Ceramics — Open Access Journal

The main issue to tune controlled devices by the application of a DC magnetic field comes up against the high value of the field’s intensity required for their implementation. This work presents an implementation of magneto-dielectric materials (MDM) specifically manufactured for their integration in antenna devices operating in VHF band. The twofold objective is: (i) reduction in antenna size, (ii) frequency tuning of the antenna using a low intensity magnetic control. A notable permeability variation of MDM samples is observed when the symmetry of the lines of the control field, with an intensity less than 10 Oe, is consistent with the one of the structures in the magnetic domains. The MDM allows a miniaturization of 20% of an inverted-F antenna (IFA) antenna structure, and an agility of about 2.5% for a control field of 1.5 Oe. Full article

In the field of metal matrix composites (MMC), spark plasma sintering (SPS) technique has been used so far for the manufacture of particle, whisker and short-fiber reinforced alloys. In this work, SPS technique is employed for the first time to produce continuous fiber reinforced light metals. For this purpose, metal matrix composite prepregs with aluminum as a surface coating on carbon fiber textiles are manufactured by twin arc wire spraying and subsequently consolidated by SPS in the semi-solid temperature range of the alloy. Shear thinning rheological behavior of the metal alloy at temperatures between solidus and liquidus enables the infiltration of fiber rovings under reduced forming loads. SPS offered a better controlled and more efficient heat transfer in the green body and faster consolidation cycles in comparison with alternative densification methods. Fully densified samples with no porosity proved the suitability of SPS for densification of MMC with a remarkable stiffness increase in comparison with samples densified by thixoforging, an alternative consolidation method. However, the pulse activated sintering process leads to a quite strong fiber/matrix adhesion with evidence of aluminum carbide formation. Full article

We developed a new ceramic from raw material mainly composed of iron (III) oxide. The measured attenuation coefficient of the ceramic for high-energy gamma rays was in the range 0.268–0.355, which is approximately 40% of that of lead and twice that of concrete. The measured penetrating dose of the ceramic is half of that of concrete. Thus, the novel ceramic material named RASHIX may serve as a novel ceramic alternative for the wide variety of radiation shielding materials used in construction. Full article

Combining stainless steel with zirconia components by powder technological shaping routes for manufacturing of multifunctional parts is an advantageous and promising one-step method making expensive and time-consuming additional joining steps redundant. However, several requirements for co-shaping and co-sintering of the very different compound partners have to be met. The microstructural and chemical constitution of the interface between both materials plays an important role for the mechanical properties, durability and corrosion resistance of the manufactured parts. In the present study, different shaping techniques for co-shaping of stainless steel and zirconia are introduced. The microstructure and the interphase properties of metal/ceramic hybrid parts have been investigated for samples made by tape casting, subsequent lamination and co-sintering. Nevertheless, the results of this study are valid for components made by other hybrid shaping processes as well. The interfaces were characterized by TEM, FESEM, EDX, and X-ray diffraction. Furthermore, the hydrothermal stability of the material compound was investigated. Full article

The types of blue ceramics are monotonous, mainly alumina and zirconia ceramics, and their colors are not pure, with some green tones (−a* value is not close to 0). In this paper, aluminate blue ceramics (LaMgAl_11−xCo_xO₁₉) doped with Co were prepared by the high temperature solid-phase reaction method, which enriched the blue ceramics system. The effect of Co content on the color of ceramics was studied, and the optimal doping amount of Co was found. X = 1.0 is the bluest color of the material (−b* = 35.36), and there is almost no noise effect (−a* = −2.71). By studying the effect of temperature on the system, it is found that the color effect is best when the temperature reaches 1450 °C. When the temperature exceeds 1450 °C, it can only promote the synthesis of LaMgAl₁₁O₁₉ phase, and has no effect on the color of ceramics samples. Based on the material’s pure and bright colors, and good color stability at room temperature, it has great potential in the decoration industry, such as the preparation of jewelry or building decoration materials. Full article

The energy transition from the incineration and gasification of fossil fuels to the incineration and gasification of biomass refractory linings is being held up by a severe corrosion issue, caused by high alkali contents and the wide variety of biomass sources. Incinerators optimized for fossil fuels are commonly lined with mullite, Al₂O₃-Cr or SiC-based refractory products; however, those materials are not always suitable for the use of organic fuels. Hibonite (CaO·6Al₂O₃)-based refractory products have shown promising performance because of their high resistance against alkali attacks. Indeed, previous works have shown that the reaction between calcium hexa-aluminate and an alkali does not lead to the strong volume expansion observed with other mineral phases, such as corundum or andalusite. The present work aims to describe the reactions kinetics occurring between hibonite-based raw materials and biomass ashes. Therefore, the three main oxides contained in an average biomass, namely, CaO, SiO₂ and K₂O, were selected to examine the high temperature reactions with a calcium hexa-aluminate matrix. The resulting phase composition and microstructure were compared with the performance of an alumina matrix through, respectively, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The post-mortem observations show a higher extent of reaction for the alumina than for the calcium hexa-aluminate. Moreover, the microstructure of the alumina matrix suffered a strong chemical spalling, while the calcium hexa-aluminate microstructure remained undamaged after the corrosion. Full article

Creep behavior is very important for the selection of refractory materials. This paper presents a methodology to measure the compressive creep behavior of fired magnesia materials at elevated temperatures. The measurements were carried out at 1150–1500 °C and under compression loads from 1–8 MPa. Creep strain was calculated from the measured total strain data. The obtained creep deformations of the experimental investigations were subjected to detailed analysis to identify the Norton-Bailey creep law parameters. The modulus of elasticity was determined in advance to simplify the inverse estimation process for finding the Norton-Bailey creep parameters. In the next step; an extended material model including creep was used in a finite element analysis (FEA) and the creep testing procedure was reproduced numerically. Within the investigated temperature and load range; the creep deformations calculated by FEA demonstrated a good agreement with the results of the experimental investigations. Finally; a finite element unit cell model of a quarter brick representing a section of the lining of a ferrochrome (FeCr) electric arc furnace (direct current) was used to assess the thermo-mechanical stresses and strains including creep during a heat-up procedure. The implementation of the creep behavior into the design process led to an improved prediction of strains and stresses. Full article

Electrical discharge machinable ceramics provide an alternative machining route independent on the material hardness which enables manufacturing of customized ceramic components. In this study a composite material based on an alumina/zirconia matrix and an electrically conductive titanium nitride dispersion was manufactured by hot pressing and characterized with respect to microstructure, mechanical properties and ED-machinability by die sinking. The composites show a combination of high strength of 700 MPa, hardness of 17–18 GPa and moderate fracture resistance of 4.5–5 MPa√m. With 40 kS/m the electrical conductivity is sufficiently high to ensure ED-machinability. Full article

Yttria stabilized zirconia (Y-TZP) has become a standard material in a variety of biomedical and mechanical engineering applications due to its high strength and toughness. In order to obtain improved properties in terms of strength, hardness and low temperature degradation resistance second phases, typically alumina are added. In this study an alumina toughened zirconia recipe with 20 vol% alumina in a 2Y-TZP matrix was modified by progressive substitution of alumina by up to 10 vol% cerium hexaaluminate (CA6). Samples were produced by hot pressing. The cerium hexaaluminate was synthesized in situ by reduction of tetravalent ceria and reaction sintering with alumina at 1450 °C. The materials reach attractive 4-point bending strength values of greater than 1170–1390 MPa at a fracture resistance of 6.4–7 MPa√m. Vickers hardness is slightly reduced from 1405 HV10 to 1380 HV10 with increasing CA6 fraction. Results show that substitution of alumina by low amounts CA6 does not lead to drastic changes in the mechanical properties. Hardness is slightly reduced while strength reaches a flat maximum at 4 vol% CA6 substitution. The toughness slightly declines with CA6 addition which is caused by reduced transformability of the tetragonal zirconia phase despite a slight coarsening of the matrix observed upon CA6 addition. Full article

Mortarless refractory masonry structures are widely used in the steel industry for the linings of many high-temperature industrial applications including steel ladles. The design and optimization of these components require accurate numerical models that consider the presence of joints, as well as joint closure and opening due to cyclic heating and cooling. The present work reports on the formulation, numerical implementation, validation, and application of homogenized numerical models for the simulation of refractory masonry structures with dry joints. The validated constitutive model has been used to simulate a steel ladle and analyze its transient thermomechanical behavior during a typical thermal cycle of a steel ladle. A 3D solution domain and enhanced thermal and mechanical boundary conditions have been used. Parametric studies to investigate the impact of joint thickness on the thermomechanical response of the ladle have been carried out. The results clearly demonstrate that the thermomechanical behavior of mortarless masonry is orthotropic and nonlinear due to the gradual closure and reopening of the joints with the increase and decrease in temperature. In addition, resulting thermal stresses increase with the increase in temperature and decrease with the increase in joint thickness. Full article

Refractory monolithics for steel ladle linings are typically products with low porosities and high bulk densities. They achieve high temperature, penetration, and corrosion resistance. Despite the high density of these products, which is due to the low porosity of the aggregates, their matrices still exhibit a high amount of pores. Since calcium magnesium aluminate (CMA) has already proven its resistance to penetration and corrosion as a binder in the matrix, this paper investigated if alumina spinel refractories containing microporous calcium magnesium aluminate aggregates can withstand conditions that occur in a steel ladle wall. The objective was to reduce the castable density with the advantage of a lower material requirement for a ladle lining and reduced heat and energy losses. This was achieved by replacing dense alumina aggregates by up to 38% of porous CMA aggregates (grains with 30 vol% porosity), which resulted in a bulk density reduction from 3.1 g/cm³ for the dense alumina castable to 2.8 g/cm³ for the 38% CMA aggregates containing castable. However, the despite the higher porosity, penetration, and corrosion resistance and thermomechanical properties were not impacted negatively for a model alumina spinel castable. A postmortem investigation was conducted on a newly developed dry-gunning mix that was installed in a steel ladle wall on top of a slag penetrated castable and that achieved a service life of 31 heats versus only 18 heats for the reference mix that contained dense alumina and spinel aggregates. This new repair mix contained the newly designed porous CMA aggregates, which in this case partly replaced the dense alumina and spinel aggregates. These porous aggregates consisted of magnesium aluminate and calcium aluminate micro-crystals. The postmortem study revealed two important phenomena that can explain the improved performance: at the hot face in contact with steel and slag, a thin densified zone was observed that blocked the slag penetration into the porous matrix and the porous aggregates. Iron oxides were almost completely blocked from penetration, and only some manganese oxide was observed in the penetrated zone together with some silica and lime from the slag. Clusters of calcium aluminate (CA₆) and magnesium aluminate (MA) spinel build the refractory back-bone on the hot side of the material and gussets filled with mostly glassy calcium aluminum silicates close to the hot face and gehlenite further inside the penetrated zone. Alumina grains had a reaction rim consisting of CA₂ or CA₆ and a very intimate connection to the surrounding matrix unlike the CMA-free mix that showed micro cracks around the alumina grains. At the colder side, the gunning mix with CMA aggregates showed a very good connection to the substrate, supported by a hercynite formation in the gunning mix resulting from a cross-reaction with remains of iron oxide on the CMA containing repair mix. Furthermore, macroscopic observations of a CMA aggregate containing alumina magnesia castable in the metal zone of a steel ladle revealed that macro cracks developed only very slowly, which resulted in a superior service life. Full article

In cement processing, which involves the production of clinker in rotary kilns, the main refractories used in the transition and burning zones are magnesia–spinel bricks. These bricks present suitable chemical and thermomechanical properties, not to mention that they can be easily landfilled. Among the main wear mechanisms of these bricks in the kiln, the infiltration of alkaline salts is noteworthy and occurs through the open pores of the refractory. In this way, the coating—a clinker layer adhered to the brick surface—appears as a protection mechanism of the lining against infiltration. Thus, the objective of this investigation is to run a qualitative coating test based on the contact method, and quantitative coating test based on the sandwich method to check the suitability of the methodologies and to evaluate the coating adherence on two different magnesia–spinel bricks. It was possible to distinguish the superior adherence ability of brick B in both coatings due to the higher porosity and the presence of nonreacted ZrO₂. Despite the similarity between the test results, the quantitative sandwich-coating test is preferable because it does not depend on subjective analysis. Full article

The microstructure of a direct-bonded chromite-magnesia refractory brick, typically used in copper and platinum converters, was modified by adding different amounts of nano-size TiO₂ to the raw material mixture. Bricks with 0, 1, 3, 5, and 7 mass% TiO₂ were produced and compared in terms of spinel formation; the role of the tetravalent cation Ti⁴⁺ in the bonding phase; as well as changes in density, porosity, thermal expansion, and internal stress. This was done through a comprehensive XRD and SEM-EDS study. It was found that Ti is accommodated in the secondary spinel that has formed, where Mg in excess of unity in the tetrahedral site combines with an equal amount of Ti in the octahedral sites to maintain charge balance. The 1 mass% TiO₂ brick had the lowest bulk density (but not significantly different from the original chromite-magnesia brick), the smallest difference in unit cell volumes between the primary and secondary spinels, and the lowest stress arising from the smallest difference in linear thermal expansion coefficients of the phases present. The calculated porosities correspond well with experimentally determined apparent porosity values, whereas the linear thermal expansion coefficients calculated at 1392K are similar to the values measured from 293 to 1273 K. Full article

To avoid the proneness to degradation due to coking in the operation of solid oxide fuel cells (SOFCs) directly running on methane (CH₄) fuels, a modified porous anode of the Ni_1−XCo_X/YSZ (yttria-stabilized zirconia) cermet prepared by an impregnation method is presented. The influence of the Co alloying content on the cermet microstructure, SOFC characteristics, and prolonged cell performance stability has been studied. Co was incorporated into Ni and formed a solid solution of Ni_1−XCo_X alloy connected with the YSZ as the cermet anode. The porous microstructure of the Ni_1−XCo_X/YSZ cermet anode formed by sintering exhibited a grain growth with an increase in the Co alloying content. The electrochemical performance of the cells consisting of the Ni_1−XCo_X/YSZ cermet anode, the YSZ electrolyte, and the LSM (La_0.8Sr_0.2MnO₃) cathode showed an enhancement by the Ni_1−XCo_X impregnation treatment for the respective supply of H₂ and CH₄ to the anode. The cell using the Ni_0.75Co_0.25/YSZ cermet anode (the Ni_0.75Co_0.25 cell) showed the highest cell performance among the cells tested. In particular, the performance enhancement of this cell was found to be more significant for CH₄ than that for H₂; a 45% increase in the maximum power density for CH₄ and a 17% increase for H₂ at 750 °C compared with the performance of the cell using the Ni/YSZ cermet anode. Furthermore, the prolonged cell performance stability with a continuous CH₄ supply was found for the Ni_0.85Co_0.15 and Ni_0.75Co_0.25 cells at least for 60 h at 750 °C. These enhancement effects were caused by the optimum porous microstructure of the cermet anode with the low anodic polarization resistance. Full article

Corrosion is one of the most common wear mechanisms of refractories. Corrosive attacks lead to chemical and microstructural changes. Hot corrosion compromises chemical and/or physical interactions. Thus, the process is complex and not yet fully understood. Currently, corrosion is investigated post mortem by means of X-ray diffraction or scanning electron microscopy. These methods have the drawback that some information is lost on cooling. In-situ measurements, however, take measurements within the process. In resonant frequency and damping analysis (RFDA), a sample is excited to vibrate by a mechanical impulse. The vibrating sample emits an acoustic signal. This is recorded with a microphone and evaluated by means of Fast Fourier Transformation (FFT). We measured the change of the frequency of a low cement castable during the corrosion process. Further simplified experiments with less complex materials were done to confirm the results. Distinctive points of the curves could be correlated to specific corrosion phenomena, like melting or infiltration. The applied methods include a first characterization of the material with open porosity, density and in-situ high-temperature (HT)-RFDA measurements as well as a study of the slag behavior. Full article

A simple, efficient synthesis approach for designing large ceramic pieces, herein termed chromium (III) oxide (Cr₂O₃) material, is provided. The process can be called the replica technique, or replication. The elaboration of a material with a unique morphology is a result of a ceramic salt coating that has been previously dissolved in ethylene glycol as the solvent; this process is performed on a carbon material surface that is selected as a template. Here, the carbon template was carbon fiber. After a heat treatment to convert the ceramic precursor to the corresponding ceramic oxide followed by the removal of the template, hollow ceramic oxide wires were obtained. The resulting material was characterized by X-ray diffraction, Raman and Fourier transform infrared spectroscopies, and scanning electron microscopy. The material exhibited a multiscale architecture, assembling nanosized nodules to form micron-sized tubes that assemble themselves into a centimetric structure. Objects with such tailored architectures can be used in a large variety of applications in fields as diverse as pyrotechnics, adsorption, and catalysis. Full article

In this work, the flexure strength and fracture propagation mechanisms in yttria tetragonal zirconia (3YTZP) dense composites with 1 and 5 vol.% exfoliated graphene nanoplatelets (e-GNP) were assessed. The composite powders were processed by dry planetary ball milling to exfoliate the as-received GNP, and then densified by spark plasma sintering (SPS). The hardness and Young’s modulus were measured by Vickers indentation and the impulse-echo technique, respectively. Flexural strength and modulus were estimated by four-point bending tests. Finally, cracks originated by Vickers indentations were analyzed by scanning electron microscopy (SEM). The Raman spectra and SEM observations showed a reduction in the number of graphene layers and most remarkably in the lateral size of the e-GNP, achieving a very homogeneous distribution in the ceramic matrix. The hardness, elastic modulus, and flexural strength of the 3YTZP matrix did not vary significantly with the addition of 1 vol.% e-GNP, but they decreased when the content increased to 5 vol.%. The addition of e-GNP to 3YTZP increased its reliability under bending, and the small lateral size of the e-GNP produced isotropic fracture propagation. However, the energy dissipation mechanisms conventionally attributed to the larger GNP such as fracture deflection or blocking were limited. Full article

This article outlines the current state-of-the-art binder jetting (BJT) additive manufacturing of functional ceramics. The impact of printing parameters, heat treatment processing, and testing conditions on the observed performance of these ceramics is discussed. Additionally, this article discusses the impact of physical properties such as density and mechanical strength on the overall performance of these functional ceramics. Although printing parameters and initial feedstock are crucial for the printability of the desired parts, other factors play an important role in the performance of the ceramic. Thermal post-processing is crucial to achieve optimized functional properties, while the testing orientation is key to obtaining the maximum output from the part. Finally, future research directions for this field are also discussed. Full article

ZrO₂ (3Y-TZP) matrix composites with 30 vol % Zr metallic particles were obtained by spark plasma sintering (SPS) using a colloidal processing method. The microstructure and mechanical properties of this novel ceramic–metal composite have been studied. The fracture toughness of composites is slightly higher than the values corresponding to monolithic zirconia. Scanning electron microscope (SEM) observations of the crack path show that the major contributions to toughening are the resulting crack blunting and branching that occurs at crack tips in the metallic particles before the onset of crack propagation. Plastic deformation of the metallic particles is strongly influenced by the constraint induced by the different phase arrangements. This system can be considered as a particulate composite with a periodic residual stress field, in which the metal phase is under strong compression due to the residual thermal stresses as a consequence of the coefficient of thermal expansion mismatch. Therefore, the plastic deformation of the metallic particles in this composite is likely to be reduced to a large extent. Full article