Process of pulse electrodeposition nanocrystalline chromium from trivalent chromium bath

Nanocrystalline chromium coating was prepared by pulse electrodeposition from trivalent chromium bath containing carboxylate-urea as complexing agent. The effects of electrodeposition parameters such as current density, bath temperature and solution concentration on the thickness and electrodeposition velocity of Cr deposited films were investigated. The crystallographic structures, morphology and chemical composition of Cr deposited films were analyzed by means of XRD, SEM and EDS. The results indicate that the deposited films with thickness up to 11.2 μm possess a smooth and clean appearance, and the grain size is less than 100 nm. The coating is pure chromium and the Cr deposit has face-centered cubic （fcc） structure and exhibits a （210） growth preference. Both the electrodeposition velocity and thickness exist maximum under different concentration complex agents, ureas, acetates, different temperatures and current densities. Compared with direct current electrodeposition, the thicker coating and finer grains can be obtained at lower temperature and current density by pulse electrodeposition. The electrodepostion velocity is about 0.24 μm/min, which is faster than that by direct current electrodeposition. In l mol/L H2SO4, 3.5% NaCl and 10% NaOH solution, corrosion potential of Cr pulse-deposited film is about 100 mV higher than that of direct current. Corrosion and passivation current densities are lower and the nanocrystalline exhibits better corrosion resistance.     

Why the decorative chromium coating electrodeposited from trivalent chromium electrolyte containing formic acid is darker

The color of the decorative chromium coatings electrodeposited from trivalent chromium electrolytes containing formic acid or formate is usually darker than that from conventional hexavalent chromium electrolytes. For the purpose of clarifying the reason for this situation, X-ray diffraction (XRD), selected area electron diffraction (SAED), electron probe microanalyzer (EPMA) and high-resolution transmission electron microscopy (HRTEM) were employed to investigate the phases and fine microstructure of the typical decorative chromium coating produced from a typical trivalent chromium electrolyte containing formic acid. The results show that the coating is amorphous embedded with the nanocrystals of graphite, Cr₂₃C₆ and body-centered cubic structure chromium (bcc Cr). The presence of the nanocrystal graphite with strong infrared emission performance is the main reason for the darker color of the coating.     

Preparation and characterization of graphite-nickel composite coatings by automatic brush plating

Composite coatings of nickel with G particles were produced on AISI 1045 carbon steel substrate by using a newly developed automatic brush plating system. Pure nickel coating was also prepared for comparative study. The volume percent incorporation of G powder in the composite coatings was investigated with respect to its concentration in bath and relative anode to cathode speed. It was shown that the volume percentage of G was strongly affected by these parameters. The G particle distribution in the composite coatings was uniform across the coating at low concentration of G in bath and agglomerated on the surface at high concentrations. The wear and friction properties of G-Ni composite coatings containing different amounts of G particles were studied. The results revealed that hardness, wear resistance and friction coefficient are dependent on volume percentage of G in composite coating. In this study, it was shown that G-Ni composite coating with 15% G possessed the best wear-resistance property.     

碳热还原法制备纳米碳化铬粉末及其特性表征

以纳米Cr2O3和纳米碳黑为原料,采用碳热还原法制备纳米碳化铬(Cr3C2)粉末。采用XRD、SEM和TEM等测试手段对反应产物进行表征。结果表明:当碳含量为28%(质量分数)、反应温度为1 100℃及保温时间为1 h时,反应产物为单一的Cr3C2,平均晶粒尺寸为25.6 nm;反应产物分散较好且颗粒呈球形或类球形,无明显团聚现象,颗粒尺寸在30 nm左右;试样表面主要由Cr、C和O这3种元素组成,O 1s谱主要包括3个峰(Oa,Oh和Od),分别对应于O、OH和Cr2O3;C 1s谱主要包含4个峰(Cf,Cc,Cd和Ce),分别对应污染碳、碳化铬(Cr3C2)及其他类型的碳化铬Cr3C2 x(0≤x≤0.5)。     

Linear sweep voltammetry of the electrodeposition of copper from a methanesulfonic acid bath containing a perfluorinated cationic surfactant

The influence of a perfluorinated, cationic surfactant, DuPont™ ForaFac® 1098, on the electrodeposition of copper from a CH₃SO₃H bath was investigated. The background electrolyte contained 0.005 mol dm^− 3 hydroquinone and 12.5vol.% (1.93 mol dm^− 3) methanesulfonic acid, surfactant (0.002 to 0.12 vol.%) and copper ion (0.02 to 0.5 mol dm^− 3) at 23 °C. The effects of electrode rotation speed, surfactant concentration and copper ion concentration were investigated. Linear sweep voltammetry was used to identify the charge transfer, mixed control and mass transport control regions. Changes in the limiting current density, copper nucleation potential and hydrogen evolution potential are discussed. The shift in copper nucleation potential was also investigated as a function of the surfactant and copper ion concentrations. Copper was electrodeposited, at a constant potential, onto a rotating cylinder electrode and the surface morphology was characterised using scanning electron microscopy.     

Preparation and characterization of electroless Ni-P-Fe3O4 composite coatings and evaluation of its high temperature oxidation behaviour

Ni-P coatings modified with synthetic magnetite were prepared by electroless technique from a Ni-P plating bath containing magnetite powder. The coatings morphology was studied by means of scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The corrosion resistance at room temperature of the Ni-P films modified with magnetite was evaluated by means of electrochemical impedance spectroscopy (EIS), where the composite films exhibited a better behaviour. The films resistance to high temperature oxidation was evaluated by cyclic oxidation tests, SEM/EDS and X-ray diffraction analysis (XRD), where the coating with iron oxides appears to be more protective.     

Development of metallised polyester fabric by electroless copper for aircraft application using glyoxylic acid as reductant

Electroless copper deposition on polyester fabric using glyoxylic acid (CHOCOOH) as a reductant has been investigated. Surface morphology, composition and crystal structure of copper coating on polyester fabric were characterised by scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction, respectively. The surface resistance of copper-plated polyester fabric was evaluated. When the concentration of glyoxylic acid was 12?g?L^?1, the deposition rate was 49.3?mg?cm^?2?h^?1 and the surface resistance was at a minimum of 24.8?mΩ?sq^?1, which has a potential application in electromagnetic interference shielding for aircraft.     

Preparation and characterization of fibrous NiO particles by thermal decomposition of nickelous complex precursors

The influences of pyrolytic conditions, including temperature, time, the flow rate of air, and the heating rate, on the morphology, average size and specific surface area of the NiO particles were investigated, and the composition and morphologies of the products were characterized by using of XRD, SEM and BET. It is found that fibrous NiO particles were produced under the optimal conditions. A suitable range of pH for preparing dispersive precursors was chosen according to analysis of zeta potential. Based on the observations of NiO precursors growth and SEM morphology of the precursor, the oriented attachment was proposed for the well-aligned growth of the NiO precursor fibres. The final product NiO inherits the morphology of the precursor.     

马来酸-丙烯酸共聚物络合超滤处理含锰废水(英文)

用马来酸-丙烯酸共聚物(PMA-100)作络合剂,采用PVB中空纤维膜,研究络合-超滤处理含锰废水。测定了高聚物的羧基含量以及Mn(II)与PMA-100的络合反应速率,研究聚合物与重金属质量比(P/M)、pH、外加盐浓度等因素对锰离子截留率(R)和膜通量(J)的影响。结果表明:高聚物中羧基含量为9.5 mmol/g,对Mn(II)质量浓度为10 mg/L的模拟废水,在pH=6.0时,Mn(II)与PMA-100的络合在5 min内基本可完成,络合率达99.6%。在一定P/M下,pH在2.5~7.0范围内,截留率和膜通量均随着pH的增加而增大;在一定pH下,截留率随着P/M的增加而增加,但膜通量基本不变。外加盐的存在使截留率下降,在同样离子强度下,CaCl2的影响远大于NaCl的。     

Preparation of titanium mineral from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching

Titanium mineral was prepared from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching. The leaching behaviors of elements like Fe, V, Mn, Al, Mg, Ca, and Si were highly related to the reduction degree. The phase compositions of the reduced materials and the leached residues were analyzed by XRD to identify the effect of reduction degree on the leaching mechanisms. The results showed that the concentrates were reduced to iron metal and titanomagnetite at 800?1000 °C for 0.5 h, and the above elements of Fe and impurities were easily leached. Deeper reduction led to the formation of ilmenite and Mg?Al spinel, which hindered leaching. Mg-bearing anosovite appeared in the further reduced materials, and the leaching rates of impurities became much lower. An upgraded titanium mineral with a normalized TiO₂ grade of 70.3% was achieved by H₂ reduction at 850 °C for 0.5 h and acid leaching, which is a satisfactory Ti resource for the preparation of titanium oxide by sulfate process.     

Preparation and characterization of nanostructured Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-13wt.%TiO<Subscript>2</Subscript> ceramic coatings by plasma spraying

Nanostructured and conventional Al₂O₃-13wt.%TiO₂ ceramic coatings were prepared by plasma spraying with nanostructured agglomerated and conventional powders, respectively. The microstructure and microhardness of the coatings were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and microhardness measurement. Meanwhile, the friction and wear behaviors were analyzed and compared using a ball-on-disk tribometer. The results show that the conventional coating has lamellar stacking characteristic and has some pores. However, the nanostructured coating shows a bimodal microstructure, which is composed of both fully melted regions and partially melted regions. According to the microstructural difference, the partially melted regions can be divided into liquid-phase sintered regions (a three-dimensional net or skeleton-like structure: Al₂O₃-rich submicron particles embedded in the TiO₂-rich matrix) and solid-phase sintered regions (remained nanoparticles). The microstructural characteristics of the liquid-phase sintered region are formed due to the selective melting of TiO₂ nanoparticles during plasma spraying. On the other hand, the TiO₂ and Al₂O₃ nanoparticles of the solid-phase sintered regions are all unmelted during plasma spraying. Due to the existence of nanostructured microstructures, the nanostructured coating has a higher microhardness, a lower friction coefficient, and a better wear resistance than the conventional coating.     

酸碱复合催化溶胶-凝胶法制备 SiO2减反膜及膜性能研究

采用酸催化法、碱催化法和酸碱复合催化法制备了SiO2溶胶,进而制得SiO2减反膜。表征了薄膜的表面形貌,测定了薄膜的透射率和硬度。结果表明,不同催化溶胶制得的膜层在表面形貌、减反效果和薄膜硬度等方面存在明显差异:酸催化得到的薄膜,孔隙率和透过率最低,但硬度和抗划伤性最好;碱催化得到的薄膜,孔隙率和透过率最高,但硬度和抗划伤性最差;酸碱复合催化得到的薄膜,孔隙率、透过率、硬度和抗划伤性能介于以上二者之间,性能与酸碱复合催化溶胶的制备工艺密切相关。     

Preparation and characterization of mullite whiskers from silica fume by using a low temperature molten salt method

Mullite whiskers were prepared from silica fume in molten Al₂(SO₄)₃-Na₂SO₄ mixture salts at low temperatures. The resulting mullite whiskers, as well as the nucleation and growth mechanism in the molten environment, have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TG-DTA) techniques. XRD studies showed that the materials obtained were orthorhombic mullite. SEM, TEM and HRTEM results revealed that the mullite whiskers were single crystal fibers with diameters ranging from 30 to 150 nm and lengths of over several microns. According to thermodynamic analysis, mullite phase might be spontaneously formed in molten salts as the temperature reached the decomposition temperature of aluminum sulfate (1023 K). Moreover, the mullite crystals grew along [1 1 1] crystal plane firstly and developed into fibrous microstructure finally.