Fabrication of ultrahigh density ZnO-Al_2O_3 ceramic composites by slip casting

The conditions of ZnO-Al2O3 aqueous suspensions and slip casting were optimized to obtain dense green compacts and further to obtain high density ZnO-Al2O3 ceramic composites.The Zeta potential of raw powders was measured.ZnO and Al2O3 powders have lower Zeta potential than-45 mV commonly at pH 8-10.3 with polyacrylic acid(PAA)added.The influence of pH and the mass fraction of the additives on the stability and fluidity of the suspensions added with PAA and polyethylene glycol(PEG) was investigated by experiments of viscosity and sedimentation.The suspensions have the lowest viscosity and the best stability at pH 9 with 0.2%PAA(mass fraction).The maximum density of green compacts is 66.6%of theoretical density(TD)with compacting and homogeneous green particles.An ultrahigh density sintered compact(>99.6%TD)could be obtained after pressureless sintering at 1 400℃for 2 h.

Preparation of YSZ solid electrolyte by slip casting and its properties

Fully stabilized YSZ solid electrolyte was prepared by slip casting. The density was measured according to the Archimedes principle and the linear shrinkage was calculated from measuring the sizes of samples before and after sintering. XRD analysis was conducted to verify the phase structure of both the starting YSZ powder and the prepared YSZ electrolyte. The microstructure of fracture surface and the electrical properties of the samples sintered at different temperatures were investigated via SEM and a complex impedance method, respectively. By comparison of the properties and features among the samples, a slip casting method was established to be a simple way to manufacture high-quality YSZ electrolyte at the sintering temperature of 1550℃ for 3 h, which provides a new approach for YSZ electrolyte with complex shapes and mass production.

Electrical Properties and Applications of (ZrO_2)_(0.92)(Y_2O_3)_(0.08) Electrolyte Thin Wall Tubes Prepared by Improved Slip Casting Method

mole fraction) yttria-stabilized zirconia electrolyte thin wall tubes were p repared by i mproved slip casting method. The length and wall thickness of the tubes are 266 mm and 0.4～0.9 mm, respectively and the relative density is 96.7%. The microstr ucture and electrical properties of samples sintered at different temperatures w ere studied using SEM and ac impedance spectroscopy. The effect of sintered dens ity, grain and grain boundary on the electrical properties of the samples was analyzed. The research results show that the density of the samples increase s gradually with increasing sintering temperatures. The microstructure of sample s strongly influences its electrical properties, and the electrical properti es of samples enhance with the increase of sintered density. The ionic conductiv ity of grain and grain boundary is increased as the sintering temperature incre ases. Better sinterability of the samples was obtained at the sintering temperat ure of 1650 ℃. The maximum open circuit voltage and short circuit current for s ingle cell is 0.946 V and 1.84 A, respectively. The maximum output power of sing le cell is 0.46 W at the temperature of 850 ℃.

Preparation and properties of gradient Al_2O_3-ZrO_2 ceramic foam by centrifugal slip casting method

The aim of the present research is to provide a novel technique for preparing gradient Al 2 O 3-ZrO 2 ceramic foams.This technique used epispastic polystyrene spheres to array templates and centrifugal slip casting to obtain cell struts with gradient distribution of Al 2 O 3 and ZrO 2 particles and high packing density.Aqueous Al 2 O 3-20vol.% ZrO 2 slurries with 20vol.% solid contents were prepared and the dispersion and rheological characteristics of the slurries were investigated.The settling velocity and mass segregation of Al 2 O 3 and ZrO 2 particles at different centrifugal accelerations were calculated and studied.The drying behavior,macrostructure,microstructure,compressive property and resistance to thermal shock of the sintered products were also investigated.The results show that the difference of settling velocity of Al 2 O 3 and ZrO 2 particles increases and mass segregation becomes acute with an increase in centrifugal acceleration.The cell struts prepared at a centrifugal acceleration of 1,690 g have high sintered density(99.0% TD) and continuous gradient distribution of Al 2 O 3 and ZrO 2 particles.When sintered at 1,550 o C for 2 h,the cell size of gradient Al 2 O 3-ZrO 2 foam is approximately uniform,about 1.1 mm.With the porosity of gradient Al 2 O 3-ZrO 2 ceramic foams increasing from 75.3% to 83.0%,the compressive strength decreases from 4.4 to 2.4 MPa,and the ceramic foams can resist 8-11 repeated thermal shock from 1,100 o C to room temperature.

Centrifugal slip casting for preparing open-cell Al_2O_3 foam

Centrifugal slip casting in prefabricated template was used to prepare open-cell Al2O3 foams. Aqueous α- Al2O3 slurries with up to 50% solid contents (volume fraction) were prepared. The sedimentation of slurries during centrifugation was discussed with respect to the hydronamic conditions at large particle concentrations. The effect of solid contents on mass segregation was observed. Segregation phenomena were hindered for slurries with high solid loadings exceeding 50% (volume fraction). The dried and sintered behaviors of samples were analyzed. The cell struts in green bodies had good particles packing and showed high green density (63.4% theory density). After sintered at 1500 ℃, the cell struts of final products had high sintered density (98.8% theory density) and homogeneous microstructure. The porosity of final products is 75.6%

Functionally graded Al_2O_3-ZrO_2 composite prepared by centrifugal slip casting and its mechanical properties

Compositionally graded composite of alumina-20%zirconia (volume fraction) was fabricated by using centrifugal casting incorporated with relatively thin slip. An EPMA analysis exhibited a nearly linear variation of the alumina/zirconia ratio along the centrifugal direction; zirconia tended to accumulate in the bottom section, while alumina in the top section. Such a graded structure exhibited a considerably higher flexural strength when the alumina rich surface was subjected to a tensile stress than compositionally uniform composite of the same average composition. Fracture toughness measurement across the specimen thickness by indentation method revealed that the crack lengths along the vertical and horizontal directions were different. The anisotropy of the fracture toughness was accounted for by the variation of the residual stress across the specimen thickness.

Cone-shaped cylindrical Ce_(0.9)Gd_(0.1)O_(1.95) electrolyte prepared by slip casting and its application to solid oxide fuel cells

A cone-shaped gadolinium doped ceria（Ce0.9Gd0.1O1.95,GDC） electrolyte cylinder with a thin wall was fabricated using slip cast-ing technique.The diameter of the larger open end of the cone-shaped cylinder was 0.85 cm,the length was 1.0 cm,and the thickness of the wall was 0.026 cm after sintering.Both the electrolyte and electrode powders were fabricated by using a glycine-nitrate process.A single solid oxide fuel cell（SOFC） was prepared with the cone-shaped electrolyte,NiO-GDC（70：30 wt.%） anode and Sm0.5Sr0.5CoO3（SSC） cathode.Its electrochemical performance（I-V curve） and electrochemical impedance spectroscopy（EIS） were studied with humidified hydrogen as the fuel and air as the oxidant.The maximum output power density was about 300 ？mW/cm2 at 700 oC.The EIS results showed that the dominant loss of the SOFC was from the ohmic resistance of the electrolyte.

Preparation of transparent Y_2O_3 ceramic by slip casting and vacuum sintering

In the present work transparent Y2O3 ceramics were made by slip casting and vacuum sintering of nanopowders with sodium poly-acrylic acid（PAA-Na） as dispersant.The rheological properties of Y2O3 nanopowder slurry were investigated using different amounts of dis-persant and solid contents.The microstructures and transmittance of the sintered ceramics were also studied by means of scanning electron microscopy（SEM） and ultra-violet visible spectrometry.The results showed that rheological behaviors of the Y2O3 nanopowder slurry were effectively promoted by sodium polyacrylic acid.Highly dispersive and stable slurries were obtained as the dispersant was added over 1.0 dwb% under the fixed conditions of pH 11 and 45 wt.% solid content.All the slip cast green bodies were sintered into highly dense ceramics after sintering at 1700 oC for 5 h in vacuum,wherein the sample added with 1.1% sodium polyacrylic acid exhibited the highest relative den-sity of 99.36% and transmission of 30% at 800 nm wavelength.

Slip casting and pressureless sintering of Ti3AlC2

Slip casting and subsequent pressureless sintering(PLS)allow the preparation of complex-shaped and large-sized Ti3AlC2 components for many potential applications.The behaviors of the suspensions,green compacts,and sintered samples of Ti3AlC2 were studied in this paper.The optimized condition of 1 wt%of arabic gum as dispersant at pH=10 results in a Ti3AlC2 suspension for slip casting Ti3AlC2 green compacts without macro defects or cracks.The sintering temperature and Al4C3 embedding powder are found to dominate the properties of the sintered Ti3AlC2 samples.The Ti3AlC2 sample sintered at 1450℃for 1.5 h with Al4C3 embedding powder reaches the best properties,namely 95.3%relative density,hardness of 4.18 GPa,thermal conductivity of 29.11W·m-1·K-1,and electrical resistivity of 0.39μΩ·m.The findings in this work may pave the way for the application of MAX phases with large size and complex shape.

CeO_(2)/MoSi_(2)改性ZrB_(2)-SiC陶瓷的烧结性能及耐烧蚀性能

无压烧结ZrB_(2)-SiC陶瓷可制备复杂形状构件,但致密化难且耐烧蚀性能有待提高,因此亟需研究能够改善陶瓷致密化的有效烧结助剂。本文采用CeO_(2)和MoSi_(2)为烧结助剂,在1850℃无压烧结1 h条件下制备了ZrB_(2)-SiC陶瓷,研究了CeO_(2)和MoSi_(2)对ZrB_(2)-SiC陶瓷烧结性能和耐烧蚀性能的影响。结果表明,当5%(体积分数)的烧结助剂中CeO_(2)和MoSi_(2)体积比为1∶1时,ZrB_(2)-SiC陶瓷的烧结性能、耐烧蚀性能最佳。烧结助剂在烧结过程中形成Ce-Mo液相,陶瓷颗粒在液相的表面张力下重排和传质,Ce-Mo液相促进陶瓷颗粒在毛细力下形成烧结颈,填充于陶瓷颗粒的间隙中,并在降低陶瓷晶粒的晶界能时促进致密化进程,最终获得无压烧结密度为5.02 g/cm^(3)、相对密度为89.71%、维氏硬度为14.04 GPa的ZrB_(2)-SiC陶瓷。相对于未添加烧结助剂时,实际密度提高了53%,维氏硬度提高了43%。在烧蚀过程中,烧结助剂适量补充SiO_(2)后可促进黏度适宜的玻璃相自愈合,并提高ZrO_(2)的稳定性,使ZrB_(2)-SiC陶瓷具有最好的耐烧蚀性能,此时ZrB_(2)-SiC陶瓷质量烧蚀率为-1.62 mg/s,线烧蚀率为0.33μm/s。

氧化铝坩埚在注浆成型中的颗粒偏析调控

高性能坩埚的研究对高温合金的发展至关重要,鉴于坩埚制备过程中容易产生颗粒偏析导致坩埚微观结构不均匀、综合性能较差等问题,采用注浆成型法制备了高温合金熔炼用Al_(2)O_(3)坩埚,研究了分散剂、固相含量在注浆成型中对Al_(2)O_(3)坩埚颗粒偏析的影响,并结合颗粒偏析的理论分析进行探讨,以减少成型过程中颗粒偏析现象对坩埚造成的不良影响。当加入0.3 wt%柠檬酸铵和0.3 wt%阿拉伯树胶作为分散剂,固相含量为66 vol%时实现了注浆成型Al_(2)O_(3)坩埚中颗粒偏析的调控,制备的Al_(2)O_(3)坩埚结构均匀,可用于高温合金熔炼。

公路隧道上跨水工隧洞节点设计关键技术研究

以某分离式高速公路隧道上跨既有水工隧洞工程为例,结合类似项目设计经验,对大断面公路隧道上跨水工隧洞节点各关键环节进行设计,主要包括基底注浆设计、上跨节点防排水设计、上跨节点监测设计、施工组织设计等,对上跨水工隧洞节点设计要点及关键技术进行总结,给出上跨水工隧洞节点设计建议,为类似项目提供借鉴。

岩溶地区深厚卵石层地层中跨江桥梁桩基施工技术

以南方地区某工程桥梁桩基施工为例,对岩溶发育地层中施工遇到的桩孔漏浆、塌孔等问题进行分析。从泥浆技术参数、钢护筒根进、钻进成孔参数等方面进行重点论述,阐述了水泥浆液的黏度、比重、含沙量的控制指标,按照地质情况制定钢护筒尺寸,并优化钢护筒施工工艺。通过分析优化钢护筒跟进、深孔注浆加固工艺,有利于优化桩基施工技术,减少不必要的施工误差。

陶瓷壳体零件制作工艺的研究

陶瓷材料可以被用来制作壳体类零件。由于陶瓷坯体在干燥和烧结过程中的收缩率较大,约5%-20%,并且受到多种因素影响,导致壳体零件尺寸精度较低,限制了陶瓷壳体的应用。为了提高陶瓷壳体零件的尺寸精度,本文首先利用注浆成型的方法制作了一个圆柱形陶瓷壳体试件,测量尺寸,计算材料收缩率。然后设计了一个电器仪表外壳,根据收缩率数据将模型放大,采用3D打印的方法制作模芯,并利用此模芯制作石膏模具。最后采用相同的注浆成形工艺参数,制作出陶瓷壳体零件。实验结果表明,这种二次注浆成形工艺能够抵消陶瓷材料收缩,并避免影响因素,使壳体零件尺寸的相对误差小于1%。

注浆成型SiC多孔陶瓷的工艺和性能研究

选用SiC颗粒作为多孔陶瓷的骨料材料,长石、石英、粘土组成的低共熔混合物形成晶界玻璃相结合剂,活性炭作为成孔剂,采用注浆成型工艺,对多孔陶瓷的性能进行了研究.SiC骨料颗粒的Zeta电位等电点对应的pH值为5.2,注浆浆料的pH值在8～12的范围内具有很好的流动性和稳定性;烧成温度的提高,使SiC多孔陶瓷的气孔尺寸分布范围缩小,但基本孔径不变;晶界玻璃相的高温粘性流动在SiC晶粒之间形成“桥架”结构,提高了两者之间的粘结能力;高温下,SiC颗粒的氧化产物参与晶界反应,生成新的针状莫来石相,使SiC多孔陶瓷的强度出现异常提高.

无水乙醇注浆成型制备YAG透明陶瓷

以无水乙醇作为分散介质,采用注浆成型工艺和真空烧结技术制备了光学质量良好的YAG透明陶瓷.双面抛光、厚度为3mm的YAG透明陶瓷样品(烧结温度1800℃)在可见光范围内的直线透过率为79%左右,在近红外波段的透过率为80%左右,接近理论透过率84%.样品的平均晶粒尺寸约为30μm,晶界处和晶粒内部均无杂质和第二相存在,也几乎没有气孔的残留.采用无水乙醇做分散剂进行注浆成型是一种很有发展潜力的透明陶瓷成型方法.

改进注浆法制备(ZrO_2)_(0.92)(Y_2O_3)_(0.08)电解质薄管的电学性能及应用

用改进注浆法制备出长度为 2 2 6～ 2 6 6mm ,厚度为 0 4～ 0 9mm ,相对密度为 96 7%的 (ZrO2 ) 0 .92 (Y2 O3 ) 0 .0 8电解质薄管 ,用SEM和交流阻抗谱研究了样品的微结构和电学性能 ,分析了烧结密度、晶粒和晶界对样品电学性能的影响 ,考察了用该电解质薄管组装的固体氧化物燃料电池的性能。结果表明 :样品的致密度随烧结温度的升高而逐渐增大 ,样品的微结构对其电学性能有强烈的影响 ,样品的电学性能随烧结密度的增加而增大 ,晶粒电导率和晶界电导率也随烧结温度升高而得以改善 ,16 5 0℃烧结的样品具有较好的烧结性能。单电池的最大开路电压和短路电流分别为 0 946V和 1 84A ,85 0℃时最大输出功率为 0 46W。

管状YSZ电解质的制备及其在固体氧化物燃料电池中的应用

以 8mol %钇稳定化氧化锆 (YSZ)为原料 ,以阿拉伯树胶为分散剂和粘接剂 ,采用改进注浆法制备出长度为 2 2 6～2 60mm、壁厚为 0 .4～ 0 .9mm的致密YSZ电解质薄管。设计并制出带有一定锥度的空芯石膏模 ,研究了球磨时间对成型料浆稳定性的影响 ,烧结温度对YSZ样品致密度的影响。研究结果表明 :球磨时间在 75～ 14 0min的范围内料浆的稳定性较好 ,随烧结温度的升高 ,样品的致密度提高。用这种YSZ薄管制成固体氧化物燃料电池 ,电池的电学性能随温度的升高而明显提高 ,三节电池串联的最大功率为 2 .2W。

管状多孔陶瓷膜载体的研制

对α－Ａｌ２Ｏ３多孔陶瓷的性能与起始粉料的关系进行了研究设计了脱外模熔模芯的注浆成型新工艺，成功地制备出外观圆直、管壁光滑的无机膜载体研究了烧结制度对陶瓷基管性能的影响，用扫描电镜观察了管的微观结构及形貌特征，并测定了气孔率及其孔径分布实验制备的载体管其内径７ｍｍ，壁厚１．５ｍｍ，管长２０ｃｍ，平均孔径１μｍ，孔隙率达４３％，可直接用于工业微滤过程。

小型CPL用高性能烧结毛细芯的研制

采用粉浆浇注工艺和氢气还原烧结工艺研制小型CPL用烧结镍毛细芯,通过优选粉浆液固比、添加剂的种类与数量、浆料pH值等参数制备了符合设计要求的烧结毛细芯.测试了毛细芯孔径、孔隙分布特征、孔径分布、孔隙度、渗透率等性能参数,分析了烧结气氛、温度、时间对毛细芯性能的影响.试验结果表明,研制的毛细芯孔隙度在68%以上,孔隙尺寸约4 μm,渗透系数在10-12～10-13 m2之间.