Electrophoretic deposition of hydroxyapatite nanostructured coatings with controlled porosity

Hydroxyapatite (HA) coatings with controlled porosity were prepared by electrophoretic deposition (EPD) method. Carbon black (CB) particles were used as the sacrificial template (porogen agent). Two component suspensions containing different concentrations of HA and CB particles were prepared in isopropanol. It was found that the finer and positively charged HA nanoparticles are heterocoagulated on the coarser and negatively charged CB particles to form CB–HA composite particles with net positive charge. The deposition rate from the suspensions with WR (C_CB/C_HA ratio) of 0.25 was faster than that of those with WR: 0.5 at initial times of EPD. However the situation was reversed at longer EPD times. It was also found that the amount of porosity in the coatings increases as the CB concentration in the suspension increases (15%, 24%, 31%, 43% for the coatings deposited from the suspensions with 20 g/L HA nanoparticles and 0, 5, 10 and 20 g/L CB particles, respectively).     

In-situ study of mass and current density for electrophoretic deposition of zinc oxide nanoparticles

In this study, zinc oxide nanoparticles were synthesized by the hydrothermal microwave-assisted method, followed by its deposition using electrophoretic deposition (EPD) method. An investigation of the characteristics of the synthesized nanoparticles was carried out using X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The morphology and size distribution of the nanoparticles were examined by the images obtained from Transmission Electron Microscope (TEM). The in-situ variations of mass and current density were investigated during the EPD. The effect of different parameters such as the solvent type at various voltages (20 and 40 V) was investigated on EPD kinetics. By increasing the voltage from 20 to 40 V in the methanol, the mass of the deposited film was increased up to about 38%. Similarly, in the ethanol, an increase equal to 39% was observed. The morphology and porosity of deposited nanoparticles were studied by analyzing the images of the Scanning Electron Microscope (SEM). It was observed that the porosity of the film in the ethanol was more than the methanol, at similar potentials. The increase in porosity at the voltage of 20 V was almost 3.1% and at 40 V, it was approximately 4.4% with respect to methanol. Initial current densities in methanol at 20 and 40 V were about 18 and 29% more than ethanol, respectively.     

Critical particle concentration in electrophoretic deposition

The role of particle concentration in electrophoretic deposition (EPD) was investigated with two different suspension systems. The first system consisted of positively charged TiO₂ nanoparticles dispersed in isopropanol with 1 vol% water. The second system consisted of negatively charged polystyrene (PS) microbeads dispersed in isopropanol. Constant voltage EPD was performed using suspensions with variable particle concentration (0.013–0.43 vol% TiO₂ and 0.06–11.4 vol% PS). Threshold concentration values were identified for both systems after EPD at 100 V (250 V cm^?1) for 1 min. Below these values the deposited mass deviated from the trend dictated by Hamaker's equation. Higher applied voltages and longer deposition times were tested and the results suggested that the threshold concentration did not depend on those parameters. A phenomenological model of particle deposition was proposed, which accounts for the local electrochemical conditions close to the substrate in relation to particle size.     

Electrophoretic deposition (EPD) of nanohydroxyapatite - nanosilver coatings on Ti13Zr13Nb alloy

Titanium and its alloys are the biomaterials most frequently used in medical engineering, especially as parts of orthopedic and dental implants. The surfaces of titanium and its alloys are usually modified to improve their biocompatibility and bioactivity, for example, in connection with the deposition of hydroxyapatite coatings.The objective of the present research was to elaborate the technology of electrophoretic deposition (EPD) of nanohydroxyapatite (nanoHAp) coatings decorated with silver nanoparticles (nanoAg) and to investigate the mechanical and chemical properties of these coatings as determined by EPD voltage and the presence of nanoAg. The deposition of nanoHAp was carried out at two voltage values, 15 and 30 V. The decoration of nanoHAp coatings with nanoAg was carried out using the EPD process at a voltage value of 60 V and a deposition time of 5 min. The thickness of the undecorated coatings was found to be 2.16 and 5.14 µm for applied EPD voltages of 15- and 30-V, respectively. The release rate of silver nanoparticles into an artificial saliva solution increased with exposure time and EPD voltage. The corrosion current, between 1 and 10 nA/cm², was significantly higher for undecorated nanoHAp coatings and close to that of the substrate for decorated nanoHAp coatings. The hardness of the undecorated nanoHAp coatings obtained at 15 and 30 V of EPD voltage attained 0.2245±0.036 and 0.0661±0.008 GPa, respectively. Resistance to nanoscratching was higher for thicker coatings. The wettability angle was lower for coatings decorated with nanoAg.     

Relationship between the process parameters and the saturation point in electrophoretic deposition

We used the electrophoretic deposition (EPD) process to fabricate a composite with glass frit and investigated the EPD parameters to find the optimum deposition time by understanding the relationship between the process parameters of zeta potential (ZP), pH, deposition yield and saturation point in a slurry. A binder and a dispersing agent were mixed properly with glass frit (0.2–25 μm, d₅₀ = 8.77 μm) in an ethyl alcohol medium for the preparation of the slurry. The pH and ZP were in an inverse relationship to each other due to the generation of H₃O⁺ ions with the addition of the dispersing agent in the slurry. The acidic nature of the slurry resulted in a decrease of the pH and an increase of the ZP. Otherwise, the pH increased with the addition of the glass frit in the slurry because H₃O⁺ ions were absorbed on the glass frit. Therefore, the OH^? ions correspondingly increased. The saturation point of EPD was strongly correlated with the variation of the pH in the slurry; this is caused by a chemical reaction between the ethyl alcohol and the ions that make up the glass frit. An adjustment of the pH variation and the saturation point in the slurry can be established with respect to the optimum deposition time in the slurry.     

MnFe2O4 bulk,nanoparticles and film: A comparative study of structural and magnetic properties

MnFe₂O₄ bulk sample was synthesized by conventional solid state reaction method, at 1350 °C. Nanoparticles with mean size of 〈D〉_TEM=10.4(±1.1) nm were prepared by thermal decomposition of metal nitrates, at 350 °C. And a film sample was prepared by pulsed laser deposition of bulk ferrite on MgO(100) at substrate temperature of 600 °C. Then a comparative study of the structural and magnetic properties of the samples has been carried out using different measurements. X-ray diffraction pattern of bulk and nanoparticles samples confirmed formation of spinel phase. The film sample showed an epitaxial growth on MgO in (400) direction. Saturation magnetization of nanoparticles at 300 K, M_S=33 emu/g, was comparable with film sample, M_S=38 emu/g, both being ∼2.5 times smaller than that of bulk sample (M_S=82 emu/g). The results showed the importance of surface effects in the film sample and nanoparticles. The obtained zero coercivity of bulk sample at 300 K and the low value of 8 Oe at 5 K is attributed to soft magnetic behavior of the MnFe₂O₄. On the other hand, nanoparticles showed superparamagnetic behavior at 300 K; and blocked state with a large coercivity of 730 Oe at 5 K. The film sample showed non-zero corecivity at both 5 and 300 K which reveals higher magnetic anisotropy of film compared to the bulk ferrite.     

Computational analysis of airflow and nanoparticle deposition in a combined nasal–oral–tracheobronchial airway model

In light of the exponentially increasing industrial production and consumer use of ultrafine particles, deposition in the human lung is of great environmental and biomedical concern, especially for children, asthmatics and the elderly. Considering spherical nanoparticles in the 1–100 nm mean-diameter range and different breathing routes with Q_total=30 and 60 L/min, local deposition fractions and global surface concentrations were predicted employing an experimentally validated computer simulation model. It was found that the change in breathing route (from nasal to oral breathing) not only significantly influences nanoparticle deposition in the regions of nasal and oral cavities, nasopharynx and oropharynx, but also measurably affects depositions from pharynx to bronchial airways for tiny nanoparticles (≤5 nm). The effect of breathing routes on deposition of larger nanoparticles (>5 nm) after the pharynx tends to be minor. The impact of different outlet flow-rate ratios generated by downstream resistances, e.g., caused by airway inflammation or tumors, is discussed in this study as well. Specifically, different outlet pressures primarily influence the velocity profiles and nanoparticle deposition fractions at that particular branch and adjacent bifurcations. In addition, the impact of change in outlet flow rate ratio on total deposition is confined to all same-level bifurcations and direct upstream-level bifurcations. The mass transfer coefficients of depositing nanoparticles (in terms of Sherwood number) can be well correlated as a function of Reynolds number and Schmidt number. The influence of downstream resistance on the Sherwood number in bronchial airways is smaller than intra-subject effects, i.e., variations of bifurcation levels and geometric parameters.     

Electrostatic self-assembly of graphene–silver multilayer films and their transmittance and electronic conductivity

By alternating deposition of graphene oxide (GO) sheets and silver nitrate by means of an electrostatic self-assembly method, a GO–Ag⁺ film was prepared. After thermal annealing, a graphene–silver nanoparticle (GE–Ag) multilayer film, with high transparency and electrically conductivity, was obtained. The transmittance of a film with four assembly cycles was 86.3%, at a wavelength of 550 nm, better than that of a pure GE film (73.8%). While the surface resistance was 97 kΩ □^?1, much lower than that of a pure GE film (430 kΩ □^?1). The Ag nanoparticles play a crucial role in improving the properties of the GE–Ag film, acting as conductive paths and light-trapping nanoparticles, which not only reduces the reflection of the film, but also prevents the GE sheets from aggregation and provides conductive paths between sheets, improving the electrical conductivity.     

Electrophoretic deposition of hydroxyapatite-chitosan-CNTs nanocomposite coatings

Three component suspensions of hydroxyapatite (HA), chitosan and CNTs were prepared in ethanol base solution (15 vol% water and 0.05 vol% acetic acid). The adsorption of HA nanoparticles on CNTs was investigated by FTIR and SEM analysis. It was found that HA nanoparticles are adsorbed on CNTs via chemical bonding between -NH₂ groups of chitosan (adsorbed on their surface) and -COOH groups of CNTs. Current density as well as kinetics of EPD was studied at 60 V. It was found that current density increases or remains nearly constant during EPD due to the rise in water electrolysis as deposit grows on the substrate. Deposition weight against EPD time showed a linear trend due to the absence of any voltage drop over the deposit during EPD. The incorporation of chitosan and CNTs in the microstructure of coatings was confirmed by TG/DTA and SEM analysis. CNTs exhibited high efficiency in reinforcing the microstructure of coatings and preventing from their cracking. CNTs incorporation in the coatings improved their mechanical properties (adhesion strength, hardness and elastic modulus) and corrosion resistance.     

0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 thick films prepared by electrophoretic deposition from an ethanol-based suspension

We have investigated the processing of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (denoted PMN–PT) thick films using an electrophoretic deposition process (denoted EPD), with the PMN–PT particles suspended in an ethanol-based suspension. The zeta-potential and the viscosity were measured to identify the conditions for the preparation of a stable suspension suitable for the EPD. The applied voltage, the deposition time, the chemical composition of the suspension and the concentration of the powder were investigated in order to obtain a high-quality PMN–PT deposit with a target thickness of about 50 μm. The PMN–PT thick films prepared from stoichiometric and PbO-excess suspensions by sintering at 950 and 1100 °C were examined by X-ray powder-diffraction analysis and scanning electron microscopy. The highest functional response was obtained for a homogeneous, dense, crack-free PMN–PT thick film prepared from a PMN–PT suspension with excess PbO. The film was deposited at a constant voltage of 10 V and for a time of 120 s, followed by sintering at 1100 °C in a PbO-rich atmosphere. The film's properties were as follows: a dielectric permittivity ? of 20,250 at a T_m of 172 °C, a remanent polarization of 17 μC/cm² and a coercive field of 5 kV/cm.     

Tubular graphene nanoribbons with attached manganese oxide nanoparticles for use as electrodes in high-performance supercapacitors

Graphene nanoribbons (GNRs) with tubular shaped thin graphene layers were prepared by partially longitudinal unzipping of vapor-grown carbon nanofibers (VGCFs) using a simple solution-based oxidative process. The GNR sample has a similar layered structure to graphene oxide (GO), which could be readily dispersed in isopropyl alcohol to facilitate electrophoretic deposition (EPD). GO could be converted to graphene after heat treatment at 300 °C. The multilayer GNR electrode pillared with open-ended graphene tubes showed a higher capacitance than graphene flake and pristine VGCF electrodes, primarily due to the significantly increased surface area accessible to electrolyte ions. A GNR electrode with attached MnO₂ nanoparticles was prepared by EPD method in the presence of hydrated manganese nitrate. The specific capacitance of GNR electrode with attached MnO₂ could reach 266 F g⁻¹, much higher than that of GNR electrode (88 F g⁻¹) at a discharge current of 1 A g⁻¹. The hydrophilic MnO₂ nanoparticles attached to GNRs could act as a redox center and nanospacer to allow the storage of extra capacitance.     

Fabrication of textured alumina by orienting template particles during electrophoretic deposition

(0 0 1)-Textured α-alumina has been processed by electrophoretic deposition (EPD) and templated grain growth. The mechanism of platelet template orientation during EPD was examined with respect to the impact of the electric field force, gravity and hydrodynamic force in two different deposition cells with vertically or horizontally positioned deposition electrodes. A sharp (0 0 1) ‘fibre texture’ was obtained after templated grain growth during sintering of a deposit formed from a stirred 5 vol% platelet containing suspension in a vertical deposition cell. The texture was characterized by means of the Lotgering factor, texture index and electron backscattering diffraction (EBSD).     

A hybrid microreactor/microwave high-pressure flow system of a novel concept design and its application to the synthesis of silver nanoparticles

This article reports on a microreactor/microwave high-pressure flow hybrid apparatus of a novel concept design, which includes both the microreactor and a spiral reactor, and its efficient use in the synthesis of silver nanoparticles of relatively uniform sizes (4.3 ± 0.7 nm) under microwave irradiation. By contrast, under otherwise identical experimental conditions but with conventional heating, the nanoparticle size was non-uniform (8.3 ± 2.7 nm) and the spiral reactor walls were covered with a silver mirror deposit. Formation of the nanoparticles was monitored by UV–visible spectroscopy (plasmonic absorption band; LSPR), TEM and by small-angle X-ray scattering (SAXS). Both the spiral microreactor and the spiral quartz reactor of the hybrid system played an important role in the synthesis, with the microreactor providing the environment wherein mixing of the aqueous solution of [Ag(NH₃)₂]⁺ and the solution of glucose (the reducing agent) and poly(N-vinyl-2-pyrrolidone) (PVP; stabilizer/dispersing agent) occurred. The microwaves provided the thermal energy to effect a uniform growth of the silver nanoparticles at temperatures above 120 °C. Mixing the two solutions by conventional methods (no microreactor) failed to yield such nanoparticles even under microwave irradiation and no formation of a silver mirror occurred in the inner walls of the spiral reactor.     

Fabrication technologies for oxide–oxide ceramic matrix composites based on electrophoretic deposition

Electrophoretic deposition (EPD) was used to fabricate alumina matrix composites with high volume fraction of woven fibre mat (Nextel™ 720) reinforcement in a multilayer structure. Colloidal suspensions of Al₂O₃ nanoparticles in ethanol medium with addition of 4-hydrobezoic acid were used for EPD. Two different techniques were developed for fabrication of Al₂O₃ matrix/Nextel™ 720 fibre composites. The first method is a combination of standard EPD of single fibre mats with a subsequent lamination procedure to fabricate the multilayered composite. The second method involves the simultaneous infiltration of several (three or more) Nextel™ 720 fibre mats by EPD in a tailor-made cell. The composites exhibit a homogeneous matrix microstructure, characterised by a very high particle packing density and relatively low porosity after sintering at 1300 °C. The EPD cell allows production of relatively large bodies (10 cm diameter). By combination of the multilayer EPD infiltration and lamination processes developed here, thick ceramic matrix composite components (>10 mm thickness) can be fabricated, which opens the possibility of greater industrial application of the materials.     

Characterization of silica-coated silver nanoparticles prepared by a reverse micelle and hydrolysis–condensation process

Described herein is the synthesis of individually silica-coated silver nanoparticles using a reverse micelle method followed by hydrolysis and condensation of tetraethoxysilane (TEOS). The size of a silica-coated silver nanoparticle can be controlled by changing the reaction time and the concentration of TEOS. By maintaining the size of a silver nanoparticle as a core particle at around 7 nm, the size of a silica-coated silver nanoparticle increased from 13 to 28 nm as the reaction time increased from 1 to 9 h due to an increase in silica thickness. The size of silica-coated silver nanoparticles also increased from 15 to 22 nm as the TEOS concentration increased from 7.8 to 40 mM. The size of a silica-coated silver nanoparticle can be accurately predicted using the rate of the hydrolysis reaction for TEOS. Neither the dispersion nor the film of silica-coated silver nanoparticles exhibited any peak shifting during surface plasmon resonance (SPR) at around 410 nm, whereas, without silica coating, the SPR peak of Ag film shifted to 466 nm.     

Electrophoretic deposition of functionally-graded NiO–YSZ composite films

Functionally-graded NiO–8 mol % YSZ composite films were prepared by a controlled voltage-decay electophoretic deposition (EPD) process. The films consisted of three layers with varying NiO concentrations and porosities. Effects of different parameters including the type of the organic media, solid concentration, NiO:YSZ ratio, and iodine on the stability of EPD suspensions and deposition kinetics were studied. A stable NiO–YSZ suspension was attained in isopropanol with NiO–YSZ ratio of 60:40 and iodine concentration of 0.5 mM. The composite film contained varying NiO concentration from 46 wt.% near the substrate to 32 wt.% close to the electrolyte with 42 wt% NiO in the intermediate region. The thickness of each layer is about 10, 44 and 68 μm, respectively. The prepared anode could be promising for solid oxide full cells as it compromises good contact to the electrode with higher corrosion resistance and active reaction zone with the electrolyte.     

Voltage switchable surface-modified carbon black nanoparticles for dual-particle electrophoretic displays

In order to produce the black color for electrophoretic display (EPD) applications in dual-particle systems, a primary-like sized carbon black (PCB) surface modification method is developed and the electrophoretic properties of the resulting functionalized particles are reported. The PCB surface was chemically modified by hydroxylation and subsequent esterification. The final capping material of the PCB nanoparticle surface was a bulky fatty oleic acid, which was expected to improve dispersion stability and to produce electrostatic chargeability in a low dielectric medium. The zeta potential calculated from the measured electrophoretic mobility with a charge control agent was −31 mV. When the negatively chargeable oleic acid-capped PCB nanoparticles mixed with the positively chargeable polymer-coated white TiO₂ nanoparticles, the PCB nanoparticles showed electrophoretic movement at an applied bias voltage of less than 5 V, which demonstrated potential application for very low voltage operation in EPDs.     

Thin film yttria-stabilized zirconia electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by chemical solution deposition

A 500 nm thick thin film YSZ (yttria-stabilized zirconia) electrolyte was successfully fabricated on a conventionally processed anode substrate by spin coating of chemical solution containing slow-sintering YSZ nanoparticles with the particle size of 20 nm and subsequent sintering at 1100 °C. Incorporation of YSZ nanoparticles was effective for suppressing the differential densification of ultrafine precursor powder by mitigating the prevailing bi-axial constraining stress of the rigid substrate with numerous local multi-axial stress fields around them. In particular, adding 5 vol% YSZ nanoparticles resulted in a dense and uniform thin film electrolyte with narrow grain size distribution, and fine residual pores in isolated state. The thin film YSZ electrolyte placed on a rigid anode substrate with the GDC (gadolinia-doped ceria) and LSC (La_0.6Sr_0.4CoO_3?δ) layers deposited by PLD (pulsed laser deposition) processes revealed that it had fairly good gas tightness relevant to a SOFC (solid oxide fuel cell) electrolyte and maintained its structural integrity during fabrication and operation processes. In fact, the open circuit voltage was 1.07 V and maximum power density was 425 mW/cm² at 600 °C, which demonstrates that the chemical solution route can be a viable means for reducing electrolyte thickness for low- to intermediate-temperature SOFCs.     

Electrophoretic deposition of La0.6Sr0.4Co0.8Fe0.2O3−δ cathodes on Ce0.9Gd0.1O1.95 substrates for intermediate temperature solid oxide fuel cell (IT-SOFC)

Porous thick films of La_0.6Sr_0.4Co_0.8Fe_0.2O_3?δ (LSCF) on Ce_0.9Gd_0.1O_1.95 (CGO) substrates were prepared by the electrophoretic deposition (EPD) method. Organic suspensions of different compositions containing LSCF ceramic particles were investigated with the aim to determine the optimal composition of the suspension and EPD conditions. Stainless steel substrates were used in order to determine the optimal parameters for the EPD process. The best results were achieved with solutions containing acetylacetone, iodine and starch. The EPD conditions leading to uniform LSCF films were: applied voltage 20 V and deposition time 120 s, with the electrodes separated 1.5 cm. EPD was also demonstrated to be a simple and useful method for making porous LSCF cathodes on CGO substrates. It was shown that the microstructure of the films can be controlled by changing the applied voltage, deposition time and concentration of additives in suspension.     

Phase equilibria for the 2-ethoxyethyl acetate and 2-(2-ethoxyethoxy)ethyl acetate in supercritical CO2 at various temperatures and pressures up to 20 MPa

The (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems at 313.2, 333.2, 353.2, 373.2 and 393.2 K as well as pressures up to 20.59 MPa have been investigated using variable-volume high pressure view cell by static-type. The solubility curve of 2-ethoxyethyl acetate and 2-(2-ethoxyethoxy)ethyl acetate in the (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems increases as the temperature increases at a constant pressure. The (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems exhibit type-I phase behavior. The experimental results for the (CO₂ + 2-ethoxyethyl acetate) and (CO₂ + 2-(2-ethoxyethoxy)ethyl acetate) systems correlate with the Peng–Robinson equation of state using a van der Waals one-fluid mixing rule including two adjustable parameters. The critical properties of 2-ethoxyethyl acetate and 2-(2-ethoxyethoxy)ethyl acetate are predicted with the Joback–Lyderson group contribution and Lee–Kesler method.