放电等离子烧结La0.67Sr0.33MnO3-δ粉体的输运性质

用自蔓延高温合成技术合成La0.67Sr0.33MnO3-δ粉体.探讨了放电等离子烧结的烧结温度对合成粉体的显微结构和输运性质的影响.扫描电镜和密度测试结果表明:放电等离子烧结后的晶粒大小均匀,烧结体致密度高.随着烧结温度的升高,样品的电阻率明显下降.由于氧缺位的存在,金属-绝缘相转变温度随着烧结温度的升高而降低.相对于传统的固相烧结,放电等离子工艺制得的样品的致密度较高导致颗粒间的巨磁电阻有所提高.     

水热合成钛酸铋粉体的烧结性能研究

以Ri4TbO12材料为研究对象，通过：XRD，SEM，TEM和BET表征手段，探讨了固相法和水热法制备工艺，放电等离子体烧结(spark plasma sintering，SPS)和普通烧结对Bi4Ti3O12粉体烧结性能及其陶瓷显微结构的影响。水热合成法使传统固相合成钛酸铋粉体的烧结温度从1000℃降低到900℃，而SPS进一步降低了水热合成Bi4Ti3O12粉体的烧结温度约130℃；固相合成和水热合成钛酸铋粉体普通烧结后的最高体密度分别为7．94g／cm^3(98％)和7．67g／cm。(95．6％)。固相合成钛酸铋粉体普通烧结后，显微结构均匀。晶粒大约2～3gm；水热合成粉体SPS烧结后，晶粒接近等轴状，粒径尺寸介于175～200ilm之间，分布均匀，随着烧结温度的升高，Bi4Ti3O12陶瓷的晶粒从等轴状长大变成片状，并且呈现出明显的定向排列。     

EDTA-硝酸盐法制备La0.8Sr0.2Ga0.85Mg0.15O3-δ及其性能

用EDTA-硝酸盐法合成了中温固体氧化物燃料电池的电解质La0.8Sr0.2Ga0.85Mg0.15O3-δ(LSGM).BET法测定了前驱粉体的比表面积.XRD和DTA-TG曲线综合分析了合成过程中的化学反应.热膨胀仪和交流阻抗谱测定了其烧结性能和电化学性能.DTA-TG结果表明粉体在800℃左右开始形成钙钛矿结构,1200℃烧结就可以形成具有完整的钙钛矿结构LSGM样品;XRD表明用该方法合成的LSGM具有纯度高、杂相少等优点;烧结收缩率曲线显示烧结温度比固相法合成低了200℃左右;交流阻抗谱结果计算得到LSGM样品在800℃的电导率为7.5 S/m.     

新型MAX相陶瓷Mo2Ga2C的放电等离子烧结

Mo2Ga2C是一种新型MAX相，该材料粉体已经可以被稳定的制备。但是Mo2Ga2C粉体不容易被烧结为致密的块体。本文采用放电等离子烧结技术(SPS)高温处理Mo2Ga2C粉体，通过对制备样品的物相组成和微观结构的表征，研究Mo2Ga2C的烧结性能。SPS烧结Mo2Ga2C 的最佳工艺参数为：烧结温度700℃，保温时间20min，轴向压力30MPa。在此条件下SPS烧结Mo2Ga2C样品相对密度达到71.81%。延长保温时间比升高烧结温度对Mo2Ga2C的致密化有更明显的助益；而增大轴向压力对样品的致密化产生负影响。相对于热压烧结，SPS可以在较低的温度快速制备Mo2Ga2C样品，但是制备的样品的致密度较低。     

La2/3Sr1/3MnO3(La1.4Sr1.6Mn2O7)/Ce0.8Gd0.2O2-δ复合阴极的微观结构及热膨胀性能

采用固相反应法制备La2/3Sr1/3MnO3(LSMO3)粉体,用溶胶-凝胶法分别制备La1 4Sr1 6Mn2O7(LSMO7)和Ce0.8Gd0.2O2-δ(CGO)粉体.分别将LSMO3和LSMO7粉体与CGO粉体以1∶1的质量比均匀混合,在300MPa下冷等静压成型,并在1 500℃烧结2 h,制备了LSMO3/CGO和LSMO7/CGO复合阴极材料.研究了2种复合阴极材料的微观结构和热膨胀性能.结果表明:LSMO3/CGO与LSMO7/CGO烧结体在150～1 000℃温度范围内的平均线性热膨胀系数分别为1.52×10-5/K和1.53×10-5/K,与CGO固体电解质具有相近的热膨胀性能.烧结体断面形貌分析表明:LSMO3/CGO复合阴极具有与CGO相似的断面显微结构.     

溶胶-凝胶法制备La0.65Sr0.35MnO3及其光催化性能

采用溶胶-凝胶法合成了以Sr取代部分稀土金属La的La0.65Sr0.35MnO3样品,经XRD衍射分析确定其具有钙钛矿的晶体结构,并对其进行了光催化活性实验.结果表明:在700℃时,La0.65Sr0.35MnO3样品平均粒径为19 nm;在太阳光照射下,LA0.65Sr0.35MnO3降解亚甲基蓝溶液120 min时,其降解率达到90%.     

阴极材料用Pr0.6-xNdxCa0.4FeO3-δ陶瓷的特性

以Pechini法合成了ABO3型钙钛矿结构的Pr0.6-xNdxCa0.4FeO3-δ(x=01,0.3,0.5)系列稀土复合氧化物粉体.用Fourier变换红外光谱和激光共焦Raman光谱对粉体烧结后样品的化学键及物相进行了表征.用热膨胀仪测定烧结样品的热膨胀系数.通过扫描电镜观察样品用作阴极材料时的微结构及阴极/电解质[钐掺杂氧化铈(samarium-doped ceria,SDC)]复合层的断口形貌.结果表明:1 200℃煅烧2h的样品的主晶相为正交钙钛矿,x=0.3的样品是正交与立方相的混合晶.在室温～1 000 ℃范围内,烧结样品的平均热膨胀系数为12.76x10-6/K,与SDC及La0.8Sr0.2Ga0.85Mg0.15O3-δ(LSGM)电解质的热膨胀系数一致.烧结样品内部孔隙分布均匀,孔隙率约35%,阴极/电解质复合层界面清晰.将复合氧化物粉体和SDC在1 200℃煅烧10h没有检测出第三相.     

MnO2对边界层陶瓷电容器的影响

为了提高边界层陶瓷电容器(GBBLC)的性能,采用非匀相共沉淀法制备了CuO包裹的BaTiO3粉体,并加入MnO2以改善样品的性能,按照普通电子陶瓷的制备工艺制得一系列样品,测试了样品的密度、体积收缩率,并研究了样品的显微结构。结果发现：样品致密性得到明显改善,最大体积收缩率超过40％,CuO具有明显促烧作用,烧结温度可降至1100℃;MnO2能够提高样品的性能,使气孔率明显减小。     

Ca^2＋掺杂对La0.8Sr0.2Ga0.8Mg0.2O3-δ电解质烧结活性及微结构的影响

用甘氨酸-硝酸盐法（GNP）合成了Ca^2＋掺杂的中温固体氧化物燃料电池电解质粉体La0.8Sr0.2Ga0.8Mg0.2O3-δ（LSCGM）（x=0．02,0．04,0．06,0．08,0．10）。用SEM和XRD等手段对产品的成相过程及微结构进行了表征,用Archimedes排水法进行样品的密度测试。研究结果表明：在La0.8Sr0.2Ga0.8Mg0.2O3-δ体系中引入Ca^2＋可提高粉体的烧结活性,促进坯体的致密化。随着Ca^2＋含量的增加,材料的烧结致密度逐渐提高,x=0．10时相对密度最大。     

钙–硼共掺铌酸钾钠基无铅压电陶瓷的微波制备及性能

采用传统固相技术和微波技术合成铌酸钾钠基陶瓷(Na_(0.535)K_(0.48))Nb_(0.91)Sb_(0.09)O_3 (NKNS)粉体,用微波技术合成的粉体为原料,分别采用传统烧结和微波烧结制备(Na_(0.535)K_(0.48))Nb_(0.91)Sb_(0.09)O_3+x%CaO–B_2O_3 (NKNS–x CB)陶瓷样品,并研究了掺杂剂含量、两种烧结工艺对陶瓷相结构和性能的影响。结果表明:在相同温度下,微波技术合成NKNS陶瓷粉体所用的时间是传统固相技术所用时间的1/6。与传统烧结相比,微波烧结使NKNS–x CB陶瓷的烧结时间缩短3/4,且在相同的温度下微波烧结的样品具有较高的致密度和较好的电学性能。x=0.50的陶瓷样品在1 020℃微波烧结30 min具有优异的电学性能:d_(33)=225 pC/N,k_p=40.2%,ε_r=647。表明微波技术是一种很有应用前景的NKN基陶瓷制备技术。     

Microstructure and flexural strength of hafnium diboride via flash and conventional spark plasma sintering

Microstructure evolution in bulk hafnium diboride ceramics prepared by spark plasma sintering in flash regime was compared with conventional spark plasma sintering. The conventional and flash spark plasma sintering resulted in ceramics with a high relative density exceeding 96% of their theoretical density. A remarkably fine grain size distribution was noticed for the specimen prepared in the flash regime. This atypical microstructure evolution provides a possible insight into the mechanism of flash sintering for conductive bulks. The room temperature flexural strength of the hafnium diboride processed by flash SPS was 650 MPa which is 140 MPa higher than the sample produced by conventional SPS.     

Defects and microstructure of highly conducting Al-doped ZnO ceramics obtained via spark plasma sintering

Al-doped ZnO ceramics were sintered by conventional sintering method and spark plasma sintering (SPS) respectively. Electrical properties and microstructure have been investigated by various measurements. The samples sintered via SPS exhibit a huge electrical conductivity, up to 3.0 × 10⁵ S/m at room temperature, which was much higher than that of the sample sintered via the conventional sintering. Structural and morphorlogical characterizations pointed out that the further incorporation of Al ions and the absence of a secondary phase, contribute to the increase of the carrier concentration. Raman spectroscopy revealed the occurrence of structural distortions and a disorder induced by Al doping. Photoluminescence spectra were interpreted by different electronic active defects such as the defect complexes (Al_Zn-Zn_i) which play a key for the high electrical conductivity. Thus, SPS and Al doping modified the microstructure and the concentration of the electronic active defects to ensure high electrical conductivities in doped ZnO-based ceramics.     

Rapid sintering of nanocrystalline ZrO2(3Y) by spark plasma sintering

SPS (spark plasma sintering) process was used to sinter nanocrystalline ZrO₂ (3Y). It was found to be different with the usual rapid sintering method, the density of the samples kept increasing with the rising of the sintering temperature. A higher density could be reached at a lower temperature and shorter dwelling time than that by hot-pressing under the similar pressures. In contrast to the samples with a differential densification from edge to center prepared by a rapid hot-pressing, no obvious densification gradient could be found in the samples sintered by SPS. The grain sizes of the Y-TZP obtained by SPS were smaller than those by the pressureless sintering method, while the grain growth speed was much higher under SPS conditions. All these unique sintering behaviors were explained by the special sintering process of SPS.     

Sintering behavior of 8YSZ-Ni cermet: Comparison between conventional,FST/SPS,and flash sintering

Cermets are ceramic metal composites. The metallic phase in the cermet typically undergoes oxidation during sintering in air. Electric field-assisted sintering processes such as field-assisted sintering technology/spark plasma sintering (FAST/SPS) and flash involves very high heating rates, short processing time and low processing temperature. The main aim of this work was to see if field-assisted sintering techniques can prevent the oxidation of the metallic phase in the cermet. Sintering behavior of 8YSZ-5 wt.% Ni cermet was studied by three different techniques namely; conventional sintering, FAST/SPS and flash sintering. Phases and microstructure were analyzed through X-ray diffraction and scanning electron microscopy, respectively. Temperature and time required for sintering the samples via FAST/SPS and flash sintering was significantly lower than that during conventional sintering. In addition, we found limited grain growth during FAST/SPS and flash sintering. During conventional sintering in reducing atmosphere (Ar and vacuum), Ni particles retained their elemental state, however the extent of densification was poor in the cermet. FAST/SPS in argon and vacuum resulted in almost complete densification (relative density > 97%) and Ni particles were retained in their elemental state in the cermet. During flash sintering in air, the samples sintered to a high densification (relative density ∼98%), however, Ni particles were completely oxidized.     

Sintering behavior and mechanical properties of spark plasma sintering SiO2-MgO ceramics

SiO₂-MgO ceramics containing different weight fractions (0, 0.5, 1, 2, and 4 wt%) of SiO₂ powder were prepared by mixing nano MgO powder, and the powder mixtures were densified by spark plasma sintering (SPS). The effect of SiO₂ addition and SPS method on the sintering behavior, microstructure and mechanical properties were investigated. Results were compared to specimens obtained by conventional hot pressing (HP) under a similar sintering schedule. The highest relative density, flexural strength and hardness of 2 wt% SiO₂-MgO ceramics reached 99.98%, 253.99 ± 7.47 MPa and 7.56 ± 0.21 GPa when sintered at 1400 °C by SPS, respectively. The observed improvement in the sintering behavior and mechanical properties are mainly attributed to grain boundary "strengthening" and intragranular "weakening" of the MgO matrix. Furthermore, the spark plasma sintering temperature could be decreased by more than 100 °C as compared with the HP method, SPS favouring enhanced grain boundary sliding, plastic deformation and diffusion in the sintering process.     

Synthesis of dense NiZn ferrites by spark plasma sintering

Dense NiZn ferrites were fabricated by spark plasma sintering (SPS) at 900 °C and 20 MPa in short periods. The powder was densified to 98% of the theoretical density by the SPS process. The SPS disks exhibited a higher saturation magnetization (Ms), up to 272 emu/cm³, than did the disks sintered by the conventional process. A higher coercivity (Hci) was obtained when the green bodies were sintered by the SPS process for 5 min. A modest holding time is essential to obtain fine grain and uniformity in the SPS process. Secondary crystallization, inhomogeneous microstructure and intragranular pores were found as a result of the rapid sintering and relatively longer holding time in the SPS process. Infrared (IR) spectra were also measured in the range from 350 to 700 cm⁻¹ to study the efforts of the SPS process on NiZn ferrites.     

Effect of sintering temperature on the structural and magnetic properties of MgFe2O4 ceramics prepared by spark plasma sintering

Spark plasma sintering (SPS) is a powerful technique to produce fine grain dense ferrite at low temperature. This work was undertaken to study the effect of sintering temperature on the densification, microstructures and magnetic properties of magnesium ferrite (MgFe₂O₄). MgFe₂O₄ nanoparticles were synthesized via sol–gel self-combustion method. The powders were pressed into pellets which were sintered by spark plasma sintering at 700–900 °C for 5 min under 40 MPa. A densification of 95% of the theoretical density of Mg ferrite was achieved in the spark plasma sintered (SPSed) ceramics. The density, grain size and saturation magnetization of SPSed ceramics were found to increase with an increase in sintering temperature. Infrared (IR) spectra exhibit two important vibration bands of tetrahedral and octahedral metal-oxygen sites. The investigations of microstructures and magnetic properties reveal that the unique sintering mechanism in the SPS process is responsible for the enhancement of magnetic properties of SPSed compacts.     

Ti_2AlC陶瓷增强TiAl基材料的研究

国内外很多学者用自蔓延高温合成法、自蔓延高温合成同电弧熔炼铸造技术相结合法、放电等离子烧结等方法合成了TiAl/Ti2AlC复合材料。最近,作者以Ti、Al、TiC粉为原料,用原位热压的方法合成了该复合材料。本文综述了TiAl/Ti2AlC复合材料的几种制备方法、力学及抗氧化性能的研究情况。