Rheological Behaviour of Some Dispersions for Long Lasting Protection of Copper-Aluminium Contacts in Power Transmission Equipment (original) (raw)
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The work presented in this article involves the study of rheometric profile of several rheological additives in two-component (2K) high build epoxy zinc phosphate primer and two-component high build aliphatic polyurethane topcoat. Viscosity profile and thixotropic behavior at different shear rates have been determined for both the paints using Physica MCR 301 Rheometer of Anton Paar. The valuable information derived from these measurements led to better insight into the influence of these rheological additives on important paint properties like flow and leveling, sag control, in-can settling during storage, etc. Rheometric results were also compared with the results obtained during the actual application of these experimental coatings on mild steel panels. From the rheological study it was concluded that the thickeners based on surfacemodified clay and organically modified castor oil derivative work well in epoxy zinc phosphate primer whereas polyurea-based thickener showed better results than other rheological additives in the case of the 2K polyurethane system. Measurement of low shear and high shear viscosity response of different thickeners helps in predicting storage and application behavior of these coatings which correlates well with the actual observation.
Materials & Design, 2013
Novel isotropic conductive adhesives (ICAs) filled with metal-coated polymer spheres have been introduced in order to improve the mechanical reliability compared to conventional silver-filled ICAs. The topic of this study is the rheology of an epoxy filled with monodisperse polymer spheres with or without Ag coating. In trials with uncoated spheres, the viscosity increases with increasing sphere fraction, while the sphere diameter (6 vs. 30 lm) only has a minor effect. With 45 vol% of spheres (giving an ICA with adequate electrical properties), the Ag coating on the spheres has a large effect on the rheology of the adhesive paste. Compared to the epoxy with uncoated spheres, the epoxy with Ag-coated spheres exhibits higher viscosity, higher storage and loss moduli, and a higher ratio of storage modulus to loss modulus (about 10 times). Furthermore, the viscosity of the epoxy with coated spheres increases with time in oscillatory measurements with low to intermediate frequencies.
New generation of protective coatings intended for the power industry
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This article presents the fundamentals of the production technology of multi component composite coatings of a zonal structure designed for the protection of components and appliances against corrosive and erosive wear at elevated and high temperatures. They can be also applied to seal the surfaces of thermally sprayed coatings. In a technological variant of the process, an external ceramic coating containing aluminium and chromium oxides was produced. An aluminium phosphate binder was used as a component of ceramic seal and of the coating. Flow charts of the binder and ceramic coatings fabrication are presented here. The structure and phase composition of selected coatings have been determined and some examples of their application in the domestic power industry have been presented.
Electrochimica Acta, 1999
Copper pipes which are widely used in the refrigerator industry can sometimes work in high humidity atmospheres and in aggressive conditions which can produce dangerous corrosion phenomena of the pipes. Moreover, the design of the refrigerator cooling circuit can introduce some other corrosion problems because copper pipes are frequently in electrical contact with aluminium pipes causing serious galvanic attack on the less noble metal. In order to eliminate these corrosion phenomena, the insulation of capillary copper tubes, used for the production of regenerative heat exchanger, was proposed, by the application of organic coatings. The protection of copper capillary tubes was obtained using the same technology (coextrusion) and the same resins (polyvinylformal or polyestherimide layer followed by a polyamideimide layer) employed for insulating copper wires for electrical motors. The barrier properties and adhesion of the selected organic coatings have been studied using coated copper samples in the as received conditions or after pipe bending or coating scratching, in order to simulate actual defects which can be introduced during refrigerator assembly. EIS proved to be a very useful technique in order to evaluate the protection properties of the selected coatings. PVF coatings showed good barrier properties only when 60 mm thickness coating was applied. Nevertheless, when arti®cial defects were produced in the coating, barrier properties were remarkably diminished. In fact, mechanical deformation increased water permeability and coating delamination easily occurred at scratches. PE coatings showed better barrier properties, even applying a thinner coating (40 mm). Mechanical deformation, in the range of 10% elongation, was sustained by this coating without suering a clear decrease of its barrier properties. Moreover, this kind of coating showed better resistance to coating delamination processes, probably because of better adhesion to the metal substrate. Such property could be greatly enhanced for both kind of coatings using a suitable surface pretreatment.
Corrosion Science, 2005
ABSTRACT The electrochemical and transport properties and thermal stability of epoxy coatings electrodeposited on aluminium and modified aluminium surfaces (anodized, phosphatized and chromatized–phosphatized aluminium) have been investigated during exposure to 3% NaCl solution. From the results obtained from electrochemical impedance spectroscopy (EIS), gravimetric liquid sorption experiment and thermogravimetric analysis (TGA) it can be concluded that electrochemical and transport properties of epoxy coatings on anodized and chromatized–phosphatized aluminium are significantly improved with respect to the same epoxy coatings on aluminium and phosphatized aluminium: higher values of pore resistance and charge-transfer resistance and lower values of coating capacitance and double-layer capacitance, from EIS; smaller values of diffusion coefficient of water through epoxy coating, from sorption measurements and smaller amount of absorbed water inside the coating, from TGA. On the other hand, the somewhat lower thermal stability of these coatings was obtained.
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The effects of different copper fillers with different morphology and particle size have been studied in terms of electrical resistivity and thermal stability on the electrically conductive adhesives. The copper fillers used in this study were prepared by wet chemical reduction, electrolytic and gas atomization method, respectively. The as cured ECAs filled with different type of Cu fillers showed significant difference in electrical resistivity. Cu filler with smaller particle size showed higher packing density and larger surface area, which would enhance formation of conductive channels and increased conductive network in the ECAs, leading to a lower electrical resistivity. In addition, thermal stability of the ECAs were investigated under high temperature exposure at 125°C and high humidity aging at 85°C/85% RH for 1,000 h. Results showed that ECAs with Cu fillers of relatively small particle size and rough particle surface have excellent thermal stability due to enhanced adhesion and contact area between Cu fillers and the polymer matrix. A very low resistivity at an order of magnitude of 10 -4 X cm could be maintained for these ECAs after 1,000 h at 125 and 85°C/85% RH.
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Rheological properties of materials are related to their response to applied stress. The field induced chain formation of a large number of organic and inorganic substances such as starch, aluminium oxide, ferric oxide, carbon black, ion-exchange resins, and polymer powders have been studied mainly in insulating oils. Much less is studied and understood the clectrorheological effect of pigments in polymer dispersions. Titanium dioxide is one of the most frequently used surface coatings due to its highquality and ecologically acceptable properties. In the present paper the authors first review the basic principle ofclectrorheology. then it is followed by experimental studies on structuring and rheological properties.
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SN applied sciences, 2021
The purpose of this paper was determining the effects of two nanoparticles additions in a commercial epoxy coating system on rheology characterization. Two kinds of hybrid organic-inorganic silicates (benzytallowdimethylammonium salts with bentonite) were studied, APA, with C 14-16 organic chain and, HT, with C 2-4 organic chain. A 2 2 factorial design, with two categorical nanoparticules factors was applied. The experimental data of viscosity were fit to three different rheological constitutive models: Herschell-Bulkley, Carreau-Yasuda and Cross. The best fit was obtained by Herschel-Bulkley model. The APA nanoparticle had substantial changes in yield stress values, but no effect was observed when HT had been isolated. Two thixotropic models were analyzed for the epoxy system, and the better performance was observed for the model with two rheological parameters. The presence of nanoparticule in epoxy coating reduced around 40% the recovery time. The addition of nanoparticules changes the rheological properties of a commercial coating. The X-Rays Diffraction analyses were done to observe the dispersions degree and exfoliations in the epoxy system. The crystalline peak of nanoparticles had lost for all coating formulations. The electromagnetic interference shielding attenuation was 60% in the formulations with high content of both nanoparticles. The APA and HT improved hence, the anticorrosion performance of the epoxy coating for 720 h in chloride solution. Corrosion resistance had the best performance in the coating with high concentration of carbon black and nanoparticles.