Lanthanum Cerium Research Articles

Ultra-precision machining of cerium-lanthanum alloy with atmosphere control in an auxiliary device

Cerium–lanthanum alloys are the main component of nickel–metal hydride batteries, and they are thus an important material in the green-energy industry. However, these alloys have very strong chemical activity, and their surfaces are easily oxidized, leading to great difficulties in their application. To improve the corrosion resistance of cerium–lanthanum alloys, it is necessary to obtain a nanoscale surface with low roughness. However, these alloys can easily succumb to spontaneous combustion during machining. Currently, to inhibit the occurrence of fire, machining of this alloy in ambient air needs to be conducted at very low cutting speeds while spraying the workpiece with a large amount of cutting fluid. However, this is inefficient, and only a very limited range of parameters can be optimized at low cutting speeds; this restricts the optimization of other cutting parameters. To achieve ultraprecision machining of cerium–lanthanum alloys, in this work, an auxiliary machining device was developed, and its effectiveness was verified. The results show that the developed device can improve the cutting speed and obtain a machined surface with low roughness. The device can also improve the machining efficiency and completely prevent the occurrence of spontaneous combustion. It was found that the formation of a build-up of swarf on the cutting tool is eliminated with high-speed cutting, and the surface roughness (Sa) can reach 5.64 nm within the selected parameters. Finally, the oxidation processes of the cerium–lanthanum alloy and its swarf were studied, and the process of the generation of oxidative products in the swarf was elucidated. The results revealed that most of the intermediate oxidative products in the swarf were Ce3+, there were major oxygen vacancies in the swarf, and the final oxidative product was Ce4+.

Synthesis and Characterization of Fluorite-Type La2Ce2O7 Plasma Sprayable Powder for TBCs Application

This work focuses on the fabrication of lanthanum cerate (La2Ce2O7, LC) powders via two chemical routes: modified Pechini sol-gel method and solid-state synthesis. The synthesized LC powders were heat treated in the temperature range of 1000–1400 °C for 6 h and investigated as a material for thermal barrier coating (TBC) applications. For this purpose, the powder morphology, chemical composition, crystal structure and thermal stability were studied. Scanning electron microscopy (SEM) of the synthesized powders revealed an agglomerated structure consisting of fine and uniformly distributed grains. Energy-dispersive X-ray spectroscopy (EDXS) indicated that the chemical compositions of the LC powders were similar to the stoichiometric ratio of La2Ce2O7. A cubic fluorite structure was observed by X-ray diffraction analysis (XRD) after calcining the LC powder prepared by solid-state synthesis at 1300 °C. In contrast, there was always a fluorite structure in the LC powder synthesized by the Pechini sol-gel method after heat treatment over the entire temperature range. The thermal behavior of the LC powders was analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) in the temperature range of 25–1300 °C. Neither an obvious mass change nor a visible energy change was observed within the tested temperature range, indicating high phase stability of the LC powder and its suitability for TBC applications. Spheroidization on the prepared LC powders was also investigated, revealing that powder size and morphology had a significant impact on the spheroidization efficiency.

Hot corrosion behavior of hybrid double-layered LZ/LZC + YSZ thermal barrier coatings made using powder and solution precursor feedstock

Lanthanum zirconate (La2Zr2O7; LZ) and cerium doped lanthanum zirconate (La2(Zr0.7Ce0.3)2O7; LZC) has gained immense attention as thermal barrier coating (TBC) materials because of their superior thermophysical properties, high-temperature phase stability and chemical inertness than yttria-stabilized zirconia (YSZ). In the present study, LZ and LZC double-layered TBCs are prepared by solution precursor plasma spray process (SPPS) as a top layer over the atmospheric plasma sprayed YSZ coatings, and their hot corrosion behavior is studied. The as-deposited SPPS coatings exhibited single phases, and the microstructural morphologies reveal a hierarchically structured surface with vertically cracked microstructure. Exposure to the high temperature corrosion process results in damage of the morphology and microstructure within the SPPS layer by forming lanthanum vanadate (LaVO4) and lanthanum cerium vanadate ((LaCe)VO4) in LZ and LZC coatings, respectively, while leaching out zirconia (ZrO2). In the case of conventional YSZ, the corrosive salts infiltrate entirely through the coating and result in complete densification and associated phase changes. While combining the above aspects, the hybrid double-layered architecture of LZ/YSZ and LZC/YSZ coatings can be beneficial to protect the underlying YSZ layer against the detrimental infiltration of molten corrosive salt.

Effect of lanthanum cerium methionine on the properties of natural rubber

Lanthanum cerium methionine was synthesized using the metathesis method and its molecular formula was confirmed as La0.35Ce0.65Cl3(C5H10NO2S)3·2H2O via Inductively Coupled Plasma Optical Emission Spectrometer, FTIR, and thermogravimetry-differential scanning calorimetry characterization methods. Lanthanum cerium methionine can significantly reduce the activation energy of the vulcanization reaction. The vulcanization kinetics model is used to fit the vulcanization curve of the rubber, and the obtained vulcanization activation energy of lanthanum cerium methionine for rubber is E1 = 76.89 KJ/mol, E2 = 102.36 KJ/mol and E3 = 126.00 KJ/mol. The above value is lower than pristine rubber. The Kissinger method and Flynn–Wall–Ozawa method were used to analyze the activation energy of thermal-oxidative degradation of vulcanized rubber. It was found that the rubber added with lanthanum cerium methionine exhibited higher thermal-oxidative degradation activation energy compared to that of pristine rubber; in addition, it was more difficult to age under the same environment. These results indicated that lanthanum cerium methionine can be not only used as a vulcanization accelerator, but also plays a role in resisting thermal and oxygen aging.

Cobalt Element Effect of Ternary Mesoporous Cerium Lanthanum Solid Solution for the Catalytic Conversion of Methanol and CO2 into Dimethyl Carbonate.

A citric acid ligand assisted self-assembly method is used for the synthesis of ternary mesoporous cerium lanthanum solid solution doped with metal elements (Co, Zr, Mg). Their textural property was characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption-desorption, X-ray photoelectron spectroscopy and TPD techniques, and so on. The results of catalytic testing for synthesis of dimethyl carbonate (DMC) from CH3OH and CO2 indicated that the DMC yield reached 316 mmol/g on Ce-La-Co solid solution when the reaction temperature was 413 K and the reaction pressure was 8.0 MPa. It was found that Co had synergistic effect with La and Ce, doping of Co on the mesoporous Ce-La solid solution was helpful to increase the surface area of the catalyst, promote CO2 adsorption and activation, and improve the redox performance of solid solution catalyst. The conversion of Co2+ to Co3+ resulted in the continuous redox cycle between Ce4+ and Ce3+, and the oxygen vacancy content of the catalyst was increased. Studies have shown that the catalytic performance of Ce-La-Co solid solution is positively correlated with oxygen vacancy content. On this basis, the reaction mechanism of DMC synthesis from CO2 and CH3OH on the catalyst was speculated.

Enhanced ammonia synthesis activity of Ru-supported cerium–lanthanum oxide induced by Ti substitution forming mesopores

Ru/Ce0.5La0.5−xTixO1.75+0.5x solid solutions with high Ce4+ reducibility and a large number of mesopores were synthesized and their ammonia synthesis activity was investigated.

In English

X-ray phase and thermogravimetric analysis, scanning electron microscopy and energy-dispersion spectroscopy were used to study the products of phase formation during the precipitation of lanthanum and cerium salts in the presence of silver nitrate and recipients of precipitators, nucleating agents and hydrolysis regulators. Thermogravimetric analysis shows the completion of the La(OH)3 lattice dehydroxylation process at a temperature of ~ 300 °С and probable destruction of sulfates at a temperature of ~ 340 °С. The phase interaction of lanthanum oxide(III) with silver ends at T ~ 400 °C. The DTG curve shows a two-stage weight loss, which characterizes the destruction of lanthanum and silver hydroxides (250 °C) and the removal of sulfates (~ 340 °C), respectively. According to the TG, the total weight loss is 21.6 %. For the cerium-containing system the only endothermic effect of dehydroxylation of cerium hydroxide at T = 250 °C with its conversion into cerium dioxide is observed. The destruction of nitrates (anionic component of solutions) takes place at the temperature of 400 °C. Weight loss takes place at T = 150 °C and is 53.9 %. Thus, on the basis of TG-DTA data, it can be assumed that the formation of composites particles based on lanthanum and cerium oxides, modified with silver, ends at the temperature of 400 °C. The X-ray diffraction data shows that at the initial stage the system undergoes the formation of cerium and lanthanum hydroxides, and during lyophilization of the precipitate (T = 160 °C) the crystal lattice of hydroxides partial dehydroxylation takes place with the formation of trigonal oxides La2O3 and Ce2O3. It has been found that the presence of silver cations in the solution can affect the phase composition of lyophilized structures and the formation of the CeO2 phase. It is shown that the hydroxylamine chloride injection into the system can initiate the silver restoration on the lanthanum oxide surface and also partially restore it to the LaO phase. Temperature treatment of the samples (T = 400 °С) promotes homogenization of the precipitate composition: formation of 30 nm cerium dioxide particles with silver clusters evenly distributed on its surface, and hexagonal lanthanum oxide plates with individual silver particles as the second phase. In three-component systems, two modifications of lanthanum oxides (trigonal and cubic), cerium dioxide and metallic silver are formed. It is found that the chemical composition of the precipitates contains the main elements – La, Ce, O, Ag and impurity – S or Cl, as the anionic component of the initial solutions, N and K in the composition of the initial suspension. It is shown that the morphology of the samples is represented by hexagonal structures of lanthanum hydroxide and oxide, spherical and pseudocubic particles of cerium dioxide and lanthanum oxide, spherical clusters of silver.

Effect of Lanthanum Cerium Cysteine on Cure Characteristics, Mechanical Properties, and Thermooxidative Aging for Natural Rubber

In this work, a novel additive lanthanum cerium cysteine (LC-Cys), with the molecular formula La0.35Ce0.65(Cys)3Cl3·3H2O, was successfully synthesized through complex decomposition reaction of L-Cysteine and chlorinated rare earths. The effects of additive LC-Cys on cure characteristics, mechanical properties, and thermooxidative aging were investigated. LC-Cys as a multifunctional additive was applied to increase the curing rate and reduce the content of zinc oxide in the presence of the sulfur vulcanization system. It was found that the vulcanizates filled with (5ZnO/2LC-Cys) exhibited the highest modulus, which indirectly indicated the high crosslink and stiffness of the vulcanizates. Moreover, the vulcanizates with LC-Cys showed excellent mechanical properties and resistance to thermooxidative aging. Compared to NR composites filled with normal ZnO, LC-Cys even enhanced the mechanical strength and thermooxidative aging properties with 40% lower ZnO addition.

Development of lanthanum cerate based thermal barrier coatings with enhanced resistance to ingestion by volcanic ash particles

Lanthanum cerate (LC) is one of the potential candidates for thermal barrier coatings (TBCs) by virtue of its high melting point and favorable thermophysical properties. Infiltration of silicate in LC coating was found to be effectively arrested by forming La-Ce apatite. To qualify LC based material for next-generation TBCs, it is essential to understand the role of rare earth oxides (REOs) dopants that can manage the thermal expansion coefficient values and provides improved performance in volcanic ash infiltration resistance. Accordingly, various REOs doped LC was synthesized, plasma sprayed to generate free-standing coupons, and evaluated their volcanic ash infiltration resistance.

Preparation and study of cerium lanthanum zirconate fibres

ABSTRACT LZ7C3 fibres with nanostructures have been synthesised by the sol–gel method combined with electrostatic spinning technology and a high-temperature-resistant LZ7C3 ceramic material prepared by high-temperature calcination. The formation process of the ceramic fibre was studied and its properties characterized by differential thermal analysis, X-ray diffraction and infrared spectroscopy. The microstructure of the fibre was analysed by scanning electron microscopy and transmission electron microscopy, and the properties of the fibre were determined. The results showed that many conditions, such as calcination temperature and silica-sol content, have a pivotal influence on the crystal phase composition and morphology. By comparing the effects of these conditions, ceramic materials with exceptional properties have been prepared.

Decomposition of 2-naphthol in water and antiviral activity by CoO<i><sub>x</sub></i> modified (Ce<sub>0.8</sub>,Bi<sub>0.2</sub>)O<sub>2−δ</sub> and (Ce<sub>0.8</sub>,La<sub>0.2</sub>)O<sub>2−δ</sub> in the dark or under visible light

Using hydrothermal processing, we prepared a cerium bismuth solid solution oxide ((Ce0.8,Bi0.2)O2−δ, CBO) and a cerium lanthanum solid solution oxide ((Ce0.8,La0.2)O2−δ, CLO). The resultant powders possessed fluorite-type crystal structure. They also decomposed 2-naphthol in water in the dark. From their valence change and temperature dependence, we infer that the Mars–van Krevelen (MvK) mechanism of Ce contributes to this decomposition activity. These materials showed higher decomposition activity under visible light. Modification of CoOx onto these materials enabled an apparent bandgap decrease and the MvK mechanism of Ce and Co, which led to higher decomposition activity in the dark and under visible light. The CBO activity was higher than that of CLO on the decomposition of 2-naphthol in water, but the CLO antiviral activity was higher than that of CBO. Results suggest that the CLO antiviral activity results from virus deactivation by direct contact with the powder surface.

Extraction-Pyrolysis Synthesis and Luminescence Properties of Lanthanum–Cerium Phosphates Activated by Terbium

Extraction-Pyrolysis Synthesis and Luminescence Properties of Lanthanum–Cerium Phosphates Activated by Terbium

Adsorptive and photocatalytic performance of perovskite material for the removal of food dye in an aqueous solution

Lanthanum cerate (La2Ce2O7), a perovskite nanomaterial, has been synthesized by using the gel combustion method to remove carcinogenic and neurotoxic dye FD&C Yellow 5 from its aqueous solution and the same has been also explored to investigate the photocatalytic behavior towards the degradation of food dye. The synthesized material has been extensively characterized using various techniques such as XRD, FT-IR, SEM, BET surface area and through pHZPC. The effect of various operational parameters like solution pH, temperature, and initial dye concentration were investigated to explore the optimum dye removal percentage. To gain the mechanistic perceptive of the dye removal process, various kinetic models were used. Pseudo-second order kinetic model was found to be well suited in describing the sorption system. The intra-particle diffusion model suggested that the film diffusion process controls the overall rate of the dye and perovskite interaction process.Further, equilibrium data interpretation was appraised through various isotherm models and adsorption data found to be consistent with the Freundlich model suggesting multilayer coverage of dye species over the surface of perovskite particles and maximum adsorption capacity was evaluated as 133.3 mg/g at 323 K. Thermodynamic parametric investigation indicated that the dye adsorption process was feasible, spontaneous and endothermic. The activation energy of the adsorbate-adsorbent interaction process was found to be 5.26 kJ/mol, suggesting a physisorption mechanism governs the adsorption process. Photocatalytic efficiency of the perovskite was also scrutinized for dye concentrations 10, 25 and 50 mg/L and dye degradation of 89%, 75% and 69% was observed for each tested concentrations, respectively.

Doped lanthanum cerate pyrochlore for multicolor luminescent phosphor: Decisive role of energy transfer and defects

Designing of efficient luminescent materials requires proper understanding of energy transfer, defect evolution and dopant local structure. The present work is a perfect amalgam wherein we have thoroughly investigated the concentration dependent host sensitized energy transfer, defect evolution and local structure of europium ion in La2Ce2O7 (LCO) pyrochlore material. Raman spectroscopy suggested stabilization of defect fluorite structure for LCO as well as LCO:Eu3+ (LCOE) but degree of structural distortion as well as oxygen vacancies (OVs) increases with increase in europium ion concentration. Diffuse reflectance spectroscopy suggested band gap narrowing at higher doping level owing to enhanced density of OVs. Positron annihilation lifetime spectroscopy suggested an increase in the formation of oxygen vacancies and vacancy clusters near the surfaces at higher doping. As a result, LCO, on irradiation with 250 nm ultraviolet photon showed visible emission due to OVs as well charge transfer transition. On Eu3+ doping emission spectra was rich in host as well as europium emission and host to europium energy transfer increases with increase in europium ion concentration. This get's reflected as violet blue emission at lower doping and yellowish white at higher doping level ≥7.5% under host excitation and orange-red emission under 471 nm dopant excitation. Europium ion emission spectral profiles in LCOE suggested stabilization of Eu3+ in CeO6 octahedra as is also confirmed using lifetime spectroscopy. Judd-Ofelt measurement further reflected higher branching ratio for 5D0→7F2, internal quantum yield ~48% and high Ω2 compared to Ω4. This work highlights the importance of local dopant site, HSET, excitation photon and defects in designing color tunable luminescent materials and is expected to play an important role in designing the phosphor converted light emitting diodes (pc-LEDs).

Finite element modelling of Lanthanum Cerate (La2Ce2O7) coated piston used in a diesel engine

Nowadays, the performance of IC engines and its components are improved by having a thermal barrier coating which decreases the heat losses and the harmful emissions such as hydrocarbons and the NOx emissions. The steady-state temperature of a diesel engine piston with a ceramic coating has been determined in this analysis. The Al–Si piston is used in this analysis and the ceramic material which is used for coating the crown is Lanthanum Cerate (La2Ce2O7). Temperature distributions are investigated and further compared with an uncoated piston. All the investigations are performed by using finite element method (FEM) based on the software ANSYS Workbench. The piston model is created in the ANSYS Workbench and convection boundary conditions are considered for further analysis. The coating thickness is in the range of 0.4–1.6 mm for the analysis of temperature. In the coated piston, the increased maximum temperature is 45.5% for 0.4 mm thick coating. The temperature at the top surface increases with coating thickness and it also leads to the depletion of substrate surface temperature and stress. Lanthanum cerate is a better ceramic material than magnesium zirconate due to its low thermal conductivity.

Electrochemical performance of lanthanum cerium ferrite nanoparticles for supercapacitor applications

Lanthanum cerium ferrite nanoparticles has been synthesized for the first time via hydrothermal and co-precipitation method. The structural and morphological study of the nanoparticles have been examined using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). The electrochemical study of J1 and J2 electrodes have been examined using three electrode system in 6 M KOH electrolyte using cyclic voltammetry (CV), galvanostatic charging-discharging (GCD) and electrochemical impendence spectroscopy (EIS). The highest specific capacitance of 1195 F/g has been obtained at a scan rate of 10 mV/s from hydrothermal synthesis nanomaterial electrode (J2) and long cycling life 92.3% retention after 2000th cycles. Furthermore, the energy density and power density of the J2 electrode at a current density of 5 A/g was 59 Wh/kg and 9234 W/kg, respectively. Hence, the fabricated J2 electrode is a favorable candidate for super-capacitor applications.

Hot corrosion properties of plasma sprayed La2Ce2O7/YSZ vis-à-vis La2Ce2O7/cluster paired zirconia thermal barrier coatings

Bilayered thermal barrier topcoats have lead to a remarkable breakthrough in overcoming the disadvantages of the conventional yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The present work is devoted to studying the hot corrosion properties of two different bilayered ceramic topcoats, viz., (i) lanthanum cerium oxide with the formula La2Ce2O7 (LCO)/YSZ and LCO/cluster paired zirconia (gadolinia, dysprosia and yttria stabilized zirconia -(Gd,Dy,Y)SZ) plasma sprayed TBCs. Plasma spray grade YSZ and (Gd,Dy,Y)SZ are prepared by co-precipitation and solution combustion techniques as reported in the literature. The effect of thickness of the plasma sprayed top LCO layer in bilayered LCO/YSZ and LCO/(Gd,Dy,Y)SZ TBC systems under Type I hot corrosion condition is examined. The LCO/(Gd,Dy,Y)SZ bilayered coating with 100 μm LCO thickness exhibits better hot corrosion resistance than the LCO/YSZ system. The phase transformation of t′-ZrO2 to m-ZrO2 in LCO/(Gd,Dy,Y)SZ (100/150 μm) TBC is reduced markedly (60%) compared to LCO/YSZ (100/150 μm) TBC.

Investigation of Microwave and Thermal Processing of Electrode Material of End-of-Life Ni-MH Battery

Ni-metal hydride (NiMH) batteries should be recycled, as they contain base metals (Ni, Co) and rare earth elements (La, Ce). In this study, thermal and microwave treatments are investigated as a pre-treatment method for decomposing electrode material (Ni(OH)2 and LaNi5). The kinetic analysis of thermal decomposition electrode material yields the activation energy of 41.3 kJ/mol. The maximum percentage of lanthanum nickel oxide phase and cerium oxide phase is obtained at 1000°C of thermal treatment and 15 min of microwave exposure. The formation of melted balls of Ni and its oxide (Ni ~ 72.8%) was observed in microwave exposure, and the tendency of ball formation decreased with increasing exposure time. The effect of microwave exposure and thermal treatment on the acid leaching (1 M HCl, at S/L-1:20, at 70°C for 2 h) was studied. The leaching results showed NiO and CeO2 phases in the leach residue of thermal and microwave treated products.

Enhanced photocatalytic degradation of nigrosine dye from its aqueous solution using La2Ce2O7 nanoparticles

In the present work, removal of nigrosine dye from its aqueous solution via combined photocatalysis and adsorption has been reported using ternary catalyst lanthanum cerate under visible light. The catalyst has been synthesized by citric acid assisted sol-gel method. XRD graph reveals that the average crystallite size of sample is found to be approximate 4.0 nm having cubic fluorite structure. There is 64.45% oxygen. 17.76% lanthanum and 17.79% cerium atoms present in the material, as observed by EDS result. FESEM results shows that obtained particles are in the form of rice grain shape arranged densely in homogeneous manner. TGA curve shows that there is a evaporation of moisture, nitrate and carbon. Two exothermic peaks are observed at about 170°C and 200°C in the DTA curve. The UV-Visible spectrum gives the band gap of lanthanum cerate and it is 3.0 eV. A spectrophotometer has been used to follow the photocatalytic degradation of nigrosine dye at specific intervals of time. The effect of various parameters such as pH, concentration of dye, photocatalyst dosage and light intensity has been studied on the rate of degradation. A tentative mechanism for degradation of nigrosine has been proposed involving superoxide and hydroperoxyl radicals as main oxidizing species.

Evaluation of oxidation and thermal insulation capability of nanostructured La2(Zr0·7Ce0.3)2O7/YSZ functionally graded coatings

In the present work, nanostructured La2(Zr0·7Ce0.3)2O7/YSZ functionally graded coatings were prepared by applying the atmospheric plasma spraying process. The La2(Zr0·7Ce0.3)2O7 compound was synthesized via the calcination process to get a nanostructured precursor precipitate at 600 °C. Two types of nanostructured functionally graded coatings were applied on the Hastelloy X substrates coated with NiCrAlY and 8YSZ. The agglomerates of La2(Zr0·7Ce0.3)2O7 were then used to apply the type I coating. Type II coating was then applied by the plasma spraying of the heat-treated agglomerates of La2(Zr0·7Ce0.3)2O7. The results of the phase and microstructural analysis showed that a nano-composite microstructure comprising the main phases of lanthanum zirconate with the partial solubility of cerium cation (LZ) and the solid solution of cerium lanthanum zirconate (LC) was formed in both types of coatings. Type II coating was relatively denser; so, it could be considered as a dense nanostructured coating. The results of the oxidation tests also showed that only the type II coating had higher oxidation resistance, as compared to that of the conventional YSZ coating. Parabolic oxidation rate constant of this coating was equal to 0.114 μm2/h. On the other hand, the oxidation rate constant for the type I coating and conventional YSZ coating was measured to be 0.141 μm2/h and 0.147 μm2/h, respectively. In addition, the results of the thermal insulation capability test indicated that the thermal barrier capability of the type I coating was 59% higher than that of the conventional YSZ coating. However, under similar conditions, this percentage was 29% for the type II coating.