Addition Of Rare Earth Oxides Research Articles

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.

Probation on Abrasion of Ceramic Cutting Tools

Abrasion of ceramic based and ceramic coated cutting tools is the highlighted problem, but little progress has been made. A detailed study of carbides, nitrides, borides, oxides, whiskers or metal additives of small amount and a variety of anti-wear mechanism was given so that the wear resistance of ceramic matrix tool can be greatly improved. A variety of abrasion of ceramic coated cutting tools was also studied, such as adhesive abrasion resistance, grinding abrasion resistance, fretting abrasion resistance, fatigue abrasion resistance, corrosion abrasion resistance, hot crack abrasion resistance, diffusion abrasion resistance and phase change abrasion resistance, etc. For example, with the increase of metal content in metal carbide ceramic coating, its hardness decreases; and coating hardness is different when coated with different coating technique, and its abrasion performance is also related to shape, size, distribution and post-processing of laser remelting. Abrasion extent, key factors, abrasion mechanism and applied range were also described. It is noticed that addition of rare earth oxides can improve strength, toughness, density, microstructure, phase composition of ceramic cutting tools and reduce sintering temperature.

Effects of Behaviors of Aluminum Nitride Ceramics with Rare Earth Oxide Additives

The effects of three types of additives, Y 2O 3, Nd 2O 3 and Er 2O 3 on the behaviors of AlN ceramics were investigated. The experimental results showed that the sintering temperature could be decreased and the mechanical behavior could be improved by adding rare earth oxide in AlN ceramics. The highest strength and fracture toughness of AlN ceramics with 2% Y 2O 3 addition were 311 MPa and 3.5 MPa·m 1/2, respectively. Second phase of AlN ceramics with Y 2O 3 addition was identified as Y 3Al 5O 12 formed by the reaction with Al 2O 3, meanwhile that with Nd 2O 3 was identified as NdAlO 3. The fracture behavior of AlN ceramics with Y 2O 3 and Nd 2O 3 were a mixed mode of transgranular fracture and intergranular fracture. Because of the high evaporation rates of Er 2O 3 (1.2 × 10 −5 g·cm −2), no aluminium erbium oxide was found in the AlN ceramics doped with Er 2O 3. So the dielectric loss tanger(tanδ) and thermal conductivity of AlN ceramics doped with Er 2O 3 were best.

Au/M xO y/TiO 2 catalysts for CO oxidation: Promotional effect of main-group, transition, and rare-earth metal oxide additives

Au/TiO 2 catalysts are active for CO oxidation, but they suffer from high-temperature sintering of the gold particles, and few attempts have been made to promote or stabilize Au/TiO 2. Our recent communication addressed these issues by loading gold onto Al 2O 3/TiO 2 prepared via surface-sol–gel processing of Al( sec-OC 4H 9) 3 on TiO 2 [W.F. Yan, S.M. Mahurin, Z.W. Pan, S.H. Overbury, S. Dai, J. Am. Chem. Soc. 127 (2005) 10480–10481]. In our current full paper, Au/Al 2O 3/TiO 2 catalysts were prepared alternatively by thermal decomposition of Al(NO 3) 3 on TiO 2 followed by loading gold, and the influences of the decomposition temperature and Al 2O 3 content were systematically surveyed. This facile method was subsequently extended to the preparation of a battery of metal oxide-modified Au/TiO 2 catalysts virtually not reported. It was found that Au/TiO 2 modified by CaO, NiO, ZnO, Ga 2O 3, Y 2O 3, ZrO 2, La 2O 3, Pr 2O 3, Nd 2O 3, Sm 2O 3, Eu 2O 3, Gd 2O 3, Dy 2O 3, Ho 2O 3, Er 2O 3, or Yb 2O 3 could retain significant activity at ambient temperature even after aging in O 2–He at 500 °C, whereas unmodified Au/TiO 2 lost its activity. Moreover, some 200 °C-calcined promoted catalysts showed high activity even at about −100 °C. The deactivation and regeneration of some of these new catalysts were studied. This work furnished novel catalysts for further fundamental and applied research.

Enhancement of the red emission in CaTiO 3:Pr 3+ by addition of rare earth oxides

Enhancement of the 1D 2– 3H 4 red emission of CaTiO 3:Pr 3+ with addition of rare earth oxides Ln 2O 3 (Ln = Lu, La, Gd) is reported. Ca 2+ and Ti 4+ in CaTiO 3 can be substituted by Ln 3+ ions as donors and acceptors, respectively. Ca 2+ and Ti 4+ vacancies, as quenching centers in the host, are effectively suppressed by the self-compensation, leading to the increase of lifetimes and then the emission efficiency of 1D 2. The red fluorescence intensity for CaTiO 3:Pr 3+ phosphor co-doped with 5 mol% Lu 2O 3 is nearly 3 times greater than that of the Lu-free samples.

Effect of rare earth oxide additions on oxidation behavior of AISI 304L stainless steel

AISI 304L stainless steel powder compacts containing 2 vol% high purity rare earth oxides were prepared by mixing the different powders in a vibratory mill followed by pressing. The compacts thus obtained were sintered in a vacuum furnace and isothermal oxidation measurements were carried out in a muffle furnace, in air, up to 200 hours at 900 °C. The oxidized surfaces were examined in a scanning electron microscope and micro regions of the reaction products were studied using energy dispersive analysis. The addition of rare earth oxides decreased the oxidation rate of the stainless steel. Further evidence of predominant oxygen ion diffusion controlling the overall oxidation process in rare earth containing chromium oxide forming alloys has been observed.

Effect of Addition of Rare Earth Oxide Concentrates on Oxidation Resistance of AISI 304L

Rare earth elements are often added to chromium dioxide forming alloys to improve its high temperature oxidation resistance. The rare earths can be also added as oxide dispersions. Significant cost reductions are possible if rare earth oxide concentrates can be used instead of pure rare earth oxides, the former being the precursor to obtaining pure rare earth oxide. In this study the effect of adding pure and concentrates of rare earth oxides to AISI 304L on its oxidation behavior has been evaluated. AISI 304L stainless steel powder compacts containing 2 vol% of pure lanthanum and yttrium oxides or their concentrate were prepared by milling followed by pressing. The compacts were vacuum sintered and isothermally oxidized in air for up to 200h at 900°C. The parabolic rate constants were determined and the reaction products examined using a scanning electron microscope. X-ray diffraction analysis of the reaction products was also carried out. The compacts with pure rare earth oxides and the concentrates exhibited similar oxidation behavior.

INFLUENCE OF ADDITION OF RARE EARTH ELEMENTS ON THERMAL BARRIER COATINGS MICRO STRUCTURAL EVOLUTION

Decreasing thermal diffusivity of YSZ can increase the thermal barrier effect. Thermal diffusivity is in direct proportion to lattice oscillation amplitude and frequency. The addition of rare earth oxide into YSZ may induce the lattice distortion, which will result in the change of lattice oscillation frequency. In the present work, combined with the experiment, a theoretical study was proposed to investigate the effect of the rare earth elements on the thermal barrier effect of YSZ using first-principal calculations implemented CASTEP program. It has been found that the addition of the rear earth element can make larger lattice distortion and favorable to reduce the thermal conductivity. The calculation results are in agreement with our experimental results.

Effect of rare earth oxide addition on microstructures of ultra-fine WC–Co particulate reinforced Cu matrix composites prepared by direct laser sintering

This paper presents a detailed investigation into the influence of the rare earth (RE) oxide (La 2O 3) addition upon the densification and the resultant microstructural characteristics of the submicron WC–Co particulate reinforced Cu matrix composites prepared by direct laser sintering. It is found that the relative density of the laser sintered sample with 1 wt.% La 2O 3 addition increased by 11.5% as compared with the sample without RE addition. The addition of RE element favored the microstructural refinement and improved the particulate dispersion homogeneity and the particulate/matrix interfacial coherence. The metallurgical functions of the RE element in improving the sinterability were also addressed. It shows that due to the unique properties of RE element such as high surface activity and large atomic radius, the addition of trace RE element can decrease the surface tension of the melt, resist the grain growth coarsening and increase the heterogeneous nucleation rate during laser sintering.

Effect of Rare Earth Oxide Additives on the Phase Transformation Rates of Si3N4

Fully dense Si3N4 sintered with rare‐earth (RE=La, Nd, Gd, and Yb) oxide additives were fabricated by hot pressing. They were mainly composed of the α‐phase, which enabled the investigation of the α–β transformation kinetics without the effect of porosity. The phase transformation kinetics was found to be linear. The activation energies for the phase transformation were 677, 546, 487, and 424 kJ/mol for RE=La, Nd, Gd, and Yb, respectively, and showed a good correlation with the ionic radii of RE atoms, which was discussed in conjunction with the segregation behaviors of RE atoms at the interface.

Effect of rare-earth oxide addition on luminescence properties of rare-earth silicon oxynitrides

Effect of rare-earth oxide addition on luminescence properties of rare-earth silicon oxynitrides

Effect of RE oxides on the microstructure of the coatings fabricated on titanium alloys by laser alloying technique

Abstract Composite coatings were fabricated on the surface of pure titanium and Ti–6Al–4V by laser alloying with boron and graphite powders. The results show that with the addition of Ce 2 O 3 and Y 2 O 3 , not only the compounds but also the microstructures of the coatings are refined compared with that without rare earth (RE) oxides. The mechanism of the microstructural refinement by the addition of RE oxides is discussed in this paper.

Molten carbonate fuel cell cathodes: Improvement of the electrocatalytic activity

The purpose of this work is to improve the electrocatalytic activity of Li–Ni mixed oxides by the addition of rare earth oxides (cerium or lanthanum). The influence of cerium and lanthanum on the electrocatalytic activity of these compounds was investigated by means of electrochemical impedance spectroscopy (EIS). The stability of these compounds was studied in a mixture of 62% lithium carbonate and 38% potassium carbonate at high temperature under an atmosphere rich in carbon dioxide to accelerate their dissolution. The morphology and the crystalline structure of the samples were not affected by the incorporation of cerium or lanthanum. The samples impregnated with CeO 2 or La 2O 3 showed lower resistance to charger-transfer processes than the sample without earth rare oxides. Both cerium and lanthanum improved the charger-transfer processes for oxygen reduction in an atmosphere rich in carbon dioxide. The reason may be due to cerium oxide acting as oxygen donor, and lanthanum oxide capturing CO 2, and the partial pressure of carbon dioxide on the surface of electrode.

Effects of Rare-Earth Oxides on Temperature Stability of Acceptor-Doped BaTiO3

The effects of rare-earth oxides (Yb2O3, Ho2O3, Er2O3) on the temperature stability of acceptor doped BaTiO3 dielectrics were studied. The samples doped with 1 mol % rare-earth oxides exhibited the highest dielectric constants. Substantial reductions in grain size were observed in the specimens with 1 mol % rare-earth oxides (∼0.6 µm) compared with the nondoped specimens (∼1.5 µm). As the rare-earth oxide content was increased, the Curie point progressively moved to higher temperatures. The addition of rare-earth oxides improved the temperature dependence of the dielectric constants of the acceptor-doped BaTiO3–rare-earth oxide systems over the whole temperature range studied (-55 to 150°C), and the temperature coefficient of capacitance(TCC) curves satisfied the X8R requirements for >2 mol % Yb2O3 and >3 mol % Er2O3 or Ho2O3.

Structure and properties of rare earth-doped lead borate glasses

Influence of rare earth oxide (Nd 2O 3, Er 2O 3) addition on structure and glass properties has been investigated in PbO–B 2O 3–Al 2O 3–WO 3 system. With an increasing of rare earth concentration, intensity of OH band drastically decreases and IR transparency is slightly shifted to the longer wavelengths. The ErBO 3 crystalline phase has been identified basing on X-ray diffraction analysis. In opposite to the neodymium oxide, the erbium oxide plays the role as glass-modifier and influences on BO 3 ↔ BO 4 conversion, what was stated by infrared spectroscopy.

Effect of rare earth oxide additives on the performance of NiMH batteries

To date, we have performed research on nickel–metal hydride (NiMH) batteries used in many applications and have found that addition of rare earth oxides to the nickel electrode and the hydrogen-storage alloy (MH) electrode improves battery performance significantly. Because heavy rare earth oxides of such as Er, Tm, Yb and Lu have remarkable properties that shift the oxygen evolution overpotentials of nickel electrodes to more noble potentials, it is possible to improve high-temperature charge efficiency of nickel–metal hydride secondary batteries by adding them to nickel electrodes. Furthermore, addition of heavy rare earth oxides to MH electrodes depresses an acceleration of the alloy corrosion and improves service life of the battery at high temperatures. Accordingly, addition of heavy rare earth oxides is effective for NiMH batteries used in high-temperature applications such as electric vehicles (EVs), hybrid vehicles (HEVs) and rapid charge devices. In this study, we discussed how the addition of heavy rare earth oxides affects NiMH battery characteristics.

Effects of Rare-Earth Additives in Li ∕ Na Eutectic Carbonate for Decreasing the Solubility of NiO

For the commercial application of molten carbonate fuel cells (MCFCs) under high-pressure operation, Ni shorting may be a problem. To improve the MCFC cathode stability, the solubility of rare-earth oxides and the effects of the addition of these rare-earth oxides to the molten carbonates have been studied. The solubilities of , and in the eutectic carbonate were , and (mole fraction) at 923 K and . The NiO solubility was reduced by the rare-earth oxide addition. However, the effects of the , and addition were much smaller than that of . This difference would be caused by the low solubilities of , and compared with that of [ (mole fraction)]. The relationship between the solubility of NiO and the composition of the carbonate melt with a cation additive has also been discussed.

Effect of metal oxides on the pyrolysis residues of poly(ethylene terephthalate): Formation of carbonaceous submicron, nano-scale filaments and mesoporous compounds

Thermal decomposition of mixture of poly(ethylene terephthalate) (PET) and metal oxide has been investigated. Morphology of pyrolysis residues has been observed by using scanning electron microscopy. Among various oxides examined the addition of zinc oxide or trivalent rare earth oxide (Ln 2O 3) resulted in the formation of porous fibre-like structures with the diameter of ∼1 μm for ZnO and ∼100 nm (or thinner) for Ln 2O 3. The formation process as well as thermal decomposition behaviour has been studied by various analytical methods. The thermal decomposition of PET on single crystal ZnO indicated that the unique morphology was due to the oxygen-terminated surface of the metal oxide. Furthermore, pore structures of the carbonaceous compounds from various PET–metal oxide mixtures have been determined by nitrogen adsorption isotherm at −196 °C. It was found that the carbonaceous compounds obtained from PET–Fe 2O 3 and PET–Ln 2O 3 had large mesopore volumes. This was confirmed also by the adsorption study of large molecules such as humic acid (HA).

Thermoelectric Properties of p-Type Fe<SUB>0.9</SUB>Mn<SUB>0.1</SUB>Si<SUB>2</SUB> with Rare-Earth Oxide Addition

The effects of rare earth oxide dispersion on the thermoelectric properties of the Mn-doped p-type β-FeSi2 (Fe0.9Mn0.1Si2) were investigated. The Fe0.9Mn0.1Si2 powders were mechanically alloyed with Y2O3 powder (0.5–4 mass%) and subsequently hot pressed. The added Y2O3 was dispersed in the β phase matrix as a fine particles around 10 nm in size. The thermal conductivity of the sample was significantly reduced by Y2O3 addition, which was caused by enhancing phonon scattering due to fine Y2O3 dispersion. It was also found that the added Y2O3 was partially decomposed in the sample, resulted in solution of elemental Y in the β phase as a p-type dopant. The Seebeck coefficient was slightly improved when a small amount of Y2O3 (0.5 and 1 mass%) was added. The improvement of the Seebeck coefficient could not be explained only by the fine dispersion of Y2O3 and the Y doping as a p-type dopant. The slight increase in the Seebeck coefficient was also observed in the case of the samples with addition of small amounts of La2O3 powder.

Gas pressure sintering of SiC sintered with rare-earth-(III)-oxides and their mechanical properties

The sintering behaviour of LPS-SiC and the influence of the size of the rare-earth cations on the secondary phase characteristics were investigated with different rare-earth oxide additions. In all cases, the most important sintering mechanism was found to be the solution-reprecipitation process. This fact was corroborated by TEM and EDS analyses. Post-sintering annealing resulted in devitrification of the secondary phases coupled with anisotropic grain growth due to the phase transformation from β-SiC to α-SiC. Improved fracture toughness of the annealed materials was attributed to crack deflection by the elongated grains. SEM microstructural analyses were performed in order to elucidate structure–property relationships. A comparative study in reference to the additive system Y 2O 3–AlN demonstrates significantly improved high-temperature properties of the Lu 2O 3-containing SiC ceramics.