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1.
Jinshu Wang Wei Liu Zhiyuan Ren Fan Yang Yiman Wang Meiling Zhou 《Materials Research Bulletin》2010,45(3):324-328
Y2O3-Mo cermet cathodes were prepared by mechanical mixing of Y2O3 and Mo powder. The prepared cermet cathode provides a certain secondary emission yield (3.09), about 1.8 times lower than that for the cathode prepared by sol-gel method. It was found that the cathode prepared by sol-gel method had a smaller grain size, which could be attributed to its higher emission property. The energy distributions of primary electrons in the cathodes with different grain sizes have been simulated by Monte Carlo method. Based on the calculation results, the emission models of the cathodes are established and presented. The cathodes with different grain sizes exhibited different ways of emission. Two types of emission, of reflection emission and transmission emission, existed in the cathode with small grain sizes whereas only transmission emission existed in the cathode with large grain sizes. 相似文献
2.
采用液相共沉淀法和固相合成法分别制备411(4BaO:CaO:Al2O3)铝酸盐前驱粉末, 在钨网氢气炉中高温烧结. 采用喷雾干燥法结合两步氢气还原法制备出亚微米氧化钪掺杂钨粉. 随后经过压制, 烧结, 浸渍, 水洗, 退火等工艺获得具有亚微米结构的含钪扩散阴极, 并研究含钪扩散阴极的电子发射性能. 实验结果表明, 液相共沉淀法制备的铝酸盐在1500℃烧结后, 铝酸盐中Ba5CaAl4O12衍射峰最强, 结晶程度最高. 液相共沉淀法含钪扩散阴极, 脉冲发射电流密度在850℃达到37.89 A/cm2. 在激活过程中, 阴极表面形成“Ba-Sc-O”发射活性层, “Ba-Sc-O”发射活性层存在提高了阴极热电子发射能力, 降低了含钪扩散阴极的蒸发速率. 相似文献
3.
Sub-micrometer Sc2O3–W powder with a narrow particle size distribution has been obtained by a sol–gel method combined with two-step hydrogen reduction process. Based on the obtained powder, the W–Sc2O3 targets have been sintered via spark plasma sintering (SPS) at 1300 °C. The W–Sc2O3 targets have the average grain size of about 1 μm. Both the sintering temperature and holding time are much lower than those of the targets prepared with micrometer sized powders. The obtained W–Sc2O3 targets have a high comparative density of 96.4% and rockwell hardness of 86.4 HRC. Using the target, the scandate cathode deposited with a film containing 5% Sc2O3 and 95% W has been obtained by pulsed laser deposition (PLD) method. This cathode has good emission property, i.e., the highest thermionic emission current density reaches 43.09 A/cm2 of Jdiv at 900 °Cb after being activated for 8 h, which is much higher than that of scandate cathode without film. Scandium (Sc) supplied by the film on the surface during the activation forms a Ba–Sc–O active layer, which helps to the emission. 相似文献
4.
In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys. 相似文献
5.
《Advanced Powder Technology》2023,34(9):104133
In this research, porous W matrixes for dispenser Ba-W cathodes were prepared by metal injection molding (MIM) using W powders with different particle shapes as raw materials. Other than investigating the effect of the powder particle shape on the pore characteristics of the porous W matrix, the influence of the powder particle shape on the emission properties of the Ba-W cathode was also investigated. Irregular W powder particles had higher surface roughness and specific surface area than the spherical W particles, resulting in sinuous pore channels and higher pore-specific surface area in the prepared W matrix. The emission current density of the cathode processed from the irregular powder was thus improved as the level of Ba–O dipoles, covered on the emission surface, was increased. This is due to the high pore-specific surface area offering a high contact area between W and impregants in the cathode. 相似文献
6.
Jianxin WANG) Qin WANG) Xianping WANG) Chun LI) Qianfeng FANG) )Key Laboratory of Materials Physics 《材料科学技术学报》2008,24(5):761-765
A cost-efFective technique, including nanocrystalline powder preparation using a modified Pechini method and a two-step low-temperature sintering route, was developed for the synthesis of high performance La2Mo2O9- based oxide-ion conductors. The optimum parameters of the compaction pressure, the first step and 'the second step sintering temperatures for the synthesis of fine grained, high density and uniform La2Mo2O9- based oxide-ion conductors were determined by a series of sintering experiments. High density and uniform sintered La2Mo2O9 samples with average grain size from 0.8 to 5 μm and La1.96K0.04Mo2O8.96 sample with average grain size as small as 500 nm were synthesized by using this cost-efFective method. The impedance measurement results show that the as-fabricated La2Mo2O9-based ceramics possess much higher ionic conductivity than that obtained by solid state reaction method. It is found that in the range of 0.8-5μm the grain size of dense La2Mo2O9 samples prepared from the nanocrystalline powders has little influence on their conductivities. 相似文献
7.
采用烧结法制备阴极材料(La0.85Sr0.15)y(Mn-zCrz)(y=0.85,1;z=0.1,0.2)。研究了多孔锰酸镧致密ZrO2(8mol%Y2O3)界面的成分变化和显微形貌。 相似文献
8.
Ag含量对NiFe2O4基金属陶瓷惰性阳极性能的影响 总被引:1,自引:0,他引:1
为了提高NiFe2O4陶瓷阳极材料的力学性能和抗热震性,向原料中加入金属Ag,采用粉末冶金法制备了Ag/NiFe2O4金属陶瓷惰性阳极.研究了Ag含量对材料微观结构、抗弯强度以及抗热震性的影响.研究结果表明随着Ag含量的增加,惰性阳极材料的晶粒尺寸逐渐减小,说明Ag能够有效抑制陶瓷基体晶粒的长大.而且随着Ag含量的增加,材料的结构越来越致密,说明Ag在一定程度上能够促进烧结.对材料的力学性能和抗热震性测试结果发现,Ag能提高材料的强度,随着Ag含量的增加,材料的抗弯强度逐渐增大,抗热震性在银含量为10%处达到最大值. 相似文献
9.
以SnO2纳米粉和La2O3纳米粉为原料,采用高能球磨技术,结合正交试验设计,制备了经过高能球磨的纯SnO2纳米粉体和掺杂适量La2O3的SnO2纳米粉体。利用传统的厚膜气敏传感器制备工艺,制备了纯SnO2厚膜气敏传感器及掺杂一定量La2O3的SnO2厚膜气敏传感器。并对其本征电阻及其对乙醇、汽油、丙酮、氢气和CO等气体的敏感特性进行了测试。结果表明各因素对综合气敏性能影响的显著性水平由大到小依次为La2O3掺杂浓度〉烧结时间〉老化时间〉烧结温度。同时,通过分析还得到了最佳组合工艺。La2O3掺量为5%(质量分数),烧结时间为2h,老化时间为7d,烧结温度为650℃条件下制备的气敏元件的综合气敏性能最好,其中对1.0×10-3乙醇蒸气的灵敏度达107.2,对相同浓度的干扰气体的选择性分别为S乙醇/S汽油=11.3,S乙醇/S丙酮=9.1。 相似文献
10.
《Materials Letters》2005,59(8-9):1046-1049
The tracks of cathode spots produced after arcing on the surfaces of nanostructured W alloys were investigated using a scanning electron microscope (SEM). For nanostructured W–2%ThO2 cathodes, the distribution of cathode spots was dispersed and their geometrical properties were completely controlled by the shape and size of ThO2. For nanostructured W–20%Cu cathodes, the spots were also separated on Cu-rich phase. The results showed that cathode spots on the surface of nanostructured W alloys were quite different from those on the surface of commercial W alloys with coarse grain size, and the microstructure of the cathode materials had significant influence on the cathode spots propagation. Also, space-charge regions induced by internal electric field at the interface which responded to the effect of microstructure on cathode spots were suggested. 相似文献
11.
采用真空热压烧结法制备La2O3-TiC/W复合材料,并对其组织结构和力学性能进行了研究。结果表明:在一定成分范围内,La2O3和TiC的加入提高了复合材料的力学性能,La2O3和TiC共同作用时的强化效果强于La2O3和TiC单独作用的强化效果,但La2O3-TiC/W复合材料的密度和相对密度随TiC含量的增加而下降,并进而影响硬度和弹性模量的提高, 适量的La2O3有益于相对密度的提高;抗弯强度在1%La2O3 5%TiC/W成分含量时出现最大值901MPa,而断裂韧性在成分含量为0.5%La2O3-10%TiC/W时出现最大值10.07MPa·m1/2。本研究中,1%La2O3-5%TiC/W成分配比时具有较好的综合力学性能。La2O3-TiC/W复合材料的强化机制为细晶强化和载荷传递,韧化机制为细晶韧化、裂纹偏转和桥接。 相似文献
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13.
Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable aluminum nitride (AlN) powder to be fully densified. It is addressed that pure AlN sintered by SPS has relatively low thermal conductivity. In this work, SPS of AlN ceramic was carried out with Y2O3, Sm2O3 and Li2O as sintering aids. Effects of additives on AlN densification, microstructure and properties were investigated. Addition of sintering aids accelerated the densification, lowered AlN sintering temperature and was advantageous to improve properties of AlN ceramic. Thermal conductivity and strength were found to be greatly improved with the present of Sm2O3 as sintering additive, with a thermal conductivity value about 131 Wm−1K−1 and bending strength about 330 MPa for the 2 wt% Sm2O3-doped AlN sample SPS at 1,780 °C for 5 min. XRD measurement revealed that additives had no obvious effect on the AlN lattice parameters. Observation by SEM showed that AlN ceramics prepared by SPS method manifested quite homogeneous microstructure. However, AlN grain sizes and shapes, location of secondary phases varied with the additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of liquid phases. 相似文献
14.
采用放电等离子烧结法(SPS)制备了不同TiB2颗粒粒径的3wt% TiB2/Cu复合材料,研究了3wt% TiB2/Cu复合材料致密度、导电率、硬度和耐电弧侵蚀性能随TiB2颗粒粒径的变化规律,重点分析了不同TiB2颗粒粒径的3wt% TiB2/Cu复合材料耐电弧侵蚀行为。结果表明:3wt% TiB2/Cu复合材料致密度和硬度随TiB2颗粒粒径的增大而略有降低;TiB2颗粒粒径越小,TiB2/Cu复合材料的综合性能越好。随着TiB2颗粒粒径的增大,3wt% TiB2/Cu复合材料耐蚀稳定性降低,3wt% TiB2/Cu阴极材料的损耗量明显增加;当TiB2颗粒粒径为10 μm时,3wt% TiB2/Cu复合材料的耐电弧侵蚀性能最佳。电弧蚀形貌观察表明:不同TiB2颗粒粒径的3wt% TiB2/Cu复合材料经电弧侵蚀后,3wt% TiB2/Cu复合材料均由阴极向阳极发生转移;随着TiB2颗粒粒径的增大,阴极质量损耗逐渐增加,触头表面电弧侵蚀面积增加;而在Cu基体中引入较小的TiB2颗粒,有利于减弱电接触实验过程中TiB2/Cu复合材料的喷溅现象。 相似文献
15.
以氢直流电弧法制备CeHx纳米粉末, 再采用放电等离子(SPS)反应液相烧结纳米CeHx和微米B的混合粉末, 制备了高性能CeB6多晶块体热阴极材料. 研究了SPS制备CeB6的烧结反应式及反应液相烧结机制, 确定SPS烧结CeB6的最佳工艺为: 压力50MPa, 烧结温度1500℃, 保温时间5min. 实验结果表明, SPS制备得到了高纯单相CeB6多晶块体, 纯度达到99.89%, 相对密度达到99.61%, 维氏硬度达到2051kg/mm2, 抗弯强度达到254.2MPa. 样品在1600℃温度下拐点发射电流密度达到20.38A/cm2, 功函数为2.42eV. 与传统制备法相比, SPS制备显著降低了CeB6的烧结温度, 缩短了烧结时间, 提高了力学和发射性能. 相似文献
16.
Hiroaki Muta Ken Kurosaki Masayoshi Uno Shinsuke Yamanaka 《Journal of Materials Science》2008,43(19):6429-6434
Nitride fuel is a promising nuclear fuel in fast breeder reactor (FBR) or accelerator-driven subcritical reactor (ADSR) system.
In this study, high-density UN pellets were prepared by Spark plasma sintering (SPS) technique. The sample density strongly
depended on the sintering temperature and pressure, and the pellets with 90% of theoretical density were easily obtained with
low sintering temperature and short sintering time without any milling process. The grain size and pore size were much smaller
compared with those for samples prepared by conventional sintering process. Despite of the small grain size, the thermal conductivity
remains the high value. The SPS process permits easy densification of nitrides without any deterioration of thermal and mechanical
properties, considered to be suitable as a preparation method of nitride fuels. 相似文献
17.
研究一种以溶胶-凝胶作为前躯体制备纳米La2O2CO3粉体的新方法,以柠檬酸和硝酸镧为原料,采用凝胶自蔓延燃烧法制备纳米La2O2CO3粉体,并利用X射线衍射、差热分析、透射电镜等手段对合成产物进行表征,确定最佳的工艺条件。结果表明:在前驱溶液的pH值为2,烘干温度为400℃,煅烧温度为600℃时,可以制备出平均晶粒尺寸为30 nm的La2O2CO3颗粒,且粉体的粒径均匀,粒径分布狭窄。 相似文献
18.
Jun-Young Cho Tae-Ho An Soo Young Shin Hwang Sun Kim Young Seok Kim Hyunick Shin Sung-Hwan Bae Miyoung Kim Seong-Hyeon Hong Chan Park 《Bulletin of Materials Science》2018,41(6):157
The effects of sintering conditions on the microstructure and mechanical properties of the sintered SiC prepared using the SiC powder recovered from the kerf loss sludge were investigated. The recovered SiC powders were consolidated by spark plasma sintering (SPS) and conventional sintering methods. The effects of sintering temperature, time and methods (SPS and conventional sintering) on the phase, grain size and density of SiC were systematically studied. The Vickers hardness of spark plasma-sintered (SPSed) samples was higher than that of conventional sintered samples due to small grain size. When holding time was increased from 10 to 30 min, the grain size and relative density of SPSed samples were also increased, which lead to the almost constant Vickers hardness by competing effects of grain size and relative density. When holding time was over 30 min, no appreciable change of the relative density and grain size were observed, which can lead to similar values of Vickers hardness. SPS process can be used to make SiC with high density and hardness at relatively low temperature compared with the conventional sintering process. 相似文献
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20.
A typical approach involving Pechini method and spark plasma sintering (SPS) method was presented for the preparation of high density Li5+x Srx La3--x Bi2O12 (x = 0, 1) ceramics. Phase formation, microstructure, grain size and electrical properties of the specimens were examined using XRD, SEM and alternating current impedance spectroscopy (ACIS). Dense Li5La3Bi2O12 and Li6SrLa2Bi2O12 ceramics with pure garnet-like phase, relative density of 97% and average grain size of about 5 μm were fabricated using this approach. The total conductivities at 298 K of Li5La3Bi2O12 and Li6SrLa2Bi2O12 ceramics prepared by the SPS method are 5.1×10-5 and 6.8×10-5 S/cm, respectively, 2 times higher than that of samples prepared by the conventional sintering method. 相似文献