Mechanical properties of La2O3 doped diamond-like carbon films

Twelve La₂O₃ doped diamond-like carbon (DLC) nanofilms were deposited using unbalanced dual-magnetron sputtering. AFM, XRD, Raman spectroscopy, AES, XPS, TEM, contact surface profiler and nanoindenter were employed to investigate the structure and tribological properties of deposited films. The results show that the La₂O₃ doped DLC films are amorphous. La₂O₃ doping obviously decreases internal stress, and effectively increases the elastic modulus. This results from the dissolving and dissolution of La₂O₃ within the amorphous DLC matrix. Furthermore, the friction coefficient of the doped DLC films decreases, and adhesion strength increases. These are attributed to the lubrication function of La₂O₃ and the formation of transition layer at interface, respectively.     

Effect of MoSi2/rare earth composite particles on microstructure and mechanical properties of molybdenum

MoSi₂/La₂O₃ and MoSi₂/Y₂O₃ composite particles were prepared by mechanical milling and doped into molybdenum by solid-solid method, respectively. Rods with a diameter of 17 mm were made by pressing and sintering. The effects of different composite particles on microstructures and strength of the as-sintered molybdenum were investigated. Results show that the MoSi₂/La₂O₃ and MoSi₂/Y₂O₃ composite particles transformed to La₂O₃/Mo₅Si₃ and Y₂O₃/Mo₅Si₃ composite particles due to the in situ reaction between Mo and MoSi₂ during sintering process. Mo₅Si₃/La₂O₃ and Mo₅Si₃/Y₂O₃ composite particles can reduce the grain size and improve both strength and toughness of sintered molybdenum significantly. Mo₅Si₃/Y₂O₃ composite particles contribute more to the strength, while the effect of Mo₅Si₃/La₂O₃ on toughness is greater than that of Mo₅Si₃/Y₂O₃.     

Microstructure and characterization of La2O3 and CeO2 doped diamond-like carbon nanofilms

Seven kinds of hydrogen-free La₂O₃ and CeO₂ doped DLC films with thickness of 220-280 nm were deposited on Si (100) substrates by unbalanced magnetron sputtering. Nanoparticles with diameter of 20-30 nm are formed on the surface of films. The surface roughness Ra of films is in the range of 1.5-2.0 nm. C, La, Ce and O elements distribute uniformly along the depth direction, and C, La, and Ce elements diffuse into the Si substrate at the interface. X-ray photoelectron spectroscopy confirms that the La₂O₃ and CeO₂ form within the DLC amorphous films, and Raman spectra indicate the obvious amorphous characteristics of DLC films. High-resolution transmission electron microscopy shows the nanocrystallines structure with diameter of 2-3 nm of 16% La₂O₃ and 10% CeO₂ doped DLC films, and Fourier transformation spectroscopy also exhibits the obvious crystalline characteristics. In this work, the microstructure of two kinds of rare earth oxides doped DLC composite films is measured and analyzed.     

La2O3含量对Al2O3/Cu基复合材料组织与性能的影响

以La₂O₃粉、Al粉、CuO粉为反应物原料、纯铜为基体,采用原位合成技术和近熔点铸造法制备颗粒增强Cu基复合材料,研究La₂O₃对Al-CuO体系制备的Cu基复合材料组织及性能的影响。结果表明：添加La₂O₃可获得纳米Al₂O₃颗粒,且弥散分布于Cu基体中,制备的材料组织更加细小、均匀,其材料的电导率及摩擦磨损性能明显提高。当添加0.6%wtLa₂O₃,复合材料的电导率达到90.2%IACS,磨损量达到最小,相比未添加La₂O₃,其导电率提高10.1%,磨损量减小36.6%。     

Thermal conductivity and thermal cycle life of La2O3 and HfO2 doped ZrO2-Y2O3 coatings produced by EB-PVD

The effects of La₂O₃ and HfO₂ addition on thermal conductivity and thermal cycle life of EB-PVD YSZ coatings were investigated. La₂O₃ and HfO₂ were selected as additives, because they significantly suppress the sintering of YSZ. The developed coating showed low thermal conductivity as well as high resistance to sintering. Burner rig tests confirmed that the developed coating have a superior thermal insulating effect and have a longer life than that of a coating with conventional composition.     

Preparation, microstructure and properties of molybdenum alloys reinforced by in-situ Al2O3 particles

The conventional molybdenum alloys, lacking of hard particles enhancing wear property, have relative poor wear resistance though they are widely used in wear parts. To resolve the above question, Mo alloys reinforced by in-situ Al₂O₃ particles are developed using powder metallurgy method. The in-situ α-Al₂O₃ particles in molybdenum matrix are obtained by the decomposition of aluminum nitrate after liquid-solid incorporation of MoO₂ and Al(NO₃)₃ aqueous solution. The α-Al₂O₃ particles well bonded with molybdenum distribute evenly in matrix of Mo alloys, which refine grains of alloys and increase hardness of alloys. The absolute density of alloy increases firstly and then decreases with the increase of Al₂O₃ content, while the relative density rises continuously. The friction coefficient of alloy, fluctuating around 0.5, is slightly influenced by Al₂O₃. However, the wear resistance of alloy obviously affected by the Al₂O₃ particles rises remarkably with the increasing of Al₂O₃ content. The Al₂O₃ particles can efficiently resist micro-cutting to protect molybdenum matrix, and therefore enhances the wear resistance of Mo alloy.     

Gd3+掺杂La2Mo2O9的相稳定性及热导率

La2Mo2O9具有极低的热导率,但其在580℃左右会发生α-β相变,严重影响其性能和应用。本实验以Gd203掺杂La2Mo2O9制备了一系列La2-xGdxMo2O9 (x=0.0~0.5)固溶体,研究了掺杂Gd3+对La2Mo2O9相稳定性和热导率的影响。结果表明,随着Gd3+掺杂量的增加,相变得到有效抑制,当x≥0.2时样品以β相存在。样品的热导率随Gd3+掺杂量的增加先减小后增加,室温下在x=0.2时达到最低,此后缓慢上升,但所有样品的热导率均小于1 W/(m·K)。     

La2O3掺杂氧化铝气凝胶的制备与耐温性能研究

以仲丁醇铝为前驱体,采用溶胶-凝胶法结合丙酮-苯胺原位生成水技术,通过乙醇超临界干燥,制备出不同含量(1.5 mol%~12 mol%)La₂O₃掺杂的氧化铝气凝胶。采用电子扫描电镜(SEM)、透射电子显微镜(TEM)、X线衍射仪(XRD)、N₂吸附分析仪等仪器表征了La₂O₃掺杂对氧化铝气凝胶的微结构和耐温性能的影响。结果表明：La₂O₃的引入使氧化铝气凝胶的形貌由球状颗粒向大的片状结构转变。适量的La₂O₃掺杂能提高氧化铝气凝胶的比表面积,9 mol% La₂O₃掺杂的氧化铝气凝胶比表面积最大。通过La₂O₃掺杂,能够抑制氧化铝晶粒在高温下的生长和α-Al₂O₃的相变,提高氧化铝气凝胶的耐温性能。1200℃热处理后,La₂O₃掺杂的氧化铝气凝胶仍维持在θ-Al₂O₃,比表面积为86.5 m₂/g,高于未掺杂的氧化铝气凝胶(46 m₂/g)。     

La2O3含量对搅拌摩擦加工制备Ni /Al复合材料组织和性能的影响

采用搅拌摩擦加工方法在Al基体中添加不同La₂O₃含量的混合粉末(Ni+La₂O₃),制备 (Ni+La₂O₃)/Al复合材料。采用SEM、EDS、 EPMA及XRD对复合区微观结构及相组成进行分析,采用室温拉伸试验对 (Ni+La₂O₃)/Al复合材料力学性能进行了测试。结果表明,随着La₂O₃含量的增加,(Ni+La₂O₃)/Al复合材料的组织和性能先变好后变差。当La₂O₃添加量达到5%时,复合材料中Al₃Ni增强颗粒分布均匀、颗粒数量最多,块状的Ni粉团聚减少,其抗拉强度达到最大值215MPa,相比Ni/Al复合材料(抗拉强度176MPa),其抗拉强度提高了22%;当La₂O₃的添加量为7%时,复合材料中Al₃Ni增强颗粒含量减少,块状Ni粉团聚重新出现,抗拉强度下降至201MPa。     

激光熔覆纳米La2O3添加镍基合金涂层的耐磨与显微组织研究

本研究以激光工艺制备了添加纳米La2O3初料的镍基涂层。激光熔覆之前,高能球磨机充分混合的Ni60A和La2O3粉床预置于基体30CrMnSiNi2A表面。La偏聚于枝晶间从而限制了二次枝晶的成长和熟化。显微组织得到了细化。由于更高的La富集,涂层上表面显微组织细化更为显著,这一现象的上述解释得到EPMA结果佐证。同时EPMA结果说明Fe稀释会造成涂层硬度降低。熔覆涂层经过RE显微组织细化和净化,硬度、耐磨性均相对基体金属显著提升,而涂层中裂纹和孔隙均未出现。Ni60A-La涂层的摩擦系数曲线COF明显低于基体和Ni60A涂层,Ni60A-La磨擦体积损失率分别少于基体和Ni60A涂层数值的1/10和1/5,显微硬度值是基体4倍。     

SNDC/La2Mo2O9复合电解质材料的制备及性能表征

本文采用甘氨酸-硝酸盐法(GNP)和溶胶凝胶法分别合成了Sm_0.1Nd_0.1Ce_0.8O_1.9(SNDC) 和La₂Mo₂O₉(LAMOX)粉末,并用常压烧结的方法制备了不同比例的SNDC和LAMOX的复合材料,通过XRD和SEM等手段表征了不同复合比例样品的物相和表面形貌并测试了烧结样品的电导率。结果表明,复合样品的电导率在相变点前后随着复合量增加变化趋势相反,其中LAMOX含量为20mol%的样品在550℃时的电导率能达到0.01S/cm,高于同温度下SNDC电导率。     

La2O3改性ZrB2-SiC涂层C/C复合材料全温域抗氧化行为研究

采用高温反应熔渗工艺制备了ZrB2-SiC和La2O3改性ZrB2-SiC涂层C/C复合材料,对比了2种涂层试样在中温(7001100℃)、高温(12001500℃)和超高温(2000℃以上)3个温域范围内的抗氧化性能。结果表明:7001100℃范围内,随着温度的升高,La2O3改性涂层试样的抗氧化性能提升幅度在逐渐提高。1200℃1500℃范围内,涂层均表现出良好的长时抗氧化性能,La2O3改性ZrB2-SiC在1200℃下恒温氧化250 h后,仍保持微量的增重;涂层复合材料良好的高温抗氧化性能主要其在是由于氧化过程中涂层表面形成的La-Si-O复合玻璃层和钉扎相ZrSiO4的协同作用提升了氧化膜的高温稳定性。在2000℃以上的氧乙炔火焰烧蚀环境下,La2O3的添加使得ZrB2-SiC涂层的质量烧蚀率和线烧蚀率均降低了近50%,其主要归因于表层La-Si-O和ZrO2玻璃层对烧蚀缺陷的愈合作用。     

溶液等离子喷涂铈酸镧热障涂层的制备及表征

采用溶液前驱体等离子喷涂(solution precursor plasma spray,SPPS)方法制备了La2Ce2O7涂层。通过SEM、XRD、EDS、激光导热仪对制备的涂层进行了表征,应用STA-FTIR-QMS联用技术对La2Ce2O7干燥前驱体的分解过程进行了研究,分析了前驱体的分解温度及分解过程,从而确定了喷涂温度为450℃。通过正交实验确定了雾化压力0.1MPa、电流700A、送液速率23 mL/min为最佳喷涂工艺参数,用此参数喷涂20遍制备的La2Ce2O7涂层厚度达到121μm,相对密度为92.4%,硬度为2.1 GPa。结果表明,得到了热导率较低、元素分布均匀、具有萤石结构的La2Ce2O7热障涂层。     

Effects of K2O-Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K₂O and Li₂O-doping (0.5, 0.75 and 1.5 mol%) of Fe₂O₃/Cr₂O₃ system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe₂O₃:0.15Cr₂O₃. The techniques employed were TGA, DTA, XRD, N₂ adsorption at −196 °C and catalytic oxidation of CO oxidation by O₂ at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe₂O₃ upon heating at 500 and 600 °C. K₂O and Li₂O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe₂O₃ together with K₂FeO₄ and LiFe₅O₈ phases. However, the heavily Li₂O-doped sample consisted only of LiFe₅O₈ phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K₂O and Li₂O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K₂O and Li₂O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K₂O and Li₂O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.     

网孔结构La2Sn2O7粉体的制备及其在Ag-电接触材料的制备及性能研究

以五水四氯化锡和硝酸镧为原料,采用化学共沉淀法在烧结温度920℃条件下合成了锡酸镧粉体。通过高能球磨法+成型烧结工艺制得Ag-La₂Sn₂O₇电接触复合材料。重点考察了胶凝剂浓度、烧结工艺对La₂Sn₂O₇粉体形貌及物相的影响,并对Ag- La₂Sn₂O₇电接触材料的物理性能进行了分析。研究结果表明：以碳酸氢铵为胶凝剂,于烧结温度920℃,2h条件下获得具有网孔结构的La₂Sn₂O₇粉体;于成型压力1200MPa,烧结温度900℃,6h条件下制得的Ag-La₂Sn₂O₇电接触材料表现出较佳的电阻率和硬度值。经过热挤压工艺,Ag-La₂Sn₂O₇电接触材料发生了大塑性变形,颗粒在热挤压过程中发生流动变形,形成类纤维状结构的排列分布状态,表现出更低的电阻率。     

钼合金MoSi2涂层高温热震行为与裂纹扩展

采用料浆烧结法在钼合金表面制备了MoSi₂涂层,利用内热法测试了涂层室温～1600℃抗热震性能,通过扫描电镜(SEM)、电子探针(EPMA)、波谱分析(WDS)和X射线衍射(XRD)等测试手段分析了不同热震次数的涂层微观形貌、组织结构以及裂纹萌生扩展。结果表明：涂层可承受室温～1600℃热震400次,热震过程中涂层由原始的MoSi₂-Mo₅Si₃双层结构演变为SiO₂-MoSi₂-Mo₅Si₃多层结构,涂层热震初期形成纵向裂纹并不断向基体扩展,热震后期裂纹贯穿涂层到达基体,MoO₃挥发使涂层/基体界面应力增大产生横向裂纹,导致涂层剥落失效。     

Effect of Bi2O3 on structure and wetting studies of Bi2O3-ZnO-B2O3 glasses

Glasses with different Bi₂O₃ contents (37-42 mol%) have been prepared by conventional melt quench technique. The IR and Raman studies indicate that these glasses are made up of [BiO₆], [BiO₃], [BO₃] and [BO₄] basic structural units. The vibrations of [BiO₃] and [BO₃] become stronger as the content of Bi₂O₃ increases, which makes glass structure loosened. Viscosity of the glasses was measured by using a Rheotronic III paralleled plate rheometry, which shows that the viscosity of glass samples decreased when the content of Bi₂O₃ increased at the same temperature (400-460 °C). The temperature range which suits for glasses sealing was calculated by using the approximation of Arrhenian behaviour. The wetting performance of Bi₂O₃-ZnO-B₂O₃ glasses was described by using high-temperature microscope, which also proves that the structure of investigated Bi₂O₃-ZnO-B₂O₃ glasses become loosened due to the increasing of the content of Bi₂O₃.     

In-situ TiB2 and Al2O3 formation by DC plasma spraying

In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B₂O₃ and TiO₂ powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB₂ and Al₂O₃ are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions.     

Magnetic properties of Al2O3-Cr2O3 solid solutions

Solid solution ceramics (Al₂O₃)_x(Cr₂O₃)_1−x with different x in the range of 0 < x < 1 were synthesized via traditional ceramic production method. X-ray diffraction results and Rietveld refinements indicated that all samples possessed rhomb-centered structure and continuous solid solutions were synthesized. The samples were composed of irregular grains with several micrometers in diameter. Temperature dependence of magnetization measurements showed monotonous decreasing Néel temperature with increasing x and percolation effect happened with threshold of x = 0.65. As x became higher, weak ferromagnetism was observed in the samples. Field dependence of magnetization measurements further confirmed the weak ferromagnetism in the samples with x = 0.7, 0.8 and 0.9.