Ceramics, Volume 6, Issue 1 (March 2023) – 45 articles

Because new zirconia materials are constantly being developed, the aim was to identify and qualitatively synthesize research on how processing and time-related factors affect the properties of high translucent (HT) zirconia intended for monolithic restorations. Cochrane Library, PubMed, Scopus, Web of Science, and reference lists were searched for in vitro and clinical studies. Eligibility and risk of bias were assessed. A synthesis of 142 publications was performed. HT 3Y-TZP was the most common, followed by 5YSZ, 4YSZ, and multilayer. In the laboratory, HT 3Y-TZP should be sintered according to the manufacturer’s recommendation and polished before glazing to favour strength, roughness, and wear behaviour. In the clinic, polishing is necessary after grinding to favour roughness and aging resistance. Over time, when using hydrothermal aging, t–m phase transformation and reduced translucency are expected, without affecting the strength and roughness. The strength of 4YSZ and 5YSZ is unaffected. However, the time-related methods are of questionable clinical significance. The evidence of all other factors’ effects on the properties of HT zirconia is lacking or limited; thus, these factors are of relevance for future research. There is a high heterogeneity of study designs and methods, and the results are brand-dependent. Full article

The problem of the formation and estimation of a thermoradiant and temperature field in ceramics Thermal- Environmental-Barrier Coatings (TBC/EBC) has been considered with complex heat transfer but under the influence of the penetrating intense radiant component. The authors proposed to analyze not only TBC but also EBC from the point of view of the optics of semitransparent scattering and absorbing media in the range of ~0.4–4 μm of external radiant action. This paradigm allows us to continue the study of ceramic fibers embedded in ceramic matrix CMCs (C/C, C/SiC, SiC/SiC) as a traditional class of opaque materials. However, at the same time, mullites, Al₂O₃/Al₂O₃ have been reviewed as a class of semitransparent elements for designing CMCs. The relevance of studying the effect of oriented fibers on the formation of thermoradiation and temperature fields in a semitransparent material was noted. Modeling the scattering asymmetry coefficient influence (scattering phase function) on the generation of the subsurface thermal radiation source was carried out. The methodology for calculating the thermoradiative field in a semitransparent medium (with relative absorption, scattering indexes, and scattering asymmetry coefficient) was used under a one-dimensional two-flux model as the first approximation for solving the radiative heat transfer equation. Calculations of temperature profiles in opaque and semitransparent ceramics were presented under heat load typical for the combustion chambers operating regime of diesel and gas turbine engines. Full article

Zirconolite is a candidate ceramic wasteform under consideration for the immobilisation of the UK civil PuO₂ inventory. In the present work, a baseline dual-substituted zirconolite with the target composition (Ca_0.783Gd_0.017Ce_0.2)(Zr_0.883Gd_0.017Ce_0.1)(Ti_1.6Al_0.4)O₇ was fabricated by hot isostatic pressing (HIPing). In order to optimise the microstructure properties and improve the obtained yield of the zirconolite phase, a range of planetary ball milling parameters were investigated prior to consolidation by HIP. This included milling the batched oxide precursors at 400 rpm for up to 120 min, the pre-milling of CeO₂ (PuO₂ surrogate) to reduce the particle size and using a CeO₂ source with finer particle size (<5 µm). The HIPed zirconolite product consisted of both zirconolite-2M and zirconolite-3T polytypes in varying proportions; however, an additional perovskite phase was obtained in varying quantities as a secondary phase. Ce L₃-edge X-ray absorption spectroscopy was utilised to determine the Ce oxidation state. In this study, the ideal milling parameter for the fabrication of zirconolite waste forms was defined as 60 min at 400 rpm. Full article

The aim of this work was to study the mechanisms of polymorphic transformations in ZrO₂ ceramics under irradiation with heavy ions, as well as to determine the nature of structural distortions in the case of t-ZrO₂ → c-ZrO₂ type transformations and associated anisotropic deformations. The samples of ZrO₂ ceramics were irradiated with Kr¹⁵⁺ heavy ions with an energy of 150 MeV and fluences of 10¹¹–10¹⁶ ion/cm². During evaluation of the structural changes depending on the irradiation fluence, it was found that at low irradiation fluences (10¹¹–10¹² ion/cm²), the main role is played by deformation distortions of the crystal lattice, which have a pronounced anisotropic character. Meanwhile, at fluences above 10¹³ ion/cm², the main role is played by polymorphic transformations of the t-ZrO₂ → c-ZrO₂ type, followed by amorphization of the damaged layer at fluences above 10¹⁵ ion/cm². It was established that the anisotropic distortion of the crystal lattice is more pronounced along the crystallographic a axis, as well as the (011) texture orientation, which is characteristic of t-ZrO₂. The polymorphic transformation processes of the t-ZrO₂ → c-ZrO₂ type occur at irradiation fluences of 10¹³–10¹⁴ ions/cm², which are characterized by the formation of an overlap of local areas of defects that appear along the trajectory of ions in the material. The dependences of changes in the strength and thermophysical properties of ZrO₂ ceramics on the irradiation fluence were obtained. The mechanisms of influence of the structural disorder and polymorphic transformations on the decrease in strength and crack resistance were established. Full article

Zirconolite-structured ceramics are candidate wasteform materials for the immobilisation of separated Pu. Due to the refractory properties of zirconolite and other titanates, removing residual porosity remains challenging in the final wasteform product when utilising a conventional solid state sintering route. Herein, we demonstrate that the addition of CuO as a sintering aid increases densification and promotes grain growth. Moreover, zirconolite phase formation was enhanced at lower process temperatures than typically required (≥1350 °C). CuO addition allowed an equivalent density to be reached using process temperatures of 250 °C lower than the undoped composition. At 150 °C lower than the undoped zirconolite, the addition of CuO resulted in a favourable microstructure and phase assemblage, as confirmed via X-ray diffraction and scanning electron microscopy. Secondary phases of CaTiO₃ and Ca_0.25Cu_0.75TiO₃ were observed at some processing temperatures, which may prove deleterious to wasteform performance. The use of a CuO sintering aid provides an avenue for the further development of the thermal processing of ceramic wasteform materials. Full article

In this study, the structural integrity of mullite (3Al₂O₃·2SiO₂) films, deposited on silicon carbide (SiC) substrates using chemical vapor deposition (CVD), was investigated via increasing load nanoscratch tests. The films were configured by mullite columns of stoichiometric composition growing from a silica-rich layer in contact with the SiC substrate. Controlled damage was induced in the 3Al₂O₃·2SiO₂ films at relatively low scratch loads. Radial and lateral cracking were applied until final delamination and repeated chipping were achieved as the load increased. The intrinsic integrity of the 3Al₂O₃∙2SiO₂ film and the performance of the coated 3Al₂O₃·2SiO₂/SiC system, regarded as a structural unit, were analyzed. With the aid of advanced characterization techniques at the surface and subsurface levels, the configuration and morphology of the damage induced in the coated system by the nanoscratch tests were characterized, and the scratch damage micromechanisms were identified. Finally, the adhesion of the film, in terms of energy of adhesion and interfacial fracture toughness, was determined using different models proposed in the literature. The results from this investigation contribute to the understanding of the mechanical performance and structural integrity of EBC/SiC-based systems, which over the past few years have increasingly been implemented in novel applications for gas turbines and aircraft engines. Full article

This study aimed to investigate four dental adhesive cements and develop a new method for constructing a bi-layered bone holder for implant testing. Hahn^TM Tapered Titanium Implants (Glidewell Laboratories) were embedded in mono- and bi-layered holders, and the implant components were assembled. First molar zirconia crowns and crowns for the tensile bond strength test were milled and sintered. Three self-adhesive resin cements (SARC) and one resin-modified glass ionomer (RMGI, Glidewell Laboratories) cement were used to cement the crowns on the abutment. Tensile bond strength, compressive load, and oblique load tests were performed on the implants. The Glidewell Experimental SARC (GES, Glidewell Laboratories) and RMGI cements had the highest tensile bond strength after thermocycling. The implant assemblies with these two cements had the highest mean compressive strength after thermocycling. Under oblique load, the implants with Denali (Glidewell Laboratories) and GES had the highest strength before thermocycling. However, after thermocycling, Dencem (Dentex) and RMGI had the highest strength under an oblique load. The GES cement and RMGI cement had a better overall performance with zirconia crowns and titanium abutments. In addition, a novel technique for constructing an artificial, bi-layered bone holder was successfully developed to mimic the natural structure of the jawbone. Full article

Thanks to the layer-by-layer creation of components, additive manufacturing (AM) processes enable the flexible production of components with highly complex geometries, that were previously not realizable or only with very great effort. While AM technologies are very widespread in the research sector, they have so far only been used industrially in a few individual areas of application. The manufacturing costs are one reason for this. In this work, a new approach for the optimized arrangement of components in the building box and its potential for reducing the manufacturing costs are presented, illustrated by a selected example, and a discussion. Three types of cylinders, which differ in geometry and/or inclination, are required in quantities of around 1000 each. The optimization aims at an arrangement with the smallest possible number of printing jobs. Compared to the solution obtained by the current automatic software tool that is based on the bounding box method, the optimized arrangement leads to a 70% increase in the number of components on a building platform or, in other words, to a 44% reduction in the number of building platforms needed to manufacture 980 components of each type. Finally, a three-step method is proposed, to optimize the manufacturing preparation for AM components automatically in the future. Full article

Some solid solutions with the chemical composition K_xFe_yTi_8-yO₁₆ (KFTO) and a hollandite-like structure were successfully synthesized by modified sol–gel method. The obtained powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ceramic pellets based on KFTO powders were obtained by compressing and sintering at 1080 °C for 4 h. The sinters were characterized by X-ray and impedance spectroscopy. XRD results show that KFTO powders have a mono-phase tetragonal structure at x = 1.4–1.8 and y = 1.4–1.6. However, it was recognized that the hollandite-like phase could be broken during sintering to form TiO₂ and Fe₂TiO₅ crystals distributed throughout the volume of the ceramics. A frequency dependency of dielectric properties for the sinters was studied by impedance spectroscopy. It was found that an increase in the TiO₂ (rutile) phase during the sintering contributes to a decrease in dielectric losses. At the same time, the KFTO ceramics with reduced content of potassium had increased permittivity. The contribution of electron-pinned defect dipoles (EPDD) and internal barrier layer capacitance (IBLC) in the permittivity of the obtained ceramics was estimated using the Havriliak–Negami equation. It is shown that the KFTO ceramics have the polydisperse characteristic of dielectric relaxation. The observed grain and grain boundary dipole relaxation times were 1.03 × 10⁻⁶ to 5.51 × 10⁻⁶ s and 0.197 to 0.687 s, respectively. Full article

Ceramic materials in Na₂O-CaO-P₂O₅ system were obtained by firing cement-salt stone made from pastes based on powder mixtures including calcium citrate tetrahydrate Ca₃(C₆H₅O₇)₂∙4H₂O, monocalcium phosphate monohydrate (MCPM) Ca(H₂PO₄)₂∙H₂O and/or sodium dihydrogen phosphate NaH₂PO₄. The phase composition of the obtained samples of cement-salt stone after adding water, hardening and drying included brushite CaHPO₄∙2H₂O, monetite CaHPO₄ and also unreacted Ca₃(C₆H₅O₇)₂∙4H₂O, Ca(H₂PO₄)₂∙H₂O and/or NaH₂PO₄. The phase composition of ceramics in Na₂O-CaO-P₂O₅ system obtained by firing cement-salt stone was formed due to thermal conversion of hydrated salt and heterophase reactions between components presented in samples during firing. The phase composition of ceramic samples based on powder mixture of Ca₃(C₆H₅O₇)₂∙4H₂O and Ca(H₂PO₄)₂∙H₂O after firing at 900 °C included β-calcium pyrophosphate (CPP) β-Ca₂P₂O₇. The phase composition of ceramic samples based on powder mixture of Ca₃(C₆H₅O₇)₂∙4H₂O, and NaH₂PO₄ after firing at 900 °C included β-sodium rhenanite β-CaNaPO_4. The phase composition of ceramic samples based on powder mixture of Ca₃(C₆H₅O₇)₂∙4H₂O, Ca(H₂PO₄)₂∙H₂O and NaH₂PO₄ after firing at 900 °C included β-Ca₂P₂O₇, β-CaNaPO_4, double calcium-sodium pyrophosphate Na₂CaP₂O₇, and Na-substituted tricalcium phosphate Сa₁₀Na(PO₄)₇. Obtained ceramic materials in Na₂O-CaO-P₂O₅ system including biocompatible and biodegradable phases could be important for treatments of bone tissue defects by means of approaches of regenerative medicine. Full article

Bucchero is a well-known class of Etruscan ceramics, characterized by being entirely black both on the surface and in the body. In the present investigation, a representative set of bucchero sherds from the excavations of the Etruscan town of Tarquinia (Viterbo, Italy) was analyzed through flame atomic absorption spectroscopy (FAAS), Fourier-transform infrared spectroscopy (FTIR) and near-infrared (NIR) reflection spectroscopy. Both elemental and mineralogical composition data were treated with methods of multivariate analysis. It was thus possible to discriminate between local and imported production, to estimate the firing temperature and to verify the origin of the grey-black color in this peculiar ceramic class. Furthermore, a virtual reconstruction of a bucchero vase starting from fragments was also attempted on the basis of chemical analysis data. Full article

Fine powders of brushite CaHPO₄·2H₂O, ardealite Ca(HPO₄)_x(SO₄)_1−x·2H₂O (Ca(HPO₄)_0.5(SO₄)_0.5·2H₂O), and calcium sulfate dihydrate CaSO₄·2H₂O—all containing sodium chloride NaCl as a reaction by-product—were synthesized from 0.5 M aqueous solution of calcium chloride CaCl₂, sodium hydrophosphate Na₂HPO₄ and/or sodium sulfate Na₂SO₄. Powder of ardealite Ca(HPO₄)_x(SO₄)_1−x·2H₂O (Ca(HPO₄)_0.5(SO₄)_0.5·2H₂O) was synthesized by precipitation from aqueous solution of calcium chloride CaCl₂ and mixed-anionic solution simultaneously containing the hydrogen phosphate anion HPO₄²⁻ (Na₂HPO₄) and sulfate anion SO₄²⁻ (Na₂SO₄). Sodium chloride NaCl, presenting in compacts based on synthesized powders of brushite CaHPO₄·2H₂O, ardealite Ca(HPO₄)_x(SO₄)_1−x·2H₂O (Ca(HPO₄)_0.5(SO₄)_0.5·2H₂O) and calcium sulfate dihydrate CaSO₄·2H₂O, was responsible for both low-temperature melt formation and the creation of phase composition of ceramics. Heterophase interaction of components led to the resulting phase composition of the ceramic samples during heating, including the formation of chlorapatite Ca₅(PO₄)₃Cl in powders of brushite and ardealite. The phase composition of the ceramics based on the powder of brushite CaHPO₄·2H₂O containing NaCl as a by-product after firing at 800–1000 °C included β-Ca₂P₂O₇, and Ca₅(PO₄)₃Cl. The phase composition of ceramics based on the powder of ardealite Ca(HPO₄)_x(SO₄)_1−x·2H₂O (Ca(HPO₄)_0.5(SO₄)_0.5·2H₂O) containing NaCl as a by-product after firing at 800 and 900 °C included β-Ca₂P₂O_7, CaSO₄, and Ca₅(PO₄)₃Cl; after firing at 1000 °C, it includedCaSO_4, Ca₅(PO₄)₃Cl and Ca₃(PO₄)₂/Ca₁₀Na(PO₄)₇, and after firing at 1100 °C, it included CaSO₄ and Ca₅(PO₄)₃Cl. The phase composition of ceramics based on powder of calcium sulfate dihydrate CaSO₄·2H₂O containing NaCl as a by-product after firing at 800–1100 °C included CaSO₄ as the predominant phase. The phase composition of all ceramic samples under investigation consisted of biocompatible crystalline phases with different abilities to biodegrade. For this reason, the created ceramics can be recommended for testing as materials for treatment of bone defects using regenerative medicine methods. Full article

The development of a collagen-based composite scaffold to repair damaged bone is one of many important issues in tissue engineering. In this study, pure collagen, collagen/β-tricalcium phosphate (β-TCP), collagen/calcium silicate (CS), and collagen/β-TCP/CS scaffolds were fabricated using the freeze-drying method. The phase compositions, microstructures, and mechanical properties were characterized using X-ray diffraction, scanning electron microscopy, and a universal testing machine, respectively. In addition, cell viability was evaluated using an MTT assay. Finally, the correlations between the density, mechanical properties, and biodegradation behaviors of pore size distributions were discussed. Full article

Control of bipolar conduction is essential to improve the high-temperature thermoelectric performance of materials for power generation applications. Recently, Hf(Te_1−xSe_x)₂ alloys have gained much attention due to their potential use in thermoelectric power generation. Increasing the Se alloying content significantly increases the band gap while decreasing its carrier concentration. These two factors affect bipolar conduction substantially. In addition, the weighted mobility ratio is estimated from the experimental electronic transport properties of Hf(Te_1−xSe_x)₂ alloys (x = 0.0, 0.025, 0.25, 0.5, 1.0) by using the Two-Band model. From the bipolar thermal conductivity also calculated using the Two-Band model, we find that it peaks near x = 0.5. The initial bipolar conductivity increase of x < 0.5 is mostly due to the decrease in the weighted mobility ratio and carrier concentration with increasing x. For x > 0.5, the drop in the bipolar conductivity can be understood with significant band gap enlargement. Full article

This study examines the impact of calcium-rich fly ash as an additive on metakaolin-based geopolymers. Six types of fly ash (FA1-FA7) from different thermal power plants in the Czech Republic were collected and characterized based on their physical and chemical properties. The addition of fly ash into the geopolymers was evaluated through a multicriteria assessment that focused on density and mechanical properties. By using a multi-criteria approach, the assessment provides a comprehensive and holistic evaluation of the material, allowing for a more informed decision about the optimal addition of additives. This approach helps to minimize any negative impact on the material’s properties while maximizing the utilization of the by-product. The result is an optimized geopolymer mixture with improved properties and increased sustainability, as the by-product is used beneficially. Furthermore, calcium content is the key factor that affects the physical properties of geopolymers by accelerating the curing time. This rapid process can result in reduced strength with increasing fly ash content. The multicriteria assessment revealed that the optimal condition is achieved using fly ash (FA2) from the Loucovice thermal power plant (5.2 wt.% Ca) that was treated at a temperature of 615 °C. The flexural strength of FA2-based geopolymers increased by 13% compared to concrete (standard). However, the addition of fly ash significantly reduced the compressive strength of geopolymers throughout the range of specimens. The Charpy impact strength of FA2 was higher than the standard due to the presence of unburned biomass solids in the ash structure that can absorb energy easily. Full article

The paper presents the results on the development of an optical coating for a single-crystal ZnGeP₂ substrate based on a selenide-oxide pair of materials (ZnSe/Al₂O₃). The obtained coating ensures the operation of OPO in the mid-IR range up to 5 μm wavelengths. The possibility of ZnSe sputtering by the IBS method is shown. The obtained optical coating has a high laser-induced damage threshold (LIDT) value at a 2097 µm wavelength: $W_o^E=3.51$ J/cm² in energy density and $W_o^P$= 101 W/cm² in power density at a 10 KHz pulse repetition frequency and a pulse duration of 35 ns. Thus, it is shown for the first time that the pair of materials ZnSe/Al₂O₃ can be used for the deposition of optical coatings by the IBS method with high LIDT values for ZnGeP₂ optical elements operating in the mid-IR range. Full article

Recent studies have revealed the outstanding thermoelectric performance of Bi-doped n-type SnSe. In this regard, we analyzed the band parameters for Sn_1−xBi_xSe (x = 0.00, 0.02, 0.04, and 0.06) using simple equations and the Single Parabolic Band model. Bi doping suppresses the carrier-phonon coupling while increasing the density-of-states effective mass. The n-type SnSe is known to have two conduction bands converge near 600 K. Bi doping changes the temperature at which the band convergence occurs. When x = 0.04, its weighted mobility maximized near 500 K, which indicated the possible band convergence. The highest zT of the x = 0.04 sample at mid-temperatures (473–573 K) can be attributed to the engineered band convergence via Bi doping. Full article

A series of LaF₃:Ce³⁺ phosphors for application in photodynamic therapy are synthesized using a one-stage solvothermal synthesis. The synthesis conditions; type and quantity of stabilizer; concentration of activator providing the maximum intensity of UV- and X-ray-excited luminescence; lowest size; and highest colloidal stability of the phosphor nanoparticles are found. As a result of this study, the following parameters are determined using cerium content 5% mol. ethanol as the reaction medium for the solvothermal synthesis and polyvinylpyrrolidone as the stabilizer at an optimized amount. Full article

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. Full article

On-site pXRF analysis in various French collections (Musée du Louvre, Musée national des Arts asiatiques-Guimet, Paris) of porcelains decorated with painted enamels from the Qing Dynasty, in particular porcelains bearing an imperial mark, identifies the types of enamels/glazes, the ions and coloring phases or the opacifier. The study of the elements associated with cobalt (nickel, manganese, arsenic, etc.) and of the impurities of the silicate matrix (yttrium, rubidium and strontium) differentiates the use of ‘Chinese/Asian’ raw materials from ones imported from Europe by the initiative of the European missionaries (chiefly Jesuits) present at the Court (Beijing). Particular attention is paid to the analysis of the blue color of the marks and to the elements associated with the use of gold or copper nanoparticles as well as to the compositions of the pyrochlore phases (tin yellow, Naples yellow). The comparison is extended to pXRF and Raman microspectroscopy measurements previously made on other Qing imperial porcelains as well as on Cantonese productions (on porcelain or metal) from different Swiss and French museums and blue-and-white wares of the Ming and Yuan Dynasties (archaeological and private collections). Full article

The paper studies LiNbO₃ (LN) crystals with a near-stoichiometric composition (NSLN). The study establishes the possibility of different physical methods to reveal NSLN crystals’ exact composition. The main goal was to establish how precisely these methods can reveal a NSLN composition, including a defective structure. This structure determines properties that are important for the application of the crystals. Two NSLN crystals with a different Li/Nb ratio have been studied by IR and NMR spectroscopy. NSLN crystals have been grown from a congruent melt with different K₂O flux contents (5.0 and 5.5 wt%). The data on NSLN have been compared with the data on congruent (CLN) crystals. CLN are the most widely used LN crystals. The study has established that analysis of the IR spectra can determine the Li/Nb ratio within [Li₂O] = 48.6 – 50.0 mol% range, while the ⁹³Nb NMR spectra has a wider range of sensibility. LN crystals’ stoichiometry or the Li/Nb ratio determine the concentration of antisite defects Nb_Li. Niobium substitutes lithium in its octahedron. Such defects appear up to [Li₂O] = 49.9 mol%. Thus, the study shows that IR and NMR spectroscopy are sensitive methods that can complement each other when determining the precise LN composition (Li/Nb ratio) and the presence of intrinsic defects in the crystals. Full article

Aluminum nitride (AlN) is an excellent material for heat sinks and is used, for example, in high-performance electronics, high-power LEDs and photovoltaics. In order to meet the constantly increasing demands on substrate materials and heat sinks resulting from the permanent increase in power density and resulting heat in electronic components, new types of components made of high-performance materials with highly complex geometries are required. In this work, AlN based on a commercial powder (“TOYALNITE^®”-JCGA-BLY5 by Toyal Europe), was successfully qualified for an AM technology through suspension and process development for CerAM VPP—a DLP-based vat photo polymerization technology. The properties of the components were characterized along the entire process chain, achieving densities of 3.33 g/cm³ (>99% Th.D.) and excellent thermal conductivities of more than 180 W/mK, which are comparable to state-of-the-art for conventionally manufactured AlN components. Homogeneous microstructures of good quality confirm the measured density and thermal conductivity. A complex-shaped component usable for an exemplary heating–cooling application demonstrates the potential of this development. Full article

The use of ashes derived from various waste sources as supplements to synthesized ceramic reinforcement in metal matrices has been established. However, studies involving a combination of particulates from three different sources are rare. In a bid to further knowledge in this aspect of research and develop a green aluminium composite for automobile applications, the present investigation studied the implication of adding palm kernel shell ash (PKA), rice husk ash (RHA), and waste steel particles (STP) to the morphology and strength behaviour of Al-6061-T6 alloy. The experimental design was undertaken via the Box–Behnken design (BBD) of the response surface method. A 4% STP at a constant dose was mixed with PKA and RHA at varying proportions and stirring temperatures according to the BBD. The experimental outcome revealed that the responses were greatly influenced by microstructural evolution. From the surface plots, 2–4% RHA and PKA enhanced tensile and flexural strengths, while 4–6% led to a decline in strength. Meanwhile, 2–6% of the particles are favourable to the enhancement of tensile and compressive strengths and moduli. Temperatures between 700 and 800 °C favored response improvement, whereas temperatures between 800 and 900 °C were detrimental to responses. Developed regression models for the responses were validated to be good representations of the experimental outcomes. The optimum mix was obtained at 4.81% PKA, 5.41% RHA, and a stirring temperature of 803 °C. The validation experiment conducted portrayed reliable responses with <5% deviation from the predicted values, thereby certifying the models to be statistically fit for future predictions. Full article

Additive manufacturing and 3D printing methods based on the extrusion of material have become very popular in recent years. There are many methods of printing ceramics, but the direct extrusion method gives the largest range of sizes of printed objects and enables scaling of processes also in large-scale applications. Additionally, the application of this method to ceramic materials is of particular importance due to its low cost, ease of use, and high material utilization. The paper presents the most important literature reports on ceramics printed by direct extrusion. The review includes articles written in English and published between 2017 and 2022. The aim of this literature review was to present the main groups of ceramic materials produced by extrusion-based 3D printing. Full article

Ceramic samples of polycomponent solid solutions (SSs) Na_0.90K_0.05Cd_0.05NbO₃ (Cd-modified KNN) and [(Na_0.90K_0.05Cd_0.05)_0.95REE_0.05]NbO₃, where REE = La, Pr, Tb, Dy, Ho, were obtained by the uniaxial hot pressing (UHP) method. The crystal lattice structures, morphological features of the microstructure, and dielectric and thermophysical properties of these ceramics have been investigated. For the first time, their strength characteristics (Young’s modulus) and the critical stress intensity factor of the mode I K_ic have been estimated. Photoluminescent properties have been compared in SSs [(Na_0.90K_0.05Cd_0.05)_0.95REE_0.05]NbO₃ in the visible wavelength range. Full article

Composites made of carbon-fiber-reinforced carbon (C/C or CFC) are high-performance materials with a wide range of properties, making them especially suitable for the design of thermally and mechanically highly stressed components. As the production process of these high-performance materials is currently still very expensive, new concepts for an economical manufacturing process are required. This paper focusses on an innovative approach that uses the polymer-based pultrusion process for shaping with a subsequent carbonization step to C/C. In this process, carbon fibers (CF) and a phenolic resin were used to manufacture a semi-finished product made of unidirectional (UD) carbon-fiber-reinforced plastic (CFRP) with a fiber volume content of 66%. The C/C composite shows dimensional stability and has a flexural strength of approx. 240 MPa and a flexural modulus of approx. of 135 GPa with an elongation of 1.8%. Full article

Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes. Full article

The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na_1+2xZr_2−xCo_x(PO₄)₃ ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na_1+2xZr_2−xCo_x(PO₄)₃ submicron powders with the NaZr₂(PO₄)₃ structure (NZP, kosnarite type) were obtained by the solid-phase method. The starting reagents (NaNO₃, ZrOCl₂·8H₂O, NH₄H₂PO₄, CoCl₂·6H₂O, ethanol) were mixed with the addition of ethyl alcohol. The resulting mixtures were annealed at 600 °C (20 h) and 700 °C (20 h). The obtained phosphates crystallized in the expected structure of the NaZr₂(PO₄)₃ type (trigonal system, space group R$\overline{3}$c). Thermal expansion of the powders was studied with high-temperature X-ray diffraction at temperatures ranging from 25 to 700 °C. CTEs were calculated, and their dependence on the cobalt content was analyzed. Na_1+2xZr_2−xCo_x(PO₄)₃ ceramics with high relative density (93.67–99.70%) were obtained by Spark Plasma Sintering (SPS). Ceramics poor in cobalt (x = 0.1) were found to have a high relative density (98.87%) and a uniform fine-grained microstructure with a grain size of 0.5–1 µm. Bigger cobalt content leads to a smaller relative density of ceramics. During the sintering of ceramics with high cobalt content, anomalous grain growth was observed. The powder compaction rate was shown to be determined by creep and diffusion intensity in the Na_1+2xZr_2−xCo_x(PO₄)₃ crystal lattice. SPS activation energy in ceramics increased as the cobalt content grew. The microhardness and fracture toughness of ceramics did not depend on their cobalt content. Full article

The results of a study of the processes involved in the production of indium oxide In₂O₃ powder, which is widely used to create transparent and electrically conducting ceramics, are described. The powder was produced in a flow of rare gas (argon or helium) at atmospheric pressure under conditions for the formation of metal-containing plasma in a non-arc discharge mode. The discharge operated in pulsed mode with a pulse repetition rate of 70 kHz and pulse duration of 12 μs. The discharge current was 670 mA and discharge voltages were 180 V and 250 V when the working gases were argon and helium, respectively. These parameters ensure a mode in which the indium cap of a molybdenum cathode suffers thermal erosion. The morphology and elemental and phase composition of the erosion products were studied using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. It was shown that the structure of the synthesized powder particles corresponded to a phase of indium oxide (III) with a body-centered cubic (bcc) lattice with lattice parameter a = 1.013 nm. The powder particles, regardless of the working gas (Ar or He), consisted of non-stoichiometric indium oxide In₂O₃ with a nanocrystalline structure. The average particle diameter was <d> = 13–16 nm. Full article