喷雾反应法制备电子陶瓷用钛酸钡

首次在液滴“微反应器”中借用均相沉淀反应的原理 ,即通过水解剂 (草酸二甲酯 )水解出的草酸与液滴中的钡钛离子发生共沉淀反应生成草酸氧钛钡 ,进而煅烧制得钛酸钡粉体。用化学分析方法测定产物中的Ba/Ti物质的量比 ,用XRD、TEM、LS - 2 30粒度仪分别对产物的晶型、形貌及粒度进行表征。结果表明 ,采用该法制备的是组分分布均匀、粒度小且分布窄 ,形貌为球型的纯四方相钛酸钡粉体     

并流共沉淀法合成Dy_(2)O_(3)-ZrO_(2)纳米粉体EI北大核心CSCD

采用并流化学共沉淀法合成了Dy_(2)O_(3)掺杂ZrO_(2)(DySZ)纳米粉体材料,系统研究稳定剂掺杂量、阳离子浓度、反应系统pH值和煅烧温度对粉体材料物相组成、晶体结构和微观形貌的影响。结果表明:不同合成工艺条件下,DySZ粉体材料均具有纳米尺度特征,球形颗粒尺寸为10~30 nm,Dy_(2)O_(3)的掺杂可以起到稳定晶型的作用;稳定剂掺杂量对DySZ粉体的物相组成具有明显影响,掺杂量为10%(质量分数)时可合成单一四方相结构的DySZ粉体;DySZ粉体材料的四方度和微观形貌对稳定剂掺杂量、阳离子浓度、反应体系pH值和煅烧温度均不敏感,但其平均晶粒尺寸随稳定剂掺杂量、阳离子浓度和反应体系pH值的升高略有降低,随煅烧温度的提高而显著增加。     

化学沉淀法制备YAG透明陶瓷粉体研究进展

YAG透明陶瓷作为激光增益介质,在国防和民用领域具有广泛的应用。因其制备周期短、成本低、易于实现大尺寸制备等优势,是单晶和玻璃材料的理想替代品。而纯度高、分散性好、粒径分布均匀的YAG纳米粉体是制备高性能YAG激光透明陶瓷的关键。本文分析了液相沉淀法中影响YAG透明陶瓷粉体性能的主要因素,回顾了国内外在液相沉淀法制备YAG纳米粉体方面的研究进展,并对液相沉淀法制备球形钇铝石榴石粉体的研究前景和发展方向进行了展望。     

无机颗粒增强聚合物基复合材料耐磨性能影响因素研究进展

为了更好地指导无机颗粒增强聚合物基耐磨复合材料的优化设计,全面回顾了复合材料各组分对复合材料耐磨性能的影响。根据复合材料组成,将无机颗粒增强聚合物基复合材料耐磨性能影响因素分成5类:纳米/微米无机颗粒填充量、纳米/微米填充颗粒粒径、不同粒径无机颗粒的级配、无机颗粒与纤维的协同增强和无机颗粒表面处理。从能量角度,即各因素对材料内部结合键的断裂所吸收的外部冲击功和摩擦功的影响,分析了各因素对复合材料耐磨性能的影响。在回顾前两个因素对复合材料耐磨性影响时,发现都存在使材料耐磨性能最佳的最佳颗粒填充量和最佳颗粒粒径。对于微米颗粒(粒径50μm),颗粒填充量比粒径对复合材料耐磨性能影响更大,应尽可能提高颗粒最佳填充量。对于纳米颗粒,颗粒粒径则是影响材料耐磨性能的关键因素,应尽可能降低最佳颗粒粒径。另外,颗粒的表面改性和级配都能通过提高颗粒最佳填充量和综合力学性能来提高复合材料的耐磨性能。无机颗粒与纳米纤维的混杂填充使复合材料同时具备最优的耐磨性能、摩擦系数以及优异的变载荷适应性。     

The scattering of electro-elastic waves by a spherical piezoelectric particle in a polymer matrix

This paper is devoted to the study of scattering of plane harmonic waves by a piezoelectric sphere with spherical isotropy embedded in an unbounded isotropic polymer matrix. The scattered displacement field and the electric potential in the matrix are expressed in terms of spherical vector wave functions and spherical harmonic functions, respectively. For the field points inside the inhomogeneity, new displacement functions are introduced. Expansion of the new displacement functions and the electric potential in terms of spherical harmonic functions, the equations of motion and electrostatic lead to four second order ordinary differential equations (odes), where three of them are coupled. The coupled system of odes is solved by the generalized Frobenius series. This approach is readily used to handle low and high frequencies. Three different types of piezoelectric inhomogeneities, PZT-4, PZT-5H, and BaTiO₃ are considered and the associated piezoelectric effects on the electro-mechanical fields, differential and total scattering cross-sections are addressed.     

Nanostructured micronized solid dispersion of crystalline-amorphous metronidazole embedded in amorphous polymer matrix prepared by nano spray drying

In this study metronidazole drug was encapsulated by hydroxypropyl methylcellulose and polyvinylpyrrolidone polymers from solutions using nano spray drying technology. The influence of the process parameters and formulation variables were investigated on product morhology and structure, production yield and entrapment efficiency. The use of surface active admixtures (polyvinyl alcohol, Tween-80 and Pluronic F68) increased the product yield substantially. The entrapped metronidazole was partially in crystalline and amorphous state in both amorphous polymers as confirmed by DSC and powder X-ray diffraction measurements. In the composites with hydroxypropyl methylcellulose the degree of crystallinity was between 50.2 and 81.0%, and with polyvinylpyrrolidone between 35.0 and 50.0% (with respect to the drug content). Melting point decrease phenomena was observed by differential scanning calorimetry between bulk metronidazole and spray dried products. Peak broadening was indicated by powder X-ray diffraction measurements, which could be the result of formation of small drug crystallites. The TEM images showed beside the larger crystals (200–400 nm) a fraction of smaller crystals (20–50 nm in diameter), which are in good correlation with the calculated coherent scattering domain sizes of 19–87 nm based on X-ray data. The drug-polymer composites produced by nano spray drying process were identified as crystalline-amorphous nanostructured micronized solid dispersions.     

Synthesis,microstructure and mechanical properties of ZrB2 nano and microparticle reinforced copper matrix composite by in situ processings

Copper matrix composite reinforced with ZrB₂ particles was prepared by in situ reaction in two different ways: by mechanical alloying and subsequent hot pressing, i.e. mechanical alloying and followed by laser melting process. Microstructural changes during mechanical alloying, hot pressing and laser melting of Cu, Zr and B powder mixtures were studied using scanning electron microscopy and X-ray diffraction. In particular, changes in the Cu particle size, structural parameters of the powder mixtures and formation of new ZrB₂ and CuZr phases during hot pressing, i.e. laser melting were investigated. The mechanisms of in situ formation of reinforcement particles and hardening effects in the copper composite were also studied. Large supersaturation which is possible with laser melting process results in homogeneous nucleation of CuZr precipitates and the presence of finer CuZr precipitates and ZrB₂ reinforcements in the Cu matrix. This affected on significantly higher degree of Cu matrix hardening compared to composites obtained by mechanical alloying and hot pressing.     

Synthesis of Y-Ba-Cu-O superconducting material by citrate chemical route—some observations

We present an overview of our powder synthesis procedure and give some initial results concerning the superconducting properties of YBa₂Cu₃O_7−x .