纳米3Y-TZP粉体的制备及烧结曲线研究

采用共沉淀法制备纳米3Y-TZP粉体,并利用DSC-TG,XRD和TEM等测试方法对3Y-TZP的物理化学性能进行表征。通过研究纳米3Y-TZP粉体的烧结曲线,分析3Y-TZP素坯在烧结过程的致密化和显微结构。结果表明:在600℃下煅烧2h后,可获得晶粒尺寸为13nm,晶形发育良好、团聚较少的纳米3Y-TZP粉体。在烧结过程中,不同烧结阶段中的扩散机制不同,在烧结后期晶粒尺寸发生显著长大。     

柠檬酸法、氨水沉淀法和碳酸氢铵沉淀法制备的钇铝石榴石纳米粉体性能的比较

采用3种方法制备了纯相钇铭石榴石(yttrium aluminum garnet,YAG)纳米粉体。对不同方法制备的粉体的物理性能、素坯的微观特征、烧结性能和烧结体的透明性能进行了比较。结果表明：柠檬酸法制备的粉体,晶粒形状不规则,且有团聚体存在,该粉体的素坯显微结构不均匀,粉体烧结活性很差．1780℃保温3h烧结的样品的相对密度仅为79％,烧结体不透明。氨水沉淀法制备的粉体,晶粒尺寸较小,素坯的显微结构也不均匀．粉体烧结性能较好,达到完全致密化的温度为1700℃．此粉体经过1700℃保温3h真空烧结制备的烧结体呈半透明。碳酸氢铵沉淀法制备的粉体,晶粒形状为椭球形,分散性良好,该粉体素坯的显微结构均匀．样品达到完全致密化的温度仅为1450℃,此种粉体所制成的素坯经过1700℃保温3h真空烧结后,烧结体具有一定的透明度。因此．碳酸氢铵沉淀法制备的YAG纳米粉体有希望成为比较理想的制作透明YAG陶瓷的粉体。     

Y—TZP陶瓷晶粒生长的控制

为了获得超细晶粒的Y-TZP陶瓷,制备了无团聚体的素坯,研究了在烧结过程中的晶粒生长和气孔变化的规律。在烧结初期,晶粒与气孔同时增大;在烧结中期,气孔的表面扩散是晶粒生长的主要机理;烧结后期,随着烧结温度的提高,晶界扩散是晶粒生长的主要机理。实验结果进一步表明:在1250℃,2h的烧结条件下,可获得晶粒尺寸仅为100～150nm的Y-TZP陶瓷。     

ZrO_2-Y_2O_3超细粉烧结动力学的研究

通过对ZrO_2-Y_2O_3纳米级粉末烧结动力学过程的研究,分析了陶瓷的致密化机理。实验结果表明:超细粉末在烧结初期,晶界扩散起主要作用。在存在团聚体的粉末中,由于团聚体与基体间界面应力的相互作用,致使烧结体的密度降低,影响了陶瓷的显微结构,从而限制了在烧结后期获得细晶粒的陶瓷体。对于无团聚体的粉末,通过烧结过程中晶粒生长过程的控制,可获得相对密度达98.5%(1250℃保温2h),且晶粒尺寸仅为160nm的Y-TZP陶瓷体。     

直接干压成型与真空烧结技术制备Nd:YAG透明陶瓷

以高纯氧化物粉体为原料,采用直接干压成型与固相反应烧结技术制备Nd:YAG透明陶瓷,并对其光学透过率和烧结致密化行为进行了研究。结果表明,经1 760℃烧结10 h后,250 MPa成型压力下的样品透过率最高,在1 064 nm处达到83.8%。其素坯的气孔率为40.5%,气孔平均孔径74.5 nm。烧结后陶瓷的显微结构致密,晶界干净清晰,断裂方式为沿晶断裂。将250 MPa成型压力下获得的陶瓷素坯在不同温度和时间下烧结,得到致密化轨迹、晶粒生长曲线以及显微结构演变等信息。通过理论拟合,得出低温下陶瓷致密化和晶粒生长的控制机制为晶界扩散。     

固相烧结--Ⅲ实验:超细氧化锆素坯烧结过程中的晶粒与气孔生长及致密化行为

研究了超细Y-TZP和YSZ粉料成型体在烧结中期的晶粒生长、气孔生长和致密化行为.根据作者前文[1,2]提出的致密化方程,可以满意地解释粉体及其成型体的性质,如初始颗粒尺寸、成型密度和气孔尺寸分布等对烧结的影响. 实验发现:成型体中的晶粒生长基本不受成型体性质的影响,但气孔生长同时受晶粒生长和致密化的影响,前者使气孔尺寸与晶粒尺寸同步生长,后者导致气孔收缩. 晶粒生长和致密化虽受不同的机制驱动,但通过同样扩散途径完成,使烧结中期的晶粒尺寸与密度呈线性关系. 理论分析和实验结果表明,成型体性质不改变这一线性关系,但可以改变直线的斜率,而升温速率对直线斜率的影响不大. 较大的二面角、较高的素坯密度、较窄的颗粒和气孔尺寸分布有利于获得较小的晶粒生长和较高的烧结密度.     

锆钛酸锶的烧结及其介电性能表征

以四氯化钛、氧氯化锆、硝酸锶和氢氧化钠为原料,采用共沉淀法在25℃反应90℃陈化2h制备了锆钛酸锶(SrTixZr1-xO3)粉体,用X射线衍射(XRD)表征了锆钛酸锶粉体的物相.用透射电子显微镜表征了锆钛酸锶粉体的粒径.并采用干压成型法压制素坯进行烧结;确定了烧结制度为:升温速率3℃/min,1 400℃保温4h.对烧结后的陶瓷坯体进行介电性能表征,在1 kHz下SrTio.7 Zr0 3 O3陶瓷坯体的相对介电常数为135.6,介电损耗tanδ为24.4×10-3;SrTi0 5 Zro.5 O3陶瓷坯体的相对介电常数为122.3,介电损耗tanδ为137.38×10-3.     

高能球磨对YAG陶瓷制备的影响(英文)

通过高能球磨法处理Y2O3-Al2O3(yttrium aluminum garnet,YAG)混合粉体,对球磨产物进行煅烧、成型以及烧结,并对固相反应中的物相变化、YAG粉体形貌以及YAG陶瓷密度、力学性能及显微结构进行表征和分析,确定了最佳的球磨时间和粉体煅烧温度.研究表明:经过40h高能球磨,得到的球磨产物具有良好的活性.采用传统固相法制备的YAG粉体,需要在1 500℃煅烧,该方法处理的YAG粉体在1 200℃煅烧2 h,可以得到活性较高的YAG粉体,使粉体的煅烧温度下降了300℃.利用常压烧结在1 550℃烧结坯体2h,得到致密的YAG陶瓷,明显改善了YAG陶瓷制备技术.     

高密度纳米钛酸钡素坯的制备和对烧结的影响

10nm钛酸钡粉在7MPa的压力下预成型后再在0．5～6GPa的压力下冷等静压。素坯的相对密度从0.5GPa的49.6%增加到6GPa时的69.2%。素坯在6GPa的压力下冷等静压后在烧结温度为1000℃,保温时间为2h的条件下常压烧结得到的钛酸钡陶瓷的晶粒尺寸约为400nm,相对密度大于99％。没有经过高压的相同的素坯在1150℃,保温时间为2h后得到的钛酸钡陶瓷的晶粒大小约为1200nm。实验结果表明：超高压成型能显著增加素坯的密度;高密度的素坯能降低陶瓷的烧结温度。     

微波烧结制备碳酸化多孔羟基磷灰石纳米陶瓷

采用活性炭辅助微波烧结的方法制备多孔碳酸化磷酸钙纳米陶瓷。通过考察多孔陶瓷坯体在不同烧结温度的线收缩率和抗压强度得到合适的烧结温度。1000℃微波烧结得到多孔碳酸化磷酸钙纳米陶瓷：抗压强度约为2.5MPa,平均晶粒尺寸约为132nm,孔隙率约为75%。与常规陶瓷相比,该种陶瓷抗压强度相当、晶粒尺寸更小并且微观结构更均匀...     

Fabrication of YAG transparent ceramics by two-step sintering

Yttrium aluminum garnet (YAG) nanopowders with mean particle size of about 50 nm synthesized by a modified co-precipitation method were used to sinter bulk YAG ceramic by two-step sintering method. Full densification was achieved by heating the sample up to 1800 °C followed by holding at 1550 °C for 10 h. Transparent YAG ceramics were obtained by suppressing grain-boundary migration while promoting grain-boundary diffusion during the two-step sintering process. The microstructure of the YAG ceramic is homogeneous without abnormal grain growth and the transmittance of the sintered sample is 43%.     

Synthesis,sintering and microstructure of 3Y-TZP/CuO nano-powder composites

Nanocrystalline 3Y-TZP and copper-oxide powders were prepared by co-precipitation of metal chlorides and copper oxalate precipitation respectively. CuO (0.8 mol%) doped 3Y-TZP powder compacts were prepared from the nanocrystalline powders. Dilatometer measurements on these compacts were performed to investigate the sintering behaviour. Microstructure investigations of the sintered compacts were conducted. It is found that additions of the copper-oxide powders in the nanocrystalline 3Y-TZP leads to an enhancement of densification, formation of monoclinic zirconia phase and significant zirconia grain growth during sintering.     

Dense fine-grained biphasic calcium phosphate (BCP) bioceramics designed by two-step sintering

In this study, dense, fine-grained biphasic calcium phosphate bioceramics were designed via the two-step sintering method. The starting powder was nanosized calcium-deficient hydroxyapatite, whose phase composition, average particle size and morphology were characterized by XRD, FTIR, Raman spectroscopy, laser diffraction and FE-SEM. The phase transformations of the initial powder during heating up to 1200 °C were examined using TG/DSC. At first, conventional sintering was performed and the recorded shrinkage/densification data were used to find out the appropriate experimental conditions for two-step sintering. The obtained results show that two-step sintering yields BCP ceramics, consisting of hydroxyapatite and β-TCP, with full dense, homogeneous structure with average grain size of 375 nm. Furthermore, BCP ceramics obtained by the two-step sintering method exhibit improved mechanical properties, compared to conventionally sintered BCP.     

Densification and grain growth of Gd2Zr2O7 nanoceramics during pressureless sintering

Gd₂Zr₂O₇ nanoceramics were fabricated using pressureless sintering method, in which the nanopowders were synthesized via solvothermal approach. The effects of starting powders on grain growth and densification during sintering of ceramics were revealed. Two distinct pressureless sintering methods were investigated, including conventional and two-step sintering. The sample grain size increases abruptly as sintering temperature increases during conventional sintering. In contrast, in two-step sintering, abnormal or discontinuous grain growth was suppressed in the second step, leading to Gd₂Zr₂O₇ nanoceramics formation (average grain size 83 nm, relative density ∼93%). Such distinct behaviors may originate from the interplay between kinetic factors such as grain boundary migration and diffusion. Moreover, suppression of grain growth and promotion of densification in the two-step sintering are mainly due to dominant role of grain boundary diffusion during the second-step sintering process.     

热压烧结细晶粒氧化铝陶瓷(英文)

以沉淀法制各的商业α-Al2O3粉体为原料,自制镁铝硅玻璃为烧结助剂,采用热压烧结工艺低温制备高性能氧化铝陶瓷.用Archimedes法、电子探针和三点弯曲法研究了氧化铝陶瓷的致密化行为、显微结构和力学性能.结果表明:在1400℃烧结的氧化铝陶瓷的相对密度高达98.9%,晶粒细小,平均晶粒尺寸约为0.6μm,晶界上有莫来石相析出,样品的抗弯强度和断裂韧性分别达442MPa和4.7MPa·m1/2.     

Two-Step Sintering of Ceramics with Constant Grain-Size, II: BaTiO3 and Ni–Cu–Zn Ferrite

We investigated the preparation of bulk dense nanocrystalline BaTiO₃ and Ni–Cu–Zn ferrite ceramics using an unconventional two-step sintering strategy, which offers the advantage of not having grain growth while increasing density from about 75% to above 96%. Using nanosized powders, dense ferrite ceramics with a grain size of 200 nm and BaTiO₃ with a grain size of 35 nm were obtained by two-step sintering. Like the previous studies on Y₂O₃, the different kinetics between densification diffusion and grain boundary network mobility leaves a kinetic window that can be utilized in the second-step sintering. Evidence indicates that low symmetry, ferroelectric structures still exist in nanograin BaTiO₃ ceramics, and that saturation magnetization is the same in nanograin and coarse grain ferrite ceramics.     

Densification mechanism and microstructure characteristics of nano- and micro- crystalline alumina by high-pressure and low temperature sintering

Fully dense ceramics with retarded grain growth can be attained effectively at relatively low temperatures using a high-pressure sintering method. However, there is a paucity of in-depth research on the densification mechanism, grain growth process, grain boundary characterization, and residual stress. Using a strong, reliable die made from a carbon-fiber-reinforced carbon (C_f/C) composite for spark plasma sintering, two kinds of commercially pure α-Al₂O₃ powders, with average particle sizes of 220 nm and 3 μm, were sintered at relatively low temperatures and under high pressures of up to 200 MPa. The sintering densification temperature and the starting threshold temperature of grain growth (T_sg) were determined by the applied pressure and the surface energy relative to grain size, as they were both observed to increase with grain size and to decrease with applied pressure. Densification with limited grain coarsening occurred under an applied pressure of 200 MPa at 1050 °C for the 220 nm Al₂O₃ powder and 1400 °C for the 3 μm Al₂O₃ powder. The grain boundary energy, residual stress, and dislocation density of the ceramics sintered under high pressure and low temperature were higher than those of the samples sintered without additional pressure. Plastic deformation occurring at the contact area of the adjacent particles was proved to be the dominant mechanism for sintering under high pressure, and a mathematical model based on the plasticity mechanics and close packing of equal spheres was established. Based on the mathematical model, the predicted relative density of an Al₂O₃ compact can reach ～80 % via the plastic deformation mechanism, which fits well with experimental observations. The densification kinetics were investigated from the sintering parameters, i.e., the holding temperature, dwell time, and applied pressure. Diffusion, grain boundary sliding, and dislocation motion were assistant mechanisms in the final stage of sintering, as indicated by the stress exponent and the microstructural evolution. During the sintering of the 220 nm alumina at 1125 °C and 100 MPa, the deformation tends to increase defects and vacancies generation, both of which accelerate lattice diffusion and thus enhance grain growth.     

高纯度氧化铝粉体颗粒细化对烧结致密化及透光性能的影响

以法国Baikowski公司高纯度氧化铝粉体为参照,选取大连瑞尔精细陶瓷有限公司产超高纯度氧化铝粉体为研究对象。采用研磨处理,以改善国产氧化铝粉体的形貌、粒径及其分布。分别采用硅钼电炉中常压烧结和真空气氛下在1850℃烧结2种不同的烧结方式评价了研磨后粉体的烧结性能和用于制备半透明氧化铝陶瓷的可行性。结果表明:经过研磨改性处理后,粉体的粒径分布和比表面积接近于法国粉体;在1600℃常压烧结得到的氧化铝陶瓷达到理论密度的97%,具有均一的晶粒尺寸(～5μm)。添加MgO为烧结助剂,在真空下烧结得到了半透明氧化铝陶瓷,在波长为200～1100nm范围直线透过率最大值达到16%。     

Microstructure Refinement of Sintered Alumina by a Two-Step Sintering Technique

For a few oxide ceramics, the use of an initial precoarsening step prior to densification (referred to as two-step sintering) has been observed to produce an improvement in the microstructural homogeneity during subsequent sintering. In the present work, the effect of a precoarsening step (50 h at 800°C) on the subsequent densification and microstructural evolution of high-quality alumina (Al2O3) powder compacts during constant-heating-rate sintering (4°C/min to 1450°C) was characterized in detail. The data were compared with those for similar compacts that were sintered conventionally (without the heat treatment step) and used to explore the mechanism of microstructural improvement during two-step sintering. After the precoarsening step, the average pore size was larger, but the distribution in pore sizes was narrower, than those for similar compacts that were sintered conventionally to 800°C. In subsequent sintering, the microstructure of the precoarsened compact evolved in a more homogeneous manner and, at the same density, the amount of closed porosity was lower for the compacts that were sintered by the two-step technique, in comparison to the conventional heating schedule. Furthermore, a measurably higher final density, a smaller average grain size, and a narrower distribution in grain sizes were achieved with the two-step technique. The microstructural refinement that was produced by the two-step sintering technique is explained in terms of a reduction in the effects of differential densification and the resulting delay of the pore channel pinch-off to higher density.     

Analysis of reactions during sintering of CuO-doped 3Y-TZP nano-powder composites

3Y-TZP (yttria-doped tetragonal zirconia) and CuO nano powders were prepared by co-precipitation and copper oxalate complexation–precipitation techniques, respectively. During sintering of powder compacts (8 mol% CuO-doped 3Y-TZP) of this two-phase system several solid-state reactions clearly influence densification behaviour. These reactions were analysed by several techniques like XPS, DSC/TGA and high-temperature XRD. A strong dissolution of CuO in the 3Y-TZP matrix occurs below 600 °C, resulting in significant enrichment of CuO in a 3Y-TZP grain-boundary layer with a thickness of several nanometres. This “transient” liquid phase strongly enhances densification. Around 860 °C a solid-state reaction between CuO and yttria as segregated to the 3Y-TZP grain boundaries occurs, forming Y₂Cu₂O₅. This solid-state reaction induces the formation of the thermodynamic stable monoclinic zirconia phase. The formation of this solid phase also retards densification. Using this knowledge of microstructural development during sintering it was possible to obtain a dense nano–nano composite with a grain size of only 120 nm after sintering at 960 °C.