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(RE2O3) was added into t...

Effect of mixed rare earth oxides and CaCO_3 modification on the microstructure of an in-situ Mg_2Si/Al-Si composite

The effects of mixed rare earth oxides and CaCO3 on the microstructure of an in-situ Mg2Si/Al-Si hypereutectic alloy composite were investigated by optical microscope,scanning electron microscope,and energy dispersive spectrum analysis. The results showed that the morphol-ogy of the primary Mg2Si phase particles changed from irregular or crosses to polygonal shape,their sizes decreased from 75 μm to about 25 μm,and the compound of both the oxide and CaCO3 was better than either the single mixed rare earth o...

Preparation of Rare Earth Hydroxide and Oxide Nanoparticles by Precipitation Method

A series of rare earth hydroxide and oxide nanoparticles have been prepared by precipitation method with alcohol as the dispersive and protective reagent. Transmission electron microscope （TEM） images indicate that the particles are spherical in shape and smaller than 100 nm in size. The crystallite sizes of cubic Ln2O3 have lanthanide shrinking effect, while average crystal lattice distortion rates possess lanthanide swelling effect. The diffraction peak intensity of heavy rare earth oxide nanometer powders is remarkably stronger than that of light rare earth oxide nanometer powders. The variation of diffraction intensity with atomic number presents an inverted W type, forming a double peak structure. Fourier transform infrared （FTIR） spectrums reveal that Ln2O3 nanopowders have higher surface activity than that of ordinary Ln2O3 powders. The UV-vis spectra show that Ln-O bond of these particles is slightly blue-shifted, and its absorption intensity decreases.

Preparation and Characterization of Microporous Nano-Tungsten Trioxide and Its Photocatalytic Activity after Doping Rare Earth

Aqueous sols and gels of tungstic acid were prepared from Na2WO4 with protonated cation-exchange resin. Nano-tungsten oxide of a microporous lamella was synthesized by means of washing of WO3· 2H2O with distilled water under ultrasonic wave agitation and centrifuging repeatedly, and the specific surface area tended to increase gradually with washing and centrifuging. The sample of centrifuged 7 h has more than 2 times highs specific surface area and more high photocatalytic activity . The mechanisms are also discussed.

Mechanism of Cracking Resistance of Hardfacing Specimens of Steel 5CrNiMo Improved by Rare Earth Oxide

The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.

Phase Behavior and Crystal Structure of Perovskite-Type Rare Earth Complex Oxides

Several compounds of rare earth complex oxides containing manganese and titanium were synthesized in Ar, and their crystal structures were analyzed by powder X-ray diffraction data and Rietveld method. Structures of A0.67Ln0.33 Mn0.33Ti0.6703（A = Ca or Sr and Ln = rare earth） were found to have orthorhombic symmetry with the space group Pnrna, and their interatomic distances and bond angles were obtained. This space group was also derived from electron microscopic study. Electrical conductivity of Cao.67Ln0.33Mn0.33Ti0.6703 for several rare earth elements showed a semiconducting property with the activation energy of 0.4 eV. Some of these compounds of the strontium system show the antiferromagnetic properties below 10 K.

Hydrogen production from coke oven gas over LiNi/γ-Al_2O_3 catalyst modified by rare earth metal oxide in a membrane reactor

The performance of LiNi/γ-Al2O3 catalysts modified by rare earth metal oxide （La2O3 or CeO2） packed on BCFNO membrane reactor was discussed for the partial oxidation of methane （POM） in coke oven gas （COG） at 875 ℃. The NiO/γ-Al2O3 catalysts with different amounts of La2O3 and CeO2 were prepared with the same preparation method and under the same condition in order to compare the reaction performance （oxygen permeation, CH4 conversion, H2 and CO selectivity） on the membrane reactor. The results show that the oxygen permeation flux increased significantly with LiNiREOx/γ-Al2O3 （RE = La or Ce） catalysts by adding the element of rare earth especially the Ce during the POM in COG. Such as, the Li15wt%CeO29wt%NiO/γ-Al2O3 catalyst with an oxygen permeation flux of 24.71 ml·cm^-2·min^-1 and a high CH4 conversion was obtained in 875 ℃. The resulted high oxygen permeation flux may be due to the added Ce that inhibited the strong interaction between Ni and Al2O3 to form the NiAl2O4 phase. In addition, the introduction of Ce leads up to an important property of storing and releasing oxygen.

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

Roles of rare earth oxide （RE2O3） additives in millimeter-wave（MM） sintering of AIN 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 AIN, densification temperature decreased with the decrease of the ionic radius of rare earth ion and was closely related with the eutectic temperature in the RE2Oa-Al2O3 binary system. The lowest densification temperature in the millimeter-wave sintering of AIN with Yb2O3 additive was attributed to the largest heating rate of Yb2O3-Al2O3 binary oxide under millimeter-wave radiation. Furthermore, the lowest densification temperature could be attained while selecting the Yb2O3 content so as to form the intergranular phase with the eutectic composition in the Yb2O3-Al2O3 binary system. The result showed good agreement with the above mentioned during the sintering of Si3N4 with Yb2O3-Al2O3 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 Yb2O3 added AINs.

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

Effects of flaky rare earth oxide additives including Er2O3,Tm2O3,and Yb2O3,Lu2O3 on high temperature and high rate discharge performance of nickel electrodes were investigated.The discharge efficiency at 0.2C reached 96% at 60 oC 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 ...

Effect of Roasting Conditions of Rich Cerium Rare Earth Carbonate on Crystallite Morphology and Polishing Ability of Ceria-Based Rare Earth Oxide

The granule shape and crystal structure of the the ceria-based rare earth oxide which were roasted at 600～1050 ℃ for 2～6 h and then cooled in furnace, cooled out of furnace or cooled in water were studied by means of XRD and SEM. The results revealed that the rich cerium rare earth carbonate could be changed into the rare earth oxide which was a kind of sandwich made of globose granule whose diameter was between 0.5～3.0 μm after being roasted in 900 ℃ for 2 h. This kind of crystal lattice in rare earth oxide belonged to face-centered cubic lattice and its space between crystal surface {111} and {200} (viz. L111 and L200) would enlarge as the roasting temperature increasing. With increasing roasting temperature, L111 would rise straightly upward, and L200 would rise straightly upward when roasting time was 2～4 h but changed little when roasting time was 4～6 h. The glass-polishing experiments found that the polishing ability of the ceria-based rare earth oxide was the best as L111 was 43～53 nm and the L200 was 43～56 nm.

Effects of Rare Earth Oxides on Viscosity,Thermal Expansion,and Structure of Alkali-Free Boro-Aluminosilicate Glass

Effects of rare earth oxides（Y2O3,La2O3,and Er2O3） on the viscosity,thermal expansion,and structure of alkali-free boro-aluminosilicate glasses were investigated by the rotating crucible viscometer,dilatometry and FT-IR absorption spectra.The results showed that the melting temperature of alkali-free boroaluminosilicate glasses decreased from 1 697.55 to 1 662.59,1 674.37 and 1 640.87 ℃ with the introduction of 1 mol%La2O3,Y2O3 and Er2O3,respectively.However,the glass transition temperature Tg,dilatometric softening temperature T_d and coefficient of thermal expansion of alkali-free boro-aluminosilicate glasses increased when adding the rare-earth oxides.At high temperatures,incorporating rare earth oxides into glass resulted in the peak at about 1 085 cm^-1 towards lower wavenumber and the absorption band in the region of 850-1 260 cm^-1 broader,which indicated that rare earths acted as network modifiers and increased the numbers of non-bridging oxygen in the glass melts.However,the rare earths had an opposite effect and accumulated the glass structure at low temperatures near Tg.

Study on rare earth/alkaline earth oxide-doped CeO_2 solid electrolyte

Five types of rare earth/alkaline earth oxide-doped CeO2 superfine-powders were synthesized by a low-temperature combustion technique. The relevant solid electrolyte materials were also sintered by pressureless sintering at different temperatures. The results of X-ray diffraction and transmission electron microscopy showed that the grain size of the powders was approximately 20-30 nm, and rare earth/alkaline earth oxides were completely dissolved into ceria-based solid solution with fluorite structure. The electrical conductivities of the SmzO3-CeO2 system were measured by the ac impedance technique in air at temperatures ranging from 513-900℃. The results indicated that the ionic conductivities of Srno.2oCe0.8Ol.875 solid electrolyte increase with increasing sintering temperature, and the relationship between the conductivities and measuring temperature obeys the An＇henius equation. Then the SmzO3-CeO2 material was further doped with other rare earth/alkaline earth oxide, and the conductivities improve with the effective index.

Electric-magnetic-force characteristics of rare earth barium copper oxide superconductor high-field coils based on screening effect and strain sensitivity

Rare earth barium copper oxide(REBCO)is the most researched and commercialized second-generation high-temperature superconducting material.Due to the anisotropic structure,strong deformation sensitivity,and central field errors caused by screening current effects,it is still a challenge for commercialization applications.In this study,the transversely isotropic constitutive relationship is selected as the mechanical model based on the structural characteristics of REBCO tapes,and suitable microelements are selected to equate the elastic constants using their average stress-strain relationships.Then,a two-dimensional axisymmetric model for coils wound by single-layer tapes is constructed to analyze the dependence of the electric-magnetic-force distribution in the tape on the strain.Finally,the anisotropic approximation of the homogenized bulk method is used to equate large-turn high-field coils,and the electric-magnetic-force distribution characteristics of the coils with/without screening effects and mechanical strain conditions are investigated,respectively.The results reveal that the mechanical strain has a weakening effect on the electromagnetic field distribution of superconducting tapes,but causes a significant enhancement in the force field distribution.In the presence of 0.5% mechanical strain,the maximum weakening of the peak value of the current density and the critical current density inside the high-field coil can reach about 8% and 13%,respectively,with a nearly 5 times increase in the peak stress.The screening current makes the current field distribution inside the coil improve by about 10 times.The screening current induced magnetic field can reach up to 0.8 T,making the relative error of the high-field coil center up to 7.8%.

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 A1N 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 A1N ceramics. For A1N 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 A1N ceramics doped with 3 wt.% Er203, which favored the improvement of the thermal conductivity of A1N ceramics.

Glass-forming Ability and Chemical Stability of Magneto-optical Glass Heavily Doped with Rare Earth Oxide

The glass-forming region of B2O3-Al2O3-SiO2 （BAS） glass heavily doped with rare earth oxides was investigated by an effective method, and the chemical stability was investigated by powder method. Influences of rare earth oxides on the glass-forming ability and the chemical stability of the BAS glass were also discussed. The experimental results show that the BAS glass-forming region expands firstly with the increase of the Tb2O3 content up to 30mol% and then shrinks. The acid-resistant capacity of the BAS glass doped with rare earth oxides is the lowest, the water-resistant capacity is secondary, and the alkali-resistant capacity is the best. Besides, the glass chemical stability can be improved by doping appropriate amount of rare earth oxides. Moreover, the stronger the ionic polarization ability of the rare earth ions is, the better the chemical stability of the BAS glass will be.

Quench characteristics and mechanical responses during quench propagation in rare earth barium copper oxide pancake coils

Quench and mechanical behaviors are critical issues in high temperature superconducting(HTS)coils.In this paper,the quench characteristics in the rare earth barium copper oxide(REBCO)pancake coil at 4.2K are analyzed,and a two-dimensional(2D)axisymmetric electro-magneto-thermal model is presented.The effects of the constituent materials,background field,and coil size are analyzed.An elastoplastic mechanical model is used to study the corresponding mechanical responses during the quench propagation.The variations of the temperature and strain in superconducting layers are compared.The results indicate that the radial strain evolutions can reflect the transverse quench propagation and the tensile hoop and radial stresses in superconducting layers increase with the quench propagation.The possible damages are discussed with the consideration of the effects of the background field and coil size.It is concluded that the high background field significantly increases the maximum tensile hoop and radial stresses in quenching coils and local damage may be caused.

Studies on Gas Sensitive Materials of γ-Fe_2O_3 Doped with Rare Earth Oxides

Fine powders of γ-Fe_2O_3,doped with Y_2O_3,CeO_2,Eu_2O_3 or Tb_2O_3 have been prepared by the chemical co-precipitation method.The sensitivity of gas sensation has been measured with respect to the relative resist- ance change in the ceramic matrix upon introduction of inflammable gases.The structure of the materials has been studied with X-ray diffraction spectroscopy(XRD),electron diffraction spectroscopy( ED) and transmis- sion electron microscopy(TEM).The addition of rare earth oxides,which improves ceramic microstructure of γ-Fe_2O_3,improves gas sensitivity of γ-Fe_2O_3.The stability can be increased because of the increase of phase transition temperature.In addition,the selectivity of gas sensation of γ-Fe_2O_3 can be improved because of the variation of rare earth oxides.

Effects of Rare Earth Oxide on Microstructure of Zinc Varistors

The influence of Pr6O11 on the microstructure of ZnO varistors was researched. The results of experiment indicate that addition of Pr6O11 leads to the change of the formation process of the spinel phase. A lot of pyrochlore phases （ Bi3Zn2Sb3O14 ） produce at about 700℃, and decompose to fine spinel phase （Zn7Sb2O12） when the temperature reaches to 900℃.This type of spinel phase makes ZnO crystal size minor. Also, the phase contained the Pr and different Pr oxides, which makes the whole material crystal size more uniform and compact. The fine structure improves the threshold voltage by about 60%, and modifies nonlinear coefficient of the ZnO material.

SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION

In this paper,the influence of crystal-field on the Luminescence properties of Eu^(2+) in complex oxides are studied theoretically by using purely electrostatic model,the dependence of the 4f^65d levels on Eu-O bond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f^65d energy band in cubic or in octahedral fields will be inversely proportional to R^5,where R is the distance of Eu^(2+) to oxygen ligand.The value of R affects slightly the location of the centre of 4f^65d energy band.According to the exper- imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites of Eu^(2+) and degree of covalency of Eu-O bond on luminescence properties of Eu^(2+).Some regularity of fluorescence spectrum was observed. In alkali-alkaline earth-phosphates,the splitting extent of 4f^65d band (△E) becomes smaller as the Eu-O bond distance (R) increases.In Na_(3-x)(PO_4)_(1-x)(SO_4)_x and Na_(2-x)CaSi_(1-x)P_xO_4 hosts,d-d emission peak of Eu^(2+) will shift to shorter wavelength with the increase of x's value. The crystal structure data show that Eu^(2+) in K_2Mg_2(SO_4)_3 is affected more strongly by crystal-field and covalancy than in KMgF_3,so K_2Mg_2(SO_4)_3:Eu^(2+) emits blue light (E_(em)~m=400nm) and KMgF_3:Eu^(2+) produces ultraviolet fluorescence.

Effect of Rare Earth Oxides on Catalysts Mo-Te System

Surface compositions,structures,and acidities of the Mo-Te-Fe-Ni catalysts added with La_2O_3,CeO_2, Pr_6O_(12),Nd_2O_3 and Sm_2O_3 were measured and related with the activities of the catalysts for selective oxidation of olefins.It was found that adding rare earth elements to the Mo-Te catalysts increases obviously their selectivities to methacrolein(MAL),and the yield percentage of MAL changes periodically with the increase of atomic numbers of rare earth elements added,and the highest yield was obtained with the catalyst containing CeO_2.The addition of CeO_2 to 9-component Mo-Te catalyst increases not only the activity of the catalyst, but also its thermostability remarkably.The mechanism of rare earth elements in the catalysts was discussed.