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...

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.

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 ...

Effects of various rare earth oxides on morphology and size of oxide dispersion strengthening(ODS)-W and ODS-Mo alloy powders

Ultrafine oxide dispersion strengthening(ODS)-Mo and ODS-W alloy powders containing different types of oxide nanoparticles were successfully synthesized by spraying method(solid−liquid mixing method)combined with the reductions with carbon black and hydrogen in sequence.It is concluded that the solution concentration and type of rare earth oxide have no effect on the grain size of ODS-Mo alloy powder,but have obvious effect on that of ODS-W alloy powder.The higher the concentration of rare earth solution is,the smaller the average grain size of ODS-W alloy powder is.Furthermore,compared with doping with CeO_(2),the grain sizes of reduction products of La_(2)O_(3) and Y_(2)O_(3) doped WO_(3) are relatively larger.Compared with the undoped case,there is almost no change for grain size of ODS-Mo alloy powder,while the grain size of ODS-W alloy powder becomes much larger.This is probably due to the appearance of the composite oxide(such as La_(2)WO_(6))formed by the reaction between tungsten oxide and rare earth oxides,which promotes the heterogeneous nucleation and growth of tungsten grains during the reduction process of ODS-W,while there is no complex oxide composed of molybdenum and rare earth oxides in the reduction process of ODS-Mo.

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.

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.

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.

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.

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.

Significantly improved high k dielectric performance:Rare earth oxide as a passivation layer laminated with TiO_(2) film

In order to achieve a super gate dielectric performance,rare earth oxides featuring for large band gap,good thermodynamic stability and relatively high k value were selected to be laminated with TiO_(2)film to prepare bilayer dielectric films.As an example,the microstructure,morphology,band gap structure and electrical performance of TiO_(2)-Y_(2)O_(3)bilayer films were systematically investigated.Results show that stacking sequence of TiO_(2)and Y_(2)O_(3)sublayers has a significant impact on the dielectric performance and Y_(2)O_(3)film as a passivation layer can effectively improve electrical properties.Besides,the electrical behaviors analysis of TiO_(2)-Y_(2)O_(3),Y_(2)O_(3)-TiO_(2),Y_(2)O_(3)and TiO_(2)samples was carried out by impedance spectra and equivale nt circuit.The result shows that TiO_(2)-Y_(2)O_(3)/Si sample holds the largest internal re sistance of 74665Ωamong four samples.Moreover,the most outstanding properties of Pt/TiO_(2)-Y_(2)O_(3)/Si capacitor are achieved by varying the thickness of sublayers and annealing temperature.500℃-annealed bilayer film with 17 nm-TiO_(2)and 3-nm Y_(2)O_(3)displays a k value of 28.24,which is more than 1.4 times that of current commercial HfO_(2).Further,Schottky emission was determined to be leakage current transport mechanism for TiO_(2)-Y_(2)O_(3)bilayer films.Inspired by this result,the electrical performance of more general Pt/TiO_(2)-REOs/Si MOS capacitors(RE=Sc,La,Ce,Gd and Pr)was measured.The combination of TiO_(2)film and REOs passivation layer with the satisfying performance provides promising candidates for future Si-based integrated circuit(IC).

Structure-from-Motion Photogrammetry and Rare Earth Oxides can quantify diffuse and convergent soil loss and source apportionment

Accurately quantifying rates of soil erosion requires capturing both the volumetric nature of the visible,convergent fluvial pathways(also known as rills)and the subtle nature of the less-visible,diffuse pathways(interrill areas).The aim of this study was to use Rare Earth Oxide(REO)tracers and Structure-from-Motion(SfM)photogrammetry to elucidate retrospective information about soil erosion rates and sediment sources during different soil erosion conditions,within a controlled laboratory environment.The experimental conditions created erosion events consistent with diffuse and convergent erosion processes.REO tracers allowed the sediment transport distances of over 2 m to be described,and helped resolved the relative contribution of diffuse and convergent soil erosion;interrill areas were also iden-tified as a significant sediment sources soil loss under convergent erosion conditions.While the potential for SfM photogrammetry to resolve sub-millimetre elevations changes was demonstrated,under some conditions non-erosional changes in surface elevation,such as compaction,exceeded volumes of soil loss via diffuse erosion.The discrepancies between SfM Photogrammetry calculations and REO tagged sediment export were beneficial,identifying that during soil erosion events sediment in both aggregate and particle form is deposited within the convergent features,even when the rill extended the full length of the soil surface.The combination of SfM photogrammetry and REO tracers has provided a novel platform for building a spatial understanding of patterns of soil loss and source apportionment between rill and interrill erosion.

Rare earth oxides and their supported noble metals in application of environmental catalysis

Volatile organic compounds(VOCs),methane,carbon monoxide,soot,automotive exhaust,and nitrogen oxides are harmful to the atmosphere and human health.It is urgent to strictly control their emissions.Heterogeneous catalysis is an effective pathway for the removal of these pollutants,and the critical issue is the development of novel and high-performance catalysts.In this review,we briefly summarize the preparation methods,physicochemical properties,catalytic activities,and related reaction mechanisms for the above pollutants removal of the rare earth oxides,mixed rare earth oxide,rare earth oxidesupported noble metal,and mixed rare earth oxide-supported noble metal catalysts that have been investigated by our group and other researchers.It was found that catalytic performance was associated with the factors,such as specific surface area,pore structure,particle size and dispersion,adsorbed oxygen species concentration,reducibility,reactant activation ability or interaction between metal nanoparticles and support.Furthermore,we also envision the development trend of such a topic in future work.

Effects of rare earth oxide on hardfacing metal microstructure of medium carbon steel and its refinement mechanism

The electrodes for hardfacing medium carbon steel with six additions of rare earth oxide were developed in this work. By means of optical microscopy and scanning electron microscopy, the microstructure, inclusion and the fractograph of the hardfacing metal were observed. Then, the effects of rare earth oxide on microstructure and inclusions in hardfacing metal were analyzed. The effectiveness of rare earth oxide as heterogeneous nuclei of δ-Fe was calculated with the misfit theory. The results showed that, the microstructure of hardfacing metal was composed of ferrite and small amount of pearlite. The microstructure was refined at first and then coarsened with the increase of rare earth oxide addition. The fractograph was changed from brittle to equiaxed dimples, then became quasi-cleavage and cleavage gradually. The calculated results showed that, the ferrite grain size could be refined because that LaAlO3 as heterogeneous nuclei of δ-Fe was moderately effective, and the ferrite grain size was coarsened because the misfits between Ce2O3 and δ-Fe, Ce2O2S and δ-Fe were increased with futher increase of rare earth oxide addition.

Effect of rare earth oxides on the morphology of carbides in hardfacing metal of high chromium cast iron

The flux cored wires with different amounts of rare earth （RE） oxides additions for hardfacing （harden-face-welding） the workpieces of high chromium cast iron were studied in this work.The morphology of carbides in hardfacing metal was observed,and the type of the carbides was determined by optical microscopy,scanning electron microscopy （SEM）,energy dispersive spectrometer （EDS） and X-ray diffraction （XRD）.Based on the data of effect of RE on carbides morphology,the refined reason for carbide by RE oxide was discussed with the misfit theory.The results showed that,the microstructure of hardfacing metal was composed of martensite,residual austenite and M7C3 carbides.With the increasing amount of RE oxide additions,the volume fraction and roundness of the carbides were increased,however,the area and perimeter of carbides were decreased.It indicated that carbides in hardfacing metal could be refined and spheroidized by adding RE oxides in flux cored wires.

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.