Preparation and properties of electroless Ni-P-SiO2 composite coatings

Dispersible SiO₂ nanoparticles were co-deposited with electroless Ni-P coating onto AISI-1045 steel substrates in the absence of any surfactants in plating bath. The resulting Ni-P/nano-SiO₂ composite coatings were heat-treated for 1 h at 200 °C, 400 °C, and 600 °C, respectively. The hardness and wear resistance of the heat-treated composite coatings were measured. Moreover, the structural changes of the composite coatings before and after heat treatment were investigated by means of X-ray diffraction (XRD), while their elemental composition and morphology were analyzed using an energy dispersive spectrometer (EDS) and a scanning electron microscope (SEM). Results show that co-deposited SiO₂ particles contributed to increase the hardness and wear resistance of electroless Ni-P coating, and the composite coating heat-treated at about 400 °C had the maximum hardness and wear resistance.     

Preparation and characterization of nickel nano-Al2O3 composite coatings by sediment co-deposition

Ni-Al₂O₃ composite coatings were prepared by using sediment co-deposition (SCD) technique and conventional electroplating (CEP) technique from Watt's type electrolyte without any additives. The microstructure, hardness, and wear resistance of resulting composites were investigated. The results show that the incorporation of nano-Al₂O₃ particles changes the surface morphology of nickel matrix. The preferential orientation is modified from (2 0 0) plane to (1 1 1) plane. The microhardness of Ni-Al₂O₃ composite coatings in the SCD technique are higher than that of the CEP technique and pure Ni coating and increase with the increasing of the nano-Al₂O₃ particles concentration in plating solution. The wear rate of the Ni-Al₂O₃ composite coating fabricated via SCD technique with 10 g/l nano-Al₂O₃ particles in plating bath is approximately one order of magnitude lower than that of pure Ni coating. Wear resistance for SCD obtained composite coatings is superior to that obtained by the CEP technique. The wear mechanism of pure Ni and nickel nano-Al₂O₃ composite coatings are adhesive wear and abrasive wear, respectively.     

Influence of phytic acid concentration on coating properties obtained by MAO treatment on magnesium alloys

Anodic coatings were prepared by microarc oxidation (MAO) on AZ91HP in a base solution of 10 g/L NaOH with and without the addition of 0-12 g/L phytic acid (C₆H₁₈O₂₄P₆). The influences of C₆H₁₈O₂₄P₆ and its concentration on the conductivity and breakdown voltage were studied. The morphologies and compositions of anodic coatings were determined by environmental scanning electron microscope (ESEM) and energy dispersive X-ray spectroscopy (EDX). Potentiodynamic polarization test was performed in 3.5 wt.% NaCl solution to evaluate the corrosion resistance of anodic coatings. The results showed that with the increase of C₆H₁₈O₂₄P₆ concentration, the solution conductivity decreased while the values of breakdown voltage increased. EDX analysis showed that the coatings formed in solutions with C₆H₁₈O₂₄P₆ addition contained Mg, Al, O, C, P and a trance of Na. The addition of C₆H₁₈O₂₄P₆ into the base solution was helpful in coating formation and the coatings formed in the solution containing 8 g/L C₆H₁₈O₂₄P₆ exhibited the best pore uniformity and corrosion resistance.     

Electrodeposition and characterization of Ni-Y2O3 composite

Nano-sized Y₂O₃ particles were codeposited with nickel by electrolytic plating from a nickel sulfate bath. The effects of the incorporated Y₂O₃ on the structure, morphology and mechanical properties (including microhardness, friction coefficient and wear resistant) of Ni-Y₂O₃ composite coatings were studied. It is observed that the addition of nano-sized Y₂O₃ particles shows apparent influence on the reduction potential and pH of the electrolyte. The incorporated Y₂O₃ increases from 1.56 wt.% to 4.4 wt.% by increasing the Y₂O₃ concentration in the plating bath from 20 to 80 g/l. XRD results reveal that the incorporated Y₂O₃ particles favour the crystal faces (2 0 0) and (2 2 0). SEM and AFM images demonstrate that the addition of Y₂O₃ particles causes a smooth and compact surface. The present study also shows that the codeposited Y₂O₃ particles in deposits decrease the friction coefficient and simultaneously reduce the wear weight loss. Ni-Y₂O₃ composite coatings reach their best microhardness and tribological properties at Y₂O₃ content 4.4 wt.% under the experiment conditions.     

Investigation on corrosion and wear behaviors of nanoparticles reinforced Ni-based composite alloying layer

In order to investigate the role of amorphous SiO₂ particles in corrosion and wear resistance of Ni-based metal matrix composite alloying layer, the amorphous nano-SiO₂ particles reinforced Ni-based composite alloying layer has been prepared by double glow plasma alloying on AISI 316L stainless steel surface, where Ni/amorphous nano-SiO₂ was firstly predeposited by brush plating. The composition and microstructure of the nano-SiO₂ particles reinforced Ni-based composite alloying layer were analyzed by using SEM, TEM and XRD. The results indicated that the composite alloying layer consisted of γ-phase and amorphous nano-SiO₂ particles, and under alloying temperature (1000 °C) condition, the nano-SiO₂ particles were uniformly distributed in the alloying layer and still kept the amorphous structure. The corrosion resistance of composite alloying layer was investigated by an electrochemical method in 3.5%NaCl solution. Compared with single alloying layer, the amorphous nano-SiO₂ particles slightly decreased the corrosion resistance of the Ni-Cr-Mo-Cu alloying layer. X-ray photoelectron spectroscopy (XPS) revealed that the passive films formed on the composite alloying consisted of Cr₂O₃, MoO₃, SiO₂ and metallic Ni and Mo. The dry wear test results showed that the composite alloying layer had excellent friction-reduced property, and the wear weight loss of composite alloying layer was less than 60% of that of Ni-Cr-Mo-Cu alloying layer.     

Effect of the dispersibility of ZrO2 nanoparticles in Ni-ZrO2 electroplated nanocomposite coatings on the mechanical properties of nanocomposite coatings

ZrO₂ nanoparticles was uniformly co-deposited into a nickel matrix by electroplating of nickel from a Watts bath containing particles in suspension which were monodispersed with dispersant under DC electrodeposition condition. It was found that morphology, orientation and hardness of the nanocomposite coatings with monodispersed ZrO₂ nanoparticles had lots of difference from the nanocomposite coatings with agglomerated ZrO₂ nanoparticles and pure nickel coatings. Especially, the result of hardness showed that only a very low volume percent (less than 1 wt.%) of monodispered ZrO₂ nanoparticles in Ni-ZrO₂ nanocomposite coatings would result in higher hardness of the coatings. The hardness of Ni-ZrO₂ nanocomposite coatings with monodispersed and agglomerated ZrO₂ nanoparticles were 529 and 393 HV, respectively. The hardness value of the former composite coatings was over 1.3 times higher than that of the later. All these composite coatings were two-three times higher than that of pure nickel plating (207 HV) prepared under the same condition. The strengthening mechanisms of the Ni-ZrO₂ nanocomposite coatings based on a combination of grain refinement strengthening from nickel matrix grain refining and dispersion strengthening from dispersion state of ZrO₂ nanoparticles in the coatings.     

Study of deposition patterns of plating layers in SiC/Cu composites by electro-brush plating

SiC reinforced copper composite coatings were prepared by electro-brush plating with micron-size silicon carbide (SiC) ranging from 1 to 5 μm on pure copper sheet in this paper. The micro-structural characterizations of SiC/Cu composite coatings were performed by optical microscope and Scanning Electron Microscope (SEM) coupled with spectrometer, to study co-deposition mechanism of SiC/Cu. It was found that there were three different patterns of SiC deposition in plating layers during electro-brush plating process, i.e. the particles could deposit inside copper grains, in grain boundaries, or in holes of the surface. To investigate deposition mechanism of each pattern, size of SiC and copper grains was compared. By comparison of size of copper grains and hard particles, SiC were either wrapped in copper grains or deposited in grain boundaries. Moreover, electro-brush plating layers at different brush velocities and current densities were obtained respectively, to analyze the microstructure evolution of the composite coatings. The hardness of plating layers was measured. The results indicated at the current density of 3 A/dm², the SiC/Cu coating was compact with SiC content at a high level and the hardness reached a maximum.     

Micromechanical and thermal behaviour of gel grown pure- and sodium-modified copper tartrate crystals

Results regarding micromechanical characteristics of gel grown pure- and sodium-modified copper tartrate crystals, bearing composition CuC₄H₄O₆·3H₂O, (Cu)_0.77(Na)_0.23C₄H₄O₆·3H₂O and (Cu)_0.65(Na)_0.35C₄H₄O₆·H₂O, as obtained on using indentation induced hardness testing technique are reported. Thermal behaviour of these crystals in the temperature ranging from room temperature (∼25 °C) to about 600 °C is also reported. Pure copper tartrate crystals are found to be thermally more stable than the sodium-modified ones. Dependence of Vickers’ hardness number H_v on load ranging from 0.049 to 2.94 N on two different planes for all the three compositions is analyzed. It is shown that after initial rise in the value of H_v, the same achieves saturation at a load of 0.49 N. Modification of copper tartrate crystal by introducing sodium in its lattice brings about a change in the micromechanical characteristics. The saturation value of H_v decreases with increase in the concentration of sodium ions. The results on (0 0 1) and (1 1 1) planes for both pure and modified copper tartrate crystals suggest hardness anisotropy. Relative difference of hardness between the two planes and yield strength for both pure and modified copper tartrate crystals is worked out. The experimental results are analyzed for applicability of Meyer’s law and Proportional Specimen Resistance Model. It is suggested that the experimental results indicating reverse ISE phenomenon may be explained in terms of the existence of a distorted zone near the crystal-medium interface. The integral method of Coats and Redfern approximation applied to the thermoanalytical data suggests “Random Nucleation Model” for the reaction kinetics of these crystals. Non-isothermal kinetic parameters such as activation energy, frequency factor and order of reaction are calculated.     

Study on the Morphological and Mechanical Properties of Nylon 6/ABS/Nano-SiO2 Composites

The mechanical properties and morphology of the composites of nylon 6, acrylonitrile-butadiene-styrene (ABS) rubber, and nano-SiO₂ particles were examined as a function of the nano-SiO₂ content. A mixture with separation and encapsulation microstructures existed in the nylon 6/ABS/nano-SiO₂ at lower nano-SiO₂ content, and ABS and nano-SiO₂ improved the toughness synergistically, while obvious agglomeration appeared at higher nano-SiO₂ content and the impact strength decreased. Moreover, the addition of nano-SiO₂ particles also affected the dispersion of the rubber phase, resulting in the appearance of smaller rubber particles. The deformation and toughening mechanisms of the composites were also investigated; they resulted from rubber voiding, crack forking, and plastic deformation of the matrix.     

Effect of sodium citrate as complexing on electrochemical behavior and speciation diagrams of CoFeNiCu baths

In this study, the effects of addition of sodium citrate dosages and different pH levels on the electrochemical behavior of CoFeNiCu alloy baths (electrolytes containing metal ions) were investigated. Stability (Pourbiax) diagrams and also speciation diagrams of cobalt, iron, nickel and copper, in conventional and citrate-added CoFeNiCu bath, were calculated by ChemEQL V.3.0 software. Stability diagrams showed that addition of 20 g?L^?1 sodium citrate to the bath increased the pH of formed detrimental metal hydroxides (especially Fe(OH)₃ from pH 3.4 to pH?~?6.9) through forming stable complexed species that were more stable than metal hydroxides at low pH levels (< ~3). According to the speciation diagrams, both pH level and sodium citrate dosage had noticeable effect on the distribution of species in the baths. Generally, at low pH level and/or sodium citrate dosage, Co⁺⁺, Fe⁺⁺, Ni⁺⁺, and Cu⁺⁺ species were dominant. The concentration of complexed species of Co(C₆H₅O₇)^? ( at pH?>?~ 7.5 or sodium citrate dosage?>?~ 30 g?L^?1), Fe(C₆H₅O₇)^? (at pH?>?~ 5.5 or sodium citrate dosage?>?~ 25 g?L^?1), Ni(C₆H₅O₇)^? (at pH?>?~ 6 or sodium citrate dosage?>?~ 30 g?L^?1), and Cu(OHC₆H₅O₇)^2? ( at pH?>?~ 8 or sodium citrate dosage?>?~ 20 g?L^?1) became significant. The effects of sodium citrate and reverse potential (E _λ) on cyclic voltammetry curves were also studied. The addition of sodium citrate in the bath shifted the reduction potential of metals towards more negative potentials. Moreover, in order to deposit cobalt, iron, and nickel simultaneously with copper, it was necessary to increase E _λ value gradually with sodium citrate dosage; otherwise, only copper would have deposited from citrate-added CoFeNiCu bath. The study of speciation diagrams showed that reduction of metals from CoFeNiCu bath with natural pH (no acid or base is added to adjust pH and it was?~?5.2) and containing 20 g?L^?1 of sodium citrate mainly occurred directly from complexed species.     

Influence of C3H8O3 in the electrolyte on characteristics and corrosion resistance of the microarc oxidation coatings formed on AZ91D magnesium alloy surface

Ceramic coatings were fabricated on AZ91D Mg-alloy substrate by microarc oxidation in Na₂SiO₃-NaOH-Na₂EDTA electrolytes with and without C₃H₈O₃ addition. The effects of different concentrations of C₃H₈O₃ contained in the electrolyte on coatings thickness were investigated. The surface morphologies, RMS roughness, phase compositions and corrosion resistance property of the ceramic coatings were analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and electrochemical corrosion test respectively. It is found that the addition of C₃H₈O₃ into silicate electrolyte leads to increase of the unit-area adsorptive capacity of the negative ions at anode-electrolyte interface and thus improves the compactness and corrosion resistance of the MAO coating. The coating thickness decreases gradually with the increase of concentrations of C₃H₈O₃ in the electrolyte. The oxide coating formed in base electrolyte containing 4 mL/L C₃H₈O₃ exhibits the best surface appearance, the lowest surface RMS roughness (174 nm) and highest corrosion resistance. In addition, both ceramic coatings treated in base electrolyte with and without C₃H₈O₃ are mainly composed of periclase MgO and forsterite Mg₂SiO₄ phase, but no diffraction peak of Mg phase is found in the patterns.     

Particle-size measurements in flames using light scattering and dissymmetry ratios

Particle-size measurements have been performed above a flat-flame burner using C₂H₆/O₂ and C₂H₄/O₂ mixtures and the assumption that a self-preserving distribution (s.p.d.) obtains for spherical particles. The absence of significant deviations from sphericity for the particles has been verified. Dissymmetry ratios were measured for parallel polarized light from an argon-ion laser at 4880 Å. The measured results are compared with previously obtained data for CH₄/O₂ mixtures and show differences in the rates and amounts of particulate growths, with the growth curves for all three gases leveling off at about 40–50 mm above the burner rim. The rates of particulate growths downstream of the flame are ordered as follows in the gas mixtures: C₂H₄/O₂>C₂H₆/O₂>CH₄/O₂.     

Microstructure and mechanical properties of reactive magnetron sputtered Ti-B-C-N nanocomposite coatings

Ti-B-C-N nanocomposite coatings with different C contents were deposited on Si (1 0 0) and high speed steel (W18Cr4V) substrates by closed-field unbalanced reactive magnetron sputtering in the mixture of argon, nitrogen and acetylene gases. These films were subsequently characterized ex situ in terms of their microstructures by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), their nanohardness/elastic modulus and facture toughness by nano-indention and Vickers indentation methods, and their surface morphology using atomic force microscopy (AFM). The results indicated that, in the studied composition range, the deposited Ti-B-C-N coatings exhibit nanocomposite based on TiN nanocrystallites. When the C₂H₂ flow rate is small, incorporation of small amount of C promoted crystallization of Ti-B-C-N nanocomposite coatings, which resulted in increase of nano-grain size and mechanical properties of coatings. A maximum grain size of about 8 nm was found at a C₂H₂ flux rate of 1 sccm. However, the hardness, elastic modulus and fracture toughness values were not consistent with the grain size. They got to their maximum of 35.7 GPa, 363.1 GPa and 2.46 MPa m^1/2, respectively, at a C₂H₂ flow rate of 2 sccm (corresponding to about 6 nm in nano-grain size). Further increase of C content dramatically decreased not only grain size but also the mechanical properties of coatings. The presently deposited Ti-B-C-N coatings had a smooth surface. The roughness value was consistent with that of grain size.     

Electrodeposited nickel-cobalt composite coating containing MoS2

Ni-Co/MoS₂ composite coatings were prepared by electrodeposition in a Ni-Co plating bath containing nano-sized MoS₂ particles to be co-deposited. The polarization behavior of the composite plating bath was examined on a PAR-273A potentiostat/galvanostat device. The friction and wear behaviors of the Ni-Co/MoS₂ composite coatings were evaluated with UMT-2MT test rig in a ball-on-disk contact mode. The morphologies of the original and worn surfaces of the composite coatings were observed on scanning electron microscope (SEM). It was found that the introduction of MoS₂ nano-particulates in the electrolyte caused the shift towards larger negatives of the reduction potential of the Ni-Co alloy coating, and the co-deposited MoS₂ showed no significant effect on the electrodeposition process of the Ni-Co alloy coating. However, the co-deposited MoS₂ led to changes in the surface morphology and structure of the composite coating as well. Namely, the peak width of the Ni-Co solid solution for the composite coating is broader as compared to that of the Ni-Co alloy coating. The co-deposited MoS₂ particulates were uniformly distributed in the Ni-Co matrix and contributed to increase tribological properties of the Ni-Co alloy coating.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Preparation and wear resistance of pulse electrodeposited Ni-W/Al2O3 composite coatings

The aim of this work is to obtain the electroplating parameters for preparation of Ni-W/Al₂O₃ composite coating with high tungsten content, high micro-hardness and excellent wear resistance by pulse plating procedure. Our results showed that the duty cycle is a dominant parameter for the tungsten content in the coating and the tungsten content increases significantly with increasing duty cycle. The further analysis showed the great influence of tungsten content on micro-hardness of the coating. A maximum micro-hardness of about 859 Hv was obtained in pulse electrodeposited Ni-W/Al₂O₃ composite with tungsten content of 40 wt.% at a peak current density of 20 A/dm², a duty cycle of 80%, a pulse frequency of 1000 Hz and a particle loading of 10 g/L alumina in the plating bath. Although the hardness of Ni-W/Al₂O₃ composite coating was only slightly affected by the alumina content of the deposits prepared in present investigation, the alumina content effect on the tribological characteristic of Ni-W/Al₂O₃ composite coatings is significant. The friction coefficient was lowered to 0.25 and the wear loss was reduced to 1.05 mg by setting the control factors according to the values mentioned above for obtaining the coating with the highest micro-hardness.     

Formation of soot particles in pyrolysis and oxidation of aliphatic and aromatic hydrocarbons: Experiments and detailed kinetic modeling

Experiments on pyrolysis and oxidation of rich mixtures of various aliphatic and simple aromatic hydrocarbons in reflected shock waves have been performed. The mixtures C₂H₂/Ar, C₂H₆/Ar, C₂H₄/Ar, C₂H₄/O₂/Ar, CH₄/Ar, CH₄/O₂/Ar, C₃H₈/Ar, C₃H₆/Ar, toluene/Ar, and benzene/Ar were studied. The yield of soot and the temperature of soot particles were determined experimentally by the double-beam absorption emission method. The kinetic model of soot formation during the pyrolysis and oxidation of rich mixtures of aliphatic and aromatic hydrocarbons complemented with a set of nucleations of soot particles from both polyaromatic fragments and unsaturated aliphatic hydrocarbons was suggested. This kinetic model of soot formation was successfully tested. It describes the experimental literature data on the yield of the products of pyrolysis and oxidation of acetylene and diacetylene in a shock tube. The results of our experiments and kinetic calculations of the time, temperature, and concentration dependences are in good agreement for all hydrocarbons under study. All the kinetic parameters of the model remained strictly constant.     

Structure and mechanical properties of Ni-P electrodeposited coatings

The coatings with different phosphorus contents were obtained by varying the concentration of H₃PO₃ in the electroplating bath. With the increase of phosphorus content, the structure of the Ni-P electrodeposited coatings transformed from microcrystalline to a mixture of nanocrystalline and amorphous phases, then to amorphous phase. A high hardness value of 710 HV_0.1 of as-deposited Ni-P coating was obtained at 8.3 at.% phosphorus content, and high wear resistance was accordingly achieved. The refined nanocrystalline grains with average size of about 7 nm were found to be responsible for the high hardness and improved wear resistance of the as-deposited Ni-P electrodeposited coating.     

Ti-B-C-N纳米复合薄膜结构及力学性能研究

利用反应磁控溅射方法在单晶硅和高速钢(W18Cr4V)基片上制备出不同C含量Ti-B-C-N纳米复合薄膜. 使用X射线衍射和高分辨透射电子显微镜研究了Ti-B-C-N纳米复合薄膜的组织和微观结构,用纳米压痕仪测试了它们的硬度和弹性模量. 结果表明,利用往真空室通入C₂H₂气体的方法制备得到的Ti-B-C-N纳米复合薄膜中,在所研究成分范围内只发现TiN基的纳米晶. 当C₂H₂流量较小时,C元素的加入可以促进Ti-B-C 关键词： Ti-B-C-N薄膜 磁控溅射 微观结构 力学性能     

Process of direct copper plating on ABS plastics

The processes of direct copper plating on ABS plastics were investigated by atomic force microscopy (AFM), ultraviolet-visible absorption spectrometry (UV-vis) and X-ray fluorescence spectroscopy (XRF) techniques. The substrates were etched by CrO₃/H₂SO₄ solution containing Pd²⁺ ions, catalyzed by Pd/Sn colloids solution and accelerated in an alkaline solution containing copper ions. The Pd²⁺ ions in etching solution can reduce the surface roughness and enhance the colloids adsorption. The good dispersivity colloids have excellent catalysis and its UV-vis peaks broaden. After acceleration, when the stability of Cu²⁺-complex is relatively low, Sn²⁺ was oxidized by Cu²⁺ in the alkaline solution meanwhile Cu₂O can be formed. The disproportionation reaction of Cu₂O will proceed and metallic copper forms between the Pd particles, so the conductivity of ABS surface increased. The copper particles play an important role in determining the uniformity of the propagation of copper plating. The particles of copper plating layer were uniformity and fine. The atomic concentration and the thickness of copper layer were analyzed by XRF.