亚毫米级氧化锆陶瓷微珠的制备与表征

以丙烯酰胺体系为基础,以柠檬酸铵(AC)为分散剂,过硫酸铵(APS)为引发剂,以液体石蜡,催化剂四甲基乙二胺(TEMED)为外部介质体系,将钇稳定氧化锆(YSZ)通过凝胶注模成型工艺制备氧化锆陶瓷微珠.采用热分析仪、X-射线衍射仪、扫描电子显微镜、阿基米德排水法等测试手段分别对烧成过程的物理化学变化、物相组成、显微结构...     

热等离子体超高温化学转化的过程研发和应用进展

概述了热等离子体超高温化学转化的原理、研发和应用进展。热等离子体可提供超高温反应条件,以及具有可调控的氧化、还原或惰性的气体氛围的优点,因而是一种独特的化工外场强化手段,可为劣质化石化原料以及一些工业中间产物及废弃物的清洁、高效转化提供新的技术方式,也成为现代反应工程的重要前沿领域之一。同时,热等离子体化学转化过程反应条件苛刻,是传递和反应强耦合的复杂过程,如何将热等离子独特的反应性质与物质转化需求合理结合,实现过程的清洁、高效、可控,并保证过程的经济性,是科研探索和工业实践中必须面对的问题。本文以典型热等离子体化学转化过程展开讨论,包括等离子体法乙炔、固废物处理、纳米材料制备等,展望了热等离子体技术在能源、化工、环境、材料等领域独特的发展前景。     

Transitional behavior of polymeric hollow microsphere formation in turbulent shear flow by emulsion diffusion method

Polymeric hollow microspheres have attracted growing attention because of their unique properties and extensive applications. We report a facile emulsion diffusion process to fabricate polylactic acid (PLA) hollow microspheres driven by viscous turbulent fluid flow. The process involves the emulsification of PLA–ethyl acetate solution in the water–glycerol medium under high viscous turbulent shear flow where emulsion droplets coalesce into multiple emulsions, and the solidification of PLA by the diffusion of ethyl acetate. The addition of glycerol changed the viscosity of the continuous aqueous phase, resulting in the transition of fluid flow from inertial turbulent to viscous turbulent dominant regime and thus PLA particle size and shape from solid nanospheres to hollow microspheres. The emulsification temperature also needs to exceed the glass transition temperature of PLA to form hollow microstructure. This method allows the easy control of PLA particle shape and size for different applications.     

聚(α-氰基丙烯酸异丁酯)微球的制备

以α-氰基丙烯酸异丁酯为原料,通过乳化法制备了聚(α-氰基丙烯酸异丁酯)微球。考察了体系pH、表面活性剂浓度、单体浓度、反应时间等对微球的影响,并用激光粒度分析仪对微球粒径进行了表征,用透射电子显微镜对微球的形貌进行了观察。结果表明:在泊洛沙姆188质量分数为1.0%,α-氰基丙烯酸异丁酯体积分数为0.8%,体系pH为2.5条件下反应3 h可得粒径140 nm左右的微球。所得微球形貌规整,表面光滑,粒径分布均匀。     

Fabrication of high aspect ratio boron nitride nanotube–ZrB₂ composites and the effect of dispersion

Ultrahigh-temperature ceramics (UHTCs) exhibit remarkable hardness and resistance to oxidative ablation, making them suitable for use in hypersonic environments, such as hypersonic aircraft and space shuttles. However, their low fracture toughness limits their applications as engineering materials. In this study, zirconium diboride, an extremely hard and oxidation-resistant UHTC, was sintered with high aspect ratio boron nitride nanotubes (BNNTs) to improve the fracture toughness of UHTC. Although the high aspect ratio BNNTs tend to become entangled and are inefficient in improving the fracture toughness of the composite, the use of plasma functionalization can effectively disperse the BNNTs in UHTC, resulting in the increase in the fracture toughness of the UHTC composite.     

Effect of tantalum solid solution additions on the mechanical behavior of ZrB2

Mechanical properties and microstructure were compared for zirconium diboride and two zirconium diboride solid solutions containing 3 and 6 at% tantalum diboride. X-ray diffraction indicated that the ceramics were nearly phase-pure and that tantalum dissolved into the ZrB₂ lattice to form (Zr,Ta)B₂ solid solutions. Microstructural analysis indicated that samples achieved nearly full relative density with average grain sizes that ranged from 3?5 μm. The three compositions had similar values of Young’s modulus (510?531 GPa), shear modulus (225?228 GPa), Vickers hardness (15.2–16.4 GPa), and flexural strength (391?452 MPa). Fracture toughness ranged from 2.6 to 3.7 MPa m^1/2 and with increasing tantalum content, the fracture mode changed from predominantly intergranular to predominantly transgranular. Diboride solid solution materials had comparable properties to the single metal diboride, but differences in microstructure, secondary phases, and strain state among the three ceramics partially obscured the actual effects of the solid solution on fracture behavior.     

二硼化锆系复合材料研究进展

ZrB2系复合材料具有高熔点、高硬度、高导热率等优良性能，是一种性能优异的高温结构材料，具有广泛的应用前景。本文概述了ZrB2基复合材料．如：ZrB2-Ni，ZrB2-SiC，ZrB2／B4C-Ni等的研究现状，并对其力学性能进行了评价；总结了近年来国内外在ZrB2基复合材料烧结工艺方面的研究进展。     

Solution-Based Synthesis of Submicrometer ZrB2 and ZrB2–TaB2

Zirconium diboride and a zirconium diboride/tantalum diboride mixture were synthesized by solution-based processing. Zirconium n -propoxide was refluxed with 2,4-pentanedione to form zirconium diketonate. This compound hydrolyzed in a controllable fashion to form a zirconia precursor. Boria and carbon precursors were formed via solution additions of phenol–formaldehyde and boric acid, respectively. Tantalum oxide precursors were formed similarly as zirconia precursors, in which tantalum ethoxide was used. Solutions were concentrated, dried, pyrolyzed (800°–1100°C, 2 h, flowing argon), and exposed to carbothermal reduction heat treatments (1150°–1800°C, 2 h, flowing argon). Spherical particles of 200–600 nm for pure ZrB₂ and ZrB₂–TaB₂ mixtures were formed.     

Aqueous Gelcasting and Pressureless Sintering of Zirconium Diboride Ceramics

Dense (97.3%) zirconium diboride (ZrB₂) ceramics were obtained via gelcasting and pressureless sintering. Four wt% B₄C was used as sintering aid. ZrB₂, SiC, and B₄C can codisperse well in the alkaline region, using a polyacrylate dispersant. Compared with monolithic ZrB₂ (Z), the mechanical properties of ZrB₂‐SiC (ZS) were enhanced. The Vickers hardness and fracture toughness of ZS were (13.1 ± 0.6) GPa and (2.5 ± 0.4) MPa m^1/2, respectively.     

微孔膜乳化与悬浮聚合结合法制备均一PST-DVB多孔微球

使用自制的微孔膜乳化装置,通过微孔膜乳化结合悬浮聚合方法,批量制备了微米级的聚(苯乙烯-二乙烯基苯)(PST-DVB)微球. 实验中采用孔径为5.2 mm的微孔膜,考察了膜线剪切力、管线速度和膜乳化压力对微球粒径及其分布的影响,以及膜乳化压力和膜线剪切力对分散相流速的影响. 研究结果表明,膜线剪切力在合适的范围内对微球粒径影响不大,而管线速度在14.38~26.49 m/min之间、膜乳化压力在0.008~0.012 MPa之间时,所制备微球的尺寸均一. 研究还发现膜乳化压力是影响分散相流速的最主要因素. 研究结果为装置的规模化放大奠定了理论基础.     

Comparison of freeze drying and spray drying to obtain porous nanostructured granules from nanosized suspensions

This work studies the spray drying and freeze drying of different nanosized ceramic materials and the physicochemical characteristics of the obtained granules. Colloidal suspensions of alumina, titania, and a 87/13 mixture were studied. The influence of temperature, pressure, nozzle diameter, and solids loading on the morphology and characteristics of dried granules were evaluated. It was demonstrated that these processing parameters have practically no influence, and the only parameter determining the granules characteristics is the solids content of the suspensions, in both processes. Spray drying leads to a monomodal distribution with higher granule size, while freeze drying produces more porous granules, with a bimodal intragranular distribution. The flowability of spray-dried powder is better than that of the freeze-dried powder and suit better the requirements of a feedstock targeted to obtain coatings by plasma thermal spraying whereas freeze drying can produce high porosity, softer granules.     

Evaluation of ultra-high temperature ceramics foraeropropulsion use

Among the ultra-high temperature ceramics (UHTC) are a group of materials consisting of zirconium diboride or hafnium diboride plus silicon carbide, and in some instances, carbon. These materials offer a good combination of properties that make them candidates for airframe leading edges on sharp-bodied reentry vehicles. These UHTC perform well in the environment for such applications, i.e. air at low pressure. The purpose of this study was to examine three of these materials under conditions more representative of a propulsion environment, i.e. higher oxygen partial pressure and total pressure. Results of strength and fracture toughness measurements, furnace oxidation, and high velocity thermal shock exposures are presented for ZrB₂ plus 20 vol.% SiC, ZrB₂ plus 14 vol.% SiC plus 30 vol.% C, and SCS-9a SiC fiber reinforced ZrB₂ plus 20 vol.% SiC. The poor oxidation resistance of UHTCs is the predominant factor limiting their applicability to propulsion applications.     

纳米SiO2对石灰基材料性能影响研究进展

作为一种应用广泛的无机纳米材料,纳米SiO2颗粒尺寸小、比表面积大、表面吸附性强,在改性石灰早期强度低和耐久性方面效果显著.综述了纳米SiO2对石灰基材料力学性能、耐久性以及改性机理等方面的研究进展,并基于上述综述提出了纳米SiO2改性石灰基材料当前存在的问题,结合纳米SiO2改性石灰的应用情况,展望了该类材料未来的发展方向.     

膜乳化法原理及其制备单分散高分子微球的进展

介绍了膜乳化法的原理及其影响因素,由膜乳化法制备的单分散高分子微球具备粒径均一、分布可控等特点;综述了由膜乳化法制备的单分散高分子微球在化妆品、生物医药、化工等相关领域的应用研究进展.     

Chemical Vapor Deposition Synthesis Carbon Nanosheet–Coated Zirconium Diboride Particles for Improved Fracture Toughness

Carbon nanosheet–coated micron zirconium diboride particles were achieved by an atmospheric chemical vapor deposition in the presence of methane gas without catalyst. The microstructures and carbon structure for the novel particles were characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. In addition, the growth process of hybrid particles was analyzed by thermodynamic theory. The results showed that zirconium diboride particles were coated by carbon nanosheets uniformly. The carbon nanosheets/zirconium diboride particles were employed to fabricate ceramic composite using spark plasma sintering process. The fracture toughness of the composite was improved up to 5.9 MPa·m^0.5 with only 0.9 wt% of carbon nanosheets, which was 40.9% higher than that of the composite without carbon nanosheets. The toughening mechanisms were mainly known as carbon nanosheets crack bridging and pulling out which lead to the formation of crack deflection in the novel composite.     

Exploring inexpensive processing routes to prepare dense TiB2 components

Titanium diboride (TiB₂) is considered one of the most suitable candidate materials for applications as wettable cathodes in redesigned aluminium smelting cells. In this work, titanium diboride compacts have been produced from powders using a wet colloidal processing approach combined with pressureless sintering for densification. The approach has good potential to reduce the manufacturing cost compared to hot-pressing. Owing to the elevated cost of the raw materials, the possibility of mixing powders with different particle sizes (more expensive fine and less expensive coarse powder) has been explored. The outcome of this study is very promising, since using two different particle sizes improved the particle packing of the green material resulting in sintered densities around 80% of the theoretical density at 2000°C.     

SiC porous structures obtained with innovative shaping technologies

SiC structures with porosities ranging between 20–60% have been fabricated using two methods emulsification and freeze casting. While emulsification results in foam-like isotropic materials with interconnected pores, freeze casting can be used to fabricate highly anisotropic materials with characteristic layered architectures. The parameters that control the pore size and final porosity have been identified (solid content in the initial suspensions, emulsification times or speed of the freezing front). We have found that liquid state sintering (suing Al₂O₃ and Y₂O₃ as additives) at 1800 °C on a powder (SiC/Al₂O₃) bed provides optimum consolidation for the porous structures. The mechanical strength of the materials depends on their density. Freeze casted materials fabricated with bimodal particle size distributions (a controlled mixture of micro and nanoparticles) exhibit higher compressive strengths that can reach values of up to 280 MPa for materials with densities of 0.47.     

Facile synthesis of zirconium phosphonate-functionalized magnetic mesoporous silica microspheres designed for highly selective enrichment of phosphopeptides

In this work, we present a facile approach for the synthesis of zirconium phosphate (ZrP)-functionalized magnetic silica mesoporous microspheres for the selective enrichment of phosphopeptides. At first, magnetic mesoporous silica microspheres were prepared by directly coating mesoporous silica onto Fe3O4 magnetic microspheres, and then addition of phosphate onto the magnetic mesoporous silica microspheres was performed using 3-(trihydroxysilyl)propyl methylphosphate. The obtained phosphate-modified magnetic mesoporous microspheres were monodispersed with a mean diameter of 350 nm, and had an obvious mesoporous silica shell (～65 nm). Finally, the resultant phosphate-functionalized magnetic mesoporous microspheres were incubated in ZrOCl2 solution with gentle stirring overnight for the loading of Zr4+ cations. The obtained Zr4+-functionalized materials were applied to the selective enrichment of phosphopeptides from both standard protein digestion and real samples. The enriched peptides were analyzed by MALDI-TOF MS and LC-ESI MS. Experimental results demonstrated that zirconium phosphonate-modified magnetic mesoporous silica microspheres show excellent potential for the selective enrichment of phosphopeptides.     

相反转乳化—液中干燥法制备线型氯甲基化聚苯乙烯微球

采用相反转乳化—液中干燥法成功制备出在2~40μm粒径可控且分散性较好的线型氯甲基聚苯乙烯(PCM S)微球,考察了搅拌速度、油相/水相比例、乳化分散体系的组成及加入量等因素对微球粒径及粒径分散度的影响;用扫描电子显微镜观察了微球的形貌。研究结果表明,采用相反转乳化—液中干燥法可制备出球形度极好的PCM S微球;搅拌速度、乳化分散体系的组成与加入量对PCM S微球的粒径都有很大的影响,而影响微球粒径分散系数的主要因素是搅拌速度与油相/水相的比例,分散剂的量对分散系数也有很大的影响。     

Kinetics of Formation of a Platelet-Reinforced Ceramic Composite Prepared by the Directed Reaction of Zirconium with Boron Carbide

The kinetics of formation of a new class of ceramic composite material, zirconium diboride platelet-reinforced zirconium carbides, are discussed. These materials are prepared by the directed reaction of molten zirconium with boron carbide to form a ceramic material composed of zirconium carbide matrix containing a controlled amount of residual zirconium metal. Results from interrupted growth studies, differential thermal analysis, adiabatic reaction temperature calculations, and kinetic measurements have been used to study the kinetics of the process. The reaction is very fast and proceeds parabolic ally with time with a rate constant between 1.6 X 10^-2 and 3.9 X 10^-2 cm²/_s. The proposed mechanism suggests that when molten zirconium contacts boron carbide, the molten zirconium exothermically reacts with the boron carbide to form a boron-rich liquid. Further reaction is sustained by the continuous dissolution of the boron carbide as the boron-rich liquid is drawn into the boron carbide. The product is a zirconium carbiride/zirconium carbide/zirconium composite which homogenizes quickly at the reaction temperature to yield a uniform product microstructure throughout the composite. Two alternative rate-limiting steps are discussed and the implications of each are explored.