Addition Of Rare Earth Oxides Research Articles

Effects of flaky rare earth oxide additives on the high temperature performance of nickel electrodes

Effects of flaky rare earth oxide additives including Er 2O 3, Tm 2O 3, and Yb 2O 3, Lu 2O 3 on high temperature and high rate discharge performance of nickel electrodes were investigated. The discharge efficiency at 0.2C reached 96% at 60 °C for electrodes with 1 at.% flaky rare earth oxides. The high rate discharge performance for electrodes with flaky rare earth oxides were improved significantly, for example, discharge efficiency at 5C improved from 50% to 70%. The results showed that the end charging potential of the nickel electrodes with flaky rare earth oxides were higher than that without rare earth oxide additives, but lower than that with normal rare earth oxide additives. The CVs experimental results suggested that flaky rare earth oxides increased the oxygen evolution potential and improved the reversibility of nickel electrodes.

Characterization of rare-earth doped Si3N4/SiC micro/nanocomposites

Influence of various rare-earth oxide additives (La2O3, Nd2O3, Sm2O3, Y2O3, Yb2O3 and Lu2O3) on the mechanical properties of hot-pressed silicon nitride and silicon nitride/silicon carbide micro/nano-composites has been investigated. The bimodal character of microstructures was observed in all studied materials where elongated ?-Si3N4 grains were embedded in the matrix of much finer Si3N4 grains. The fracture toughness values increased with decreasing ionic radius of rare-earth elements. The fracture toughness of composites was always lower than that of monoliths due to their finer Si3N4/SiC microstructures. Similarly, the hardness and bending strength values increased with decreasing ionic radius of rare-earth elements either in monoliths or composites. On the other hand, the positive influence of finer microstructure of the composites on strength was not observed due to the present defects in the form of SiC clusters and non-reacted carbon zones. Wear resistance at room temperature also increased with decreasing ionic radius of rare-earth element. Significantly improved creep resistance was observed in case either of composite materials or materials with smaller radius of RE3+. .

Rare earth oxides as nanoadditives in 3-D nanocomposite scaffolds for bone regeneration

Nanocomposite scaffolds of bioactive glass foams containing tailor made rare earth oxide (i.e. nanoceria) additives were demonstrated to enhance the production of collagen by HMSCs (Human Mesenchymal Stem Cells) compared to bioactive glass scaffolds without nanoceria. The addition of osteogenic supplements was not required for this to occur. Two different preparations of nanoceria were successfully incorporated in 3-D bioactive glass foam scaffolds and were compared with bioactive scaffolds without nanoceria. The nanoparticles had individual particle sizes of 3–5 nm while the agglomerate size varied from 5–15 nm. Preliminary investigations show that nanoceria is non toxic to the cells. After 10 days of culture, nanoceria containing scaffolds showed enhanced osteoblastic differentiation of HMSCs and collagen production compared to the scaffolds without nanoceria even in the absence of any osteogenic supplements (i.e. ascorbic acid, dexamethasone and β-glycerophosphate). This could be due to the incorporation of nanoceria, which acts as an oxygen buffer thereby regulating the differentiation of HMSCs. Further investigations are currently underway to determine the role of the nanoceria controlled oxygen buffering on the HMSC differentiation.

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

Particulate reinforced metal matrix composite (PR-MMC) has excellent properties such as good wear resistance, corrosion resistance and high temperature properties. Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles. Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements, was favorable for the formation of in-situ synthesized carbide particles. In this paper, rare earth oxide (RE 2O 3) was added into the clad powder mixture to investigate the effects of RE 2O 3 on the in-situ carbide particle formation in Fe-based composite coatings. Through the analysis using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS) and transmission electron microscope (TEM), it was revealed that: (1) Adding RE 2O 3 to the Fe-based powder mixture could effectively reduce cracks and porosities and the coating surface was more smooth; (2) The solubility of carbon could be improved which increased the eutectic degree of the microstructure; (3) RE 2O 3 could promote the nucleation of the reinforcement particles as heterogeneous nuclei. During the precipitating process of the carbide particles, some RE 2O 3 powders still existed while others react with carbon in the melt to form rare earth carbides. Both of them acted as heterogeneous nuclei for the formation of particles.

Effects of rare earth oxide additives on the thermal behaviors of aluminum nitride ceramics

The effects of Y2O3 and Er2O3 on the sintering behaviors, thermal properties and microstructure of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased; the relative density and thermal behavior can be improved by adding rare earth oxide in AlN ceramics. For AlN ceramics with 3 wt.% Er2O3 additive, the relative density is 98.8%, and the thermal conductivity reaches 106 W·m−1·K−1. The microstructure research found that no obvious aluminum erbium oxide was found in AlN ceramics doped with 3 wt.% Er2O3, which favored the improvement of the thermal conductivity of AlN ceramics.

Influence of additive system (Al2O3-RE2O3 , RE = Y, La, Nd, Dy, Yb) on microstructure and mechanical properties of silicon nitride-based ceramics

Silicon nitride based ceramics have been widely used as structural ceramics, due mainly to their thermo-mechanical properties such as high density, high thermal shock resistance, corrosion resistance and chemical stability. The aim of this study was to determine the influence of rare earth and aluminum oxide additions as sintering aids on densification, microstructure and mechanical properties of silicon nitride. Silicon nitride mixtures with 91 wt. (%) Si3N4 and 9% wt. (%) additives were prepared and sintered. The density, microstructure and mechanical properties of the sintered specimens of these mixtures were determined. In most specimens, scanning electron microscopic examination and X ray diffraction analysis revealed elongated grains of β-Si3N4 with aspect ratio of about 2.0 and dispersed in a glassy phase. The density of the sintered specimens was higher than 94% of the theoretical density (td) and specimens with La2O3 and Al2O3 additions exhibited the highest value. The results of this investigation indicate that the rare earth ion size influences densification of silicon nitride, but this correlation was not observed in specimens containing two different rare earth oxides. The hardness values varied in direct proportion to the density of the specimens and the fracture toughness values were influenced by the composition of the intergranular glassy phase.

Effects of Re 2O 3 (Re = La, Nd, Y and Yb) addition in hot-pressed ZrB 2–SiC ceramics

ZrB 2–20 vol% SiC composites with 3 vol% Re 2O 3 rare-earth oxide (Re = La, Nd, Y or Yb) were hot pressed to near full-density at 1900 °C. The La 2O 3 and Nd 2O 3 additions not only caused the formation of an amorphous grain boundary phase and enhanced densification, but also resulted in substantial ZrB 2 and SiC grain growth. In contrast, the Y 2O 3 and Yb 2O 3 additions resulted in the formation of crystalline (Y/Yb) 2Zr 2O 7 and enhanced densification without ZrB 2 and SiC grain growth. The hardness was improved by the rare-earth oxide addition, especially with Y 2O 3 and Yb 2O 3. The La 2O 3 and Nd 2O 3 only had a minor effect on the fracture toughness, whereas the Y 2O 3 and Yb 2O 3 additions increased the fracture toughness. The type of Re 2O 3 addition was found to influence the nature of the grain boundary and the concomitant fracture and toughening mechanisms.

Effects of Rare-Earth Oxides on Time-Dependent Dielectric Properties of Mn-Doped BaTiO3

The effects of rare earth oxides on dielectric properties of BaTiO3 have been investigated. The addition of R2O3 (R: Dy, Ho, Yb) significantly decreased the capacitance change with time under a DC electric field. Yb-doped specimens exhibited the lowest aging rate in the second stage, which is due to the larger population of defect dipoles associated with oxygen vacancies. The DC bias aging behavior of Mn-doped BaTiO3 was also suppressed by rare-earth oxides. The addition of rare-earth oxides led to an increase in the leakage current of BaTiO3. Specimens codoped with rare-earth and manganese oxides showed lower leakage currents with moderate DC bias aging rates.

Sintering, high temperature strength and oxidation resistance of liquid-phase-pressureless-sintered SiC–AlN ceramics with addition of rare-earth oxides

SiC–AlN composites can be pressureless sintered with the addition of rare-earth oxides (RE = Y, Yb, Er, Lu, Ho, Sm, Ce) and without protective powder bed. Sintered bodies showed high density (≥97% T.D.) and were mainly composed by 2H SiC–AlN solid solution with additive containing grain boundary phases. The high temperature strength and oxidation resistance of the composites were also investigated and correlated with the cationic radii of the oxide additives. The flexural strength at 1500 °C increased from 269 MPa to 587 MPa as direct consequence of the rare-earth cationic radius decrease. The specific weight gain during oxidation at 1500 °C for 200 h showed the same behaviour, decreasing from 12.60 mg/cm 2 to 3.13 mg/cm 2.

Modification of Fe–Mn mixed oxide COS removal sorbent by rare-earth oxides addition

In order to develop highly active sorbent for COS removal, Fe–Mn mixed oxides doped with CeO 2, La 2O 3 or Sm 2O 3 were studied. The effects of these promoters on the structural properties of Fe–Mn oxides were investigated by XRD, BET, TPR and TEM techniques. XRD results revealed that the degree of crystallinity of Fe–Mn oxide phase decreased due to the addition of rare-earth oxides. Doping with CeO 2, La 2O 3 or Sm 2O 3 led to an increase in BET surface area of the sample. TPR studies showed that the reactivity of the reduction of doped samples increased in the temperature range of 300–450 °C. In addition, the desulfurization test was performed at 325 °C with a gas hourly space velocity of 1000 h −1. It was found that the addition of 3% La 2O 3 greatly improved the absorption sulfur capacity of the sorbent, while the sorbent doped 3% CeO 2 achieved a sufficiently high purifying degree before breakthrough.

ZnO varistors with high voltage gradient and low leakage current by doping rare-earth oxide

The surge arrester of 1000 kV gas-insulated substation (GIS) needs ZnO varistor with high voltage gradient to effectively improve the potential distribution along ZnO varistor column inside the metal-oxide surge arresters. In this paper, the electrical and structural parameters of ZnO varistors are changed by doping with some rare-earth oxides, and the mechanism which leads these changes is discussed. When rare-earth oxide additives are added into ZnO varistors, the growing speed is slowed down due to the stabilization of the new spinel phases formed in the grain-boundary by rare-earth oxide additives, then the size of ZnO grains is smaller, and the voltage gradient of varistor increases obviously. By adding suitable amount of oxides of metal Co and Mn, the leakage current can be effectively decreased and the nonlinearity coefficient increased. The novel ZnO varistor samples sintered with the optimal additives have a voltage gradient of 492 V/mm, and the nonlinearity coefficient of 76, but their leakage currents are only 1 μA.

The role of La2O3 in direct laser sintering of submicrometre WC–Cop/Cu MMCs

This paper presents a detailed investigation of the influence of rare earth (RE) oxide (La2O3) addition on densification and microstructure of direct laser sintered submicrometre WC–Cop/Cu metal matrix composites (MMCs) possessing 50.0 wt% reinforcement (WC–Co). It was found that with increasing La2O3 addition to a suitable amount (1.0 wt%), the particulate dispersion was homogenized and the particulate/matrix interfacial bonding was improved. However, with an excessive addition of La2O3 (1.5 wt%), a heterogeneous microstructure consisting of highly accumulated particulates was present. The exact metallurgical roles of RE element in direct laser sintering of particulate reinforced MMCs were addressed. It showed that a proper addition of RE element (i) decreased surface tension of the melt and enhanced solid–liquid wettability; (ii) dragged and/or pinned grain/phase boundaries and resisted grain coarsening and particulate aggregating. However, the balling phenomenon occurred and the activity of RE atoms decreased at an even higher La2O3 content, thereby producing detrimental effects on laser forming ability.

Preparation and laser induced damage properties of rare earth doped BAS glass

Rare earth doped B 2O 3-Al 2O 3-SiO 2 glass (RE x BAS, x=5, 10, 20; RE=La, Sm) were prepared by solid state reaction method. Optical transmission spectra of such glass were characterized by ultraviolet spectrometers, and 1064 nm laser induced damage performance was investigated through the method of “1-on-1”. The results indicated that there was a strong absorptive peak near 1064 nm in Sm x BAS glass, the peak was enhanced with increasing x. While La x BAS glass was transparent to 1064 nm laser, at the same time, the results of laser induced damage showed that the anti-laser induced damage performance of such glass was strengthened with the addition of rare earth oxide. Furthermore, the laser induced damage threshold (LIDT) of Sm x BAS glass was significantly higher than that of La x BAS glass. Consequently, Sm 3+ doping was favor in the improvement of anti-laser induced damage performance for BAS glass.

Roles of rare earth oxide additives in millimeter-wave sintering of AlN

Roles of rare earth oxide (RE 2O 3) additives in millimeter-wave(MM) sintering of AlN were investigated from the standpoints of phase diagram, heating characteristics of rare earth oxides, and morphology of intergranular oxide phase. In the millimeter-wave sintering of AlN, densification temperature decreased with the decrease of the ionic radius of rare earth ion and was closely related with the eutectic temperature in the RE 2O 3-Al 2O 3 binary system. The lowest densification temperature in the millimeter-wave sintering of AlN with Yb 2O 3 additive was attributed to the largest heating rate of Yb 2O 3·Al 2O 3 binary oxide under millimeter-wave radiation. Furthermore, the lowest densification temperature could be attained while selecting the Yb 2O 3 content so as to form the intergranular phase with the eutectic composition in the Yb 2O 3-Al 2O 3 binary system. The result showed good agreement with the above mentioned during the sintering of Si 3N 4 with Yb 2O 3-Al 2O 3 additive. From TEM observation, it was verified that film-like intergranular oxide phase formed under millimeter-wave radiation was favorable for attaining high thermal conductivity in the Yb 2O 3 added AlNs.

High performance rare earth oxides LnO x (Ln = La, Ce, Nd, Sm and Dy)-modified Pt/SiO 2 catalysts for CO oxidation in the presence of H 2

The catalytic activities of low-temperature CO oxidation and preferential CO oxidation (PROX) in rich-H 2 stream over the Pt/SiO 2 and rare earth oxides modified Pt/SiO 2 catalysts have been investigated. The addition of rare earth oxide additives to the Pt/SiO 2 catalyst can promote the catalytic performance remarkably. The catalytic activities for PROX are dependent on the basicities of these oxides. The higher basic strength leads to higher activity. For Pt–CeO 2/SiO 2, the catalytic activity depends strongly on the content of CeO 2 and on the mole ratio of CO/O 2. XRD and H 2-temperature-programmed reduction (TPR) results show that the additives not only improve the dispersion of metallic Pt on the support surface, but also increase the reducibility of PtOx in Pt–CeO 2/SiO 2. The formation of the Pt–Ce alloy decreases the electron back-donation from the Pt 5d orbital to the 2 σ* orbital of CO, and consequently suppresses CO–Pt bonding, resulting in the lowered CO coverage.

Effects of Rare Earth Oxides on Microstructures and Properties of Magnesia Refractories

The effects of Y2O3, La2O3 and Nd2O3 on the sintering, microstructure and mechanical properties of magnesia refractories were investigated. Addition of rare earth oxide (ReO) to magnesia refractories increases the bulk density, decreases the porosity and improves the mechanical strength of the refractories. The improved sinterability was attributable to the vacancies generation associated with the solid-solution reactions between MgO and ReO. In the samples with ReO, rare earth silicate phases form at magnesia grain boundaries, providing additional bonding between magnesia grains and between magnesia grains and matrix. Consequently, the samples with ReO showed much higher high temperature strengths than those without ReO.

Fabrication and Biocompatibility of Gradient Bioceramic Coatings on Titanium Alloy Substrate by Laser Cladding

Based on a high power CO2 laser beam passing by pyramid polygon mirror, the bioceramic coatings of gradient composition were fabricated on titanium alloy substrate (Ti-6Al-4V). The relations among laser processing parameters, microstructure and biocompatibility of the gradient bioceramic coatings were investigated. The results indicated that the contents of rare earth oxide additions had an immediate effect on the formation of bioactive phases. The gradient bioceramic coatings showed favorable biocompatibility in vivo after they were implanted into canine femur for 45, 90, and 180 days, respectively. The bioceramic coatings of Ca/P=1.4 and 0.6wt.% Y2O3 totally combined with new bones merely implanted for 45 days. Furthermore, the MTT (Methyl Thiazolyl Tetrazolium) colorimetry results of cell proliferation demonstrated that the cell growth distinctly increased on the gradient bioceramic coatings by laser cladding compared with the un-treated titanium alloy substrate.

Purification of chemical feedstocks by the removal of aerial carbonyl sulfide by hydrolysis using rare earth promoted alumina catalysts

The effect of rare earth doping of alumina catalysts is investigated for the carbonyl sulfide (COS) hydrolysis reaction (COS + H2O = CO2 + H2S). The effect of the catalyst preparation method is described and discussed, and three methods are compared, namely: impregnation by incipient wetness, coprecipitation and deposition precipitation. The most effective catalysts are prepared using the incipient wetness impregnation method. The addition of rare earth oxides, namely Y2O3, Gd2O3, Nd2O3, La2O3, increases the basicity of the material as shown by pulsed CO2 chemisorption and the basicity increases with the amount of rare earth oxide added. CO2 TPD shows that the La2O3-doped alumina has the strongest basic sites. The promoted catalysts are all effective for the COS hydrolysis reaction and the best results are obtained with Y2O3-doped materials, as these have the most pronounced promotion of activity over the reaction timescale we have examined. The combination of the results for COS conversion with the H2S selectivity data and the effects of H2S pre-treatment shows that a highly active catalyst also has a high H2S selectivity. The La2O3-doped materials deactivate rapidly and have poor H2S selectivities, and we propose that the higher basicity of this material leads to reaction with the acidic COS and H2S leading to the formation of the less basic lanthanum sulfide. This study has presented results for the first time showing that an alumina catalyst for COS hydrolysis can be promoted by the addition of rare earth oxides, and this is related to the enhanced basicity of the promoted catalyst.

Comparison of corrosion modes of oxidation and sulphidation of weld metal with rare earth oxides

Through addition of rare earth oxides into the coating of electrodes, the high temperature oxidation and sulphidation resistance of weld metal were studied. The weight loss test results showed that the addition of rare earth oxides could improve the high temperature resistance of weld metal, especially in sulphidation environment. The reasons for the difference of corrosion rate between oxidation and suphidation were studied with the application of SEM. It was believed that different corrosion modes were the main reasons for that: oxidation rate was mainly decided by the Cr content of the weld metal and sulphidation rate was mainly decided by the inner corrosion occurring in the grain boundary. The marked effect of rare earth oxides in sulphur environment was related to the corrosion mechanism.

Improving the hydration resistance of lime-based refractory materials

Studies to improve the hydration resistance of lime-based materials are reviewed. The methods described include densification of the lime aggregate by addition of sintering aids and surface treatment. Methods for assessing hydration resistance are also reviewed. Additions of ZrO2, TiO2 (including Ti chelating compounds) and rare earth oxides can improve the hydration resistance of CaO aggregate by, it is believed, enhancing solid state sintering without sacrificing refractoriness via formation of hydration resistant solid solutions. Fe2O3, Al2O3 (as well as Al chelating compounds and Al metal), CuO and V2O5, act as liquid forming aids. These additives improve the sintering of lime and subsequently the hydration-resistance via formation of liquids at high temperature which cool to produce hydration-resistant solids surrounding the lime polycrystals. However, the liquids formed may significantly reduce the refractoriness of lime materials, thus eroding their particular advantage. The same problem is thought to arise on addition of salts such as CaCl2 and NaF. The hydration resistance of CaO aggregates can also be improved by surface carbonation and surface treatment using acids, phosphates, machine oils, silicones and fluxes. Surface carbonation of CaO aggregate is proving to be a promising experimental method, but practical problems currently limit its application on an industrial scale. A combination of the two methods mentioned above should therefore be even more effective in improving the hydration resistance of CaO refractory materials.