Effect of grain size on corrosion behavior of electrodeposited bulk nanocrystalline Ni

Nanocrystalline (NC) and coarse-grained Ni with different grain sizes (from 16 nm to 2 μm) were fabricated by direct current electrodeposition. Effect of grain size on the electrochemical corrosion behavior of these Ni deposits in different corrosion media was characterized by using potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and immersion corrosion test. Results show that in the NaOH or NaCl solution, the NC Ni exhibits improved corrosion resistance with the decrease of grain size. But in H2SO4 solution, the higher grain boundary density accelerates corrosion due to no passive process and the corrosion resistance of NC Ni decreases with refining grain size. The distinct experimental results of NC Ni in corrosion behavior can be reasonably explained by the positive or negative effect of high-density grain boundaries in different corrosion media.     

Microstructure and properties of nanocrystalline nickel coatings prepared by pulse jet electrodeposition

The fabrication of nanocrystalline nickel coatings was conducted by pulse jet electrodeposition on the substrate of 45# carbon steel. The effects of average current density on the surface morphology, microstructure, average grain size and microhardness of nickel coatings were investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and microhardness measurement. In addition, the corrosion resistances of coating and substrate were compared. It is revealed that the nickel coatings prepared by pulse jet electrodeposition exhibit a fine-grained structure with a smooth surface and a high density, although some pores and defects are still present in coatings. With the increase of average current density, the average grain size of nickel coatings is reduced at first and then increased. The coating with the optimum compactness, the smallest average grain size (13.7 nm) and the highest microhardness are obtained at current density of 39.8 A/dm2. The corrosion resistance is obviously increased for the coatings prepared by pulse jet electrodeposition; however, the corrosion rate is increased after a certain period due to the penetration of the corrosive media.     

Nanocrystalline Mg and Mg alloy powders by hydriding-dehydriding processing

The process of mechanically assisted hydriding and subsequent thermal dehydriding was proposed to produce nanocrystalline Mg and Mg alloy powders using pure Mg and Mg-5.5%Zn-0.6%Zr(mass fraction)(ZK60 Mg) alloy as the starting materal.The hydriding was achieved by room-temperature reaction milling in hydrogen.The dehydriding was carried out by vacuum annealing of the as-milled powders.The microstructure and morphology of both the as-milled and subsequently dehydrided powders were characterized by X-ray diffraction analysis(XRD) ,transmission electron microscopy(TEM) ,and scanning electron microscopy(SEM) ,respectively.The results show that,by reaction milling in hydrogen,both Mg and ZK60 Mg alloy can be fully hydrided to form nanocrystalline MgH2 with an average grain size of 10 nm.After subsequent thermal dehydriding at 300℃,the MgH2 can be turned into Mg again,and the newly formed Mg grains are nanocrystallines,with an average grain size of 25 nm.     

高能球磨法合成纳米晶NiZn铁氧体的结构和磁性

报告了作者利用机械球磨方法成功制备纳米晶NiZn铁氧体软磁材料的实验结果。实验样品具有很好的单相结构,所形成材料典型晶粒尺度为10～50nm。结合纯Fe3O4球磨样品,初步估算其样品的合成效率大约为27%～44%,这一结果可利用两步合成及中间纳米颗粒的高活性给予理解。对本实验利用球磨方法直接获得的NiZn铁氧体样品表现出较低的磁化强度σm和较大的矫顽力Hc,其典型值为43Am2kg-1和377×103(4π)-1A/m。从实用化角度而言,必要的热处理将是必要的。实验进一步证明,除了传统的机械合金化制备纳米晶软磁合金材料以外,利用高能球磨制备纳米晶NiZn软磁铁氧体也将是一种有效可行的新方法。     

非晶纳米晶合金材料的工艺技术、产业化和应用

介绍了国内外利用快淬技术制备非晶纳米晶合金材料的产业现状以及这一领域材料工艺技术的研究开发动态和非晶纳米晶材料的应用情况。     

FeZrNbBCu非晶和纳米晶合金高温磁性能研究

利用单辊熔淬法制备了FeZrNbBCu非晶薄带,然后通过非晶晶化方法得到纳米晶合金.研究了FeZrNbBCu非晶和纳米晶合金的磁性能与温度的关系.非晶态合金晶化升温过程中磁导率~温度曲线中出现了一个Hopkinson峰,而在晶化后的样品中没有出现,并根据各向异性的变化和磁化强度与温度的关系进行了合理的解释.对于非晶样品和晶相体积分数小的合金样品,当温度接近残余非晶居里温度时,磁导率急剧减小;而对于非晶相含量很少的样品,其磁导率随温度升高而缓慢下降,根据双相合金中交换作用模型进行了解释.     

化学镀Co-B合金(Ⅱ)

纳米晶合金具有独特的物理性能.通过化学镀方法获得纳米晶Co-B合金,分别研究了沉积层厚度和热处理温度对其矫顽力和比饱和磁化强度的影响.结果表明,开始阶段,随着镀层厚度的增加,矫顽力逐渐减小,而当镀层厚度大于0.6 μm时,矫顽力随镀层厚度的增加而逐步升高;比饱和磁化强度则始终随镀层厚度增加呈上升趋势.开始阶段,随着热处理温度的上升,矫顽力上升,当热处理温度高于450℃时,矫顽力开始减小;热处理温度对比饱和磁化强度影响较为复杂.     

钨对化学镀Ni-W-P合金镀层结构及性能的影响

通过不同的化学镀工艺配方,获得了4种不同钨含量的化学镀Ni-W-P三元合金镀层.研究了钨含量对镀层结构、硬度及在5%H2SO4溶液中耐蚀性的影响规律.研究发现,化学镀Ni-W-P三元合金镀层的结构受镀层中钨含量的影响较大,非晶态Ni-W-P三元合金镀层所需磷含量较非晶态Ni-P二元镀层所需磷含量要低,并且钨含量越高,所需磷含量越少;镀层硬度随镀层结构从非晶态→混晶态→纳米晶态转变而增加;镀层的耐蚀性随镀层中钨含量增加而变好,且非晶态镀层较混晶态和纳米晶态镀层更易形成钝化区.     

纳米金刚石复合涂层紧压模的应用

通过在紧压导体绞制 紧压工艺中使用的纳米金刚石复合涂层紧压模与普通硬质合金模的分析比较 ,认为纳米金刚石复合涂层紧压模具有使用寿命长、节省资源、提高生产率和产品质量、减少模具库存等优点     

磷钨酸/纳米晶TS-1催化剂高效择形催化氧化脱硫

采用浸渍法合成了纳米晶TS-1负载磷钨酸的HPW-Nano-TS-1催化剂,31P MAS-NMR,FT-IR,UV-vis表征结果表明,合成的负载型催化剂上磷钨酸保持Keggin骨架结构。以模型有机硫化物的正辛烷溶液为模拟油的吸附脱硫试验结果表明,噻吩、苯并噻吩和二苯并噻吩在纳米晶TS-1及HPW-Nano-TS-1样品上吸附达到平衡的时间逐渐增加,饱和吸附量相应减少。磷钨酸的引入提高了纳米晶TS-1对于大分子有机硫化物二苯并噻吩的氧化脱除活性。在温度60 ℃的反应条件下,噻吩的脱除率高于98.0%,二苯并噻吩的脱除率为58.0%,3种模型有机硫化物氧化脱除由易到难的顺序为：噻吩>二苯并噻吩>苯并噻吩,与常规的TS-1沸石或者多酸催化剂的活性顺序存在明显的差异,这是纳米晶TS-1沸石对于有机硫分子氧化反应的择形作用、扩散效应和磷钨酸在催化氧化脱硫过程中的电子云密度综合作用的结果。