Ceramics, Volume 7, Issue 4 (December 2024) – 40 articles

Double perovskite materials have emerged as key players in the realm of advanced materials due to their unique structural and functional properties. This research mainly focuses on the synthesis and comprehensive characterization of Ba₂CoWO₆ double perovskite nanopowders utilizing a high-temperature conventional solid-state reaction technique. The successful formation of Ba₂CoWO₆ powders was confirmed through detailed analysis employing advanced characterization techniques. Rietveld refinement of X-ray diffraction (XRD) and Raman data established that Ba₂CoWO₆ crystallizes in a cubic crystal structure with the space group Fm-3m, indicative of a highly ordered perovskite lattice. The typical crystallite size, approximately 65 nm, highlights the nanocrystalline nature of the material. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) discovered a distinctive morphology characterized by spherical shaped particles, suggesting a complex particle formation process influenced by synthesis conditions. To probe the electronic structure, X-ray Photoelectron Spectroscopy (XPS) identified cobalt and tungsten valence states, critical for understanding dielectric properties associated with localized charge carriers. The semiconducting character of the synthesized Ba₂CoWO₆ nanocrystalline material was confirmed through UV-Visible analysis, which revealed an energy bandgap value of 3.3 eV, which aligns well with the theoretical predictions, indicating the accuracy and reliability of the experimental results. The photoluminescence spectrum exhibited two distinct emissions in the blue-green region. These emissions were attributed to the transitions ³P₀→³H₄, ³P₀→³H₅, and ³P₀→³H₆, primarily resulting from the contributions of Ba²⁺ ions. The dielectric characteristics of the compound were analyzed across a different range of frequencies, spanning from 1 kHz to 1 MHz. Magnetic characterization using Vibrating Sample Magnetometry (VSM) revealed antiferromagnetic behavior of Ba₂CoWO₆ ceramics at room temperature, attributed to super-exchange interactions between Co³⁺ and W⁵⁺ ions mediated by oxygen ions in the perovskite lattice. Additionally, first-principles calculations based on the Generalized Gradient Approximation (GGA+U) with a modified Becke–Johnson (mBJ) potential were employed to gain a deeper understanding of the structural and electronic properties of the materials. This approach involved systematically varying the Hubbard U parameter to optimize the description of electron correlation effects. These results deliver an extensive understanding of the structural, optical, morphological, electronic, and magnetic properties of Ba₂CoWO₆ ceramics, underscoring their potential for electronic and magnetic device applications. Full article

Barium silicates have been investigated as high-expansion components of solid oxide fuel cells (SOFCs) and, therefore, their synthesis and expansion have been the subject of intensive research in recent years. In this article, we briefly present a new process to make glass–crystalline composites, as well as two novel findings related to a synthesis route of sanbornite (BaSi₂O₅) and the fast in situ formation of a high-expansion sanbornite composite from a Pyrex-type glass powder. The low-temperature synthesis, composition, and expansion of one type of novel glass composite are described. The composites are made by the reaction of BaCO₃ and Pyrex-type powders at 850–950 °C for a short time of one hour. The composites are well sintered and hard, and their linear coefficient of thermal expansion is about 12.3 × 10⁻⁶ C⁻¹. The crystalline-phase formation, dilatometer measurements, SEM data, and possible applications of the composites are presented and discussed. Full article

Refractory flue walls in anode baking furnaces are exposed to harsh conditions during operation, affecting the structural properties of the material. The flue walls in industrial furnaces degrade over time to the point where they no longer perform as intended and must be replaced. Earlier studies of spent refractory lining from anode baking furnaces have shown considerable densification of the flue wall bricks, where the densification varies significantly from the anode side to the flue side of the brick. The observed densification is proposed to be caused by high-temperature creep, and the aim of this work was to determine whether the uneven densification across the brick could be modeled using a finite element method (FEM) implementing high-temperature steady-state creep. Finite element modeling was used to model steady-state creep for a material similar to that used in the baking furnace. Thermal and physical parameters and boundary conditions were chosen to simulate the conditions in an anode baking furnace. Refractory samples of pristine and spent lining from the baking furnace were also analyzed with X-ray computed tomography (CT), with a reduction in the porosity confirming the densification during operation. The FEM modeling demonstrated that high-temperature creep could explain the observed densification in the spent flue walls. The present findings may be useful in relation to increasing the lifetime of industrial flue walls. Full article

Transition (Ti, Zr) metal-substituted calcium hexaorthophosphate CaTi_4-zZr_z(PO₄)₆ coatings with an NaSICon structure were deposited by atmospheric plasma spraying (APS) onto Ti6Al4Veli substrates using a statistical design of experiments (SDE) methodology. Several coating properties were determined, including chemical composition, porosity, surface roughness, tensile adhesion strength, shear strength, and solubility in protein-free simulated body fluid (pf-SBF) and TRIS-HCl buffer solution. The biological performance evaluation involved cell proliferation and vitality studies and osseointegration tests of coated Ti6Al4Veli rods intramedullary implanted in sheep femora. After a 6 months observation time, a satisfactory gap-bridging potential was apparent as shown by a continuous, well-adhering layer of newly formed cortical bone. These tests suggest that the coatings possess a suitable osseoconductive potential and present an enhanced expression of bone growth-supporting non-collagenous proteins and cytokines, a high cell proliferation, spreading and vitality, and substantial osseointegration by strong bone apposition. The moderate intrinsic ionic conductivity of CaTi_4-zZr_z(PO₄)₆ compounds can be augmented by doping with highly mobile Na⁺ or Li⁺ ions to levels that suggest their use in electric bone growth stimulation (EBGS) devices, able to treat nonunion (pseudoarthrosis) and osteoporosis, and that may also support spinal stabilisation by vertebral fusion. Full article

High-temperature structural materials face severe degradation challenges due to oxidation and corrosion, leading to reduced long-term stability and performance. This review comprehensively examines the interfacial migration mechanisms of reactive elements (REs) such as Ti, Al, and Cr in Ni/Fe-based alloys, emphasizing their role in forming and stabilizing protective oxide layers. We discuss how these oxide layers impede ion migration and mitigate environmental degradation. Key findings highlight the importance of selective oxidation, oxide layer healing, and the integration of novel alloying elements to enhance resistance under ultra-supercritical conditions. Advanced insights into grain boundary engineering, alloy design strategies, and quantum approaches to understanding charge transport at passive interfaces are also presented. These findings provide a foundation for developing next-generation high-temperature alloys with improved degradation resistance tailored to withstand extreme environmental conditions. Full article

Thirteen porcelains assigned to Sèvres factory productions and a few references to the other contemporary factories (Chantilly, Limoges, and Venice) have been studied on-site with a portable X-ray fluorescence (pXRF) spectrometer in order to control the provenance attribution. Characteristic XRF signals of major elements (Si, Ca, K, Pb) and minor/trace (Au, Bi, As, Ti, Co, Cu, Zn, Ni, Y, Zr, Rb, and Sr) elements are compared for the paste, blue mark, various glazed (colored) areas, and gilding. The comparison of peak intensities clearly distinguishes different types of hard- and soft-paste porcelain, made from either similar or distinct raw materials. The analysis of transition elements associated with cobalt identifies three types of cobalt blue and reveals that du Barry-style decoration on certain artifacts was typical of 19th-century production. On-site comprehensive studies of the two famous Etruscan-style breast bowls from Rambouillet Castle dairy, using pXRF and Raman spectroscopy, confirm the use of soft-paste porcelain for the cup and hard-paste for its support, providing detailed information on the use of gold nanoparticles in the burgundy-colored decoration. Full article

The microwave dielectric properties of (1−x)Ca_0.6(La_0.9Y_0.1)_0.2667TiO₃-x(Nd_1/2La_1/2)(Mg_(1+δ)1/2Ti_1/2)O₃ ((1−x)CYTO-xNLMTO) ceramics were investigated in this study. It was discovered that the addition of 1 wt% CuB₂O₄ effectively enhanced the densification and improved the microwave dielectric properties of (1−x)CYTO-xNLMTO, where δ = 0.02. The new ceramic systems of (1−x)CYTO-xNLMTO could achieve ultra-low loss and a high dielectric constant. The novel ceramic systems comprising (1−x)CYTO-xNLMTO exhibited remarkably low loss and a significantly high dielectric constant. Full article

Water contamination has become a global concern, and the prevalence of complex substances known as emerging contaminants constitute a risk to human health and the environment. This work focused on an innovative approach of integrating sonolysis and photocatalysis to remove a standard textile dye efficiently. A highly photo-active, bismuth ferrite (BiFeO₃) nanocatalyst with single particle sizes between 86 and 265 nm was obtained by a novel one-pot combustion method using a deep eutectic solvent as a precursor. The said catalyst was thoroughly characterized and evaluated for photocatalytic and sono-photocatalytic degradation of rhodamine B (RhB). Photocatalytic experiments were conducted under visible light irradiation (450–600 nm). Sono-photocatalytic (SPC) experiments were conducted, focusing on the influence of operational parameters (frequency, power, and pH) on the degradation performance. High-frequency values of 578, 866, and 1138 kHz were explored to promote cavitation dynamics and reactive species generation, improving removal efficiency. Results demonstrated that when sonolysis and photocatalysis were performed separately, the degradation efficiency ranged between 85 and 87%. Remarkably, when the combined SPC degradation was carried out, the RhB removal reached about 99.9% after 70 min. It is discussed that this behavior is due to the increased generation of OH^• radicals as a product of the cavitation phenomena related to the ultrasound-assisted process. Moreover, it is argued that SPC significantly improves reaction kinetics and mass transfer rates, facilitating catalyst dispersion and contact with the RhB molecules. Finally, the stability of the catalyst was evaluated in five repeated RhB removal cycles, where the activity remained consistently strong. Full article

X-ray computed tomography (XRT) has gradually established its position as a non-destructive and, therefore, reproducible three-dimensional (3D) investigation technique, allowing for material- and geometry-independent applications. In the context of this study, XRT provides an enhanced understanding of thermal-induced microstructural changes in an andalusite-based refractory, which are not apparent from the limited two-dimensionality of conventional optical investigation techniques. By subjecting an andalusite-based sample to an XRT scan after temperature treatments of T = 110 °C, 800 °C, 1000 °C, 1200 °C and 1400 °C, the XRT technique in this study introduced a novel perspective on the sintering process of andalusite refractory materials. The XRT investigation focused on the thermal-induced defect and crack evolution of the castable as a function of temperature. In addition to general sintering phenomena, this includes the formation of a capillary network filled with silica-rich glass phases (SiO₂) due to the mullitization of andalusite. The results of the XRT analysis indicate the existence of glass bridges within these structures. Full article

This study aimed to evaluate zirconia dental implant surfaces patterned using Nd:YAG laser or conventional milling techniques against Streptococcus oralis adhesion and biofilm formation. Zirconia dental implant discs were subjected to surface patterning treatments and categorized into four groups: groove texturing by conventional milling (GM), pore texturing by conventional milling (PM), groove texturing by Nd:YAG laser (GL), and pore texturing by Nd: YAG laser (PL). Streptococcus oralis CECT 907T was cultivated on enriched blood agar plates and then transferred to a brain–heart infusion modified medium and incubated at 37 °C under anaerobic conditions until reaching the exponential growth phase. The bacterial suspension was then seeded on 24-well plates containing the treated discs. The viability of bacteria within the biofilm was determined based on colony-forming unit (CFU) counts, while the total biofilm was quantified by measuring its biomass. A qualitative analysis was conducted using scanning electron microscopy (SEM) images to evaluate the bacterial morphology. The statistical analysis of multigroup comparisons was performed using Kruskal–Wallis test with post hoc pairwise comparison, as well as Mann Whiney U test, with significance set at p < 0.05. After both 1 h and 24 h of incubation of Streptococcus oralis on the discs, all groups showed similar results, with no statistically significant differences (p > 0.05). A comparison of the Nd: YAG laser-treated surfaces with conventionally milled surfaces, as well as grooves versus pores for CFU counts, also revealed no statistically significant differences (p > 0.05) for both 1 h and 24 h of culture. Biomass quantification at both the 1 h and 24-h time points showed similar results across the groups, without statistical differences. When comparing the conventionally machined surfaces to Nd: YAG laser-treated surfaces in terms of biomass, no significant differences were observed (p > 0.05). Similarly, the comparison between groove-patterned surfaces and pore-patterned surfaces showed no statistically significant difference. The groove and pore patterns on zirconia surfaces with Nd: YAG laser or conventional milling did not change the Streptococcus oralis adhesion and biofilm formation behavior. Additional studies are recommended to expand our knowledge in this area. Full article

Weak clayey soils in construction are considered problematic due to their high compressibility and low bearing capacity. This study proposes an environmentally friendly replacement for conventional soil stabilizers through the use of geopolymer (GP) containing Cashew Nut Shell Ash (CNSA) to improve soil characteristics. In this study, the CNSAGP was compared with lime-stabilized soil for unconfined compressive strength (UCS), durability, and improved microstructure. The experimental outcomes showed that 9 M + CNSAGP with 4% CNSA provided a UCS of 1900 kPa, which was higher than the lime-stabilized soil (6% lime with 4% CNSA) at 1400 kPa. Durability test results revealed that the CNSAGP-treated sample had better protection against water damage with a strength loss of about 18%, while the lime-treated sample had a strength loss of about 25%. Thermal stability analysis showed that CNSAGP had lower LOI values compared to lime-stabilized samples (0.17% at 900 °C), which indicates CNSAGP’s heat resistance. Microstructure analysis revealed that CNSAGP-stabilized soil was less porous, the microstructure being denser because of reactions of aluminosilicate and pozzolanic activity. Moreover, it affected the soil’s alkalinity, making it better, and improved Atterberg limits, which affected the plasticity and workability. These findings show that CNSAGP is a long-lasting and eco-friendly means of soil stabilization with higher strength, thermal stability, and durability than traditional methods and can be used in engineering. Full article

The aim of this work is to compare the traditional uniaxial pressing with an innovative shaping technique, Digital Light Processing (DLP), in the preparation of porous mullite (3Al₂O₃·2SiO₂) supports to be functionalized with an active coating for CO₂ capture. Indeed, the fabrication of complex geometries with 3D-printing technologies allows the production of application-targeted solid sorbents with increased potentialities. Therefore, this research focused on the effect of the purity of the selected raw materials and of the microstructural porosity of 3D-printed ceramic substrates on the Metal Organic Frameworks (MOFs) coating efficiency. Two commercial mullite powders (Mc and Mf) differing in particle size distribution (D₅₀ of 9.19 µm and 4.38 µm, respectively) and iron oxide content (0.67% and 0.38%) were characterized and used to produce the substrates, after ball-milling and calcination. Mc and Mf slurries were prepared with 69 wt% of solid loading and 5 wt% of dispersant: both show rheological behavior suitable for DLP and good printability. DLP 3D-printed and pressed pellets were sintered at three different temperatures: 1350 °C, 1400 °C and 1450 °C. Mf 3D-printed samples show slightly lower geometrical and Archimedes densities, compared to Mc pellets, probably due to the presence of lower Fe₂O₃ amounts and its effect as sintering aid. Mullite substrates were then successfully functionalized with HKUST-1 crystals by a two-step solvothermal synthesis process. Ceramic substrate porosity, depending on the shaping technique and opportunely tuned controlling the sintering temperature, was correlated with the functionalization efficiency in terms of MOFs deposition. Three-dimensional-printed substrates exhibit a higher and more homogeneous HKUST-1 uptake compared to the pressed pellets as DLP introduces desirable porosities able to enhance the functionalization. Therefore, this work provides preliminary guidelines to improve MOFs coating on mullite surfaces for CO₂ capture applications, by opportunely tuning the substrate porosity. Full article

Bone infections, particularly osteomyelitis, present significant clinical challenges due to their resistance to treatment and risk of progressing to chronic disease. Conventional therapies, including systemic antibiotics and surgical debridement, often prove insufficient, especially in cases where biofilms form or infection sites are difficult to access. As an alternative, calcium phosphate bioceramics have emerged as a promising strategy for treating bone infections. These materials offer key advantages such as biocompatibility, osteoconductivity, and the ability to be engineered for controlled drug delivery. Calcium phosphate bioceramics can serve as scaffolds for bone regeneration while simultaneously delivering antibiotics locally, thus addressing the limitations of systemic therapies and reducing infection recurrence. This review provides an overview of osteomyelitis, including its pathogenesis and conventional treatment approaches, while exploring the diverse therapeutic possibilities presented by calcium phosphate bioceramics. Special attention is given to hydroxyapatite, tricalcium phosphate, and their composites, with a focus on their therapeutic potential in the treatment of bone infections. The discussion highlights their mechanisms of action, integration with antimicrobial agents, and clinical efficacy. The dual capacity of calcium phosphate bioceramics to promote both bone healing and infection management is critically evaluated, highlighting opportunities for future research to address current challenges and enhance their clinical application in orthopedics and dentistry. Future research directions should focus on developing calcium phosphate bioceramic composites with enhanced antibacterial properties, optimizing drug-loading capacities, and advancing minimally invasive delivery methods to improve clinical outcomes. Further in vivo studies are essential to validate the long-term efficacy and safety of calcium phosphate bioceramic applications, with an emphasis on patient-specific formulations and rapid prototyping technologies that can personalize treatment for diverse osteomyelitis cases. Full article

Carbon nanotube (CNT)/graphene ceramic composites with outstanding properties are expected to replace a number of components currently used in the automotive and aerospace industries in the future. Consequently, this area of research has progressed significantly. This review paper, therefore, delves into the enhancement of ceramic properties through the integration of graphene and CNTs. These reinforcements are known to mitigate the inherent brittleness of ceramics, thereby unlocking their potential for applications in sectors requiring high mechanical reliability, such as the aerospace, automotive, and biomedical industries. By summarizing recent research, this paper outlines various preparation methods, including ball milling, heat pressing and spark plasma sintering, and discusses how these techniques contribute to improved mechanical and thermal performance. This review emphasizes the critical role of graphene and CNT ratios, sizes, and their synergistic effects in enhancing fracture toughness, machinability, and overall structural integrity. Thus, this paper provides a comprehensive overview of the current research in this area and discusses the potential of these technologies. Full article

ZnO and TiO₂ are both well-known electron transport materials. Their comparison of performance is considered advantageous and novel. Therefore, a viable electrospinning route was considered for the development of highly polycrystalline TiO₂ and ZnO nanofibers as an electron transport material (ETM) for perovskite solar cells. The materials were well-characterized in terms of different analytical techniques. The X-ray diffraction detected polycrystalline structural properties corresponding to TiO₂ and ZnO. Morphological analysis by scanning electron microscopy revealed that the nanofibers are long, uniform, and polycrystalline, having a diameter in the nanometer range. Optoelectronic properties showed that TiO₂ and ZnO exhibit absorption values in the ultraviolet and visible ranges, and band gap values for TiO₂ and ZnO were 3.3 and 3.2 eV, respectively. TiO₂ bandgap and semiconductor nature were more compatible with Electron Transport Layer (ETL) compared to ZnO. Electrical studies revealed that TiO₂ nanofibers have enhanced values of conductivity and sheet carrier mobility compared to ZnO nanofibers. Therefore, higher photovoltaic conversion efficiency was achieved for TiO₂ nanofibers (10.4%) compared to ZnO (8.5%). Full article

For the first time, a theoretical investigation has been conducted into the structural, electrical, elastic, and optical properties of innovative bismuth-layered structure ferroelectric (BLSF) materials XTi₄Bi₄O₁₅ (where X = Sr, Ba, Be, and Mg). For all of the calculations, PBE-GGA and the ultra-soft pseudopotential plane wave techniques have been implemented with the DFT-based CASTEP simulation tool. Based on the exchange correlation approximation, the calculations reveal that XTi₄Bi₄O₁₅ (X = Sr, Ba, Be, and Mg) materials demonstrate direct band-gap semiconductor behavior with an estimated density functional fundamental gap in the range from 1.966 eV to 2.532 eV. The optical properties of these materials exhibit strong absorption and low reflection in the visible range. Moreover, the estimations of the elastic properties of the materials have shown mechanical stability and ductile behavior (due to B/G > 1.75), where G and B denote the shear modulus and the bulk modulus. Based on the above-mentioned highlights, it can be confidently stated that these materials are promising potential candidates for photovoltaic applications and solar cells due to their suitable direct band gap and high absorption coefficient. Full article

The utilisation of carbonation treatments to produce building materials is emerging as a valuable strategy to reduce CO₂ emissions in the construction sector. It is of great importance to regulate the degree of carbonation when the mineralisation process is combined with hydration, as a high CO₂ uptake may impede the development of adequate strength. A significant number of studies focus on attaining the maximum carbonation degree, with minimal attention paid to the examination of the evolution of CO₂ uptake over the initial stages of the process. In this context, the present study aims to investigate the evolution of CO₂ uptake over time during carbonation. Ordinary Portland Cement (OPC) is employed as material, with aqueous carbonation selected as the mineralisation process. This investigation encompasses a range of carbonation durations, spanning from 5 to 40 min. The analysis of the evolution of the mineral composition with time demonstrated that the rate of the carbonation reaction accelerates in the initial minutes, resulting in the conversion of all the portlandite produced during the hydration process in the initial 10 min. Quantitative analysis of the carbonation degree indicated that the CO₂ uptake at 40 min is equal to 19.1%, which is estimated to be approximately 70% of the maximum achievable value. By contributing to the understanding of the early carbonation mechanisms in aqueous conditions of OPC, this study provides valuable support for further investigation focused on the use of cement mineralisation processes to produce building materials. Full article

A set of experimental and measurement techniques to study the influence of a plasma jet on the main material parameters of piezoelectric ceramics has been presented. A series of plasma experiments has been carried out using a pulsed plasma jet system. It allows of a metered-dose exposure to plasma of different composition and fluence with a constant particle flux density of 10²¹/m², energy flux density of 0.1 MJ/m² and average particle energy of 100–200 eV in a pulse duration of 15 μs. The study of the effects that a repeated exposure to an extreme heat flux of helium and hydrogen plasmas has on the near-surface layer structure and basic material parameters of mass-produced piezoelectric ceramic samples has been presented. The main result of the research is an experimental confirmation of the surface micro-structuring starting after just a few cycles of plasma exposure while only a slight decrease of the main material parameters as well as the preservation of polarization has been observed for two types of different compositions of PZT-ceramics. A further increase in the number of exposure pulses leads to practically no change of main material parameters of both ceramics, even showing a tendency for recovery instead. Full article

In this study, Ni/Ba co-doped NaNbO₃ ceramics (NBNNO_x) were synthesized using a solid-state method to explore the effects of Ni²⁺ and Ba²⁺ ion substitution on the structural, optical, and dielectric properties of NaNbO₃. X-ray diffraction (XRD) confirmed that the ceramics retained an orthorhombic structure, with crystallinity improving as the doping content (x) increased. Significant lattice distortions induced by the Ni/Ba co-doping were observed, which were essential for preserving the perovskite structure. Raman spectroscopy revealed local structural distortions, influencing optical properties and promoting relaxor behavior. Diffuse reflectance measurements revealed a significant decrease in band gap energy from 3.34 eV for undoped NaNbO₃ to 1.08 eV at x = 0.15, highlighting the impact of co-doping on band gap tunability. Dielectric measurements indicated relaxor-like behavior at room temperature for x = 0.15, characterized by frequency-dependent anomalies in permittivity and dielectric loss, likely due to ionic disorder and structural distortions. These findings demonstrate the potential of Ni/Ba co-doped NaNbO₃ ceramics for lead-free perovskite solar cells and other functional devices, where tunable optical and dielectric properties are highly desirable. Full article

Multi-component ultra-high-temperature ceramics (MC-UHTCs) are promising for high-temperature applications due to exceptional thermo-mechanical properties, yet their wear characteristics remain unexplored. Herein, the wear behavior of binary (Ta, Nb)C, ternary (Ta, Nb, Hf)C, and quaternary (Ta, Nb, Hf, Ti)C UHTCs synthesized via spark plasma sintering (SPS) is investigated. Gradual addition of equimolar UHTC components improves the wear resistance of MC-UHTCs, respectively, by ~29% in ternary UHTCs and ~49% in quaternary UHTCs when compared to binary UHTCs. Similarly, the penetration depth decreased from 115.14 mm in binary UHTCs to 73.48 mm in ternary UHTCs and 44.41 mm in quaternary UHTCs. This has been attributed to the complete solid solutioning, near-full densification and higher hardness (~up to 30%) in quaternary UHTCs. Analysis of the worn-out surface suggests pull-out, radial, and edge micro-cracking and delamination as the dominant wear mechanisms in binary and ternary UHTCs. However, grain deformation and minor delamination are the dominant wear mechanisms in quaternary UHTCs. This study underscores the potential of MC-UHTCs for tribological applications where material experiences removal and inelastic deformation under high mechanical loading. Full article

In this study, the design of mixture experiments was used to find empirical models that could predict, for a first approximation, the relative density, flexural strength, Vickers hardness and fracture toughness of sintered composites in order to identify further areas of research in the Al₂O₃-TiB₂-TiC ternary system. The composites were obtained by spark plasma sintering (SPS) of these mixtures at 1700 °C, 80 MPa and a dwell of 3 min. The obtained experimental results were analyzed in the statistical analysis software Minitab 17, and then, different regression models were obtained for each property. Based on the selected models, contour plots were made in the Al₂O₃–TiB₂–TiC simplex for a visual representation of the predicted results. By combining these plots, it was possible to obtain one common zone in the Al₂O₃–TiB₂–TiC simplex, which shows the following combination of physical and mechanical properties for sintered samples: relative densities, flexural strength, Vickers hardness, and fracture toughness of than 99%, 500 MPa, 18 GPa, and 7.0 МPa·m^1/2, respectively. For a first approximation in determining the further area of research, the obtained models describe well the behavior of the studied properties. The results of the analysis showed that the design of mixture experiments allows us to identify the most promising compositions in terms of mechanical properties without resorting to labor-intensive and financially expensive full-scale experiments. Our work shows that 10 different compositions were required for preliminary analysis. Full article

Zirconia ceramics are used in a wide range of applications, including dental restorations, bioimplants, and fuel cells, due to their accessibility, biocompatibility, chemical resistance, and favorable mechanical properties. Following the development of 3D printing technologies, it is possible to rapidly print zirconia-based objects with high precision using stereolithography (SLA) and digital light processing (DLP) techniques. The advantages of these techniques include the ability to print multiple objects simultaneously on the printing platform. To align with the quality standards, it is necessary to focus on optimizing processing factors such as the viscosity of the suspension and particle size, as well as the prevention of particle agglomeration and sedimentation during printing, comprising the choice of a suitable debinding and sintering mode. The presented review provides a detailed overview of the recent trends in preparing routes for zirconium oxide bodies; from preparing the suspension through printing and sintering to characterizing mechanical properties. Additionally, the review offers insight into applications of zirconium-based ceramics. Full article

This work aimed to evaluate the fatigue limit of the zirconia ceramic composite stabilized with yttria and ceria reinforced with alumina platelets (ZrO₂CeYAl₂O₃) and characterize the mechanical properties of sintered specimens. Bar-shaped specimens were compacted by uniaxial pressing in a rigid die and sintered at 1500 °C-2 h. Subsequent characterizations included quantitative phase analysis by X-ray diffractometry, determination of density, modulus of elasticity, microhardness, fracture toughness, four-point flexural strength, and fatigue limit. Observations of fracture mechanisms were carried out using confocal and scanning electron microscopy (SEM). The sintered samples presented values above 98% of relative density. Complex microstructures with equiaxed, homogeneously distributed submicrometer grains and planar alumina platelets were observed by SEM. The composite samples showed high values of fracture toughness due to the transformation, during the test, from the tetragonal to monoclinic phase, causing an increase in volume and creating compression zones around the crack, making it difficult to propagate. The average flexural strength reached 445.55 MPa, with a Weibull modulus (m = 16.8), revealing low flexural rupture stress data dispersion. In the composite evaluated in this work, the occurrence of the tetragonal → monoclinic transformation that occurs in the Ce-TZP present at the triple points and grain boundaries during cyclic loading produces “crack tip shielding”, that is, a restricted elastic zone (zone shielding) that surrounds the crack tip. This phenomenon leads to a reduction in the stress intensity factor at the tip of the crack and slows down its growth, generating an increase in the fatigue resistance of the composite. Full article

This Technical Note presents the continuation of the results regarding the synthesis, and physical and rheological evaluation of geopolymers for space applications. In the first part, the ability of these geopolymers to resist cosmic radiation was evaluated. This second part of the research aims to present the synthesis of the geopolymers, their physical and rheological evaluation, and the fabrication of panels for placement in nanosatellites and deployer systems. Manufacturing the 2 mm-thick geopolymer panel proved to be quite a challenge due to the nature of geopolymers. Three geopolymer formulations MKG-01, MKG-02, and MKG-03 were synthesized with an adequate balance of fluidity and malleability required to manufacture the panels. The formulations offered an open window of approximately 8 h. The mass loss in the formulations was closely related to the solid/liquid ratio of the formulation. The MKG-01 presented lower viscosity and low shear stress for handling, indicating a more homogeneous dispersion than the more viscous samples MKG-02 and MKG-03. Full article

This study presents the fabrication possibilities of ultra-high-temperature ceramics of ZrB₂-30 vol.%SiC and (ZrB₂-HfB₂)-30 vol.% SiC composition using the reaction spark plasma sintering of composite powders ZrB₂(HfB₂)-(SiO₂-C) under two-stage heating conditions. The phase composition and microstructure of the obtained ceramic materials have been subjected to detailed analysis, their electrical conductivity has been evaluated using the four-contact method, and the electron work function has been determined using Kelvin probe force microscopy. The thermal analysis in the air, as well as the calcination of the samples at temperatures of 800, 1000, and 1200 °C in the air, demonstrated a comparable behavior of the materials in general. However, based on the XRD data and mapping of the distribution of elements on the oxidized surface (EDX), a slightly higher oxidation resistance of the ceramics (ZrB₂-HfB₂)-30 vol.% SiC was observed. The I-V curves of the sample surfaces recorded with atomic force microscopy demonstrated that following oxidation in the air at 1200 °C, the surfaces of the materials exhibited a marked reduction in current conductivity due to the formation of a dielectric layer. However, data obtained from Kelvin probe force microscopy indicated that (ZrB₂-HfB₂)-30 vol.% SiC ceramics also demonstrated enhanced resistance to oxidation. Full article

In this work, we report, for the first time, a comparative study on the effects of different solvents on the properties of LiNbO₃ (LN) nanostructures. The solvothermal synthesis method was successfully used with three different solvents: 1—water, 2—methanol, and 3—benzyl. The structural and optical properties of the as-prepared nanoparticles were studied using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis absorbance, Raman spectroscopy, and photoluminescence (PL). Nanoparticles of a very small size, with an average size between 3 and 10 nm, were obtained for the first time. The photocatalytic activities of the three synthesized LiNbO₃ nanoparticles were studied in relation to the photodegradation of a complex and heavy reactive black 5 dye for a wastewater treatment application. The LiNbO₃ synthesized with deionized water showed a higher photocatalytic activity than those synthesized using other solvents, such as methanol or benzyl. Full article

Paving blocks might encounter diverse environmental conditions during their lifespan. The durability of paving blocks is determined by their capacity to endure various exposure conditions. Synthetic fibers have been used in mortar and concrete to improve their properties. This research investigates the influence of including banana fiber (BF) on the physical and mechanical characteristics of mortar. Five different mortar mixes were developed, with varying amounts of BF ranging from 0 to 2% by volume. Testing included ultrasonic pulse velocity, compressive strength, flexural strength, total water absorption, and sorptivity. Specimens were cured for up to 90 days. The results indicate that using 0.5% BF resulted in an improvement in compressive and flexural strength compared to the control mix. There was an increase in total water absorption and the water absorption coefficient in the presence of fibers. There appeared to be good correlations between the compressive strength and the other properties examined. Full article

This work is part of a research project aimed at producing ceramic-like materials, without the need for an initial sintering, for potential applications in catalysis or filtration at temperatures up to 1000 °C. In that context, cordierite-derived materials were prepared from recycled cordierite powder (automotive industry waste) bonded with metakaolin-potassium silicate geopolymer. The principle is that these materials, prepared at temperatures below 100 °C, acquire their final properties during the high-temperature commissioning. The focus is on the influence of the K/Al ratio and cordierite fraction on the stability of the dimensions and porosity during heating at 1000 °C, and on the final Young’s modulus and coefficient of thermal expansion. Conventional and high-temperature XRD evidenced the absence of crystallization of the geopolymer binder and interaction with the cordierite filler during the heating stage when K/Al = 1 or 0.75. By contrast, crystallization of kalsilite and leucite, and diffusion of potassium ions in the structure of cordierite is evidenced for K/Al = 1.5 and 2.3. These differences strongly influence the shrinkage due to sintering and the final properties. It is shown that a K/Al ratio of 0.75 or 1 is favorable to the stability of the porosity, around 25 to 30%. Moreover, a low coefficient of thermal expansion of 4 to 4.5 × 10⁻⁶ K⁻¹ and a Young’s modulus of 40 to 45 GPa is obtained. Full article

The development of sensors that can monitor ultraviolet radiation has many implications for daily life, and even more so if the focus is on low-cost solution processes and the use of eco-friendly materials. In this study, we produced a UV-sensor based on Sn-doped ZnO thin films grown by spray pyrolysis, with a doping content ranging from 1 to 10 at.%. The study focuses on the characterization of the films and the device, and their potential for UV detection. Structural analysis via XRD, FESEM, and STEM confirms the polycrystalline nature of the films, with a hexagonal single-phase wurtzite structure of ZnO. Although the dopant content in the films was widely varied, optoelectronic properties such as transmittance, resistivity, energy gap, density, and carrier mobility are not significantly modified. Sprayed Sn-doped ZnO films demonstrated high sensitivity to ultraviolet light, whether monochromatic or that coming from solar radiation. Outdoor measurements showed promising performance of the UV-sensor, indicating its potential applicability for real-time UV monitoring and potential use. Overall, sprayed Sn-doped ZnO thin films offer a viable and low-cost solution for the fabrication of UV-sensors with desirable properties such as a wide and direct bandgap, high sensitivity, and ease of fabrication. Full article

The suitability of microsilica as a raw material for the production of ceramic mullite–silicate proppants was assessed. The chemical and mineralogical compositions of the initial materials were studied. The mineral composition of bauxite is mainly represented by gibbsite Al(OH)₃ and, to a lesser extent, kaolinite Al₄[Si₄O₁₀](OH)₈, with impurities of hematite and quartz. It is established that, in order to obtain mullite–silicate proppants, compositions containing 10–20% microsilica are optimal. The sintering of these compositions occurs at 1350–1380 °C. A lightweight ceramic proppant was obtained with a bulk density of 1.21–1.41 g/cm³, breaking ratio at 51.7 MPa of 19.1–20.3%, and sphericity and roundness of 0.7–0.9, and the optimal roasting temperature was determined as 1370–1380 °C. Full article