Sintering behaviour of slip-cast Al2O3 – Y-TZP composites

The sintering behaviour of alumina–Y-TZP composites prepared by slip-casting technique were studied. Slip-cast samples containing varying amounts of Y-TZP ranging up to 90 vol% were prepared and evaluated. Sintering studies were carried out at 1450°C to 1600°C. Sintered samples were characterised where appropriate to determine phases present, grain sizes, bulk density and mechanical properties. Good correlation was obtained between the calculated prepared powder density and experimental results. The sintered bulk density of the composites was observed to increase with increasing Y-TZP content and sintering temperature up to 1550°C. Maximum hardness values (>14 GPa) were obtained for all samples containing <60 vol% Y-TZP and when sintered at 1550°C. It has been found that the additions of up to 50 vol% Y-TZP was effective in suppressing Al₂O₃ grain growth.     

云母微晶玻璃/Y-TZP复相材料的制备和力学性能

本文用烧结法制备了云母微晶玻璃／－TZP复相材料,用X光衍射分析（XRD）法测定了材料断裂过程中氧化锆的相变体积分数,用拉曼微探针谱测定了相变区宽度,并对增韧机制进行了研究．结果表明：氧化锆的加入可以显著提高材料的力学性能．当加入40vol％ZrO₂时,云母微晶玻璃的强度和断裂韧性分别可达446MPa和4．8MPam^1／2氧化锆的相变分数随氧化锆含量的增加而减小,而相变区宽度随氧化锆含量的增加而增大;氧化锆主要通过应力诱导相交增韧机制来提高云母微晶玻璃的断裂韧性,但随着氧化锆含量的增加,裂纹在氧化锆颗粒附近的偏转会进一步提高材料的断裂韧性．     

高固含量Y-TZP悬浮液的流变学特性

采用聚丙烯酸盐（ Ｎａ Ｐ Ａ Ａ、 Ｎ Ｈ_４ Ｐ Ａ Ａ） 作为分散剂, 制备了高固相含量（ ～５０ｖｏｌ％ ） 的 Ｙ Ｔ Ｚ Ｐ悬浮液研究了分散剂、粉体粒径和固含量对 Ｙ Ｔ Ｚ Ｐ 悬浮液流变学性能的影响结果表明： 分散剂的含量为１.８ｗｔ％ 时对悬浮液有最好的分散效果悬浮液的粘度随粒径的增加而降低, 高固含量浆料的流动曲线符合 Ｂｉｎｇｈａｍ 模型同时对分散剂的吸附分散机理进行了分析和讨论     

Properties of lead zirconate-alumina ‘nanocomposites’

Microstructures, Vickers hardness and dielectric properties of PbZrO₃ ceramics with co-additions of 0.5-5 vol% Al₂O₃ nanoparticles have been investigated. The additive inhibited grain growth, with average grain size decreasing from ∼13 μm for PbZrO₃ to ∼1 μm for the nanocomposites. The mode of fracture also changed, from predominantly inter-granular in PbZrO₃ to a mixed-mode of intra- and inter-granular fracture in the composite samples. Vickers hardness values increased from 2.9 GPa for PbZrO₃ to 4.1 GPa for the sample with 1 vol% Al₂O₃, but there was a more gradual increase for higher Al₂O₃ contents. Plots of relative permittivity versus temperature indicated subtle differences which were attributed to a chemical reaction between the additive and matrix during sintering. X-ray powder diffraction showed that lead aluminium oxides were the principal products of this reaction.     

TiN-Al2O3纳米复合材料的力学性能和导电性能

以纳米TiN和α-Al₂O₃粉体为原料,采用球磨混合法制备了纳米TiN-Al₂O₃复合粉体,通过热压烧结得到致密烧结体.研究了纳米TiN颗粒对Al₂O₃材料力学性能和导电性能的影响,实验结果表明:在Al₂O₃基体中加入15vol％TiN纳米颗粒时,Al₂O₃材料的弯曲强度和断裂韧性分别从370MPa和3.4MPa·m^1/2提高到690MPa和5.1MPa·m^1/2,随着TiN添加量的增加,复合材料的电阻率逐渐降低,在25vol％TiN时达到最低值(6.5×10^-3Ω·cm).     

Y_2W_3O_(12)/Ni复合材料的制备及热膨胀性能

为研究Ni基Y2W3O12复合材料的热学性能,首先,采用二次焙烧法制备了负膨胀材料Y2W3O12;然后,将Y2W3O12与金属Ni进行混合,并在1 200℃、50 MPa的条件下热压烧结制得40vol%Y2W3O12/Ni复合材料;最后,对复合材料的成分及热膨胀性能进行了研究。结果表明:在热压烧结过程中,由于Ni的还原性比W差,相对于对比试样40vol%Y2W3O12/Cr复合材料中发生的复杂化学反应,40vol%Y2W3O12/Ni复合材料的两相之间并未发生反应,使40vol%Y2W3O12/Ni复合材料保持了较低的热膨胀系数;经数次循环退火释放热应力及去除Y2W3O12相的结晶水后,40vol%Y2W3O12/Ni复合材料在170~800℃温度范围内的热膨胀系数趋于稳定,约为3.4×10-6 K-1,与理论设计值4.0×10-6 K-1相近。     

Dispersion stability of Y-TZP/Ce-TZP powder system and slip casting

The zeta potential and apparent viscosity measurements of 3Y-TZP, 12Ce-TZP and 3Y-TZP/12Ce-TZP suspensions, has allowed the slip casting conditions for the preparation of multilayer composites have been examined. The influence of heat treatment on the sintered density, microstructure and crystalline phase of multilayer composites was also studied. The isoelectric point of both 3Y-TZP and 12Ce-TZP suspensions was near pH 8 and that of 3Y-TZP/12Ce-TZP was at pH 8.6. The suspensions exhibited pseudoplastic flow, showing a decrease in viscosity with increasing shear stress. A small (0.3 wt%) addition of an organic deflocculant gave 3Y-TZP and 3Y-TZP/12Ce-TZP suspensions with 15 and 20 vol% solid contents an appropriate fluidity for slip casting, but an additional electrolyte was required to reduce viscosity in 12Ce-TZP. Dense (>98% of theoretical) multilayer composites with grain size of 0.3–2.2 m were obtained after sintering at 1500°C.     

Sintered Hydroxyapatite/Polyetheretherketone Nanocomposites: Mechanical Behavior and Biocompatibility

Hydroxyapatite nanorods (nHA) are employed to fill polyetheretherketone (PEEK) composites. The PEEK/nHA nanocomposites containing 15.1–38.2 vol% nHA are fabricated by powder processing and sintering. Their mechanical, thermal and in vitro cell properties are investigated. The tensile strength and fracture strain of PEEK‐ nanocomposites filled with 21.6 and 29.2 vol% nHA match closely with those of human cortical bones. Sintered 15.1 and 29.2 vol% nHA/PEEK nanocomposites exhibit excellent biocompatibility. The 29.2 vol.% nHA/PEEK nanocomposite promotes adhesion and proliferation of mouse and human osteoblasts effectively.     

微波多元醇法制备单分散Ni1-xZnxFe2O4/MWCNTs与磁性能

以多壁碳纳米管(MWCNTs)为模板,三乙二醇(TREG)为溶剂,采用微波多元醇法制备MWC-NTs负载组成可控的Ni1-xZnxFe2O4(x=0.4、0.5、0.6)纳米复合材料Ni1-xZnxFe2O4/MWCNTs。其结构和形貌通过XRD、SEM、TEM和EDX进行表征,用VSM测试样品的磁性,并探讨了微波功率、微波时间对镍锌铁氧体负载的影响。结果表明立方系尖晶石结构的单分散Ni1-xZnxFe2O4磁性纳米粒子均匀负载在碳纳米管表面,平均粒径约为6nm;其磁性能与镍锌铁氧体的组成有关,随着Zn含量的增加,饱和磁化强度(Ms)先增大后减小,当x=0.5时Ms达到最大值。矫顽力(Hc)都比较小,在室温下表现为超顺磁性。     

聚电解质分散剂对Y-TZP悬浮液性能的影响

通过聚电解质聚丙烯酸铵（NH₄PAA）和聚甲基丙烯酸铵（NH₄PMAA）的合成与在Y－TZP粉体上的等温吸附实验及红外分析发现,悬浮微粒的表面状态由于聚电解质的吸附而得到改善;ζ电位测定表明,阴离子型分散剂使粉体的等电点（IEP）降低,浆料的流变性能也因为分散剂的加入而有了明显的改善．     

Fabrication and characterization of titanium-matrix composite with 20 vol% hydroxyapatite for use as heavy load-bearing hard tissue replacement

Titanium-matrix composite with 20 vol% HA ceramic was fabricated by hot pressing technique and the microstructure of the composite was studied by transmission electron microscope (TEM). The mechanical and biological properties of the composite were investigated by mechanical and in vivo studies. The experimental results by TEM observation show the bonding state of Ti/HA interface in Ti-20 vol% HA composite with the relative density of 97.86% is good, however, there exists an interfacial transition zone between Ti and HA. In Ti matrix of the composite and pure Ti metal, an interesting substructure comprised of screw dislocations with Burgers vectors b of 1/3 〈 11ˉ20〉 was found. Screw dislocations are straight and regularly distributed, and cross slip can be observed. The subgrain boundaries consist of dislocation network walls with equidistant dislocation lines in the same direction. Elastic modulus and Vicker's hardness of Ti-20 vol%HA composite are 102.6 GPa and 3.41 GPa respectively. Owing to the existence of 20 vol% HA ceramic, bending strength and fracture toughness of the composite decrease sharply to 170.1 MPa and 3.57 MPa ⋅ m^1/2 respectively, which are only about 17.5 and 12% of those of pure Ti metal. In vivo studies indicate Ti-20 vol% HA composite has good biocompatibility, and even better osteointegration ability than pure titanium, especially in the early stage after the implantation. In conclusion, Ti-20 vol% HA composite is suitable for heavy load-bearing hard tissue replacement from the point of view of both mechanical properties and biocompatibility.     

Sintering behavior of Ni/Y2O3-ZrO2cermet electrodes of solid oxide fuel cells

The sintering behavior of Ni/Y₂O₃-ZrO₂(YSZ) cermet electrode coating on 3 mol% Y₂O₃-ZrO₂electrolyte was studied under moist and dry hydrogen atmosphere at 1000°C for up to 2000 h. The sintering behavior of Ni/YSZ cermet electrodes was dominated by the agglomeration and grain growth of Ni particles in the cermets, which was critically related to the content of Ni and YSZ phases in the cermet. For pure Ni electrode coating, the sintering was substantial and cross plane cracks and isolated Ni island were formed after sintering at 1000°C for only 250 h. However with the addition of YSZ phase, the sintering of Ni/YSZ cermet anode coatings was significantly reduced. For the cermet composition of Ni (50 vol%)/YSZ (50 vol%), the change in the surface porosity and pore size distribution after sintering at 1000°C for 2000 h was very small. The microstructural stability of the Ni (50 vol%)/YSZ (50 vol%) cermet electrodes was also demonstrated by the performance stability tested under current load of 250 mAcm^–2at 1000°C for over 2500 h.     

Thermal Properties of Maleated Polyethylene/Layered Silicate Nanocomposites

Nanocomposites are a new class of composites in which the reinforcing phase dimensions are on the order of nanometer scale. In particular, the layered silicates are considered to be good candidates for the preparation of polymer-inorganic nanocomposites. The mechanical and thermal properties of polymer can be altered by adding a few vol% of the nano-particles. The effect of the nano-sized particles on thermophysical properties such as melting and crystallization, coefficient of thermal expansion, and thermal conductivity was studied. After preparing the PEMA/layered silicate nanocomposites, the thermophysical properties were investigated by the differential scanning calorimetry and 3 methods. The content of layered silicate was varied from 0.5 to 5 vol%.     

Combustion synthesis and mechanical properties of molybdenum disilicide composites reinforced with SiC particulate

Intermetallic composites of molybdenum disilicide reinforced with silicon carbide were produced by combustion synthesis of the elemental powders. The combustion reaction was initiated near 700°C and completed within a few seconds. The end product was a porous composite which was subsequently hot pressed to >97% theoretical density. The grains of the matrix were 8–14 m in size surrounded by SiC particulate reinforcement of 1–5 m. The mechanical properties of the composites improved with increasing SiC reinforcement. The hardness of the materials increased from 10.1 GPa to 12.7 GPa with the addition of 20 vol% SiC reinforcement, while the strength increased from 195 MPa to 299 MPa. The fracture toughness also increased from 2.79 MPa m1/2 to 4.08 MPa m1/2 with 20 vol% SiC. © 1998 Chapman & Hall     

Mechanical properties of Al2O3 particle-Y-TZP matrix composite and its toughening mechanism

Dense Al₂O₃ particle-Y-TZP matrix (Al₂O₃<40 vol%) composite was prepared by pressureless sintering at 1550°C. Composites with 10–30 vol% Al₂O₃ particles showed enhanced fracture toughness, bending strength and Vicker's hardness as compared to single-phase Y-TZP. The highest strength (1150 MPa) and highest toughness (12.4 MPa m^1/2) were obtained for the composite containing 10 vol% Al₂O₃. It was found that, in addition to the contribution by the crack-deflection effect, the enhanced phase transformation from tetragonal to monoclinic during fracture was the main toughening mechanism in operation in the composites.     

Microstructure and mechanical properties of yttria-stabilized tetragonal zirconia polycrystals containing dispersed TiC particles

The microstructure and mechanical properties of hot-pressed yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) ceramics containing up to 30 vol % TiC particles were studied. Adding TiC particles to Y-TZP improved the bending strength and fracture toughness. With 20 vol% TiC particles the maximum bending strength and fracture toughness reached 1073±30.4 MPa and 14.56±0.25 MPa m^1/2, respectively. The residual tensile stress induced by the thermal expansion difference between ZrO₂ and TiC must have inhibited the tetragonal-monoclinic transformation. The stress-induced phase transformation was therefore not the dominant toughening mechanism. High-densities of dislocations within TiC particles and microcracking were detected by TEM. The improved toughness of the materials is considered to be the result of crack deflection, crack bowing of TiC particles and microcracking toughening of ZrO₂.     

Fe高温浸渗法制备防静电3Y-TZP陶瓷及其性能研究

以3Y-TZP陶瓷为基体, 采用还原Fe粉包埋、高温浸渗的表面改性方法, 制备防静电性能与力学性能兼备的ZrO₂陶瓷。研究了浸渗时间、浸渗温度对ZrO₂陶瓷表面电阻率及硬度的影响, 结果表明：随着浸渗时间延长, 浸渗温度升高, 表面电阻率降低, 硬度下降。在1000℃浸渗4 h, ZrO₂防静电陶瓷表面电阻率由10¹⁴ ?/□以上降低至8.3×10⁷ ?/□, 硬度由12.7 GPa降低至11.23 GPa。采用XRD、SEM、XPS等方法对防静电ZrO₂陶瓷的显微结构、化学组成及防静电机理进行了分析。结果表明, 浸渗过程中, 发生由t-ZrO₂转变为m-ZrO₂相变; Fe元素以Fe₃O₄、FeO、单质Fe的形式存在晶界处, 从而使ZrO₂陶瓷具备了防静电性能。     

Tough yttria-stabilized zirconia ceramic by low-temperature spark plasma sintering of long-term stored nanopowders

Weakly agglomerated 1.75 and 3 mol% yttria stabilized zirconia nanopowders were used in this study after six years of storage in vacuum-processed plastic containers. The proper storage conditions of the Y-TZP nanopowders avoided the hard agglomeration. Untreated and bead-milled nanopowders were used to obtain dense ceramics by slip casting and subsequent low-temperature sintering. Fully dense nanostructured 1.75Y-TZP and 3Y-YZP ceramics with and without doping of 1 wt% Al2O3 were produced by an optimized spark plasma sintering (SPS) technique at the temperatures of 1050-1150 degrees C at a pressure of 100 MPa. The SPS has revealed the clear advantage of consolidation of the weakly agglomerated nanopowders without preliminary deagglomeration. The Vickers hardness of both the low-temperature and spark plasma sintered samples was found to lie in the range of 10.98-13.71 GPa. A maximum fracture toughness of 15.7 MPa m(1/2) (average 14.23 MPa m(1/2)) was achieved by SPS of the 1.75Y-TZP ceramic doped with 1 wt% Al2O3 whereas the toughness of the 3Y-TZP ceramics with and without alumina doping was found to vary between 3.55 and 5.5 MPa m(1/2).     

ZnO·2.56Al2O3透明陶瓷凝胶注模成型与烧结制备

锌铝尖晶石透明陶瓷是典型的结构功能一体化材料, 具有优异的光学、热学以及介电性能。本研究以ZnAl₂O₄和Al₂O₃为原料, 通过凝胶注模成型制备ZnAl₂O₄-Al₂O₃复相陶瓷初坯。实验探究了分散剂含量、pH以及固相量对ZnAl₂O₄-Al₂O₃混合料浆流变学特性的影响, 制得固相量为50vol%的低黏度稳定料浆。浇注成型后的坯体通过无压烧结和热等静压反应烧结制备透明陶瓷。最终获得的ZnO·2.56Al₂O₃透明陶瓷样品在厚度为1.8 mm下可见光波段透过率达到70%, 红外波段透过率达到80%以上, 维氏硬度为(11.34±0.17) GPa, 杨氏模量为285 GPa。     

复合掺杂8YSZ陶瓷性能的研究

以3Y-TZP/Bi_2O_3为复合添加剂制备8YSZ陶瓷材料,研究了复合掺杂对材料致密化、相组成、显微结构、力学性能及电学性能的影响.结果表明,3Y-TZP/Bi_2O_3复合添加剂的引入有利于材料的致密化,样品的烧结机理由固相烧结转变为液相烧结.引入3Y-TZP/Bi_2O_3后样品中出现了单斜相,且单斜相含量随四方相含量的增加而增加.材料的致密化使其具有良好的力学性能,同时对其电学性能也有一定的影响.