Ceramics, Volume 3, Issue 2 (June 2020) – 8 articles

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