Effect of Cerium on Microstructures and High Temperature Oxidation Resistance of An Nb-Si System In-Situ Composite

Nb-16Si-24Ti-6Cr-6A1-2Hf-xCe （x =0, 0.05, 0.1,02.5, 0.5, 1 （%, atom fraction）） in situ composites were prepared by arc melting The microstmcture and the effect of rare earth element cerium on 1250℃ oxidation resistance of the composites were investigated with scanning electron microscopy （SEM） and X-ray energy disperse spectrum （EDS）, as well as X-ray diffraction （XRD）. The experimental results showed that the high temperature oxidation resistance of the alloy was improved by adding a proper amount of cerium （Ce）. The effect of Ce was considered as the concurrent of the following three factors： first, the oxide of Ce formed in the interface reduced the internal oxidation rate; second, the lath shaped oxide containing Ce increased the cracking resistance and reduced the expansion of the oxide scale; and third, the decrease of the sificide volume fraction on account of Ce addition reduces the power of the sample resisting oxygen penetration.     

粉末冶金法制备WC-Ni3Al复合材料的组织与性能

在WC粉末中直接添加Ni、Al元素粉末,通过在液相烧结过程中反应合成Ni3Al来制备WC-Ni3Al复合材料,对该材料进行组织结构观察及力学性能测定,分析铝含量对合金致密化和镍铝相形成种类的影响,并对材料的抗氧化性能进行测试。结果表明,制备的WC-Ni3Al复合材料具有圆钝的WC晶粒形貌,粘结相中除Ni3Al相外还有少量的NiAl和Ni相;铝含量对WC-Ni3Al材料致密度的影响主要与高熔点的NiAl的形成量有关。与普通WC-15Ni硬质合金的抗弯强度(1 900 MPa)和硬度(82.6 HRA)相比,WC-15Ni3Al复合材料具有低的室温抗弯强度和高的硬度,分别为1 170 MPa和86.5 HRA。随Ni3Al含量(质量分数)从15%增加到30%,WC-30Ni3Al复合材料的室温抗弯强度增加,而硬度降低,分别为1 660 MPa和81.7 HRA,其高温抗氧化性能比WC-30(Co-Ni-Cr)硬质合金提高1个数量级。     

Effect of Yttrium and Cerium Addition on Microstructure and Mechanical Properties of AM50 Magnesium Alloy

To develop magnesium alloy with low cost, high strength and excellent elevated temperature properties, effect of Y and Ce addition on microstructure and mechanical properties of AM50 magnesium alloy was studied. Result showed that addition of small amount of Y and Ce to AM50 alloys resulted in refinement of microstructure. Owing to the improvement of microstructure, the mechanical properties of alloys at both ambient and elevated temperature were increased. AM50 alloy containing 0.6 % Ce-0.3 % Y （mass fraction） had good refinement effect and relatively ideal mechanical properties.     

Preparation and CO conversion activity of ceria nanotubes by carbon nanotubes templating method

Ceria nanotubes with high CO conversion activity by means of carbon nanotubes as removable templates in the simple liquid phase process were fabricated under moderate conditions. The pristine CNTs were first pretreated by refluxing in a 30% nitric acid solution at 140 ℃ for 24 h, then dispersed in an ethanolic Ce（NO3）3.6H2O solution with ultrasonic radiation at room temperature for 1 h. Under vigorous stirring, NaOH solution was added drop by drop into the above ethanolic solution until the pH value was 10. The product was collected and repeatedly washed with ethanol and on drying at 60 ℃, the CeO2/CNT composites were obtained. Then, the as-prepared composites were heated at 450 ℃ in an air atmosphere for 30 min to remove CNTs. The ceria nanotubes were characterized by X-Ray Diffraction （XRD）, Transmission Electron Microscopy （TEM）, and X-Ray Photoelectron Spectrum （XPS）. The results showed that the ceria nanotubes were polycrystalline face-centered cubic phase and were composed of lots of dense cefia nanoparficles. The diameter of cefia nanotubes was about 40-50 nm. Catalytic activity of the product for CO oxidation was carded out at the region of 30-300 ℃ in a U-shaped quartz reactor with feeding about 0.15 g of the catalyst, which was loaded on Al2O3 carder. The inlet gas composition was 1.0% CO and 28% O2 with N2 as balance, and the rate of flow was kept at 40 ml/min. The catalytic products were analyzed by gas chromatography. The as-repared CeO2 nanotubes showed higher CO oxidation activity, which indicated that the morphology of ceria products affected the catalytic performance. The ceria nanotubes supported on Al2O3 demonstrated that conversion temperature for CO oxidation to CO2 was lower than that for bulk catalysts.     

Fabrication of Ce-doped(Gd_2Y)Al_5O_(12)/Y_3Al_5O_(12) composite-phase scintillation ceramic

In this paper, a novel Ce(Gd_2 Y)Al_5O_(12)/Ce:Y_3Al_5O_(12)(Ce:GYAG/Ce:YAG) composite scintillation ceramic was designed and fabricated by a solid-state reaction method. The phase, luminescence and scintillation properties were investigated. The Ce:GYAG/Ce:YAG composite ceramic consisting of two-phase has a broad emission band ranging from 500 to 750 nm. The total mass attenuation coefficient of Ce:GYAG/Ce:YAG is 0.3864 cm~(-1), in between those of Ce:YAG and Ce:GYAG ceramics. In addition, the composite ceramic had a high light yield of 20430 ph/MeV. By controlling the ratio of GYAG and YAG, the composite ceramic can realize a spectrum design and total mass attenuation coefficient control to meet the requirements for wide-X-ray-energy-range detectors.     

稀土Y离子注入对形成不同类型氧化膜合金的高温抗氧化性能的影响

：研究了稀土Ｙ离子注入对ＦｅＣｒ,ＦｅＣｒＡｌ及ＮｉＣｒ合金高温抗氧化性能的影响。结果表明,对于主要形成Ｃｒ２Ｏ３膜的ＦｅＣｒ和ＮｉＣｒ合金,通过离子注入Ｙ可以明显提高其高温抗氧化性能,但对形成Ａｌ２Ｏ３膜的ＦｅＣｒＡｌ合金,离子注入对合金抗氧化性能没有影响,添加稀土Ｙ则使ＦｅＣｒＡｌ合金抗氧化性能大大提高。分析了氧化前、后氧化膜结构变化,认为早期形成的Ｙ２Ｏ３膜对高温氧化时金属离子的扩散有不同的影响     

稀土Y、Ce对钼合金力学性能的影响

实验以MoO2和Ce(NO3)3.6H2O、Y(NO3)3.6H2O为原料,通过固-液掺杂、还原、烧结、拉伸制备钼合金丝。通过XRD、扫描电镜以及力学性能试验,研究了稀土元素Y、Ce在粉末及钼合金中的存在形式以及对钼合金力学性能的影响。结果表明:Y、Ce元素分别以CeO2和Y2O3形式存在于钼粉中,Y对钼粉颗粒长大的抑制效果高于Ce;钼合金中,稀土Y和Ce作用不同,Y抑制晶粒的长大,延迟烧结;而Ce促进烧结,使烧结完全致密化;钼合金丝中,CeO2质点以纤维状存在,有利于提高钼丝的塑性,而Y2O3质点以球状颗粒存在,钼合金丝的室温和高温抗拉强度较高。Y、Ce的共同作用,MYCe合金丝综合力学性能好。     

热压烧结原位合成Coss/Co3Mo2Si复合材料

为优化过渡金属硅化物的中低温脆性, 以金属粉末为原料通过热压烧结制备了Co₃Mo₂Si增强、Co基固溶体(Co_ss)增韧Co_ss/Co₃Mo₂Si复合材料, 并对其微观组织结构及力学性能进行了研究。结果表明: Co_ss/Co₃Mo₂Si复合材料主要由Co₃Mo₂Si三元金属硅化物相和Co_ss相组成, 两相均匀分布; Co₃Mo₂Si三元金属硅化物相质量分数增加材料的硬度升高, 但抗弯强度降低, Co_ss相质量分数增加材料的相对密度和抗弯强度均升高; 抗弯强度的最大值可由单一Co₃Mo₂Si相的335.7MPa提高到Co_ss/Co₃Mo₂Si复相的756.2MPa。     

Study of cerium ion in (Y0.95La0.05)2O3:Ce

(Y0.95La0.05)2O3: Ce3+ nano-powder was synthesized by co-precipitation method and sintered at 800 and 900 oC. All the samples were cubic phase characterized by X-ray diffraction (XRD) analysis. The samples sintered at the lower temperature exhibited luminescence. According to the distinguishable structure of Ce 3d peaks and the shift of O 1s lines in the X-ray photoelectron spectroscopy (XPS), luminescence was further confirmed to originate from Ce3+ ions. Effects of introducing La3+ into Y2O3 were discusse...     

Phase relations of a silicide/silica reaction couple at 2273 K

The phase relations of a zirconium silicide/silica reaction couple have been investigated at 2273 K in air. After annealing times from 4 to 49 hours, the reaction couples, created by encapsulating zirconium disilicide in a quartz ampule, developed an interdiffusion zone and an inner core consisting of solidified zirconium silicide. The interdiffusion zone consisted of a silica layer, zirconia precipitates, and prior liquid silicide globules dispersed in prior liquid silica. Zirconia precipitates formed from the oxidation of the silicide melt between the protective silica layer and the two liquid regions of silicide and silica, as a result of oxygen diffusion. At 2273 K, the inner core consisted of liquid zirconium silicide (ZrSi)_L, although the microstructure analysis indicated formation of proeutectic ZrSi₂ and a eutectic microstructure of ZrSi₂ and Si upon solidification. A constant oxygen potential developed within the interdiffusion zone and protected the silicide from oxidation even after 49 hours at temperature.     

Preparation of La0.9RE0.1MnO3 Ultra-fine Particles Used for CH4 Oxidation

Ｐｅｒｏｖｓｋｉｔｅ ｔｙｐｅｏｘｉｄｅｓ (ｇｅｎｅｒａｌｆｏｒｍｕｌａＡＢＯ3 )ｈａｖｅｂｅｅｎａｔｔｒａｃｔｉｎｇｍｕｃｈａｔｔｅｎｔｉｏｎｆｏｒｍｏｒｅｔｈａｎｔｗｏｄｅｃａｄｅｓｄｕｅｔｏｔｈｅｉｒｐｏｔｅｎｔｉａｌｃｏｍｍｅｒｃｉａｌａｐｐｌｉｃａｔｉｏｎｓａｓｃａｔａｌｙｓｔｓｆｏｒｖａｒｉｏｕｓｒｅａｃｔｉｏｎｓ :ｏｘｉｄａｔｉｏｎｏｆＣＯ[1～ 3 ] ａｎｄｌｉｇｈｔｈｙ ｄｒｏｃａｒｂｏｎｓ[4～ 7] ,ｃｏｍｂｕｓｔｉｏｎｏｆｎａｔｕｒａｌｇａｓｏｒＣＨ4 [8～ 1 1 ] (ｔｏｃｏｎｔｒｏｌＮ…     

Effects of Cerium on the Mechanical Properties of the ZA22／Al_2O_3 Composites

ＥｆｆｅｃｔｓｏｆＣｅｒｉｕｍｏｎｔｈｅＭｅｃｈａｎｉｃａｌＰｒｏｐｅｒｔｉｅｓｏｆｔｈｅＺＡ２２／Ａｌ_２Ｏ_３ＣｏｍｐｏｓｉｔｅｓＹｕＳｉｒｏｎｇ；ＨｅＺｈｅｎｍｉｎｇ；ＭｅｎｇＣｈａｎｇｓｈｅｎｇ；ＣｈｅｎＫａｉ（ＪｉｌｉｎＵｎｉｖｅｒｓｉｔｙｏ...     

铈对ZG75CrMo钢中非金属夹杂物及钢性能的影响

探讨了铈对ＺＧ７５ＣｒＭｏ钢中夹杂物及钢性能的影响。研究表明，与ＺＧ７５ＣｒＭｏ钢相比，ＺＧ７５ＣｒＭｏ（Ｃｅ）钢中夹杂物的含量减少且性态改变，塑韧性、抗热疲劳性和抗高温氧化性均有明显提高。     

Catalytic oxidation of formaldehyde over CeO_2-Co_3O_4 catalysts

A series of CeO_2-Co_3O_4 mixed oxide catalysts with different Co/(Co+Ce) atomic ratios were synthesized by citric acid sol-gel method and used for catalytic oxidation of formaldehyde(HCHO). Many techniques such as Brumauer-Emmett-Teller(BET), X-ray diffraction(XRD), scanning electron microscopy(FE-SEM), temperature programmed reduction(H_2-TPR), temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy(XPS) were used to characterize catalysts. The results of catalytic performance tests showed that the catalyst CeO_2-Co_3O_4 with Co/(Co+Ce) ratio of 0.95 exhibited the best performance, and the temperature of complete oxidation of HCHO was 80 oC. The analytical results indicated that the addition of CeO_2 enhanced the specific surface area of Co_3O_4 and the fine dispersion of both of them. Moreover, the strong interaction between CeO_2 and Co_3O_4 resulted in the unique redox properties, which enhanced the available surface active oxygen and led to high valence state of cobalt oxide species. All those effects played crucial roles in the excellent performance of CeO_2-Co_3O_4 for the HCHO oxidation.     

Synthesis, heat resistance, and optical properties of boron silicide and materials based on it

Conditions of synthesis from elements of pure superfine powder of boron silicide B₄Si are investigated. It is shown that the silicide phase forms on boron particles and B₄Si particles inherit the shape and size of initial boron particles, which makes it possible to control the particle size of the powder obtained. The oxidation of pure boron silicide and materials based on it in air and their optical properties are studied. It is shown that chromium diboride added to boron silicide increases the oxidation resistance of B₄Si and hardly decreases its absorbance. The B₄Si-CrB₂ material can be successfully introduced into the compositions of heat-protective coatings operating in air at 1300 °C. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 45–52, 2007.     

钼合金制备工艺的研究进展

纯金属钼存在低温脆性、再结晶脆性、抗高温氧化能力较差等明显缺点,极大限制了其应用范围,通过在钼基体中添加第二相(稀土氧化物(La_2O_3、Ce_2O_3、Y_2O_3)和碳化物(TiC、ZrC、HfC))形成的钼合金因具有良好的高温性能、较低的韧脆转变温度、较高的再结晶温度受到了国内外学者的广泛关注。本文对三种钼合金制备工艺(固–固掺杂、固–液掺杂和液–液掺杂)进行了总结,并对其发展趋势做出了展望,结果表明采用液–液掺杂工艺能显著提高材料的均匀性和力学性能。     

Photoluminescence properties of Ce3+ doped YSiO2N blue-emitting phosphors

Oxonitridosilicate phosphors with compositions of Y 1-x Ce x SiO 2 N (x=0-0.1) were synthesized by a new synthetic route based on a solid state reaction among YSi, CeSi, SiO 2 and Y 2 O 3 compounds at high temperature and high pressure. The photoluminescence properties dependent on Ce concentration and temperature were investigated. Concentration quenching occurred when the doped Ce 3+ concentration was more than 3 mol.%. The emission spectra showed red shifts from 430 to 447 nm with the increased Ce concentration from 0.5 mol.% to 10 mol.%. The quenching temperature was estimated as ～380 K. The chromaticity coordinates of the excitation and emission spectra were stable against the temperature. This study showed these YSiO 2 N:Ce 3+ phosphors the potential applications in the three-RGB phosphor-converted white LEDs.     

Rare Earth Doping Effects on Properties of Ceria-Zirconia Solid Solution

Ce0.6Zr0.3RE0.1O2(RE=Y, La, Pr, Tb)solid solutions were prepared by co-precipitation technique and characterized by a series of methods. XRD and FT-Raman results show that Ce0.6Zr0.3RE0.1O2 has cubic fluorite structure. The different dopant ion radii bring different effect on the cell parameter of Ce0.6Zr0.3RE0.1O2. The X-ray photoelectron spectroscopy (XPS) results show that the binding energy of Ce3d, Zr3d and O1s for Ce0.6Zr0.3RE0.1O2 rises compared with that for Ce0.6Zr0.4O2, indicating that dopant elements change chemistry environment of solid solutions which is available to improve redox performance. Compared with Pd/Ce0.6Zr0.4O2, doping Y and La does not change air/fuel (A/F) characteristic of TWCs, but doping Pr and Tb widens A/F operating window and makes HC, CO and NO have higher conversion. The light-off temperature of Pd/Ce0.6Zr0.3La0.1O2 is corresponding to that of Pd/Ce0.6Zr0.4O2. However, the light-off temperatures of Pd/Ce0.6Zr0.3M0.1O2 (M=Y, Pr, Tb) are lower than that of Pd/Ce0.6Zr0.4O2, which keep much lower after high temperature treatments. Among Pd/Ce0.6Zr0.3RE0.1O2, Pd/Ce0.6Zr0.3Tb0.1O2 represents wider A/F operating window, higher conversion, lower light-off temperature and better high-temperature resistance.     

A novel green-yellow emitting phosphor Ca1.5Y1.5Al3.5S1.5O12：Ce^3＋ and its luminescence properties

We described the synthesis and luminescence of Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ phosphor for light emitting diode (LED). The crystal-linity, morphology, structure, and luminescence spectra were examined by X-ray diffraction, field emission-scanning electron microscopy and photoluminescence spectroscopy. The results showed that Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ phase was a dominating phase with little impurity phase peaks of Y2O3 when the sintered temperature reached to 1400 oC. Field emission scanning electron microscopy (FE-SEM) images showed the particle size of the phosphor was about 3 μm. Meanwhile, the excitation and emission spectra indicated that the as-prepared phosphors could be effectively excited by blue (460 nm) light and the excitation spectrum showed a broad band extending from 400-500 nm, while emission spectrum showed a broad yellow band peaking at 534 nm. The decay curve at the emission peak consisted of fast and slow components. The Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ should be a promising yellow phosphor for near blue-based white-light-emitting diodes (LEDs).     

Influence of Cerium and Yttrium on Cu-Cr-Zr Alloys

Testing results shows that alloying with Ce and Y improves the hardness and softens temperature of cold worked Cu-Cr-Zr alloys obviously, while the conductivity was fluctuant with the variation of RE content. Observation and analysis indicate that micro-dosage RE elements helps to refine microstructure and morphology of Cu-Cr-Zr-RE alloys, suppress microstructure coarsening and improves homogeneous level of Cu-Cr-Zr alloys. Alloying with 0.01% Ce causes about 1% IACS increment of conductivity, and reduces about 2%～3.5% IACS conductivity after alloying with 0.03%～0.04% RE (Ce or Ce Y) for Cu-Cr-Zr alloys. The microstructure of as-cast Cu-Cr-Zr alloy is refined after alloying with 0.01% Ce while the plasticity is improved slightly. Alloying with 0.01%～0.04% RE improves the softening temperature of deformed Cu-Cr-Zr alloys about 20～40 K; hardness is also improved about 20～35 HV. Test data indicate that alloying with Ce Y raises softening temperature and hardness of Cu-Cr-Zr alloys more notably than alloying with pure Ce.