Segregation Of Ce Research Articles

Effect of rare earth cerium and impurity tin on the hot ductility of a Cr-Mo low alloy steel

The specimens of 1Cr-0.5Mo low alloy steel, undoped, Sn-doped and Ce+Sn-doped, were austenitized at 1300 °C and then cooled down to different temperatures in the range of 700–1050 °C, followed by tensile tests with the aid of a Gleeble machine. The reduction of area (RA) obtained from the test was employed to evaluate the hot ductility of the steel. The tested specimens were characterized using different techniques. Minor Sn could considerably reduce the RA values of the steel in the whole temperature range, and the hot ductility curve could be widened and deepened. Nevertheless, minor Ce could improve the hot ductility of the Ce+Sn-doped steel by fully suppressing the Sn-induced hot ductility deterioration. FEGSTEM microanalysis showed that the Sn or Ce and Sn atoms segregated to austenite grain boundaries in the Sn-doped or Ce+Sn doped specimens. The detrimental effect of Sn on the hot ductility could be attributed mainly to the segregation of Sn as it could decrease the grain boundary cohesion and in turn enhanced the grain boundary sliding and cracking. However, this detrimental effect of Sn could be counteracted by the segregation of Ce which could increase the grain boundary cohesion and in turn restrained the grain boundary sliding and cracking. Accordingly, a minor addition of rare earth Ce could be an effective method of suppressing the detrimental effect of impurity elements on the hot ductility of a Cr-Mo low alloy steel.

Effect of Rare-Earth Cerium on Impurity Tin-Induced Hot Ductility Deterioration of SA508-III Reactor Pressure Vessel Steel

The samples of SA508-III reactor pressure vessel steel, undoped, doped with Sn, and doped with Sn + Ce, are heated at 1300 °C and then cooled down to different temperatures between 650 and 1050 °C, followed by tensile deformation until fracture using a Gleeble machine. The steel hot ductility evaluated by the reduction of area (RA) is determined at each test temperature. The tested samples are characterized using scanning electron microscopy, optical microscopy, and field emission gun scanning transmission electron microscopy. The steel exhibits a hot ductility trough and Sn substantially deteriorates the hot ductility of the steel by deepening and widening the ductility trough. However, Ce can well suppress this Sn-induced hot ductility deterioration. Grain boundary segregation of Sn or Sn + Ce occurs in the Sn-doped or Sn + Ce-doped samples. The segregation of Sn is primarily responsible for the hot ductility deterioration as it weakens grain boundary, thereby enhancing grain boundary sliding and deteriorating hot ductility. The segregation of Ce is mainly responsible for the suppression of the deterioration as it strengthens grain boundary, thereby restraining grain boundary sliding and suppressing Sn-induced hot ductility deterioration.

Structural and optical study of Ce segregation in Ce-doped SiO1.5 thin films

Cerium doped SiO1.5 thin films fabricated by evaporation and containing silicon nanocrystals were investigated by atom probe tomography. The effect of post-growth annealing treatment has been systematically studied to correlate the structural properties obtained by atom probe tomography to the optical properties measured by photoluminescence spectroscopy. The atom probe results demonstrated the formation of Ce-Si rich clusters upon annealing at 900 °C which leads to a drastic decrease of the Ce-related luminescence. At 1100 °C, pure Si nanocrystals and optically active cerium silicate compounds are formed. Consequently, the Ce-related luminescence is found to re-appear at this temperature while no Si-nanocrystal related luminescence is observed for films containing more than 3% Ce.

Effect of rare earth cerium on brittleness of simulated welding heat-affected zones in a reactor pressure vessel steel

The welding coarse-grained heat-affected zones (CGHAZs) in the undoped and Ce-doped samples of SA508CL-3 reactor pressure vessel steel were simulated using a Gleeble 1500D thermomechanical simulator with a peak temperature of 1320 °C at the heat inputs of 30, 50 and 100 kJ/cm, respectively. The ductile-to-brittle transition temperature (DBTT) of the simulated CGHAZs was evaluated along with microstructural and microchemical characterizations. The results indicated that Ce could substantially lower the DBTT of the CGHAZs by its microstructural and microchemical effects. After the thermal cycling of welding, the microstructure in the Ce-doped samples was apparently finer than that in the undoped samples, regardless of the lath bainite obtained at the heat inputs of 30 and 50 kJ/cm or the granular bainite acquired at the heat input of 100 kJ/cm, leading to lower DBTTs for the Ce-doped samples. Moreover, grain boundary segregation of Ce occurred apparently in the Ce-doped samples and exhibited a non-equilibrium characteristic. The segregation of Ce could play an important role in lowering the DBTT of CGHAZs or toughening the CGHAZs.

Effect of rare earth cerium on the creep properties of modified 9Cr–1Mo heat-resistant steel

The creep properties of modified 9Cr–1Mo steel specimens, undoped and doped with 0.053wt% Ce, which were normalized at 1055°C and tempered at 760°C, were examined under different engineering stresses (150–210MPa) and temperatures (600–650°C). The creep behavior of the steel followed the temperature-compensated power law and Monkman–Grant equations. The creep activation energy for the Ce-doped steel (662kJ/mol) was apparently higher than that for the undoped one (541kJ/mol). The 100MPa-stress creep lifetime and 105h creep rupture strength were estimated between 600 and 650°C. At ∼600°C where the steel component was usually operated in engineering practice, the 100MPa-stress creep lifetime of the Ce-doped steel was about 2.3 times as long as that of the undoped steel and the 105h creep rupture strength of the former was about 7% higher than that of the latter. These indicated that Ce could substantially improve the creep properties of the steel. The segregation of Ce to grain or subgrain boundaries, carbide/matrix interfaces and dislocations could account for the improvement in the creep properties.

The effect of Ce on the high temperature oxidation properties of a Fe–22%Cr steel: microstructural investigation and EELS analysis

The effect of a 10 nm Ce coating layer on long term oxidation behaviour (up to 3000 hours) of a Fe–22%Cr ferritic stainless steel for solid oxide fuel cell (SOFC) interconnect application is investigated. Scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) analysis showed segregation of Ce to the grain boundaries of Cr,Mn spinel layer adjacent to the scale-gas interface. The findings in this study are in line with the grain boundary blocking model for the Ce effect mechanism. However, segregation of Ce was observed at the grain boundaries of the (Cr,Mn) spinel in the vicinity of the scale-gas interface. No evidence of Ce segregation was found in the grain boundaries of the chromia layer, neither any Ce rich particle was observed in the chromia layer after longer exposure times.

Crystal growth and dopant segregation of Ce:LiSrAlF6 and Eu:LiSrAlF6 crystals with high dopant concentrations

Ce:LiSrAlF6 and Eu:LiSrAlF6 crystals with different dopant concentrations were grown by the micro-pulling-down method. The crystals with high dopant crystal included the secondary phase as clusters with the plate shape in BSE images. The secondary phases were identified CeF3 and EuF2, respectively, by the EDS analysis and powder-XRD measurement. Eu concentration against the Sr sites in the Eu 2% doped LiSAF crystal were most uniform in the range 0.9–1.6atm% using the EPMA.

Influence of cerium on hot workability of 00Cr25Ni7Mo4N super duplex stainless steel

The effect of Ce on hot workability of 00Cr25Ni7Mo4N steel melted in vacuum induction furnace was studied by Gleeble thermal simulation machine and scanning electron microscopy (SEM). The results showed that ductility of the steel with Ce addition was increased significantly because of increasing content of austenite, segregation of Ce at grain boundaries and modification of inclusion. The optimum range of Ce content in the steel was 0.030 wt.%–0.047 wt.%, and the optimum value was about 0.047 wt.%. The effect of rare earth on the improvement of hot workability would decrease after adding 0.062 wt.% Ce because of generation of bigger aggregated inclusions and formation of brittle intermetallic phases (Ce-Fe-Cr-Mn-Mo). The temperature of steady plastic deformation of the steel with Ce addition was reduced to 1000 °C at a strain rate of 10/s and 1050 °C at a strain rate of 50/s, respectively.

The dependence of the oxygen-exchange properties of Ce0.5Zr0.5O2 on the method of synthesis

The oxygen-exchange properties of Ce0.5Zr0.5O2 samples prepared by the traditional coprecipitation method with the use of a biotemplate (pine wood sawdust) were studied by the temperature-programmed reduction and oxidation methods. The use of the template and the presence of alkali and alkaline-earth metal cations in it provides a high mobility of oxygen and a high capacity with respect to oxygen in the biomorphic oxide. Impurities cause the segregation of Ce- and Zr-enriched phases under high-temperature treatment conditions, which worsens the redox properties of the biomorphic sample. Nevertheless, the ability of the biomorphic sample to play the role of an “oxygen buffer” remains high compared with the coprecipitated oxide subjected to similar treatments.

Effect of post-annealing temperature on the microstructure and magnetic properties of Ce:YIG thin films deposited on Si substrates

Amorphous Ce1Y2Fe5O12 (Ce:YIG) thin films deposited on single crystal Si(100) and thermally oxidized Si(100) substrates by pulsed laser deposition were annealed in the temperature range of 700–1000°C in air. The annealing temperature dependence of microstructure and magnetic properties of Ce:YIG films was studied using X-ray diffraction combined with vibrating sample magnetometer. The results show that single phase of polycrystalline Ce:YIG thin films can be obtained by the post-annealing of as-deposited films at the temperature of 700°C. However, two steps of phase segregation of Ce:YIG occur as the post-annealing temperature increases: at first, Ce:YIG is decomposed into YIG and non-magnetic CeO2 when annealed at 800°C; then YIG continues to be decomposed forming Fe2O3 when the temperature is increased up to 900°C. Consequently, the saturation magnetization of Ce:YIG films decreases first and then increases with the post-annealing temperature going up, which indicates that the saturation magnetization of Ce:YIG films is mainly related to the phase composition of the films. Meanwhile, the presence of SiO2 buffer layer can significantly enhance the saturation magnetization of Ce:YIG films.

Beneficial Effects of Ce Implantation into Preformed Cr2O3Scales on the Subsequent Oxidation of Ni–20Cr Alloy

The influence of Ce implantation into preformed Cr2O3 scales with a dose of 1 × 1017 ions/cm2 on the subsequent oxidation behavior of Ni–20Cr alloy at 1050°C in air has been investigated. The pre-oxidation was carried out at 1050°C in air for 0.5 and 1 hr respectively Cr2O3 and NiCr2O4 formed on Ni–20Cr alloy. The oxidation rate was decreased remarkably due to Ce implantation regardless of whether it was implanted into the alloy or into the pre-formed oxide scales, and the beneficial effect decreased with increasing pre-oxidation time, the alloy implanted directly with Ce had the lowest oxidation rate constant. During cyclic oxidation (350 cycles) Ce implantation played a similar benefical effect on the oxide-spallation resistance for blank and pretreated alloys. The result indicates that Ce incorporated into the oxide scale affected the diffusion of the reaction species and also the spallation resistance of the oxide scales. The change of the oxidation process is attributed to the segregation of Ce at the oxide grain boundaries

Advances in the scintillation performance of LSO:Ce single crystals

We investigated the scintillation characteristics of 2186 LSO crystals that were cut from over 400 crystal boules. We measured the light output and energy resolution of all crystals, and also measured the decay times of a broad sampling of the crystals. We observed a significant reduction in the variation of both light output and decay time in this population of crystals compared to the results previously published in 1998. The reduced variation in scintillation properties may be attributed to better control of the populations of the two Ce scintillation centers in LSO, as well as better control of the effect of quenching centers, and the effects of Ce segregation during crystal growth.

Growth of Si Thin Films on CeO2/Si(111) Substrate Using Electron-Beam Evaporation

The growth mechanism of Si film on a CeO2(111)/Si(111) substrate has been investigated using X-ray diffraction (XRD), double crystal XRD (DCXRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We have epitaxially grown a CeO2 film on the Si(111) surface by deposition of CeO2 at 640°C. When Si was deposited at 620°C on the CeO2(111)/Si(111) substrate using a high-vacuum e-beam evaporator, it was observed from XRD analysis that the Si film grew along the [111] direction. The TEM and AFM images showed that the top Si layer consists of large mountains and deep valleys. The XPS data showed no segregation of Ce on the Si layer surface. However, there was slight diffusion of Ce along the top layer Si grain boundary. These analysis results reveal that at the early stage of deposition, Si crystal nuclei are formed on a domain of the CeO2 film on Si(111) and grow three-dimensionally along the [111] direction, and eventually these merge into large mountains.

Scintillation properties of LSO:Ce boules

We investigated the scintillation characteristics of 1880 LSO crystals that were cut from 76 crystal boules. We measured the light output and energy resolution of all 1880 crystals, and also measured the decay times of 1169 of the crystals. We observed trends in light output and energy resolution that were not previously evident from studies of small numbers of crystals, and in addition, a correlation between light output and decay time became evident for the first time. The results may be interpreted in terms of the properties of the two Ce scintillation centers in LSO, the effect of quenching centers, and the effects of Ce segregation during crystal growth.

Segregation of Ce in Ca 0.55Sr 0.45Ga 2S 4:Ce thin films during annealing

Surface and interfacial segregation of cerium in sputter-deposited Ca 0.55Sr 0.45Ga 2S 4:Ce (thiogallate) films during annealing between 550°C and 750°C has been studied. Composition vs. depth of the thiogallate thin films was determined using secondary ion mass spectrometry (SIMS) and microstructure was examined using transmission electron microscopy (TEM). Cerium segregation to the ambient/thiogallate surface was driven by oxide formation, while segregation to the thiogallate/insulator was driven by formation of a Ce–Zn–O–S quaternary phase.

95/06283 Performance characteristics of a water-in-oil-fired stream generator for a 300-MW power plant

The specimens of 1Cr-0.5Mo low alloy steel, undoped, Sn-doped and Ce+Sn-doped, were austenitized at 1300 °C and then cooled down to different temperatures in the range of 700–1050 °C, followed by tensile tests with the aid of a Gleeble machine. The reduction of area (RA) obtained from the test was employed to evaluate the hot ductility of the steel. The tested specimens were characterized using different techniques. Minor Sn could considerably reduce the RA values of the steel in the whole temperature range, and the hot ductility curve could be widened and deepened. Nevertheless, minor Ce could improve the hot ductility of the Ce+Sn-doped steel by fully suppressing the Sn-induced hot ductility deterioration. FEGSTEM microanalysis showed that the Sn or Ce and Sn atoms segregated to austenite grain boundaries in the Sn-doped or Ce+Sn doped specimens. The detrimental effect of Sn on the hot ductility could be attributed mainly to the segregation of Sn as it could decrease the grain boundary cohesion and in turn enhanced the grain boundary sliding and cracking. However, this detrimental effect of Sn could be counteracted by the segregation of Ce which could increase the grain boundary cohesion and in turn restrained the grain boundary sliding and cracking. Accordingly, a minor addition of rare earth Ce could be an effective method of suppressing the detrimental effect of impurity elements on the hot ductility of a Cr-Mo low alloy steel.

95/06284 A practising engineer's experiences in overcoming inherent design problems in thermal power station boilers

The specimens of 1Cr-0.5Mo low alloy steel, undoped, Sn-doped and Ce+Sn-doped, were austenitized at 1300 °C and then cooled down to different temperatures in the range of 700–1050 °C, followed by tensile tests with the aid of a Gleeble machine. The reduction of area (RA) obtained from the test was employed to evaluate the hot ductility of the steel. The tested specimens were characterized using different techniques. Minor Sn could considerably reduce the RA values of the steel in the whole temperature range, and the hot ductility curve could be widened and deepened. Nevertheless, minor Ce could improve the hot ductility of the Ce+Sn-doped steel by fully suppressing the Sn-induced hot ductility deterioration. FEGSTEM microanalysis showed that the Sn or Ce and Sn atoms segregated to austenite grain boundaries in the Sn-doped or Ce+Sn doped specimens. The detrimental effect of Sn on the hot ductility could be attributed mainly to the segregation of Sn as it could decrease the grain boundary cohesion and in turn enhanced the grain boundary sliding and cracking. However, this detrimental effect of Sn could be counteracted by the segregation of Ce which could increase the grain boundary cohesion and in turn restrained the grain boundary sliding and cracking. Accordingly, a minor addition of rare earth Ce could be an effective method of suppressing the detrimental effect of impurity elements on the hot ductility of a Cr-Mo low alloy steel.

Analytical Electron- and Atomic Force Microscopy Study of Multilayered Oxide Films Formedon Ce-DOPED Ni

ABSTRACTOxide films up to 200 nm thick were grown at high temperatures on Ni substrates implantedwith 2x1016 Ce ions/cm2. The surface morphology, microstructure and microchemistry were examined by AFM and TEM/STEM techniques. It has been found that the oxide films are composed of three well defined sublayers, with essentially different microstructure and Ce concentration. The outer layer is composed of NiO and CeO2 nanocrystals with a size less than 5 nm. The same two phases are also present within the middle layer, although the NiO grains are much larger in comparison to nano-sized CeO2. In addition, Ce segregation along the NiO grain boundaries is detected in this layer. The inner layer is the thickest one and is composed of pure NiO grains. Oxide films having such a complex structure are characterized by a very low diffusion rate for both metal and oxygen ions. Oxygen isotope experiments revealed that the diffusion processes within the oxide film are controlled by the Ce-rich layers.

Redistribution of Ce and La during processing of Ce(La)-TZP/Al2O3 composites

Abstract The dispersion of second-phase particles, platelets or fibres in a ceramic body offers possibilities of considerable improvements in mechanical properties. In such second-phase reinforced composites the materials properties are to a large extent controlled by the structure of the internal interfaces, i.e. the phase and grain boundaries. The microstructure/microchemistry of aluminadispersed ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP/20A) were characterized by means of analytical TEM/STEM techniques. Local variation in the concentration of Ce stabilizer as well as of La additives and Si impurities during processing of the composite ceramics were studied by EDS X-ray analysis with high spatial resolution. Emphasis was put on the segregation of Ce and La in interface regions. Evidence was found for the presence of a vitreous intergranular phase situated in small pockets at triple grain junctions. The addition of small fractions of La 2 O 3 in TZP resulted in interreaction between matrix constituents and Al 2 O 3 particles. In this reaction a stable crystalline Al-Ce-La-Zr mixed oxide phase is formed, effectively reducing the fraction of residual vitreous intergranular phase, resulting in improved fracture toughness in this material.

Effect of Ion‐Implanted Cerium on the Growth Rate of Chromia Scales on Ni‐Cr Alloys

The oxidation kinetics of Ni‐30 Cr and Ce‐implanted Ni‐30 Cr alloys are studied at low oxygen partial pressures in the temperature range 900–1100°C. The growth rate of scales on the Ce‐implanted alloys is slower by at least an order of magnitude. The growth rate decreases with increasing Ce concentration but is independent of the ambient oxygen partial pressure. Oxide scales on the Ce‐implanted alloys grow predominantly by inward oxygen diffusion. Microstructural characterization of the oxide scale shows segregation of Ce to oxide grain boundaries and the presence of second‐phase particles. These observations have led to a model in which Ce dopes into , in both the grain boundary and the lattice regions, consuming Cr interstitials through an equilibrium between and Cr interstitials. The consumption of Cr interstitials retards chromium transport to such an extent that inward oxygen diffusion via doubly ionized oxygen vacancies becomes the dominant mode of transport during oxide scale growth.