Additional Thermal Treatment Research Articles

Production and characterization of geopolymers containing electric arc furnace dust (EAFD) for hazardous metals sequestration

The present research deals with the production and characterization of geopolymers prepared by mixing metakaolin with sodium silicate, sodium hydroxide solution and different amounts of electric arc furnace dust derived from the production of carbon steel, to be used by the construction industry. Specimens with compositions containing 90, 80, 70, 60 and 50 g of metakaolin and respectively 10, 20, 30, 40 and 50g of electric arc furnace dust powder were prepared. A blank composition containing metakaolin, sodium silicate, sodium hydroxide solution and free from electric arc furnace dust were also prepared for comparison. After production and hardening, all samples were characterized regarding compressive strength and water absorption. Hardened samples with compositions containing 10 and 30g of electric arc furnace dust were then submitted to a release test in order to evaluate the heavy metals elution. It has been observed that the addition of electric arc furnace dust worsens the pastes workability during their production in this way limiting the amount of electric arc furnace dust which may be added to the geopolymeric matrix. However, samples containing 90 g of metakaolin and 10 g of electric arc furnace dust still maintain fair compressive strength (about 27 MPa), low water absorption (about 28 %) and display limited elution of heavy metals. An additional thermal treatment of 1h at 700 °C, performed to induce sintering of the geopolymeric composites and therefore to reduce their porosity, did not lead to materials with improved performances.

Large area pulsed laser deposition of memristive Pr0.7Ca0.3MnO3 heterostructures for neuromorphic computing

Heterostructures of the perovskite Pr0.7Ca0.3MnO3 (PCMO) and a tunnel oxide such as AlOx are highly interesting memristive devices for emulating synaptic properties in neuromorphic circuits. Future chip generations with these memristive elements requires PLD systems which enables PCMO growth on a full wafer. To address the issue of plume broadening in this study, a slit system was used to localize the deposition region, thereby eliminating the need for excessive scanning. This study investigates the effect of the slit system and process gas pressure on plume broadening. This investigation has been used to parameterize a simulation software to assess the effectiveness of different movement speeds and to develop strategies for homogeneous deposition, adjustable to a chosen film thickness in the order of twenty nanometers. We used these strategies to fabricate area dependent switching memory cells on a standard 4″ Si wafer using the material combination of Pr0.7Ca0.3MnO3 and AlOx. The influence of the aluminum oxide thickness on the switching shows that the IV loop starts to exhibit a hysteresis for AlOx thicknesses ≥ 3 nm. An increase in AlOx thickness leads to an increase in resistance and capacitive charging. An additional thermal treatment reduces the resistance and the switching voltage and increases the ratio between low resistive and high resistive state. Devices without thermal treatment of the PCMO are compatible for back end of line processing of standard CMOS technology.

Effect of Health Status and Heat-Induced Inactivation on the Proteomic Profile of Plasma Rich in Growth Factors Obtained from Donors with Chronic Inflammatory Skin Conditions.

Atopic dermatitis, psoriasis and lichen sclerosus are among the most challenging conditions treated by dermatologists worldwide, with potentially significant physical, social and psychological impacts. Emerging evidence suggests that autologous-platelet-rich plasma could be used to manage skin inflammation. However, the presence of soluble autoimmune components could hinder their therapeutic potential. The aim of this study was to analyze the proteomic profile of plasma rich in growth factors (PRGFs) obtained from donors with inflammatory skin conditions to evaluate the impact of skin health status on the composition and bioactivity of PRGF-based treatments. Venous blood from healthy volunteers and patients with psoriasis, lichen sclerosus and atopic dermatitis was processed to produce PRGF supernatant. Half of the samples were subjected to an additional thermal treatment (56 °C) to inactivate inflammatory and immune molecules. Proteomic analysis was performed to assess the protein profile of PRGFs from healthy and non-healthy patients and the effect of Immunosafe treatment. Differential abundance patterns of several proteins related to key biological processes have been identified, including complement activation, blood coagulation, and glycolysis- and gluconeogenesis-related genes. These results also demonstrate that the thermal treatment (Immunosafe) contributes to the inactivation of the complement system and, as a consequence, reduction in the immunogenic potential of PRGF products.

Eco-efficient plastering mortars for improved indoor comfort − The influence of A. dealbata bark addition

The passive contribution of indoor coatings to improve interior comfort is an eco-efficient challenge nowadays. Gypsum is one of the more eco-efficient binders available to produce plasters. Acacia dealbata is an invasive plant species in many countries, and the management of its wood waste for fires prevention is imperative. This study intends to evaluate the effect of using Acacia dealbata bark waste, directly after milling (raw) or with additional thermal treatment (1 h at 250 ⁰C), as an addition to an industrial gypsum-based plastering mortar to passively improve indoor comfort. To prevent the biological colonization, air lime is also added. Two clay-based plasters are used for comparison, as this type of plaster is known for being highly hygroscopic, together with a reference gypsum plaster. Results show that both the gypsum-bark mortars fulfill the standard requirements and do not show biological vulnerability. They doubled the moisture buffering of the reference gypsum plaster and got closer to the hygroscopic performance of the clay plasters. The very similar results between the two gypsum-bark mortars suggest that the thermal treatment of bark is not an eco-effective choice. So, the raw bark-added gypsum mortar is selected as a promising coating material to passively contribute for indoor comfort in an innovative, eco-efficient, way.

Impact of lipids on the functional, rheological, pasting and thermal properties of ultrasound-processed canary seed flours

Canary seed, a gluten-free cereal, is renowned for its high content of fats, starch, and proteins. The extraction of oil is often necessary to extend flour shelf life or obtain purified starch and protein fractions. Similar to many gluten-free flours, it may require additional thermal treatments to enhance its suitability to formulate several food products. Thus, this study investigated the impact of ultrasound (US) treatment on the techno-functional and physicochemical properties of both whole (WCS) and defatted (DWCS) canary seed flours. The US treatment slightly increased water and oil absorption capacities in WCS. Lipids in the flour and treatment temperature affected the surfactant properties. Untreated and treated defatted DWCS flours exhibited higher emulsifying activity (up to +36%) and foaming capacity (up to +340%) than WCS. The presence of lipids and US treatment influenced protein extraction, with changes in albumins (WCS and DWCS), globulins (DWCS) and prolamins (WCS) recovery. US treatment altered pasting and rheological properties of all studied flours, impacting viscosity and starch-lipid complex formation. Rheological properties were lipid-dependent, and defatted samples formed stronger gels. US treatment decreased gelatinization enthalpy in WCS (up to −9.5%) and increased it in DWCS (up to +11.3%) flours. Moreover, lipids significantly influenced retrogradation, which was absent in untreated and treated WCS flours. US-treated flours displayed similar diffraction patterns to untreated samples, but with reduced intensities as temperature increased. The untreated defatted sample exhibited a 9% lower crystallinity. These findings highlight the benefits of US treatment and defatting for improving gluten-free food products formulated with canary seed flour.

Structural and morphological studies on yttrium-doped magnesium aluminate spinel powders synthesized by mixed-fuel solution combustion synthesis approach

The incorporation of yttrium ions into the structure of magnesium aluminate spinel can be an effective approach to modify its microstructure, enhancing its formation, sintering behavior, and mechanical properties. In this work, a mixed-fuel solution combustion synthesis approach was used to prepare yttrium-doped spinel powders with the composition MgAl2-xYxO4 (x=0; 0.02; 0.06 and 0.10). It was shown that combustion of magnesium-, aluminum- and yttrium-nitrate salts solution in the presence of a mixture of specific fuels for each metal nitrate enables the direct production of crystalline spinels without the need for additional thermal treatment. Structural and morphological characterization showed that the main phase in all samples is a spinel phase (S.G. Fd3-m), while periclase (MgO), monoclinic yttrium aluminate (Y4Al2O9), and yttrium aluminum garnet (Y3Al5O12) were found in small portion in some samples. The average crystallite size increased in Y3+-substituted samples relative to undoped MgAl2O4, from 15 nm up to 40 nm. The lattice parameter increased with increase in yttrium content, ranging from 8.071 ? to 8.086 ?. The specific surface area of the synthesized powders spans from 8.2 m?/g for the undoped powder to 3.3 m?/g for the Y3+- substituted spinels with the maximum added yttrium content.

Synergistic effects of dry-brush compatibility and shear stress on rapid alignment of lamellar microstructures for block copolymer reflectors

Because of the high viscosity of severe chain entanglements, a time-consuming process of aligning microstructural orientation in high molecular-weight (Mw) block copolymer photonic crystal films imposed limitations on efficient mass production. In this study, the effective alignment of the block copolymer microstructures in the film state can be carried out within approximately a few minutes. This achievement was realized through the synergistic localized compatibility of dry brush and shear stress during the spin-casting process. The orientation and orderliness of the microphase-separated lamellar structure in as-spun poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) films can be meticulously controlled by introducing blends with PS homopolymer (hPS) of varying Mws (Mw,hPS) and cholesteric liquid crystal mesogen (Chol). Within the ternary blended films of hPS/PS-b-P4VP(Chol), the wet-brush miscibility by blending low-Mw hPS with a small molecular weight ratio (α) of Mw,hPS to Mw,bPS (Mw of the PS block chain) of α <1 results in the formation of disoriented lamellar structures, whereas dry-brush localization by introducing high-Mw hPS with α∼0.9 yields highly parallel-aligned lamellar structures to the substrate after spin casting, even with a massive quantity of additive hPS (∼59 wt%). The dry-brush compatibility can be demonstrated by morphological observation in the ternary blended film after extraction of the hPS. As a result, without any further efforts, such as additional solvent or thermal annealing treatments, the as-spun ternary blended film can exhibit visible structural colorations with controlled wavelengths by alternating the quantity of hPS. This provides an accessible solution for rapidly producing flexible photonic crystals featuring tunable photonic band gaps.

Cold sintering of BaZr0.8Y0.2O3-ẟ ceramics: Phase formation and grain boundary properties

Electrochemical devices based on the proton conducting ceramic BaZrO3 have shown their immense potential for efficient energy conversion and gas separation processes at intermediate temperatures. A major drawback of this material class is the inevitably high sintering temperature, which is necessary to reach sufficient densities for gas tightness. Recently, cold sintering has been applied to densify BaZrO3 – BaCeO3 solid solutions at low temperatures using a partial dissolution of the Ce-rich phase. Here, we apply the method to BaZr0.8Y0.2O3-ẟ (BZY20), which is a Ce-free proton conducting ceramic. We show that densification by cold sintering is viable at temperatures between 150 °C and 250 °C under uniaxial pressures of 400 MPa and deionized water as a sintering aid. The dissolution of yttrium from BZY20 during cold sintering acts as the trigger for densification at low temperatures but forms Y(OH)3 as an instable side product. Therefore, we developed a two-step cold sintering process that adds an additional thermal treatment between 900 and 1100 °C directly after the cold sintering process to enable electrochemical characterization and transmission electron microscopy investigations.

Advancing the additive manufacturing of PLA-ZnO nanocomposites by fused filament fabrication

ABSTRACTPoly(lactic acid)-zinc oxide (PLA-ZnO) nanocomposites for fused filament fabrication have potential applications in the biomedical field as they combine the bio-compatibility of PLA with the antibacterial properties of ZnO. This work investigates the effects of masterbatch mixing strategy, ZnO concentration and ZnO surface treatment (silanisation) on the printability and the mechanical performance of the nanocomposites as a pre-requirement to the wider uptake of these materials. The results showed that the printability decreased as the filler loading increased. However, the surface treatment of the ZnO powder enhanced the matrix-filler interfacial interactions and reduced the thermal degradation of PLA. This ameliorated the printability and the tensile properties of the nanocomposites filled with up to 5 wt.% of ZnO. Moreover, despite the additional thermal treatment, melt-mixing prevented the degradative effect induced by the solvent used for solvent mixing. Future work will focus on assessing the antibacterial properties of the nanocomposite FFF parts.

The Mechanism of the Formation of Binary Compounds Between Zn and S Impurity Atoms in Si Crystal Lattice

The paper presents the results of an experimental study of surface morphology, elemental composition, electrophysical and optical properties of Si samples earlier doped with impurity atoms of Zn and S. The results of the study revealed a sufficient concentration of Zn and S elements on Si surface after diffusion (3.1% and 2.6% by weight, respectively). After additional thermal treatment at different temperatures, i.e., at 850°C and 875°C, the samples of I group have regained their initial parameters. However, it’s noteworthy that the mobility of charge carriers in group I samples was comparatively lower than that in group II samples allegedly under the influence of Zn and S binary molecules. After additional heat treatment of all samples at a temperature of 875°C, the authors have studied optical absorption coefficients. And their band gap energies were determined using the Tauc Plot method. According to the results of the study, the optical band gaps in group II and III samples were 1.12 eV, whereas the band gap energy in group I samples after additional thermal treatment at a temperature of 875 °C turned out to be 1.31 eV. Having theoretically calculated the band gap by applying Vegard’s law, the authors suggested that the new structure must be of Si0.92ZnS0.08 - type.

Temperature‐Dependent Photoredox Catalysis for CO2 Reduction Coupled with Selective Benzyl Alcohol Oxidation over ZnIn2S4/In2O3 Heterostructure

CO2 reduction (CO2RR) with selective benzyl alcohol (BA) oxidation in a single photoredox reaction can simultaneously utilize photogenerated electrons and holes to realize efficient production of fuels and value‐added chemicals. Herein, a unique 2D/1D ZnIn2S4/In2O3 (ZIS/In2O3) heterostructure is developed displaying outstanding performance for photoredox catalysis. As is unequivocally illustrated by various advanced ex situ/in situ characterizations and theoretic calculations, the notable catalytic performances originate from the built‐in interfacial electric field within the ZIS/In2O3 heterostructure, which strongly ameliorates the separation and transport of charge carriers. Remarkably, the catalytic activity can further be boosted after coupling the additional thermal treatments, and the product selectivity is highly temperature dependent. Thereby, the precise formation of targeted products, which can serve as valuable industrial products and fuels can be controlled by changing the reaction temperatures, including obtaining the syngas with different H2/CO ratios from CO2 reduction, as well as benzaldehyde, hydrogenated benzoin, and dibenzyl ether (never reported for BA during photocatalysis) from the BA conversion. This study offers a constructive and inspiring contribution to reasonably developing photoredox catalysts, which can fully utilize photogenerated electrons and holes, as well as demonstrate how to controllably yield the targeted products by coupling thermo‐ and photoredox catalysis.

FeN4 active sites generated on dipyridylpyridazine functionalized reduced graphene oxide for high-performance air electrode in a Zn-air battery

The growing global electricity demand requires the development of cost-effective energy conversion and storage systems, integrating inexpensive, eco-friendly, and high-efficiency catalysts. Oxygen reduction reaction (ORR) is considered crucial process to achieve high-power-density fuel cells and Zn-air batteries (ZABs). The latter have attracted the attention of scientific community due to its high theoretical energy density, reliable safety and low-cost. However, several limitations must be overcome, designing ORR catalysts thought versatile and economical synthetic routes. In this sense, the non-noble iron–nitrogen-carbon materials (FeNC) have been reported as the most potential candidates for attaining superior activity toward ORR in substitution of the high-priced commercial Pt-C catalysts. Herein, Diels-Alder surface adducts based on dipyridylpyridazine units have been created along 2D surface of reduced graphene oxide (rGO) nanosheets for the controlled generation of FeN4 active sites at the edges through successive solvent-free mechanochemical reactions and an additional thermal treatment. The optimized catalyst provided high content of pyridinic-N, graphitic-N and Fe2+ species, contributing to the excellent activity delivered as electrocatalyst for ORR processes. In addition, a flooded ZAB assembled with this material as cathodic/air electrode exhibited excellent specific capacities of 4.94 and 2.77 A·h·g−1 at -1 and -5 mA, respectively, improving the catalytic performance obtained for the 10 wt% Pt-C benchmark electrocatalyst.

Magnetron Sputtering Deposition of High Quality Cs3Bi2I9 Perovskite Thin Films.

Nontoxic all-inorganic perovskites are among the most promising materials for the realization of optoelectronic devices. Here, we present an innovative way to deposit lead-free, totally inorganic Cs3Bi2I9 perovskite from vapor phase. Taking use of a magnetron sputtering system equipped with a radiofrequency working mode power supply and a single target containing the correct ratio of CsI and BiI3 salts, it was possible to deposit a Cs3Bi2I9 perovskitic film on silicon and soda-lime glass. The target composition was optimized to obtain a stoichiometric deposition, and the best compromise was found with a mix enriched with 20% w/w of CsI. Secondly, the effect of post-deposition thermal treatments (150 °C and 300 °C) and of the deposition on a preheat substrate (150 °C) were evaluated by analyzing the chemical composition, the morphology, the crystal structure, and the optical properties. The thermal treatment at 150 °C improved the uniformity of the perovskite film; the one at 300 °C damaged the perovskite deposited. Depositing on a preheated substrate at 150 °C, the obtained film showed a higher crystallinity. An additional thermal treatment at 150 °C on the film deposed on the preheated substrate showed that the crystallinity remains high, and the morphology becomes more uniform.

Facile and versatile fabrication process for AgNW/GZO transparent composite electrodes for photovoltaic applications by atmospheric pressure plasma jet

Transparent conductive oxide (TCO) must have high electrical conductivity and optical transmittance. Using higher doping concentrations improves the conductivity but often at the expense of transmittance in the near-infrared regime. Using thicker film to improve the conductivity is not preferable as it significantly reduces the transmittance. Silver nanowire (AgNW)/ TCO composite film has been proposed as a viable method to address this dilemma. However, AgNWs often require additional thermal treatment to weld the nanowires to reduce the contact resistance. Also, thermal treatment apparatus, such as lasers, cannot be easily integrated into the TCO deposition setup, adding extra cost for handling samples. Here we use an atmospheric pressure plasma jet (APPJ) to fabricate AgNW/ TCO composite films—APPJ successfully welds the AgNWs and covers them with a thin gallium-doped ZnO or GZO protective layer simultaneously. The AgNW weight significantly affects the optoelectronic and morphological properties and can be tailored to fit the requirements of particular photovoltaic applications. Our perovskite solar cells with the AgNW/GZO front electrodes exhibit a ∼21% increase in power conversion efficiency. Furthermore, unlike conventional methods, our approach is vacuum-free and does not require additional processes, such as lasers, to treat the AgNW network, which may greatly reduce operational complexity.

Spark Discharge Synthesis and Characterization of Ge/Sn Janus Nanoparticles.

Germanium-tin nanoparticles are promising materials for near- and mid-infrared photonics thanks to their tunable optical properties and compatibility with silicon technology. This work proposes modifying the spark discharge method to produce Ge/Sn aerosol nanoparticles during the simultaneous erosion of germanium and tin electrodes. Since tin and germanium have a significant difference in the potential for electrical erosion, an electrical circuit damped for one period was developed to ensure the synthesis of Ge/Sn nanoparticles consisting of independent germanium and tin crystals of different sizes, with the ratio of the atomic fraction of tin to germanium varying from 0.08 ± 0.03 to 0.24 ± 0.07. We investigated the elemental and phase composition, size, morphology, and Raman and absorbance spectra of the nanoparticles synthesized under different inter-electrode gap voltages and the presence of additional thermal treatment directly in a gas flow at 750 °C. The research shows that the in-flow thermal treatment of aerosol-agglomerated nanoparticles produced special individual bicrystalline Janus Ge/Sn nanoparticles with an average size of 27 nm and a decreasing absorption function with a changing slope at 700 nm.

Comparative Analysis of Synthesis Routes for Antimony‐Doped Tin Oxide‐Supported Iridium and Iridium oxide Catalysts for OER in PEM Water Electrolysis

AbstractThis study investigates and compares four different deposition methods for an iridium‐based catalyst on antimony‐doped tin oxide support for oxygen evolution reaction in water electrolysis. Different synthesis routes often lead to varying properties of the resulting catalyst and can result in performance disparities. Here, some of the most prominent methods are carried out on the same support material and evaluated with special focus on the deposition yield of Ir and thus cost efficiency along with electrochemical performance. The catalysts are also assessed based on their chemical composition, namely Ir or IrO2‐based, with an additional thermal treatment to convert Ir to IrO2 species. The chosen synthesis routes result in different Ir species to obtain tetragonal IrO2 a modified Adams fusion approach delivers the best controllable and highest Ir loading and thus superior electrochemical performance. As far as metallic Ir catalysts are concerned, a wet‐chemical reduction‐based synthesis results in the most desirable catalyst, which however falls behind the Adams fusion catalyst upon thermal treatment to IrO2. The work in this study is a comprehensive analysis of different synthesis influences and recommends practices for laboratory‐based syntheses and an outlook on industrial viability.

Can Severe Plastic Deformation Tune Nanocrystallization in Fe-Based Metallic Glasses?

The effects of severe plastic deformation (SPD) by means of high-pressure torsion (HPT) on the structural properties of the two iron-based metallic glasses Fe73.9Cu1Nb3Si15.5B6.6 and Fe81.2Co4Si0.5B9.5P4Cu0.8 have been investigated and compared. While for Fe73.9Cu1Nb3Si15.5B6.6, HPT processing allows us to extend the known consolidation and deformation ranges, HPT processing of Fe81.2Co4Si0.5B9.5P4Cu0.8 for the first time ever achieves consolidation and deformation with a minimum number of cracks. Using numerous analyses such as X-ray diffraction, dynamic mechanical analyses, and differential scanning calorimetry, as well as optical and transmission electron microscopy, clearly reveals that Fe81.2Co4Si0.5B9.5P4Cu0.8 exhibits HPT-induced crystallization phenomena, while Fe73.9Cu1Nb3Si15.5B6.6 does not crystallize even at the highest HPT-deformation degrees applied. The reasons for these findings are discussed in terms of differences in the deformation energies expended, and the number and composition of the individual crystalline phases formed. The results appear promising for obtaining improved magnetic properties of glassy alloys without additional thermal treatment.

Hydrothermally-Derived Silver-Decorated Nanocrystalline Anatase Photocatalyst for Reactive Violet 2 Photodegradation

A photocatalyst comprised of Ag nanoparticles dispersed on an anatase matrix has been prepared using a simple hydrothermal method without additional thermal treatment. The prepared material was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy, and N2 adsorption–desorption isotherms. The prepared catalyst activity was evaluated by photocatalytic degradation of C.I. Reactive Violet 2 (RV2) aqueous solution under UVA and visible light illumination. SEM revealed the non-uniform dispersion of silver particles throughout the matrix composed of fine particles. According to XRD analysis, the matrix was composed of pure anatase with a crystallite size of 8 nm calculated through the Scherrer equation. HRTEM micrograph analysis showed that anatase nanoparticles possess a spherical morphology and a narrow size distribution with an average particle size of 8 nm with more active anatase {100} crystal surface exposed, while silver nanoparticles were between 60 and 90 nm. A bandgap of 3.26 eV has been calculated on the basis of the DRS UV-Vis spectrum, while a specific surface area of 209 m2g−1 has been established from adsorption isotherms. Thus, through a simple synthesis approach without subsequent thermal treatment, the agglomeration of nanoparticles and the reduction of specific surface area have been avoided. Prepared nano Ag/anatase photocatalyst exhibits excellent efficiency for the photodegradation of RV2 under UVA and visible irradiation.

Luminescence properties of BaMO4:Eu3+ (M: Mo or W) phosphors derived from co-precipitation reaction

Luminescent BaMO4:xmol%Eu3+ materials (M: Mo or W, and x: 0, 2, 4, 6, 8, and 10 mol%) were successfully obtained by a coprecipitation method at room temperature without additional thermal treatment, leading to highly crystalline materials with reduced reaction times and low manufacturing cost. Structural analyses by powder X-ray diffraction and vibrational Raman techniques of the [WO4]2- and [MoO4]2- groups confirm a characteristic scheelite-type structure. The results indicate an average crystallite size at around 30 nm, and a highly pure phase has been supported by Rietveld refinement. SEM-EDS data of BaMO4:xmol%Eu3+ materials identified polycrystalline particles with bipyramidal-like morphology and homogeneous europium ion distribution. Additionally, the band gap energy (Eg) of barium molybdate and tungstate materials were calculated from reflectance data by the single-constant Kubelka-Munk function. Furthermore, the emission intensity, lifetime, and intrinsic emission quantum yield (QEu3+Eu3+) of the materials have been determined and discussed. The luminescent properties of these materials are significantly influenced by the LMCT excitation bands (O2- → Mo6+, W6+, and Eu3+) as well as their intense red emission bands assigned to Eu3+ transitions. The experimental intensity parameter values Ω2 and Ω4 were evaluated from the emission spectra, using the magnetic dipole 5D0 → 7F1 transition as the standard reference. It was observed that the Ω2 values are much higher than the Ω4 values. This result is related to the fact that the 5D0 → 7F2 transition presents a much higher intensity than 5D0 → 7F1 one suggesting a low local symmetry around the Eu3+ ion, which might be due to angular distortions in the local coordination geometry. The high QEu3+Eu3+ values (60–79%) indicated an overall high emission intensity for the prepared phosphors. These are special photonic features of the Eu3+-doped molybdate and tungstate, suggesting they could be suitable for luminescent materials applications.

Effect of annealing treatments on the mechanical behaviour of UHTCMCs prepared by mild polymer infiltration and pyrolysis

Cf/ZrB2–SiC composites were produced by water-based slurry impregnation followed by six cycles of polymer infiltration and pyrolysis at 1000 °C. Despite the mild temperature of pyrolysis, the flexural strength of this composite showed values in excess of 500 MPa even at elevated temperature, up to 1400 °C. The abrupt decay of strength at 1500 °C stimulated the need to investigate the effect of additional thermal treatments enabling the crystallization of the amorphous polymer derived SiC(O). Annealing treatments, carried out between 1400 °C and 1900 °C, led to evident microstructural changes that in turn affected the flexural strength measured both at room temperature and at 1500 °C. The microstructural evolution was carefully analysed and 1400 °C was identified as the best trade-off between temperature of the annealing treatment and mechanical performance. After annealing at 1400 °C, the strength of the composite at room temperature decreased from the initial 500 MPa for untreated samples to 300 MPa due to the creation of new porosity, but this strength value was then maintained up to 87% at 1500 °C. Annealing at higher temperatures were detrimental for microstructure and strength.