Nd-Fe-B磁体烧结过程晶粒长大行为的研究

定量描述了Nd-Fe-B磁体烧结过程晶粒长大行为，分析了烧结温度、烧结时间、合金粉末粒度及其分布对烧结过程晶粒长大的影响，讨论了烧结过程晶粒长大机制。在Nd-Fe-B磁体烧结过程开始之后的0—1h时间区段，晶粒长大迅速；随着烧结时间的延长，晶粒长大速度减小。合金粉末平均粒度增大，或者合金粉末粒度分布范围增宽，显著促进Nd-Fe-B磁体烧结过程中晶粒的长大。在Nd-Fe-B磁体的烧结过程中，存在两类晶粒长大机制，即Nd2Fe14B颗粒的溶解与析出、Nd2Fe14B颗粒的并合与长大。Nd2Fe14B颗粒的并合与长大不仅使磁体的平均晶粒尺寸增大，也使晶粒尺寸分布范围增宽，是烧结Nd-Fe-B磁体显微组织中出现异常大晶粒的根本原因。     

Dry Sintering Meets Wet Silver‐Ion “Soldering”: Charge‐Transfer Plasmon Engineering of Solution‐Assembled Gold Nanodimers From Visible to Near‐Infrared I and II Regions

Achieving highly tunable and localized surface plasmon resonance up to near infrared (NIR) regions is a key target in nanoplasmonics. In particular, a self‐assembly process capable of producing highly uniform and solution‐processable nanomaterials with tailor‐made plasmonic properties is lacking. We herein address this problem through a conjunctive use of wet Ag⁺ soldering and dry thermal sintering to produce nanodimer‐derived structures with precisely engineered charge‐transfer plasmon (CTP). The sintered dimers are water soluble, featuring gradually shifted CTP spanning an 800 nm wavelength range (up to NIR II). Upon silica removal, the products are grafted by DNA to offer surface functionality. This process is also adaptable to DNA‐linked AuNP dimers toward plasmonic meta‐materials via DNA‐guided soldering and sintering.     

Pd/CZ三效催化剂中钯的团聚现象研究

通过浸渍法制备了一系列负载0.5%（重量百分比）Pd的氧化铈-氧化锆（NDK-84,由日本新日本电工株式会社提供）催化剂材料,并通过全面的表征手段,包括扫描电子显微镜（SEM）、透射电子显微镜（TEM）、高分辨透射电子显微镜（HR-TEM）、元素分布、X-射线衍射（XRD）,氮气吸脱附测试与比表面积和孔径分布分析（BET）、X射线光电子能谱（XPS）等,研究了不同Pd前驱体和不同热老化处理条件、H₂还原条件对Pd在铈锆固溶体上的分散、生长与烧结行为的影响,并评估了它们的三效催化活性.结果表明,热老化处理过程与还原过程显著影响了Pd在氧化物载体表面上的分散,因此导致不同的催化活性.     

BiVO4的添加对Nd0.2Ce0.8O1.9电解质微观结构和性能的影响

采用溶胶凝胶法制备BiVO₄（BV）和Nd_0.2Ce_0.8O_1.9（NDC）粉末,研究BV的加入对NDC电解质结构、形貌及电性能的影响。实验结果表明,NDC-5BV电解质的微观结构更致密,700℃时总电导率（σ_t）提高至3.35×10^-2 S·cm^-1,极化电阻（R_p）降低34%以上。单电池在700℃时的最大功率密度（MPD）为514 mW·cm^-2,开路电压（OCV）在70 h内可以保持良好的长期稳定性。     

Enhancement in age hardenability of sintered Ti–5Fe alloy by Zr addition processed by pulsed electric current sintering

The age-hardenable Ti–5Fe–5Zr (wt. %, 5Zr) alloy has been consolidated by pulsed electric current sintering, following a β solution treatment, and the results are compared with a Ti–5Fe (0Zr) alloy. The precipitation sequence measured at 640°C ageing is β?+?athermal ω?→?β?+?isothermal ω?→?β?+?α. At the peak hardness isothermal ω phase forms at 20?s of ageing. The Zr addition retards the precipitation kinetics of the α phase; as a result, the α phase nucleates at latest at 300?s ageing in the overaged state. Fe is partitioned into β, while it is depleted from the α phases. There is Zr enrichment near the α/β interface when the α phase precipitates due to a solute drag effect; the growth rate of the α phase in the 5Zr alloy is significantly reduced compared with that in the 0Zr alloy.     

铝素坯烧结过程微结构演化的实时观测

为实现对金属粉末压坯烧结过程的实时观测,从而验证现有的相关理论,本文利用同步辐射CT(SR-CT)技术,对铝压制陶瓷坯体的固相烧结过程进行实时投影成像;应用滤波反投影算法和数字图像处理技术,得到了陶瓷坯体在整个固相烧结过程中内部微结构演化的三维重建图像,实现了对铝压制陶瓷坯体整个固相烧结过程的无损原位观测,得到了样品由烧结中期进入烧结后期的完整的演化过程图像。通过重建图像,清晰观测了样品的固相烧结过程:在烧结前、中期(烧结时间t<180min、温度T<600℃),烧结颈形成并随烧结时间生长;由烧结中期开始进入后期时(烧结时间t≥180min、温度T≥600℃),样品内部结构演化加剧,气孔由相互连通演化为相互孤立并球化。进一步在实验图像的基础上分析了二面角等烧结特征的变化情况,得到烧结颈尺寸与时间对数有较好的线性关系,并可根据曲线分辨中期、后期。统计了样品在不同烧结时间的孔隙率,得到了孔隙率随烧结时间和烧结时间对数的变化曲线;分析了样品在不同烧结阶段的致密化特点,得到了烧结中期孔隙率和时间对数的线性关系。实验结果验证了现有的烧结理论,并为进一步完善烧结理论以及建立扩散和本构模型提供了高质量的实验数据。     

Healing and photon diffusion during sintering of high-T latex particles

A steady-state fluorescence technique was used to examine the annealing of films formed from high-T latex particles above the glass transition temperature. The films were prepared by sintering pyrene-labeled poly(methyl methacrylate) latex particles. During the annealing processes, the transparency of the film changed considerably. Direct fluorescence emission from excited pyrene was monitored as a function of annealing temperature to detect these changes. Scanning electron microscopy in conjunction with Monte Carlo simulations of photon diffusion in latex film were used to interpret the fluorescence results. Healing temperature and time were measured at the point where the fluorescence emission intensity becomes maximum. This was associated with the longest optical path of a photon in latex film during healing of particle(SINGLEBOND)particle boundaries. Healing activation energy was measured and found to be 10 kcal/mol. © 1996 John Wiley & Sons, Inc.     

添加剂对高碱煤钠迁移和灰分烧结温度的影响

选取三种不同的添加剂（高岭土、SiO₂和Al₂O₃）,研究它们对高碱准东煤钠迁移和灰分烧结温度的影响,并且添加比例为1%-5%。结果表明,三种添加剂的钠捕集效率依次为：高岭土 > SiO₂ > Al₂O₃。钠捕集效率随着添加比例的增加而升高,但受温度影响比较复杂。高岭土的钠捕集效率在600-1000℃先增加后减小,并在900℃达到最大值,其余两种随温度的升高均减小。准东煤灰的烧结温度为803℃,添加高岭土后,烧结温度随添加比例的增加先降低后上升。当添加比例为3%时,因为钙长石和钙黄长石的低温共熔反应而达到最小值。SiO₂的添加比例为5%时,由于透辉石的生成和SiO₂本身的"骨架"作用,烧结温度迅速升高到879℃。Al₂O₃对烧结温度的影响最小。     

Nitrogen uptake of nickel free austenitic stainless steel powder during heat treatment—an XPS study

In austenitic stainless steel nitrogen stabilizes the austenitic phase, improves the mechanical properties and increases the corrosion resistance. Nitrogen alloying enables to produce austenitic steels without the element nickel which is high priced and classified as allergy inducing. A novel production route is nitrogen alloying of CrMn‐prealloyed steel powder via the gas phase. This is beneficial as the nitrogen content can be adjusted above the amount that is reached during conventional casting. A problem which has to be overcome is the oxide layer present on the powder surface which impedes both the sintering process and the uptake of nitrogen. This study focuses on whether heat treatment under pure nitrogen is an appropriate procedure to enable sintering and nitrogen uptake by reduction of surface oxides. X‐ray photoelectron spectroscopy (XPS) in combination with scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS) are used to investigate the surface of powdered FeMn19Cr17C0.4N heat treated under nitrogen atmosphere. The analyses showed reduction of iron oxides already at 500 °C leading to oxide‐free metallic surface zones. Mn and Cr oxides are reduced at higher temperatures. Distinct nitrogen uptake was registered, and successful subsequent sintering was reached. Copyright © 2014 John Wiley & Sons, Ltd.