Morphological and electrochemical characterization of electrodeposited Zn–Ag nanoparticle composite coatings

Silver nanoparticles with an average size of 23 nm were chemically synthesized and used to fabricate Zn–Ag composite coatings. The Zn–Ag composite coatings were generated by electrodeposition method using a simple sulfate plating bath dispersed with 0.5, 1 and 1.5 g/l of Ag nanoparticles. Scanning electron microscopy, X-ray diffraction and texture co-efficient calculations revealed that Ag nanoparticles appreciably influenced the morphology, micro-structure and texture of the deposit. It was also noticed that agglomerates of Ag nanoparticles, in the case of high bath load conditions, produced defects and dislocations on the deposit surface. Ag nanoparticles altered the corrosion resistance property of Zn–Ag composite coatings as observed from Tafel polarization, electrochemical impedance analysis and an immersion test. Reduction in corrosion rate with increased charge transfer resistance was observed for Zn–Ag composite coatings when compared to a pure Zn coating. However, the particle concentration in the plating bath and their agglomeration state directly influenced the surface morphology and the subsequent corrosion behavior of the deposits.     

Synthesis,characterization and surface modification of ZnCrFeO4 nanoparticles

The aim of this research was to investigate zinc chromium ferrite (ZnCrFeO₄) nanoparticles, synthesized using the sol gel technique with nanoparticle size controlled through a two-stage annealing process. Stage one was a low temperature firing which produced low quality nanocrystals with an average size of 15 nm. This was followed by a second firing stage at high temperature which enhanced the crystal quality. The nanoparticles were then coated with a bio-compatible shell to form a stable suspension in the ferrofluid carrier. The resulting nanoparticles were found by electron microscopy, atomic force microscopy and X-ray diffraction studies to have excellent crystal quality. The average size was 8.5 nm. Preliminary cell culture studies indicated the ZnCrFeO₄ nanoparticles were non-toxic. The relatively high measured value of the relaxivity r₂ showed that the nanoparticle coating was effective in substantially reducing aggregation and enhancing the properties of the nanoparticles associated with contrast enhancement in MRI.     

Fabrication of thermochromic composite using monodispersed VO2 coated SiO2 nanoparticles prepared by modified chemical solution deposition

Monodispersed thermochromic VO₂ particles were fabricated by VO₂ coating onto monodispersed SiO₂ nanoparticles with the modified chemical solution deposition technique using vanadium isopropoxide solution and monodispersed SiO₂ particle suspension solution. The average size of the resultant VO₂–SiO₂ particle was 57 nm and the coating thickness of the VO₂ layer was 6 nm. A thermochromic composite was fabricated using the VO₂–SiO₂ particles and a poly lactose acid polymer as a transparent matrix, and the transmittance of the composite at a high temperature was 10% less than that at a low temperature.     

Antimicrobial activity of composite nanoparticles consisting of titania photocatalytic shell and nickel ferrite magnetic core

Reverse micelle and hydrolysis have been combined to synthesize composite nanoparticles consisting of anatase–titania photocatalytic shell and nickel ferrite magnetic core. The average particle size of the composite nanoparticles was in the range of 10–15 nm. The photocatalytic shell of titania is responsible for the photocatalytic and anti-microbial activity and nickel ferrite magnetic core is responsible for the magnetic behavior, studied by superconducting quantum interference device. The anatase TiO2 coated NiFe₂O₄ nanoparticles retains the magnetic characteristics of uncoated nanocrystalline nickel ferrites, superparamagnetism (absence of hysteresis, remanence and coercivity at 300 K) and non-saturation of magnetic moments at high field. The magnetic measurements results encourage their application as removable anti-microbial photocatalysts. Bacterial inactivation with UV light in the presence of titania-coated NiFe₂O₄ nanoparticles is faster than the action with UV light alone.     

Electroless deposition of Ni–W–P–B4C nanocomposite coating on AZ91D magnesium alloy and investigation on its properties

In the present work, electroless deposition of quaternary Ni–W–P–B₄C composite coatings on AZ91D magnesium alloy was investigated. The coatings were characterized to study their microstructure, crystallite size, morphology, microhardness and corrosion resistance and compared with Ni–P and Ni–P–B₄C composite coatings, prepared with the same method. The hardness of the Ni–W–P–B₄C composite coatings was around 1290 MPa which was more than that of the Ni–P and Ni–P–B₄C coatings (about 700 and 1200 MPa, respectively). According to polarization test results, the Ni–W–P–B₄C composite coating exhibits less and more corrosion rates with respect to the Ni–P–B₄C and the Ni–P coatings, respectively. X-ray diffraction (XRD) analysis results for the Ni–W–P–B₄C coating showed that the Ni–W–P–B₄C coating has a combination of amorphous and nanocrystalline structures. Also, Williamson–Hall analysis on the X-ray patterns revealed that the Ni–W–P–B₄C coating has an average crystallite size of 1.5 nm.     

Preparation of cobalt ferrite nanoparticles by using spent Li-ion batteries

Cobalt ferrite nanoparticles are a soft magnetic material have been extensively used in many electronic and magnetic applications. In this study, Co_0.8Fe_2.2O₄ nanoparticles with particle size of about 23.5 nm were directly synthesized by sol–gel auto-combustion and calcination methods using spent Li-ion batteries as raw materials. The overall process involves four steps: formation of homogeneous sols; formation of dried gels; combustion of the dried gels; and calcination of the dried gels after combustion at 1173 K for 2 h. The DTA–TG and IR were used to study the auto-combustion and thermal decomposition of the precursor, the morphology and structure of cobalt ferrite nanoparticles were characterized by XRD and TEM techniques. Moreover, the precise metal ion stoichiometry of cobalt ferrite nanoparticles was analyzed by ICP. The results revealed that the auto-combustion process was considered as a heat-induced exothermic oxidation–reduction reaction between nitrate ions and carboxyl group. The XRD patterns of calcination the dried gels after combustion confirmed the single phase spinel structure for the synthesized materials. The crystallite size was calculated from the most intense peak (3 1 1) using the Scherrer equation. The TEM photograph also shown that cobalt ferrite nanoparticles were well-dispersed and with little aggregation.     

Microstructural and electrical properties of varistors prepared from coated ZnO nanopowders

This paper describes a solution-based technique for fabrication of varistor grade composite nanopowders. The method consists of coating major varistor dopants on the surface of the ZnO nanoparticles. As a result, a homogenous mixture of dopants and ZnO nanoparticles will be achieved. TEM results indicated that a composite layer of dopants with the average particle size of 9 nm on the surface of ZnO nanoparticles has been successfully prepared. Sintering of the coated powders was performed in temperatures as low as 850 °C and final specimens with average particle size of 900 nm and density of 98.5% were achieved. In comparison to conventional mixing, varistors prepared from coated nanopowders exhibited superior electrical properties and microstructure homogeneity. The improvement of electrical properties can be attributed to small grain size, homogenous distribution of dopants and elimination of large Bi-Pockets. In addition, the processing route of schottky barrier formation is quite different from what is generally considered as the method of barrier formation in ZnO grain boundaries.     

Decorating carbon nanotubes with Cobalt nanoparticles

A magnetic composite of multiwalls carbon nanotubes (MWNTs) decorated with Cobalt nanoparticles was synthesized successfully by a simple chemical precipitation and deoxidization method. The composite was analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The pattern of XRD indicated that MWNTs and Cobalt nanoparticles coexisted in the composite. The TEM images revealed that the Cobalt nanoparticles were distributed on the surface of the MWNTs, with the size ranging from 5 to 15 nm. The hysteresis loops of the decorated MWNTs were measured by a vibrating sample magnetometer (VSM), the ferromagnetic signature emerged with the saturated magnetization of 5.8 emu/g, and the coercive of 310 Oe.     

SiO2或TiO2纳米粒子/含氟聚丙烯酸酯复合涂层的制备及其防腐蚀性能

通过在含氟聚丙烯酸酯(PFHI)溶液中添加固体纳米粒子,经涂覆热固化后得到了厚度约为1 μm的SiO₂或TiO₂纳米粒子/PFHI复合涂层,考察了SiO₂或TiO₂两种纳米粒子质量分数对复合涂层表面性质和防腐蚀性能的影响。利用Tafel极化曲线和电化学交流阻抗(EIS)测试研究了复合涂层在3.5wt% NaCl溶液中的电化学防腐蚀性能,并运用XPS、衰减全反射傅里叶变换红外光谱(ATR-FTIR)、TG-DTA、SEM、光学接触角(OCA)手段对复合涂层进行表征。结果表明,添加SiO₂或TiO₂纳米粒子均可大幅提高PFHI涂层的电化学防腐蚀性能,SiO₂与PFHI质量比为0.3的SiO₂/PFHI复合涂层电荷转移阻抗值R_ct与PFHI涂层相比上升了2个数量级。SiO₂或TiO₂纳米粒子增大了涂层表面粗糙度,与PFHI紧密结合形成致密的复合涂层,提高了涂层的疏水性和致密性,从而改善了涂层的抗腐蚀性能。      

Wear behaviors of Fe-based amorphous composite coatings reinforced by Al2O3 particles in air and in NaCl solution

In this paper, the influence of the addition of Al₂O₃ particles on the microstructure and wear properties of Fe-based amorphous coatings prepared by high velocity oxygen fuel (HVOF) has been studied. The wear behaviors of the composite coatings were evaluated against Si₃N₄ in a pin-on-disk mode in air and in 3.5 wt.% NaCl solution. It was found that the Al₂O₃ particles were homogenously distributed in the amorphous matrix and the composite coatings exhibited improved wear resistance and reduced coefficient of friction (COF) in both air and wet conditions as compared to the monolithic amorphous coating. The composite coating reinforced with 20 wt.% Al₂O₃ particles exhibit the best wear performance, which, for example, has extremely low COF (< 0.2) and high wear resistance (2–3 times higher than monolithic amorphous coating). Detailed analysis on the worn surface indicated that the wear mechanism for the amorphous and composite coatings is similar and is dominated by oxidative delamination in air and by corrosion wear in 3.5% NaCl solution. The enhanced wear resistance is mainly attributed to the addition of Al₂O₃ particles which exhibit high hardness, good corrosion resistance and excellent chemical and thermal stability.     

Effect of TiO2 nanoparticles aggregation in silicate thin coating films on photocatalytic behavior for antifouling materials

Two types of disperser namely, a high speed agitation bead mill and a colloidal mill, were used for the dispersion behavior control of TiO₂ nanoparticles (20 nm in average primary diameter) in an aqueous suspension. A composite thin film raging in thickness from 90 to 400 nm was prepared from the coating suspension following the addition of a commercial ethyl silicate oligomer binder into the prepared suspension by means of a spray coating method. The mean aggregate size of TiO₂ nanoparticles in the aqueous suspension was found to be 80 nm and 290 nm in diameter, respectively, when using the agitated bead and colloidal milling methods. Large aggregates on the order of several hundred nanometers were found to remain in the suspension after colloidal milling. Further, a fine dispersion of TiO₂ nanoparticles in the thin film produced using the agitation bead milling process promoted the photocatalytic activity and enhanced transparency of the film for visible light. The aggregate structure of TiO₂ nanoparticles in an aqueous suspension was well maintained in the film prepared by a spray coating process.     

Coating of TiO2 nanoparticles with PbS thin films and preparation of PbS nanoparticles using a one-pot sonochemical reaction under the multibubble sonoluminescence conditions

Preparations of PbS-coated titanium dioxide (TiO₂) and lead sulfide (PbS) nanoparticles under ultrasonic field at the multibubble sonoluminescence (MBSL) conditions were tested in water solutions. Under the optimal MBSL conditions (20 kHz and 220 W power input), PbS nanoparticles (diameter = 40-50 nm) were prepared by treating lead nitrate and thioacetamide for 20 min in water solutions. The size of PbS nanoparticles was found to be easily increased to about 90 nm in diameter by increasing the reactant concentration twice. A similar sonochemical reaction with TiO₂ nanoparticles (about 20-30 nm in diameter) gave rise to PbS-coated TiO₂ nanoparticles with a core/shell structure. The PbS thin film coating was quite uniform and the average coating depth of PbS on the TiO₂ nanoparticles was about 2-3 nm under the described conditions. It is interesting to note that the coating depth was found to be controlled to 2-10 nm range by increasing the amounts of reactants for Pb and S twice with a sonication time of 30 min.     

SiO2粒径对Ni-Co-SiO2复合镀层性能的影响

长期暴露在海洋环境中的钢质紧固件的腐蚀问题严重影响了海洋工程装备和设施的服役安全性。电镀合金镀层是紧固件常用的防护方法,其中,镍钴合金镀层具有较好的耐蚀性。通过向Ni-Co镀液中添加不同粒径的SiO₂颗粒,利用电沉积技术在45钢基体上制备Ni-Co-SiO₂复合镀层。之后,分析了SiO₂粒径对复合镀层表面形貌和显微结构的影响,评价了复合镀层在3.5%（w）的NaCl溶液中的耐蚀性能,并对复合镀层的显微硬度和摩擦系数进行了测试。结果表明,随着镀液中SiO₂粒径的增大,复合镀层表面的SiO₂分布均匀性先增大后减小,当SiO₂粒径为70 nm时,镀层表面形成较完整的SiO₂膜层。动电位极化和电化学阻抗谱测试表明,掺杂70 nm的SiO₂的复合镀层具有最好的耐蚀性。随着镀液中SiO₂粒径增大,复合镀层的硬度逐渐降低,但其对摩擦系数的影响较小。      

Effect of nano-TiO2 particles size on the corrosion resistance of alkyd coating

The coating system containing various sizes (∼10, 50, 100, 150 nm) of nano-TiO₂ were prepared and investigated for corrosion protection of carbon steel in 1.0 M H₂SO₄ using polarization, EIS and transmission electron microscopy (TEM) techniques. It was found that nano-TiO₂ particles improved the corrosion resistance of alkyd coatings. The corrosion resistance occurs via physical adhesion on the metal surface. O₂ and H₂O permeability of coating decreased with decrease in the nano-TiO₂ size. The inhibition efficiency was found to increase with decreasing the size of nano-TiO₂ and with decreasing the temperature.     

电化学方法评价纳米炭黑复合涂料的防腐性能

通过表面接枝改性获得了亲油性的纳米炭黑粒子,扫描探针显微镜(SPM)和透射电镜(TEM)测试结果表明:炭黑粒子的尺寸为24～300nm.在超声场下,将纳米炭黑均匀分散到醇酸调和漆中,制备了纳米炭黑复合涂料,抗Cl-离子腐蚀能力提高.采用电化学方法(阳极极化和交流阻抗)对纳米复合涂料的耐蚀性进行了评价,测试结果与浸泡腐蚀实验结果完全一致.     

Low temperature fabrication of ZnO-whey protein isolate nanocomposite

Nanocrystalline zinc oxide (ZnO) particles coated with whey protein isolate (WPI) were fabricated in the weak basic aqueous solution condition at near room temperature. The X-ray diffraction and transmission electron microscopy measurements confirmed the nanoscaled composite structure of ZnO-WPI. The average composite granules size was about 300 nm and the embedded ZnO nanoparticles were uniform and monodisperse with an average diameter of 65 nm.     

Micelle based synthesis of cobalt ferrite nanoparticles and its characterization using Fourier Transform Infrared Transmission Spectrometry and Thermogravimetry

Cobalt ferrite (CoFe₂O₄) nanoparticles of average size 4 nm with narrow size distribution are synthesized by reverse micelle approach. The nanoparticles are characterized using powder X-ray diffraction (XRD), Dynamic Light Scattering (DLS), Theromogravimetric analysis (TGA) and Fourier Transform Infrared Transmission Spectrometry (FTIR). Three successive transformations are observed in the thermogram that correspond to the loss of solvent and surfactant; onset of the amorphous to crystallize conversion; and isochemical transformation, i.e. migration of cations between octahedral and tetrahedral sites in the inverse spinel structure. The isochemical transformation is further confirmed by FTIR. The IR absorption bands observed at 460 and 615 cm⁻¹ in the as-prepared CoFe₂O₄ nanoparticles correspond to the ferrite skeleton of octahedral and tetrahedral sites, respectively. The peak intensity at 615 and 460 cm⁻¹ is shifted to 601 and 440 cm⁻¹, respectively upon annealing at 320 and 400 °C. These results confirm migration of cations from the octahedral to the tetrahedral sites.     

Effect of divalent metal hydroxide solubility product on the size of ferrite nanoparticles

We study the effect of divalent metal hydroxide solubility product on the size and magnetic properties of nanoparticles formed during co-precipitation. We synthesized ferrite nanoparticles by varying the solubility product from 10^− 13 to 10^− 17 by using different divalent cations of Mn, Co, Fe and Zn, where the average particle size decreased from 29.1 to 8.9 nm. The Mn, Co and Fe ferrites were magnetic in nature with saturation magnetization of 44.6, 47.38 and 56.19 emu/g respectively, whereas the Zn ferrite was paramagnetic. The increase in particle size observed with increasing solubility product of divalent metal hydroxide is in agreement with the nucleation theory.     

Wear and corrosion studies of graphite‐aluminum composite reinforced with micro/nano‐TiB2 via spark plasma sintering

The demand for lightweight materials in the automobile and aerospace industries has led to various researches on graphite and graphite‐aluminum composites. The aim of this study was to investigate the effect of the addition of micron/nano TiB₂ particles on the properties of graphite‐aluminum composite particularly the wear resistance. The powders were sintered at 550 °C and 50 MPa with more attention on the effect of the sintering temperature on densification, microhardness, coefficient of thermal expansion, wear and frictional force. The results show that the addition of nano TiB₂ reduces the densification while improving the hardness of Gr?Al composite with the lowest value being 96.0 % of relative density and the highest microhardness of 43.58 HV 0.1. The coefficient of thermal expansion and frictional force of the composite materials increases with increasing TiB₂ content and heating rate (100 °C/min–150 °C/min). TiB₂ particles enhance the wear resistance of graphite‐aluminum composite. The addition of micro/nanoparticles of TiB₂ to graphite‐aluminum composite increases its corrosion rate with improved passivation behavior in 3.5 wt.% NaCl solution. Nevertheless, 5 wt.% nano (100 °C/min) TiB₂ additions do not affect the overall corrosion rate. This work has shown that we can take advantage of some of the properties of TiB₂ to improve the performance of graphite‐aluminum composite.     

Low temperature synthesis of nanocrystalline lithium ferrite by a modified citrate gel precursor method

Single phase nanocrystalline lithium ferrite is synthesized by a modified citrate gel precursor technique. Ferrite nanoparticles of average size of 8 nm, obtained after calcination of the citrate gel made by the usual method at 450 °C, show superparamagnetic behavior. However, small amounts of -Fe₂O₃ is formed as an impurity phase due to the initial formation of some -Fe₂O₃ phase. On the other hand, when the pH of the mixed solution is increased to 7 after the addition of ammonia solution, a lower calcination temperature of 200 °C is sufficient for the formation of single phase lithium ferrite nanoparticles of size 30 nm. No impurity phases are detected when the nanocrystalline powders are calcined at higher temperatures. The magnetic properties of the ferrite nanoparticles of different sizes obtained by calcining the powders at different temperatures are studied.