纳米和微米ZrB_2-SiC粉末对涂层高温抗氧化性能的影响

选用纳米团聚粉末和常规微米商用ZrB_2-SiC粉末,利用超音速等离子喷涂在310S耐热不锈钢基体上制备高温抗氧化ZrB_2-SiC复合涂层。采用XRD、SEM、EDS分析涂层组织结构;拉伸法测定涂层结合强度;静态高温氧化法表征涂层抗高温氧化性能。优化了喷涂距离,研究纳米和微米ZrB_2-SiC粉末对涂层形貌、组织结构及性能的影响。结果表明:纳米团聚粉末(n-ZS)涂层表面孔隙和微裂纹较微米商用粉末(m-ZS)涂层大幅减少,涂层更为致密;n-ZS涂层结合强度达到44.6 MPa,较m-ZS涂层提升了约67%;经过1 100℃、50 h的高温氧化试验,n-ZS涂层增重明显低于m-ZS涂层,氧化倾向低,具有更好的高温抗氧化能力。     

等离子喷涂制备ZrB_2-SiC涂层及其抗氧-丙烷焰流烧蚀性能

为提高C/C复合材料的抗高温烧蚀性能,利用大气等离子喷涂技术在C/C复合材料表面制备ZrB_2-SiC复合涂层,并对其进行抗高温氧-丙烷焰流烧蚀试验。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)及能谱分析仪(EDS)对涂层的物相成分、微观形貌等进行检测分析。结果表明:大气等离子喷涂能在C/C复合材料表面制备出均匀致密的ZrB_2-SiC复合涂层,涂覆有ZrB_2-SiC涂层的C/C复合材料分别承受1 600、1 700和1 800℃的氧-丙烷焰流烧蚀300 s后依次增重0.63%、0.76%和0.71%,而烧蚀600s后试样质量烧蚀率分别为9.42×10~(-5)、2.04×10~(-4)和1.04×10~(-3)g/s。ZrB_2-SiC涂层显著提高了C/C复合材料的抗烧蚀性能,涂层氧化生成的玻璃态SiO_2能有效填充孔隙。直到SiO_2耗尽,涂层烧蚀后的孔洞成为环境中的氧进入基体的通道,导致基体烧蚀。     

喷涂用MoSi2粉末的制备及其在等离子弧中的熔化特性

采用喷雾干燥和真空烧结技术制备MoSi2团聚颗粒,以MoSi2团聚粉末为原料,通过大气等离子喷涂法制备二硅化钼涂层,借助XRD、扫描电镜及能谱对团聚体粉末在等离子焰流中的熔化特性和涂层的组织结构进行研究.结果表明:团聚粉末在1200℃真空热处理1 h后,粉末的流动性和松装密度分别提高55.6%和42.0%,适合等离子喷涂用.MoSi2颗粒经过高温等离子焰流后,粉末熔化充分,大多数团聚体粉末发生烧结过程,颗粒的平均粒度减小,形成较致密的球形颗粒.在喷涂过程中,部分四方相MoSi2(t)转变为六方相MoSi2(h)或氧化形成了少量的Mo<,5>Si3相,涂层中的富钼相呈"网状"组织结构.     

纳米Al_2O_3对等离子喷涂ZrC-ZrSi_2复合涂层结构与性能的影响

大气等离子喷涂ZrC-ZrSi_2陶瓷涂层的孔隙率高,提高等离子喷涂ZrC-ZrSi_2陶瓷涂层的致密度成为亟待解决的问题。在TC4钛合金表面采用大气等离子喷涂ZrC-ZrSi_2复合粉和ZrC-ZrSi_2-Al_2O_3复合粉分别制备两种复合涂层。研究纳米Al_2O_3对等离子喷涂ZrC-ZrSi_2复合涂层组织结构与性能的影响。结果表明,添加了Al_2O_3的ZrC-ZrSi_2复合涂层的组织结构更为致密,相较于ZrC-ZrSi_2复合涂层具有更优异的力学性能。熔点相对较低的Al_2O_3能够在喷涂焰流中先熔化,熔融态的Al_2O_3能够填充在ZrC-ZrSi_2复合涂层的孔洞处,提高复合涂层的致密度,改善涂层的力学性能。研究成果可为提高大气等离子喷涂制备含高熔点组分复合涂层的致密度提供指导。     

等离子喷涂纳米Al2O3-13TiO2陶瓷涂层研究

以常规和纳米团聚体Al2O3-13TiO2(ω/%,下同)复合陶瓷粉末为原料,采用等离子喷涂工艺在TiAl合金表面制备常规和纳米结构陶瓷涂层.用扫描电镜(SEM)和X射线衍射(XRD)仪分析粉末和涂层形貌、微观结构及相组成,同时对纳米结构涂层的微观组织形成机制进行了讨论.结果表明:常规复合陶瓷涂层呈典型的等离子喷涂层状堆积特征;纳米结构复合陶瓷涂层由部分熔化区以及与常规等离子喷涂类似的片层状完全熔化区组成.根据组织结构的不同,部分熔化区又分为亚微米A12O3粒子镶嵌在TiO2基质相的三维网状或骨骼状结构的液相烧结区和经过一定长大但仍保持在纳米尺度的残留纳米粒子的固相烧结区,不同的部分熔化组织源于复合陶瓷粉末中A12O3与TiO2之间的熔点差异.由于等离子喷涂过程中涂层沉积时的快速凝固作用,不管是常规还是纳米涂层都以亚稳相γ-A12O3为主.     

激光重熔纳米Al2O3-13%TiO2陶瓷涂层组织及性能

为了进一步提高等离子喷涂纳米Al2O3-13%TiO2(质量分数, 下同)复合陶瓷涂层的性能,在γ-TiAl基体材料表面采用激光重熔工艺对涂层进行处理,研究了激光重熔对涂层微观组织和性能的影响.用扫描电镜(SEM)和显微硬度计分析了涂层形貌、微观结构和显微硬度,同时对涂层的磨损特性进行了考察.结果表明,等离子喷涂纳米陶瓷涂层由纳米颗粒完全熔化区和部分熔化区两部分组成,仍然具有等离子喷涂态的典型层状结构.经过激光重熔后,形成了致密细小的等轴晶重熔区、烧结区和残余等离子喷涂区,由于激光快速加热和快速冷却加工特点,在重熔区仍保留了部分来源于原等离子喷涂部分熔化区的残留纳米粒子.与常规等离子喷涂陶瓷涂层相比,纳米结构涂层可在一定程度上提高其硬度和耐磨性,经过激光重熔后其硬度和耐磨性进一步提高.     

材料结构与制备工艺对热障涂层显微组织的影响

以常规和纳米团聚体ZrO2-7%Y2O3陶瓷粉末为原料,采用等离子喷涂和等离子喷涂+激光重熔复合工艺在TiAl合金表面制备了常规和纳米结构热障涂层。用扫描电镜(SEM)分析了粉末结构及制备工艺对涂层显微组织的影响。结果表明:用常规等离子喷涂法制备的陶瓷涂层为典型的层状堆积特征;而用等离子喷涂法制备的纳米结构涂层则由纳米颗粒完全熔化区和部分熔化区组成,呈两相结构。由于受到激光功率、能量密度、激光作用区温度场分布、陶瓷导热系数和涂层厚度等因素的综合影响,经激光重熔后,涂层呈现出明显的分层结构特征:上部为致密的柱状晶重熔区,下部为残余等离子喷涂区。由于激光重熔纳米结构涂层重熔区中残余纳米粒子的增韧作用,其晶界强度较高,从而导致断口有相当数量的穿晶断裂,而激光重熔常规涂层重熔区的断口基本是沿晶断裂。     

YSZ/Sm_2Zr_2O_7复合粉体制备及性能

采用球磨造粒法制备Sm_2Zr_2O_7(SZO)和Y_2O_3部分稳定ZrO_2(YSZ)复合粉体,对造粒团聚体的尺寸、形貌及相结构进行了表征。并采用大气等离子制备SZO/YSZ复合涂层,研究等离子喷涂过程对复合粉体相结构和相稳定性的影响。用扫描电子显微镜(SEM)和X射线衍射(XRD)分析了YSZ/SZO复合粉体和涂层的微观组织和相结构,并利用差示扫描量热法(DSC)研究复合粉体稳定性。结果表明:SZO和YSZ复合团聚粉体表面光滑致密,室温呈混合相结构。在室温～1200°C范围内无相变发生,说明YSZ/SZO粉末在该范围内较为稳定。等离子喷涂YSZ/SZO涂层呈典型层状组织结构,涂层成分和组织分布较为均匀,与单一SZO涂层相比,复合陶瓷涂层结合强度得到了提高。但等离子喷涂过程中SZO与YSZ发生离子扩散,粉体稳定性下降,SZO发生有序-无序转变,涂层呈现单一萤石结构。     

等离子喷涂纳米复合陶瓷涂层的组织结构及其形成机理

以Al2O3-13%TiO2(质量分数)团聚体复合陶瓷粉末为材料,采用等离子喷涂工艺在TiAl合金表面制备纳米结构陶瓷涂层.用扫描电镜(SEM)和X射线衍射仪(XRD)分析粉末和涂层形貌、微观结构及相组成,讨论涂层的微观组织形成机理.结果表明:纳米结构复合陶瓷涂层由部分熔化区以及与常规等离子喷涂类似的片层状完全熔化区组成;根据组织结构的不同,部分熔化区又分为液相烧结区(亚微米Al2O3粒子镶嵌在TiO2基质相的三维网状或骨骼状结构)和固相烧结区(经过一定程度长大但仍保持在纳米尺度的残留纳米粒子);等离子喷涂使部分α-Al2O3以及全部θ-Al2O3转变为亚稳态γ-Al2O3;纳米结构复合陶瓷涂层中的完全熔化区、液相烧结区及固相烧结区分别由等离子喷涂过程中纳米团聚体粉末中温度高于Al2O3熔点、介于TiO2熔点到Al2O3熔点之间以及低于TiO2熔点区域沉积获得,纳米结构涂层中不同部分熔化组织源于复合陶瓷粉末中Al2O3与TiO2之间的熔点差异.     

TiAl合金表面激光重熔纳米陶瓷涂层

采用等离子喷涂和激光重熔复合工艺在TiA l合金表面制备了纳米A l2O3-13wt%TiO2复合陶瓷涂层。为了使重熔后的陶瓷涂层保留一定的纳米结构组织,采用相对较低的激光功率和能量密度进行重熔。用扫描电镜(SEM)和X射线衍射仪(XRD)分析了涂层形貌、微观结构和相组成。结果表明,等离子喷涂纳米陶瓷涂层由纳米颗粒完全熔化区和部分熔化区两部分组成,具有等离子喷涂态的典型层状结构;由于受到激光功率、能量密度、陶瓷材料热物性参数和涂层厚度等因素的综合影响,重熔后陶瓷涂层出现了明显的分层结构特征;依据组织形态的不同,可将其大致分为:重熔区、烧结区和残余等离子喷涂区。重熔区由致密细小的等轴晶组成,并且保留了部分来源于原等离子喷涂部分熔化区的残留纳米粒子。由于等离子喷涂过程中涂层沉积时的快速凝固作用,涂层以亚稳相-γA l2O3为主,经过激光重熔处理后,-γA l2O3又重新转变为稳定相-αA l2O3。     

改进型镁扩散法制备高临界电流密度MgB2超导体性能研究

本文采用一种改进型镁扩散法成功制备出密度达到1.95g/cm₃的MgB₂超导块材。论文研究了不同的热处理条件对MgB₂块材的超导转变温度(T_c)和临界电流密度(J_c)性能的影响。采用最佳热处理条件制备的MgB₂超导体T_c和J_c分别达到了38.1K和0.53MA/cm₂(10K,自场)。为了改进镁扩散法MgB₂超导体中弱的高场磁通钉扎性能,本文还研究了nano-Pr₆O₁₁和C掺杂对MgB₂超导体的临界电流密度和不可逆场(H_irr)的影响。结果表明C掺杂的MgB₂超导体临界电流密度在10K,6T下达到了10₄A/cm₂,该结果比未掺杂MgB₂超导体在同样条件下性能提高了两个量级,甚至比固态反应法制备的nano-C掺杂MgB₂超导体性能更好。利用该方法制备的nano-Pr₆O₁₁掺杂的MgB₂超导体在10K,2T下也比未掺杂样品J_c提高达9.4倍。根据大量的实验结果和理论分析我们提出基于改进型镁扩散法和化学掺杂,包括纳米粒子和C掺杂,很有可能是一种制备高性能MgB₂超导体非常有效的途径。     

废旧锂离子电池中Li, Fe和V的回收及xLiFePO4-yLi3V2(PO4)3的制备

由于LiFePO_4和Li_3V_2(PO_4)_3材料的特征相近,制备方法类似,提供了一种从废旧LiFePO_4和Li_3V_2(PO_4)_3混合电池中回收Li、Fe和V,再制备xLiFePO_4-yLi_3V_2(PO_4)_3的方法。在空气气氛中600℃热处理1h后,去除粘结剂PVDF使活性物质与集流体分离。调节Li、Fe、V和P摩尔比,球磨、锻烧,配制不同比例的xLiFePO_4-yLi_3V_2(PO_4)_3(x:y=5:1,7:1,9:1)复合电极材料。表征了其形貌、结构和电化学性能,结果表明,回收制备的复合材料将同时具备LiFePO_4和Li_3V_2(PO_4)_3两种材料的电化学性能,能显著改善LiFePO_4的倍率性能。     

Improved capacity and rate capability of Ru-doped and carbon-coated Li4Ti5O12 anode material

Pure Li₄Ti₅O₁₂, modified Li₄Ti₅O₁₂/C, Li₄Ru_0.01Ti_4.99O₁₂ and Li₄Ru_0.01Ti_4.99O₁₂/C were successfully prepared by a modified solid-state method and its electrochemical properties were investigated. From the XRD patterns, the added sugar or doped Ru did not affect the spinel structure. The results of electrochemical properties revealed that Li₄Ru_0.01Ti_4.99O₁₂/C showed 120 and 110 mAh/g at 5 and 10 C rate after 100 charge/discharge cycles. Li₄Ru_0.01Ti_4.99O₁₂/C exhibited the best rate capability and the highest capacity at 5 and 10 C charge/discharge rate owing to the increase of electronic conductivity and the reduction of interface resistance between particles of Li₄Ti₅O₁₂.It is expected that the Li₄Ru_0.01Ti_4.99O₁₂/C will be a promising anode material to be used in high-rate lithium ion battery.     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

Alloyed W–(Co,Ni,Fe)–C phases for reaction sintering of hardmetals

It has been shown that W–Co–C phases could dissolve a substantial amount of metals such as V, Cr and Ta, which are known to positively influence the microstructure of hardmetals with respect to uniform grain size distribution and fine grain size. This offers a tool to circumvent the conventional doping of hardmetals with individual carbides. In the present study we used double- and triple-alloyed κ-W₉Co₃C₄ (i.e. κ-(W,V,Cr)₉Co₃C₄ and κ-(W,V,Cr,Ta)₉Co₃C₄) and applied a variety of sintering experiments to obtain WC–Co, WC–(Ti,Ta,Nb)C–Co and WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. We also prepared κ-W₉Fe₃C₄, alloyed κ-W₉Ni₃C₄, and κ-W₉(Fe/Ni)₃C₄, and used the latter for sintering.     

Effects of Mo and Al Additions on the Sulfidation Behavior of 310 Stainless Steel

The high-temperature sulfidation behavior of 310stainless steel (310SS) with Mo and Al additions (up to10 at.%) was studied over the temperature range700-900°C in pure-sulfur vapor over the range of 10^-3 to 10^-1 atm. Thecorrosion kinetics followed the parabolic rate law inall cases and the sulfidation rates increased withincreasing temperature and sulfur pressure. Thesulfidation rates decreased with increasing Mo and Al contents and it wasfound that the addition of 10 at.% Mo resulted in themost pronounced reduction among the alloys studied. Thescales formed on 310SS with Mo additions were complex, consisting of an outer layer of ironsulfide (with dissolved Cr), (Fe,Ni)₉S₈, andCr₂S₃/Cr₃S₄(with dissolved Fe), and an inner heterophasic layer ofFe_1-xS,Cr₂S₃/Cr₃S₄,NiCr₂S₄,Fe_1.25Mo₆S_7.7, FeMo₂S₄, andMoS₂. The scales formed on 310SS with Mo andAl additions had a similar mixture as above, except thatAl_0.55Mo₂S₄ was alsoobserved in the inner layer. The formation ofMoS₂ andAl_0.55Mo₂S₄ partly blocked the transport of cations throughthe inner scale, resulting in the reduction of thesulfidation rates compared to 310SS.     

The high-temperature corrosion behavior of Nb-Al alloys in a H2/H2S/H2O gas mixture

The corrosion behavior of pure Nb and three Nb Al alloys containing 12.5, 25, and 75 at.% Al was studied over the temperature range of 800–1000°C in a H₂/H₂S/H₂O gas mixture. Except for the Nb-12.5Al alloy consisting of a two phase structure of -Nb and Nb₃Al, other alloys studied were single phase. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants increased with increasing temperature, but fluctuated with increasing Al content. The Nb-75Al alloy exhibited the best corrosion resistance among all alloys studied, whose corrosion rates are 1.6–2.2 orders of magnitude lower than those of pure-Nb (depending on temperature). An exclusive NbO₂ layer was formed on pure Nb, while heterophasic scales were observed on Nb-Al alloys whose compositions and amounts strongly depended on Al content and temperature. The scales formed on Nb-12.5Al consisted of mostly NbO₂ and minor amounts of Nb₂O₅, NbS2, and -Al₂O₃, while the scales formed on Nb-25Al consisted of mostly Nb₂O₅ and some -Al₂O₃. The scales formed on Nb-75Al consisted of mostly -Al₂O₃ and Nb₃S₄ atT 900°C, and mostly -Al₂O₃ , Nb₃S₄ and some AlNbO₄ at 1000°C. The formation of -Al₂O₃ and Nb₃S₄ resulted in a significant reduction of the corrosion rates.     

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.     

固相-水热法制备LiFePO4-Li3V2（PO4）3复合材料及其电化学性能（英文）

分别采用固相-水热法和球磨法制备磷酸亚铁锂-磷酸钒锂复合正极材料(LiFePO4-Li3V2(PO4)3)。电化学性能测试表明,LiFePO4-Li3V2(PO4)3复合正极材料的电化学性能远远高于 LiFePO4和 Li3V2(PO4)3单独作为正极材料的性能,并且以固相-水热法制备的复合材料性能优于以球磨法制得的复合材料。研究发现 LiFePO4-Li3V2(PO4)3复合材料有 4 个氧化还原峰,相当于 LiFePO4 和 Li3V2(PO4)3 氧化还原峰的叠加。采用固相-水热法制备的LiFePO4-Li3V2(PO4)3 复合材料形貌较为规则,且有新相物质产生,这是导致其电化学性能较好的原因。     

Synthesis of lanthanum carbonate nanoparticles via sonochemical method for preparation of lanthanum hydroxide and lanthanum oxide nanoparticles

Lanthanum carbonate nanoparticles were synthesized from the reaction of lanthanum acetate and Na₂CO₃ under sonication via sonochemical method. Lanthanum hydroxide nanoparticles were prepared by facial hydrothermal processing from the resulted product at 110 °C for 24 h. The role of surfactant, calcination temperature and sonication time were investigated on the morphology and particle size of the products. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), and Fourier transform infrared (FT-IR) spectra. La₂O₃ nanoparticles were obtained by calcinations of the nanoparticles of lanthanum carbonate at 600 °C.