Development of electroless Ni-Zn-P/nano-TiO2 composite coatings and their properties

Ni-Zn-P-TiO₂ composite coatings were successfully obtained on low carbon steel by electroless plating technique. Deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis (EDS) studies. The hardness and microstructure of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ composite coatings were analyzed. The change in microstructure and higher hardness was noticed for heat treated composite. The corrosion resistance behavior of as plated and heat treated Ni-Zn-P and Ni-Zn-P-TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5 wt% NaCl solution. The composite coating exhibited enhanced corrosion resistance property over Ni-Zn-P coating.     

Electrodeposition and tribological properties of Ni-SrSO4 composite coatings

Ni-SrSO₄ composite coatings were electrodeposited on superalloy Inconel 718 from a Watts electrolyte containing a SrSO₄ suspension. Ni-SrSO₄ coatings were investigated by scanning electron microscope, microhardness tester, and friction and wear tester in sliding against a bearing steel ball under unlubricated condition. The incorporation of SrSO₄ into Ni matrix increases the microhardness of electrodeposited coatings. Ni-SrSO₄ composite coating exhibits a distinctly low friction coefficient and a small wear rate as contrasted with pure Ni coating and the substrate. The effect of SrSO₄ particles on microstructure and tribological properties of Ni-SrSO₄ composite coatings is discussed.     

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.     

Influence of heat treatment on tribological properties of electroless Ni-P and Ni-P-Al2O3 coatings on Al-Si casting alloy

Evolution of tribological properties of electroless Ni-P and Ni-P-Al₂O₃ coating on an Al-10Si-0.3Mg casting alloy during heat treatment is investigated in this work. The pre-treated substrate was plated using a bath containing nickel hypophosphite, nickel lactate and lactic acid. For preparation of fiber-reinforced coating Al₂O₃ Saffil fibers pre-treated in demineralised water were used. The coated samples were heat treated at 400-550 °C/1-8 h. Tribological properties were studied using the pin-on-disc method. It is found that the best coating performance is obtained using optimal heat treatment regime (400 °C/1 h). Annealing at higher temperatures (450 °C and above) leads to the formation of intermetallic compounds that reduce the coating wear resistance. The reason is that the intermetallic phases adversely affect the coating adherence to the substrate. The analysis of wear tracks proves that abrasion is major wear mechanism, however due to the formed intermetallic sub-layers, partial coating delamination may occur during the pin-on-disc test on the samples annealed at 450 °C and above. It was found that fiber reinforcement reduces this scaling and increases wear resistance of coatings as compared to the non-reinforced Ni-P coatings.     

Microstructure and properties of Ni-Co/nano-Al2O3 composite coatings by pulse reversal current electrodeposition

Ni-Co/nano-Al₂O₃ (Ni-Co/Al₂O₃) composite coatings were prepared under pulse reversal current (PRC) and direct current (dc) methods respectively. The microstructure of coatings was characterized by means of XRD, SEM and TEM. Both the Ni-Co alloy and composite coatings exhibit single phase of Ni matrix with face-centered cubic (fcc) crystal structure, and the crystal orientation of the Ni-Co/Al₂O₃ composite coating was transformed from crystal face (2 0 0) to (1 1 1) compared with alloy coatings. The hardness, anti-wear property and macro-residual stress were also investigated. The results showed that the microstructure and performance of the coatings were greatly affected by Al₂O₃ content and the electrodeposition methods. With the increasing of Al₂O₃ content, the hardness and wear resistance of the composite coatings enhanced. The PRC composite coatings exhibited compact surface, high hardness, better wear resistance and lower macro-residual stress compared with that of the dc composite coatings.     

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.     

Electrodeposition and properties of Zn-nanosized TiO2 composite coatings

Nanosized TiO₂ particles were prepared by sol-gel method. The TiO₂ particles were co-deposited with zinc from a sulphate bath at pH 4.5 using electrodeposition technique. The corrosion behavior of the coatings was assessed by electrochemical polarization, impedance, weight-loss and salt spray tests. Wear resistance and microhardness of the composite coating was measured. The smaller grain size of the composite coatings was observed in the presence of TiO₂ and it was confirmed by the images of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.     

Tribological properties of heat-treated electroless Ni-P coatings on AZ91 alloy

Influence of heat treatment regime on adhesion and wear resistance of Ni-P electroless coating on AZ91 magnesium alloy is investigated in this work. The pretreated substrate was plated using a bath containing nickel sulphate, sodium hypophosphite and sodium acetate as main constituents. The coated samples were heat treated at 400-450 °C for 1-8 h. Adhesion of coating was estimated from the scratch test with an initial load of 8.80 N. Wear resistance was studied using the pin-on-disc method. It was found that there is no significant dependence of the coating wear resistance on heat treatment regime, as the formation of Al-Ni intermetallic sub-layers that reduce coating adhesion is limited to regions where Al₁₇Mg₁₂ phase is present in the substrate. Moreover, the coating shows good sliding properties due to the formation of oxide glazes in the wear track.     

Structure and infrared emissivity of collagen/SiO2 composite

Collagen/SiO₂ composites were prepared in aqueous suspensions. Adsorption behaviors of collagen onto the surfaces of SiO₂ spheres were studied. Structure and thermal properties were measured with FTIR, SEM, TEM, and TGA-DTA. The results showed that the self-aggregation of collagen macromolecules was taken place during the adsorption of collagen on SiO₂ sphere. The morphology of collagen evolved from line to microfibrils with the increase in the concentration of collagen along with the distortion of SiO₂. Interfacial interactions of electrostatic forces and hydrogen bonding between the collagen macromolecule and SiO₂ sphere had a vital effect on the adsorption of collagen. The amount of the collagen adsorption was increased with the increase of the collagen concentration, yet decreased in increased pH value of the solution. It was found that the composites exhibited lower infrared emissivity values in the wavelength ranged from 8 to 14 μm than not only pure collagen but also SiO₂ sphere, and the value of infrared emissivity was related to the adsorption amount of collagen in the composites.     

Preparation and characterization of SiO2/ZrO2/Ag multicoated microspheres

A new type of multicoated silica/zirconia/silver (SiO₂/ZrO₂/Ag) core-shell composite microspheres is synthesized in this paper. In the process, ZrO₂-decorated silica (SiO₂/ZrO₂) core-shell composites were firstly fabricated by the modification of zirconia on silica microspheres through the hydrolysis of zirconium precursor. Subsequently, on SiO₂/ZrO₂ composite cores, silver nanoparticles were introduced via ultrasonic irradiation and acted as “Ag seeds” for the formation of integrate silver shell by further reduction of silver ions using formaldehyde as reducer. The resulting samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared, energy-dispersive X-ray, and UV-vis spectroscopy, indicating that zirconia and silver layers were successfully coated on the surfaces of silica microspheres.     

Microstructures and tribological properties of plasma sprayed WC-Co-Cu-BaF2/CaF2 self-lubricating wear resistant coatings

A promising WC-Co-Cu-BaF₂/CaF₂ self-lubricating wear resistant coating was deposited via atmospheric plasma spraying (APS) process by using homemade feedstock powders composed of WC-Co, Cu and BaF₂/CaF₂ eutectic. The as-prepared cermet coatings had better frictional behavior comparing with the WC-Co coating. Moreover, the often-occurred decarburization of WC in APS process was noticeably improved due to the binding of copper and BaF₂/CaF₂ phase, which not only offered effective solid lubrication, but also acted as bind phases to mend the microstructure and protected WC from decomposition. The optimized specimen contained 10 wt.% Cu and 10 wt.% BaF₂/CaF₂ in a WC-Co matrix, which had excellent frictional and wear performance. The wear mechanism of the self-lubricating wear resistant coating was discussed with the microstructures, compositions and mechanical properties of the composite materials in detail.     

Microstructure and properties of TiB2-containing coatings prepared by arc spraying

Low cost arc spraying and cored wires were used to deposit composite coatings consisting of TiB₂ and TiB₂/Al₂O₃ hard particles in a Ni(Cr) and stainless steel 304L matrix. Four coatings were prepared namely Ni(Cr)-TiB₂, Ni(Cr)-TiB₂/Al₂O₃, 304L-TiB₂ and 304L-TiB₂/Al₂O₃. The microstructural characteristics of powders and coatings were observed by scanning electron microscopy (SEM). Phase compositions of powders were analyzed by X-ray diffraction (XRD). Although all the analyzed coatings exhibited similar lamella structure, remarkable differences not only in the morphology of hard phase and matrix but also in the size and distribution of hard phases were observed from one coating to another. Tribological behavior of the coatings was analyzed in room temperature dry sliding wear tests (block-on-ring configuration), under 75 N at low velocity (0.5 m/s). The coatings showed far high wear resistance than low carbon steel substrate under same conditions examined. Wear loss of 304L-TiB₂ and Ni(Cr)-TiB₂ coatings were lower nearly 15 times than that of steel substrate. TiB₂ hard phases in coatings bonded well with metal matrix contributed to high wear resistance.     

XPS investigation of diffusion of two-layer ZrO2/SiO2 and SiO2/ZrO2 sol–gel films

Two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were deposited on K9 glass substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy (XPS) technique was used to investigate the diffusion of ZrO₂/SiO₂ and SiO₂/ZrO₂ films. To explain the difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films, porous ratio and surface morphology of monolayer SiO₂ and ZrO₂ films were analyzed by using ellipsometry and atomic force microscopy (AFM). We found that for the ZrO₂/SiO₂ films there was a diffusion layer with a certain thickness and the atomic concentrations of Si and Zr changed rapidly; for the SiO₂/ZrO₂ films, the atomic concentrations of Si and Zr changed relatively slowly, and the ZrO₂ layer had diffused through the entire SiO₂ layer. The difference of diffusion between ZrO₂/SiO₂ and SiO₂/ZrO₂ films was influenced by the microstructure of SiO₂ and ZrO₂.     

Deposition and characterization of binary Al2O3/SiO2 coating layers on the surfaces of rutile TiO2 and the pigmentary properties

Binary Al₂O₃/SiO₂-coated rutile TiO₂ composites were prepared by a liquid-phase deposition method starting from Na₂SiO₃·9H₂O and NaAlO₂. The chemical structure and morphology of binary Al₂O₃/SiO₂ coating layers were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, TG-DSC, Zeta potential, powder X-ray diffraction, and transmission electron microscopy techniques. Binary Al₂O₃/SiO₂ coating layers both in amorphous phase were formed at TiO₂ surfaces. The silica coating layers were anchored at TiO₂ surfaces via Si-O-Ti bonds and the alumina coating layers were probably anchored at the SiO₂-coated TiO₂ surfaces via Al-O-Si bonds. The formation of continuous and dense binary Al₂O₃/SiO₂ coating layers depended on the pH value of reaction solution and the alumina loading. The binary Al₂O₃/SiO₂-coated TiO₂ composites had a high dispersibility in water. The whiteness and brightness of the binary Al₂O₃/SiO₂-coated TiO₂ composites were higher than those of the naked rutile TiO₂ and the SiO₂-coated TiO₂ samples. The relative light scattering index was found to depend on the composition of coating layers.     

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.     

Preparation and characterization of PES/TiO2 composite membranes

Polyethersulfone (PES)/TiO₂ composite membranes were prepared by phase inversion method with nano-TiO₂ as additive. The influence of TiO₂ on the morphologies and the performances of PES/TiO₂ membranes were investigated through the methods of SEM, XRD, TGA, contact angle goniometer, mechanical strength tests and filtration experiments. The results showed that the structure of membrane was not obviously affected by addition of TiO₂, and the performances such as hydrophilicity, thermal stability, mechanical strength and anti-fouling ability of membrane were enhanced through adding TiO₂ nanoparticles. At 0.5 wt.% TiO₂ content, the composite membrane has an excellent performance, however higher TiO₂ content (than 0.5 wt.%) resulted in defective pore structure of the membranes and decline of the performances, such as permeability and mechanical strength. TGA and mechanical strength analyses indicated good compatibility between polymers and TiO₂ nanoparticles.     

Effects of coating parameters on the morphology of SiO2-coated TiO2 and the pigmentary properties

SiO₂-coated TiO₂ powders were prepared by the chemical deposition method starting from rutile TiO₂ and Na₂SiO₃. The SiO₂-coated TiO₂ powders were characterized by X-ray photoelectron spectroscopy, Zeta-potential analysis, Fourier transform infrared spectroscopy, and transmission electron microscopy. The evolution of island-like and uniform coating layers was found to depend upon the ratio of Na₂SiO₃ to TiO₂, reaction temperature, and pH. The whiteness and brightness of the SiO₂-coated TiO₂ powders increased in response to an increase in the SiO₂ loading, but there was a maximum value among the light scattering indexes. The SiO₂-coated TiO₂ powders possessed more negative Zeta potentials than the naked TiO₂. The dispersibility of the SiO₂-coated TiO₂ powders with the continuous and uniform SiO₂ coating layers was higher than that of the naked TiO₂ and the SiO₂-coated TiO₂ powders with the island-like SiO₂ coating layers.     

Preparation and characterization of amine-functionalized SiO2/TiO2 films for formaldehyde degradation

This paper investigated the gaseous formaldehyde degradation by the amine-functionalized SiO₂/TiO₂ photocatalytic films for improving indoor air quality. The films were synthesized via the co-condensation reaction of methyltrimethoxysilane (MTMOS) and 3-aminopropyltrimethoxysilane (APTMS). The physicochemical properties of prepared photocatalysts were characterized with N₂ adsorption/desorption isotherms measurement, X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FT/IR). The effect of amine-functional groups and the ratio of MTMOS/APTMS precursors on the formaldehyde adsorption and photocatalytic degradation were investigated. The results showed that the formaldehyde adsorption and photocatalytic degradation of the APTMS-functionalized SiO₂/TiO₂ film was higher than that of SiO₂/TiO₂ film due to the surface adsorption on amine sites and the relatively high of the specific surface area of the APTMS-functionalized SiO₂/TiO₂ film (15 times higher than SiO₂/TiO₂). The enhancement of the formaldehyde degradation of the film can be attributed to the synergetic effect of adsorption and subsequent photocatalytic decomposition. The repeatability of photocatalytic film was also tested and the degradation efficiency was 91.0% of initial efficiency after seven cycles.     

A facile synthesis of monodisperse CoFe2O4/SiO2 nanoparticles

Aminated-CoFe₂O₄/SiO₂ magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. By optimizing the preparation conditions, monodisperse CoFe₂O₄/SiO₂ NPs with high amino groups’ density were obtained, which is necessary for enzyme immobilization. TEM confirm that the sample is a core/shell structure. These aminated-CoFe₂O₄/SiO₂ NPs have narrow size distributions with a mean size of about 60 nm. Moreover, the aminated-CoFe₂O₄/SiO₂ NPs can be easily dispersed in aqueous medium. The experimental results also show that the NPs have superparamagnetism, indicating that the aminated-CoFe₂O₄/SiO₂ NPs can be used as an effective carrier for the enzyme immobilization.     

Development and evaluation of electroless Ag-PTFE composite coatings with anti-microbial and anti-corrosion properties

Electroless Ag-polytetrafluoroethylene (PTFE) composite coatings were prepared on stainless steel sheets. The existence and distribution of PTFE in the coatings were analysed with an energy dispersive X-ray microanalysis (EDX). The contact angle values and surface energies of the Ag-PTFE coatings, silver coating, stainless steel, titanium and E. coli Rosetta were measured. The experimental results showed that stainless steel surfaces coated with Ag-PTFE reduced E. coli attachment by 94-98%, compared with silver coating, stainless steel or titanium surfaces. The anti-bacterial mechanism of the Ag-PTFE composite coatings was explained with the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The anticorrosion properties of the Ag-PTFE composite coatings in 0.9% NaCl solution were studied. The results showed that the corrosion resistance of the Ag-PTFE composite coatings was superior to that of stainless steel 316L.