【作者】 徐坚；

【导师】 熊惟皓；

【作者基本信息】 华中科技大学 ， 材料学， 2004， 硕士

【摘要】 粉煤灰空心微珠是火电厂排放出粉煤灰中的一种中空、轻质、细小的球形颗粒,主要化学成分是莫莱石和石英。通过对其表面进行金属化改性处理,使金属或合金能够均匀包覆在微珠的表面,可取代纯金属粉体用作电磁波吸收(RAM)或电磁屏蔽(EMI)材料。由于粉煤灰空心微珠主要成分是硅酸盐类物质,对化学镀无催化作用,因而传统上,在进行粉体化学镀之前需经敏化、活化两步预处理,以在空心微珠表面形成一定的催化活性中心。本论文对粉体化学镀工艺进行了改进,采用较廉价的AgNO3代替PdCl2作为活化剂、以化学镀液中的H2PO2-代替Sn2+作还原剂,直接在化学镀溶液中完成活化过程,在空心微珠表面形成具有催化作用的单质银,制备了NiCoP合金均匀包覆的空心微珠粉体。扫描电镜(SEM)与能谱分析仪(EDX)的观察分析结果表明,在空心微珠表面上均匀包覆合金涂层。X射线衍射(XRD)和磁强计分析表明,未经热处理的包覆合金涂层为非晶态结构,无明显的铁磁性;经热处理后的包覆合金涂层转变为晶态结构,表现出较强的铁磁性,有利于吸收电磁波。探讨了这种改进化学镀工艺的可能机理,认为固体在溶液中吸附离子是粉体化学镀的关键,超声波振荡是空心微珠粉体化学镀反应进行的必要条件之一。并讨论了在敏化预处理工艺完全一致的情况下,化学镀溶液中各组分的浓度、pH值、反应温度及装载量等因素对粉体化学镀孕育期的影响。最后,提出了一些有待继续深入探讨的问题。更多还原

【Abstract】 Fly-ash cenospheres are primarily a by product in thermal power plant, which are characterized by their fine, lightweight, smooth surface and inner hollow. The main composition of fly ash cenospheres is quartz and mullite. Fly-ash cenospheres that are coated with metal or metal alloys can replace metal powder to be used as Rader Absorbing Material (RAM) or EMI—shielding materials for their lower density than that of pure metal powder. The most important problem in this application is how to make metal or metal alloys uniformly deposited on the surface of the fine particles and finally clad the particle.Electroless NiCoP alloys coating of cenosphere particles were demonstrated in the present investigation. As providing non-catalytic surface for electroless, cenosphere particles were experiencing a two-step process involving sensitization and activation to produce some catalytic clusters on the surface so as to make them suitable for subsequent deposition. In our ameliorative procedure, replacing the conventional PdCl2 activator with AgNO3 activator and replacing Sn2+ with H2PO2- as the reducing agent decreased the overall cost of the coating process and simplified the whole process.SEM and EDX characterized the cenosphere particles after the coating process. It showed that NiCoP alloys uniformly covered the surface of the cenospheres under the given coating conditions. The XRD analysis indicated that the coating alloys were amorphous,therefore,having no ferromagnetism while they changed to be crystal and had somewhat ferromagnetism after the coating being heat-treated. Next, the possible mechanism of electroless NiCoP alloys coating of cenosphere particles was suggested. The ions’ adsorption process at the solid-solution interface was the key step in this improved procedure and the ultrasonic vibration was necessary to the electroless reaction.Finally, how the concentration of all constitutes、pH、the temperature of the electroless solution 、the loading and some other factors affected the incubation period of the electroless was discussed, in the end, some questions worth further studying were given out.更多还原