influenced by the type and amount of stabilizer, the grain size and the thermal conditions during sintering and operation. Within this contribution coarse grained zirconia self-flowing castables based on a yttria stabilized zirconia co-stabilized by magnesia are developed; bars and a model monoblock stoppers are cast. After sintering the mechanical and thermo-mechanical properties are evaluated. The influence of different stabilizers and the contribution of the binder to the phase evolution during sintering and operation and thus the influence on the thermo-mechanical properties are investigated.

The fabrication of MgO–C refractories containing MgO–C recyclates is a current approach for saving resources and energy. However, it must be ensured that the steel quality is not adversely affected, particularly with regard to non-metallic inclusions. The present study investigates MgO–C refractories containing different proportions of MgO–C recyclates (up to 83%) in contact with 16MnCr5 steel melt and a slag. A recyclate-free MgO–C material served as a reference. The tests were performed in a steel-casting simulator. By an automated feature analysis of the solidified steel, manganese sulfide and complex alumina-manganese sulfide inclusions were found to be the predominant ones in all steel samples. No negative influence of the recyclate on the inclusion count and the size distribution of the inclusions, the latter being determined for the sum of alumina and alumina-manganese sulfide as well as for the manganese sulfide inclusions, was observed.

In-depth analysis of the non-metallic inclusion population in solidified metals is essential considering the high cleanliness requirements for metallic components. For this purpose, automated feature analysis (AFA) is a powerful inclusion analysis tool, providing statistical supported information about quantity, elemental composition, morphology and size of inclusions. However, thorough data evaluation is imperative to ensure accurate and reliable results. The paper introduces the key principles of evaluating AFA data, emphasizing its capabilities and constraints by utilizing four large datasets obtained from solidified steel blocks, each containing a minimum of 4000 features. Additionally, methodologies for identifying characteristic inclusion species within a dataset, constructing suitable rulefiles for inclusion classification through statistical analyzes, and interpreting the resulting outcomes are presented. The size distribution of inclusions is analyzed using population density functions, focusing on the absolute inclusion count within specific size ranges. Cluster analysis is presented considering the inclusions‘ positional parameters.

The development and evaluation of novel stainless steel-based composites for direct contact with liquid aluminum alloys has been carried out. The Steel Ceramic Composite consisted of 60 vol% 316L stainless steel powder and 40 vol% of MgO or TiO2 ceramic powder. The sample were manufactured using uniaxial pressing and subsequent surface pre-oxidation at 850, 1000 °C for 24 h.The corrosion resistance of composite was investigated against molten AlSi7Mg0.3 alloy using crucible corrosion tests. The tests were carried out at 850 °C for 24 h and 168 h. The influence of pre-oxidation on the corrosion resistance of the samples was analyzed using XRD and SEM/EDS. The corrosion phases formed in the aluminum alloy were investigated using SEM/EDS/EBSD and PSEM/ASPEX/AFA and included the assessment of aluminum alloy contamination by evaluation of corrosion precipitation content, quantity and size. The sample Steel-MgO exhibited excellent corrosion resistance with negligible contamination of the aluminum alloy.

The objective of this study was to investigate the variability of flexural strength for flame-sprayed ceramic components and to determine which two-parametric distribution function was best suited to represent the experimental data. Moreover, the influence of the number of tested specimens was addressed. The stochastic nature of the flame-spraying process causes a pronounced variation in the properties of potential components, making it crucial to characterise the fracture statistics. To achieve this, this study used two large data sets consisting of 1000 flame-sprayed specimens each. In addition to the standard Weibull approach, the study examined the quality of representing the experimental data using other two-parametric distribution functions (Normal, Log-Normal, and Gamma). To evaluate the accuracy of the distribution functions and their characteristic parameters, random subsamples were generated by resampling of the experimental data, and the results were assessed based on the sampling size. It was found that the experimental data were best represented by either the Weibull or Gamma distribution, and the quality of the fit was correlated with the number of positive and negative outliers. The Weibull fit was more sensitive to positive outliers, whereas the Gamma fit was more sensitive to negative outliers.

Modern, high-quality steelmaking requires a comprehensive understanding of the behavior of refractories in service. Therefore, MgO–C refractories with different MgO grade were immersed once and twice into a steel melt at 1600 °C and 1680 °C, respectively, in a near-industrial steel casting simulator. The same materials were tested in static crucible melting tests. A coherent MgO layer containing low-melting phases and MgAl2O4 crystal-like structures formed on the specimens’ surface. The morphology and frequency of these structures were strongly related to the MgO grade of the specimens and the immersion procedure. A lower MgO grade caused an increased formation of low-melting phases, which contributed to a denser layer formed on the specimens’ surface, hampering gas diffusion and the formation of MgAl2O4 crystal-like structures. An increased steel melt temperature and the double immersion had a similar effect. Conversely, an excessive formation of MgO and/or MgAl2O4 was observed when the formed layer contained less low-melting phases.

Two magnesia-carbon (MgO–C) recyclates were investigated with respect to their utilization as raw materials for MgO–C refractories. X-ray diffraction and backscattered electron diffraction were used for phase analysis of the recyclate aggregates. In addition, the gas released from one of the recyclates when it came into contact with water was analyzed in a mass spectrometer. MgO–C samples with different recyclate contents were produced. During coking, the samples showed different behavior depending on the recyclate used. Whereas those containing the first recyclate showed a slight shrinkage, a significant increase in volume was observed in the case of the specimens that contained the second recyclate. The volume increase could be reduced by thermal pretreatment of this recyclate at 380 °C. As a result, better bulk density and porosity values were obtained. However, an even stronger positive effect was achieved by replacing the pitch-based binder used in the binder system with a novolak-based.

A combined filtration system was investigated for the first time in the present work. A reactive filter was immersed in a steel melt containing artificially generated endogenous inclusions. After extracting the filter, the melt was poured through a second filter and into a crucible where it cooled down. The second filter had a pure aluminum oxide flame-sprayed coating, in order to prevent reactions and only remove pre-existing inclusions. It was observed that the immersion of a reactive, coated filter generally resulted in larger inclusions. When no casting was performed, or when the second filter was omitted, smaller remaining inclusions were found. Calcium aluminate based coatings resulted in the creation of new multiphase inclusions (and less alumina). Although these results cannot be directly compared with state-of-the-art industrial filtration procedures, active filtration seems so far the most promising approach to produce steel of improved quality. In addition, filters with a calcium aluminate-based coating might be interesting in the production of steel with tailored inclusions for special applications.

In the present work, graphene nanoplatelets were successfully embedded into polymer fibers produced by electrospinning. A simple water-ethanol-based system was developed, without any dispersing additives. Microscopy investigations on the fibers revealed that, after reaching a certain graphene load, this aligned itself along the fiber length, forming a continuous path. Preliminary mechanical tests showed low values of tensile strength and Young's modulus, which is common in the case of polymer fiber mats. Antibacterial tests revealed that both pure graphene as well as graphene-containing fibers inhibited bacterial growth in a similar way. These fibers will be tested as additives for carbon-bonded refractories containing recycled material, in order to improve their thermomechanical properties and prevent the bacterial degradation of environmentally friendly binders.

The pressure drop of a ceramic foam filter is an important characteristic indicating the resistance to fluid flow through the filter. Filtration experiments have shown that filtration efficiency increases with decreasing functional pore size. However, this improvement comes at the cost of a higher pressure drop. Furthermore, trials with increased roughness of filter struts showed an improved filtration behavior. Comparing the influence of these filter properties on the filter efficiency is of high interest in terms of filtration per pressure drop. Therefore, the sensitivity of the pressure drop with respect to surface roughness needs to be known. In the study, the pressure drop of ceramic foam filters was measured for different functional pore sizes, porosities, and surface roughness in a water-based test facility at NTNU in Trondheim, Norway. The flow velocity was varied in the range of 0.6–80 cm/s, allowing the determination of the Darcy and non-Darcy permeability coefficients.

Three-dimensionally printed fine-grained refractory ceramics ready for use in contact with liquid steel based on developed one-step thermal debindable ceramic filaments that do not require any chemical solvent pre-debinding are investigated. This work exhibits the most favourable debinding and sintering regimes with an excellent form stability and reproducibility of printed products ensured. The structure of the sintered products was examined with computed tomography. The designed inner geometry with micro-porosity introduced during debinding combined with pre-designed printed macro-cavities enabled the outstanding thermal-shock performance of the specimens. The functionality of the sintered refractory products in the form of casting nozzles was preliminarily tested in contact with steel melt using a hot-stage microscope. The structure of the specimen was subsequently examined with laser scanning microscopy and scanning electron microscopy. The mechanical properties of printed samples were studied via mercury intrusion porosimetry, compressive strength testing, and spatial tensile strength testing. According to the results, the cold crushing strength of the 3D-printed specimens in the printing direction was comparable to that of pressed fine-grained alumina specimens (50–60 MPa). The measured porosity was 21.5 vol% with a pore size less than 10 µm, which is suitable for applications in contact with molten steel. In order to show thermal-shock resistance of the 3D-printed casting nozzle, a 100 kg steel-melt flow test was performed in a steel-casting simulator with the nozzle surviving all related thermal shocks as well as the ferrostatic pressure of the melt. The evaluated composition and production route of the filaments can be utilized to produce one-step, thermally debindable, thermal-shock-resistant refractory parts with a complex inner structure that are applicable in an industrial environment.

The partial replacement of primary raw materials for the production of refractories with recycled ones gains in importance, as it contributes to the conservation of natural resources, energy saving, and reduction in greenhouse gas emissions. In this work, the use of a magnesia–carbon (MgO-C) recyclate in the fractions 3–6, 1–3, and 0–1 mm as a raw material for MgO-C refractories was investigated. The recyclate was examined via optical and scanning electron microscopy. Using mixtures with different recyclate contents up to 82 wt%, MgO-C specimens were prepared to study the influence of the recyclate on their chemical composition, structure, and properties. The substitution of primary raw materials with the recyclate did not cause a decrease in the MgO content analyzed after carbon burnout, but the contents of the individual impurities changed. A comparison of the MgO-C that contains 82 wt% recyclate with the recyclate-free material through computed tomography indicated a change in the size distribution of the MgO grains. The porosity increased, and the cold modulus of rupture decreased with increasing recyclate content, whereas the thermal shock resistance improved. At a recyclate content of 40 wt%, the refractoriness under load was only slightly lower than that of the recyclate-free material.

Abstract The influence of two industrially fabricated MgO‐C specimens differing in the MgO grade of the used MgO raw material on the population of nonmetallic inclusions via immersion tests was investigated. The immersion tests were performed in molten, Al‐treated 42CrMo4 steel at 1600°C and 1680°C in a steel casting simulator for 30 min. The inclusion population remaining within the solidified steel was characterized by the help of an EDS‐aided automated scanning electron microscope using an automated feature analysis. Several thousands of inclusions were detected and fully classified considering both their size and their elemental composition. The presented work reveals the impact of the MgO grade of the immersed MgO‐C specimens on the characteristics of the remaining nonmetallic inclusion population in dependency on the temperature of the molten steel. Significant differences in the total number of remaining inclusions and in regards to their size and species were exhibited and in‐depth analyzed. The paper contributes to the understanding of inclusion evolution mechanisms and propose potentially occurring phenomena based on the gained results.

Abstract Recycling of used refractories – in particular closed‐loop recycling – gains in importance because of both ecological and economic benefits, such as the conservation of natural resources, reduced landfilling, and the reduction of greenhouse gases and energy consumption. In this work, the use of a magnesia‐carbon (MgO‐C) recyclate for the production of MgO‐C refractories is investigated. Using fused magnesia, the mentioned MgO‐C recyclate, graphite, novolak, and a modified coal tar pitch, test specimens with different recyclate contents (0, 40, 65, and 82 wt%) were prepared on a laboratory scale. The apparent porosity, which is usually higher in recyclate‐based refractories than in recyclate‐free ones, increased by 14% from the specimens made exclusively from virgin raw materials to those made from the mixture containing 82 wt% recyclate. The dynamic Young's modulus and cold modulus of rupture decreased, but the thermal shock resistance was improved by the use of the recyclate.

The technology of multi-wire sawing is well established in the production of silicon wafers but can also be applied in the production of ceramic substrates. In this study, the influence of the Al2O3-grain size of the alumina ceramic on the efficiency of the multi-wire slurry process was investigated. The grain size of HIPed alumina ceramics was changed by heat treatment processes at 1350 °C and 1400 °C. A B4C slurry was used for the investigation of the cutting of high purity alumina ceramic. With increasing grain size of the ceramic, the efficiency of the sawing process increases. The analysis of the as-cut surface morphology of the substrates shows a change in material removal from trans- to intergranular micro-fracture with increasing grain size. Furthermore, grain coarsening leads to substrates with increased roughness values and reduced biaxial strength.

For more than 20 years, the sidewalls and bottom of steel ladles have been lined with carbon-bonded magnesia (MgO-C) and magnesia-alumina bricks (MAC). The alumina raw materials react with magnesia forming a spinel, which decreases open porosity and slag infiltration. The amount, grain size, and chemistry of the added spinel impact the properties of spinel-containing MgO-C. Corrosion tests have been performed in a steel casting simulator at 1580 °C using 18CrNiMo7-6 steel and Fe-rich slag as corrosion medium. Digital light microscopy and SEM/ EDS (scanning electron microscope with energy dispersive spectroscopy) were used to evaluate the corrosion mechanisms. The metal casting simulator test showed that the addition of CaO-MgO-Al2O3 aggregates results in the highest corrosion resistance against molten steel and synthetic basic slag compared to alumina-rich spinel aggregates.

The influence of TiO2 addition on the high-temperature electrochemical characteristics of stainless-steel-based materials was investigated by means of differential potential measurement, electrochemical polarization and impedance spectroscopy. A new three-electrode approach was utilized which incorporated a liquid aluminum alloy AlSi7Mg0.3 as the reference electrode, barium carbonate BaCO3 as the solid-state electrolyte, and stainless steel or a stainless steel-TiO2 composite as the working electrode. The potential differences between the steel-based working electrodes and the liquid-aluminum-alloy reference electrode were measured for 85 h throughout the whole experiment, including the heating and cooling period. The experiments were performed at 850 °C. The determination of the high-temperature open circuit potential (ECorr) in reference to the liquid aluminum alloy was carried out via potentiodynamic polarization. The polarization-related changes in the impedance characteristics were evaluated by the correlation of impedance responses before and after the polarization. The addition of 40 vol% TiO2 resulted in a reduction in the potential of the steel-TiO2 composite and led to the formation of a more uniform electrode–electrolyte interface. The reaction products on the surface of the working electrodes were investigated by means of SEM/EDS and XRD. They consisted of mixed oxides within the Fe-O, Ba-Fe-O and Ba-Cr-O systems.

The aim of this study is the investigation of a technological synthesis of MgAlON, which is a prospective coating material on ceramic foam filters for the filtration of magnesium, aluminum, and other metal melts. Thermodynamic calculations are performed, and the synthesis is carried out at 1500 °C in nitrogen atmosphere using samples consisting of different fractions of Al2O3, MgO, and AlN as starting materials. The effect of the quantity of these components on the conversion degree of the educts is evaluated. Furthermore, the effect of the holding time at the synthesis temperature, as well as the composition points or regions showing the highest conversion degree, are determined. XRD analysis is performed to evaluate the phase fractions and lattice parameters of the spinel after the respective reaction, and the nitrogen content of selected samples is evaluated. Sessile drop tests using AlSi7Mg are performed at 950 °C on selected sintered samples, determining their wettability, and therefore, applicability of the material in light metal melt filtration.

The influence of powder bed density on the final density and microstructure of aluminum oxide parts manufactured by direct selective laser melting has been studied. Iron oxide and manganese oxide nanoparticles were used to improve laser absorption by over eighty percent. To achieve such values, flowable doped alumina granules were prepared by spray drying. Thermal treatment of the granules at 1600 ​°C and consecutive mixing with coarse alumina allowed improvement of the tapped powder densities, reaching a maximum value of 56.4% of the theoretical density. This led to laser processed parts with densities up to 98.6% measured by tomographic microscopy. Measurements with an integrating sphere and an UV-VIS-NIR spectrophotometer employing Kubelka-Munk theory show the decrease of absorptance caused by thermal pre-treatment. 3D mapping by X-ray μ-beam fluorescence contrast tomography and high resolution synchrotron powder diffraction provide information about the variation of dopant distribution and composition within the granules.

In the previous research works, ZnAl2O4 material was considered as one of the solutions for the decopperization process of molten steels; up to 33% of decopperization efficiency was reported by utilising the ZnAl2O4 filter. In order to verify the decopperization possibility of ZnAl2O4 materials, iron-based alloys with various copper and carbon contents were interacted with ZnAl2O4 substrates in a heating microscope under an argon gas atmosphere at 1600 °C. Fe-Cu alloys were found to react with the ZnAl2O4 substrate during the interaction process, and a reaction layer with a complex composition around the alloy droplet was formed; however, Cu was not detected in the reaction layer. Cu was later found infiltrated inside of the ZnAl2O4 substrates. Furthermore, the Cu-Zn compounds were detected when the copper content in Fe-Cu alloys was 10 wt% Cu. After interaction experiments, copper was decreased in all cases. Thereby, the copper evaporation and infiltration into the ZnAl2O4 substrate were considered as the reasons for copper loss. Moreover, oxygen dissolved in melt was found to have a great effect on the copper evaporation process.

Mullite reticulated porous ceramics (RPC) are one of the key components for porous media burner, the mechanical properties of mullite RPC decided the service life of the burner. However, the irregularities of cellular structure made it difficult to reveal the fracture behavior of mullite RPCs. In this study, the three-dimensional (3-D) structures of mullite RPCs were analyzed by X-ray computed tomography. The strength and damage behavior of mullite RPCs were respectively investigated via the compression tests and finite element modeling based on the actual 3-D model, also the corresponding strengthening mechanism was proposed. The results indicated that the reconstructed 3-D model exhibited the real microstructure of mullite RPCs, containing the hollow struts and strut defects. The Young's modulus calculated from actual 3-D structures was lower than that from Gibson-Ashby theory. In addition, the surface defects preceded triangular tips to generate the area of stress concentration, leading to the fracture behavior first occurred at the strut defects. With the formation of dense strut in mullite RPCs, the stress uniformly distributed in the whole solid skeleton, thus significantly improving the damage resistance of mullite RPCs.

In this study, a novel metal matrix composite based on 60 vol% 316L stainless steel and 40 vol% MgO manufactured by powder metallurgy technology was developed. The corrosion resistance of the developed steel–MgO composite material against molten aluminum alloy AlSi7Mg0.3 was investigated by means of wettability tests and long-term crucible corrosion tests. The wettability tests were carried out using the sessile drop method with the capillary purification technique in a hot-stage microscope (HSM). Static corrosion tests were performed in molten aluminum alloy at 850 °C for 168 h to evaluate the impact of pre-oxidation of the composite surface on the corrosion resistance. The pre-oxidation of steel–MgO composites was carried out at 850 and 1000 °C for 24 h, based on preliminary investigations using thermogravimetry (TG) and dilatometry. The influence of the pre-oxidation on the composite structure, the corrosion resistance, and the phase formation at the interface between the steel–MgO composite and aluminum alloy was analyzed using SEM/EDS and XRD. The impact of the steel–MgO composite material on the composition of the aluminum alloy regarding the type, size, and quantity of the formed precipitations was investigated with the aid of ASPEX PSEM/AFA and SEM/EBSD. It was revealed that the pre-oxidation of the steel–MgO composite at 1000 °C induced the formation of stable MgO-FeO solid solutions on its surface, leading to a significant increase of long-term corrosion resistance against the liquid aluminum alloy.

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 °C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 °C and 30 min). The conventional test yielded contact angles of around 92°, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157°. Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 µm up to 50 µm and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer.

The aim of this paper is to prepare nano-functionalized ceramic foam filters from carbon-bonded alumina. The carbon-bonded filters were produced via the Schwartzwalder process using a two-step approach. The prepared ceramic foam filters were further coated using graphene oxide. Graphene oxide was prepared by the modified Tour method. The C/O of the graphene oxide ratio was evaluated by XPS, EDS and elemental analysis (EA). The amount and type of individual oxygen functionalities were characterized by XPS and Raman spectroscopy. The microstructure was studied by TEM, and XRD was used to evaluate the interlayer distance. In the next step, filters were coated by graphene oxide using dip-coating. After drying, the prepared composite filters were used for the purification of the water containing lead, zinc and cadmium ions. The efficiency of the sorption was very high, suggesting the potential use of these materials for the treatment of wastewater from heavy metals.

The mechanical properties of a metal-matrix composite foam are investigated by interrupted in-situ compressive deformation experiments within an X-ray computed tomography device (XCT). Each in-situ experiment generates a sequence of reconstructed 3D images of the foam microstructure. From these data, the deformation field is estimated by registring the images corresponding to three consecutive steps. To this end, the generic registration framework of the itk software suite is exploited and combined with several image preprocessing steps. Both segmented (binary) images having just two grey values for foreground (strut structure) and background (pore space) and the result of the Euclidean distance transform (EDT) on pore space and solid phase are used. The estimation quality is evaluated based on a sequence of synthetic data sets, where the foam’s microstructure is modelled by a random Laguerre tessellation. For large deformations, a combination of non-rigid registration for the EDT images and partwise-rigid registration on strongly deformed regions of the binary images, yields surprisingly small estimation errors.

Lightweight linear cellular composite materials on basis of austenite stainless TRIP- (TRansformation Induced Plasticity-) steel as matrix with reinforcements of MgO partially stabilized zirconia (Mg-PSZ) are described. Two-dimensional cellular materials for structural applications are conventionally produced by sheet expansion or corrugation processes. The presented composites are fabricated by a modified ceramic extrusion powder technology. Characterization of the microstructure in as-received and deformed conditions was carried out by optical and scanning electron microscopy. Magnetic balance measurements and electron backscatter diffraction (EBSD) were used to identify the deformation-induced martensite evolution in the cell wall material. The honeycomb composite samples exhibit an increased strain hardening up to a certain engineering compressive strain and an extraordinary high specific energy absorption per unit mass and unit volume, respectively. Based on improved property-to-weight ratio such linear cellular structures will be of interest as crash absorbers or stiffened core materials for aerospace, railway, or automotive applications.