NaCl-KCl-NdCl3-AlCl3熔盐体系电解制备Nd-Al合金及机理

在700℃的NaCl-KCl体系中,采用循环伏安法、方波伏安法和开路计时电位法等电化学测试方法研究了钨电极上Nd(Ⅲ)的电化学行为以及与Al(Ⅲ)共沉积的电化学过程。结果表明:在低扫描速率(0.1～0.5V·s~(-1))下,NaCl-KCl-NdCl_3熔盐中Nd(Ⅲ)的还原是一步交换3个电子的准可逆过程,该还原过程由扩散步骤控制,扩散系数约为1.2×10~(-5) cm~2·s~(-1)。将AlCl_3引入NaCl-KCl-NdCl_3熔体后,循环伏安、方波伏安以及开路计时电位测试结果表明,电解过程中形成了3种Nd-Al金属间化合物(Nd_3Al_(11)、NdAl_3和NdAl_2),其形成机理为Nd在预先沉积的Al上发生欠电位沉积。通过电动势法,计算了700℃时Nd-Al金属间化合物的热力学参数,如两相共存下Nd的活度和相对偏摩尔吉布斯自由能以及Nd-Al金属间化合物的标准吉布斯自由能。在-2.3 V下进行恒电位电解5 h制备了Nd-Al合金,所得合金由Nd_3Al_(11)、NdAl_3、NdAl_2和Al4种物相组成。     

Al2O3包覆LiNi0.03Co0.05Mn1.92O4正极材料的制备及其电化学性能

以Al(NO3)3?9H2O为包覆原料，通过燃烧法制备得到LiNi0.03Co0.05Mn1.92O4@Al2O3正极材料。通过X射线衍射(XRD)，场发射扫描电子显微镜(FESEM)和透射电镜(TEM)等表征手段对材料的结构和形貌进行分析，并通过恒电流充放电、循环伏安(CV)、交流阻抗(EIS)等测试分析材料的电化学性能。结果表明，Al2O3包覆没有改变LiNi0.03Co0.05Mn1.92O4的尖晶石型结构，包覆层厚度约10.6nm。LiNi0.03Co0.05Mn1.92O4@Al2O3正极材料电化学性能得到了明显改善，1 C和10 C倍率下初始放电比容量分别为119.9 mAh?g-1和106.3 mAh?g-1，充放电循环500次后容量保持率分别为88.4%和78.2%，而未包覆的LiNi0.03Co0.05Mn1.92O4在1 C和10 C倍率下初始放电比容量分别为121.2 mAh?g-1和104.0 mAh?g-1，500次循环后容量保持率分别为84.1%和67.6%。LiNi0.03Co0.05Mn1.92O4@Al2O3活化能为32.92 kJ?mol-1，而未包覆材料的活化能为36.24 kJ?mol-1，包覆有效降低了材料Li+扩散所需克服的能垒，提高了材料的电化学性能。     

化学镀制备的纳米Ag/SnO_2复合粉末的烧结性能研究

采用化学镀法制备出具有包覆结构的纳米Ag/SnO_2复合粉末,并通过粉末冶金工艺制备AgSnO_2复合块体材料。对包覆型纳米复合粉末的烧结性能和致密化行为进行研究。分析了相关工艺参数对复合材料致密度、硬度以及导电率等性能的影响。结果表明:化学镀法制备的纳米Ag/SnO_2复合粉末具有较好的包覆结构且粒径较均匀,但存在一定量的吸附杂质,经650℃预烧处理后可去除大部分杂质。经真空烧结后可获得比未预烧样品更高的致密度、硬度和导电率。     

化学镀法制备低钴含量WC-Co复合粉体及其放电等离子烧结

对WC粉体进行化学活化预处理,然后采用超声辅助化学镀法制备低钴含量WC-Co(≤1 mass%)复合粉体,采用放电等离子烧结(SPS)技术,制备了少粘结相WC-Co硬质合金材料。研究了化学活化预处理工艺对WC粉体表面化学镀Co的影响以及少量均匀包覆的Co对试样烧结致密化过程、显微组织结构及力学性能的影响。试验结果表明:化学活化预处理后的WC粉体出现了大量的层错、位错等缺陷,在缺陷周围产生点阵畸变和应力场,较大的表面能减小了金属与陶瓷界面接触角,提高了二者之间的润湿性,降低了化学镀过程的形核功,实现化学镀钴过程;与纯WC粉体烧结试样相比,少量Co在WC-Co复合粉体中的均匀分布,大大降低了烧结温度,促进了粉体烧结致密化进程,各项性能得到显著提高,密度达15.56 g/cm3,硬度为2409 HV30,断裂韧性为9.2 MPa.m1/2。     

纳米晶镍块体的制备及烧结致密度研究

以高能球磨法和直流氢电弧等离子蒸发法两种不同工艺制备纳米晶镍粉体,并结合预压烧结工艺制备了纳米晶镍块体试样,研究了纳米晶镍块体结构、形貌的变化.运用TEM技术观察了两种粉体的形貌,并给出了选区电子衍射图;运用XRD、Archimedes法等分析手段对纳米晶镍块体的致密度及晶粒尺寸进行测定,并对两种试样进行了对比分析,表征结果显示,随着烧结温度的升高,纳米晶镍块体试样的晶体尺寸增大,晶格应变减小,同时致密度增加;高能球磨试样晶粒生长速率和致密度升高速率比等离子蒸发试样的快.     

Pd/ZrO2-Al2O3催化剂中载体制备对CH4转化活性的影响

为推动ZrO2-Al2O3在天然气汽车尾气净化催化剂中的实际应用，并阐明其制备条件对负载催化剂转化活性的影响机制，文章以ZrO2-Al2O3复合氧化物为载体，采用等体积浸渍法制备了Pd/ZrO2-Al2O3催化剂，并在连续流动固定床反应器上研究了ZrO2-Al2O3复合氧化物的制备对催化剂低温CH4氧化活性的影响。结果表明：制备方法中，相比于浸渍法和胶溶法，沉淀法更能提高催化剂活性；锆源、铝源优选中，以Zr(NO3)4为锆源、拟薄水铝石为铝源时能获得较高的催化活性；组分配比中，以w (ZrO2): w (Al2O3)=10:90的催化活性最高。XRD、低温N2吸附、CO脉冲吸附的结构表征表明，ZrO2-Al2O3复合氧化物的大的比表面积、孔容、孔径是促进贵金属Pd分散，提升催化剂低温CH4转化活性的关键因素。     

W-Ni/TiC复合材料的制备与组织

采用化学活化预处理对Ti C粉体进行镀前预处理,预处理后通过化学镀制备Ni-W包覆Ti C复合粉体,再将2%Ni-W包覆Ti C复合粉体与W粉混合,采用不同压力压制后烧结获得了W-Ni/Ti C复合材料。通过扫描电子显微镜(SEM)和能谱分析仪(EDS)观察和分析了Ti C陶瓷粉体预处理前后形貌、包覆后复合粉体的形貌和成分、以及不同压力压制W-Ni/Ti C烧结体形貌和成分,探讨了Ni-W包覆Ti C复合粉体和W-Ni/Ti C复合材料形成过程,压制压力对烧结体的影响规律。结果表明,化学镀方法能够制备Ni-W包覆Ti C复合粉体,粉体包覆均匀性良好,所获得的W-Ni/Ti C复合材料与相同工艺下烧结的纯钨相比具有较好的致密性,且随着压制压力的增大,致密性更高。     

二氧化钌电阻涂层电阻温度特性研究

以二氧化钌为导电相的厚膜电阻涂层具有电阻稳定性好和电阻温度系数低等优点,被广泛应用于厚膜集成电路。本文分别以连续铝硅酸盐纤维增强二氧化硅(AS_f/SiO₂)复合材料和氧化铝陶瓷为基材,采用丝网印刷工艺在两种基材表面印制了二氧化钌电阻涂层,并通过数字图像相关法、有限元分析法和XRD应力测定法系统研究了25~700°C范围内电阻涂层和基材之间的热匹配特性,分析了涂层的电阻温度特性。结果表明,由于电阻涂层的热膨胀系数大于AS_f/SiO₂复合材料,导致烧结其上的电阻涂层在室温状态受到残余拉应力,高温状态下该拉应力被释放,导电颗粒间的距离减小,势垒电阻减小,宏观表现为涂层电阻随测试温度升高而减小,呈现负的电阻温度特性。相反,由于电阻涂层的热膨胀系数小于氧化铝陶瓷,烧结其上的电阻涂层在室温状态受到残余压应力,高温状态压应力释放导致导电颗粒间的距离增大,势垒电阻增加,电阻涂层呈现正的温度特性。     

LaMgAl11O19涂层的CMAS侵蚀行为研究

为了研究服役过程中38CaO-5MgO-8AlO1.5-49SiO_2(CMAS)对镁基六铝酸镧(LaMgAl_(11)O_(19))的高温侵蚀行为,利用大气等离子喷涂技术制备了LaMgAl_(11)O_(19)涂层。通过SEM、EDS和XRD表征了1050、1250℃下LaMgAl_(11)O_(19)涂层被CMAS侵蚀后的微观组织和相结构。结果表明,LaMgAl_(11)O_(19)涂层中在1250℃被侵蚀24 h后的腐蚀产物是CaAl_2Si_2O_8和MgAl_2O_4。此外,通过研究侵蚀层厚度与侵蚀温度、侵蚀时间的关系,计算得到了在1050～1250℃温度下,CMAS侵蚀LaMgAl_(11)O_(19)涂层的反应活化能为94.1 kJ/mol。     

放电等离子烧结温度对超细晶W-40Cu复合材料的影响

采用高能球磨法制备了W-40Cu超细晶复合粉体,继而进行了放电等离子烧结(SPS),获得了致密的超细晶W-40Cu块体复合材料,着重研究了烧结温度对复合材料组织和性能的影响.结果表明,随着烧结温度升高,材料的致密度、硬度和电导率也随之升高;在950℃烧结5 min的W-40Cu复合材料,W颗粒尺寸约300～500 nm,相对致密度达98％,显微硬度HV为287,电导率为17.9 MS/m.     

Preparation and Properties of W-15Cu Composite by Electroless Plating and Powder Metallurgy

用化学镀和粉末冶金的方法制备出W-15Cu复合材料。首先用化学方法对W粉表面预处理,然后在其表面化学镀铜。得到的复合粉末用图谱进行表征。发现用化学镀的方法制备出的W-15Cu复合粉末纯度非常高,且W颗粒均匀、被Cu致密的包覆着。呈现出包状结构。这种复合粉末表现出优异的压制性能,压坯分别在300, 400, 500, 600 MPa的压制压力下成形。压坯在1250 ℃温度下保温90 min烧结后,从其断口形貌可以发现W颗粒没有明显的长大,且W颗粒表面特征并没有发生改变,仍然表现出预处理后的表面特征。对烧结体的相对密度、硬度、抗弯强度和电导率同样进行了表征     

W-Ni/Yb2O3复合材料的制备及烧结性能研究

本文首先采用化学镀获得Ni-Yb2O3复合粉体,然后通过机械球磨制备了不同成分的W-（0.2、0.5、1、2）wt% Ni/Yb2O3复合粉末,最后在1600℃下烧结3h获得了W-Ni/Yb2O3复合材料。采用场发射扫描电子显微镜(FE-SEM)研究分析了Ni-Yb2O3复合粉体形貌、W-Ni/Yb2O3复合材料表面形貌。测定了W-Ni/Yb2O3复合材料相对密度、显微硬度和热导率。实验结果表明,W-Ni/Yb2O3复合材料的相对密度和显微硬度随着Ni-Yb2O3含量增加而增加,Ni-Yb2O3的加入促进了钨基材料的烧结致密化;同时,添加Ni-Yb2O3复合粉使钨基材料的晶粒得到细化,但对钨基材料导热性起到降低的作用。     

Microstructural and mechanical evaluation of Al-TiB2 nanostructured composite fabricated by mechanical alloying

Production of bulk Al-TiB₂ nanocomposite from mechanically alloyed powder was studied. Al-20 wt.% TiB₂ metal matrix nanocomposite powder was obtained by mechanical alloying (MA) of pure Ti, B and Al powder mixture. A double step process was used to prevent the formation of undesirable phases like Al₃Ti intermetallic compound, which has been described in our previous papers. The resultant powder was consolidated by spark plasma sintering (SPS) followed up by hot extrusion. The structural characteristics of powder particles and sintered samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness measurements were conducted on the cross section of powder particles and sintered sample and the tensile behavior of extruded samples was evaluated. The results showed that the prepared Al-20 wt.% TiB₂ nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20 wt.% TiB₂ showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively, which are much higher than those reported for similar composites made by other processes.     

Novel method for preparation of silver-tin oxide electrical contacts

A novel method of coating tin oxide particles with silver by an electroless plating process has been developed to produce silver-tin oxide electrical contact materials. A powder metallurgy process has been developed to consolidate the electroless plated silver- tin oxide composite powders. The effect of the various plating conditions on the morphology of the composite powder was studied using the transmission electron microscope (TEM) and the scanning electron microscope (SEM). An optical microscope and electron microprobe analysis (EMPA) were used to characterize the structure of the sintered silver-tin oxide compact. Ductility and hardness were measured to ensure that the mechanical properties are adequate, and electrical conductivity was also measured.     

Effects of silver powder particle size on the microstructure and properties of Ag-Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> electrical contact materials prepared by spark plasma sintering

Ag-Yb₂O₃ electrical contact materials were fabricated by spark plasma sintering (SPS). The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope (OM), and the fracture morphologies were observed by scanning electron microscopy (SEM). The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder (5 μm), homogeneous and fine microstructure was obtained by fine silver powder (≤0.5 μm). At the same time, the electrical conductivity, microhardness, and tensile strength of the sintered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples (both by fine and coarse silver powders) is more than 95%. The fracture characteristics are ductile.     

Enhanced sintering of an Fe-Ni-P coated composite powder prepared by electroless nickel plating

An Fe-8.2 % Ni-6.0 % P powder was prepared by electroless nickel plating on a carbonyl iron powder, where phosphorous appeared as a contaminant of the plating process. Because of the high phosphorous concentration, persistent liquid phase sintering was effective at temperatures higher than 1000 °C. The sintered microstructure was dramatically different from the conventional approaches, where a low concentration of phosphorous was added in the form of Fe₃P. Sintering the alloy at a temperature as low as 1050 °C for 30 min yielded a sintered density of 98.6% theoretical and rounded grains having an average grain size of 53 μm. The rounded grains were surrounded by a large volume fraction of intergranular (Fe,Ni)₃P phase, arising from the high phosphorous concentration, which slightly deteriorated the magnetic saturation but significantly increased the electrical resistivity of the alloy. Generally speaking, the magnetic saturation of the sintered alloy was improved with respect to the iron-phosphorus, iron-nickel, or iron-silicon alloys fabricated by powder processing.     

Nano-attached tungsten particle synthesis and sintering behaviors

The reduction of sintering temperatures in industrial processes is advantageous for both energy efficiency and material properties in powder metallurgy. Based on the well-known size effects of nano-particles on sintering processes, nano-particles were intentionally used as a homogeneous sintering activator for micro-particles in this study. Two kinds of tungsten bimodal feedstocks which consisted of nano-particles and microparticles were prepared and sintered by spark plasma sintering processed. Even at the low sintering temperature of 1,250 °C and the short sintering time of 300 sec, relatively high densities could be achieved. Depending on the content of the nano-particles in the charged feedstock, the sintered body exhibited different morphological features. Density, field emission scanning electron microscopy, transmission electron microscope was used for analysis.     

Spark plasma sintering on mechanically activated W-Cu powders

Mechanically activated W-Cu powders were sintered by a spark plasma sintering system (SPS) in order to develop a new process and improve the properties of the alloy. Properties such as density and hardness were measured. The microstructures of the sintered W-Cu alloy samples were observed by SEM (scanning electron microscope). The results show that spark plasma sintering can obviously lower the sintering temperature and increase the density of the alloy. This process can also improve the hardness of the alloy. SPS is an effective method to obtain W-Cu powders with high density and superior physical properties.     

Preparation and properties of W–Cu–Zn alloy with low W–W contiguity

The W–Cu–Zn alloy with a-brass matrix and low W–W contiguity was prepared by method of electroless copper plating combined with spark plasma sintering(SPS) method.The effects of process and parameters on the microstructure and mechanical properties of the alloy were investigated.The W–Cu–Zn alloy with a relative density of 96 % and a W–W contiguity of about 10 % was prepared by original fine tungsten particles combined with wet mixing method and SPS solid-state sintering method at 800 °C for 10 min.The microstructure analysis shows that Cu–Zn matrix consists of nano-sized a-brass grains,and the main composition is Cu_3Zn electride.The nano-sized Cu was coated on the surface of tungsten particles by electroless copper plating method,and the fairly low consolidation temperature and short solid-state sintering time result in the nano-sized matrix phase.The dynamic compressive strength of the W–Cu–Zn alloy achieves to1000 MPa,but the alloy shows poor ductility due to the formation of the hard and brittle Cu_3Zn electrides.The fine-grain strengthening and the solution strengthening of the Cu–Zn matrix phase are responsible for the high Vickers microhardness of about 300 MPa for W–Cu–Zn alloy.     

烧结过程中WC晶粒形貌的变化

采用粉末冶金工艺烧结了纯WC,制备了WC-10%Co硬质合金,利用JSM5600LV扫描电镜观察不同烧结温度下制备的试样WC颗粒/晶粒形貌。结果表明:纯WC进行烧结时,烧结过程中在表面张力的作用下,系统向能量最低趋势发展,WC晶粒保持球形或类球形;在有钴的存在下,界面张力状态发生了改变,为了达到系统的稳定状态,WC/Co接触界面向平直化发展,烧结温度达到共晶温度之后,在溶解-析出机理的作用下,WC晶粒有选择性长大,形状更加规则化,最终导致WC/Co界面平直。