Constant Voltage Conditions Research Articles

The dual property of number and velocity fluctuations of charge carriers in a macroscopic conductor under thermodynamic equilibrium conditions

Fluctuation-dissipation relations are complemented by relating the macrovariables conductance and resistance, that describe dissipation, to the microvariables variance of carrier number and drift velocity fluctuations, that are the noise sources for constant voltage and constant current operation conditions, respectively. Thermal equilibrium implies a relationship between these two noise sources which follows from the reciprocity property of conductance and resistance. The boundary conditions of the measurement select the proper microscopic source of fluctuations to be related to the dissipation. An important consequence is that the source of shot noise, being associated with fluctuations of the carrier number inside the sample, is already present under equilibrium conditions, while the time scale of the source changes from an effective transport time to a current transit time when going from equilibrium to nonequilibrium conditions.

Modeling of high temperature proton exchange membrane fuel cell start-up processes

In this study, a three-dimensional dynamic multi-phase model is developed for the high temperature proton exchange membrane fuel cell (HT-PEMFC) to study its start-up processes. Two different kinds of start-up methods which are constant voltage and constant current density are investigated and compared with each other under the same conditions. It is found that the constant voltage mode can make HT-PEMFC reach its normal operating temperature faster than the constant current density. During both the constant voltage and constant current density conditions, there is liquid water produced in the catalyst layer of the cathode zone because the cell temperature is under 100 °C. The effects of surrounding environment are also analyzed and investigated. It is found that the heat convection coefficient has an important influence on the HT-PEMFC start-up process. The final cell temperatures under different conditions are obtained and the start-up durations are compared. To shorten the start-up time, a new non-heating method, variable voltage start-up strategy, is proposed and compared with the traditional assisting heating method. It is shown that the HT-PEMFC start-up performance is improved significantly by using this new variable voltage start-up strategy.

Universal dispersing agent for electrophoretic deposition of inorganic materials with improved adsorption, triggered by chelating monomers

Poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) is a polymeric functional material with a number of unique physical properties, which attracted significant interest of different scientific communities. Films of PAZO were deposited by anodic electrophoretic deposition (EPD) under constant current and constant voltage conditions. The deposition kinetics was analyzed under different conditions and the deposition mechanism was discussed. New strategy was developed for the EPD of different inorganic materials and composites using PAZO as a dispersing, charging, binding and film forming agent. It was found that PAZO exhibits remarkable adsorption on various inorganic materials due to the presence of chelating salicylate ligands in its molecular structure. The salicylate ligands of PAZO monomers provide multiple adsorption sites by complexation of metal atoms on particle surfaces and allow for efficient electrosteric stabilization of particle suspensions. The remarkable performance of PAZO in its application in EPD have been exemplified by deposition of a wide variety of inorganic materials including the single element oxides (NiO, ZnO, Fe2O3) the complex oxides (Al2TiO5, BaTiO3, ZrSiO4, CoFe2O4) different nitrides (TiN, Si3N4, BN) as well as pure Ni metal and hydrotalcite clay. The use of PAZO can avoid limitation of other dispersing agents in deposition and co-deposition of different materials. Composite films were obtained using PAZO as a co-dispersant for different inorganic materials. The deposit composition, microstructure and deposition yield can be varied. The EPD method offers the advantages of simplicity, high deposition rate, and ability to deposit thin or thick films.

Effect of fluoride and water content on the growth of TiO2 nanotubes synthesized via ethylene glycol with voltage changes during anodizing process

In this work, titanium foils were anodized in ethylene glycol solutions containing different amounts of water and fluoride to determine their effects on the top morphology and crystalline structure of the formed titania nanostructures. Anodizing was performed for 2 h by using titanium foils as both anode and cathode applying a squared-pulse voltage profile composed of one step at 80 V for 3 min followed by another at 20 V for 5 min; constant voltage conditions were also used to study the nanostructure formation on the surface. We found the formation of nanostructured titania on the surface of the anodized foil when small amounts of water and fluoride are present in the anodizing solution. The top of these nanostructures is irregular when no water is added, but is expected to change with different amounts of water and fluoride in the ranges of 1 - 9% and 0.05 - 0.5%, respectively. Synthesis parameters also change nanotube morphology. The morphology and structure properties of the samples were studied by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). Formation of TiO2 nanotubes by anodization method are strongly correlated to conditions like fluoride concentration and applied voltages. Tube length varying between 2 and 7 μm, exhibiting different diameters and wall thicknesses were obtained. When an alternate voltage was applied, the wall of the nanotubes presented evenly spaced rings while nanotubes with smooth wall form were observed when constant voltage was applied. Reflection peaks corresponding to Brookite, Anatase, and Rutile of TiO2 phases were observed from XRD measurements. A correlation between the effects of synthesis parameters on nanotube formation and morphological properties is presented. TiO2 nanotubes prepared by electrochemical anodization have excellent performance in various applications such as photocatalysts, solar cells, gas sensors, and biomedical applications.

A Modular Approach to Power Flow Regulation Solution

The operating modes of generations and the voltage states of power system must be solved when calculating and analyzing the power flow problem with operation demands. The generation variable differential were derived as well as the complete principle of variable differential analysis was formed, based on the model of expanded power flow with constraints, by using the implicit function differential method, the linear composing relation between the voltage variable differential and the expanded correction equations which included the equations of PQV node and branch power, solutions were also proposed. This new solving method is not featured in minimum variables however it is featured as a one-time simultaneous solution. Through the IEEE 5 bus system, the analyzing cases of total differential sensitivity and operation under conditions of constant line power and constant node voltage were carried out, these cases described the fact that the mixed variable solving method of power flow regulation has a simple form, small calculation volume and efficiency.

Fabrication of Self-Ordered Porous Alumina via Etidronic Acid Anodizing and Structural Color Generation from Submicrometer-Scale Dimple Array

Highly ordered anodic porous alumina with a large-scale cell diameter was successfully fabricated via anodizing in a new electrolyte, etidronic acid (1-hydroxyethane-1,1-diphosphonic acid). High-purity aluminum specimens were anodized in a 0.3M etidronic acid solution under constant current density and voltage conditions. Etidronic acid anodizing at 210 to 270V at the appropriate temperature caused the anodic porous alumina to exhibit self-ordering behavior, and periodic nanostructures measuring 530 to 670nm in cell diameter were fabricated on the aluminum substrate. The self-ordering voltage and the corresponding cell diameter could be increased without burning by systematically increasing the stepwise voltage. Two-step etidronic acid anodizing without nanoimprinting can easily yield the formation of highly ordered anodic porous alumina with a large-scale cell diameter. A submicrometer-scale dimple array fabricated via etidronic acid anodizing and subsequent selective oxide dissolution gave rise to bright structural color with a rainbow distribution.

CATHOLYTE-CONDITIONING ENHANCED ELECTROKINETIC REMEDIATION OF Co AND Pb POLLUTED SOIL

The feasibility of catholyte-conditioning to enhance the electrokinetic (EK) remediation of cobalt and lead polluted soil has been investigated in this study. Electrokinetic experiments were conducted using an EK cell 10 cm in width, 10 cm in height, and 50 cm in length. Plate type electrode of graphite was used as electrode material. Two experiments were conducted under constant voltage condition (2 V/cm). The pH values of the soil significantly affect the removal of Co and Pb ions. Due to electrolysis reaction, soil pH increases near the cathode and without pH conditioning, metals precipitate as hydroxides. This problem is solved by the addition of nitric acid (0.1N) in the catholyte compartment. Significant movement of metals was observed through the soil with high removal efficiency. Results showed that catholyte conditioning using nitric acid increased the removal of cobalt and lead from the soil and, consequently, the maximum removal achieved was 73.84% and 62.88% for cobalt and lead, respectively. These EK tests indicate that the increased experimental time induced a higher removal efficiency of cobalt and lead. The results suggest that longer treatment periods will result in further transport of cobalt and lead in the sample. Also, it indicated that the highest quantities of cobalt and lead moved towards the catholyte, particularly at upper 5 cm. On the basis of the experimental results, we conclude that the electrokinetic remediation, using 0.1N HNO3 as catholyte-conditioning, is suitable for extracting cobalt and lead from polluted soil.

Through-Silicon-Via(TSV) Filling by Electrochemical Deposition with Pulse-Reverse Current

TSV interconnection was widely investigated for next generation integrated-circuit(IC) which has significantly innovated function, excellent performance and high efficiency. Especially, TSV filling process by Cu electrochemical deposition occupied almost 40% of cost in the total TSV process. Therefore, a plenty effort has been put into decrease the processing time and prevent the formation of defects such as void or seam which could cause critical electrical and mechanical problems in the device. In the past, TSV filling studies were mainly focused on the function of chemical additives or bottom-up filling mechanism. In these kinds of researches, TSV filling process window was extremely limited because the applied current in the electrochemical process was a simple direct current or a constant voltage condition. Therefore, TSV filling by electrochemical deposition with pulse current was reported by our group for achieving the extensively wide process window. In this study, TSV filling by electrochemical deposition with pulse-reverse current was carried out for achieving even more extended process window.Electrochemical deposition experiments were carried out in the 1 M CuSO4 electrolyte with suppressor and accelerator. TSV (diameter: 6 μm, depth: 60 μm) coupon sample and Pt electrode was used as working and counter electrode, respectively. Pulse-reverse current was consisted with the peak current (ipeak) and the reverse current (irev) that applied during the on time (ton) and the reverse time (trev) period, respectively. (figure 1) During the on time and reverse time period, deposition and dissolution of Cu was occurred, respectively. The average current (iavg) could be calculated by equation in the figure 1. Peak current density and on time used in this study was fixed to 450 mA/cm2 and 2 μs, respectively. Vertically filled shapes of electrodeposited TSVs were observed by optical microscope (OM). Through achieved images, “bottom-up filling ratio” and “side wall growth ratio” was calculated for analyzing the TSV filling performance.Figure 2a shows the effect of reverse current density. The average current density and processing time was fixed to 2 mA/cm2 and 15 min, respectively. Bottom-up filling ratio was decreased with decreased reverse current. However side wall growth ratio was increased. These results were mainly caused by following reasons. Desorption of suppressor on the side wall during the reverse time was accelerated by increased reverse current. Even the ion depleted layer might be thicker due to decreased anodic current efficiency during the reverse time. Insufficiently relaxed ion depleted layer caused increasing the peak overpotential during the on time period. High overpotential caused accelerating the desorption rate of suppressor. Therefore, inhibition effect on the side wall was decreased, and thicker side wall was formed. Bottom-up filling ratio was naturally decreased because diffusing cupric ions from the top to the bottom of the via was preferentially consumed on the side wall.Figure 2b shows the effect of increased average current density in fixed reverse current density (irev = 5 mA/cm2). Both bottom-up filling ratio and side wall growth ratio was increased as average current density increased due to increased average current density. However, TSV filling mode was suddenly changed to conformal filling at the 5 mA/cm2. This result was mainly caused by following reason. Reverse time was decreased to increase the average current density in fixed reverse current condition. Decreased reverse time caused insufficient ion supplying to the ion depleted layer and ion depleted layer thickness was increased. Therefore, decreased bottom-up filling and increased side wall growth was occurred due to same reason as case of controlling the reverse current.

Characterization of polyetheretherketone particle suspensions for electrophoretic deposition

ABSTRACTSuspensions of polyetheretherketone (PEEK) using mixture of ethanol and isopropanol as solvent were prepared to carry out PEEK electrophoretic deposition (EPD). The rheological behavior and suspension structure of PEEK particles dispersed in co‐solvents were investigated over a range of pH values (1–10) and shear rates (γ = 101−3 × 102 s−1). These PEEK suspensions generally exhibited a pseudoplastic flow behavior, indicating the occurrence of particle aggregation in the liquid medium. The maximum solids fraction (ϕm) showed an estimated value of ϕm = 2.9 wt %. Using a suspension with 3 wt % PEEK concentration, PEEK coatings on stainless steel substrates were obtained by EPD at constant voltage condition. The influence of the electrolyte conductivity on PEEK EPD from ethanol–isopropanol suspensions was studied. Experimental results showed that high‐conductivity ethanol‐based suspensions yield non‐uniform deposits, while low‐conductivity suspensions resulted in uniform coatings. The difference in the deposition behavior is due to the different pH of the suspensions and the relationship of pH with suspension conductivity. pH = 8 was the optimal value for this system in terms of deposition results. The surfaces of EPD PEEK coatings were homogenous and a qualitatively good adhesion between the PEEK deposits and the substrate was confirmed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40953.

Morphological investigation of anodized TiO2 nanotubes fabricated using different voltage conditions

The morphology of TiO2 nanotube layers fabricated by electrochemical anodization in an ethylene glycol solution containing 0.5wt% NH4F was investigated as a function of several voltage conditions. The effects of voltage sweep rate, retention time, and initial sweep voltage on the surface pore structure and tube length were observed in detail by scanning electron microscopy (SEM). It was clearly seen that worm-like porous structures on the TiO2 nanotube layers were formed during the voltage sweep process. These porous structures changed to round-shaped individual pores with longer tubular layers under constant voltage conditions. The initial sweep voltage also affected the pore size, even when the same final voltage was applied. These findings indicate that voltage conditions are very important factors in determining the surface and layer structure of anodized TiO2 nanotubes.

Electrophoretic deposition of yttria-stabilised zirconia powder from aqueous suspensions for fabricating ceramics with channel-like pores

Abstract Electrophoretic deposition with simultaneous gas bubble formation by electrolysis can be used for producing ceramic green bodies, typically few millimetres in thickness, with unidirectionally aligned channel-like pores. The method is successfully applied to yttria-stabilised zirconia. Two types of aqueous suspension compositions are investigated. Suspensions with acetic acid additions are particularly suitable for forming green bodies with fine pore channels. Only small amounts of acetic acid, promoting the gas evolution, are needed for this purpose. Dissolution of yttria in the acidic range has to be considered, but the required low acid concentrations do not measurably affect the yttrium content of the deposits. Yttria dissolution can be minimised by a suspension composition containing an anionic polyelectrolyte and ammonia instead of acetic acid. The ammonia concentration influences the size of the tubular pores of the deposits formed under constant-voltage conditions. Using structured deposition electrodes, the regularity of the pore arrangement can be enhanced.

Electrolytic Removal of Phosphorus in Wastewater with Noble Electrode under the Conditions of Low Current and Constant Voltage

Electrolytic Removal of Phosphorus in Wastewater with Noble Electrode under the Conditions of Low Current and Constant Voltage

Development of a fast and selective separation method to determine histamine in tuna fish samples using capillary zone electrophoresis

This paper reports on the development of a fast and selective separation method by capillary zone electrophoresis (CZE) for the determination of histamine in tuna fish samples. The background electrolyte was composed of 60mmolL−1 hydroxyisobutyric acid and 10mmolL−1 sodium hydroxide at pH 3.3. The internal standard used was imidazole. Separations were performed in a fused uncoated silica capillary (32cm total length, 8.5cm effective length and 50μm internal diameter) with direct UV detection at 210nm. The samples and standards were injected hydrodynamically (50mbar, 3s) from the outlet capillary end (nearest to the detector) and the electrophoretic system was operated under normal polarity and constant voltage conditions of 30kV (positive polarity on the injection side). The migration time of histamine in the proposed method was only 0.34min. The method was then validated and different tuna fish samples were analyzed. Good linearity (R2>0.999), a limit of detection 0.14mgL−1, intra-day precision better than 3.5% (peak area of sample), and recovery in the range of 94–108% were obtained. The results of the histamine concentration determined in the samples by the CZE method were compared with the LC–MS/MS method.

Applications of Graphene Electrophoretic Deposition. A Review

This Review summarizes research progress employing electrophoretic deposition (EPD) to fabricate graphene and graphene-based nanostructures for a wide range of applications, including energy storage materials, field emission devices, supports for fuel cells, dye-sensitized solar cells, supercapacitors and sensors, among others. These carbonaceous nanomaterials can be dispersed in organic solvents, or more commonly in water, using a variety of techniques compatible with EPD. Most deposits are produced under constant voltage conditions with deposition time also playing an important role in determining the morphology of the resulting graphene structures. In addition to simple planar substrates, it has been shown that uniform graphene-based layers can be deposited on three-dimensional, porous, and even flexible substrates. In general, electrophoretically deposited graphene layers show excellent properties, e.g., high electrical conductivity, large surface area, good thermal stability, high optical transparency, and robust mechanical strength. EPD also enables the fabrication of functional composite materials, e.g., graphene combined with metallic nanoparticles, with other carbonaceous materials (e.g., carbon nanotubes) or polymers, leading to novel nanomaterials with enhanced optical and electrical properties. In summary, the analysis of the available literature reveals that EPD is a simple and convenient processing method for graphene and graphene-based materials, which is easy to apply and versatile. EPD has, therefore, a promising future for applications in the field of advanced nanomaterials, which depend on the reliable manipulation of graphene and graphene-containing systems.

Electrophoretic assembly of organic molecules and composites for electrochemical supercapacitors

Electrophoretic deposition (EPD) method has been developed for the fabrication of 1-pyrenebutyric acid (PBH) films from aqueous solutions. The films can be deposited at constant voltage or potentiodynamic conditions. The method allowed the formation of 0.1–2μm thick films, containing needle-shape PBH particles. The deposition mechanism involved the electrophoresis, pH decrease at the anode surface, charge neutralization and formation of insoluble PBH films. The film morphology and shape of the PBH particles are controlled by the π–π stacking mechanism of the polyaromatic PBH molecules. The important finding was the possibility of controlled EPD of multiwalled carbon nanotubes (MWCNTs) using PBH as a charging, dispersing and film forming agent. It was found that at low voltages or low PBH concentrations the deposits contained mainly MWCNT. The increase in the deposition voltage or/and PBH concentration resulted in co-deposition of MWCNT and needle-shape PBH particles. The new approach to the deposition of MWCNT was used for the fabrication of composite MnO2–MWCNT films for electrodes of electrochemical supercapacitors, which showed a specific capacitance of 250Fg−1. The EPD method developed in this investigation paves the way for the deposition of other small organic molecules and composites and their applications in new materials and devices, utilizing functional properties of the organic molecules, CNT, and other advanced materials.

Thin Films of Europium (III) Doped-TiO<sub>2</sub> Prepared by Electrophoretic Deposition from Nanoparticulate Sols

Colloidal sol-gel is a common method used for the preparation of stable and homogeneous sols and thin films. The nanoparticulate sols can be easily deposited by EPD, which is a versatile technique for producing denser and thicker coatings than those produced by other techniques like dipping. A complete characterization of the sols, such as colloidal stability and electrophoretic mobility, which can be determined through zeta potential measurements, as well as the influence of deflocculants in the surface properties, is needed before using electrophoretic deposition. In this work, we have prepared sols of TiO2with an alkoxide:water molar ratio of 50:1 and Eu (III) doped-TiO2(2 mole % Eu (III)) using as precursors titanium (IV) isopropoxide and europium (III) acetate hydrate, respectively. The stability of the particulate sols was studied in terms of conductivity, zeta potential and viscosity evolution. Anatase stable sols, after peptization and without the use of any additive, were deposited on stainless steel substrates by electrophoretic deposition under both constant current and constant voltage conditions. Using different intensities and deposition times we have obtained thin films with different features (thicknesses and morphology) and different optical properties. The presence of europium (III) increases particle size, viscosity and peptization time and decreases the band gap of TiO2.

Maxwell equation for conductivity of dielectrics as the basis of direct relationship of ionic electrical conductivity and mechanical losses in glasses. New problems of physical chemistry of glass

Use of the Maxwell equation for the conductivity of dielectrics and the theory of mechanical losses in glasses caused by ionic shifts has made it possible to calculate directly the temperature of the "ionic" max� imum of mechanical losses using data on direct current conductivity. The Maxwell equation was used without changes, in the view accepted in electromagnetic theory. An intuitive physicochemical interpretation of the nature of ionic conductivity measured at constant voltage as a relaxation process was suggested. Verification of the suggestion equation's validity was performed for onealkali glasses in silicate, borosilicate, phosphate, borate, and germanate systems. The ratio of calculated and experimental values of the temperature of the "ionic" internalfriction maximum corresponds to 0.995 ± 0.034 and does not depend on the frequency of measurements of internal friction (it changed by four orders) or the parameters characterizing conductivity. These results also confirm the validity of the Maxwell equation for the conductivity of dielectrics. The possi� bility of describing the direct current ionic conductivity of glasses as a Debye relaxation transition proved in this work is a consequence of the constant voltage condition. The design of a theory for the condition of nat� ural decay of a given potential, when the Kohlrausch relaxation regularity becomes valid, represents a princi� pally important problem of physics and physical chemistry of disordered systems.

Investigations on electrical characteristics and reliability properties of MOS capacitors using HfAlO x on n-GaAs substrates

Radio frequency sputtering system is employed to fabricate metal oxide semiconductor (MOS) capacitors using an ultra-thin layer of HfAlO x dielectric deposited on n-GaAs substrates with and without a Si interface control layer incorporated in between the dielectric and the semiconductor. Measurements are performed to obtain capacitance voltage ( C– V) and current voltage ( I– V) characteristics for GaAs/Si/HfAlO x and GaAs/HfAlO x capacitors under different constant voltage and constant current stress conditions. The variation of different electrical parameters such as change in interface trap density, hysteresis voltage with various values of constant voltage stress and the dependence of flat band voltage, fractional change in gate leakage current density, etc. with stress time are extracted from the C– V and I– V data for capacitors with and without a Si interlayer. Further the trap charge density and the movement of trap centroid are investigated for various injected influences. The dielectric breakdown and reliability properties of the dielectric films are studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t bd ⩾ 1350 s) is observed for HfAlO x gate dielectric with a silicon inter-layer under the high constant voltage stress at 8 V. Compared to capacitors without a Si interlayer, MOS capacitors with a Si interlayer exhibit improved electrical and breakdown characteristics, and excellent interface and reliability properties.

High-Power Piezoelectric Characteristics of Sr<sub>2</sub>Bi<sub>4</sub>Ti<sub>5</sub>O<sub>18</sub>-Ca<sub>2</sub>Bi<sub>4</sub>Ti<sub>5</sub>O<sub>18</sub>-Based Ferroelectric Ceramics

The high-power piezoelectric characteristics of lead-free piezoelectric ceramics, based on a bismuth layer-structured ferroelectric, MnCO3-doped (Sr0.7Ca0.3)2Bi4Ti5O18(abbreviated as SCBT0.3 + Mnxwt%), were studied. SCBT0.3 + Mnxwt% lead-free ceramics showed an extremely high mechanical quality factor (Qm) of more than 3000 in the (33) vibration mode under small-amplitude vibration. The high-power piezoelectric characteristics of SCBT0.3 + Mnxwt% were measured using the high-power measurement method based on frequency sweep driving under a constant voltage condition. It was found that the vibration velocityv0-pof SCBT0.3 + Mn 0.2 wt% linearly increased up to approximately 3.0 m/s. Therefore, the Mn-doped SCBT0.3-based ceramics are a promising candidate for lead-free high-power applications.

Detection of Paraquat in Oral Fluid, Plasma, and Urine by Capillary Electrophoresis for Diagnosis of Acute Poisoning

The aim of this work was to develop a simple and fast method for the detection of paraquat in oral fluid, plasma, and urine by capillary electrophoresis with diode-array detection (CE-DAD), to diagnose of acute poisoning related to this herbicide. The use of oral fluid in analytical toxicology has been established for drugs of abuse, but not for diagnosis of pesticides poisoning. Oral fluid was collected without stimulation using absorbent cotton swabs. Sample preparation included diluting, vortex mixing, and centrifuging of biological fluid, using ethyl paraquat as internal standard. CE-DAD analyses were performed in a fused-silica capillary, and separation was performed under constant voltage condition of 21 kV, with detection at 195 nm. The electrolyte was a 40 mmol/L phosphate buffer at pH 2.50. The proposed method provided a fast and simple assay for the determination of paraquat in human oral fluid, plasma, and urine. To our knowledge, this is the first mention of use of oral fluid as a biological fluid diagnosis of quaternary ammonium herbicide poisoning. After validation, the method was applied to two cases of acute poisoning by this herbicide.