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  • Open access
  • 129 Reads
Corrosion Resistance Test of Electroplated Metals using Fast Electrochemical Non-Destructive Analysis
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Corrosion testing is a very important step in quality control for metal industrial processes. Especially for electroplated goods, corrosion resistance is a primary indicator of surface quality. International Standard Organization has established several standards that use Electrochemical Impedance Spectroscopy (EIS), alone or combined with other electrochemical techniques, to determine corrosion resistance of metal surfaces such ISO 16773 for testing coated and uncoated metallic specimens and ISO 17463 specially designed for organic-coated metal surfaces. EIS is a versatile procedure for the accelerated evaluation of the anti-corrosion performance of coatings: unlike other standard procedures is generally a non-destructive method. EIS works applying an electrical sinusoidal perturbation with a fixed frequency and measuring electrical impedance Z of the sample. Measuring impedance at different frequencies and analysing the data it is possible to postulate the structure of an equivalent circuit and extract corrosion resistance data. This approach is commonly used for high-impedance coatings, in this study we will explore EIS as well as the OCP measurement, the corrosion current and other techniques to find the best option for low-impedance metallic coatings analysis. The objective of this study is to develop a method to determine corrosion resistance for electroplated goods that can give results as reliable as other more diffuse and traditional destructive corrosion testing techniques (such as corrosion tests in artificial atmosphere ISO 9227 and ISO 17228) with a non-destructive process and in a fair less amount of time.

  • Open access
  • 162 Reads
Study on the effect of milling parameters on HE-MA nanostructured Al-Graphene cermet particles

Nanocrystalline grains have proven to be excellent reinforcing elements in nanostructured particulate materials. On the other hand, carbon allotropes, especially graphene and carbon nanotube (CNT), exhibit elastic modulus in the range of 1 TPa (theoretical) and tensile strength in multiple orders greater than that of steel. This study aims at synthesizing high-strength nanostructured ceramic-metallic (cermet) particle feedstock in a high-energy mechanical alloying (HE-MA) process based on an Al-graphene composite comprehensive design-of-experiments (DoE). The goal is to optimize milling process parameters, including milling time, batch composition, ball-to-power (BPR) ratio, and milling agent, for the particles to be eventually fed into a high-pressure cold spray coatings development. The milled powders are characterized using SEM, EDS, XRD, and laser particle diffractometer to study the morphology and microstructure, elemental composition, grain size and crystal orientation, and particle size distribution (PSD), respectively. Results show it was possible to attain required structure and PSD at a 10:1 BPR with 5-mm diameter ball, at 1200 rpm, and 4 h of milling.

  • Open access
  • 319 Reads
Corrosion resistance of anodic layers grown on 304L stainless steel at different anodizing times and stirring speeds

Different chemical and physical treatments have been used to improve the properties and functionalities of steels. The anodizing is one of the most promising treatments, due to its versatility and easy industrial implementation, since it allows obtaining different microstructures on the surface, in order to be employed in different industrial sectors. The present work has studied the influence of the anodizing time (15, 30, 45 and 60 min), as well as the stirring speed (0, 200, 400 and 600 rpm), on the morphology and the resistance corrosion behavior of anodic layers grown in 304L stainless steel. The anodic layers were characterized morphologically, compositionally and electrochemically, in order to determine the influence of these parameters on their corrosion behavior in a 0.6 M NaCl saline solution. The results show that the generation of anodic layers at different times propitiates the definition of nonporous morphologies, while the phenomena of dissolution of the layers that increase with the time of anodizing. However, the resistance to corrosion decreases respect to the non-anodized 304L SS. On the other hand, the effect of the stirring speed during the generation of these anodic layers does not seem to influence the corrosion behavior in the saline medium studied.

  • Open access
  • 99 Reads
Synthesis and Characterization of a Polyurethane Phase Separated to Nano Size in Epoxy Polymer
Published: 15 March 2019 by MDPI in 1st Coatings and Interfaces Web Conference session Surface Characterization

Epoxy resins are widely applicable in industries such as aircraft, automobiles, coatings, and adhesives because of their good chemical resistance and excellent mechanical and thermal properties. However, on an external impact, the crack propagation of epoxy polymers weakens the overall impact resistance of the materials. Therefore, many impact modifiers have been developed to reduce the brittleness of epoxy polymers. Polyurethanes as an impact modifier can improve the toughness of polymers. Although it is known that polyurethanes are phase-separated in the polymer matrix after curing, connecting polyurethanes to the polymer matrix has been problematic for enhancing the mechanical properties of polymers. In this study, we introduced epoxy functional groups into polyol backbones, which is different from other studies that focused on modifying capping agents to achieve a network structure between the polymer matrix and polyurethane. We confirmed the molecular weight of the prepared polyurethane with gel permeation chromatography. Moreover, the prepared material was added to the epoxies to evaluate the changes in the mechanical and thermal properties of the materials. Furthermore, we conducted tensile, flexural strength, and impact resistance measurements. The experimental results are discussed in detail.

  • Open access
  • 196 Reads
Effectiveness of two different hydrophobic topcoats for increasing of durability of exterior coating systems on oak wood

Top hydrophobic layer can increase durability of exterior coatings on wood. Two hydrophobic topcoats—synthetics and water-based acrylate resin with wax additives were researched as top layer on twenty-four different coating systems applied on oak wood in this experiment. Artificial accelerated weathering lasted six weeks. Changes of color, gloss, surface wetting were evaluated, and microscopic analyses of coated surfaces were done. The results have shown that top hydrophobic layer increases durability of tested coating systems in most cases. However, the effectiveness of the two researched hydrophobic topcoats was different depending on the specific tested coating systems.

  • Open access
  • 297 Reads
Cavitation erosion and sliding wear mechanisms of AlTiN and TiAlN films deposited on stainless steel substrate

Stainless steel grade AISI 304 is one of the most widespread modern structural material, alas its sliding wear and cavitation wear resistance are limited. Thus, AlTiN and TiAlN coatings can be deposited for increasing the resistance to wear of stainless steel components. The aim of the work was to investigate the cavitation erosion and sliding wear mechanisms of magnetron sputtered AlTiN and TiAlN coatings deposited on SS304 stainless steel. AlTiN and TiAlN films were deposited on a stainless steel substrate grade AISI 304. Films surface morphology and structure were examined using a profilometer, light optical microscope (LOM) and scanning electron microscope (SEM). The mechanical properties (hardness, elastic modulus) were tested by nanoindentation tester. The adhesion of deposited coatings was determined by means of the scratch test and Rockwell test. Cavitation erosion tests were performed according to ASTM G32 (vibratory apparatus) with stationary specimen procedure. Sliding wear tests were conducted using a nano-tribo testes i.e. ball-on-disc apparatus. Wear mechanisms are strongly contingent upon the structure and morphology of the tested materials. In relation to stainless steel substrate, the PVD films present a superior resistance to sliding wear and cavitation erosion. Higher resistance was noticed for AlTiN than for TiAlN film, mainly due to its superior hardness and elastici modulus. Cavitation erosion mechanism of both, AlTiN and AlTiN coatings is prone to embrittlement, imputable to fatigue processes that result in coating rupture and spallation that consist in coating fragmentation, formation of pits and finally detachment from the substrate. In contrary to PVD coatings, steel substrate is characterized by developed cavitation erosion wear with roughened surface and plastically deformed, semi-brittle, eroded surface. Sliding wear of thin films is based on micro-ploughing mechanism. For stainless steel adhesive sliding wear mode and plastic deformation with smearing, material transfer and grooving were observed. It was confirmed that various fluid machinery components made from austenitic stainless steel that undergo cavitation erosion, can be prevented by deposition of AlTiN and TiAlN films.

  • Open access
  • 370 Reads
Nanotechnology to Improve the Performances of Hydrodynamic Surfaces

The nature continues to inspire scientists to adapt solutions in order to satisfy the human needs and attain unreachable performances with new technologies. In this study, the super-hydrophobicity of the Lotus leaf is our source of inspiration. The duplication of this natural phenomenon may enhance the maritime metallic surfaces corrosion and its mechanical friction. In our case, we are investigating super-hydrophobic maritime surfaces using a simple, low cost and scalable coating method. A hydrothermal method is used to create zinc oxide (ZnO) nanorods (NRs) and an evaporation method to apply the Octadecyltrimethoxysilane (ODS). At the end, the super-hydrophobic surface (SHS) is obtained on a maritime aluminum substrate coated by a commercial epoxy paint. The characterization of our SHS gives high water contact angle (WCA) and small sliding angle (SA) of water droplets on the treated surface. We have raised the WCA of the epoxy painted aluminum surface from 98° to more than 152° and reduce the SA of 46° to lower than 7°. We have also studied the sliding speed (SS) that have been largely raised from 0.04 m s−1 in the epoxy case to 1.3 m s−1 after treatment.

  • Open access
  • 281 Reads
Application of Calixresorcinarenes as Chemical Sensors

Calixresorcinarenes and calixarenes have seen extensive usage as receptors for cations, anions and even neutral molecules. Incorporation of binding capabilities and chemical groups that respond to analytes complexation has given these macrocycles additional advantages in applications as efficient selective chemical sensors. Three major types of macrocyclic calixresorcinarenes namely C-dec-9-en-1-ylcalix[4]resorcinarene (CAL 11U), C-trans-2, cis-6-octa-1,5-dien-1-ylcalix[4]resorcinarene (CAL 9U) and C-nonylcalix[4]resorcinarene (CAL 10) were synthesized. They differ in the alkyl/alkenyl side chains. They were characterized by different techniques (melting point measurements, Fourier Transform Infra-Red spectroscopy FT-IR, Thermal Gravimetric analysis and Differential Scanning Calorimetry coupled with Mass Spectrometry TG-DSC-MS, Nuclear Magnetic Resonance spectroscopy NMR, and Powder X-Ray Diffraction measurements PXRD). Calixresorcinarene derivatives, immobilized onto Au surfaces of quartz crystal resonators, have been successfully applied to detect the presence of lead in aqueous solution.

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