Influence of surfactants on electrodeposition of a Ni-nanoparticulate SiC composite coating

Abstract

Nickel coatings containing well-dispersed, submicron (150–500?nm) silicon carbide particles were electrodeposited on copper from an agitated, modified Watts nickel electrolyte at 60°C using current densities of 10–100?mA?cm^??2. Coumarin additions (0–5?g?dm^??3) to a bath containing 10?g?dm^??3 SiC at 6?A?dm^??2 resulted in lower microhardness but considerably reduced abrasive wear in the composite coatings. Over 20 other surfactants including anionic, cationic, and non-ionic types were evaluated for their influence on the surface and tribological properties of the nanocomposite coatings. The surfactant levels (typically 0–3?g?dm^??3) were chosen to give good particle dispersions in the bath while avoiding any obvious deposit quality problems. Coating microhardness (via nanoindentation measurement), surface coefficient of friction (COF) and abrasive wear performance of the coatings under three-body, water-based conditions were investigated. The surfactants affected the degree of silicon carbide nanosized particles incorporated into the coating, from 5 to 54?vol.-%, and altered the surface microstructure from a matte to a bright surface finish and from porous to nodular, compact coatings. The nickel-nanosized silicon carbide composite coatings showed improved resistance to abrasive wear compared to a plain nickel (PN) deposit by a factor of 2–20.     

Effect of Mo and Cu on stress corrosion cracking of ferritic stainless steel in chloride media

Stress corrosion cracking behaviour of ferritic stainless steels with copper and molybdenum additions in 42?wt-% boiling magnesium chloride at 143?±?1°C has been determined. The nature of the corrosion products was analysed by X-ray photoelectron spectroscopy (XPS). XPS results show that the presence of Fe(0), Cr(0) and Mo(0) unoxidised states on the crack tips of (copper+molybdenum) addition ferritic stainless steel cannot form the stable passive film and causes the further corrosion in the chloride solution. The addition of both copper and molybdenum to 19% Cr ferritic stainless steel causes stress corrosion cracking. The susceptibility to stress corrosion cracking increases with the growth of ε-copper precipitates, and the fracture mode changes from transgranular to intergranular with the increasing aging time. Stress corrosion cracking initiates from pitting of ε-copper phases, then propagates to molybdenum atoms, and finally propagates to the other ε-copper precipitations perpendicular to the direction of maximum strain.     

Effects of rare earth addition on microstructure of C–Mn steel

Abstract

The microstructures were observed in C–Mn steel and statistical analysis of the inclusions produced when trace amounts of rare earth were added to the steel. The results show that the content of intragranular acicular ferrite decreased in the order of being treated with La+Ce/La/Ce in C–Mn steel after the treatment of different kinds of rare earths. The optimum mass ratio of La and Ce for La+Ce combined treatment is 3:1.The best incubation time after Le+Ce (3:1) treatment is 5?min. The size of inclusion nuclei favouring intragranular acicular ferrite nucleation concentrates in the range of 1–4?μm. The disregistries between rare earth inclusions and α-Fe are small, which plays an important role in rare earth inclusions inducing intragranular acicular ferrite nucleation.     

The effect of water and guest hydrophobicity on the complexation of oligomers with solid α-cyclodextrin

α-Cyclodextrin (α-CD), a cyclic oligosaccharide, can form inclusion complexes (ICs) with polymer molecules in which α-CD molecules stack in the columnar crystal to form a molecular tube. Physical mixtures of α-CD powder and oligomeric liquids such as poly(ethylene glycol) (PEG) have been shown to spontaneously form an IC, which is accompanied by a solid-state α-CD phase transformation from the cage to the columnar crystal structure. In this paper, the phase transformation is tracked with wide-angle X-ray diffraction as a function of temperature, atmospheric water vapor content and the type of guest molecule. A first-order kinetic model is used to describe the kinetics of complexation. The time required to completely complex PEG200 (200 g/mol) at low water activities is greater than 300 h, whereas only a few hours are necessary at high water activities. Solid-state complexation of α-CD with a hydrophobic guest molecule (hexatriacontane, HTC), is also reported here for the first time. Slower complexation kinetics are observed for α-CD with HTC compared to PEG600 (600 g/mol).     

青藤碱与羟丙基-β-环糊精的包合作用研究

通过溶液共混法制备青藤碱-羟丙基-β-环糊精包合物,纯化后利用体视显微镜观察包合物的结晶形态,通过差热示重扫描、红外光谱、X射线粉末衍射及核磁共振等方式对包合物进行性质分析,并通过相溶解度法计算包合物的包合常数。结果表明青藤碱-羟丙基-β-环糊精包合物性质发生明显变化,羟丙基-β-环糊精能显著增加青藤碱的溶解度,青藤碱-羟丙基-β-环糊精包合物是一种稳定的新物质,青藤碱与HP-β-CD形成的包合物的包合分子比为1∶1,其包合常数为150.0。     

β－环状糊精与胆固醇的包合物结构研究

差示热扫描量热分析（ＤＳＣ）表明，β－环状糊精／胆固醇包合物的形成过程中，其最佳分子摩尔比为３∶１。本文的第二部分则提出了β－环状糊精／胆固醇包合物的结构模型。     

In situ characterization by localized electrochemical impedance spectroscopy of the electrochemical activity of microscopic inclusions in an X100 steel

A localized electrochemical impedance spectroscopy (LEIS) technique was used to characterize in situ the micro-electrochemical activity of inclusions contained in an American Petroleum Institute (API) X100 steel in a near-neutral pH solution. It is found that there exists an electrochemical heterogeneity between inclusions and the adjacent steel matrix. Consequently, a galvanic couple is formed to result in the locally preferential dissolution. The local electrochemical activity of the inclusion depends on its composition. A Si-enriched inclusion is associated with a high electrochemical activity, and the preferential dissolution of the inclusion generates a local microvoid, whose further dissolution initiates a corrosion pit. An aluminum oxide-enriched inclusion is more stable than the adjacent steel matrix. The preferential dissolution would occur on the steel, causing the “drop-off” of the inclusion and generating a corrosion pit.     

镁合金净化工艺研究进展

夹杂物会使镁合金性能下降,纯净化是镁合金扩大运用范围的关键之一.本文综述了镁合金净化工艺研究进展,包括熔剂净化和非熔剂净化中的吹气净化、过滤净化、沉降净化、稀土净化、复合净化等,并对镁合金净化技术的未来进行了展望.     

钢管超声波测厚示值减小的原因分析

在使用超声波测厚仪对钢管壁厚进行测量时,有时会出现示值小于钢管实际壁厚的情况,并且这些钢管内表面往往伴有许多鼓包和翘皮出现.对这种情况进行了分类统计,并取样进行分析.指出钢管超声波测厚示值减小是由分布在壁厚中间和靠近内表面区域的异常夹杂物引起的,内表面的鼓包和翘皮是由分布在壁厚靠近内表面边缘区域的异常夹杂物引起的;钢管...     

Q345D-Z25钢板探伤不合原因分析

运用金相显微镜、扫描电镜等手段,对济钢生产的70 mm厚度规格Q345D-Z25钢板进行显微组织分析。结果表明,钢板中心存在的裂纹、Mn S夹杂物以及组织偏析是造成此次钢板探伤不合的主要原因。通过提高钢水纯净度、铸坯以及钢板内部质量,探伤合格率得到显著提高。