Magnetothermal study of nanocrystalline particle formation in amorphous electroless Ni–P and Ni–Me–P alloys

The microstructure of amorphous Ni–P and Ni–Me–P materials and especially its change during the heat treatment is of great importance for their magnetic, mechanical and corrosion behavior. A new magnetic phase analysis method (magnetothermal) is presented that reveals the precipitation of nanoparticles with strong magnetic properties during phase transformation upon heat treatment. It is applied to electroless Ni–P, Ni–Cu–P and Ni–Sn–P amorphous alloys. The results acquired by this method are compared with data obtained by differential scanning calorimetry, as well as by microhardness measurements using identical heat treatment in all three cases. Due to the high sensitivity of the magnetothermal method a more detailed picture of the precipitation processes in Ni–P alloys is obtained and the new information is discussed. Magnetothermal measurements reveal several stages of precipitation of a phase with strong magnetic properties. This phase is Ni in the Ni–P alloy, and Ni(Me) solid solution in the Ni–Me–P alloys. Though Sn has a stronger effect on the Ni magnetization, Cu is more effective in preventing the appearance of high magnetization in a thermally treated Ni–Cu–P alloy. This is due to Cu incorporation in Ni particles in a quantity above four times larger than Sn.     

Chemical synthesis of TiO2 nanoparticles and their inclusion in Ni–P electroless coatings

The work addresses the preparation of Ni3P3TiO₂ nanocomposite coatings on mild steel substrate by the electroless technique. Nanosized TiO₂ particles were first synthesized by the precipitation method and then were codeposited (4 g/l) into the Ni3P matrix using alkaline hypophosphite reduced EL bath. The surface morphology, particle size, elemental composition and phase analysis of as-synthesized TiO₂ nanoparticles and the coatings were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD). Coatings with 20 µm thickness were heat treated at 400 °C for 1 h in argon atmosphere. The morphology, microhardness, wear resistance and friction coefficient characteristics (ball on disc) of electroless Ni3P3TiO₂ nanocomposite coatings were determined and compared with Ni3P coatings. The results show that as-synthesized TiO₂ nanoparticles are spherical in shape with a size of about12 nm. After heat treatment, the microhardness and wear resistance of the coatings are improved significantly. Superior microhardness and wear resistance are observed for Ni3P3TiO₂ nanocomposite coatings over Ni3P coatings.     

Preparation and characterization of Ni–P/nanodiamond coatings: Effects of surfactants

In this study, the effects of different concentrations of surfactants on the properties of the Ni–P/nanodiamond (ND) coatings were investigated. Sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) were used as the surfactants. Morphology, microhardness and some tribological properties of the coatings were evaluated and compared. Results showed that the composite coatings modified with high concentrations of SDS had smoother surface morphologies than the ones modified with CTAB and low concentrations of SDS. Moreover, it was observed that these coatings had the highest microhardness and wear resistance as well as the lowest friction coefficient (FC) among the coatings. It was found that the effect of NDs on the microhardness of as-plated composite coatings and the ones annealed at 200 °C/3 h was not significant, but became significant when heat treated at 300 °C/1 h and 400 °C/1 h.     

Synthesis,characterization and controlled release properties of zinc–aluminium-beta-naphthoxyacetate nanocomposite

An organic–inorganic nanohybrid nanocomposite was synthesized by co-precipitation method using beta-naphthoxyacetate (BNOA) as guest anion and zinc–aluminium layered double hydroxide (Zn–Al-LDH) as the inorganic host. A well-ordered nanohybrid nanocomposite was formed when the concentration of BNOA was 0.08 M and the molar ratio of Zn to Al, R = 2. Basal spacing of layered double hydroxide containing nitrate ions expanded from 8.9 to 19.5 Å in resulting of Zn–Al-BNOA nanocomposite was obtained indicates that beta-naphthoxyacetate was successfully intercalated into interlayer spaces of layered double hydroxide. It was also found out the BET surface area increased from 1.13 to 42.79 m² g^?1 for Zn–Al-LDH and Zn–Al-BNOA nanocomposite, respectively. The BJH average pore diameter of the synthesized nanocomposite is 199 Å which shows mesoporous-type of material. CHNS analysis shows the Zn–Al-BNOA nanocomposite material contains 36.2 % (w/w) of BNOA calculated based on the percentage of carbon in the sample. Release of BNOA from the lamella of Zn–Al-BNOA was controlled by the zeroth and first order kinetics at the beginning of the deintercalation process up to 200 min and controlled by pseudo-second order kinetics for the whole process. This study suggests that layered double hydroxide can be used as a carrier for organic acid herbicide controlled release formulation of BNOA.     

Corrosion performance of the electroless Ni–P coatings prepared in different conditions and optimized by the Taguchi method

This paper presents an experimental study on the influence of anionic surfactant sodium dodecyl sulfate (SDS), pH, substrate finishing and annealing temperature on the corrosion resistance of electroless nickel phosphorus (Ni–P) coatings using electrochemical techniques and optimization of process parameters based on the Taguchi method. Parameters were selected in three levels and L9 from orthogonal robust array design was used. Corrosion performance of the electroless Ni–P coatings was evaluated by polarization and electrochemical impedance spectroscopy (EIS). Scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis were used for studying surface morphology and chemical composition of the electroless Ni–P coatings. The results showed that SDS surfactant causes increasing of corrosion resistance and improves surface morphology. Finally, optimum conditions were achieved as, surfactant concentration: 1.5 g L⁻¹, pH: 5.5, substrate finishing provided with emery paper no, 2000, and annealing temperature of 200 °C.     

Sol–gel preparation and characterization of antibacterial and self-cleaning hybrid nanocomposite coatings

ZnO–TiO₂, SiO₂–TiO₂, and SiO₂–TiO₂–ZnO hybrid nanocomposite coatings were synthesized based on sol–gel precursors including tetramethoxysilane (TMOS), 3-glycidoxypropyl trimethoxysilane (GPTMS), tetra(n-butyl orthotitanate) (TBT), and zinc acetate dihydrate. The hybrid network was characterized by FTIR, FESEM, and EDAX techniques. Results indicated that inorganic particles’ size was of nanoorder (20–30 nm), with very uniform distribution and dispersion. Photocatalytic and self-cleaning activities of these coatings were further investigated by degradation of methylene blue in an aqueous solution (20 ppm) at visible light irradiation, indicating photocatalytic performance of the coatings containing ZnO and TiO₂ nanoparticles. The antibacterial effect of the coatings was investigated for inhibition and inactivation of cell growth, with the results showing the same antibacterial activity for ZnO–TiO₂ and SiO₂–TiO₂–ZnO coatings against Escherichia coli and Staphylococcus aureus; the activity was, however, higher than that of SiO₂–TiO₂ hybrid nanocomposite coatings.     

Electrochemical characterization of Ni–P and Ni–Co–P amorphous alloy deposits obtained by electrodeposition

Ni–P and Ni–Co–P amorphous alloy deposits were obtained by electrodeposition at 80 °C on carbon steel substrates. The influence of the electrolyte Co²⁺ concentration and of applied current density was investigated. The corrosion behaviour of amorphous and crystalline deposits was evaluated by polarization curves and electrochemical impedance spectroscopy in NaCl 0.1 M solution at room temperature. Impedances were measured for samples under total immersion (free potential against time) and for polarized samples in predefined regions of the polarization curves. It was found that the alloy deposit composition is highly affected by the composition of the electrolyte but displays no significant dependence on applied current density. The results showed that the presence of Co on Ni–P amorphous alloys improves the deposit performance in the studied corrosive medium. It was also verified that the amorphous structure provides higher corrosion resistance to both Ni–P and Ni–Co–P alloys.     

Synthesis and characterization of aluminum oxide–boron carbide coatings by air plasma spraying

Aluminum oxide (Al₂O₃)–boron carbide (B₄C) composites have been proposed for use as cutting tools as well as in high temperature applications due to their high hardness and fracture toughness. The air plasma spraying method was used to fabricate the composite coatings of Al₂O₃ and B₄C. Three different Al₂O₃:B₄C composition ratios of 90:10, 80:20, and 70:30 by weight were plasma sprayed on plain carbon steel substrates. The effect of B₄C content on microstructure, hardness, porosity and thermal diffusivity of the coatings were studied using scanning electron microscopy (SEM), microhardness testing, X-ray diffraction (XRD), and the flash diffusivity method. The plasma spray parameters were optimized in order to achieve a theoretical density of approximately 90%.     

Preparation and characterization of phosphine oxide containing organosilica hybrid coatings by photopolymerization and sol–gel process

A series of UV-cured organic–inorganic hybrid coating materials containing up to 20 wt.% silica were prepared by sol–gel method from tetraethoxy silane (TEOS) which is used as the primary inorganic precursor, and diallylphenylphosphine oxide monomer (DAPPO), aliphatic urethane diacrylate resin (Ebecryl 210) are employed as the source of the organic components. In addition, methacryloxypropyltrimethoxy silane (MAPTMS) was used as both a secondary inorganic source and a silane-coupling agent to improve the compatibility of the organic and inorganic phases. The DAPPO content in all the coating formulations were from 0 to 20 wt.%. The physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. These measurements revealed that all the properties of the hybrid coatings improved effectively, in case of adding the sol–gel precursor and DAPPO monomer content in the hybrid systems. The photo-calorimetric-DSC studies showed that the double bond conversion of the hybrid coatings was faster than the coating materials without silica. The thermal stabilities of the UV-cured hybrid materials were investigated by thermogravimetric analysis. The results showed that the addition of sol–gel precursor and DAPPO into the organic network also improves the thermal-oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Epoxy/polyaniline–ZnO nanorods hybrid nanocomposite coatings: Synthesis,characterization and corrosion protection performance of conducting paints

The objective of this research is the production of an epoxy coating blended with organic–inorganic hybrid nanocomposite as a corrosion inhibiting pigment applied over carbon steel grade ST37. A series of conducting polyaniline (PANI)–ZnO nanocomposites materials has been successfully prepared by an in situ chemical oxidative method of aniline monomers in the presence of ZnO nanorods with camphorsulfonic acid (CSA) and ammonium peroxydisulfate (APS) as surfactant and initiator, respectively. The synthesized polymers were characterized by X-ray diffraction pattern (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA) and electrical conductivity techniques. Synthesized nanocomposites were solved in tetraethylenpentamine (TEPA), and then prepared solution was mixed with epoxy and then was applied as a protective coating on carbon steel plates. The anti-corrosion behavior of the epoxy binder blended with PANI–ZnO nanocomposites were studied in 3.5% NaCl solution at a temperature of 25 °C by electrochemical techniques including electrochemical impedance spectroscopy (EIS) and chronopotentiometry at open circuit potential (OCP). It was observed that the epoxy coating containing conducting PANI–ZnO nanocomposites exhibited higher corrosion resistance and provided better barrier properties in the paint film in comparison with pure epoxy and epoxy/PANI coatings. In the case of conducting coatings, the OCP was shifted to the noble region due to presence of PANI pigments. Additionally, the possibility of formation of a passive film in the presence of PANI was reinforced at the substrate–coating interface. SEM studies taken from surface of the coatings showed that epoxy/PANI–ZnO hybrid nanocomposite coating systems (EPZ) are crack free, uniform and compact. Furthermore, it was found that the presence of ZnO nanorods beside PANI can significantly improve the barrier and corrosion protection performance of the epoxy coating due to the flaky shaped structure of the PANI–ZnO nanocomposites.     

A study on the electrocodeposition processes and properties of Ni�CSiC nanocomposite coatings

Ni–SiC nanocomposite coatings were prepared on a brass substrate by electrocodeposition. The electrodeposition was carried out by adding the SiC nanoparticles to a nickel-containing bath. Nickel deposition processes were analyzed by cathodic polarization curves, and the plating parameters were determined preliminarily by analyzing the effects of different technological parameters on the deposition process. Then, electrocodeposition processes were carried out with different concentrations of SiC nanoparticles in the bath. The effects of current density, stirring rate, and SiC nanoparticle’s concentration in the plating bath on the hardness of coatings were investigated by microhardness tests. Besides the microhardness tests, wearing tests and corrosion tests were also applied to the coatings with the highest hardness and coatings of pure nickel. The structures and surface morphologies of the coatings were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The experimental results show that the microhardness of the codeposited coating increases with increasing current density and attains a maximum at the SiC concentration of 6 g/L. The decrease in the microhardness at higher SiC concentrations may be due to agglomeration of nanosized particles in the plating bath. Increasing the stirring speed did not give a better quality deposition as coatings produced at low stirring rates always had higher microhardness values than did those at high stirring rates. Furthermore, the Ni–SiC nanocomposite coatings have lower friction coefficient and better corrosion resistance than those of pure nickel coatings.     

Properties of electroless and electroplated Ni–P and its application in microgalvanics

Composition, microstructure, surface morphology, mechanical properties and electrochemical behaviour of electroless (el) and electroplated (ep) Ni–P deposits are studied using XPS, SEM–EDX, AFM, nanoindentation measurements, cyclic voltammetry and capacitance measurements. Ni–P layers were compared with ep Ni films and bulk Ni. Ni–P layers prepared by both techniques contain 12–14 wt% phosphorus, present in oxidation states of P⁰ and P³⁻. El and ep Ni–P deposits are amorphous and are characterised by a relatively low average surface roughness (2 and 4 nm, respectively). The ep layers possess a rhythmic-lamellar microstructure indicating a periodic change of electrodeposition conditions. The el Ni–P layers do not show such laminated structure but exhibit small surface pores, which are absent in the ep layers. Comparable values for the hardness and the reduced elasticity modulus of el and ep coatings are determined from the nanoindentation data. The observed small differences indicate that the mechanical properties of Ni–P deposits depend not only on the phosphorus content but also on the deposit microstructure. Microelectrochemical measurements with the so-called droplet cell show that the electrochemical behaviour of both el and ep Ni–P coatings is practically identical and does not depend on the location on the sample surface. Evolution of O₂ and H₂ on Ni–P are similar to pure Ni (ep and bulk), but the corrosion resistance in acid solution is much better. The very similar properties and electrochemical behaviour of el and ep Ni–P deposits suggest that both materials are suitable for various applications in microsystem technology. For different substrates and microstructures of different size and geometry, deposition conditions have still to be optimised.     

Mechanical and tribological characterization of deep eutectic solvent assisted electroless Ni–P-hBN coating

Compositions and processing methods govern various characteristic features of electroless coatings. Electroless nickel–phosphorus (Ni–P) composite coatings containing varying amounts of hBN, deposited using a deep eutectic solvent (DES), achieved better tribological properties as compared to the coating of the same composition deposited in the conventional method. This study also attempted to determine the specific concentration of hBN particles in the electroless bath that deposits Ni–P-hBN coating with a superior combination of mechanical and tribological characteristics. Stronger bond formations of hBN particles in the Ni–P alloy matrix ensured by hBN's metallic behavior potentially influence its tribological properties.     

Deposition,structure and tribological behavior of silver–carbon nanocomposite coatings

Silver–carbon nanocomposite coatings were deposited by plasma-enhanced chemical vapor deposition and d.c. magnetron sputtering of a silver target. Coatings with various metal concentrations were prepared by changing of acetylene and argon gas mixture ratio (C₂H₂/Ar), and concentrations of more than 40 at.%Ag was achieved in this study. Transmission electron microscope revealed that silver metallic grains with typically 15 nm were dispersed in amorphous carbon host matrix. Size of the grains increased with decrease of the gas mixture ratio due to secondary or triangularly formed metal grains. Tribological behavior of the coatings was investigated using reciprocating tribometer with in-situ electrical contact resistance measurement. Low and stable friction coefficient was achieved in the specimen with relatively low Ag concentration. Elemental mapping results on the ball after the friction tests reveal that tribofilm was formed on the ball when low and stable friction was achieved, and the tribofilm was mainly composed of C and Ag. It can be concluded that formation of the tribofilm is necessary for achieving low and stable friction.     

Machine learning-assisted characterization of electroless deposited Ni–P particles on nano/micro SiC particles

In this experiment, Ni–P nanoparticles were deposited (ED) on SiC micro- and nanoparticles with different parameters. Our goal was to successfully prepare metal deposits and develop an effective method for comparing and evaluating the various procedures.During the experimental work, a three-step electroless Ni–P coating process was applied with different concentrations. The coated SiC particles were examined by scanning electron microscopy (SEM). The mass-specific surface area (SSA) of the coated SiC was measured by the Brunauer‒Emmett‒Teller (BET) method, while the volumetric-specific surface area (VSSA) was also calculated. The adhesion between the metal and the ceramic particle was analyzed by X-ray photoelectron spectroscopy (XPS).An image processing macroprogram was created (with a machine learning-based Trainable Weka Segmentation algorithm) to segment the SEM images of the ED metal particles to calculate the specific surface area (S_V).     

Deposition and characterization of nanocrystalline and amorphous Ni–W coatings with embedded alumina nanoparticles

Nanocrystalline and amorphous Ni–W coatings containing Al₂O₃ nanoparticles were electrodeposited from three different ammoniacal citrate baths by direct current (DC) method. The effects of nanoparticles on compositional, structural and morphological features of Ni–W coatings were investigated. The effects of bath chemical composition and current density on codeposition behavior of nanoparticles were also studied. Guglielmi model for particle deposition was applied to identify the kinetics of particle deposition. The presence of nanoparticles may affect on coating grain size, tungsten content and the rate of metal deposition. In addition, nanoparticles can result in more compact coatings with fewer defects. The extent of these effects depends on bath chemical composition and may be influenced by the synergistic effect of Ni on deposition of W. It was also found that the kinetics of particle deposition and the effect of current density on codeposition behavior of nanoparticles are highly dependent on bath chemical composition.     

Electrodeposition of Zn–SiC nanocomposite coatings

Zn–SiC composite coatings were obtained on mild steel substrate by electrodeposition technique with high-current efficiency. A slightly acidic chloride bath, containing SiC nanoparticles and gelatine as additive, was used. The electrodeposition was carried out under galvanostatic control with pulsed direct current; the effect of experimental parameters (temperature, average current density and particles concentration) on composition, morphology and structure of the deposit was studied. Coatings were characterized by means of scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry and Vickers microhardness measurements. Zn–SiC electrodeposits with the best characteristics were obtained by performing electrodepositions at 45 °C, with 20 g L^?1 SiC in the bath and with average current density in the range 100–150 mA cm^?2. Under these experimental conditions, homogeneous and compact coatings, with low-grain size and SiC content ranging from 1.7 to 2.1 wt%, were found to be electrodeposited. Microhardness measurements showed for these deposits an increase of about 50 % with respect to those without nanoparticles obtained in the same experimental conditions.     

Direct and pulse current electrodeposition of Ni–W–TiO2 nanocomposite coatings

Ni–W–TiO₂ nanocomposite coatings have been obtained on mild steel surface by direct current (DC) and pulse current (PC) electrodeposition from Watts bath containing an ammonical citrate complexing agent. The morphology of the coatings was explored by scanning electron microscopy (SEM), atomic force microscopy (AFM) and the composition of the electrodeposits was analyzed by energy dispersive X-ray analysis (EDX). Surface morphology studies revealed that Ni–W alloy surface was covered by long needle like crystals and Ni–W–TiO₂ composite coatings with smaller spherical sized grains. The coated surface contained 25.55% W and 5.55% Ti. XRD studies revealed that (111) plane was predominant in both Ni–W alloy deposits and Ni–W–TiO₂ composite coatings. The patterns of the electrodeposits confirmed only fcc frame work structure. Microhardness values increased with TiO₂ addition in the alloy. The corrosion resistance of Ni–W alloy deposit and TiO₂ incorporated coatings was evaluated by Potentiodynamic polarization studies in 3.5% NaCl solutions. Corrosion current densities decreased with TiO₂ inclusion in the alloy deposit. Electrochemical impedance studies revealed that the charge transfer resistance increased with TiO₂ inclusion in the alloy deposits while the double layer capacitance decreased. The PC composites coatings offer uniform surface, high microhardness and enhanced corrosion resistance than DC composites coatings.     

Synthesis and characterization of hyperbranched polyester–urethane–urea/K10-clay hybrid coatings

A series of hyperbranched polyester–urethane–urea/K10-clay hybrid coatings (AHBPE-1 and AHBPE-2) have been prepared. Initially, the polyester polyols are synthesized separately in a step-wise manner using pentaerythritol (PE), phtallic anhydride (PTA) and trimethylol propane (TMP). The cetyltrimethylammonium bromide (CTAB) modified K10-clay is used as an organoclay for the hybrid composites preparation and dispersed into the polyester matrix by ultrasonication method. This clay-dispersed polyols are used for further synthesis. The degree of branching (DB), percentage of condensation reaction and quantity of dendritic (D), terminal (T) and linear (L) units present in the polyester are calculated, from the NMR peak integration value. The NMR result suggests that, there is formation of nearly 63% of condensation product in the polyester. A structure–property correlation is established, based on the hydrogen bonding effect with increasing clay content by using the FT-IR peak deconvulation technique. The dynamic mechanical and thermal analysis (DMTA) as well as thermo gravimetric analysis (TGA) results show, an increase in room temperature storage modulus (E′), glass transition temperature (T_g) and thermal stability of the hybrid coatings with increasing clay content and NCO/OH ratio. The contact angle measurement study suggests that, the hydrophilicity of the hybrid films increases with increasing clay content and decreases with increasing NCO/OH ratio.