Addition Of Rare Earth Oxides Research Articles

Sintering of Nanocrystalline Multicomponent Zinc Oxide Varistor Powders Prepared by Ball Milling

Nanocrystalline ZnO–V2O5–MnO2–Nb2O5 varistor ceramic powder mixtures modified by different amount of Er2O3 addition (0-2 mol.%) have been prepared by high energy ball milling. Densification, microstructure and electrical characteristics of the ball milled precursor powders during isochronal sintering at 950 to 1250°C for 1 h as well as isothermal sintering for 0.25 to 2h at 1100°C have been investigated. Densification process is found to diminish slightly while growth of ZnO grain is reduced markedly with increasing Er2O3 addition due to the formation of Er-rich spinel phases at grain boundaries and triple points that restrict the grain boundary migration. It has been demonstrated that ultrafine grained multicomponent ZnO varistor ceramics can be achieved by simple conventional sintering via judicial selection of sintering time (≤ 1h) and temperature (≤ 1100°C) and amount of rare-earth oxide (Er2O3) addition (1.0 mol.%). ZnO varistor with 0.5 mol.% Er2O3 sintered at 1100°C for 0.5h exhibits best varistor property with breakdown field of 3880 Vcm-1.

Effect of the Cerium Oxide (CeO2) on the Structural and Electrochemical Properties of the LaNi5Ce Metal Hydride Anode

One of negative electrode, AB5-type alloy electrodes, have been extensively studied and applied in rechargeable Ni-MH batteries due to their excellent electrochemical characteristics. Some researchers have found that addition of rare earth oxides (La, Ce, Pr, Er, Tm, Yb) to AB5-type alloy (MH) electrode improves battery performance significantly. Cerium Oxide (CeO2) is a light rare earth oxide is widely obtained from the processing of tailings in mining activities. During this time, there is still little data for research applications of cerium oxide for electrode materials. In this paper, the effects of adding CeO2 on the performance metal hydride electrode were investigated. In order to study the effects of CeO2 on the performance of anode material, 1%, 2%, and 3% of weight ratio CeO2 was mixed to LaNi5 as an negative electrode. The powder mixtures were mechanically milled at a speed of rpm 240 for 2 hours using ball mill. The powder mixtures were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). Electrochemical characteristics were measured using electrochemical impedance spectroscopy (EIS). The powder mixing showed the presence of Ce atom substitution into LaNi5 structures that affect the electrochemical properties of the material. The addition of cerium oxide at LaNi5 increase of the value of impedance. However, the addition of the value of impedance at 1% CeO2 is not significant when compared with the addition of 2% and 3% CeO2 that actually make the electrochemical properties of LaNi5 worst. Although the addition of 1% CeO2 also slightly increases the impedance value of LaNi5, but the addition of 1% CeO2 showed increase the corrosion resistance than without the addition of CeO2 and the addition of 2% and 3% CeO2.

Modeling the impact–sliding wear characteristics of rare earth additive iron-based hardfacing alloys

This paper presents a systematic study of the effect of the cerium oxide content on the mechanical, microstructural and tribological properties of iron-based alloys. The results indicate that the microstructure of the hardfaced alloys is mainly composed of austenite, MC and M7C3 carbides. The primary austenite grain size was refined at first and then coarsened with the increase of the rare earth oxide additions. Meanwhile, the hardness of the hardfacing alloy was also increased. The increased area fraction of carbides was found to be beneficial for enhanced wear resistance. A statistical regression model was developed and verified with a number of test cases in order to evaluate the adequacy of the model. The optimal amount of rare earth was found to be less than 6 wt.%; below this composition, the microstructural, mechanical and tribological properties were excellent.

Improved Performance of Ni-Mo Based Anode for Direct Methanol Solid Oxide Fuel Cells with the Addition of Rare Earth Oxides

La2O3 and Sm2O3 are added into Ni-Mo-Ce0.8Sm0.2O1.9 (SDC) as anodes of solid oxide fuel cells with methanol as fuel. The rare earth oxides improve the catalytic oxidation of the fuel, resulting in the decrease of anodic polarization resistance. The single cell with La2O3-Ni-Mo-SDC as the anode and SDC-carbonate composite as the electrolyte exhibits a maximum power density of 765 mW cm−2 at 700°C. The oxides in the anodes also improve the stability of single cells due to the accelerated oxidation of the deposited carbon and the suppression of the deposition of carbon with a high graphitization degree.

Effect of rare earth oxides on the properties of bio-soluble alkaline earth silicate fibers

Using natural mineral wollastonite, talc and quartz sands as raw materials, rare earth oxides (La2O3, Nd2O3 and Y2O3) as additives, the bio-soluble alkaline earth silicate fibers were prepared by melting and blowing process. The viscosity of the molten materials, bio-solubility and crystallization behavior of the fiber were investigated. The results indicated that the fiber drawing temperature range could be broadened since the slope of the temperature-viscosity curve decreased with adding rare earth oxide. The addition of rare earth oxide was beneficial to the increase of crystallization temperature by strengthening the network structure of the fiber. The existence of rare earth oxide in the fibers would reduce the solubility of the fibers, which still belonged to bio-soluble fibers.

Effect of rare earth oxide (Y2O3) addition on alloyed layer synthesized on Ti–6Al–4V substrate with Ti+SiC+h-BN mixed precursor by laser surface engineering

In this study, the rare earth oxide (Y2O3) is added to the precursor powder mixture of Ti+SiC+h-BN, and the subsequent mixture is alloyed on the surface of Ti–6Al–4V substrate by laser surface engineering. The XRD spectra indicate that the alloyed layers contain TiN, TiB, Si3N4, Ti5Si3, BN, Ti2N phases in the α-Ti matrix. It is found that the micro-hardness and wear resistance of alloyed layers with Y2O3 addition are higher than those of the alloyed layer without Y2O3 addition in their precursor. The micro-hardness of alloyed layer with Y2O3 addition enhanced from 583HV to 728HV.

Electrochemical Oxidation of Ammonia over Rare Earth Oxide Modified Platinum Catalysts

Hydrogen is now considered as the main fuel source for fuel cells, but its low volumetric energy density and difficulty in handling are main obstacles for the application in transportable devices and automobiles. To overcome this problem, hydrogen careers such as methanol and NaBH4 have been proposed as alternative fuels for fuel cell systems [1]. Among them, ammonia is one of the promising candidates due to its low production cost, ease in liquefaction at ambient temperatures, and high energy density [2]. Moreover, ammonia is a carbon-free fuel which is expected to work as an incentive for the realization of a low carbon society. However, the performance of most commonly used fuel cell, polymer electrolyte fuel cells (PEFCs) employing an acidic electrolytes such as Nafion®, significantly deteriorated even with a trace amount of ammonia in hydrogen fuel [3]. In contrast, ammonia can be electrochemically oxidized in an alkaline electrolyte: The conventional alkaline fuel cell using potassium hydroxide (KOH) as an electrolyte was operated successfully with supplying ammonia directly [4]. In these circumstances, anion exchange membranes (AEMs) have been attracted much attention for electrolytes. The recent development of AEMs has increased the potential and the importance of ammonia as a fuel. Many studies on the electrochemical ammonia oxidation over Pt electrode in an alkaline aqueous electrolyte have been reported [5], [6]. Throughout these studies, it was suggested that the amount of poisonous Nad species and reactive OHad species have a great effect on the ammonia oxidation reaction over Pt electrode. The negative influence of Nad species on ammonia oxidation over the platinum group metals (Pt, Ru, Pd, Rh, and Ir) have been reported by de Vooys et al [7]. However, the contribution of OHad species to ammonia oxidation has not been discussed yet in detail. In this study, then, the Pt-based catalysts with high electrocatalytic activity for ammonia oxidation were developed by focusing on the enhancement of adsorption property of OHad species. Many preceding studies have reported that the rare earth oxide such as CeO2 changes the OH adsorption capacity of catalyst [8], [9]. In addition, rare earth oxides have been used as supporting materials of electrocatalysts for polymer electrolyte fuel cells (PEMFCs), and their stability under electrochemical environments has also been confirmed [10]. Accordingly, a series of rare earth oxides (CeO2, Y2O3, La2O3, and Sm2O3) modified Pt catalysts was prepared and its electrocatalytic activity for ammonia oxidation reaction was investigated in alkali aqueous solutions. The ammonia oxidation activity was enhanced in accordance with the amount of OHad species over electrode surface. From various electrochemical measurements, it was revealed that the rare earth oxide additive improved the supply capacity of OHad to the reactive Pt sites. Among the catalysts studied, CeO2 modified Pt electrocatalyst exhibited the highest activity; the peak current density for ammonia oxidation was 3.5 times higher than that of Pt catalyst. Furthermore, this activity enhancement was also observed at 60°C. These results indicate that the addition of rare earth oxide is one of the promising ways to design the high performance anode for direct ammonia anion exchange membrane fuel cells (AEMFCs). [1] H. Liu, C. Song, L. Zhang, H. Wang, D.P. Wilkinson, J. Power Sources 155 (2006) 95–110. [2] K. Kordesch, V. Hacker, J. Gsellmann, M. Cifrain, G. Faleschini, P. Enzinger, R. Fankhauser, M. Ortner, M. Muhr, R. R. Aronson, J. Power Sources 86 (2000) 162–165. [3] F.A. Uribe, S. Gottesfeld, T.A. Zawodzinski, J. Electrochem. Soc. 149 (2002) A293–A296. [4] E.J. Cairns, E.L. Simons, A.D. Tevebaugh, Nature 217 (1968) 780–781. [5] S. Suzuki, H. Muroyama, T. Matsui, K. Eguchi, J. Power Sources 208 (2012) 257–262. [6] F.J. Vidal-Iglesias, J. Solla-Gullón, P. Rodriguez, E. Herrero, V. Montiel, J. M. Feliu, A. Aldaz, Electrochem. Commun. 6 (2004) 1080–1084. [7] A.C.A. de Vooys, M.F. Mrozek, M.T.M. Koper, R.A. van Santen, J.A.R. van Veen, M.J. Weaver, Electrochem. Commun. 3 (2001) 293–298. [8] H. P. Boehm, Discuss. Faraday Soc., 1971, 52, 264–275. [9] C. Morterra, V. Bolis, G. Magnacca, J. Chem. Soc., Faraday Trans., 92 (1996) 1991–1999. [10] S. Sharma, B. G. Pollet, J. Power Sources 208 (2012) 96–119.

Effect of Y<sub>2</sub>O<sub>3</sub> on Microstructure and Oxidation Behavior of Aluminide Coating on Ni-Based Superalloy

The oxidation behavior of Ni-based superalloy GH586 which is treated by pack-cementation aluminizing was investigated. Scanning electron microscope and X-ray diffraction were used to analyze the microstructure of aluminide coatings and the surface morphologies of the oxide scales. Results show that the main phase of the aluminide coatings was NiAl. The aluminide coating can be formed at lower temperature due to the addition of rare earth oxide in the mixture powders. The thickness of aluminide coating at 900°C was about 110μm, and another aluminide coating with rare earth oxide Y2O3 at 800°C was about 38μm. The oxidation kinetics of aluminized specimens approximately followed a parabolic oxidation law at 1000°C. The morphology of the oxidation scales was primarily θ-Al2O3 with minor α-Al2O3. The scales of the coatings with rare earth oxide Y2O3 after oxidation was more dense.

Short Review on Rare Earth and Metalloid Oxide Additions to MgB<sub>2</sub> as a Candidate Superconducting Material for Medical Applications

MgB2 is a candidate for the fabrication of magnetic coils used in medical applications. Our review indicate that oxide additions based on the rare earth or metalloid elements show improvement of the MgB2 critical current density (Jc) and the irreversible magnetic field (Hirr) without significantly affecting the critical temperature (Tc) However, the characteristics of the additions and the technological approaches show a strong influence in controlling superconducting properties. Both additions and the technology need a careful and complex optimization in order to enhance the Jc and Hirr.

Synergistic effects of rare earth oxides on intumescent flame retardancy of Nylon 1010/ethylene-vinyl-acetate rubber thermoplastic elastomers

Synergistic effects of two kinds of rare earth oxides (REOs), samarium oxide (Sm2O3) or lanthanum oxide (La2O3) on the intumescent flame retardancy of Nylon 1010/ethylene-vinyl-acetate rubber (EVM) thermoplastic elastomers (TPE) were studied systemically. The limiting oxygen index (LOI) of intumescence flame retardant (IFR)-TPE increased from 30.5 to 32.5 and 34 when 0.5 wt% of IFR was substituted by La2O3 and Sm2O3, respectively. Sm2O3 showed higher synergistic effectivity than La2O3. Cone calorimetry tests confirmed that REOs enhanced flame retardancy of IFR-TPE. Smoke and CO production rate slightly decreased after incorporation of REOs as compared to IFR-TPEs without REOs, indicating relatively reduced combustion hazard. By thermalgravimetric analyses (TGA), it was found that the presence of REOs promoted the esterification and carbonization process in low-temperature range while enhanced the thermal stability of IFR and IFR-TPEs in high-temperature range. X-ray diffraction (XRD) proved that the interaction of Sm2O3 with IFR resulted in the formation of samarium phosphate (SmPO4) with high-thermal stability. Rheological measurements showed that the complex viscosities of the IFR-TPEs increased with the addition of REOs, which might aid in suppressing melt dripping. For mechanical properties, incorporation of REOs led to higher modulus, similar tensile strength but lower elongation at break as compared to IFR-TPEs without REOs.

From wood wastes to hydrogen – Preparation and catalytic steam reforming of crude bio-ethanol obtained from fir wood

Fir wood wastes were used to produce crude bio-ethanol by two methods: simultaneous saccharification and fermentation (SSF) and acid hydrolysis followed by the fermentation of the acid hydrolyzate. The main components of crude bio-ethanol are ethanol and acetic acid. In addition, low concentrations of a wide range of alcohols, acids, esters, ethers and aldehydes are also present. Ethanol concentration is higher in the SSF process than in the acid hydrolysis: 43.69 g/L compared to 37.53 g/L, respectively. Opposite to ethanol concentration, the acetic acid concentration is higher in the acid hydrolysis process: 16.36 g/L compared to 10.24 g/L, respectively. The crude bio-ethanol was used to produce hydrogen by catalytic steam reforming. The tested catalysts were the common Ni/Al2O3 and two rare earth oxides promoted Ni catalysts: Ni/La2O3–Al2O3 and Ni/CeO2–Al2O3 prepared by successive wet impregnation. The characterization techniques revealed that the addition of rare earth oxides improves the Ni dispersion and the reducibility of the promoted catalysts. The best feed rate which assures the optimal ratio between conversion and catalyst deactivation is 0.8 mL/min bio-ethanol. The addition of extra oxide (La2O3 and CeO2) to the support improves the ethanol conversion especially at 250 °C, but no significant effect on the acetic acid conversion was observed. At 250 °C the ethanol conversion is almost 90% for Ni/La2O3–Al2O3 and Ni/CeO2–Al2O3, but the acetic acid conversion is below 30% for all catalysts. At 350 °C both ethanol and acetic acid present maximum conversion. At this temperature the best hydrogen production is obtained for Ni/La2O3–Al2O3 due to better ethanol conversion and better selectivity for hydrogen formation. At 350 °C the promoted catalysts are stable for 4 h time on stream, different degrees of deactivation being obtained at lower temperatures.

Microstructure and dielectric properties of Ba[Ti1 − x (Ln1/2Nb1/2) x ]O3 ceramics

We have studied the microstructure and dielectric properties of barium titanate-based ceramics containing niobium oxide and rare-earth (Nd, Sm, Gd, Dy, and Tm) oxide additions in a ratio needed for the formation of mixed perovskite solid solutions with the general formula Ba[Ti1 − x(Ln1/2Nb1/2)x]O3. It was found that, after sintering at 1100–1120°C with the use of a zinc oxide-based sintering aid and manganese carbonate additions, the ceramics had a core-shell structure in which the core of the grains consisted of barium titanate and the shell consisted of a barium titanate-based solid solution. The average grain size of the major phase in the ceramics was within 0.7 μm. The ceramics contained additional phases in the form of inclusions which occasionally exceeded 5 μm in size. Their composition was determined. The Nd-, Sm-, and Gd-containing materials were shown to have the greatest potential as a base for the development of new engineering materials of stable groups with high dielectric permittivity for multilayer capacitors with electrodes containing 70% Ag and 30% Pd.

Thermal shock resistance of Si3N4 and Si3N4–SiC ceramics with rare-earth oxide sintering additives

The influence of various rare-earth oxide additives and the addition of SiC nanoparticles on the thermal shock resistance of the Si3N4 based materials was investigated. The location of SiC particles inside the Si3N4 grains contributed to a higher level of residual stresses, which caused a failure at the lower temperature difference compared to the composites with a preferential location of the SiC at the grain boundaries. A critical temperature difference increased with an increasing ionic radius of RE3+ for both the composites and the monoliths. The critical temperature difference for the composite (580 °C) and the monolith (680 °C) sintered with La2O3 was significantly higher compared to the composite and the monolith doped with Lu2O3 (430 °C). A good agreement was found between the results of the critical temperature difference estimated by the indentation quench test and that obtained by the strength retention method.

Thermodynamic properties of the Lu2O3–ZrO2 solid solutions by Knudsen effusion mass spectrometry at high temperature

The zirconium oxide based ceramics with addition of rare-earth metal oxides is widely used for production of high temperature materials. Knudsen effusion mass spectrometry was used to study vaporization processes and thermodynamic properties of solid solutions in the ZrO2–Lu2O3 system at the temperature 2700K. The Lu, LuO, ZrO and ZrO2 were found as the main vapor species over the samples studied. The ZrO2 and Lu2O3 activities, the Gibbs free energy of formation, the excess Gibbs free energy of formation in the samples studied were calculated. The activities of lutetium oxide in all concentration range of condensed phase have low negative deviation from ideal case whereas zirconium dioxide activities have strong negative deviation from ideal case.

Review of the preparation, characterization, and luminescence properties of Pr3+-doped CaTiO3 phosphors

In this paper we review the luminescence properties of Pr3+-doped CaTiO3 phosphors, the different methods of sample preparation, and characterization of the materials by use of different techniques, for example X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermo-gravimetric analysis, and atomic force microscopy. Solid-state, sol–gel (SG), and combustion methods are most often used for preparation. The high calcining temperature of the solid-state method can be reduced by addition of rare earth oxides (lanthanide series) Ln2O3 and Lu2O3. By use of tetra-n-butyl titanates and calcium nitrates as raw material in the modified solid-state method the luminous properties of samples can be optimized at lower sintering temperatures (600 °C) in less time. SG procedures lead to substantial reinforcement of red photoluminescence intensity so can be regarded as the best technique for phosphor preparation.

Laser cladding in-situ NbC particle reinforced Fe-based composite coatings with rare earth oxide addition

Over the past decade, researchers have demonstrated much interest in laser cladded metal matrix composite coatings for its good wear resistance, corrosion resistance and high temperature properties. The effects of RE on the microstructure and properties of laser coatings have also got more and more attention. In this paper, in situ Fe-NbC composite coatings with different CeO2 addition were produced on die steel by laser cladding. The formation mechanism of NbC particles was analyzed. The effects of RE on microstructure and micro-hardness of coatings were investigated. It was revealed that larger NbC particles with hard edges formed around Nb particles, and smaller flocculent NbC particles formed by the chemical reaction of Nb and solid graphite in the molten pool. CeO2 plays important roles in reducing micro-porosities, refining grains, and improving the precipitation of NbC. Therefore, the average micro-hardness and its smoothness from the top to the bottom of the coating were improved after adding CeO2.

Structure and electrical properties of Ca0.28Ba0.72Nb2O6 ceramics with addition of rare earth oxides (CeO2, La2O3)

Ca0.28Ba0.72Nb2O6 (CBN28) ceramics with addition of CeO2 and La2O3, were prepared by the conventional ceramic fabrication technique. XRD results showed that the single tungsten bronze structure of CBN28 was not changed by adding CeO2 or La2O3. SEM results indicated that both CeO2 and La2O3 dopants were effective in inhibiting the grain growth and suppressing the anisotropic growth behavior in tungsten bronze structure. It was also found that both two kinds of dopants had remarkable effects on the dielectric and ferroelectric properties of CBN28 ceramics. Compared with CBN28 ceramics, the dielectric constant around room temperature εr, dielectric loss tanδ, the degree of diffuseness γ and coercive field Ec were all ameliorated when doping proper amount of CeO2 or La2O3. The comprehensive electric performance was obtained in CBN28–0.3wt% CeO2 and CBN28–0.4wt% La2O3 ceramics. Besides, the underlying mechanism for variations of the electrical properties due to different dopants was explained in this work.

Nano Crystallite ZrO<sub>2</sub>, La<sub>2</sub>O<sub>3 </sub>and CeO<sub>2</sub>: Synthesis, Characterization and their Properties

It is well known that a minor addition of rare earth oxides can provide a beneficial effect towards various catalytic reactions. Use of rare earth oxide in different applications could improve commercial productivity in an affordable way. Among the rare earth oxides, ZrO2, La2O3 and CeO2 are very interesting due to their various characteristics showing a large range of applications in organic reactions. The changes in the molecular properties of materials at the nano scale level greatly enhance their physical properties as well as chemical properties and activity. Due to the extremely small size of the particles, an increased surface area is provided to the reactant enabling more molecules to react at the same time, thereby speeding up the process. In this work, the enhancement in the catalytic activity of these nano structured rare earth oxides has been studied under different reaction conditions. Nano crystalline ZrO2, La2O3 and CeO2 samples were synthesized using precipitation method and optimum reaction conditions have been established; whereas the corresponding bulk samples were synthesized by combustion method. The identification of phase and crystalline size of synthesized oxides have been done by X-ray diffraction, the band gape of these three oxides in both the forms has been analyzed by UV absorbance and surface area has been determined by gas adsorption analysis (BET). Moreover their different properties and the activity of nano crystallite oxides have also been compared with their bulk counterparts. Even the activity of ZrO2 is also compared with the rare earth oxides La2O3 and CeO2.

RE-Boronizing below Beta Transus Temperature on TC4 Titanium Alloy Surface

Ti6Al4V (TC4) slices were boronized with rare earth oxide (RE) addition in the agent at 950°C (below β phase transus of TC4). The morphology, phases, properties and structures of TC4 matrix and boride layers were studied. The results show that the boride layer on the surface of TC4 consists of TiB2 and TiB dual compounds. The boride layer is compact, uniform and less porous compared with that obtained at 1050°C (above β phase transus of TC4), and the hardness profile and brittleness of the layers are improved to a certain extent. Lower temperature boronizing can effectively prevent the growth of coarse β phase grains. Duplex microstructure is obtained in TC4 matrix, and the work piece distortion is reduced.

The correlation between the microstructure and macroscopic properties of (K,Na,Li)(Nb,Ta)O3 ceramic via rare earth oxide doping

Li0.05(Na0.51K0.49)0.95(Nb0.95Ta0.05)O3 (abbreviated as KNNLT) with addition of La2O3, CeO2, respectively, were prepared by a conventional ceramic fabrication technique. X-ray diffraction pattern shows that the coexistence of orthorhombic and tetragonal phase structure for KNNLT was not changed by adding La2O3 or CeO2. SEM observation indicates that these two kind dopants have a remarkable effect on the microstructure of KNNLT ceramics. The To–t (temperature for the orthorhombic to tetragonal phase) was shifted toward lower temperature by the addition of rare earth oxide and typical relaxor ferroelectric is demonstrated especially for KNNLT with high content of La2O3. An addition of 0.5% CeO2 could strengthen the piezoelectric and dielectric constant of KNNLT ceramics to some extent. KNNLT ceramics with 0.5% CeO2 obtain optimum electrical properties: d33=272 pC/N, kp=45%, εr=784 and tan δ=1.4%.