Microstructure design by mechanical alloying
Microstructure design by mechanical alloying
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DOI：
10.1016/j.jeurceramsoc.2010.02.008
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发表时间：
2010-10-01
影响因子：
5.7
通讯作者：
Homem Mello-Castanho, Sonia Regina
中科院分区：
文献类型：
--
作者：
Guisard Restivo, Thomaz Augusto;Homem Mello-Castanho, Sonia Regina
混合和共沉淀过程通常不足以获得含有多种功能成分的材料，例如必须同时工作的选择性催化剂。即使当获得均匀且精细的成分分布时，等相颗粒之间的亲和力也会导致固结（烧结）过程以及应用过程中的粗化，例如材料可能会失去高反应性。目前的工作提出了一种新的固结路线——活性表面烧结（SAS）——一旦在第一个烧结步骤中暴露出高活性表面，该路线就采用牺牲金属层来避免粗化并增加烧结过程中的扩散分布。由于在烧结气氛中建立了有限的氧势，当提供通过机械合金化（MA）处理获得的特定粉末微观结构时，SAS效应就会发挥作用。 MA 的驱动方式可产生具有层状豆荚状结构的金属陶瓷粉末颗粒，如 SEM 图像所示。这种投影形态包括镀有薄金属层或嵌入其上的陶瓷圆形颗粒。用铜和一些选定的难熔金属添加剂研究了多孔镍-氧化锆基金属陶瓷。难熔金属有望取代铜，使金属陶瓷中的铜保持纯净状态。反过来，当应用中涉及燃料重整反应时（例如在固体氧化物燃料电池中），添加铜被认为可以防止结焦。此外，Cu是期望的，因为它促进收缩并降低烧结温度。研究发现，在控制氧分压的氩气氛下运行的 SAS 工艺可将烧结温度进一步降低 100-300 摄氏度，使金属陶瓷的最终密度高于 60%TD。烧结行为取决于所选的添加剂，其中 Ag、Cu 和 Mo 是最有效的添加剂。所得烧结部件获得适合催化应用的密度和相分散。 (C) 2010 Elsevier Ltd. 保留所有权利。
Mixing and coprecipitation processes are, often, not enough in order to reach materials holding several functional components, like selective catalysts that must work simultaneously. Even though when a homogeneous and fine distribution of the constituents is obtained, the affinity between equal phase particles leads to coarsening during the consolidation (sintering) process, as well as on application, such as the material can loose high reactivity. The present work proposes a new consolidation route - sintering by activated surface (SAS) - that employs sacrificial metal layers to avoid coarsening and to increase the diffusion profiles during sintering, once high activity surfaces are exposed during the first sintering step. Regarding limited oxygen potential is established in the sintering atmosphere, the SAS effect is engaged when a specific projected powder microstructure obtained by mechanical alloying (MA) processing is provided. The MA is driven in such a way that yields cermet powders particles with lamellar pod-like like structures, as shown in the SEM image. This projected morphology comprises the ceramic round particles plated by thin metal layers or embedded on them.Porous nickel-zirconia based cermets are studied with Cu and some selected refractory metal additives. The refractory metals are expected to repeal Cu, which remains in pure state at the cermet. By its turn, Cu addition is postulated to prevent coking when fuel-reforming reactions are involved at the application (e.g. in solid oxide fuel cells). Furthermore, Cu is desired since it promotes shrinkage and lower the sintering temperatures. The SAS process running under argon atmospheres with controlled oxygen partial pressure is found to further reduce the sintering temperature by 100-300 degrees C, for cermets final densities above 60%TD. The sintering behaviour depends on the chosen additive, being Ag, Cu and Mo the most effective ones. The resulted sintered parts attain a suitable density and phase dispersion for catalysis applications. (C) 2010 Elsevier Ltd. All rights reserved.