The influence of percolation during pulsed electric current sintering of ZrO2–TiN powder compacts with varying TiN content

A series of ZrO₂–TiN composite powder compacts with varying TiN content was densified using the field assisted sintering technique, also known as spark plasma sintering or pulsed electric current sintering (PECS). The TiN content was varied between 35 and 90 vol.% in order to obtain an electrical conductive composite material that can be shaped by electrical discharge machining. The influence of the TiN content on the densification behaviour was investigated experimentally, whereas its influence on the temperature and current distribution in the PECS tool set-up was simulated using a previously developed finite element model. The predicted temperature distribution was confirmed experimentally using a double pyrometer set-up, one focusing on the outer die wall surface and one on the bottom of a borehole in the upper punch. The changing thermal and electrical properties of the sintering ZrO₂–TiN powder compacts were calculated using mixture rules. Using a double pyrometer set-up, a clear relationship could be verified experimentally between the changing electrical properties of the sintering compact and the temperature redistribution in the punch/die/sample set-up during the PECS process. The homogeneity of sintering inside the PECS equipment is discussed in detail and suggestions are made in order to promote a more homogeneous sintering process. Carbon felt, acting as a thermal insulator, was placed around the die in order to minimize the radiation heat losses and to minimize the thermal gradients during heating and the dwell period at maximum temperature. The mechanical and electrical properties of the different composite materials are discussed as functions of the TiN content.     

阴极电导率和孔隙率对熔盐电解钛精矿脱氧过程的影响

阴极的性能通常是和电解过程与电解效率有着密切的关系。本文中测量了焙烧温度对钛精矿阴极的电导率的影响。结果表明焙烧温度对钛精矿阴极导电性影响很大。钛精矿阴极电阻率随着焙烧温度升高和接触面积的增加而增大。另外本文也研究了阴极孔隙率对熔盐电解制备Ti-Fe合金还原过程的影响。结果表明阴极的孔隙率对还原过程有着直接的影响。孔隙率的增加有利于形成中间化合物CaTiO3,从而改善电流效率。     

Optimization of the synthesis conditions of LiCoO2 for lithium secondary battery by ultrasonic spray pyrolysis process

LiCoO₂ powders for lithium secondary battery were successfully prepared by the ultrasonic spray pyrolysis process. In this work, the statistical experimental design method was used to compare the characteristics (particle size, standard deviation, surface area, tab density) of the LiCoO₂ particles according to the four parameters (synthesis temperature, sintering temperature, sintering time, sintering heating rate). The optimal synthesis conditions for the synthesis of LiCoO₂ particles in ultrasonic spray pyrolysis process were to be obtained. The above-mentioned optimal conditions were used to prepare the particles with particle size 4.7 μm (standard deviation: ±1.3%) and the experimental results were in a good agreement with simulated values. The oxide powders were characterized by scanning electron microscopy, X-ray diffraction and electrochemical method including charge–discharge cycling. The characteristics as a cathode for lithium ion battery depended on the sintering temperature and sintering time. Consequently, LiCoO₂ powders made by the ultrasonic spray pyrolysis process displayed a good electrochemical performance and the experimental design method was well applied.     

Densification behaviour of pure molybdenum powder by spark plasma sintering

Pure molybdenum was sintered with SPS under various temperatures, external pressures and heating rates. The microstructure of the specimens representing the different sintering conditions was investigated by classical metallographic methods. The relative density, the microhardness and the chord length distribution were measured. Linear shrinkage, depending on time or temperature, was calculated from piston travel, which was recorded during sintering process. These results show that the main part of consolidation takes place during fast heating up. The densification behaviour is controlled mainly by sintering temperatures and applied pressure. The molybdenum powder was successfully consolidated by SPS in very short times. A relative density of 95% was reached by sintering temperatures of 1600 °C and external pressure of 67 MPa.     

Preliminary Investigation of Preparing High Burn-Up Structure in Nuclear Fuel by Flash Sintering Using CeO2 as a Surrogate

The high burn-up structure (HBS) is characterized by the grain size of 100-300 nm and a porosity of up to 20％,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO2 as a surrogate for a preliminary inves-tigation.A new experimental configuration for rapid sintering of CeO2 pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of～ 98 mA mm-2,CeO2 ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7％ were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO2 ceramics and their HBS.     

粉末粒度对SPS固相烧结La0.6Eu0.4B6阴极材料的影响

采用高能球磨法制备出La0 6Eu0.4B6纳米粉体,将球磨后的纳米粉进行放电等离子(SPS)烧结,制备出了高致密的La0.6Eu0.4B6多晶块体材料.系统研究了烧结温度、烧结压力对样品致密度和力学性能的影响.结果表明,该方法与传统热压烧结方法相比有效降低了烧结温度,制备出的样品密度、维氏硬度和抗弯强度分别达到4.71 g/cm3、23.37 GPa和295.14MPa,这些值均高于传统热压烧结方法.热电子发射结果表明,当阴极温度为1873 K时,最大发射电流密度为33.74 A/cm2.实验过程中还发现,在相同烧结工艺下,球磨纳米粉与粗粉相比,维氏硬度、抗弯强度和热电子发射电流密度分别提高了28％、58％和32％.因此,在固相烧结过程中,粉末粒度的减小,更有助于烧结性能的提高.     

Fabrication of ZnO-based thick film varistors with high potential gradient

ZnO-based thick film varistors have been fabricated by Y₂O₃ doping and low-temperature sintering, of which the sample with the best electrical properties has a high potential gradient value of 3159.4 V/mm. The effects of Y₂O₃ doping concentration and sintering temperature on the potential gradient of the samples were systematically investigated. The results show that the sample with the best electrical properties can be obtained by doping 0.08 mol% Y₂O₃ and sintering at 725°C. Under these optimum preparation conditions, the leakage current and the nonlinear coefficient are found to be 36.4 μA and 13.1. The sample with the best electrical properties has a grain size of 1.290 μm, a single grain boundary voltage of 4.08 V, a barrier height of 0.81 eV, and a depletion layer width of 10.2 nm, which are determined by thermionic emission. Small grain size with good grain boundary characteristics is beneficial to improve the electrical properties of varistors and promote the potential gradient.     

Huadong sintering model about expansion and shrinkage

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中低温用Sm1-2xEuxBaxB6阴极材料的制备及性能

采用硼/碳热还原-热压烧结集成工艺(BCTR&HP)制备了高纯致密的Sm_1-2xEu_xBa_xB₆(x=0.1,02,0.3)多晶块体,系统研究Eu&Ba掺杂SmB₆对其结构、力学性能与电学特性的影响。结果表明,BCTR&HP制备的Sm_1-2xEu_xBa_xB₆呈CsC1型简单立方单相结构,晶格常数随Eu&Ba掺杂量的增加而增大,贡献于力学性能的提高和电阻率的下降。热电子发射性能结果表明,Eu&Ba掺杂能够改善SmB₆阴极材料的发射特性,在测试温度1773 K,外加电压1 kV条件下,Sm_0.4Eu_0.3Ba_0.3B₆阴极的发射电流密度达到35.1 mA·cm^-2,零场电流密度达到21.4 mA·cm^-2,在1523~1773 K其平均有效功函数为3.6 eV,其固有的高电阻率可作为"直热式"阴极简化热子结构,具有很大的应用前景。     

Microstructural evolution and sintering kinetics during spark plasma sintering of Fe and Al blended powder

The reaction diffusion between Fe and Al during spark plasma sintering (SPS) was studied. Microstructural evolution was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the sintering kinetics was disclosed. The main interphase of the SPS sample was Fe₂Al₅ at 773–873 K. Ball-milling enabled a large number of lattice defects and grain boundaries thus the reaction kinetics was accelerated, although the direct current can also promote those defects. After milling, the phase transformation kinetics was improved from 0.207 before mill to 4.56×10^?3. Besides, this work provided more details for the generation of Joule heating. The resistance offered to the electric path was considered to be the source of Joule heating, and particularly the resistance offered by the different contact interfaces of die, punch, graphite foil and the sample played a leading role for the generation of Joule heating during spark plasma sintering.     

TiO2电化学还原法提取金属钛的阴极制备工艺

研究TiO2电化学还原法提取金属钛的阴极制备参数——烧结温度和烧结时间。采用SEM、EDS等方法研究烧结温度、烧结时间对TiO2阴极微观结构、孔隙率的影响及不同烧结条件下TiO2阴极电解产物结构和氧含量的变化。结果表明：烧结条件主要影响电极的粒度大小、孔隙尺寸和孔隙分布：在较高温度下烧结较长时间获得的电极片粒度较粗,而孔隙率的变化比较复杂。电极的颗粒尺寸、孔隙率直接影响脱氧率：粒度较小的电极在试验条件下可被充分还原;电极中的开孔和闭孔都有利于电化学还原过程的进行。在1000~1100 °C下烧结4 h获得的TiO2阴极脱氧效果较好。     

凝胶注模成形制备TiAl合金实验研究

将凝胶注模成形技术应用于制备钛铝合金中,分别以氢化钛粉和铝粉、钛粉和铝粉为原料,经过低温烧结制成TiAl合金粉,经凝胶注模成形后通过脱胶和高温无压烧结制备了TiAl合金制件。结果表明:钛、铝粉在500℃保温2 h,再在600℃保温3 h得到TiAl合金粉,氢化钛、铝粉在750℃保温3 h得到TiAl合金粉;烧结工艺分别为1450℃保温2 h和1400℃保温2 h,可以得到致密度不同的制件,它们的致密度分别为91%和96.75%。     

放电等离子烧结CuIn5合金的工艺优化

采用正交试验法确定了CuIn₅合金放电等离子烧结(SPS)的最佳工艺参数,研究了烧结温度、烧结时间、烧结压力对CuIn₅合金的致密度、硬度和导电性能的影响。结果表明:影响CuIn₅合金致密度和硬度的主要因素均为烧结温度,其次为烧结压力,烧结时间的影响最小;影响CuIn₅合金电导率的主要因素为烧结温度,其次为烧结时间和烧结压力。利用SPS技术制备CuIn₅合金的最佳工艺为烧结温度850 ℃,烧结时间5 min,烧结压力50 MPa。采用最佳工艺制备的CuIn₅合金组织均匀致密,In固溶于Cu中形成固溶体,其晶格常数为0.362 865 nm,晶格畸变率为0.38%,致密度为99.56%,显微硬度为136.3 HV0.1,导电率为37.86%IACS。     

烧结制备泡沫陶瓷过滤器工艺的优化

采用Al2 O3 和耐火粘土代替贵重的ZrO2 作为基体 ,制备泡沫陶瓷过滤器。并通过添加稀土氧化物Y2 O3 及CeO显著缩短高温烧结时间 ,提高生产效率。烧结的过滤器在液态球墨铸铁中浸泡 ,抗损坏时间延长。所制备的过滤器完全可以满足过滤液态球墨铸铁的要求。     

High density plasma assisted sputtering system for various coating processes

High density plasma assisted sputtering source (HiPASS) has been introduced to develop a remote plasma sputtering. In HiPASS the remote plasma source (RPS) was an electron beam excited plasma using a direct current discharge supplying Ar plasma (10^10–11 cm^− 3). Ar plasma was transported from the RPS to a sputtering cathode by external magnetic fields. The transported Ar ions generated a physical sputtering at the negatively biased sputtering cathode. HiPASS has an advantage that sputtering current and voltage were controllable independently. The sputtering current was dominantly controllable by the discharge power of the RPS. And sputtering voltage was applied to the sputtering cathode freely with the fixed sputtering current modulated by the discharge power of the RPS. As the discharge power of the RPS is increased from 2.4 to 8.4 kW, the sputtering current of sputtering cathode (78.5 cm²) was varied from 1.2 ± 0.1 to 3.6 ± 0.2 A. This was an improved sputtering current comparing with practical sputtering current (1 A at 78.5 cm²) of radio frequency excited remote plasma sputtering. The remote plasma sputtering with the improved sputtering current could be applied to low voltage high current sputtering for damage-free transparent conductive oxide and barrier film depositions as well as high voltage high current sputtering for hard coating applications.     

Preparation and characteristic of NASICON ceramics

Hot-pressed sintering was employed to prepare the sodium super ionic conductor (Na1+xZr2SixP3-xO12,1.8≤x≤2.2)ceramics and compare with the sample obtained from normal-press sintering. The phase formation, density, and conductivity of the hot-press sintered and the normal-press sintered samples were investigated in detail. Results show that the density of NASICON ceramics and the degree of crystallization can be improved by hot-press process efficiently. The density of the sample sintered by normal sintering is obviously lower than that sintered by hot press. XRD analysis indicates all the hot press sintered samples contain mainly monoclinic NASICON and no ZrO2 phase was found. The ionic conductivity of normal-press sintered sample is much lower than that of hot-press sintered sample. When the composition is close to Na3Zr2Si2PO12 , the dc conductivities of the hot press sintered samples were in the order of 10-3 S·cm-1.The variation of the ac conductivity with frequency in the high frequency region agrees with the power law feature of σ(ω) ∝ωn(0＜n＜1).     

空心阴极烧结粉末冶金制品工艺研究

为了克服常现粉末冶金制品烧结工艺的缺点，试验研究了空心阴极等离子烧结工艺。介绍了空心阴极烧结装置、烧结方法、空心阴极功率输出特性和应用实例。     

氧化物—空气半燃料电池用贮氢合金电极的烧结制备及其电化学特性

研究了应用在空气－氢化物半燃料电池上的制备配套金属氢化物厚型电极烧结技术，将贮氢合金与细镍粉和一定的添加剂形成浆料涂覆在泡沫镍基体，测试不同烧结参数对贮氢合金电极的电化学性能的影响，烧结电极合金的电化学活化特性和高倍率放电能力与传统的粘结式电极有较大的提高，为设计适合电动车用高能量密度空气－氢化物燃料电池，分别选用冲孔镍箔带，冲孔铜箔带和铜编织网作为集流体进行比较实验。结果表明，选定冲孔铜箔带是适宜于设计空气－氢化物燃料电池用厚型氢化物电极。     

Effects of heating rate and particle size on pulse electric current sintering of alumina

Two Al₂O₃ powders with different particle sizes were sintered by pulse electric current sintering method at different heating rates. Rapid heating reduced grain growth rate, and the level of reduction depended on the initial powder size and sintering temperature. Under certain conditions, rapid heating could enhance densification.     

不锈钢金属多孔材料固相烧结热变形特性研究

烧结工艺对多孔材料性能有很大的影响,为了获得最佳的力学性能和需要的零件形状,有必要对烧结的热变形过程进行研究。基于SVOS粘塑性本构模型,采用热力耦合计算不锈钢多孔材料在烧结过程中宏观变形。通过自由烧结实验和弯曲实验,使用4阶Gauss函数对烧结应力、体积和剪切粘度等模型参数进行了拟合。讨论了相对密度、线性收缩率等随烧结时间和温度的变化规律。结果表明：模拟过程与实验符合得较好,验证了模型的合理性。不同升温速率下,材料的线性收缩曲线变化不大,因此,升温速率对烧结过程影响较小。升温速率对计算时间影响比较大,升温速率很慢或很快时,计算不容易收敛,计算时间比较长。对模压生坯零件的烧结模拟结果表明,由于初始密度分布不均匀性导致最终密度分布的不均匀,但是密度变化范围不大。