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.     

Processing and properties of glass-bonded silicon carbide membrane supports

Porous SiC membrane supports were fabricated from SiC and glass frit at a temperature as low as 850 °C in air by a simple pressing and heat-treatment process. The effects of the initial SiC particle size and frit content on the porosity, flexural strength, and air permeation of the membrane supports were investigated. During heat-treatment, the glass frit transformed to a viscous glass phase, which acted as a bonding material between SiC particles and as a protecting layer for severe oxidation of SiC particles. The porosity of the porous SiC membrane supports could be controlled within a range of 37–46% with the present set of processing conditions. The typical flexural strength, permeability, and specific air flow rate of the porous membrane supports fabricated using 23 μm SiC particles with 15 wt% glass frit were 75 MPa, 4.2 × 10⁻¹³ m², and 32.4 L/min/cm², respectively.     

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 dye-sensitized solar modules based on a prototyping pilot line and their integration into energy storage microsystems

We successfully developed a prototyping pilot line for dye-sensitized solar modules up to 23 × 23 cm². Dedicated ceramic materials were studied for large area application: we formulated a lead-free glass frit sealant with low softening point based on the ternary system Bi₂O₃-B₂O₃-ZnO and a TiO₂ anatase screen-printable paste for semi-transparent photoanodes. Alongside traditional screen-printing, specific machines among which a thermal press, a dye injection equipment and an automatic electrolyte filler were designed and realized. A silver-free layout was adopted and the solar modules reached an efficiency close to 2%. Photovoltaic glass panels composed by interconnected DSSC modules were interfaced with custom integrated circuits to realize energy storage microsystems for two self-powered prototypes: a USB solar table for recharging of portable devices and a novel LED glass parapet for active night lighting are here presented.     

The influence of pH on particle packing in YSZ coatings electrophoretically deposited from a non-aqueous suspension

Yttria stabilized zirconia (YSZ) coatings were produced from a YSZ suspension in acetylacetone (ACAC) using electrophoretic deposition (EPD) and then sintered with substrate constraint at 1200 and 1300 °C. Before EPD, the operational pH of the suspension was adjusted by addition of acetic acid or triethanolamine (TEA) base. The effect of suspension pH on the deposition of EPD coatings was studied with respect to the suspension stability, coating density and microstructure. Results showed that the zeta potential had a high positive value on both sides of the iso-electric point (IEP). This probably resulted from the adsorption of TEA, detected by Fourier transform infrared spectroscopy. Three alkalies with different molecular structures were compared and the effect of their molecule length on the interparticle repulsion was discussed. Based on this, particle interactions were estimated for different pH suspensions. The reduced particle coagulation increased the packing density of the EPD coatings from 38% at pH 7.4 to 53% at pH 8.4. Therefore, subsequent sintering of coatings was promoted. The sinterability was evaluated by micro-hardness and microstructure. After sintering at 1200 °C, coatings made in pH 8.4 suspensions obtained a hardness of 786 MPa and had fewer big pores than coatings fabricated in pH 7.4 suspensions that had a hardness of 457 MPa.     

A study of the electrophoretic deposition of Bioglass® suspensions using the Taguchi experimental design approach

This paper presents a study of the Taguchi design method to optimise the rate of electrophoretic deposition (EPD) of Bioglass^® particles from aqueous suspensions. The effect of Bioglass^® concentration, pH and electric field was investigated. An orthogonal array of L₁₆ type with mixed levels of the control factors was utilized. Multivariate analysis of variance (MANOVA) and regression analysis based on the partial least-square method were used to identify the significant factors affecting the deposition rate and its stability during constant-voltage EPD. It was found that the pH of the suspension significantly influences the deposition rate whereas the applied electric field has the smallest effect on the deposition rate. In addition, the interaction between the Bioglass^® concentration and pH, which are key processing parameters influencing the deposition rate, was found to be significant. Although a high deposition rate was obtained at low electric field (5 V/cm) and pH 7, the instability of the suspension in particular at high Bioglass^® concentrations resulted in an increase in the variability of the deposition rate. The optimal EPD condition predicted was verified by experiments and good qualitative agreement was obtained. The experimental results and statistical analyses are discussed based on the current knowledge of the EPD of ceramic materials.     

Synthesis of glass–ceramics in the CaO–MgO–SiO2 system with B2O3, P2O5, Na2O and CaF2 additives

Glass–ceramics based on the CaO–MgO–SiO₂ system with limited amount of additives (B₂O₃, P₂O₅, Na₂O and CaF₂) were prepared. All the investigated compositions were melted at 1400 °C for 1 h and quenched in air or water to obtain transparent bulk or frit glass, respectively. Raman spectroscopy revealed that the main constituents of the glass network are the silicates Q¹ and Q² units. Scanning electron microscopy (SEM) analysis confirmed liquid–liquid phase separation and that the glasses are prone to surface crystallization. Glass–ceramics were produced via sintering and crystallization of glass-powder compacts made of milled glass-frit (mean particle size 11–15 μm). Densification started at 620–625 °C and was almost complete at 700 °C. Crystallization occurred at temperatures >700 °C. Highly dense and crystalline materials, predominantly composed of diopisde and wollastonite together with small amounts of akermanite and residual glassy phase, were obtained after heat treatment at 750 °C and 800 °C. The glass–ceramics prepared at 800 °C exhibited bending strength of 116–141 MPa, Vickers microhardness of 4.53–4.65 GPa and thermal expansion coefficient (100–500 °C) of 9.4–10.8 × 10⁻⁶ K⁻¹.     

Effects of H2O in EtOH–H2O disperse medium on the electrophoretic deposition of CaSiO3 fine powder

The effects of H₂O in the EtOH–H₂O disperse medium on the electrophoretic deposition (EPD) of CaSiO₃ fine powder were investigated. Fine CaSiO₃ powder with average diameter of 1·7 μm was prepared by the coprecipitation method. It was deposited on a stainless steel substrate by EPD in the disperse media with various H₂O concentrations (0–20·2 mass%) under a DC field of 50 V. The amount of the CaSiO₃ deposition increased with increasing H₂O up to 11·2 mass% but decreased rapidly beyond this concentration. The surface potential of the powder showed a similar trend as the amount of deposition against H₂O concentration. The effect of H₂O was summarized as follows: (1) the addition of positive charge on the surface of CaSiO₃ particles (2) the neutralization of the surface charge by OH⁻ caused by the dissolution of CaSiO₃ in the H₂O.     

Rapid in-situ solidification of SiO2 suspension by direct coagulation casting via controlled release of high valence counter ions from calcium iodate and pH shift

Rapid in-situ solidification of SiO₂ suspension under the joint action of releasing calcium ions and shifting pH has been proposed. When the suspension was heated up to 60 ℃, decomposition of calcium iodate which released calcium ions, as well as hydrolysis of diacetate (GDA) which shifted the pH toward the isoelectric point, both contributed to the solidification of suspension. The controlled coagulation of SiO₂ suspension could be realized via controlled release of high valence counter ions and pH shift at 60 ℃ within 30 min, which could considerably shorten the coagulation time compared with present reported results (1–3 h). Green body prepared by heating the SiO₂ suspension with 6.5 g L⁻¹ calcium iodate and 2.0 vol% GDA at 60 ℃ for 30 min shows uniform microstructure with compressive strength of close to 0.3 MPa. SiO₂ ceramics sintered at 1275 ℃ for 3 h possess homogeneous microstructure with bulk density of 2.06 g cm⁻³ and flexural strength of 40.3 MPa.     

Constrained sintering of YSZ/Al2O3 composite coatings on metal substrates produced from eletrophoretic deposition

Yttria stabilized zirconia/alumina (YSZ/Al₂O₃) composite coatings were prepared from electrophoretic deposition (EPD), followed by sintering. The constrained sintering of the coatings on metal substrates was characterized with microstructure examination using electron microscopy, mechanical properties examination using nanoindentation, and residual stress measurement using Cr³⁺ fluorescence spectroscopy. The microstructure close to the coating/substrate interface is more porous than that near the surface of the EPD coatings due to the deposition process and the constrained sintering of the coatings. The sintering of the YSZ/Al₂O₃ composite coating took up to 200 h at 1250 °C to achieve the highest density due to the constraint of the substrate. When the coating was sintered at 1000 °C after sintering at 1250 °C for less than 100 h, the compressive stress was generated due to thermal mismatch between the coating and metal substrate, leading to further densification at 1000 °C because of the ‘hot pressing’ effect. The relative densities estimated based on the residual stress measurements are close to the densities measured by the Archimedes method, which excludes an open porosity effect. The densities estimated from the hardness and the modulus measurements are lower than those from the residual stress measurement and the Archimedes method, because it takes account of the open porosity.     

The influence of nano alumina additions on the coefficient of thermal expansion of a LZS glass–ceramic composition

In this work a 19.58Li₂O·11.10ZrO₂·69.32SiO₂ (mol%) glass–ceramic matrix was prepared and milled in order to determine its coefficient of thermal expansion (CTE) and to study how it is influenced by the addition of nanosized Al₂O₃ particles (1–5 vol%) and submicrometric Al₂O₃ particles (5 vol%). Comminution studies from the LZS parent glass frit showed that a powder with an adequate particle size (3.5 µm) is achieved after 120 min of dry milling followed by a second step of 60 h wet milling. The obtained LZS glass–ceramic samples (fired at 900 °C/30 min) showed an average relative density of ∼98% with zirconium silicate and lithium disilicate as main crystalline phases. Prepared composites with 1, 2.5 and 5 vol% of nanosized Al₂O₃ and 5 vol% submicrometric Al₂O₃ showed average relative densities varying from 97% to 94% as the alumina content increased. The formation of β-spodumene in the obtained composites leads to reduce the CTEs, whose values ranged from 9.5 to 4.4×10⁻⁶ °C⁻¹. Composites with 5% nanosized alumina showed a CTE lower than that of the equivalent formulation with submicrometric alumina.     

Formation of MUA (mercaptoundeconic acid)-capped CDSe nanoparticle films by electrophoretic deposition

Electrophoretic deposition (EPD) has gained increasing interest for the deposition of materials such as TiO₂, carbon nanotubes and trioctylphosphine oxide (TOPO)-capped CdSe nanoparticles. In this study, a mercaptoundecanoic acid (MUA) CdSe nanoparticle film was formed by electrophoretic deposition. A colloidal suspension of TOPO-capped CdSe nanoparticles was prepared by the hot injection method, followed by ligand exchange to produce MUA-capped CdSe nanoparticles. As-prepared MUA-capped CdSe nanoparticles were washed using ethyl acetate and ethyl ether. Then, the washed nanoparticles were resuspended in ethanol and immediately used for EPD. A CdSe nanoparticle film measuring 2.75 µm in thickness was deposited at an applied voltage of 5 V and deposition time of 5 min.     

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.     

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.     

Logotype-selective electrochromic glass display

This paper describes a fabrication method of a logotype-selective electrochromic (EC) glass. The EC glass performance based on the sample size, WO₃ film thickness, and internal impedances under various applied voltages are also discussed. The logotype-selective electrochromic glass was fabricated by the sputter deposition process. Both working and counter electrode were coated with ITO/WO₃ films. The specific logotypes of “NCUT” and “NUU” can be displayed with positive and negative voltages applied to the EC glass. EC glasses of various sizes (1 cm², 4 cm², 9 cm², 25 cm², and 100 cm²) were also fabricated by sputter deposition process. When voltage (?3.5 V) was applied to the device, the active layer of the assembled device changed from almost transparent to a translucent blue color (colored). The average transmittance in the visible region of the spectrum for a 100 cm² EC device was 73% in the bleached state. The best device, with a 140 nm WO₃ active layer, had average transmittances in the colored and bleached states of 11.9% and 54.8%, respectively. Cyclic voltammogram tests showed that reproducibility of the colored/bleached cycles was good. Nyquist plots showed that increasing the device size decreased the current density, and the electrolyte impedance increased because of a low conductive electrolyte in the device.     

Influence of anionic stabilization of alumina particles in 2-propanol medium on the electrophoretic deposition and mechanical properties of deposits

The ceramic dispersions were prepared using 0.85, 1.70, 4.25, 12.75 or 21.25 wt.% of monochloroacetic, dichloroacetic or trichoroacetic acid, 15 wt.% alumina and 2-propanol. The mechanism of anionic stabilization in 2-propanolic media was described. Alumina green bodies were prepared from the stable dispersion via electrophoretic deposition (EPD). It was found that increasing dispersion conductivity significantly influenced the EPD yields. The most effective electrophoretic depositions were performed from dispersions with conductivity in range 4.0–5.3 × 10⁻⁴ S m⁻¹. Deposits with the highest green density were prepared from the dispersion stabilized by trichloroacetic acid. This behavior was explained by low voltage drop during deposition. The surface roughness was high at low dispersion conductivity and with increasing acid concentration in dispersion the surface of deposits was smoother. The mechanism of particle arrangement in deposit was discussed. Influence of stabilizer amount in the dispersion on the hardness and fracture toughness was described.     

Electrophoretic deposition of CoFe2O4 films from aqueous suspensions

CoFe₂O₄ nano-particles with average size of ～40 nm were synthesized via the chemical coprecipitation method. PAMANH₄ was used as dispersant to improve the stability of aqueous suspensions. Zeta potential and sediment volumes were tested to study the effects of pH and dispersant amounts on the stability of suspensions. The most stable suspension was obtained when using 0.6 wt.% PAMANH₄ as dispersant at pH = 10. Conductivity results showed that thoroughly dispersed suspensions were formed after being ultrasonic agitated for 30 min. CoFe₂O₄ films on Al₂O₃/Pt substrates fabricated via EPD sintered at 1250 °C exhibited preferentially oriented structure. The XRD analyses showed (2 2 0) and (5 1 1) were the preferential orientations. Anisotropy was also observed in magnetic hysteresis loops. Stronger ferromagnetic effect was observed in the in-plane orientation, with saturation magnetization of ～290 emu/cm³.     

Mechanical properties of nano-grain SiO2 glass prepared by spark plasma sintering

Silicon carbide (SiC) layers were deposited on silica (SiO₂) glass powder by rotary chemical vapor deposition (RCVD) to form SiO₂ glass (core)/SiC (shell) powder; this powder was consolidated by spark plasma sintering (SPS). SiO₂ glass powder with a particle size of 250 nm was coated with 5–10-nm-thick SiC layers. The resultant SiO₂ glass (core)/SiC (shell) powder was consolidated to form a nano-grain SiO₂ glass composite at a relative density above 90% by SPS in the sintering temperature range of 1573–1823 K. The Vickers hardness and fracture toughness of the SiO₂ glass composite at 1723 K were found to be 14.2 GPa and 5.4 MPa m^1/2, respectively.     

Properties and vibrational spectra of magnesium phosphate glasses for nuclear waste immobilization

The leaching behavior and structure of magnesium phosphate glasses containing 45–55 mol% MgO incorporated with simulated high level nuclear wastes (HLW) were studied. The leach rate of the waste glasses decrease with increasing of the simulated HLW content. The gross leach rate of the glass waste form containing 50 mol% MgO and 45 mass% simulated HLW is of the order of 10⁻⁶ g/cm² day at 90 °C, which is small enough as compared with the corresponding release from a currently used borosilicate glass waste form. The isolated ions such as dimeric (P₂O₇)⁴⁻ and monomeric (PO₄)³⁻ ions increase upon as increasing the incorporating amount of the simulated HLW. The changes in properties can be attributed to the structure changes owing to the incorporation of the simulated HLW.     

Structural,optical, and spectroscopic properties of Er3+-doped TeO2–ZnO–ZnF2 glass-ceramics

Transparent fluorotellurite glass-ceramics have been obtained by heat treatment of precursor Er-doped TeO₂–ZnO–ZnF₂ glasses. ErF₃ nanocrystals nucleated in the glass-ceramics have a typical size of 45 ± 10 nm. Based on the Judd-Ofelt theory, the main radiative parameters for the ⁴I_13/2 → ⁴I_15/2 transition have been obtained. The split of the absorption and emission bands and the reduction of the Ω₂ parameter, as compared to the glass, confirm the presence of Er³⁺ ions in a crystalline environment in glass-ceramic samples. The analysis of the ⁴I_13/2 decays suggests that a fraction of Er³⁺ ions remains in a glass environment while the rest forms nanocrystals. For the glass-ceramics, intense red and green upconversion emissions were observed with an enhancement of the ⁴F_9/2 → ⁴I_15/2 red one compared to the glass sample. The temporal evolution of the red emission together with the excitation upconversion spectra suggests that energy transfer processes are responsible for the enhancement of the red emission.