The effects of the temperature on the some parameters obtained from current-voltage and capacitance-voltage characteristics of polypyrrole/n-Si structure

The polypyrrole/n-Si structure has been directly formed onto the n-Si substrate by the electrochemical polimerization of the organic polypyrrole at 45 °C electrolyte temperature. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the structure have been determined at various temperatures in the range of 77-300 K and different frequencies. Some diode parameters have been calculated from these curves. It has been seen that the measured capacitance decreases with increasing frequency due to a continuous distribution of the interface states in the frequency range of 10 kHz-1 MHz. The barrier heights values obtained from the I-V and C-V characteristics have been compared. It has been seen that the barrier height value obtained from the C-V measurements are higher than that obtained from the I-V measurements at various temperatures. This behaviour has been attributed to the interfacial layer, the interface states and barrier inhomogeneity of the structure. Also this discrepancy can be due to the different nature of the C-V and I-V measurement techniques. A correlation seems to exist between the variation of the band gap and Fermi level energy of Si with temperature.     

The corrosion protection of mild steel by single layered polypyrrole and multilayered polypyrrole/poly(5-amino-1-naphthol) coatings

Electrochemical synthesis of polypyrrole (PPy) and top coat of poly(5-amino-1-naphthol) (PANAP) on PPy films from oxalic acid solution was achieved on mild steel (MS) by cyclic voltammetry technique. The morphology and the structure of the films were investigated by scanning electron microscopy (SEM). The corrosion performance of this multilayer coating and single PPy coating were investigated in 3.5% NaCl solution by using open circuit potential (E_ocp)–time curves, polarization curves and electrochemical impedance spectroscopy (EIS). It was found that the multilayer PPy/PANAP coating could provide much better protection than single PPy coating for corrosion of MS. It was observed that corrosion performance of coatings was increasing with immersion period. This was explained by auto-undoping properties of PPy coatings during immersion in corrosive solution. The improved corrosion performance in the presence of PANAP top coat on PPy was explained by increase in barrier effect of bilayer films.     

The electrodeposition of polypyrrole on Al alloy from room temperature ionic liquids

The direct electrodeposition of conjugated polymers onto active metals such as aluminum and its alloys is complicated by the concomitant oxidation of the metal that occurs at the positive potential required for polymer formation/deposition. We previously described an approach that uses electron transfer mediation to reduce the deposition potential of polypyrrole (PPy) on aluminum and aluminum alloy by nearly 500 mV, permitting film deposition from aqueous solution with nearly 100% current efficiency. In this report, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM⁺TFSI⁻) has been successfully employed both as the growth medium and the supporting electrolyte for directly depositing uniform and conductive PPy coatings onto Al alloy 2024-T3 surface via a potentiodynamic technique. The depositions of PPy were carried out under cyclic voltammetric conditions from 0.3 M pyrrole in ionic liquid solutions. Film morphology was characterized by atomic force microscopy, optical microscopy, and scanning electron microscopy (SEM). Energy dispersive X-ray analysis and X-ray photoelectron spectroscopy verified that the TFSI⁻ anion was incorporated into the polymer as the dopant ion. Thickness of the film was measured by SEM and film conductivity was determined by both a four-point probe technique and by conducting atomic force microscopy. Electrochemical activity of the film was assessed by cyclic voltammetry. Results from these preliminary studies will be reported. Presented at the 2007 FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in Toronto, Ont., Canada, on October 3–5, 2007.     

Synthesis and formation mechanism study of rectangular-sectioned polypyrrole micro/nanotubules

Aligned polypyrrole (PPy) micro/nanotubules were synthesized via a self-assembly method using FeCl₃ as oxidant and Acid Red 1 (C.I. 18050, 5-(acetylamino)-4-hydroxy-3-(phenylazo)-2,7-naphthalenedisulfonic acid) as dopant. PPy has a typical length of 530 μm and a unique rectangular-sectioned morphology. Its general morphology could be manipulated by varying synthetic conditions including polymerization time, monomer concentration, oxidant species, and stirring. The synthesized PPy and reaction intermediates were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and solubility tests in methanol and water. Our observation and results suggest a plausible formation mechanism of rectangular-sectioned PPy micro/nanotubules. AR1-Fe(II) complex formed from the complexation of Acid Red 1 and Fe²⁺(reduced from Fe³⁺), which precipitated in the aqueous solution, might have functioned as ‘template’ during the polymerization of pyrrole monomers. The conductivity of PPy with different morphologies was also measured and compared.     

Electrochemical investigation of conformational rearrangements of polypyrrole deposited on Al alloys

Polypyrrole (PPy) films were electrochemically deposited on AA2024 and AA6082 Al alloys by a two-step galvanostatic procedure: (1) activation in nitric acid and (2) deposition in oxalic acid. Polymeric films were electrochemically characterized through a series of cyclovoltammetric experiments, underlining differences due to the two different substrates. Interesting effects are linked to the presence of copper in AA2024, that extracted from the alloy during the deposition, is included into the polymeric matrix increasing its quality and polymerization yield. Methods and experiments based on Otero's Electrochemically Stimulated Conformational Relaxation model (ESCR) were performed in order to investigate structural changes of the polymer in function of an applied potential. PPy on AA2024 manifests a more complex redox process, involving both cations and anions, as compared to the polymer film on AA6082 that involves only anion interchange.     

Optimization of electrochemical polymerization parameters of polypyrrole on Mg–Al alloy (AZ91D) electrodes and corrosion performance

We report on the optimum electropolymerization conditions of polypyrrole (PPy) coatings on Mg alloy AZ91D electrodes from aqueous electrolytes of sodium salicylate via cyclic voltammetry (CV). Results show that initial and end potential values during the electrochemical coating procedure play an important role on the adhesion and corrosion performance of PPy films. Corrosion tests of AZ91D electrodes coated with PPy under optimized conditions show a good corrosion performance during 10 days in Na₂SO_4, without peeling off of these thin films.     

Electrochemical synthesis and redox behaviour of polypyrrole coatings on copper in salicylate aqueous solution

In this work, polypyrrole (PPy) coatings have been successfully electrodeposited on copper substrates from aqueous salicylate solutions. Homogenous and uniform films can be grown under galvanostatic or potentiostatic control without noticeable substrate dissolution. The redox behaviour obtained for the films is similar to that displayed by PPy grown under the same conditions on noble metals. Strong adherence to copper is observed as far as PPy is in its oxidised state but it is lost when the system is subjected to potentials lower than −0.5 V versus saturated calomel electrode (SCE).     

Characterisation and corrosion studies of steel electrodes covered by polypyrrole/phosphotungstate using Electrochemical Impedance Spectroscopy

Polypyrrole/PW₁₂O₄₀³⁻ hybrid material was electrosynthesised on carbon steel electrodes in acetonitrile medium. The coatings obtained were characterised by Electrochemical Impedance Spectroscopy (EIS). On free-standing polypyrrole films the electrical response was mainly due to ion–ion charge transfer resistance, with a value of 175 Ω cm². A value of 2 × 10⁻⁵ S/cm was determined for the hybrid material conductivity. A charge transfer resistance about 7000 Ω cm² was obtained due to steel/oxide interface. Corrosion tests showed an important improvement in the protection against corrosion when the carbon steel electrodes were coated by these polymeric films.     

Electrosynthesis and characterization of polypyrrole/Au nanocomposite

Polypyrrole films containing gold nanoparticles (PPy/Au) were electrosynthesized on a glassy carbon electrode. This was done by applying a constant current of 1.43 mA cm⁻² in solutions containing colloidal Au particles and pyrrole monomer. A chloroaurate medium with a citrate/tannic acid reducing/protection agent was employed for generating the Au colloids. The PPy/Au films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Also, electrochemical behaviors of the PPy/Au films were characterized by cyclic voltammetry (CV) and AC impedance measurements. Experimental results demonstrate that PPy/Au has greater conductivity and better stability than PPy. The effect of incorporated Au nanoparticles in PPy matrix was studied and the mechanism was suggested.     

Study of the anticorrosive properties of polypyrrole/polyaniline bilayer via electrochemical techniques

In this work, using electrochemical techniques the authors investigated the protective properties of a polypyrrole/polyaniline bilayer as a conductive polymer. A polypyrrole/polyaniline bilayer was deposited on carbon steel substrate by potentiostatic method. The electric capacitance and resistance of the films were monitored with the immersion time in a corrosive solution to investigate the water permeability of the films. Polypyrrole/polyaniline bilayer has a relatively low permeability and good catalytic behavior in passivation of carbon steel in longer periods. The results show that the bilayer has a better anticorrosive behavior compared to homopolymers (polypyrrole and polyaniline).     

Electrochemical preparation and redox/ion exchange properties of polypyrrole in aqueous sodium hexafluoroaluminate

Electrodeposition and redox switching performance of polypyrrole in aqueous solution of sodium hexafluoroaluminate are described. An incorporation of NaAlF₆²⁻ into the polymer phase is indicated by the EQCM analysis of electrodeposition. A SEM micrograph shows a characteristic morphology of the polymer layer. A mechanism of the redox process of polypyrrole is discussed based on CV and EQCM results involving the measurements performed as a function of a time scale of the redox cycle and a life time of the electrode. Structure determining interactions between polymer sites and counterions are indicated. Participations of ion-pair counterion, co-ion, salt, water, oxygen in the redox process of polypyrrole are discussed. A slow irreversible rearrangement in the structure/composition, inducing a change in the mechanism of the reversible redox process, is postulated to occur during the reduction process of the virgin anion-exchanging polypyrrole. Long time scale processes were observed to result in cation exchange properties accompanied by a substantial decrease in redox activity and/or CV currents of the polypyrrole electrode. The performance of the primary hexafluoroaluminate counterion electrode, prepared in aqueous solution of sodium hexafluoroaluminate, is compared to the secondary hexafluoroaluminate counterion electrode, prepared in a presence of the sodium chloride solution. In general, the CV and EQCM characteristics of the two system are similar due to pronounced contribution of the bathing electrolyte to the performance of the polymer electrode.     

Determination of the Characteristic Parameters of Polyaniline/p-type Si/AI Structures from Current-Voltage Measurements

ABSTRACT

A high-quality polyaniline/p-Si structure is produced by electrochemical deposition of soluble polyaniline on p-type silicon substrates. The polyaniline/p-Si contact has clearly demonstrated rectifying behavior by current-voltage curves studied at room temperature. The data have been analyzed and interpreted on the basis of the thermionic emission mechanism. The forward bias I-V characteristics of this device have exhibited an ideality factor of 2.15, a saturation current of 4.48 × 10^?9A, and a barrier height of 0.78 eV. The diode shows non-ideal I-V behavior with an ideality factor greater than unity that can be ascribed to the interfacial layer, the interface states, and the series resistance.     

Study of polaron and bipolaron states in polypyrrole by in situ Raman spectroelectrochemistry

The transitions from the reduced-polaron-bipolaron states of polypyrrole (ppy) were analyzed by in situ Raman spectroelectrochemistry. The distinct vibrational modes presented by the polymer in different oxidation levels were assigned to specific signatures of polaron and bipolaron states. As the polymer was oxidized from the neutral state, an intermediary phase featuring vibrational bands from both the benzoid (reduced) and the quinoid (oxidized) forms were observed. This intermediary phase was correlated to the polaron state. The results were compared with previous ESR data that confirm the presence of polaron and bipolaron states in the potential region where the vibrational modes of these phases were identified.     

On the some electrical properties of the non-ideal PPy/p-Si/Al structure

The electrical analysis of the PPy/p-Si structure has been investigated by means of I-V, C-V and C-f measurements. The diode ideality factor and the barrier height have been obtained to be n=1.78 and Φ_b=0.69 eV by applying a thermionic emission theory, respectively. At high current densities in the forward direction, the series resistance effect has been observed. In general, the barrier height obtained from C-V data is greater than obtained from the I-V. This has been explained by introducing a spatial distribution of barrier heights (BHs) due to barrier height inhomogeneities that present at the PPy/p-Si interface. The C-f measurements of the structure have been performed at various biases and it has been seen that they have a good agreement between experimental and theoretical values. The interface state density N_ss and relaxation time τ of the structure have been determined from the C-f characteristics.     

Effect of crystallization on morphology-conductivity relationship in polypyrrole/poly(?-caprolactone) blends

Electrically conducting blends, based on polypyrrole (PPy) as the conductive polymer and poly(?-caprolactone) (PCL) as an insulating polymeric matrix, were prepared by polymerizing pyrrole (Py) in its vapor state inside the PCL matrix. The roles of specific interactions between blend components as well as the crystallization of PCL matrix in the resulting morphology have been analyzed by Fourier-transform infrared spectroscopy (FTIR), thermo-optical analysis (TOA) and atomic force microscopy (AFM). The results indicate that PPy is located within both the intra and interspherulitic regions of the PCL matrix achieving a well-developed connected network. Compared with amorphous matrices, considerable conductivity (around 1 S/cm) was raised with the crystalline PCL matrix with only a relatively low level of the conductive polymer (∼5%) in the blend.     

Si3N4/Al反应烧结制备AlN/Al复合材料

研究了采用Si3N4与Al的混合粉,经压制、烧结制备AlN/Al-Si复合材料的技术方法.试验结果表明:AlN的反应生成机制属于一种连续渐进式反应形成过程,即于高温下液相Al中的Al原子渗入Si3N4的晶体点阵取代Si原子而逐渐使之向AlN晶体点阵转化的过程.被取代的Si原子从固相Si3N4中析出,扩散溶入液相Al中,冷却后形成Al-Si合金固溶体,一般呈网状分布于AlN晶体相的周围.新生成的AlN与Al-Si合金相之间表现出很好的界面亲和性.     

Si3N4／Al反应烧结制备AIN／Al复合材料

研究了采用Si，N4与Al的混合粉，经压制、烧结制备AIN／Al-Si复合材料的技术方法。试验结果表明：AIN的反应生成机制属于一种连续渐进式反应形成过程，即于高温下液相Al中的Al原予渗入Si3N4的晶体点阵取代Si原予而逐渐使之向AIN晶体点阵转化的过程。被取代的Si原予从固相Si3N4中析出，扩散溶入液相Al中，冷却后形成Al-Si舍金固溶体，一般呈网状分布于AIN晶体相的周围。新生成的AIN与Al-Si合金相之间表现出很好的界面亲和性。     

Analysis of the effect of polypyrrole synthesis conditions on its capacity to reduce hexavalent chromium

This paper reports the capacity of polypyrrole to reduce toxic hexavalent chromium (Cr(VI)). The influence of using different electrolytes during the polymer's synthesis has been studied. To improve the reduction of Cr(VI), the parameters considered were the polypyrrole morphology and the amount of conducting polymer. Polypyrrole obtained by cyclic voltammetry at a low sweep rate using KBr as supporting electrolyte showed better performance for Cr(VI) reduction compared to coatings obtained by constant potential or cyclic voltammetry at high sweep rates.     

Strategy for the syntheses of isolated fine silver nanoparticles and polypyrrole/silver nanocomposites on gold substrates

In this work, isolated fine silver nanoparticles and polypyrrole/silver nanocomposites with diameters of about 10 nm on gold substrates were first prepared by electrochemical methods. First, an Ag substrate was cycled in a deoxygenated aqueous solution containing 0.1 M HCl from −0.30 to +0.30 V versus Ag/AgCl at 5 mV/s with 30 scans. Subsequently the Ag working electrode was immediately replaced by an Au electrode and a cathodic overpotential of 0.2 V was applied under controlled sonication to synthesize Ag nanoparticles on the Au electrode. Then pyrrole monomers were encouragingly found to be polymerized on the deposited Ag nanoparticles. This polymerization is distinguishable from the known chemical or electrochemical one, due to the electrochemical activity of unreduced species of Ag_n⁺ clusters inside the nanoparticles. Also, this polymerization may be ascribed to the oxidizing agent of AuCl₄⁻, which is present on the Au electrode.     

Effect of saccharin addition on the corrosion resistance of polypyrrole coatings

Electropolymerization baths for polypyrrole coating typically consist of two main constituents: monomer and counter-ion. By adding saccharin as the third constituent, a new branch emerges in electropolymerization that will yield coatings with modified properties. In the present study, polypyrrole is galvanostatically deposited onto carbon steel in an aqueous solution containing 0.2 M pyrrole and 0.1 M oxalic acid as the supporting electrolyte with (0.25, 0.5, 2.5 g/l) and without saccharin addition. Determination of the corrosion resistance of coatings in 0.1 M NaCl solution shows that in the presence of 0.5 g/l saccharin, a more noble corrosion potential and a greater corrosion resistance are obtained. Electrochemical impedance spectroscopy (EIS) revealed that the corrosion process was under infinite diffusion control of ions during prolonged immersion. The results indicate that the lower diffusion rate of ions in the coating produced in the presence of 0.5 g/l saccharin is responsible for its better corrosion resistance. Atomic force microscopy (AFM) shows that greater compaction of the coating produced in the presence of 0.5 g/l saccharin could be the reason for its higher corrosion resistance.