Microemulsion-assisted sol–gel derived mesoporous silica nanoparticles (MNP) were functionalized with carboxyl (–COOH) ligands using (3-Triethoxysilyl) propyl succinic anhydride (TESPSA) to enable the grafting of cobalt and nickel tetra(amino)phthalocyanines (CoPc-A and NiPc-A). Electron microscopies (SEM and TEM) revealed uniform spherical nanoparticles with diameters of approximately 100 nm. Amide coupling between the amine peripheral ligands of the phthalocyanines and the surface –COOH groups of MNPs was achieved by condensation. Successful grafting via amide condensation between peripheral amine groups of phthalocyanines and surface –COOH moieties was evidenced by the appearance of characteristic amide I–III vibrational bands in FTIR spectra, despite the absence of crystalline reflections in X-ray diffraction, consistent with an amorphous hybrid framework. The 1H and 29Si MAS NMR analysis revealed systematic modifications in the local chemical environment upon sequential surface functionalization and molecular coupling. Splitting of Ni 3d orbitals resulted in the formation of an additional peak in the core-level O 1s X-ray photoelectron spectra of NiPc-A, indicating a distinct surface chemistry compared to the CoPc-A samples. Impedance spectroscopy together with comparative Arrhenius plots uncovered the conduction mechanism of samples. NiPc-A grafted MNP exhibited a hybrid conduction mechanism with increasing conductivity above 60 °C both in Ar flow and under vacuum conditions.

The effect of Li2O addition (0–10 wt.%) on the thermal properties and crystallization kinetics of Al2O3–CaO–K2O–Na2O–SiO2 glasses is systematically investigated. Increasing Li2O content modifies the silicate network, resulting in an increase in the thermal expansion coefficient (10.2 × 10−6°C−1 to 17.8 × 10−6°C−1) and a reduction in glass transition temperature (538°C to 433°C). The activation energy for viscous flow (482–529 kJ·mol⁻¹) exhibits a weak non-monotonic compositional trend, suggesting that factors other than simple network depolymerization may contribute to viscous flow behavior. Crystallization kinetics were analysed using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, supported by Akaike Information Criterion (AIC)-based model. Glasses containing 6–8 wt.% Li2O exhibit effective Avrami exponents of approximately 1.5, whereas 10 wt.% Li2O yields m ≈ 1.0, indicating a systematic change in effective crystallization kinetics with increasing lithium content. This shift is accompanied by an increase in the apparent crystallization activation energy to 261 kJ·mol−1, suggesting increased resistance to crystallization under the investigated non-isothermal conditions. X-ray diffraction identified Li2SiO3 as the dominant crystalline phase across all compositions (49–62 wt.%). Raman spectroscopy confirmed progressive depolymerization of the silicate network with increasing Li2O content, while SEM analysis supported the crystallization behavior predicted by the JMAK model. The combined thermal, structural, kinetic, and phase analysis provides a quantitative framework for designing lithium-modified aluminosilicate glasses with tailored thermal expansion and controlled crystallization.

Four glass compositions in the Y2O3–Al2O3–ZrO2 system were synthesized by flame synthesis as microspheres. The base composition derived from the Al2O3–Y2O3 eutectic (76.8 mol.

This study investigates and compares the structural and thermal properties of six glasses in the Al2O3–CaO–K2O–Li2O–Na2O–SiO2 system with varying Li2O concentration (0–10 mass

Bi-doped (0.25, 0.50, and 1.50 mol.% of Bi2O3) 2CaO-Al2O3-SiO2 glasses were prepared in two different ways (flame synthesis with a combination of solid-state reaction and conventional melting) to compare the influence of the preparation method on their thermal, optical, magnetic, and structural properties. All prepared samples were X-ray amorphous. Differential thermal analysis revealed significant differences in thermal properties of the prepared glasses depending on the preparation method. In the case of glasses prepared by flame synthesis, the glass crystallizes in one or two-steps, depending on the Bi content. Glasses prepared by the conventional melting method crystallize in a single step, independent of the bismuth content. A higher tendency toward crystallization with increasing Bi3+ addition was observed for both types of glasses, indicating the role of Bi as a nucleating agent. The photoluminescence properties of the prepared systems were studied in the visible spectral range. All prepared systems exhibited broad emissions in the spectral range from 350 to 750 nm, centered at similar to 485 nm and similar to 425 nm for glasses prepared by conventional melting and flame synthesis, respectively. Glasses prepared by conventional melting exhibit less complex magnetic properties than those prepared by flame synthesis. In glasses prepared by melting, the diamagnetic (at 300 K) and the paramagnetic (at 2 K) component of magnetization prevails, even at low magnetic fields. The glass microspheres prepared by flame synthesis were diamagnetic or weakly ferromagnetic at 300 K and paramagnetic or weakly ferromagnetic/antiferromagnetic at 2 K. These findings indicate that Bi-doped calcium-aluminosilicate glasses offer promising applications not only in optical but also, e.g., in magneto-optical devices.

Modern advances in the technology of materials based on the Al2O3-Y2O3 system compounds allowed for the development of turbomachinery, scintillation materials science, as well as lighting and laser systems. Growing single crystals and ceramic composites from melt using methods characterized by weak convective mixing (e.g., horizontally directed crystallization) presents a number of difficulties that can be avoided during the feedstock preparation stage. The lack of information in the existing literature on the process of preparing monophasic, homogeneous, and high-density raw material for single-crystal growth prompted this paper. It addresses a wide range of issues: raw material selection (the possibility of using highly active nano-powders synthesized by wet chemistry methods is considered), factors influencing the solid-state synthesis process and ways to intensify the solid-state reaction of YAG formation, the choice of green body molding method, and potential ways to increase the relative density of the feedstock. This review is devoted to the assessment of the applicability and efficiency of some technological operations from ceramic technology, including the production of optical ceramics, in the production of monophasic YAG from commercial micro-sized oxide powders by solid-state synthesis.

Ca2Al2SiO7 (gehlenite) glasses doped with Bi (0.5, 1.0 and 3.0 mol. % Bi2O3) were prepared by flame synthesis. The prepared glass microspheres were X-ray amorphous. The thermal properties of prepared glasses were studied by differential scanning calorimetry (DSC) and high temperature X-ray diffraction. The results showed a significant influence of bismuth on the thermal properties. With increasing Bi content, the crystallization pattern of gehlenite changes from a single step to a two-step one.

Bioactive glass (BG) particles with micron-sized pores are important for the construction of BG scaffolds mimicking the hierarchical pore structure of natural cortical bone. In the present work, 45S5 BG was flame synthesised after alkali activation to prepare BG microspheres with micron-sized pores (mPBGMs), which can mimic the physiological pores of cortical bone appropriate for angiogenesis, cell settlement, proliferation and migration. The effects of three parameters of the alkali activation process, namely activation time, NaOH concentration and temperature, on the bioactivity, compositions and textural properties of mPBGMs were investigated. The results showed that all the mPBGMs exhibited good bioactivity. Compared to 45S5 BG as glass feedstock, mPBGMs lost a certain amount of sodium and phosphorus. The mPBGM treated with different alkali activation processes exhibited porosities ranging from 28% to 54%, with predominant pore sizes ranging from 1-10 microns. Inspired by alkali-silica reactions, the formation of pores in mPBGMs was considered to be the result of the combined action of foaming, decomposition and dehydration of sodium silicate hydrate, sodium carbonate hydrate and calcium silicate hydrate produced during alkali activation.

The solidification processes of two compositions, hypereutectic (21.0 mol% Y2O3–79.0 mol% Al2O3) and eutectic (18.5 mol% Y2O3–81.5 mol% Al2O3), were used via the horizontal directional solidification (HDS) method to produce two ingots with dimensions of 317 × 220 × 35 mm and 210 × 180 × 35 mm, respectively. The first ingot was heterogeneous and characterized by a two-layer structure with an expressed horizontal boundary, which is parallel to the solidification direction (an experimental fact observed for the first time), separating eutectic-type ceramics in the upper layer from the lower one containing the YAG dendrites. Considering the heat transfer feature characteristic of the HDS method and its action during the solidification of materials scattering thermal radiation, an explanation of the occurrence of such structure has been proposed. On this basis, the solidification parameters of the second ingot, providing its homogeneous structure, were selected. Characterization of the crystallographic texture and microstructure of both ingots revealed the advantage of the second solidification processing conditions.

Five types of glass microspheres with alumina and 40–80 mol.

The impact of grinding on particle size, thermal behaviour, and sintering ability of yttrium aluminate glass microspheres with eutectic composition (76.8 mol % Al2O3 and 23.2 mol % Y2O3) was studied. The work was conducted with the aim of determining the optimal particle size and grinding conditions of glassy powder used for hot-pressing of ceramic and glass-ceramic materials with desired mechanical properties. The flame synthesis was used for the preparation of glass microspheres (diameter ∼ 40 μm). Ball milling procedure under different conditions was applied to adjust of size of prepared microbodies. The milled powders were subsequently hot pressed. The prepared samples (raw, milled microspheres and hot-press sintered bodies were characterised by X-ray powder diffraction, and scanning electron microscopy. Thermal analysis and particle size analysis in combination with X-ray powder diffraction and high temperature X-ray diffraction was used for detailed inspection of thermal behaviour and phase changes in raw and milled systems in the temperature interval 25-1200 °C. The samples after flame synthesis and after milling were found to be X-ray amorphous. The particle size measurements showed that the systems with a smaller average size D [0.9] ∼ 25 μm and a monomodal particle size distribution were prepared after 6h of milling. Thermal analysis in combination with X-ray and high temperature X-ray analysis indicated a difference in the crystallization mechanism of the yttrium aluminate garnet phase depending on the milling time. The bulk glass ceramic with fine lamellar eutectic microstructure and interesting mechanical properties (Vickers hardness HV=17.6 ± 0.2 GPa, indentation fracture toughness KIC = 4.3 ± 0.3 MPa.m1/2) resulted from the sintering of microspheres milled for 6h under the "gentlest" conditions (milling speed - 200 rpm, and milling balls size - 5 mm in diameter).

This study investigated the impact of La2Zr2O7 (LZ) and different types of glass on the performance of polymer-derived ceramic (PDC) coatings on AISI 441 stainless steel substrates. Four double-layer PDC-based glass-ceramic coatings containing LZ and different glass fillers were prepared by dip coating. The LZ powder was synthesised by solid-state reaction (SSR): powder morphology, crystal structure, and thermal stability were analysed. X-ray diffraction (XRD) detected a LZ pyrochlore phase after annealing at 1300 and 1400 °C with a trace of t-ZrO2. Four different glass compositions, namely BaO-Al2O3-SiO2 (BAS), BaO-Al2O3-La2O3-B2O3-SiO2 (BALBS), CaO-B2O3-SiO2 (CBS), and BaO-ZnO-MgO-B2O3-SiO2 (BZMBS), were also synthesised as fillers for PDC coatings. The glass transition and crystallisation temperatures of the glasses were determined using differential scanning calorimetry (DSC). The coating systems, consisting of a Durazane 2250 bond coat and a top coat (Durazane 1800 + LZ filler + different glass sealants), were prepared. After pyrolysis of the coatings at 900 °C, some of the glasses partially crystallised. Scanning electron microscopy (SEM) revealed that the layers containing BAS, BALBS and CBS glass were dense, with good adhesion to the substrate, and with occasional presence of larger pores and cracks. Delamination of the upper layer was observed in the coating with the BZMBS glass filler.

The presence of residual carbon in powder precursors prepared using the sol -gel method can pose significant challenges in producing ceramics and glasses of high quality. In the case of glass, carbon dioxide formation during the glass-melt heating process leads to bubble/pore formation, while in the case of ceramics, residual carbon can significantly impair its optical properties. The present study aims to identify the reasons for the persistence of residual carbon in YAG and YAG + Al2O3 (YAGA) precursor powders prepared by the sol -gel Pechini method, even under high-temperature conditions exceeding 1400 degrees C. The study seeks to provide insights to aid in the development of strategies that mitigate the impact of residual carbon on the quality of ceramics and glasses produced using sol -gel techniques. It was found that even after the annealing of the precursor at a temperature of 1200 degrees C for two hours, a small amount of carbon remains in the precursor powder. The X-ray diffraction (XRD) analysis of the YAGA precursor powders showed that the crystallisation of alumina was delayed and began at 1200 degrees C. The amount of alpha-alumina, which corresponds to its actual addition, was identified at a temperature of 1500 degrees C. Additionally, as the alumina crystallises, the carbon is released from the precursor which is the reason for microspheres blowing in the flame, even when the precursor was burnt out at a temperature of 1400 degrees C.

The paper deals with the study of the features of the process of YAG phase formation via the Solid-State Reaction (SSR) method according to the proposed multi-stage scheme, including three stages of various mechanical and thermal processing (pre-milling in a ball mill for 24, 48 and 72 h, as well as firing at 1150 °C, 1250 °C, and 1450 °C with intermediate grinding step). The commercial micrometer-sized Y 2 O 3 and Al 2 O 3 powders were used as starting materials. The phase transformation was monitored by the X-ray diffraction in each synthesis stage. The microstructure and elemental distribution of samples were studied by scanning electron microscopy and energy-dispersive X-ray spectrometry. During the work, we found the dual effects of partially reacted mixture grinding, which can accelerate or slow down the synthesis rate depending on the YAG content in the preceding stage. We have proposed a simple model including the concept of “critical YAG concentration”. When the lower limit of this parameter (over 60 %) is reached, grinding has a negative effect on the further course of the SSR. Carrying out the synthesis according to a three-stage scheme makes it possible to obtain a product with a YAG content above 90 %, regardless of the pre-milling time, and the use of a two-stage synthesis scheme provides a monophasic raw material (99 % of YAG) suitable for further single crystals growth. The increased efficiency of the multi-stage YAG synthesis scheme was demonstrated in comparison with the conventional one-stage obtaining process that yielded only up to 60% of the target phase in the temperature range up to 1500 °C.

Alumina-yttrium aluminum garnet (YAG)-zirconia composites are often produced by the melt solidification method. In the present study, we investigated the fabrication of α-Al2O3/Y3Al5O12 (YAG)/ZrO2 composite by Spark Plasma Sintering (SPS) of powders synthesized by Pechini’s sol-gel method. The ternary composites with homogenous microstructure and high density were produced by SPS at 1300°C for 15min. The addition of ZrO2 promoted the sintering of composites, resulting in a higher density and, in turn, higher hardness. A change in the indentation fracture behavior as the result of ZrO2 addition was observed.

In this work, La2Ce2O7/40 wt% YSZ (LC40Z) mixed powders were used to fabricate composite bulk ceramics with their potential use as a material for high-performance thermal barrier coatings (TBCs). For this purpose, the effect of sintering temperature on the chemical reactivity of LC and YSZ was investigated via hot-pressing at the temperatures of 1300, 1400 and 1500 & DEG;C. X-ray diffraction analysis (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) were utilized to characterize the phase and microstructure evolution in both LC40Z powder mixtures and composite bulk ceramics. Results showed that solid-solution reactions occurred between the YSZ and LC during hot-pressing of the LC40Z powder mixtures, indicated by a new phase of La2Ce0.2Zr1.8O7 (LCZ) observed in the XRD patterns. The detailed analysis of Raman spectra confirmed the gradual transition from fluorite LC to pyrochlore LCZ structure, which was demonstrated by the appearance of characteristic pyrochlore bands. All composites densified by hot-pressing exhibited a high relative density above 95%. The average grain size of the LC40Z composites increased significantly with increasing sintering temperature, while gradual pore-healing was observed. The associated mechanical properties of LC40Z ceramics were also reported. The Vickers hardness values increased with increasing sintering temperature, which is consistent with the microstructure evolution and relative density variations. The highest hardness, with a value of 10.99 & PLUSMN; 0.23 GPa, was achieved for the composite hot-pressed at 1500 & DEG;C. The fracture toughness results showed the same dependence on sintering temperature. The fracture toughness increased from 1.97 & PLUSMN; 0.15 to 2.4 & PLUSMN; 0.14 MPa m1/2, indicating that the mechanical properties of the LC40Z composites can be tailored by changing the sintering temperature during hot-pressing.& COPY; 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The Bi and Ni-doped gehlenite glasses were prepared by flame synthesis. The concentration of Bi and Ni was 0.0, 0.5 and 3.0 mol. %. Scanning electron microscopy (SEM) confirmed that spherical particles which did not contain any formations indicating the presence of crystalline phases were prepared by the flame synthesis. The amorphous nature of the prepared systems was also confirmed by the results of X-ray diffraction analysis. Both the Ni and Bi-doped gehlenite glass microspheres exhibited complex magnetic properties.

Five compositions in the system Al2O3-Y2O3 with high level of homogeneity were prepared in the form of glass microspheres by flame synthesis. The amorphous nature of prepared glasses with highly disordered structure was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman and nuclear magnetic resonance (NMR) spectroscopy. In the NMR spectra, typical signals with chemical shifts of 75, 42 and 12 ppm were observed, which were attributed to the presence of AlO4, AlO5 and AlO6 motifs in the glass structure. The ratio of individual motifs in glass samples did not change significantly with the composition. The crystallization of yttrium-aluminium garnet (YAG) phase was observed as a major process in the glasses thermally treated up to 1450 degrees C, with slow crystallization of 0- and a-Al2O3 phases detected in the temperature interval 980-1450 degrees C. IR and Raman spectra of the microspheres crystallized at 998, 1300 and 1500 degrees C for 4 h contained typical bands, that were assigned to the vibrations of AlO4 and AlO6 groups in YAG and Al2O3 structures. The comparison of 27Al and 89Y magic angle spinning (MAS) NMR spectra showed the presence of only YAG and a-Al2O3 phase in the samples crystallized at 1500 degrees C and the presence of a trace amount of 0-Al2O3 in the sample crystallized at 998 and 1300 degrees C. The yttrium aluminium perovskite (YAP) and yttrium aluminium monoclinic (YAM) phases, expected in this system, were no detected. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC

The ytterbium-aluminate microspheres with yterbium-aluminium garnet composition doped by 0.25, 0.5, 0.75, 1.0, 3.0 and 5.0 mol.% of Er2O3 were prepared by combination of sol-gel method and flame synthesis. The prepared systems were mostly X-ray amorphous with the presence of traces of ytterbium-aluminium garnet phase (YbAG), and ytterbium oxide. The thermal analysis of prepared systems shows crystallization of the prepared systems in the temperature interval 914-984 degrees C in one or two steps, depending on the Er content. Ytterbium aluminate garnet was found to crystallize as the prevailing phase in all heat-treated samples. An almost pure red up-conversion photoluminescence emission with the intensity influenced by the Er2O3 content was observed in prepared systems.

Bi doped 2CaO-Al2O3-SiO2 (gehlenite) glasses were prepared by conventional melting. The concentration of Bi3+ was 0, 0.25, 0.50 and 1.50 mol. %. The prepared samples were X-ray amorphous except of the undoped sample and the sample with the highest content of Bi3+, for which XRD records revealed traces of crystalline gehlenite. Differential thermal analysis (DTA) was used to study the thermal properties of prepared glasses, performed in the atmosphere of nitrogen at 5 different heating rates. The DTA records of all studied samples contained only one exothermic effect. Based on the results of XRD analysis, the exothermic effect was attributed to the crystallization of gehlenite. The XRD patterns of all samples measured after DTA analysis contained gehlenite as the main crystalline phase (01–074-164 COD). The DTA records measured at a heating rate of 10 °C.min−1 revealed a significant decrease in the temperatures of maxima of the exothermic peaks (from 982 °C to 943 °C) with the increasing Bi doping. The model approach using the Johnson–Mehl–Avrami-Kolgomorov (JMAK) equations with six different values (1.5, 2, 2.5, 3, 3.5 and 4) of Avrami parameters (m) was used to study crystallization kinetics of gehlenite glasses. The model that best describes the experimental data was found, using the AIC (Akaike criterium) and wAIC (Akaike weight) criteria: A (frequency factor) and Eapp (apparent activation energy) were determined. Based on kinetic parameters values, it is concluded that the nucleation rate is constant. Irrespective of the Bi content, the movement of the growth zone is controlled by diffusion and 3D growth is characteristic for the gehlenite crystals growth.