Search Results (173)

In this work, a novel potential thermal barrier coating material entropy-stabilized titanium–aluminum oxide (La_0.25Ce_0.25Nd_0.25Sm_0.25)Ti₂Al₉O₁₉ (META) was successfully synthesized by the solid-state reaction method, and its thermophysical properties, phase stability, infrared emissivity, mechanical properties, and CMAS corrosion resistance were systematically investigated. The results demonstrated that META exhibits low thermal conductivity at 1100 °C (1.84 W·(m·K)⁻¹), with a thermal expansion coefficient (10.50 × 10⁻⁶ K⁻¹, 1000–1100 °C) comparable to yttria-stabilized zirconia (YSZ). Furthermore, META displayed desirable thermal stability, high emissivity within the wavelength range of 2.5–10 μm, and improved mechanical properties. Finally, META offers superior corrosion resistance due to its excellent infiltration inhibiting. The bi-layer structure on the corrosion surface prevents the penetration of the molten CMAS. Additionally, doping small-radius rare-earth elements thermodynamically stabilizes the reaction layer. The results of this study indicate that (La_0.25Ce_0.25Nd_0.25Sm_0.25)Ti₂Al₉O₁₉ has the potential to be a promising candidate for thermal barrier coating materials. Full article

The existing Al-Ce heat-resistant alloys are not extensively utilized in high-temperature applications due to their poor room-temperature mechanical properties. In this study, the Al-10Ce-3Mg-5Zn alloy was enhanced using hot extrusion and heat treatment. The as-extruded alloy exhibited bimodal intermetallic compounds and grain structures. Additionally, high-density microcracks and twins were observed in the micron-sized intermetallic compounds. Compared with the as-cast state, the as-extruded alloy demonstrated a higher ultimate tensile strength (UTS) of 317 MPa and better elongation of 11.0%. Numerous nano-sized T phases precipitated in the α-Al matrix after the heat treatment, contributing to a further rise in UTS (365 MPa). The high strength of the alloy is primarily due to its strong strain hardening capacity, fine grain strengthening, and precipitation strengthening effect. The change in elongation mainly results from the expansion of pre-existing microcracks, twin deformation, and microstructural refinement. The heat-treated alloys exhibited superior strength retention ratios at elevated temperatures (64% at 200 °C) compared to conventional heat-resistant aluminum alloys. The results of this paper indicate that hot extrusion and heat treatment are effective for developing heat-resistant Al-Ce alloys with high room-temperature strength, offering a simple process suitable for industrial production. Full article

In this work, the novel Mg-Al-Mn-Ce-(Ca) alloy system has been developed, and large-scaled and thin-walled Mg alloy extruded profiles with an actual composition of Mg-8Al-0.57Mn-0.42Ce (AM80E), and Mg-8Al-0.57Mn-0.42Ce-0.31Ca (AM80EA) were successfully fabricated. The extruded AM80EA alloy profile exhibited a refined recrystallized grain structure (with an average size of ~6.96 μm) and high-density second phase. These abundant micro-nano precipitates effectively inhibited grain boundary migration during recrystallization, achieving obvious grain refinement and providing strong grain refinement strengthening effects. Concurrently, these high-density second-phase particles can also prevent dislocations from slipping. The fine-grain strengthening and second-phase strengthening contribute to the yield strength (YS) of ~174 MPa, the ultimate tensile strength (UTS) of ~309 MPa, and the elongation (EL) of ~13.7% of the AM80E alloy profile. Through the further addition of the Ca element, the AM80EA alloy achieves better comprehensive mechanical properties than the AM80E alloy, exhibiting a YS of ~193 MPa, UTS of ~346 MPa, and EL of ~16.5%. This study demonstrates that, through rational alloying design and extrusion process control, Mg-Al-Mn-Ce-(Ca)-based alloy profiles with excellent mechanical properties can be obtained. Relevant work would provide references for developing these cost-effective high-strength Mg alloy products and promote their industrial applications. Full article

Zirconolite is a wasteform that can immobilize Pu. Herein, zirconolites comprising Ce as a Pu simulant and Al as a charge compensator of Ce/Pu were synthesized by sintering raw CaO, ZrO₂, TiO₂, CeO₂, and Al₂O₃ powder mixtures at 1400 °C in static air. The reduction behavior and phase transformation of zirconolites during their heat treatment in an Ar–H₂ gas flow were investigated. In pure and Ce–Al co-doped zirconolite compositions, 2M-zirconolite and small amounts of perovskite were obtained after sintering. In contrast, 2M-, 4M-zirconolite and relatively large amounts of perovskite were obtained in Ce-doped zirconolite composition. All zirconolite compositions first underwent reduction at ~1050 °C by forming a small domain of perovskite phase. Ce–Al co-doped zirconolite showed a smaller fraction of phase transformation in perovskite than Ce-doped zirconolite, indicating the advantage of using a charge compensator to prevent perovskite formation. Full article

Application of rare earths (RE) as grain refiners is well-known in the technology of aluminum alloys for the automotive industry. In the current study, Al-2.4%Cu-0.4%Mg alloy (coded 220) and Al-7.5%Si-0.35%Mg alloy (coded 356.1), were prepared by melting each alloy in a resistance furnace. Strontium (Sr) was used as a modifier, while titanium boride (TiB₂) was added as a grain refiner. Measured amounts of Ce and La were added to both alloys (max. 1 wt.%). The alloy melts were poured in a preheated metallic mold. The main part of the study was conducted on tensile testing at room temperature. The results show that although RE would cause grain refining to be about 30–40% through the constitutional undercooling mechanism, grain refining with TiB₂ would lead to approximately 90% refining (heterogenous nucleation mechanism). The addition of high purity Ce or La (99.9% purity) has no modification effect regardless of the alloy composition or the concentration of RE. Depending on the alloy ductility, the addition of 0.2 wt.%RE has a hardening effect that causes precipitation of RE in the form of dispersoids (300–700 nm). However, this increase vanishes with the decrease in alloy ductility, i.e., with T6 treatment, due to intensive precipitation of ultra-fine coherent Mg₂Si-phase particles. There is no definite distinction in the behavior of Ce or La in terms of their high affinity to interact with other transition elements in the matrix, particularly Ti, Fe, Cu, and Sr. When the melt was properly degassed using high-purity argon and filtered using a 20 ppi ceramic foam filter, prior to pouring the liquid metal into the mold sprue, no measurable number of RE oxides was observed. In conclusion, the application of RE to aluminum castings would only lead to formation of a significant volume fraction of brittle intermetallics. In Ti-free alloys, identification of Ce- or La-intermetallics is doubtful due to the fairly thin thickness of the precipitated platelets (about 1 µm) and the possibility that most of the reported Al, Si, and other elements make the reported values for RE rather ambiguous. Full article

The effects of Ce content on the microstructure and phase composition of the Al-5Ti-1B refiner and the refining effect of the Al-5Ti-1B-xCe (x = 0, 1, 5, 10 wt.%) refiner on the grain size, microstructure, and mechanical properties of Al-5Mg-3Zn-1Cu alloys were studied. The results show that the addition of 1.0 wt.% Ce in the Al-5Ti-1B refiner changes the TiAl₃ phase from block to strip, and the massive Ti₂Al₂₀Ce phase is formed. When the Ce content of the Al-5Ti-1B refiner increases to 5.0 wt.%, the plate-like TiAl₃ phase is surrounded by the Ti₂Al₂₀Ce phase, and the reticulate Al₄Ce phase is formed. With the Ce content of the Al-5Ti-1B refiner further increasing to 10.0 wt.%, a lot of network distribution Al₄Ce phase is formed. The volume of the Mg₃₂(AlCuZn)₄₉ phase of the as-cast Al-5Mg-3Zn-1Cu alloys is reduced after refining with the Al-5Ti-1B-xCe refiner. The Al-5Ti-1B-1Ce refiner has the best refining effect on as-cast Al-5Mg-3Zn-1Cu alloys, and the grain size of as-cast Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B-1Ce refiner is reduced by 43% compared with as-cast Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B refiner. Compared to the aged Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B refiner, the yield strength, ultimate tensile strength, and fracture elongation of aged Al-5Mg-3Zn-1Cu alloys refined by the Al-5Ti-1B-5Ce refiner are improved by 4.0%, 4.6%, and 25.6%, respectively. Therefore, it can be seen that Al-5Ti-1B-1Ce refiner and Al-5Ti-1B-5Ce refiner have broad application prospects. Full article

The choice of efficient methods for the immobilization of high-level waste (HLW) resulting from the reprocessing of spent nuclear fuel (SNF) is an important scientific and practical task. The current policy of managing HLW within a closed nuclear fuel cycle envisages its vitrification into borosilicate (B-Si) or alumina–phosphate (Al-P) glasses. These wasteforms have rather limited waste loading and can potentially impair their retaining properties on devitrification. The optimal solution for HLW immobilization could be separating radionuclides into groups using dedicated capacious durable matrices. The phases of the Nd₂O₃–ZrO₂–TiO₂ system in this respect are promising hosts for the REE (rare earth elements: Nd, Ce, La, Pr, Sm, Gd, Y) –MA (MA: Am, Cm) fraction of HLW. In this manuscript, we present data on the composition of the samples analyzed, their durability in hot water, their behavior under irradiation, and their industrial manufacturing methods. Full article

Coal fly ash (CFA) is a commercially viable source of alumina comparable to traditional bauxite deposits. Due to its high silica content and alumina in the refractory mullite phase, the most suitable processing technique is the sinter-H₂SO₄ leach process. However, this process is energy-intensive, has low selectivity for Al, and generates a secondary solid waste residue. To develop a sustainable process that is economically attractive, Al can be extracted with REEs, Ti, and Fe as saleable products, while secondary solid waste is regenerated for further applications to achieve high-value and high-volume utilisation of CFA. This study focused on the potential extraction of selected REEs (Ce, La, Nd, Y, and Sc), Al, Ti, and Fe, using dry magnetic separation and the sinter-H₂SO₄ leach process. XRD analysis showed that CFA is predominantly amorphous with crystalline mullite, quartz, and magnetite/hematite. Further analysis using SEM-EDS and TIMA showed Al-Si-rich grains as the predominant phase, with discrete REE-bearing grains (phosphates and silicates) and Fe-oxide (magnetite/hematite) grains. Traces of REEs, Ti, Ca, Si, and Fe were also found in the Al-Si-rich grains. Discrete Fe-oxide was recovered using dry magnetic separation, and up to 65.9% Fe was recovered at 1.05 T as the magnetic fraction (MF). The non-magnetic fraction (non-MF) containing quartz, mullite, and amorphous phase was further processed for preliminary leaching studies. The leaching behaviour of Al, Ti, Fe, and the selected REEs was investigated using the direct H₂SO₄ and sinter-H₂SO₄ leaching processes. The maximum extraction efficiency was observed using the sinter-H₂SO₄ leach process at 6 M H₂SO₄, a 1:5 solid-to-liquid ratio, 70 °C, and a residence time of 10 h, yielding 77.9% Al, 62.1% Fe, 52.3% Ti, and 56.7% Sc extractions. The extraction efficiencies for Ce, La, Nd, and Y were relatively lower at 23.2%, 27.6%, 11.3%, and 11.2%, respectively. Overall, the results demonstrate that the extraction of REEs using the sinter-H₂SO₄ leach process is strongly influenced by the complex CFA phase composition and the possible formation of insoluble calcium sulphates. Appreciable extraction of Al, Fe, Ti, and Sc was also observed, suggesting a potential two-step leaching process for the extraction of REEs as a feasible option for the industrial recovery of multiple saleable products. Full article

Nanoparticles of GdAlO₃:Ce were synthesized with sodium dodecylbenzene sulfonate (SDBS) as the dispersant and ammonia as the precipitant by co-precipitation reaction to prepare precursors under different conditions. The phase composition of the precursors and the particle morphology were characterized by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The excitation and emission spectra of the resultant samples were analyzed using a photoluminescence spectroscope (PL). The results showed that the as-prepared, well-dispersed, nano-sized GdAlO₃:Ce powder displayed spherical morphology at the initial concentration of metallic salt in liquor of 0.3 mol/L; the synthesized temperature was 0 °C, and it was calcined at 1300 °C for 2 h. The relative intensity of the photoluminescence peak had the maximum value when the Ce³⁺ dopant content was 0.9 mol% (mole fraction). The concentration quench occurred when the Ce³⁺ dopant content exceeded 0.9 mol%, and the peak of the excitation spectrum appeared at a wavelength of 381 nm. Full article

This study fabricated (Al₆₃Cu₂₅Fe₁₂)₉₉Ce₁ quasicrystal-enhanced aluminum matrix composites using the hot-pressing method to investigate their interfacial reaction traits. Microstructure analysis revealed that at 490 °C for 30 min of hot-pressing, the interface between the matrix and reinforcement was clear and intact. Chemical diffusion between the I-phase and aluminum matrix during sintering led to the formation of Al₇Cu₂Fe, AlFe, and AlCu phases, which, with their uniform and fine distribution, significantly enhanced the alloy’s overall properties. Regarding compactness, it first increased and then decreased with different holding times, reaching a maximum of about 98.89% at 490 °C for 30 min. Mechanical property analysis showed that compressive strength initially rose and then fell with increasing sintering temperature. After 30 min at 490 °C, the reinforcement particles and matrix were tightly combined and evenly distributed, with a maximum compressive strength of around 790 MPa. Additionally, the diffusion dynamics of the transition layer were simulated. The reaction rate of the reaction layer increased with hot-pressing temperature and decreased with holding time. Selecting a lower temperature and appropriate holding time can control the reaction layer thickness to obtain composites with excellent properties. This research innovatively contributes to the preparation and property study of such composites, providing a basis for their further application. Full article

The relative energetic stability, mechanical properties, and thermodynamic behavior of B2-AlRE (RE = Sc, Y, La-Lu) second phases in Al alloys have been investigated through the integration of first-principles calculations with the quasi-harmonic approximation (QHA) model. The results demonstrate a linear increase in the calculated equilibrium lattice constant a₀ with the ascending atomic number of RE, while the enthalpy of formation ΔH_f exhibits more fluctuating variations. The lattice mismatch δ between B2-AlRE and Al matrix is closely correlated with the transferred electron et occurring between Al and RE atoms. Furthermore, the mechanical properties of the B2-AlRE phases are determined. It is observed that the calculated elastic constants C_ij, bulk modulus B_H, shear modulus G_H, and Young’s modulus E_H initially decrease with increasing atomic number from Sc to Ce and then increase up to Lu. The calculated Cauchy pressure C₁₂-C₄₄, Pugh’s ratio B/G, and Poisson’s ratio ν for all AlRE particles exhibit a pronounced directional covalent characteristic as well as uniform deformation and ductility. With the rise in temperature, the calculated vibrational entropy (S_vib) and heat capacity (C_V) of AlRE compounds exhibit a consistent increasing trend, while the Gibbs free energy (F) shows a linear decrease across all temperature ranges. The expansion coefficient (α_T) sharply increases within the temperature range of 0~300 K, followed by a slight change, except for Al, AlHo, AlCe, and AlLu, which show a linear increase after 300 K. As the atomic number increases, both S_vib and C_V increase from Sc to La before stabilizing; however, F initially decreases from Sc to Y before increasing up to La with subsequent stability. All thermodynamic parameters demonstrate similar trends at lower and higher temperatures. This study provides valuable insights for evaluating high-performance aluminum alloys. Full article

In this paper, FH460 special steel with rare earth element cerium (Ce) was selected, and the control group without Ce was set up. By changing the content of Ce, the microstructure, phase transition point, and mechanical properties of the test steel were observed to study the effect of trace rare earth element Ce on the microstructure and mechanical properties of high-strength marine engineering steel. The morphology and energy spectrum of inclusions in three kinds of test steels were observed by SEM, and the morphological changes in inclusions in FH460 high-strength marine engineering steel after adding Ce were investigated. The fracture morphology and energy spectrum analysis were carried out by combining the tensile test at room temperature and the gradient low temperature impact toughness test, and the effect of trace Ce on the mechanical properties of the test steel was comprehensively analyzed. The results show that the addition of Ce changes the phase transformation temperature of Ac1 and Ac3, and refines the original microstructure of the test steel. SEM observation showed that the addition of Ce changed the long strip MnS and polygonal irregular Al2O3 inclusions into ellipsoids, which reduced the size of inclusions. The gradient low temperature impact test shows that with the decrease in temperature, the fracture dimple depth of the three test sheets of steel decreases, and the Ce-containing test steel forms a deep dimple centered on rare earth inclusions, which hinders the crack propagation and significantly improves the low temperature impact toughness of the test steel. Full article

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 °C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H₂-TPR) and nitrogen adsorption–desorption at −196 °C. XRD analysis revealed in all the samples the presence of Co₃O₄ crystallites together with periclase-like and CeO₂ phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts’ preparation. The redox properties studied by H₂-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T₅₀, of 489 °C, which is ca. 40 °C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe–Co–Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed. Full article

This study investigated the effect of adding La–Ce mixed rare earths and Sr on the microstructure and mechanical properties of AlSi10MnMg alloy. The experiment utilized different combinations of modifiers, including single La–Ce rare earths, single Sr, and the combined addition of La–Ce mixed rare earths and Sr. This study compared their effects on grain refinement, the modification of the α-Al phase and eutectic silicon phase, and tensile properties and hardness. The results showed that the combined modification of Sr and mixed rare earth elements significantly refined the grains, optimized the morphology of the α-Al phase and eutectic silicon phase, and improved the overall mechanical properties of the aluminum alloy. Under the combined modification, the addition of 0.02 wt.% Sr and 0.1 wt.% RE (La–Ce mixed rare earths) exhibited the most pronounced refining effect. The secondary dendrite arm spacing (SDAS) was reduced by 59.18%. The eutectic silicon phase transformed from coarse needle-like shapes to fine fibrous or granular forms, with an aspect ratio reduction of 69.39%. Meanwhile, the alloy’s tensile strength and hardness were significantly improved. The tensile strength increased to 240 MPa, achieving an increase of 23.08%; the yield strength increased to 111 MPa, achieving an increase of 18.09%; and the elongation reached 7.3%, achieving an increase of 73.81%. This indicates that the proper addition of Sr and mixed rare earths can significantly optimize the microstructure and enhance the mechanical properties of AlSi10MnMg alloy, providing an effective method for the preparation of high-performance heat-treatment-free aluminum alloys. Full article

This study investigated the microstructural constituents and forming properties of alloy Al-1.4 wt.% Fe with different additions of Ce and/or La. The addition of rare earth (RE) elements to aluminum alloys improves their microstructures in their as-cast and heat-treated states. RE additions and appropriate heat treatment also improve their mechanical properties. The influence of the homogenization process on the microstructure and forming properties of Al-1.4 wt.% Fe alloy with various additions of Ce and/or La was investigated. When homogenizing the Al-1.4 wt.% Fe alloy at 580 °C, the majority of the homogenization process is completed after 6 h; at 600 °C, after about 5 h; and at 620 °C, after about 4 h. In the micro-alloyed Al-1.4 wt.%–Fe alloy, α-Al, stable Al13Fe4 phases in an agglomerated form, La-containing phases in a spherical form, and Ce-containing phases in a rod-shaped form are present after homogenization. The addition of La was shown to be advantageous as a micro-addition to Al–Fe alloys. Its forming properties show that the combination of Ce and La is the most favorable addition, whereby the homogenization process is fully optimized. Full article