La2O3 Content Research Articles

Effects of CaF2 and La2O3 on the phase structure of rare earth in CaO–SiO2–La2O3–CaF2 slags

The rare earth in the rare earth slag can be separated and enriched by heating and melting the rare earth slag and then slowly cooling crystallisation. In this process, it is of great significance to study the effect of chemical composition on the crystallisation of rare earth phase in slag and the effect of slag viscosity on crystal growth. The rare earth slag melt samples were prepared according to the main chemical composition of rare earth slag by using an analytical pure reagent. The effects of CaF2 and La2O3 contents on the phase structure and morphology of rare earth phase in CaO–SiO2–La2O3–CaF2 slags were studied by SEM-EDS and XRD. The relationship between the viscosity of the slag and the crystal growth behaviour was studied by measuring the melt viscosity with the cylinder rotation method. The results show that the rare earth in CaO–SiO2–La2O3–CaF2 slags exists in the form of CaLa4(SiO4)3O. The change of CaF2 and La2O3 content has no effect on the structure of rare earth phase, but the size of rare earth crystal phase changes obviously. With the increase of CaF2 and La2O3 content, the size of rare earth crystal phase increases gradually. CaF2 and La2O3 can reduce the viscosity transition temperature of slag melt and increase the crystallisation temperature range of rare earth phase to promote crystal growth.

Effect of lanthanum oxide on microstructure and mechanical properties of ZK60 magnesium alloy

Different amounts of La2O3 were added to ZK60 alloy to observe the changes in microstructure and mechanical properties of ZK60-XLa2O3 (X = 0, 0.2 wt%, 0.5 wt%) composites. Our findings reveal that within the as-cast ZK60 alloy, the Mg-Zn binary phase is manifested as rod-shaped precipitates, exhibiting a dispersed distribution predominantly along the grain boundary regions. With the increase of La2O3 addition, the rod-like Mg-Zn binary phases are gradually replaced by Mg-Zn-La ternary phases, and these Mg-Zn-La ternary phases are semi-continuously distributed around the grain boundaries. Both ZK602 and ZK605 alloys result in a corresponding improvement in ductility after extrusion. It is noteworthy that the ductility of the as-extruded ZK605 alloy is increased by 59.4% compared to ZK60 at the expense of a reduction of only 3.9% in yield strength. Taken together, the significant increase in ductility of ZK605 is mainly due to the weakening of the basal texture, which is weakened by the redox reaction of La2O3 with the α-Mg matrix, generating the La element. The decrease in yield strength of ZK605 in the extruded state is closely related to the observed grain coarsening phenomenon and the basal texture weakening. At the same time, the ultimate tensile strength of ZK605 shows a slight increase, which is mainly due to the second phase strengthening. The Mg-Zn-La ternary phase exhibits a notably hard character, and it is evident that the distribution of this phase becomes progressively denser as the La2O3 content increases.

Influence of La3+ ions on the structural, elastic, optical, and radiation shielding properties of Cr2O3-Doped heavy metal glasses

This study investigates the effect of La³⁺ rare earth ions on the structural, elastic, optical, and radiation shielding features of heavy metal borate glass (B₂O₃-PbO) doped with Cr₂O₃. Density measurements and FT-IR spectra analysis revealed the role of La3+ ions as a network modifier, where successive additions of La2O3 content led to a gradual increase in the density and an increase in the non-bridging oxygen content resulting from the structural transformation between the BO4 and BO3 units. The significant improvement in the elastic modulus and microhardness factor moduli was confirmed by calculating the change in ultrasonic velocities through the glassy system. The structural modifications induced by La³⁺ ions narrowed the band gap and increased the Urbach energy, indicating higher disorder within the glass network. The linear refractive indices increased due to increased optical basicity and electronic polarization. Optical absorption results showed that Cr⁶⁺/Cr³⁺ ions occupy octahedral/tetrahedral sites, with the tendency for Cr³⁺ cations to occupy more octahedral sites with increasing La₂O₃ content. The produced samples showed a greenish-yellow color caused by the absorption band centered at ∼415 nm associated with the electronic transition ⁴A₂g(F)→2Eg(G). The ligand field effect highlighted the significance of La³⁺ cations in increasing the crystalline field intensity surrounding Cr³⁺ cations and reducing the nephelauxetic ratio, signifying enhanced covalent character between Cr³⁺ cations and neighboring ions. Moreover, the radiation shielding capabilities of the glassy system were analyzed and compared with standard shielding materials, confirming superior shielding performance in samples with the highest La₂O₃ content.

Influence of added La2O3 on the microstructure, mechanical properties, and tribocorrosion resistance of TiB2–Ni plasma-sprayed coatings

To enhance the tribocorrosion resistance of 7075-T6 aluminum alloy in deep sea environments, TiB2–Ni coatings with varying La2O3 content were deposited on 7075-T6 aluminum alloy substrates using plasma spray technology. The effects of different La2O3 contents on the organization, structure, and properties of the coatings were analyzed. The results indicated that La2O3 incorporation suppressed brittle phase formation such as Ni3B; 1.0 wt% La2O3 addition reduced Ni3B by 16.9%. The coating's corrosion resistance significantly improved with La2O3 doping - the self-corrosion current density of the 1.0 wt% La2O3-doped coating decreased from 71.2 nA/cm2 to 30.2 nA/cm2.

Ga2O3/La2O3-γAl2O3 catalysts for CO2-assisted propane oxidative dehydrogenation to propylene

Novel Ga2O3/La2O3-γAl2O3 was investigated for ODH of propane to propylene using CO2 as a mild oxidant in a batch scale fluidized CREC Riser Simulator. La2O3 in the catalysts provided a control of both the reducibility and acidity, as shown by H2-TPR and NH3-TPD, respectively. The propane conversion and products selectivity were strong function of La2O3 content in the Ga2O3/La2O3-γAl2O3 catalysts. With increasing La2O3 content in the catalyst, propane conversion dropped slightly but the propylene selectivity and yields increased. It was proposed that the presence of La2O3 reduced the non-selective sites and the acidity of the catalysts, that contributed towards deep oxidation of propane and propylene. The improved activity and selectivity with CO2 addition implied that the as-synthesized catalyst possesses CO2 activation capability required for ODH reactions. Among the investigated catalysts, Ga2O3/La2O3-γAl2O3(1:1) exhibited the highest propane conversion (92 %) and propylene yield (56 %) at 600 ℃ in the presence of CO2.

Effect of lanthanum oxide on the radiation-shielding, dielectric, and physical properties of lithium zinc phosphate glasses

This study looked at the shielding properties, physical properties, and dielectric spectroscopy of various lanthanum oxide concentrations based on (65-x) P2O5-15 Li2O–15ZnO– 5Bi2O3- xLa2O3 with x = 0.0, 1.0, 2.0, 3.0, and 4.0 mol% glasses. When La2O3 is added, the molar volume quantities fall but the density values increase. The sample with the designation La-4.0 (4.0 mol% La2O3 content) had the highest density observed, 3.2182 g/cm3. Monte Carlo simulations and the Phy-x/PSD software were used to determine the critical gamma radiation attenuation characteristics, particularly linear attenuation coefficients and mass attenuation coefficients of glass samples under investigation. The half-value layer, mean free path, effective atomic number and effective electron density were then examined across a wide energy range (0.015–15 MeV). The findings of the investigation showed that the addition of La2O3 decreased the half-value layer and mean free path while increasing the mass attenuation coefficient, effective atomic number, and effective electron density. The results indicate that the inclusion of La2O3 appears to improve that glass system's ability to deflect gamma and neutron radiation. Over a broad frequency range, the dielectric properties were measured. The dielectric constant (ε′), which is typically steadily decreased with the addition of lanthanum, indicates an increase in the degree of electrical stiffness inside the glass network. Among the samples examined, the glass sample La-4.0 is thought to possess the best properties for electronic packaging due to its maximum propagation speed and lowest dielectric constant.

La3+-adjusted optical and ligand field parameters in low CoO impurities Na2O–ZnO borate glass matrix

The effect of La2O3 on the ligand field and optical properties of the current glass system was investigated. In detail, the absorption band at (493–499 nm) is ascribed to 4T1g (F) → 2T1g (H) transition of Co2+ in octahedral symmetry. The absorption band at (574–580 nm) is ascribed to 4A2 (4F)→4T1(4P) transitions of Co2+ in tetrahedral symmetry. On the other hand, the electronic transition at (639–644 nm) is attributed to 5T2g→ 5Eg transition of Co3+ in octahedral symmetry. Moreover, the redshift of the absorption edges reduces the optical bandgaps from 3.42 eV to 3.24 eV. Additionally, the La2O3-free glass sample exhibited a transition at ∼230 nm in the UVC region. However, this glass sample showed an displayed transparency in the UVA and UVB regions. Furthermore, the redshift of the absorption edges resulted in the glass sample with the highest La2O3 content (i.e., 8 mol%) becoming UVA transparent while blocking UVC and UVB regions. The obtained data regarding the ligand field parameters indicate an increase in the ligand field splitting (10Dq), reflecting the increased interplay strength between Co2+ in tetrahedral symmetry and its ligands. Also, the values of the nonlinear refractive index and nonlinear optical parameters increased due to the enhancement of basicity within the glass network. These findings suggest that the glass with the greatest concentration has the potential to be utilized as an optical filter that allows UVA while blocking UVC and UVB electromagnetic waves.

Impact of La2O3 incorporation on the structural, physical, mechanical properties and radiation shielding performance of basalt glasses

This study investigates the influence of La2O3 addition on the structural, physical, and radiation shielding properties of basalt-based glasses. Incorporating varying concentrations of La2O3 (0, 10, 20, 30 wt%) into basalt glasses, we aimed to evaluate the potential of La2O3 in enhancing the material's effectiveness against gamma radiation. Utilizing Ba-133 point radioactive source and Ultra Ge detector, we measured the attenuation parameters in different photon energies (81, 160, 223, 276, 302, 356, and 383 keV). The glasses exhibited an amorphous structure, as confirmed by XRD analysis, with density values ranging from 2.72 to 3.305 g/cm³, increasing with La2O3 content. The microstructural analysis indicated that La3+ ions predominantly integrate into the glass matrix, enhancing the structural integrity without forming separate phase regions. Our findings demonstrate a significant improvement in radiation protection parameters, including mass attenuation coefficients and half-value layers, with higher La2O3 concentrations. These outcomes were also supported by the data obtained for Zeff and EBF values of G1-G4 glasses. The mechanical properties of the glasses were also investigated with the Makishima-Mackenzie model and it was observed that the elastic moduli were also affected by the addition of La2O3. The enhancements observed with La2O3 additions suggest promising avenues for developing advanced shielding materials, combining the inherent advantages of basalt glasses with the high atomic weight and electron density of lanthanum compounds.

Effect of La2O3 on hardness, wear resistance and corrosion resistance of WC/Fe90 iron-based composite coatings

In this paper, WC/Fe90 iron-based composite coatings were prepared using plasma spraying technology. The influence of rare earth oxide La2O3 on the microstructure and properties of the composite coatings was studied through microstructural characterization, phase identification, microhardness, wear resistance, and corrosion resistance. The results showed that the composite coatings were mainly composed of α-Fe, M7C3, Fe-Cr, FexCy, and other reinforcing phases. The addition of La2O3 promoted the decomposition of WC particles and improved the uniformity of the coatings. When the La2O3 content reached 1.0 wt%, the hardness was the highest, reaching 885.481 HV, which was 10% higher than that of the untreated coatings. The addition of La2O3 increased the friction coefficient but still improved the wear resistance. Compared to the coatings without La2O3, the mass loss due to wear was reduced by approximately 40%. Moreover, the addition of La2O3 formed a passive film on the surface of the coatings, effectively preventing the penetration of Cl- ions and refining the grain structure of the coatings, significantly enhancing the corrosion resistance. When the La2O3 content was 1.0 wt%, the corrosion resistance of the coatings was the best.

Mössbauer, optical and structural properties of [formula omitted] ion in borate glass

Lanthanum-bearing iron lithium borate glass is a quaternary system for oxide glasses and was prepared via the melt-quenching method. The present article correlates the structure, optical, ligand field and Mössbauer data on iron lithium borate glass containing La3+. The density was measured, while the molar volume was calculated. Other physical parameters are well-described. With increasing the La2O3 content within the glass network, infrared spectra analysis reveals structural modifications such as the increase in BO4 units and the decline in both BO3 units and NBO bonds content. Furthermore, optical absorption spectra were measured. The absorption spectra disclose a plethora of electronic transitions that are related to Fe3+ in tetrahedral and octahedral sites, however, Fe2+ phase is not observed in optical spectra, but it has a clear signature in Mössbauer spectra. Besides, the glass absorption edges undergo a clear blue shift, reflecting an increased band gap energy (1.96–2.28 eV). The decline in NBO bonds justifies this trend. Bewitchingly, the values of crystal field splitting are increased, while the values of Racah parameters are decreased. This trend is justified by the decline in NBO bonds and increases electron localization around Fe cations. Mössbauer spectra confirm the existence of Fe3+ in tetrahedral and octahedral sites, while Fe2+ exists in only a tetrahedral state. With increasing La2O3 content, the isomer shift of Fe3+ in tetrahedral sites changes to be 0.312–0.329 mm/s, while the isomer shift of octahedral Fe3+ is 0.424–0.456 mm/s. These findings coincide with optical data. While the isomer shift of tetrahedral Fe2+ is 0.902–0.911 mm/s. Our results of structural, optical and ligand field associated with Mössbauer spectra open more vistas toward the utility of these samples in the optics realm.

Effect of La2O3 adding on Properties of SiC Porous Ceramic Support

In this paper, 80-90 grains of SiC as the main raw material, doped La2O3 into the binder composed of potassium feldspar, kaolinite and quartz, and then graphite and activated carbon as pore-making agents to prepare silicon carbide porous ceramic carrier. The effects of doped La2O3 content on the bending strength, porosity and filtration pressure drop of porous SiC ceramics were studied. The results show that the formation of mullite phase and the bending strength of SiC porous ceramics can be improved by adding proper amount of La2O3. Under the sintering temperature of 1300°C for 90 minutes, when the content of La2O3 in the binder is 2.5wt%, the comprehensive performance is the best, the porosity is 21.5%, the bending strength is 53.5MPa, and the filtration pressure drop is low.

Microstructure, Mechanical Properties, and Corrosion Resistance of Ag-Cu Alloys with La2O3 Fabricated by Selective Laser Melting.

Ag and its alloys, when prepared by a selective laser melting (SLM) process, have a low density and poor overall performance due to their high reflectivity when the most commonly used laser (λ = 1060 nm) is used, and they have exorbitant thermal conductivity. These characteristics lead to the insufficient melting of the powders and severely limit the applications of additive manufactured silver alloys. To improve the absorption of the laser, as well as for better mechanical properties and higher resistance to sulfidation, Ag-Cu alloys with different La2O3 contents were prepared in this work using the SLM process, via the mechanical mixing of La2O3 nanoparticles with Ag-Cu alloy powders. A series of analyses and tests were conducted to study the effects of La2O3 in Ag-Cu alloys on their density, microstructure, mechanical properties, and corrosion resistance. The results revealed that the addition of La2O3 particles to Ag-Cu alloy powders improved the laser absorptivity and reduced defects during the SLM process, leading to a significant rise from 7.76 g/cm3 to 9.16 g/cm3 in the density of the Ag-Cu alloys. The phase composition of the Ag-Cu alloys prepared by SLM was Silver-3C. La2O3 addition had no influence on the phase composition, but refined the grains of the Ag-Cu alloys by inhibiting the growth of columnar grains during the SLM process. No remarkable preferred orientation existed in all the samples prepared with or without La2O3. An upwards trend was achieved in the hardness of the Ag-Cu alloy by increasing the contents of La2O3 from 0 to 1.2%, and the average hardness was enhanced significantly, from 0.97 GPa to 2.88 GPa when the alloy contained 1.2% La2O3 due to the reduced pore defects and the refined grains resulting from the effects of the La2O3. EIS and PD tests of the samples in 1% Na2S solution proved that La2O3 addition improved the corrosion resistance of the Ag-Cu alloys practically and efficaciously. The samples containing La2O3 exhibited higher impedance values and lower corrosion current densities.

Preparation and characterization of MgO-Al2O3-SiO2 glass-ceramics with different MgO/Al2O3 ratio and La2O3 addition

MgO-Al2O3-SiO2 (MAS) glass-ceramics were prepared by traditional melting and sintering method, and the effects of MgO/Al2O3 ratios and La2O3 contents on the microstructure and physicochemical properties of MAS glass-ceramics were studied. Herein, differential scanning calorimetry (DSC), X-ray diffraction (XRD), fourier-transform infrared spectrophotometer (FTIR), Field-emission scanning electron microscopy (FESEM), density, corrosion resistance, dielectric properties and thermal expansion coefficient (CTE) were carried out to evaluate the properties of both parent glass and glass-ceramics samples. The results show that adjusting the MgO/Al2O3 ratio from 0.69 to 0.47 can increase the characteristic temperatures of transition temperature (Tg) and crystallization peak temperature (Tp) in MAS parent glass. The reduction of MgO/Al2O3 ratio could promotes the precipitation of α-cordierite phase (Mg2Al4Si5O18), and the grain size of α-cordierite phase were increased from 200 to 500 nm. When the MgO/Al2O3 ratio was 0.63, the MA-2 sample has the highest flexural strength of 127.46 MPa. Furthermore, we also investigated the influence of La2O3 addition on the structure and properties of MAS glass-ceramics by employed MA-2 sample as a reference. The results show both the Tg (742–748 °C) and Tp (936–943 °C) of parent glass exhibit a slightly increasing with the La2O3 content was increased from 0.0 to 2.0 wt%. The La2O3 addition show a negligible influence on the crystal phase and morphology of MAS glass-ceramics. With increasing of the La2O3 content, the MAS glass-ceramics samples have a larger density (2.58–2.76 g/cm3) and a better chemical stability, and the CTE (6.12–8.17 × 10−6/°C), εr (5.04–6.17), and the flexural strength (127.46–150.15 MPa) also show an increased change trends. The prepared MAS glass-ceramics can be packaged with high expansion coefficient chips (such as GaAs) and is expected to become a potential candidate of dielectric materials for electronic devices, especially for high frequency applications in integrated circuits.

Influence of the La2O3 addition on the structure and optical features of La2O3–NiO–BaO–B2O3 glass

The influence of the La2O3 addition on the microstructure, linear and nonlinear optical parameters of nickel borate glass was carefully investigated for the La2O3–NiO–BaO–B2O3 system. The La2O3 content of the present glass was varied from 0.0 to 10.0 mol%, while the glass modifiers of BaO and glass intermediate of NiO were fixed at 19 and 1.5 mol%, respectively. Based on the structural investigations, the bond density remarkably increased from 7.37 × 1019m−3 to 8.66 × 1019m−3 by a ratio of 18 % with increasing La2O3/B2O3 ratios. Additionally, the presence of Ni2+ ions as NiO6 units was confirmed by the brown shade originating from the absorption band observed at 427 nm in the optical absorbance of the studied glass. Furthermore, the Ni3+ ions do not play a role in the coloring of the glass. Moreover, the fundamental absorption edges of the glass shift towards lower energy values with increasing La2O3 concentrations, confirming the decreased behavior of the band gaps. Moreover, the linear and nonlinear refractive indices increase with increasing of La2O3 concentrations. Additionally, the ligand field characteristics of Ni cations, such as the ligand field splitting parameter and Racah parameter, exhibit opposite behaviors upon introducing additional La2O3 content. A decrease in values of the ligand field splitting, while the Racah parameters exhibit increased values. The observed outcomes demonstrate a tendency of the bonds connecting the Ni ions and their ligands to possess higher degrees of ionic nature. Based on the results, the present glass samples can function as solar thermal collectors by collecting sunlight and utilizing it for direct heating and indirect electrical power generation.

STRUCTURE, OPTICAL PROPERTIES AND PHOTOCATALYTIC ACTIVIYY OF UNDOPED, La2O3-DOPED ZnO NANOCOMPOSITES

La-doped ZnO nanocomposites with di­ffe­rent content of La2O3 (1–5%) were obtained by the Pechini method from their nitrate solutions. The solutions of Zn2+ and La3+ nitrates were preliminary obtained by dissolving of zinc and lanthanum oxides with a content of the main component of 99.99% in nitric acid. The influence of lanthanum doping the on the microstructure, morphology, optical pro­perties and photocatalytic activity of the ZnO nanopowders were examined. The properties of the nanopowders were studied by using X-ray phase analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy. The samples were subjected to X-ray powder diffraction using a DRON-3 diffractometer (Cu-K radiation) at room temperature. The scan angle was 0.05–0.1 ° in the range 2 = 15–90 °. X-ray phase ana­lysis confirms the formation of single phase of La2O3-doped ZnO powders on diffractograms. Raman light scattering and photoluminescence spectra were recorded using a Horiba Jobin‑Yvon T64000 spectrometer equipped with a CCD detector at room temperature in the inverse scattering geometry. According to SEM results, the powders characterized a conglomerate structure. The undoped ZnO has an average particle size of 43 nm, while the average particle size of La3+-doped ZnO ranges from 64 to 80 nm. It was established that the morphology of powder particles primarily depends on the content of La3+ in the material. An increase in the amount of La3+ in zinc oxide leads to an increase in the specific surface area (from 3.8 to 11.8 m2/g). In the photoluminescence spectra of ZnO powders, with increasing La2O3 concentration, bands at 400 nm are observed due to the appearance of impurities that cause of interstitial zinc and zinc vacancy defects and their broade­ning with a shift to the long-wave region. Photocatalytic properties of ZnO pow­ders doped with lanthanum oxide were in­vestigated using Methyl Orange as a model dye under Osram Ultra-Vitalux lamp (300 W) irradiation. A present result indicates that the obtained powders are potential candidate for the practical application in photocatalysis.

Utilization of investment casting shell waste in the production of cordierite-mullite-zircon composites for radiation shielding: The influence of La2O3 additive

Cordierite-mullite-zircon ceramic composites were produced via reaction sintering of investment casting shell waste, Al2O3, and MgO at 1350 °C. The influence of La2O3 addition on the crystalline phase composition, microstructure, densification behavior, mechanical strength, and radiation shielding capabilities of the cordierite-mullite-zircon composites has been investigated. The X-ray diffraction (XRD) analysis confirmed the successful synthesis of cordierite-mullite-zircon composites with up to 5 wt% La2O3 additive content. However, a higher La2O3 content, exceeding 7 wt% resulted in cordierite decomposition. Furthermore, the addition of La2O3 significantly enhanced the densification behavior and microstructural development, leading to improved flexural strength and enhanced shielding against fast neutron and gamma radiation. This research suggests the potential of the fabricated ceramic composites derived from investment casting shell waste for applications in radiation shielding.

Study on the Effect of Rare Earth Oxide Addition on the Microstructure and Properties of Ni60/WC-Ni Coatings Prepared by Laser Cladding

Rare earth oxides have been proven for their ability to refine grains and have high melting points. In this paper, different contents of rare earth oxide La2O3 were added into the Ni60/WC-Ni composite coating, in order to study its effect on the coating properties. SEM observation confirmed that the grain was refined significantly after the addition of La2O3. Energy Dispersive Spectroscopy (EDS) was applied to investigate the composition and X-Ray Diffraction (XRD) was used to measure the residual stress in the coating samples. In addition, the microhardness and wear resistance of the samples were tested. The results showed that the dilution ratio of coatings with different additions of La2O3 was in the range of 2.4 to 9.8%, and the sample with 1.0% addition of La2O3 exhibited the highest hardness of 66.1 HRC and best wear resistance with a wear volume of 9.87 × 106 μm3, and the residual stress increased from 159.4 MPa to 291.0 MPa. This implies that the performance of the coating has been obviously improved after the addition of La2O3.

Composition and Electronic Structure of La2O3/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content.

La2O3 nanoparticles stabilized on carbon nanoflake (CNF) matrix were synthesized and graphitized to produce core-shell structures La2O3/CNFs@C. Further oxidation of these structures by nitric acid vapors for 1, 3 or 6 h was performed, and surface-oxidized particles La2O3/CNFs@C_x (x = 1, 3, 6) were produced. Bulk and surface compositions of La2O3/CNFs@C and La2O3/CNFs@C_x were investigated by thermogravimetric analysis and X-ray photoelectron spectroscopy. With increasing the duration of oxidation, the oxygen and La2O3 content in the La2O3/CNFs@C_x samples increased. The electronic structures of samples were assessed by electron paramagnetic resonance. Two paramagnetic centers were associated with unpaired localized and mobile electrons and were registered in all samples. The correlation between bulk and surface compositions of the samples and their electronic structures was investigated for the first time. The impact of the ratio between sp2- and sp3-hybridized C atoms, the number and nature of oxygen-containing groups on the surface and the presence and proportion of coordinated La atoms on the EPR spectra was demonstrated.

High-temperature oxidation of ZrB<sub>2</sub>–SiC–La<sub>2</sub>O<sub>3</sub> ceramic material produced via spark plasma sintering

The study investigated the influence of La2O3 addition on the oxidation properties of composite ceramics with a composition of 80 vol. % ZrB2 and 20 vol. % SiC. The source materials utilized in this study included zirconium diboride (DPTP Vega LLC., Russia), grade 63C silicon carbide (Volzhsky Abrasive Works JSC, Russia), and lanthanum hydroxide concentrate (Solikamsk Magnesium Plant JSC, Russia), with the following elemental content (wt. %): La – 54.2, Nd – 4.3, Pr – 2.8, and trace amounts of other elements (<0.1). The La2O3 content in the charge varied between 0, 2 and 5 vol. %. The powders were mixed in a planetary mill with ethyl alcohol as the medium for 2 h, using a grinding media to powder ratio of 3:1. Consolidation of the powders was achieved through spark plasma sintering at 1700 °С, applying a pressing pressure of 30 MPa. The heating rate was 50 °С/min, and the isothermal holding time was 5 min. Oxidation was carried out in air at 1200 °С and the total oxidation time was 20 h. Oxidation experiments were conducted in air at 1200 °С, with a total oxidation time of 20 h. It was observed that the most significant weight gain occurred within the first 2–4 h of testing. Specimens containing 5 vol. % La2O3 exhibited the smallest weight gain after 20 h of exposure. Regardless of the presence of La2O3 , silicon carbide was found to be the first material to undergo oxidation. In specimens without La2O3 addition, the oxidized layer mainly consisted of silicon monoxide and dioxide. In contrast, specimens with La2O3 exhibited a predominantly oxidized layer composed of ZrSiO4 and ZrO2 . The study revealed that the introduction of La2O3 intensified the formation of zircon, which subsequently slowed down the oxidation processes in the material.

Improving the green mechanical strength and thermal shock resistance of colloidal silica‐bonded castables using La2O3

AbstractImproving the green mechanical strength of colloidal silica‐bonded corundum castables is essential to their widespread utility. The effects of varying contents (0–2 wt%) of La2O3 on the green mechanical strength of colloidal silica‐bonded corundum castables were investigated. The findings demonstrate that La2O3 has a positive impact on the green mechanical strength of colloidal silica‐bonded castables. The colloidal silica‐bonded corundum castable containing 2 wt% La2O3 exhibits higher green mechanical strength than the cement‐bonded corundum castable. Additionally, the castable shows excellent construction performance. The basic properties of La2O3 and La(OH)3 facilitate the absorption of H+ from the surface of colloidal silica to form more siloxane bonds and speed up gelation. Fourier transform infrared spectroscopy and X‐ray fluorescence spectroscopy analyses indicate that La3+ ions participate in the condensation of –Si–OH and bond the broken Si–O bonds to create Si–O–La chemical bonds. La3+ ions bridge the colloidal silica particles, leading to stable three‐dimensional network structures that result in an increased green mechanical strength of the castables. The water consumption during the hydration reaction expedites gelation, further contributing to the enhancement of the green mechanical strength of the corundum castables. Given its wide sources and stable performance, La2O3 can be considered an efficient setting agent with the potential for extensive industrial application.