Combustion synthesis and characterizations of Sm_2O_3 doped zirconolite-rich waste forms with CuO as oxidant

Zirconolite is one of the most important matrix materials for nuclear waste immobilization.In this study,Sm was employed as the surrogate of trivalent actinides.Sm-doped zirconolite-rich waste forms were readily prepared by combustion synthesis(CS) using CuO as the oxidant.Two different schemes with or without Al_2O_3 as the charge compensator were carried out simultaneously.The results demonstrate that Al_2O_3 addition results in complex phase composition.On the other hand,the samples without Al_2O_3 addition show desirable products of zirconolite and pyrochlore.The EDX analysis shows that Sm is concurrently incorporated into the Ca and Zr sites of zirconolite,which transforms to pyrochlore structure with high Sm_2O_3 contents.The aqueous durability of representative Sm-doped sample(Sm-0.6)was investigated.The 42 days normalized leaching rate of Sm is as low as 6.41×10~(-7) g/(m~2 d),which exhibits high durability of Sm-doped sample.     

CO2 sensing properties and mechanism of PrFeO3 and NdFeO3 thick film sensor

The CO_2 sensing of PrFeO_3 and NdFeO_3 sensors were investigated. Experimental results show that the resistances for PrFeO_3 and NdFeO_3 in CO_2 gas are larger than those in air and the responses for PrFeO_3and NdFeO_3 sensors increase with an increase in room-temperature relative humidity. When exposed to1000 ppm CO_2, the response of PrFeO_3 thick film based on nano-powders annealed at 700℃can reach8.44 at 160℃for the background of wet air with 58%of room-temperature relative humidity (RH),which is much larger than the corresponding value (3.03) in wet air with 25%RH. The sensing response S of NdFeO_3 thick-film sensor based on nano-powders annealed at 600℃to 3000 ppm CO_2 at the operating temperature 200℃can reach 2.36 for the background of wet air with 72%RH, which is larger than the corresponding value (1.83) in the air with 25%RH. Compared with other CO_2 sensing materials, the PrFeO_3 sensor has larger response at lower operating temperature for CO_2 gas and may be used as a new CO_2 sensing material.     

In vivo optical bioimaging by using Nd-doped LaF_3 luminescent nanorods in the second near-infrared window

Fluorescent imaging in the second near-infrared(NIR-Ⅱ, 1000-1700 nm) region has attracted enormous research interest due to its advantages of unprecedentedly improved imaging sensitivity and spatial resolution. Herein, high quality NIR-Ⅱ emissive LaF_3:Nd~(3+) nanorods(NRs) with hexagonal phase structure and controlled size were synthesized by a hydrothermal method. And the Nd~(3+) doping induced NIRⅡ luminescent intensity evolution was studied, In vivo NIR-Ⅱ bioimaging and real-time tracking reveal that these LaF3:Nd~(3+) NRs are mainly accumulated in liver and spleen. Moreover, in vivo toxicity assessment demonstrates that LaF_3:Nd~(3+) NRs feature low biotoxicity and good biocompatibility in living animals. Therefore, the NIR-Ⅱ emitting hexagonal phase LaF_3 NRs with controlled size are promising probes for optical bioimaging.     

Improvement of coercivity and thermal stability of Nd-Fe-B sintered magnets by intergranular addition of Tb80Fe20 alloy

To improve the coercivity and temperature stability of Nd-Fe-B sintered magnets for high-temperature applications, the eutectic Tb₈₀Fe₂₀ (wt%) alloy powders were added into the Nd-Fe-B sintered magnets by intergranular method to enhance the coercivity (H_cj) and thermal stability. The microstructure, magnetic properties and thermal stability of the Nd-Fe-B magnets with different Tb₈₀Fe₂₀ contents were studied. The experimental results demonstrate that the coercivity (H_cj) of the sintered Nd-Fe-B magnet is significantly enhanced from 14.12 to 27.78 kOe, and the remanence (B_r) decreases not obviously by introducing 4 wt% Tb₈₀Fe₂₀ alloy. Meanwhile, the reversible temperature coefficients of coercivity (β) and remanence (α) of the Nd-Fe-B magnets are increased from ?0.5634%/℃ to ?0.4506%/℃ and ?0.1276%/℃ to ?0.1199%/℃ at 20–170 ℃, respectively. The Curie temperature (T_C) of the Nd-Fe-B magnet is slightly enhanced with the increase of Tb₈₀Fe₂₀ content. Moreover, the irreversible flux magnetic loss (h_irr) is obviously reduced as Tb₈₀Fe₂₀ addition increases. Further analysis of the microstructure reveals that a modified microstructure, i.e. clear and continuous RE-rich grain boundary layer, is acquired in the sintered magnets by introducing Tb₈₀Fe₂₀ alloy. The associated mechanisms on improved coercivity and thermal stability were comprehensively researched.     

Effect of fluxes on synthesis and luminescence properties of BaSi2O2N2:Eu2+ oxynitride phosphors

Eu²⁺ activated BaSi₂O₂N₂ oxynitride bluish-green phosphor was synthesized adopting conventional high-temperature solid-state reaction method, in which BaF₂, Na₂CO₃ and NH₄Cl were used as the fluxes. The phase formation, size distribution and microscopic morphology were characterized to investigate the influence of adding fluxes on photoluminescence properties. The results indicate that with the addition of BaF₂ flux, the particle morphology becomes regular and size distribution narrows and the phase purity of BaSi₂O₂N₂:Eu²⁺ phosphor can be improved effectively. The photoluminescence intensity of BaSi₂O₂N₂:Eu²⁺ phosphor with BaF₂ as flux gets enhanced obviously, which is much higher than that of Na₂CO₃, NH₄Cl and without flux. The optimum content of BaF₂ flux is 4 wt%, and the maximum photoluminescence intensity of the BaSi₂O₂N₂:Eu²⁺ phosphor prepared with BaF₂ flux rises to 141%, meanwhile, the phosphors with BaF₂ flux exhibits low thermal quenching. The results indicate that the BaSi₂O₂N₂:Eu²⁺ is sort of promising bluish-green phosphor for application in full-spectra LED.     

Improved corrosion resistance and thermal stability of sintered Nd-Fe-B magnets with holmium substitution

The effects of Ho substitution for Nd on the microstructure, corrosion resistance and thermal stability of the Nd-Fe-B magnets were investigated. The(Nd,Ho)-O phase was formed with increasing Ho substitution. The results of potentiodynamic polarization and highly accelerated stress test show improved corrosion resistance with increasing Ho substitution. The optimum mass loss 0.29 mg/cm~2 is achieved.Moreover, the average temperature coefficients for remanence and coercivity in the range of 25-150℃are both closer to zero, indicating improved thermal stability. The mechanisms for the improved corrosion resistance and thermal stability are discussed in relation to the microstructure featuring the(Nd,Ho)-O phase.     

Chemical Bond and Spectral Effect of Rare Earth Compound Crystals

The chemical bond parameters and ionic polarizabilities in complex crystals are calculated.Themechanism of host influence on the nephelauxetic effect and hypersensitive transition is discussed.     

Promoting effect of tantalum and antimony additives on deNOx performance of Ce3Ta3SbOx for NH3-SCR reaction and DRIFT studies

A superior Ce-Ta-Sb composite oxide catalyst prepared using homogeneous precipitation method exhibited excellent deNOx efficiency and nearly 100% N_2 selectivity with broad operation temperature window and better resistance to higher space velocity, meanwhile strong resistance to H_2 O and SO_2. This catalyst was systematically characterized using XRD, N_2 adsorption, SEM, TEM, XPS, ESR, Raman, H_2-TPR,NH3-TPD and in situ DRIFTS. There exists a synergistic effect between Ce, Ta and Sb species. It is further indicated that the prominent deNOx performance of the Ce3 Ta3 SbOx catalyst is attributed to the elevated Ce3+ concentrations, abundant active surface oxygen species, as well as surface acidity and reducibility,which is closely linked with the synergistic effect between Ce, Sb and Ta species. Results from DRIFTS reveal that the reaction mechanism of surface-adsorbed NH3 and NO_x species is linked to temperature,the L-H mechanism mainly occurs at low temperature(300 ℃),while the E-R mechanism occurs at high temperature(300 ℃). Overall,these findings indicate that Ce3 Ta3 SbOx is promising for NO_x practical abatement.     

Effect of grain size on thermal stability and oxygen storage capacity of Ce0.17Zr0.73La0.02Nd0.04Y0.04O2 solid solutions

Nanostructured CeO_2-ZrO_2 materials are an irreplaceable constituent in catalytic systems for automobile exhaust purification due to their unique oxygen storage capacity(OSC). However, traditional CeO_2-ZrO_2 materials are easy to sinter at high temperature, which causes a sharp decrease of OSC. In this paper,La~(3+) , Nd~(3+) and Y~(3+) are chosen as dopants for CeO_2-ZrO_2 to improve anti-sintering and OSC properties.The Ce_(0.17) Zr_(0.73) La_(0.02) Nd_(0.04) Y_(0.04) O_2 powders(CZLNY) were prepared by co-precipitation method. The effects of grain sizes with different mixed chlorinated solution concentrations on performances were investigated. X-ray diffraction(XRD) and transmission electron micrograph(TEM) were performed to calculate the grain sizes of CZLNY. The specific surfaces, OSC and redox properties were investigated by N_2 adsorption/desorption and temperature programmed reduction(H2-TPR). The results show that introducing La~(3+) , Nd~(3+) and Y~(3+) into CeO_2-ZrO_2 lattice can improve the stability of phase structure and anti-sintering ability. Moreover, low concentration of mixed chlorinated solution remarkably improves structural and textural properties of CZLNY. Relatively large fresh grain exhibits superior thermal stability and OSC under the condition of being calcined at 800℃ for 3 h. The specific surface and OSC are42.37 m~2/g and 333.13 mmol/g after calcining at 1000℃ for 10 h, respectively. This is owing to the low sintered driving force of large grain and long-range migration energy of large pores during the sintering process, which are beneficial to the stability of structure in CZLNY materials.     

Magnetic property recovery in Nd-Fe-B bonded magnet wastes with chemical reaction and physical dissolution

The main difficulty for the recovery of Nd-Fe-B bonded magnet wastes is how to completely remove the epoxy resins. In this study, chemical reaction and physical dissolution were combined to remove the epoxy resins by adding ammonia-water and mixed organic solvents. Ammonia-water can react with the epoxy functional group of epoxy resin to generate polyols. Mixed organic solvents of alcohol, dimethyl formamide (DMF), and tetrahydrofuran (THF) can dissolve the generated polyols and residual epoxy resins. Under the optimum processing conditions, the epoxy resins in the waste magnetic powders are substantially removed. The oxygen and carbon contents in the recycled magnetic powder are reduced from 13500 × 10⁻⁶ to 1600 × 10⁻⁶ and from 19500 × 10⁻⁶ to 2100 × 10⁻⁶ with the reduction ratio of 88.1% and 89.2%, respectively. The recycled magnetic powder presents improved magnetic properties with M_s of 1.306 × 10⁻¹ A∙m²/g, M_r of 0.926 × 10⁻¹ A∙m²/g, H_cj of 1.170 T, and (BH)_max of 125.732 kJ/m³, which reach 99.8%, 99.4%, 95.9%, and 96.9% of the original magnetic powders, respectively.     

Nd-doped structurally disordered YSr3(PO4)3 single crystal: Growth and laser performances

Disordered-structure crystals have drawn increasing attention as promising ultrashort laser material hosts owing to their broad linewidth. Herein, a novel disordered Nd:YSr₃(PO₄)₃ (Nd:YSP) crystal with good quality was successfully grown via the Czochralski pulling technique. The absorption and fluorescence spectra of the Nd:YSP single crystal were recorded at ambient temperature. The maximum absorption cross section for Nd:YSP single crystal is found to be approximately 3.89 × 10⁻²⁰ cm². The stimulated emission cross section for Nd:YSP crystal at ∼1060 nm was determined to be 7.64 × 10⁻²⁰ cm² with the full width half maximum value of 22 nm. The fluorescence lifetime of the Nd³⁺ ions in the Nd:YSP crystal is fitted to be 288 μs. Diode-pumped continuous-wave laser operation is firstly realized at approximately 1060 nm. The maximum output power value from the Nd:YSP crystal is 714 mW, corresponding to a slope efficiency of ∼12.8%. The results indicate that the Nd:YSP crystal with a disordered structure may be a promising disordered laser host.     

Synthesis and Electrocatalytic Properties of Complex Oxides Containing Lanthanum

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Possible negative influences of increasing content of cerium on activity and hydrothermal stability of Rh/ceria-zirconia three-way catalysts

The activity and hydrothermal stability of the Rh/Ce_xZr_(1-x)O_2(x=0,0.05,0.3,0.5) model three-way catalysts for gasoline vehicle emissions control were investigated in this work.Among the Rh/Ce_xZr_(1-)_xO_2 samples with different Ce/Zr ratios,the Rh/ZrO_2 sample exhibits a significantly better activity and hydrothermal stability than the rest of the samples.The impacts of having more Ce components in the Rh/Ce_xZr_(1-x)O_2 catalysts are associated with the strong Rh-O-Ce interaction that tends to over stabilize the rhodium species.A significant amount of such rhodium atoms can be found in the bulk of the support oxides after a hydrothermal aging at 1050℃ with 10% H_2 O in air for 12 h.Differently,the sintering of rhodium on the surface of Rh/ZrO_2 catalysts is the main reason for the catalyst deactivation during the hydrothermal aging.These findings provide an example where high dispersion of supported metal induced by strong metal-support interactions does not necessarily lead to high catalytic activity.     

Hydrothermal synthesis and characterization of Dy-doped CeVO_4 nanorods used for photodegradation of methylene blue and rhodamine B

Pure CeVO_4 and Dy-doped CeVO_4 nanorods containing different weight contents of Dy dopant were synthesized by hydrothermal method.Effect of Dy dopant on photodegradation of methylene blue(MB)and rhodamine B(RhB) was evaluated under UV light irradiation within 80 min.Pure CeVO_4 and Dydoped CeVO_4 nanorods were characterized by X-ray diffraction(XRD),Raman spectroscopy,transmission electron microscopy(TEM) and UV-visible spectroscopy.In this research,CeVO_4 nanorods are tetragonal phase with the detection of main peak shift after being doped with Dy.The length of nanorods is deceased from 50 to 200 nm for pure CeVO_4 to 50-100 nm for 3% Dy-doped CeVO_4.Photodegradation of MB and RhB by CeVO_4 nanorods under UV light irradiation is improved by Dy-dopant that plays the role in accepting electrons and reducing electron-hole recombination.MB and RhB solutions degraded by 3% Dy-doped CeVO_4 nanorods was 94% and 93% within 80 min,respectively.     

Combustion synthesis of YAG:Ce phosphors via the thermite reaction of aluminum

Cerium-doped yttrium aluminum garnet(YAG:Ce) as a yellow phosphor for white light-emitting diodes(LEDs) was synthesized via a facile combustion method using Y_2 O_3, CeO_2, Al_2 O_3, Al,and NaClO_4 as raw materials. The combustion synthesis approach utilizes the strong exothermic oxidation of aluminum to realize a self-sustaining reaction. In this study, we investigated the effects of the ratios of Al_2 O_3 to AI,fluxes, and coprecipitated materials as raw materials on the luminescence properties of the synthesized YAG:Ce phosphors. When the amount of Al_2 O_3 x is varied, the combustion reaction proceeds at x ≤ 1.8,with x = 1.725 being the optimum condition for producing a high-performance product. When 5 wt%BaF2 is added, the luminescence intensity is significantly improved owing to a decrease of YAP(YAlO_3)formation with improved uniformity. However, the addition of CaF_2 and NaF does not improve the luminescence properties. To suppress the segregation of CeO_2, we used the coprecipitated material Y_2 O_3-CeO_2 as a raw material. Unlike with separate addition of Y_2 O_3 and CeO_2, Ce ions are uniformly distributed in the coprecipitated material, resulting in improved luminescence properties. The combination of BaF_2 and coprecipitated material significantly improves the internal quantum efficiency to83.0%, which is close to that of commercial phosphors.     

Tunable luminescence,energy transfer and excellent thermal stability of SrMg_2(PO_4)_2:Ce~(3+),Tb~(3+) phosphors for LEDs

A series of novel SrMg_2(PO_4)_2:Ce~(3+),Tb~(3+)(SMP:Ce~(3+),Tb~(3+)) phosphors with tunable emission spectra were produced via high temperature solid phase method.XRD,fluorescence spectrum and fluorescence lifetime for SMP:Ce~(3+),Tb~(3+)were studied in detail.Under the excitation at 308 nm,SMP:Ce~(3+),Tb~(3+) samples can emit high efficiency tunable blue-green light by controlling the proportion of dopant concentration.Through the spectral overlap and the regular change of fluorescence lifetime,it is proved that there is a significant energy transfer between Ce~(3+) and Tb~(3+) in SMP matrix and the energy transfer mechanism is determined to be an electric dipole-dipole interaction with energy transmission efficiency of 55%.In additional,Commission International de L'Eclairage(CIE) color coordinates and thermal stability were studied.All above findings suggest that SMP:Ce~(3+),Tb~(3+)can be regarded as the potential bluish green phosphor for LED applications.     

Tunable emission,energy transfer and thermal stability of Ce3+, Tb3+ co-doped Na2BaCa(PO4)2 phosphors

A series of single Ce³⁺ doped and Ce³⁺ and Tb³⁺ co-doped Na₂BaCa(PO₄)₂ (NBCP) phosphors was synthesized by conventional solid-stated reaction method. The crystal structure, luminescence properties, thermal stability and energy transfer were carefully investigated. Ce³⁺ is inferred to substitute the Ba²⁺ site in NBCP lattice. The color-tunable emission from blue to green is observed by adjusting Tb³⁺ concentration among NBCP:0.03Ce³⁺,yTb³⁺ phosphors. The energy transfer behavior from Ce³⁺ to Tb³⁺ ions is both illustrated by co-doped PL spectra and decay curves. The energy transfer efficiency is as high as 91.5%. The mechanism of energy transfer is resonance type of dipole-dipole transition. In this work, the optimal phosphor exhibits the excellent thermal stability which keeps at 94.9% of that initial value at room temperature when temperature reaches to 150 °C. The Ce³⁺ and Tb³⁺ co-doped NBCP phosphor is a promising candidate for the application in the general lighting and display fields.     

Nature of cerium on improving low-temperature hydrothermal stability of SAPO-34

To probe the function of Ce on enhancing low-temperature stability of SAPO-34,Ce/SAPO-34 with different Ce contents was prepared via one-pot method and further treated at 70℃ in 80% relative humidity for 24 h.The structural results prove that the one-pot synthesis is an effective way to introduce Ce(Ce 0.325 wt%) without influencing micro-structural and chemical composition.The lowtemperature hydrothermal stability of Ce/SAPO-34 is enhanced by Ce loading.More than 92% CHA structure and total acidity are maintained over 0.188 wt% Ce/SAPO-34,while only about 20% of that left on pure H/SAPO-34.As Ce exists as Ce3+at exchange sites on the surface of SAPO-34,the results of the linear relationship between protected surface acidity and structure/acidity conservation manifest that Ce~(3+) effectively hinders the structural collapse.This study provides new insight into surface acidity protection for solving the problem of low-temperature hydrothermal stability of SAPO-34.     

Thermal Stability of Rare Earth-Rich Phase in High Temperature Titanium Alloy

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Bioaccumulation,subcellular distribution and chemical forms of yttrium in rice seedling

Yttrium (Y) accumulation in soil is a serious environment problem in China. To understand the mechanisms involved in Y tolerance and detoxification in rice seedling, the bioaccumulation, subcellular distribution, and chemical forms of Y was investigated in the present study. The results show that the content of Y both in roots and shoots increases with the increasing concentration of Y, and a large amount of Y is stored in roots. Subcellular distribution of Y in rice indicates that the majority of Y is bound to cell wall. Meanwhile, various chemical forms of Y is absorbed by rice. The greatest amount of Y is extracted by 2% hydrate acetic acid (HAc) and 0.6 mol/L HCl (particularly 2% HAc), which indicates that most of Y is combined with un-dissolved phosphate and oxalate (particularly phosphate). Cluster analysis, based on Y abundance levels, reveals the relationship between Y distribution patterns and chemical forms. Our results imply that Y forming of precipitates with phosphate (and/or oxalate) and depositing in the cell wall may be a key strategy for Y detoxicity and tolerance in rice.