(Y1-xLax)2O3透明陶瓷的制备及性能

采用传统陶瓷生产工艺制备了(Y1-xLax)2O3(x=0～0.125)透明陶瓷.研究了陶瓷的显微结构、硬度、透光性及热导率.结果表明:La2O3可以有效促进陶瓷烧结,抑制晶粒长大.La2O3添加后,陶瓷硬度由786MPa提高到878MPa,陶瓷热导率明显降低,由16.92W/(m·K)降为5.68W/(m·K).制备...     

氟掺杂对Ca3Co4O9化合物微观结构和热电性能的影响

采用固相合成法及放电等离子烧结制备了Ca3Co4(FxO1-x)9(x=0,0.01,0.02)块体样品,系统研究了氟(F)掺杂对Ca3Co4O9微观结构和热电性能的影响。结果表明:F掺杂样品均为单一化合物。在300～900K,与纯样相比,F掺杂样品的Seebeck系数变化较小,电导率显著增大,热导率先减小后随F掺量的增加而增大。x=0.01时,样品具有最高电导率和最低热导率,分别为14×103S/m和2.16W/(m·K)。在900K,样品最大热电优值(ZT值)为0.16,较纯样品的提高了近100%。     

Ca3Co4O9陶瓷的制备和热电性能

氧化物半导体陶瓷材料是新型的中、高温热电材料。采用传统固相合成法和溶胶－凝胶法成功地制备了Ca3Co4O9陶瓷。对它们的显微结构和热电性能（Seebeck系数、电导率和热导率）进行了研究。实验结果表明，由两种方法制备得到的Ca3Co4O9陶瓷具有类似的热电性能。Ca3Co4O9陶瓷为取向无规则片状结构，属于p型半导体热电材料，其热电品质因子随温度升高而增大。Ca3Co4O9陶瓷具有大的Seebeck系数和低的热导率，但它的电导率仍然偏低，导致了它的热电品质因子比传统热电合金的热电品质因子低。     

c轴择优Ca_3Co_4O_9多晶的热电性质及激光感生横向电压效应

采用传统固相反应法制备c轴择优的错层结构Ca3Co4O9多晶材料,用热重-差示扫描量热分析、X射线衍射、扫描电子显微镜和电阻率–温度曲线、热电势–温度曲线对样品进行了表征,探究了材料热电输运性质和激光感生横向电压(laser induced transverse voltage,LITV)效应。结果表明:在800和870℃分别保温24 h条件下可获得纯相层片状Ca3Co4O9多晶,其(00l)取向因子达0.74。Ca3Co4O9多晶材料在80~300 K、336~826 K分别为金属和半导体电输运行为。336 K时Seebeck系数约130μV/K。由于声子曳引热电势的贡献,随温度升高,热电势增大。以波长为248 nm、脉宽为28 ns、能量密度为17 m J/cm2的脉冲激光照射多晶构造斜面,获得了42 m V的LITV响应,比倾斜外延Ca3Co4O9薄膜中的LITV信号小约2个数量级。由于存在偏离(00l)取向的晶粒和大量晶界,导致本征热电各向异性相互抵消,大大减小了LITV响应。     

Gd~(3+)掺杂La_(1-x)Gd_xMgAl_(11)O_(19)(x=0～1)陶瓷的制备及热学性能

以Al(OH)3,La2O3,Gd2O3和4MgCO3·Mg(OH)2·5H2O为原料,采用固相反应法在1500℃保温4h合成了镁基六铝酸镧钆(La1-xGdxMgAl11O19,x=0～1,LGMA)粉体。结果表明:合成的LGMA粉体具有畸变的磁铅石型晶体结构,形成一种镧钆共掺镁基六铝酸盐固溶体,LGMA晶粒发育良好,呈板片状,晶粒平均厚度约为350nm。采用无压烧结法在1700℃保温6h后LGMA陶瓷仍能保持其稳定的磁铅石结构。在LaMgAl11O19晶格中掺入钆离子能显著降低LGMA陶瓷的高温热导率,在800℃,GdMgAl11O19陶瓷的最低热导率为1.78W/(m·K),200～1200℃范围的平均线性热膨胀系数为9.39×10-6/K。GMA陶瓷具有较低热导率的主要原因是:在LaMgAl11O19晶格中原子质量较重的Gd3+取代La3+能够增强声子散射作用,Gd3+掺入后引起的晶格畸变对声子散射也具有重要作用。     

MgAl2O4掺杂对ZTA-MgAl2O4复相陶瓷力学及热学性能的影响

以Al_2O_3、Zr O_2、MgO为初始粉末,采用放电等离子体烧结(SPS)制备ZTA-MgAl_2O_4复相陶瓷,研究MgAl_2O_4掺杂对ZTA-MgAl_2O_4复相陶瓷微观结构,力学及热学性能的影响。结果表明:ZTA-MgAl_2O_4复相陶瓷物相包括α-Al_2O_3、t-Zr O_2和MgAl_2O_4,烧结过程中MgO与Al_2O_3完全反应生成MgAl_2O_4;随MgAl_2O_4添加量增加,复相陶瓷Vickers硬度由21 GPa逐渐降低至17.5 GPa;而断裂韧性及抗弯强度呈现先增大后减小的趋势,当MgAl_2O_4添加量为15%(体积分数)时,断裂韧性和弯曲强度达到最大值,分别为8.55 MPa·m~(1/2)和1 056 MPa;此外,相同测试温度下复相陶瓷热导率随MgAl_2O_4添加量的增加逐渐减小,如温度为50℃时复相陶瓷热导率由18.5 W/(m·K)逐渐降低到14.3 W/(m·K)。     

烧结工艺对Ca3Co4O9基热电氧化物电性能的影响

采用溶胶-凝胶化学法合成了Ca3Co4O9热电氧化物粉末,分别采用陶瓷烧结工艺方法和放电等离子烧结(Spark Plasma Sintering,SPS)的方法制备了Ca3Co4O9热电氧化物块体材料.利用X射线衍射XRD、扫描电子显微镜SEM和电输运参数测试仪分析了所得样品的物相、微观组织结构、晶粒取向度和电输运性能.结果表明,不同制备方法均可得到纯相的Ca3Co4O9热电氧化物块体材料;通过陶瓷烧结工艺方法制备的Ca3Co4O9热电氧化物块体晶粒取向度较低,但随着成型压力的增加而提高;SPS烧结的方法制备的Ca3Co4O9热电氧化物块体晶粒取向度最高;试样电性能随着晶粒取向度的提高逐渐提高,其中SPS烧结方法制备的块体材料电性能最高,在测试温度最高点700℃时功率因子达3.85 μWmK-2,远高于普通烧结试样.     

低热导率磷酸锆结合氮化硅多孔陶瓷的制备

采用无压烧结工艺制备ZrP2O7结合Si3N4多孔陶瓷,研究了孔隙率对材料抗弯强度和热导率的影响.结果表明:当孔隙率为20％q3％时,热导率为0.4～1.9 W/(m·K);当孔隙率为20％时,热导率下降至1.9 W/(m·K),但力学性能并没有明显降低.当Effective Medium Theory模型的比例系数为0.3、Maxwell-Eucken2模型的比例系数为0.7时,计算所得热导率与实验结果相符.     

Dy和Er掺杂对AlN陶瓷显微结构及性能的影响

在AlN粉末中添加稀土氧化物Dy2O3和Er2O3,采用高温烧结方法制备氮化铝陶瓷,研究了稀土掺杂对陶瓷烧结性能、显微结构及导热性能的影响。结果表明:纯氮化铝陶瓷相对密度只有90.7%,导热率为45.7W/(m·K),而添加3%的Dy2O3的AlN陶瓷相对密度为99.4%%,导热率为84.1W/(m·K),添加3%的Er2O3可使氮化铝陶瓷相对密度提高到99.1%,导热率达到115.4W/(m·k);添加Er2O3可有利于消除氮化铝陶瓷的晶界相,减少氮化铝晶粒缺陷及提高声子在晶体中的传播路程,并显著提高氮化铝陶瓷的结构致密性和导热性能。     

Er,Yb:CaF2透明陶瓷的制备及其性能研究

首先以(Ca(NO3)2·4H2O、Er(NO3)3·5H2O、Yb(NO3)3·5H2O和KF·2H2O等试剂为原料,选择化学沉淀法合成了Er,Yb:CaF2纳米粉体,采用XRD和FE-SEM技术对纳米粉体特性进行了测试与表征.以合成的纳米粉体为原料,采用真空热压烧结技术,在800℃、30 MPa条件下制备了Er,Yb:CaF2透明陶瓷,并对陶瓷样品的元素组成与分布、显微结构及热导率等特性进行了测试与表征.结果表明:合成的Er,Yb:CaF2纳米粉体为单相立方萤石结构,平均尺寸在20～40 nm,并易形成尺寸为3～5μm的团聚体;Er与Yb元素在陶瓷样品中分布均匀,陶瓷的平均晶粒尺寸为1μm左右,并由于不均匀烧结,样品中存在大尺寸的孔洞结构,随着Yb掺杂浓度的增加,陶瓷样品的热导率逐渐降低.     

放电等离子烧结制备Ca3Co4O9陶瓷及其电学性能

采用化学共沉淀与放电等离子烧结相结合的方法制备了Ca3Co4O9陶瓷.通过X射线衍射,红外光谱仪,扫描电镜等表征手段,探讨了Ca3Co4O9的形成过程,研究了不同制备工艺对陶瓷的物相,显微结构和性能的影响.实验结果表明共沉淀前驱物800℃预烧6 h或8 h后,再经放电等离子850℃,压力30 MPa下烧结5 min,可以获得纯相Ca3Co4O9陶瓷;800℃预烧6 h的烧结体密度为4.53 g/cm3,800℃预烧8 h的烧结体密度为4.78 g/cm3;前驱物预烧8 h后再经放电等离子烧结的块体具有较好的电学性能.700℃时,电阻率为8.30×10-5 Ωm,Seebeck系数为182μV/K.电导率和Seebeck系数在目前Ca-Co-O材料中是较高的.     

Redox-thermal behavior of archaeological ceramics from the North Caucasus (Russia,Bronze/Iron Age)

The firing behavior of illite-based archaeological ceramics and corresponding firing conditions were investigated, in order to identify the pyrotechnology of ceramic production at archaeological sites in the North Caucasus (Russia, Bronze and Iron Age). Direct observations of the pyrometamorphic degree in the objects by scanning electron microscope (SEM), X-ray powder diffraction (XRD), Raman and Fourier-transform infrared spectroscopy (FT-IR) revealed the thermally induced localization of the redox state within a single object and its influence on the structural distortion, dehydroxylation and total collapse of illite in the ceramics. Fundamental approaches to illite dehydroxylation kinetics and numerical simulations of oxygen diffusion and heat transfer revealed that the firing temperature and time and thickness of the sample, reactivity between oxygen and ceramic pastes and porosity evolution played a decisive role in the firing behavior of the ceramics during the firing at the sites.     

Cracking mechanism in laser directed energy deposition of melt growth alumina/aluminum titanate ceramics

Thanks to its advantages of high efficiency and near-net shaping, laser directed energy deposition (LDED) is rapidly becoming a remarkable preparation technology for high-purity ceramics. However, the cracking problem in shaping process is always a great challenge for LDED to achieve industrial application. For this purpose, alumina/aluminum titanate melt-growth ceramics (A/AT MGCs) were prepared using LDED system, and the corresponding finite element thermal analysis model was developed. The solidification behavior and cracking mechanism of A/AT MGCs were investigated based on the thermal analysis model, and the influence of process parameters on the cracking characteristics was revealed with experiments. Results show that the crack morphology and distribution are controlled by microstructure and temperature gradient together. The scanning speed of 100–150 mm/min, with better microstructure and lower temperature gradient, is a preferred process window. This study provides theoretical guidance and technical support for the cracking suppression during LDED shaping of ceramics.     

Microstructural analyses and improved ionic conductivity of La0.62Li0.16TiO3 ceramics prepared by a reactive-templated grain growth (RTGG) process

Impedance measurements were conducted for textured lithium lanthanum titanate (LLTO) ceramics prepared by the reactive-templated grain growth (RTGG) process. Four La_0.62Li_0.16TiO₃ cuboid ceramics with different degree of <110> crystal orientation were used for the measurement at temperatures from 298 to 423 K. The ionic conductivity of the specimen processed with 20% of the reactive template was one order of magnitude higher than that without a template. The high conductivity was attributed to the decrease of grain boundaries caused by the templated grain growth. No obvious anisotropic conductivity was detected for the specimens by the influence of grain and domain boundaries. Domain structures in the LLTO grains were observed by scanning electron microscopy (SEM) for all specimens.     

TiO_2及Cr_2O_3对镍渣微晶玻璃结晶过程影响及结晶动力学(英文)

介绍了利用镍弃渣制备微晶玻璃的工艺过程.通过热分析确定了基础玻璃的热处理工艺.用X射线衍射和扫描电镜研究了成核剂TiO2,Cr2O3对基础玻璃结晶的影响.用修正的Jonhson-Mehl-Avrami公式分别计算了各基础玻璃样品的结晶活化能Ea和动力学参数k(Tp),并利用Augis-Bennett公式计算了各样品的晶化指数n.对于同时加入5%TiO2(质量分数,下同)和2%Cr2O3的基础玻璃,其结晶活化能为349.63 kJ/mol,k(Tp)为0.322,晶化指数为3.8.所得样品的结晶相为普通辉石--Ca(Mg,Al,Ti,Cr)(Al,Si)2O6,其断裂强度为130.65MPa,Vickexa硬度为8.31GPa.     

以冰为模板制备氧化铝多孔陶瓷及其结构特征

以水玻璃溶液为粘结剂,以冰为造孔模板制备氧化铝多孔陶瓷。采用扫描电镜观测多孔陶瓷的显微结构。结果表明,冰是一种理想的造孔模板,浆体特性对多孔陶瓷结构影响较大,当浆体中相对固相含量增大,多孔陶瓷的孔隙会减小;当浆体粘度降低,易得到片层状与微孔复合结构的多孔陶瓷。     

Electrical properties of reduced 3YTZP ceramics consolidated by spark plasma sintering

3 mol% Yttria doped zirconia ceramics were consolidated by spark plasma sintering (SPS) at two sintering temperatures with the aim of achieving two different reduction levels. Microstructural characterization of the ceramics was performed by scanning electron microscopy (SEM). Electrical properties were investigated by means of impedance spectroscopy from room temperature up to 500 °C. The two ceramics presented a remarkably different electrical behavior. The effect of the extra electrons introduced by reduction during SPS on both the bulk and the grain boundary conductivity was analyzed and discussed.     

Porous Silicon Carbide Ceramics Produced by a Carbon Foam Derived from Mixtures of Mesophase Pitch and Si Particles

Carbon foam templates were prepared from a mixture of mesophase pitch (MP) and Si particles, followed by foaming and carbonization. Subsequent molten Si infiltrated into the carbon foam at 1500°C for 4 h in an inert atmosphere resulted in the formation of porous SiC ceramics. Micrographs were investigated by a scanning electron microscope (SEM), and phase identification of porous SiC ceramics was performed by X-ray diffraction (XRD). The flexural strength and bulk density of porous SiC ceramics were also measured and calculated. The results revealed that the flexural strength of porous SiC ceramics increases with increasing Si content and decreasing porosity. The addition of Si in MP results in an increased densification of porous SiC struts. With 50 wt% Si, porous SiC ceramics with a high flexural strength of 23.9 MPa and a porosity of 55% were obtained.     

基于冻结浆料的分层实体制造法加工陶瓷坯体

提出了一种新型陶瓷增材制造方法,浆料由陶瓷粉末、有机粘结剂和去离子水构成,单层生坯的加工过程包括:铺料、冷冻和激光扫描,层层累积成型后,将冻结状态坯体置于冷冻干燥机中干燥,得到陶瓷生坯;分析了激光加工参数和浆料固含量对于激光扫描过程的影响.结果表明:采用激光扫描图形轮廓的方式,避免了激光辐照对材料内部结构的破坏;通过与冷冻干燥技术的结合,充分保留了片层状的孔隙结构;随着激光能量密度的增大,激光扫描线的宽度和激光切割的深度增大;随着浆料固含量的增加,受陶瓷颗粒对激光能量产生散射作用的影响,激光的切割深度减小.     

Influence of nucleation agents on crystallization and machinability of mica glass–ceramics

Effects of ZrO₂, La₂O₃, CeO₂, Yb₂O₃ and V₂O₅ on the crystallization kinetics, microstructure and mechanical properties of mica glass–ceramics were investigated by the differential scanning calorimetry (DSC), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness tester. Results show that bulk crystallization can be obtained by introducing proper nucleation agents into the glass. Both Ozawa method and Kissinger method are suitable for analyzing the crystallization kinetics of mica glass–ceramic. The addition of nucleation agents has little influence on the value of n, keeping two-dimensional crystal growth mechanism. ZrO₂ and V₂O₅ are best nucleation agents in mica system. The increase of crystallization temperature is helpful for the increase of aspect ratio, and the microstructure of the glass–ceramics becomes interconnected, which contributes the improvement of the machinability of the glass–ceramics. Microhardness (H_v), cutting energy (μ¹) and machinability parameter (m) can be used for estimating the machinability of mica glass–ceramics.