Showing papers in "Journal of Coatings Technology and Research in 2012"

Electrodeposition of hydroxyapatite coating on magnesium for biomedical applications

Abstract: The effectiveness of hydroxyapatite (HA) coating prepared by electrodeposition technique in improving the corrosion resistance of commercially pure magnesium (CP-Mg) in simulated body fluid (SBF) is addressed. The coating formed in as-deposited condition is identified as dicalcium phosphate dehydrate (DCPD) (Brushite), which is converted to HA after immersion in 1 M NaOH at 80°C for 2 h. The XRD patterns and FTIR spectra confirm the formation of DCPD and HA. During electrodeposition, the H2PO4− ion is reduced and the reaction between Ca2+ ions and the reduced phosphate ions leads to the formation of DCPD, which is converted to HA following treatment in NaOH. The deposition of HA coating enables a threefold increase in the corrosion resistance of CP-Mg. The ability to offer a significant improvement in corrosion resistance coupled with the bioactive characteristics of the HA coating establish that electrodeposition of HA is a viable approach to engineer the surface of CP-Mg in the development of Mg-based degradable implant materials.

Electrodeposited nickel–phosphorous (Ni–P) alloy coating: an in-depth study of its preparation, properties, and structural transitions

Abstract: Ni–P deposits with a phosphorous content of up to 20% (wt) were obtained on AA6061 substrates by direct current electrodeposition technique from a solution containing nickel sulfate, nickel chloride, phosphorous acid, phosphoric acid, and a wetting agent (sodium lauryl sulfate). The effect of various plating parameters like current density, concentration of phosphorous acid, concentration of phosphoric acid and plating temperature on the P content of the coating as well as the rate of deposition was investigated systematically. It has been observed that the influence of current density on the P content of the deposit is largely dependent on the concentration of phosphorous acid in the plating bath. Composition, surface morphology, microstructure, and mechanical properties of the Ni–P deposits were studied using SEM, EDAX, XRD, and nanoindentation techniques. Ni–P electrodeposits with low P content in the range of 4–7 wt% of P exhibited superior microhardness of 7.74–8.57 GPa. With increasing P content in the deposit, the structure undergoes transition from crystalline to nanocrystalline and becomes amorphous above 9.14 wt% of P. Ni–P alloys with some selected compositions were subjected to heat treatment at 400°C for 1 h in a hot air oven and the resulting variation in mechanical properties was studied using nanoindentation technique.

Corrosion protection of aluminum 6061 in NaCl solution by silane–zeolite composite coatings

Abstract: Anticorrosion properties of silane–zeolite composite coatings applied on aluminum substrates have been investigated. The composite coatings were prepared with different zeolite microparticles concentration (from 500 to 8000 ppm). Physico-chemical tests (Fourier transform infrared spectroscopy, adhesion, scanning electron microscopy, and contact angle measurements) have been carried out to evaluate the homogeneity and structural properties of the coatings. The coatings that resulted were highly hydrophobic for all zeolite contents and showed a relatively good adhesion performance. Corrosion protection performances in 3.5% NaCl solution were evaluated by means of polarization tests, evidencing good barrier characteristics of the composite layer.

Electrodeposition and corrosion behavior of Zn–Ni and Zn–Ni–Fe 2 O 3 coatings

Abstract: A thin film of Zn–Ni–Fe2O3 on steel substrates was prepared by electrodeposition technique using Zn–Ni alloy plating solution with nano-sized Fe2O3 particles The cathodic polarization and cyclic voltammetry techniques were used to explain deposition process The corrosion behavior of deposits was evaluated by polarization and impedance studies Scanning electron microscope (SEM) images were used to study the surface morphology of coating The grain size and amount of Fe2O3 particles present in composite coating were measured by X-ray diffraction pattern (XRD) and energy dispersive X-ray diffraction spectrometer (EDS), respectively

An investigation of mild carbon steel corrosion inhibition in hydrochloric acid medium by environment friendly green inhibitors

Abstract: Inhibition effect of Brugmansia suaveolens (BS) and Cassia roxburghii (CR) on mild carbon steel in 1.0 M HCl solution was studied. Inhibition efficiency of plant extracts were carried out by using chemical (weight loss method) and electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy). The effect of temperature on the corrosion behavior of mild carbon steel in 1.0 M HCl with addition of plant extracts was studied in the temperature range of 300–320 ± 1 K. Inhibition efficiencies up to 94.69 for BS and 93.22 for CR can be obtained. The adsorption mechanism of inhibition was supported by FT-IR, surface analysis (SEM–EDS), and adsorption isotherms. The thermodynamic parameter values of free energy of adsorption (∆G ads) reveal that inhibitor was adsorbed on the mild carbon steel surface via both physisorption and chemisorption mechanisms.

Water transportation through organic coatings: correlation between electrochemical impedance measurements, gravimetry, and water vapor permeability

Abstract: A primary cause of coating failure is diffusion of water through organic coatings during which many corrosive species are transported to the metal-coating interface. However, water vapor permeability through the coating improves blister resistance to a certain extent. The present work describes the influence of chemical nature of the polymer on the above two properties. Attempts were also made to establish a correlation between these two properties for pigmented organic coating. Six paints were formulated and processed using six different types of binders at a constant pigment volume concentration (PVC) and specific gravity. Water ingress, water vapor permeability, and water absorption of these coatings were estimated using electrochemical impedance measurements (EIS), permeability cup method, and gravimetric method, respectively. There exists a good linear correlation between water uptake measured by EIS and water absorption measured by gravimetry. Similarly, a correlation was also noticed between water uptake by EIS and water vapor permeability. However, polyurethane type polymers did not fit into this linear correlation. Furthermore, influence of the resin chemistry on anticorrosive properties of these coatings was also studied using EIS and salt spray exposure test. Among all polymers under investigation, acrylic polyol-based polyurethane has shown the lowest water uptake, higher impedance, better salt spray resistance but higher water vapor transmission rate.

Preparation, characterization and properties of UV-curable waterborne polyurethane acrylate/SiO 2 coating

Abstract: The UV-curable waterborne polyurethane acrylate (UV-WPUA) oligomer was first prepared based on isophorone diisocyanate (IPDI), polyether polyol (NJ-220), dimethylol propionic acid (DMPA), and hydroxyethyl methyl acrylate (HEMA) via an in situ method. With the different content tetraethoxysilane (TEOS) and 3-glycidyloxypropyltrimethoxysilane (GLYMO) as coupling agents, a series of waterborne UV-WPUA/SiO2 oligomers were prepared by the sol–gel process. The physical and mechanical properties of the UV-WPUA and UV-WPUA/SiO2 hybrid coating materials were measured. The UV-WPUA and WPUA/SiO2 hybrid materials were characterized using FTIR spectra, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) measuring apparatuses to determine their structures, thermal properties, surface morphologies, etc. The results showed the SiO2 particles of the hybrid materials had wide dispersion, forming a good interfacial bonding layer on surfaces. The tensile strength, water resistance, and thermal properties of the hybrid materials were better than those of the UV-WPUA. The resulting UV-WPUA/SiO2 hybrids are promising for a number of applications, e.g., for high-performance water-based UV-curable coatings.

Synthesis of polyaniline nanofiber and anticorrosion property of polyaniline–epoxy composite coating for Q235 steel

Abstract: Polyaniline (PANI) nanofibers were prepared by direct mixed oxidation in four kinds of inorganic acids. The characterization of scanning electron microscopy (SEM) showed that high quality PANI fibers with uniform diameter and several microns length can be obtained by direct mixed oxidation, especially in a sulfuric acid system. Structural characteristics of PANI products through IR and UV spectra indicated the consistent peak distribution with the classic spectrum of the doped PANI. In addition, composite coatings of PANI–epoxy resin were prepared by mechanical grinding. The effect of PANI’s content on anticorrosion property of the composite coatings for Q235 steel was studied by the electrochemical impedance spectroscopy (EIS). Results showed that the best shielding protective effect was obtained when the amount of PANI was around 0.5% (wt%). More importantly, the effects of four different inorganic acids on anticorrosion property of the composite coatings were studied by the EIS and Tafel polarization curve. Experiments showed that the different composite coatings of PANI doped by different inorganic acids provided different protective abilities for the Q235 steel. It can be concluded that both the morphology and counter-anion would impact the anticorrosion effect of the doped PANI.

Corrosion resistance of steel treated with different silane/paint systems

Abstract: This article reports on a comparative study on the corrosion resistance of low-carbon steel substrates pretreated with different silane solutions and painted. The pure silanes used to pretreat the steel panels were 3-aminopropyltriethoxysilane (γ-APS), 3-glycidoxypropyltrimethoxysilane (γ-GPS), and bis(3-triethoxysilylpropyl)amine. The study also considered other silane solutions with ureido, amino, and epoxy organofunctional groups, and two bis-functional silanes: bis(γ-trimethoxysilylpropyl)amine (BAS) and 1,2-bis(triethoxysilyl)ethane (BTSE). A conventional phosphate-type pretreatment was also applied for reference purposes. The pretreated panels were then finished with an alkyd/polyester aminoplast base paint. As a branch test, an acrylic/urethane paint was also applied. Different tests were conducted to evaluate the anticorrosive ability of the different silane/paint systems: outdoor exposure in an atmosphere of moderate aggressivity; accelerated corrosion test (salt fog test); and electrochemical impedance spectroscopy (EIS). The results show that the steel pretreated with certain silanes, especially γ-APS, yields similar results to steel subjected to conventional phosphate pretreatment.

The effect of formulation variables on fouling-release performance of stratified siloxane–polyurethane coatings

Abstract: The effects of formulation variables, such as type of polyol, solvent type and solvent content, and coating application method, on the surface properties of siloxane–polyurethane fouling-release coatings were explored. Fouling-release coatings allow the easy removal of marine organisms from a ship’s hull via the application of a shear force to the surface. Self-stratified siloxane–polyurethane coatings are a new approach to a tough fouling-release coating system. Combinatorial High Throughput Experimentation was employed to formulate and characterize 24 different siloxane–polyurethane coatings applied using drawdown and drop-casting methods. The resulting coatings were tested for surface energy using contact angle measurements. The fouling-release performance of the coatings was tested using a number of diverse marine organisms including bacteria (Halomonas pacifica and Cytophaga lytica), sporelings (young plants) of the green macroalga (Ulva linza), diatom ((microalga) Navicula incerta), and barnacle (Amphibalanus amphitrite). The performance of the majority of the coatings was found to be better than the silicone standards, Intersleek® and Silastic® T2. An increase in solvent content in the formulations increased the surface roughness of the coatings. Coatings made with polycaprolactone polyol appeared to be somewhat rougher compared to coatings made with the acrylic polyol. The adhesion strength of sporelings of Ulva increased with an increase in solvent content and increase in surface roughness. The adhesion strengths of Ulva sporelings, C. lytica, and N. incerta were independent of application method (cast or drawdown) in contrast to H. pacifica adhesion, which was dependent on the application method.

Corrosion tests of nickel coatings prepared from a Watts-type bath

Abstract: This paper deals with the preparation and characterization of thin Ni layers. The electrodeposition was carried out galvanostatically from a Watts bath at different current densities in the range from 1 to 10 A dm−2 and for deposition times between 900 and 7200 s. The structure and the morphology of the nickel coatings were investigated by SEM and XRD techniques. The microhardness of deposited layers, the electrochemical behavior and the corrosion properties of the deposits were investigated by means of Vickers microhardness, polarization measurements, and electrochemical impedance spectroscopy (EIS). The uniform deposits showed fine grains and good protection against corrosion.

Chemical and electrochemical characterization of TiO2/Al2O3 atomic layer depositions on AZ-31 magnesium alloy

Abstract: In this study, innovative TiO2/Al2O3 mono/multilayers were applied by atomic layer depositions (ALD) on ASTM-AZ-31 magnesium/aluminum alloy to enhance its well-known scarce corrosion resistance. Four different configurations of ALD layers were tested: single TiO2 layer, single Al2O3 layer, Al2O3/TiO2 bilayer and Al2O3/TiO2/Al2O3/TiO2 multilayer deposited using Al[(CH3)]3 (trimethylaluminum, TMA), and TiCl4 and H2O precursors. All depositions were performed at 120°C to obtain an amorphous-like structure of both oxide layers. The four coatings were then investigated using different techniques, such as scanning electron microscope (SEM), stylus profilometer, glow discharge optical emission spectrometry (GDOES) and polarization curves in 0.05-M NaCl solution. The thickness of all the coatings was around 100 nm. The layers compositions were successfully investigated by the GDOES technique, although obtained data seem to be affected by substrate roughness and differences in sputtering rates between ceramic oxides and metallic magnesium alloy. Corrosion resistance showed to be strongly enhanced by the nanometric coatings, giving lower corrosion current densities in 0.05-M NaCl media with respect to the uncoated substrate (from 10−4 to 10−6 A/cm2 for the single layers and from 10−4 to 10−8 A/cm2 for the bi- and multilayers). All polarization curves on coated samples also showed a passive region, wider for the bi-layer (from −0.58 to −0.43 V with respect to Ag/AgCl) and multilayer (from −0.53 to −0.38 V with respect to Ag/AgCl) structures.

Corrosion performance of chemically synthesized poly(aniline-co-o-toluidine) copolymer coating on mild steel

Abstract: A soluble copolymer from aniline and o-toluidine [poly(aniline-co-o-toluidine)] was synthesized by chemical oxidative copolymerization using ammonium persulphate as an oxidant in hydrochloride aqueous medium. The resultant copolymer was characterized by Fourier Transform Infrared (FTIR) spectroscopy and chemically deposited on mild steel specimens using N-methyl-2-pyrrolidone (NMP) as solvent via solution evaporation method. The anticorrosive properties of copolymer coating was investigated in major corrosive environments, such as 0.1 M HCl, 5% NaCl solution, artificial seawater, distilled water and open atmosphere by conducting various corrosion tests which include: immersion test, open circuit potential (OCP) measurements, potentiodynamic polarization measurements and atmospheric exposure test. The corrosion performance of copolymer coating was also compared separately with polyaniline (PANi) and poly(o-toluidine) (POT) homopolymer coatings. The surface morphologies of polymer coatings were evaluated using scanning electron microscopy (SEM). The synthesized copolymer exhibited excellent protection against mild steel corrosion; the protection efficiency being in the range of 78–94% after 30 days of immersion. The corrosion performance of copolymer in 5% NaCl and artificial seawater was comparable, which was only marginally better than in 0.1 M HCl. In general, the performance of copolymer coating was found to be better than that of homopolymer coatings.

Model-based analysis of photoinitiated coating degradation under artificial exposure conditions

Abstract: Coating degradation mechanisms of thermoset coatings exposed to ultraviolet radiation and humidity at constant temperature are investigated. The essential processes, photoinitiated oxidation reactions, intrafilm oxygen permeability, water absorption and diffusion, reduction of crosslink density, and development of a thin surface oxidation zone are quantified and a mathematical model for degrading coatings developed. Front-tracking techniques are used to determine the rate of movement of the oxidation and ablation fronts, the positions of which define the extension of the surface oxidation zone. Three previous and independent experimental investigations with two-component, densely crosslinked, epoxy–amine model coatings were selected for verification of the mathematical model. Simulations can match and explain transient mass loss and coating thickness reduction data and are in agreement with infrared measurements of carbonyl groups formed in the surface zone. The thickness of the stable surface oxidation zone, which is established after an initial ablation lag time, is estimated by the model to 0.5–2 μm in good agreement with previous measurements. Simulated concentration profiles of active groups, oxygen, and radicals in the stable surface oxidation zone are presented and analyzed. The mathematical model can be used for obtaining a quantitative insight into the degradation of thermoset coatings and has potential, after further development, to complete commercial coatings and dynamic exposure conditions, to become a supplementing tool for predicting in-service coating behavior based on accelerated laboratory measurements.

A simple and cost-effective method for fabricating lotus-effect composite coatings

Abstract: This paper reports the fabrication of a lotus-effect coating by grafting epoxy (EP) resin on the surface of microsilica and nanosilica, respectively, and subsequent spraying. The coating shows the same structure and capability as lotus leaves, and shows a static contact angle as large as 165° and a sliding angle as small as 2.5°. SEM analysis shows that the hydrophobic capability depends on the surface structure of the coatings. This method may be suited for processing large scale or irregular surfaces.

Effect of pH and current density on the electrodeposition of Zn–Ni–Fe alloys from a sulfate bath

Abstract: An investigation was done on the influences of current density and pH on the electrodeposition behavior of Zn–Ni–Fe alloys using a sulfate bath. The bath consisted of 0.1 M ZnSO4, 0.1 M NiSO4, 0.1 M FeSO4, 0.2 M Na2SO4, 0.2 M H3BO3, and 0.01 M H2SO4. The results of Zn–Ni–Fe alloys’ codeposition revealed that the significant inhibition of Ni and Fe deposition takes place because of the presence of Zn2+ in the plating bath. A transition current density was noticed above wherein a transition from normal to anomalous deposition took place. Bright and uniform surface appearance deposits of Zn–Ni–Fe were the results obtained at pH range 2–5, and the deposits showed high corrosion resistance. During the investigation, the usage of cyclic voltammetry and galvanostatic techniques for electrodeposition were utilized, while linear polarization resistance and anodic linear sweeping voltammetry techniques were used for the corrosion study. Characterization of morphology and the chemical composition of the deposits were performed by means of scanning electron microscopy and atomic absorption spectroscopy.

Photocatalytic coatings for building industry: study of 1 year of activity in the NOx degradation

Abstract: Nitrogen oxides (NO x ) play a key role in the atmospheric reactions that create ground-level ozone and acid rain. The exploitation of building coatings acting as catalysts for NO x degradation under the effect of solar radiation represents a feasible way of wide applicability to lower NO x concentration in air. A crucial issue for the practical application of photocatalytic coatings is the actual lifetime of the active material. To investigate this aspect, two paints and two plasters (silicate and siloxane resins based) commercially available were formulated with 2% TiO2 Aeroxide P25 and tested in the photocatalytic removal of NO x in air. The results collected over 1 year show how the photoactivity lifetime of these products always decreases with their curing age, being strictly correlated to the formulation of the materials.

Organic vs inorganic light stabilizers for waterborne clear coats: a fair comparison

Abstract: As a consequence of regulatory pressure to reduce solvent emissions, there is high growth rate of “compliant technologies” such as waterborne (WB) coatings. However, a change from conventional solventborne (SB) to WB technologies should not compromise the protective function of the coatings and the used raw materials. The use of light stabilizers, such as UV absorbers (UVA) and hindered amine light stabilizers (HALS) are state-of-the-art and largely improve the coating durability and service lifetime. Today in the case of UVA one has to differentiate between inorganic and organic products: the most widely used organic UVA for coating applications are 2-(2-hydroxyphenyl)-benzotriazole (BTZ) and 2-hydroxyphenyl-s-triazine (HPT) derivatives. Inorganic products are ideally nano particulate materials—so-called mineral screeners (MS)—comprised of titanium dioxide (TiO2), zinc oxide (ZnO), or cerium oxide (CeO2). The challenge here is to convert existing products which are in general hydrophobic substances into product forms that enable easy incorporation and unproblematic dispersion into WB systems. This article describes UV absorbers which are commercially available for waterborne coatings. Different classes are tested with regard to their protective function in joinery coatings as well as with regard to their influence on coatings color and transparency. The findings of this study showed clearly that the 2-hydroxyphenyl-s-triazine class outperforms all other UVA in terms of long-term performance without influencing initial coating properties.

An improved laboratory reattachment method for the rapid assessment of adult barnacle adhesion strength to fouling-release marine coatings

Abstract: Modifications have been made to the previously described adult barnacle laboratory reattachment method to enhance and improve the overall utility of this technique for rapidly assessing the efficacy of novel fouling-release marine coating technologies. These modifications include the use of an immobilization template to secure barnacles onto the coating surfaces during the underwater reattachment process, the development of a semi-automated push-off device to enable consistent and reproducible force gauge measurements and the implementation of a software tool to measure the diameter of barnacle base plates for adhesion strength calculations. A series of experimental siloxane–polyurethane and control coatings were evaluated with both the original and improved laboratory reattachment methodologies. Significantly higher adhesion strengths were obtained on these coatings using the improved reattachment method. Furthermore, only the improved reattachment method was able to discern significant differences in the performance of the siloxane–polyurethane coatings based on differences in compositional components. In this regard, the siloxane–polyurethane coatings containing the poly-caprolactone end groups attached to the poly(dimethylsiloxane) (PDMS) backbone exhibited significantly higher reattached barnacle adhesion strengths than the aminopropyl-terminated PDMS containing coatings. It was also shown that the utilization of barnacles with 5–6 mm base plate diameters, rather than 7–8 mm diameters, significantly enhanced the strength or tenacity of adhesion to the surface of the control coatings. The results of the improved laboratory reattachment evaluation of experimental siloxane–polyurethane and control coatings were in good agreement with barnacle adhesion measurements obtained for the same coatings with static ocean immersion testing in the field.

Polarization and impedance studies on zinc phosphate coating developed using galvanic coupling

Abstract: Galvanic coupling technique is capable of producing coatings of desired thickness. Good quality coatings can be produced at low temperature. Galvanic coupling of mild steel (MS) with the other cathode materials such as titanium (Ti), copper (Cu), brass (BR), nickel (Ni), and stainless steel (SS) accelerates iron dissolution, enables quicker consumption of free phosphoric acid and facilitates an earlier attainment of point of incipient precipitation, resulting in a higher amount of coating formation. In the present investigation, potentiodynamic polarization and electrochemical impedance spectra on MS substrates phosphated using galvanic coupling are studied. This study reveals that MS substrates phosphated under galvanically coupled condition possess better corrosion resistance than the substrates phosphated under uncoupled condition.

Dynamic behavior of electroless nickel plating reaction on magnesium alloys

Abstract: In order to obtain better control over the quality of electroless nickel–phosphorous (EN) coatings on magnesium AZ91D alloy, the effects of metal salt concentrations, reducing agent, pH, and temperature on deposition rate were studied. The reaction orders and activation energy of the deposition were determined. The results show that the apparent activation energy (E a) in the EN plating reaction is approximately 38.03 kJ/mol. The deposition rate increased with increasing temperature, concentration of H2PO2 −, and pH, and decreased with increasing concentration of complexing agents. For nickel ions, the deposition rate increased gradually with increasing concentration (x) when x < 4.69 g/L. However, it decreased when the concentration exceeded 4.69 g/L. Finally, various types of the deposition reaction were also discussed. The results indicate that nickel was first deposited by replacement deposition in the initial 0.5 min, then by both replacement deposition and autocatalytic deposition in plating, and finally by autocatalytic deposition after 5 min of plating.

Dependent light scattering in white paint films: clarification and application of the theoretical concepts

Abstract: Among the numerous publications analyzing the causes and consequences of titanium dioxide crowding on the optical properties of white paint films, one notes some inconsistencies. First, a significant number of studies are inclined to describe “dependent” and “multiple” scattering of light as distinct phenomena. Second, the transition from independent to dependent light-scattering is often associated with an ill-defined “threshold” concentration. The aim of this study is to clarify the intricate connections between these two scattering regimes and in particular to show that for white paint films loaded with rutile titanium dioxide pigments, “dependent” light scattering is merely a particular manifestation of multiple scattering processes. We also clarify that the transition from independent to dependent scattering is a continuous process that cannot be formally related to a specific threshold in the pigment volume concentration. Finally, we propose a simple method based on the dependent scattering amplitude to assist paint formulators facing the task of improving the hiding power of a white paint either by increasing the quantity of pigments or by improving their spatial state of dispersion.

Nanocomposite acrylic paint with self-cleaning action

Abstract: A nanodispersion of surface-functionalized fumed silica was incorporated into an acrylic paint formulation. SEM imaging indicated good dispersion of silica within the polymer matrix. This hybrid coating showed significantly lower dirt pick-up than the equivalent paint formulation without nanosilica additive, towards both organic and inorganic ashes. Washing with running water further decreases dirt retention. This self-cleaning performance remained unchanged after several dirt/washing cycles, during a 1-month period. Surface hardness measurements indicated no significant differences between the original and composite paint films. The lower dirt pick-up was attributed to nanoroughness created by the nanosilica particles present in the film.

Characterization and property of microarc oxidation coatings on open-cell aluminum foams

Abstract: The ceramic coatings were prepared on open-cell aluminum foams by microarc oxidation (MAO) treatment in an alkaline-silicon electrolyte. The morphology, microstructure, elemental distribution, and phase composition of the MAO coatings were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, respectively. The corrosion behaviors of the coated and uncoated foams were evaluated by electrochemical polarization measurement. The results show that the MAO coatings cover the surface of open-cell aluminum foams. The coatings were composed of an external porous layer and an internal dense layer. The main phase of the MAO coating phase is γ-Al2O3. The coated aluminum foams exhibit more positive corrosion potential and lower corrosion current density compared with the uncoated aluminum foams.

Application of molecular dynamics computer simulations to evaluate polymer-solvent interactions

Abstract: In this article, systematic calculation of the radius of gyration (Rg) of a block copolymer immersed in various solvents is presented. Using atomistically detailed, molecular dynamics computer simulations, we carry out the calculation of Rg at different polymerization degrees, for each solvent. Our results show that, given a solvent and a polymerization degree, Rg can display different values. This aspect is found to be a consequence of the spatial conformation of the constitutive blocks that make up the polymer molecule. Finally, we find that there exists a correlation between Rg and the solubility parameter and that the trend in Rg predicted by our calculations agrees with previous experimental results.

Electroless nickel–phosphorus deposition on carbon steel CK-75 and study of the effects of some parameters on properties of the deposits

Abstract: Electroless nickel–phosphorus (Ni–P) deposition provides coatings with high hardness and excellent resistance to wear and abrasion. In this study, autocatalytic deposition of Ni–P alloy has been carried out on steel CK-75 sheets from bath containing nickel sulfate hexahydrate, sodium hypophosphite hydrate, thiourea, lactic acid, and sodium acetate. The effects of lactic acid concentration, pH and temperature on deposition rate, composition of deposits, and hardness have been studied. Also the changes in the hardness and structure of deposits by heat-treatment were studied by X-ray diffraction and scanning electron microscopy methods. It is shown that deposits crystallized after heat-treatment at 400°C for 1 h and crystallization to Ni and Ni3P was observed.

Biocompatibility and antibacterial performance of titanium by surface treatment

Abstract: Titanium (Ti) and its alloys are used extensively in implants due to their excellent biocompatibility and mechanical properties. However, Ti-based implant materials have specific complications associated with their applications, such as the loosening of implanted host interface owing to unsatisfactory cell adhesion and the susceptibility of the implants to bacterial infections. Hence, a surface that displays selective biointeractivity, i.e., enhancing beneficial host cell responses but inhibiting pathogenic microbial adhesion, would be highly desirable. This study aims to confer long-lasting antibacterial properties and good biocompatibility on Ti via the microarc oxidation technique. The biocompatibility of the Ti surface was evaluated by cytotoxicity test, and the bacteriostasis rate was evaluated by antibacterial efficacy. The results showed that the implant surface might be nontoxic to cell and its long-lasting antibacterial properties could be significantly improved. These results indicate that such microarc oxidation coatings are expected to have good potential in transcutaneous implant applications.

Synthesis and characterization of nanosized titanium dioxide and silicon dioxide for corrosion resistance applications

Abstract: We are reporting the preparation and characterization of nano-titanium dioxide and silica. The corrosion resistance performance of these nanopigments in silicone as well as silicone–polypyrrole Interpenetrating Polymer Network has been evaluated by impedance spectroscopy. The capacitance and resistance exerted by this nanocomposite coating were compared with the microcomposite coating and found that the nanocomposite coatings has the resistance in the order of 108 Ω cm2 in 3% sodium chloride solution, which is more than the microcomposite coating. The comparison of heat resistance performance of these composite coatings indicates that nanocomposite coatings exhibit higher heat resistance property than the microcomposite coatings.

Corrosion behavior of nanohybrid titania-silica composite coating on phosphated steel sheet

Abstract: Corrosion resistance behavior of sol–gel-derived organic–inorganic nanotitania–silica composite coatings was studied. Hybrid sol was prepared from Ti-isopropoxide and N-phenyl-3-aminopropyl triethoxy silane. The structure, morphology, and properties of the coating were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermo gravimetric analysis. The corrosion performances of the sol–gel-coated samples were investigated by electrochemical impedance spectroscopy (EIS) and standard salt spray tests. The hybrid coatings were found to be dense, more uniform, and defect free. In addition, the coatings also proved its excellent corrosion protection on phosphated steel sheet.

Influence of nickel ions for electroless Ni-P plating on polyester fabric

Abstract: Properties of electroless Ni–P plated polyester fabric mainly depend on the plating bath constituents/conditions. The effects of NiSO4 concentration of the plating bath on the deposition rate, phosphorus content, surface morphology, and crystal structure of the electroless Ni–P plated polyester fabric were investigated. The study revealed that phosphorus content in the deposits decreased at higher NiSO4 concentration. SEM micrographs showed that nodule size of the Ni–P deposits increased. All the Ni–P deposits had an amorphous structure. The electromagnetic interference (EMI) shielding effectiveness (SE) of electroless Ni–P plated polyester fabric was evaluated. With the rise of nickel ion in the solution, the EMI SE of the Ni–P plated polyester fabric increased.