Corrosion protection of PVD and paint coatings for selective solar absorber surfaces

The selective solar absorber surface is a fundamental part of a solar thermal collector, as it is responsible for the solar radiation absorption and for reduction of radiation heat losses. The surface’s optical properties, the solar absorption (á) and the emittance (å), have great impact on the solar thermal collector efficiency. In this work, two coatings types were studied: coatings obtained by physical vapor deposition (PVDs) and coatings obtained by projection with different paints (PCs) on aluminum substrates. The most common industrial high performing solar selective absorbers are nowadays produced by vacuum deposition methods, showing some disadvantages, such as lower durability, lower resistance to corrosion, adhesion and scratch, higher cost and complex production techniques. Currently, spectrally selective paints are a potential alternative for absorbing surfaces in low temperature applications, with attractive features such as ease of processing, durability and commercial availability with low cost. Solar absorber surfaces were submitted to accelerated ageing tests, specified in ISO 22975-3. This standard is applicable to the evaluation of the long term behavior and service life of selective solar absorbers for solar collectors working under typical domestic hot water system conditions. The studied coatings have, in the case of PVDs solar absorptions between 0.93 and 0.96 and emittance between 0.07 and 0.10, and in the case of PCs, solar absorptions between 0.91 and 0.93 and emittance between 0.40 and 0.60. In addition to evaluating long term behavior based on artificial ageing tests, it is also important to know the degradation mechanism of different coatings that are currently in the market. Electrochemical impedance spectroscopy (EIS) allows for the assessment of mechanistic information concerning the degradation processes, providing quantitative data as output, which can easily relate to the kinetic parameters of the system. EIS measures were carried out on Gamry FAS2 Femostat coupled with a PCL4 Controller. Two electrolytes were used, 0.5 M NaCl and 0.5 M Na2SO4, and the surfaces were tested at different immersion times up to 4 weeks. The following types of specimens have been tested: Aluminium with/without surface treatment, 3 selective paint coatings (one with a poly(urethane) binder and two with silicone binders) and 2 PVD coatings. Based on the behaviour of the specimens throughout the 4 weeks of immersion, it is possible to conclude that the coating showing the best protective properties corresponds to the selective paint coating with a polyurethane resin followed by the other paint coatings, whereas both the PVD coatings do not confer any protection to the substrate, having a deleterious effect as compared to the untreated aluminium reference.

Report : colorbond degradation model

This report documents work carried out in order to develop and prove a model for predicting the lifetime of painted metal components, with a particular emphasis on Colorbond® due to its prominent use throughout Australia. This work continues on from previous developments reported in 2002-059-B No. 12 [1]. Extensions of work included the following research: (1) Experimental proving of the leaching of chromate inhibitors from Colorbond® materials. (2) Updated models for the accumulation of salts and the time of wetness for gutters, based upon field observations. (3) Electrochemical Impedance Spectroscopy investigations aimed at correlating the corrosion rates of weathered Colorbond® with those predicted by modeling.

The effects of sintering profiles on the resistance and flatness of transparent conducting oxide substrates for DSC

The effects of sintering on several properties of FTO and ITO substates used in DSC have been investigated. FTO & ITO substrates were prepared with a range of sizes and aspect ratios - emulated laboratory style test cells through to prototype modules. Time and temperature of the sintering profiles were varied and sheet resistance and flatness measured. Electrical properties of the substrates were then further characterized by electrochemical impedance spectroscopy, and module sized devices were assembled and thickness variations over the device area were determined and related to performance.

Reduced electron recombination of dye-sensitized solar cells based on TiO 2 spheres consisting of ultrathin nanosheets with [001] facet exposed

An anatase TiO 2 material with hierarchically structured spheres consisting of ultrathin nanosheets with 100% of the [001] facet exposed was employed to fabricate dye-sensitized solar cells (DSC s). Investigation of the electron transport and back reaction of the DSCs by electrochemical impedance spectroscopy showed that the spheres had a threefold lower electron recombination rate compared to the conventional TiO 2 nanoparticles. In contrast, the effective electron diffusion coefficient, D n, was not sensitive to the variation of the TiO 2 morphology. The TiO 2 spheres showed the same Dn as that of the nanoparticles. The influence of TiCl 4 post-treatment on the conduction band of the TiO 2 spheres and on the kinetics of electron transport and back reactions was also investigated. It was found that the TiCl 4 post-treatment caused a downward shift of the TiO 2 conduction band edge by 30 meV. Meanwhile, a fourfold increase of the effective electron lifetime of the DSC was also observed after TiCl4 treatment. The synergistic effect of the variation of the TiO 2 conduction band and the electron recombination determined the open-circuit voltage of the DSC. © 2012 Wang et al.

Increased charge transfer of Poly (ethylene oxide) based electrolyte by addition of small molecule and its application in dye-sensitized solar cells

A Poly (ethylene oxide) based polymer electrolyte impregnated with 2-Mercapto benzimidazole was comprehensively characterized by XRD, UV–visible spectroscopy, FTIR as well as electrochemical impedance spectroscopy. It was found that the crystallization of PEO was dramatically reduced and the ionic conductivity of the electrolyte was increased 4.5 fold by addition of 2-Mercapto benzimidazole. UV–visible and FTIR spectroscopes indicated the formation of charge transfer complex between 2-Mercapto benzimidazole and iodine of the electrolyte. Dye-sensitized solar cells with the polymer electrolytes were assembled. It was found that both the photocurrent density and photovoltage were enhanced with respect to the DSC without 2-Mercapto benzimidazole, leading to a 60% increase of the performance of the cell.

Reusable surface confined semi-conducting metal-TCNQ and metal-TCNQF4 catalysts for electron transfer reactions

The synthesis of organic semiconducting materials based on silver and copper-TCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) and their fluorinated analogues has received a significant amount of attention due to their potential use in organic electronic applications. However, there is a scarcity in the identification of different applications for which these interesting materials may be suitable candidates. In this work, we address this by investigating the catalytic properties of such materials for the electron transfer reaction between ferricyanide and thiosulphate ions in aqueous solution, which to date has been almost solely limited to metallic nanomaterials. Significantly it was found that all the materials investigated, namely CuTCNQ, AgTCNQ, CuTCNQF4 and AgTCNQF4, were catalytically active and, interestingly, the fluorinated analogues were superior. AgTCNQF4 demonstrated the highest activity and was tested for its stability and re-usability for up to 50 cycles without degradation in performance. The catalytic reaction was monitored via UV-vis spectroscopy and open circuit potential versus time measurements, as well as an investigation of the transport properties of the films via electrochemical impedance spectroscopy. It is suggested that morphology and bulk conductivity are not the limiting factors, but rather the balance between the accumulated surface charge from electron injection via thiosulphate ions on the catalyst surface and transfer to the ferricyanide ions which controls the reaction rate. The facile fabrication of re-usable surface confined organic materials that are catalytically active may have important uses for many more electron transfer reactions.

An efficient hole transport material composite based on poly(3-hexylthiophene) and bamboo-structured carbon nanotubes for high performance perovskite solar cells

In this work, we have developed a new efficient hole transport material (HTM) composite based on poly(3- hexylthiophene) (P3HT) and bamboo-structured carbon nanotubes (BCNs) for CH3NH3PbI3 (MAPbI3) based perovskite solar cells. Compared to pristine P3HT, it is found that the crystallinity of P3HT was significantly improved by addition of BCNs, which led to over one order of magnitude higher conductivity for the composite containing 1–2 wt% BCNs in P3HT. In the meantime, the interfacial charge transfer between the MAPbI3 light absorbing layer and the HTM composite layer based on P3HT/BCNs was two-fold faster than pristine P3HT. More importantly, the HTM film with a superior morphological structure consisting of closely compact large grains was achieved with the composite containing 1 wt% BCNs in P3HT. The study by electrochemical impedance spectroscopy has confirmed that the electron recombination in the solar cells was reduced nearly ten-fold with the addition of 1 wt% carbon nanotubes in the HTM composite. Owing to the superior HTM film morphology and the significantly reduced charge recombination, the energy conversion efficiency of the perovskite solar cells increased from 3.6% for pristine P3HT to 8.3% for P3HT/(1 wt% BCNs) with a significantly enhanced open circuit voltage (Voc) and fill factor (FF). The findings of this work are important for development of new HTM for high performance perovskite solar cells.

Enhanced earth grid performance by improved conductor properties

Encroaching built environment with increased fault current levels is demanding a robust design approach and prolonged improved performance of the earth grid. With this in mind, the aim of the project was to perform a sensitivity analysis of the earth grid and an earthing performance evaluation with graphene coated conductors. Subsequent to these, a conceptual design to continuously monitor the performance of the earth grid was developed. In this study, earth grid design standards were compared to evaluate their appropriate use in determining the safety condition. A process to grow a thin film of graphene on the surface of cylindrical copper rods was developed to evaluate earthing performance in terms of conductivity and corrosion susceptibility.

Effect of laser surface treatment on microstructure and properties of MRI 230D Mg alloy

A creep resistant Mg alloy MRI 230D was subjected to laser surface treatment using Nd:YAG laser equipped with a fiber optics beam delivery system in argon atmosphere. The laser surface treatment produced a fine dendritic microstructure and this treatment was beneficial for the corrosion and wear resistance of the alloy. Long-term linear polarisation resistance and Electrochemical Impedance Spectroscopy measurements confirmed that the polarisation resistance values of laser treated material were twice as high as that for the untreated material. This improved behaviour was due to the finer and more homogenous microstructure of the laser treated surface. The laser treatment also increased surface hardness two times and reduced the wear rate by 25% due to grain refinement and solid solution strengthening.

Sputter deposited LiPON thin films from powder target as electrolyte for thin film battery applications

Lithium phosphorus oxynitride (LiPON) thin films as solid electrolytes were prepared by reactive radio frequency (rf) magnetron sputtering from Li3PO4 powder compact target. High deposition rates and ease of manufacturing powder target compared with conventional ceramic Li3PO4 targets offer flexibility in handling and reduce the cost associated. Rf power density varied from 1.7 Wcm(-2) to 3 Wcm(-2) and N-2 flow from 10 to 30 sccm for a fixed substrate to target distance of 4 cm for best ionic conductivity. The surface chemical analysis done by X-ray photoelectron spectroscopy showed incorporation of nitrogen into the film as both triply, NE and doubly. Nd coordinated form. With increased presence of NE, ionic conductivity of LiPON was found to be increasing. The electrochemical impedance spectroscopy of LiPON films confirmed an ionic conductivity of 1.1 x 10(-6) Scm(-1) for optimum rf power and N-2 flow conditions. (C) 2011 Elsevier B.V. All rights reserved.

Effect of TiO2 electrode thickness on photovoltaic properties of dye sensitized solar cell based on randomly oriented Titania nanotubes

Anatase titania nanotubes (TNTs) have been synthesized from P25 TiO2 powder by alkali hydrothermal method followed by post annealing. The microstructure analysis by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the formation of anatase nanotubes with a diameter of 9-10 nm. These NTs are used to make photo anode in dye-sensitized solar cells (DSSCs). Layer by layer deposition with curing of each layer at 350 C is employed to realize films of desired thickness. The performance of these cells is studied using photovoltaic measurements. Electrochemical impedance spectroscopy (EIS) is used to quantitatively analyze the effect of thickness on the performance of these cells. These studies revealed that the thickness of TiO2 has a pronounced impact on the cell performance and the optimum thickness lies in the range of 10-14 mu m. In comparison to dye solar cells made of P25, TNTs based cells exhibit an improved open circuit voltage and fill factor (FF) due to an increased electron lifetime, as revealed by EIS analysis. (C) 2011 Elsevier B.V. All rights reserved.

Reversibility of Mg/Mg2+ couple in a gel polymer electrolyte

Investigations on solid state rechargeable magnesium batteries are considered important similar to lithium batteries. In view of negligible hazards and less reactivity of the magnesium, in comparison with lithium, studies on rechargeable magnesium batteries are expected to have a wide scope in future. Solid polymer electrolytes, which conduct Mg2+ ions and reversibility of a Mg/Mg2+ couple are essential components of the studies. In the present investigations, the existence of reversibility of a Mg/Mg2+ couple in a gel polymer electrolyte (GPE) medium is established for the first time in literature. Results obtained by electrochemical impedance spectroscopy and cyclic voltammetry on Mg/GPE/Mg, SS/GPE/SS symmetrical cells show evidence for the reversibility. (C) 1999 Elsevier Science Ltd. All rights reserved.

Electroless Ni-W-P Coating and Its Nano-WS2 Composite: Preparation and Properties

The ternary alloy Ni-W-P and its WS2 nanocomposite coatings were successfully obtained on low-carbon steel using the electroless plating technique. The sodium tungstate (Na2WO4) concentration in the bath was varied to obtain Ni-W-P deposits containing various Ni and P contents. WS2 composite was obtained with a suitable concentration of Na2WO4 in Ni-P coating. These deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) studies. The corrosion behavior was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies in 3.5 wt % NaCl solutions, and the corrosion rates of the coatings for Ni-P, Ni-W-P, and Ni-W-P-WS2 were found to be 2.571 x 10(-5), 8.219 x 10(-7), and 7.986 x 10(-7) g/h, respectively. An increase in the codeposition of alloying metal tungsten (W) enhanced the corrosion resistance and microhardness and changed the structure and morphology of the deposits. Incorporation of WS2 nanoparticles to Ni-W-P alloy coating reduced the coefficient of friction from 0.16 to 0.11 and also helped in improving the corrosion resistance of the coating further.

Dielectric properties of novel PVA/ZnO hybrid nanocomposite films

In this study, the dielectric properties of PVA/ZnO nanocomposites films were evaluated. The composites were prepared by a solution casting technique. The dispersion and functionalization of the ZnO nanoparticles in the composite films were characterized by spectroscopic technique. The surface morphology of the PVA/ZnO nanocomposites films were elucidated using AFM. The charge transport properties were evaluated based on the dielectric and impedance spectroscopy techniques. Low ZnO loading composite shows low dielectric value at higher frequency and behaves as a lossless material. The complex impedance spectra suggest the change in conductivity, due to the change in bulk resistance of the materials and less relaxation time. Thus, all PVA/ZnO nanocomposites behave as lossless materials above 10(6) Hz indicating the composites are useful in microwave application. (c) 2012 Elsevier Ltd. All rights reserved.