BaTiO3陶瓷粉体凝胶注模成型的研究

为了研究BaTiO3粉体的凝胶注模成型，以聚甲基丙稀酰胺(PMAA—NH4)为分散剂，通过球磨制备稳定分散的BaTiO3浆料．采用正交实验设计原则，讨论了有机单体、交联剂和引发剂的用量对浆料的固化时间、坯体强度和密度的影响，确定最佳加入量(质量分数)分别为4％，1．5％和0．02％．在1340℃下烧结得到的BaTiO3陶瓷的晶粒尺寸均匀，气孔较少，致密度高，具有良好的PTC特性。     

High temperature NTC BaTiO3-based ceramic resistors

In our research it was firstly found that BaTiO₃ materials doped BaBiO₃ compounds only showed NTC effect in wide temperature scale. The effect of the composition on the microstructure and electrical properties of BaTiO₃-based NTC thermistors was studied. Major phases present in the sintered bodies were the solid solutions of BaTiO₃ compounds with a perovskite structure and BaBiO₃ compounds with a monoclinal structure. The average grain size of the samples increased with increasing BaBiO₃ contents. It is apparent that the samples' ρ₄₅₀ and B_450 / 600 constant decreased with an increase in BaBiO₃ content.     

CaZrO3 additives to enhance capacitance properties in BaTiO3 ceramic capacitors

The effects on the dielectric properties of BaTiO₃ of addition of CaZrO₃ (0–17 wt%) has been investigated. Dielectric constants ranging between 2500 and 15 500 have been obtained by using commercial grade raw materials with the starting dielectric constant of the undoped BaTiO₃ being 800. The capacitor dielectrics have also been analysed for their electrical properties, crystalline phases and microstructural features.     

模板法制备遗态Al2O3陶瓷的研究

以棉花为模板制备纤维状氧化铝陶瓷,并采用X射线衍射、扫描电镜和比表面积检测法对其微观结构及特征进行了研究。结果表明,制备得到的Al2O3成功地保留了植物纤维的结构。在不同的烧结温度下,得到的Al2O3具有不同的晶型,从低温到高温,获得的晶型从非晶态Al2O3→γ-Al2O3→α-Al2O3,物质稳定性逐渐提高。对比表面积和平均孔径的测定结构表明,不同的制备工艺对氧化铝陶瓷的比表面积和孔径影响很大。     

Polymeric encapsulation of 1-2-3 ceramic superconductors

YBa₂Cu₃O_7−x pellets have been found to degrade and lose superconducting properties when exposed to the normal atmosphere for long durations. Hence, coating the superconducting pellets with a polymer to protect it from moisture and CO₂ of the ambient atmosphere is highly desirable. In this paper the criteria of selection of a polymer and some preliminary studies on polymeric encapsulation of 1-2-3 pellets are reported. Fevitite epoxy and stycast have been found to show encouraging results.     

Improved current limiters based on mixed-phase BaTiO3 ceramic semiconductors

Very stable and highly reproducible current-limiting characteristics have been observed for polycrystalline ceramics prepared from sintering mixtures of coarse-grained, donor-doped BaTiO₃ (tetragonal) as the major phase and ultrafine, undoped cubic perovskite such as BaSnO₃, BaZrO₃, SrTiO₃ or BaTiO₃ (cubic) as the minor phase. The initial linear current-voltage (I-V) relationship becomes current-limiting with increase in applied potential and the consequent onset of thermal equilibrium. The strong current maximum of theI-V curve of donor-doped BaTiO₃ can be eliminated when the ceramics are constituted of mixed phases. The voltage drop at the insulating grain boundaries minimizes the temperature gradient between the interior and the surface, and subdues the thermal runaway. The magnitude of the limiting current, and hence the power-handling capacity, can be varied with the controlled addition of grain boundary layer modifiers and by optimizing the processing parameters. The dielectric constant versus temperature or voltage variation in power dissipation with ambient temperature and resistivity-temperature relations point to the necessity of the mixed phase character for the current-limiting property.     

Deposition of gold nanoparticles on electrospun MgTiO3 ceramic nanofibers

A simple method to deposit spherical gold nanoparticles on the surface of MgTiO3 ceramic nanofibers is presented. Electrospun MgTiO3/poly(vinyl acetate) (PVAc) hybrid nanofibers were calcined at 650 degrees C to obtain phase pure ceramic MgTiO3 nanofibers with 100-150 nm diameters. These ceramic nanofibers were immersed in an aqueous solution of HAuCl4 containing poly(vinyl alcohol) (PVA) as capping agent followed by photoreduction at 365 nm to get a novel Au-MgTiO3 nanocomposite. The formation of gold nanoparticles upon irradiation was confirmed by the appearance of a surface plasmon band (SPB) at 590 nm in the UV-visible absorption spectra. The surface morphology and elemental compositions were analyzed by the scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX), and transmission electron microscope (TEM). X-ray diffraction (XRD) and selected area diffraction (SAED) pattern in TEM revealed the crystallization of gold by exhibiting strong diffractions correspond to Au(111) and Au(200) crystalline planes in addition to the MgTiO3 diffraction.     

纳米3Y-TZP陶瓷粉体形貌的分形分析

为了应用分形理论确定纳米3Y－TZP粉体制备方法的优劣，采用共沸蒸馏法和醇水溶液加热法制备了纳米3Y－TZP粉体，利用TEM观察确定了粉体粒径尺寸和团聚体形貌，并运用分形理论分析了分形维数和粉体烧结性能的关系。结果表明：纳米粉体在颗粒尺寸相同的情况下，粉体分形维数越低，团聚体半径越小，烧结性能越好；对粉体TEM图像进行分形维数计算并与粉体红外光谱分析和烧结结果进行了比较，确定醇水溶液加热法制备纳米3Y－TZP粉体效果较好。     

Er~(3+)掺杂透明微晶玻璃光谱性质的研究

通过高温熔融法和热处理制备了含有-γBi2WO6纳米晶的Er3+掺杂透明硼铋酸盐微晶玻璃.根据X射线粉末衍射结果和Scherrer公式计算得到-γBi2WO6晶粒大小约为15 nm.由于部分Er3+离子取代Bi3+进入-γBi2WO6纳米晶相中,使得Er3+离子在1.5μm的有效发射带宽由78 nm增加到85 nm,同时Er3+离子在4I13/2能级的荧光寿命由0.67 ms增加到1.43 ms.此外,与原始玻璃相比,在Er3+掺杂硼铋酸盐微晶玻璃中观察到强烈的绿光上转换发光,其上转换发光机制可以归为双光子过程.     

Characterization of domain configurations in LiTaO3/Al2O3 ceramic composites

Characterization of domain configurations in 15 vol% LiTaO₃/Al₂O₃ ceramic composites hot-pressed sintered at 1300 °C was carried out using transmission electron microscopy and high-resolution transmission electron microscopy. Mainly banded- and wedge-shaped 90° domains, with few 180° domains, were formed in the LiTaO₃ grains within the composite. The formation of 90° domains was attributed to the large stress caused by residual polarization. Many dark dots, distributed along the 90° domain boundaries, were detected and it was confirmed that they were not a deposited second phase but a type of contrast induced by high strain. The 90° domain boundaries presented an α-type fringe contrast and no δ-type fringes were observed, indicating that they were of the non-conventional type.     

Electrophoretic deposition and its use to synthesize ZrO2/Al2O3 micro-laminate ceramic/ceramic composites

Electrophoretic deposition has been employed to synthesize yttria-stabilized zirconia (YSZ)/alumina, laminar microcomposites with a total of 80 layers, >2mm. 10 wt% solids, ethanol suspensions of YSZ or Al₂O₃ powders were deposited layer by layer. The deposited samples had a green density, ~60% theoretical. The deposition process was characterized by the rate-of-deposition as a function of voltage and the microstructure of the sintered, theoretically dense samples was characterized by optical and electron microscopy. Microindentation was used to explore the mechanical properties of the laminates.     

3D打印陶瓷铸型研究与应用进展EI北大核心CSCD

陶瓷铸型是一类应用于熔模精密铸造领域、用于成型铸件内外部结构的复杂部件。随着铸件复杂度的提升,需要更加精细、复杂的铸型来满足铸造需求,然而传统的陶瓷铸型成型手段如注射成型等存在成本高、研发周期长等问题,难以满足复杂精细结构的成型要求。3D打印技术作为一种快速成型手段能够精准成型复杂精细结构,将其应用于铸型生产,不仅能够解决复杂结构的成型问题,同时也能降低生产成本、缩短生产周期。本文主要阐述了3D打印技术在陶瓷铸型生产中的应用,从应用于铸型3D打印陶瓷材料的种类及特性、典型铸型3D打印技术及铸型打印后处理手段三个方面对3D打印技术陶瓷铸型的研究与应用进行介绍,并对该技术未来的发展进行展望,指出3D打印技术能够有效解决复杂陶瓷铸型的成型问题,从而满足复杂空心结构金属件的铸造需求。     

固相法制备BaTiO3基细晶陶瓷粉体

通过传统的固相法制备BaTiO3基细晶陶瓷粉体，讨论了在预烧温度和烧结温度相同的情况下，探讨不同施主元素的添加量对陶瓷晶粒及电性能的影响；在预烧温度和烧结温度相同的情况下，探讨不同受主杂质对陶瓷晶粒及电性能的影响；在施、受主掺杂量及烧结温度相同的情况下，探讨不同的预烧温度对陶瓷晶粒及电性能的影响．为了制备高升阻比、晶粒细小的BaTi03陶瓷，选取的材料配方为Ba1.0Ti1.01O3＋0.4％（摩尔分数）Y2O3＋0.03％（摩尔分数）Mn（NO3）2＋2％S102，粉体在1200℃预烧，保温2h，样品在1280℃烧成。上电极后测得常温电阻率为4937Ω·cm，升阻比为7．116×10^3，温度系数为14．03％，居里温度为128．4℃．     

Indentation plasticity and fracture of Si3N4 ceramic alloys

The response of a series of one- and two-phase-Si₃N₄ ceramic alloy surfaces to sharp diamond microindentation has been examined by optical and electron microscopy. The microhardness (H), which obeys the load-independent relationH=P/a ² (whereP anda are load and indent size, respectively) is nearly constant within the alloy series, indicating a retention of high covalency at large (Al and O) substitution levels. Indentation results from severe localized plasticity which is characterized by the operation of the dominant dislocation Burgers vectora[0 0 0 1] in the hexagonal lattice. The severe anisotropy in plasticity induces grain-boundary microcracking which is believed to nucleate median cracks which propagate away from the plastic zone on symmetry planes beneath the indenter. The relation between load, median crack size (c) and fracture toughness (K _c) is of the form,K _c=constant (P/c ^3/2) predicted theoretically. Values ofK _c rank correctly with those from notched-beam measurements, but there is uncertainty about the value of the constant.