Infrared spectroscopy analyses of air-CH4 or air-CO gas flows interacting with polycrystalline CeO2, La2O3 and Lu2O3 oxides

A comparative study of reactivity between air-CH4 or air-CO gas flows and CeO2, La2O3 and Lu2O3 rare earth oxides was performed using Fourier transform infrared spectroscopy analyses of CO2 gas resulted from the conversion of CH4 or CO gases. Polycrystalline samples of CeO2, La2O3 and Lu2O3 were first prepared by specific precipitation methods followed by low temperature calcination process. In the case of Lu2O3 oxide, a new specific route was proposed. Crystallite dimensions were determined by X-ray diffraction and transmission electron microscopy analyses. Morphologies were characterized using scanning electron microscopy. Specific surface areas were determined from Brunauer-Emmett-Teller (BET) technique. Using infrared spectroscopy analyses, the conversion rates of CH4 or CO into CO2 were determined from the evolutions of CO2 vibrational band intensities, as a function of time and temperature. It was clearly established that, despite its low specific surface, the Lu2O3 oxide presented the highest capacity of conversion of CH4 or CO into CO2.     

稀土对等离子束表面冶金涂层抗裂性的影响

 采用直流放电压缩电弧等离子束表面冶金技术，在Q235钢表面制备了添加La2O3和CeO2的铁基冶金涂层。研究了冶金涂层开裂的主要形式、稀土氧化物对冶金涂层组织及抗裂性的影响，初步探讨了稀土氧化物改善界面显微结构、抑制冶金涂层开裂的机制。结果表明：稀土除可与氧、硫、硼等反应外，还可固溶于晶内、晶界或晶界附近；添加适量的稀土氧化物可有效改善冶金涂层的组织和性能，抑制等离子束表面冶金涂层中的裂纹和孔洞。     

稀土氧化物对焊缝金属抗高温氧化腐蚀性能的影响

本文通过在焊条药皮中分别添加微量稀土氧化物Ｌａ２Ｏ３及ＣｅＯ２,研究其对焊条熔敷金属在空气中和含硫气氛中抗高温氧化及腐蚀性能的影响。结果表明：微量稀土氧化物在焊条药皮中的加入,对其熔敷金属抗高温氧化性能有所提高,对在含硫气氛中的抗高温腐蚀性能有显著提高,添加Ｌａ２Ｏ３的焊条熔敷金属比添加ＣｅＯ２的焊条具有更好的抗高温硫腐蚀性能。     

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In order to accurately control the rare earth content in liquid steel in electroslag remelting (ESR) process, according to the ion and molecule coexistence theory (IMCT) of slag structure and corresponding phase diagrams, a thermodynamic calculating model for the evaluation of mass action concentrations (designated by Ni for structure unit i) for La2O3-Al2O3-CaF2 slag system was formulated. The results show that the calculated values of NLa2O3 are in good agreement with the reported measured values, indicating that this calculating model can wholly embody the characteristics of the slag system. The activity of La2O3 decreases with the increasing of the Al2O3 and CaF2 content, and Al2O3 is stronger than CaF2 in decreasing the activity of La2O3. But the activity of La2O3 increase with the increasing in temperature at the composition range of 30% La2O3, 20% Al2O3, 50% CaF2. Above all, the activity of La2O3 in La2O3-Al2O3-CaF2 slag system can be quantitatively analyzed by this thermodynamic model, and this model can provide a theoretical basis for precisely controlling the lanthanum content in molten steel in ESR process.     

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 AlN 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 AlN, densification temperature decreased with the decrease of the ionic radius of rare earth ion and was closely related with the eutectic temperature in the RE2O3-Al2O3 binary system. The lowest densification temperature in the millimeter-wave sintering of AlN 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 AlNs.     

稀土氧化物复合ZrO2陶瓷的制备及应用研究进展

稀土氧化物可作为稳定剂、烧结助剂、掺杂改性剂加入到ZrO₂陶瓷材料中,能极大地提高和改善陶瓷材料的强度、韧性,降低其烧结温度,减少生产成本.文中简要综述了稀土氧化物ZrO₂陶瓷材料的制备及应用研究状况,包括Y₂O₃复合ZrO₂陶瓷粉体、富铈稀土氧化物复合ZrO₂陶瓷粉末、Nd₂O₃复合ZrO₂陶瓷材料、Pr₂O₃\Pr₆O₁₁复合ZrO₂陶瓷、La₂O₃复合ZrO₂陶瓷、Yb₂O₃复合ZrO₂陶瓷、Sm₂O₃复合ZrO₂陶瓷材料及氧化锆中掺杂多种稀土氧化物陶瓷粉体的制备和应用,分析讨论了一些需要解决的问题,并展望了稀土复合ZrO₂陶瓷制备技术及未来研究发展趋势.      

稀土固体超强酸SO42-/SnO2- Nd2O3催化合成棕榈酸甲酯

采用溶胶-凝胶法制备稀土固体超强酸催化剂SO4-/SnO2- Nd2O3,以工业棕榈酸和甲醇为原料催化合成棕榈酸甲酯.考察了氧化钕添加量、焙烧温度、硫酸浓度、醇酸质量比、催化剂用量和反应时间对酯化反应的影响.结果表明,当氧化钕添加量为5％,以2.0 mol/L硫酸浸渍后,于550℃下焙烧3h制备的催化剂性能最好.正交实验结果表明,合成棕榈酸甲酯的优化条件为:醇酸质量比为15∶25,催化剂用量为棕榈酸质量的6.0％,反应时间5h.在此条件下,酯化率为90.1％.     

Effects of rare earth oxides on dielectric properties of Y2Ti2O7 series ceramics

A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. The effects of rare earth oxide (La2O3, CeO2, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Dy2O3) and Nd2O3 doping content on the microstructure and dielectric properties of Y2Ti2O7 ceramics were investigated. The experimental results showed that the rare earth ions were considered to dissolve in Y-sites of the pyrochlore structure, different rare earth oxides and concentration had different influences on Y2Ti2O7 cerami...     

Rare earth oxide modified Cu-Mn compounds supported on TiO₂ catalysts for low temperature selective catalytic oxidation of ammonia and in lean oxygen

Selective catalytic oxidation(SCO) of ammonia was carried out over Cu-Mn compounds catalysts modified with trivalent rare earth oxide Ce2O3 and La2O3 respectively.TiO2 was used as support and different ratio of O2 were tested in order to find an appropriate O2 concentration(vol.%),and the results showed that 1%O2(vol.%) was propitious to SCO of ammonia.The effects of the two rare earth oxides modified catalysts Ce2O3-Cu-Mn/TiO2 and La2O3-Cu-Mn/TiO2 on the catalytic activity and selectivity of ammonia oxidation were investigated under the reaction condition of 500 ppm ammonia,1%O2(vol.%),at the temperature from 125 to 250 oC.The results revealed the beneficial role of Ce2O3 and La2O3 in catalytic activity at low temperature and lean oxygen concentration,while the modification with Ce2O3 and La2O3 led to the negative influence on N2 selectivity.For the catalysts modified with Ce showed lower NO and N2O selectivity than the catalysts modified with La,then the effects of different Ce loadings on catalytic activity and selectivity were also considered,in combination with catalysts preparation methods,which include incipient wet impregnation,sol-gel method and co-precipitation.Results revealed that the catalysts prepared by sol-gel method obtained preferable catalytic activity compared with the others,reaching 99% ammonia at 200 oC,whereas 96% NO was detected.It also indicated that different catalyst preparation method significantly determined production distribution.     

Catalytic Partial Oxidation of Methane over Ni/CeO2-ZrO2-Al2O3

Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.     

Partial Oxidation of Methane to Syngas over Monolithic Ni/γ-Al2O3 Catalyst——Effects of Rare Earths and Other Basic Promoters

A series of monolithic Ni/γ-Al2O3 catalysts with and without basic promoters (Na, Sr, La, Ce) were prepared. Partial oxidation of methane (POM) to syngas was carried out in a continuous-flow, fixed-bed reactor. The influences of reaction conditions, including temperature, CH4/O2 ratio and space velocity, on the performance of the catalyst were investigated. The results show that at a high space velocity of 1×105 h-1, optimal CH4 conversion can be obtained. Effects of promoters such as Na, Sr, Ce, La were also investigated, and the catalyst samples were characterized by means of temperature-programmed reduction and XRD techniques. XRD suggests that the addition of promoters has no influence on the crystal structure of Ni/γ-Al2O3 catalyst. The results show that the addition of a small amount of promoters improves the reducibility and activity of the catalyst. The side reaction CH4 2 O2→CO2 H2O, is fully restrained and 100% H2 selectivity is achieved when Ce and La are used as promoters, respectively.     

Temperature Programmed Reduction Studies on CeO2-Containing Catalysts

Temperature programmed reduction (TPR) study was carried out for CeO2/A12O3 and CeO2/ZrO2 catalysts to evaluate oxygen storage property induced by a facile redox cycling of Ce ion. The CeO2/ZrO2 catalyst possesses excellent oxygen storage activity at 373 K after reduction above 1173 K although the oxygen storage of CeO2/Al2O3 catalyst after reduction above 1173 K is poor because of the formation of CeAlO3. Consequently, the oxygen storage on the CeO2/ZrO2 catalyst smoothly occurs from low temperatures when the catalyst is reduced even at high temperatures.     

Characterization of CuO Species and Thermal Solid-Solid Interaction in CuO/CeO2-Al2O3 Catalyst by In-Situ XRD, Raman Spectroscopy and TPR

Transference of CuO species and thermal solid-solid interaction in CuO/CeO2-Al2O3 catalyst prepared by an impregnation method were characterized by in-situ XRD, Raman spectroscopy and H2-TPR techniques. For the catalyst calcined at 300℃, two kinds of CuO species coexist on the surface, that is, highly dispersed and bulk CuO crystalline phase. Four kinds of CuO species are present for the catalyst calcined at 600 ℃, ： （1） highly dispersed CuO, （2） bulk CuO on the surface, （3） bulk CuO in the internal layer of CeO2, and （4） CuAl2O4 formed from CuO-Al2O3 interaction. For the catalyst calcined at 800 ℃,C, besides very little highly dispersed and bulk CuO on the surface, most of the CuO has transferred into the internal layer of CeO2 and the mass of CuAl2O4 are increased. At 900 ℃,, all of CuO has diffused into the internal layer of CeO2 and formed CuAl2O4. The results show that the distribution of CuO species in the catalysts depends on the calcination temperature; the different CuO species can be effectively confirmed by in-situ XRD, Raman spectroscopy and H2-TPR techniques.     

CeO2-Co3O4 Catalysts for CO Oxidation

CeO2-Co3O4 catalysts for low-temperature CO oxidation were prepared by a co-precipitation method. In combination with the characterization methods of N2 adsorption/desorption, XRD, temperature-programmed reduction （TPR）, and FT-IR, the influence of the cerium content on the catalytic performance of CeO2-Co3O4 was investigated. The results indicate that the prepared CeO2-Co3O4 catalysts exhibit a better activity than that of pure CeO2 or pure Co3O4. The catalyst with the Ce/Co atomic ratio 1 ： 16 exhibits the best activity, which converts 77% of CO at room temperature and completely oxidizes CO at 45 ℃.     

稀土氧化物粒子对钼合金粉末冶金过程及力学性能的影响

试验研究了掺杂La2O3、Y2O3、CeO2稀土氧化物颗粒对钼合金的粉末物性、烧结进程、制品的烧结致密度及压力加工丝材的室温力学性能的影响规律。试验结果表明,掺杂稀土氧化物粒子细化了钼粉的粒度,降低了松装密度和粒度分布范围,同时导致粉末团聚现象增多;稀土氧化物粒子延迟了钼合金的烧结进程,降低了烧结制品的致密度,同时细化了烧结体晶粒尺寸。稀土氧化物粒子以弥散强化和细晶强化的形式,提高了钼合金丝的室温强度。CeO2显著提高了钼合金丝的室温韧性,La2O3、Y2O3则降低了钼合金丝的室温韧性。     

氧化铝基氧化物/氧化物复合材料的合成与评价

Al2O3 matrix oxide/oxide composites containing rod-like Ba-β-Al2O3 and equiaxed ZrO2 particles have been successfully synthesized by an in-situ process from a mixture of Al2O3 and BaZrO3 powders.The long-axis direction of rod-like Ba-β-Al2O3 phase is parallel to ,while the longitudinal interface between Ba-β-Al2O3 phase and Al2O3 matrix is parallel to(0001) of the Ba-β-Al2O3 phase.The mechanical properties of the composites,such as Vickers hardness and fracture toughness,are enhanced with increasing the sintering temperature.Furthermore,the presence of rod-like Ba-β-Al2O3 particles results in enhancement of fracture toughness of the in-situ synthesized composites due to crack deflection and crack bridging.     

Preferential Oxidation of CO in H2 over CuO／CeO2 Catalysts

Over the past few years, the design and researchon fuel cells have been made a great development. Avariety of fuel cells for different applications has beenunder development[1,2]: solid polymer fuel cells(SPFC), also know as proton exchange …     

La_2O_3掺杂对V_2O_5-WO_3/TiO_2催化剂SCR性能的影响

通过共沉淀法将La组分掺入到TiO_2载体中,采用浸渍法将V和W组分负载到La_2O_3-TiO_2复合氧化物上,制备出V2O5-WO3/La_2O_3-TiO_2催化剂。考察不同La_2O_3掺杂量对其NH3催化还原NO性能的影响,同时通过多种物理化学手段进行表征分析。XRD,NH_3-in situ DRIFTS,H_2-TPR,XPS和UV-vis DRS测试结果表明,元素La与Ti以La-O-Ti键相互作用,生成高度分散的镧物种,也使得TiO_2具有更好的热稳定性,但由于LaO_x物种与VO_x物种和WO_x物种之间的相互作用,降低了催化剂的氧化还原性和表面Brnsted酸数量,从而降低了其催化活性。     

Effect of rare earth doping on thermo-physical properties of lanthanum zirconate ceramic for thermal barrier coatings

The effect of rare earth doping on thermo-physical properties of lanthanum zirconate was investigated. Oxide powders of various compositions La2Zr2O7 were synthesized by coprecipitation-calcination method. High-temperature dilatometer, DSC, and laser thermal diffusivity methods were used to analyze thermal expansion coefficient （TEC）, specific heat, and thermal diffusivity. The results showed that CeO2 doped pyrochlores La2（Zr1.8Ce0.2）2O7 and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had higher TEC than La2Zr2O7 and La1.7Dy0.3Zr2O7. La2（Zr1.8Ce0.2）2O7, La1.7Dy0.3Zr2O7, and La1.7（DyNd）0.15（Zr0.8Ce0.2）2O7 had lower thermal conductivity than undoped La2Zr2O7. The Dy2O3, Nd2O3, and CeO2 codoped composition showed the lowest thermal conductivity and the highest TEC. Thermo-physical results also indicated that TEC of rare earth oxide doped La2Zr2O7 ceramic was slightly higher than that of conventional ZrO2-8Wt.% Y2O3 （8YSZ）, and its thermal conductivity was lower than that of 8YSZ.     

La-Ce-Cu复合金属氧化物的结构表征及催化性能

本文用ＮＨ４ＮＯ３共熔法合成Ｌａ－Ｃｅ－Ｃｕ系列样品。用ＸＲＤ分析了ＣｅＯ２在铜酸镧盐中的溶解度,发现大量ＣｅＯ２存在时,Ｌａ２Ｏ３、ＣｕＯ的加入导致原晶体结构发生变形,生成少量铜酸镧盐。ＸＲＦ分析了系列样品组成均为氧缺陷型化合物。ＸＰＳ研究发现,含大量ＣｅＯ２的样品高温焙烧后在ＣｅＯ２表面生成复合金属氧化物Ｌａ２ＣｕＯ４,最表面一层为少量Ｌａ２Ｏ３,并确定了其中Ｏ的属性。利用ＴＥＭ研究了部分样品的表面结构,同时研究了其ＣＯ催化氧化活性。