Advanced Materials Research Vol. 38

Abstract: Scale, corrosion and the and biological growth in industrial water handling processes result in reduced water flow though pipes, reduced heat transfer, and pump failures. Preventative treatments for these problems are based upon chemical compounds that are most often toxic and environmentally persistent. Manufacturers continue to introduce new chemicals and treatment programs onto the market, and old products have been discontinued. Many manufacturers claim that the new chemical and treatments are more environmentally friendly and safer for the plant workers and the users. The U.S. Army Engineer Research and Development Center Construction Engineering Research Laboratory has undertaken a research effort to look at these new chemical treatments. The objective of this work was to develop “green” water treatment chemicals that control biological growth, corrosion and scale while reducing or eliminating the generation of toxic substances during the manufacture, use, and disposal processes.

Abstract: While chromates as anti-corrosion pigments in primers and wash primers have disappeared in most industries, there are still quite a lot of chromated paints used in the aircraft industry. Intensive efforts to develop alternative pre-treatments to chromate conversion coatings and to chromic acid anodization have begun. The intention of this report is to give an overview of the state-of-the-art techniques about such pre-treatment/coating systems of aluminium for aircraft maintenance, which are in accordance with the latest environmental policies. The objective is to evaluate the combination of surface pre-treatment and paint as a whole.

Abstract: An alternative approach was developed for surface treatment of as-received commercial AA 2024 T3 by using a pyrrole-based silane (SiPy). For film deposition, just one immersion step is enough, followed by curing. SiPy layer structure contains both polysiloxane bonds and pyrrole oligomers, with some degree of doping, giving a highly coherent layer. The superior film quality with respect to simple polysiloxane, is probably the main reason for the better corrosion performance obtained for SiPy on 2024.

Abstract: Titanium, magnesium and zirconium alloys are widely used in industrial applications, which require high wear and corrosion resistance. However current methods of improving these properties often do not satisfy the requirements of service and functional properties. An alternative approach is the application of oxide-ceramic coatings using high temperature process. The coatings are applied by spark discharge plasma in the metal-electrolyte system at high voltages - PEO (plasma electrolytic oxidation) as an oxide synthesis method. This method has shown good results for aluminium alloys and with good prospects to be used for titanium, magnesium and zirconium alloys. Development of PEO technology to improve the wear and corrosion resistance of titanium, magnesium and zirconium alloys is discussed in this paper. It describes the methods for obtaining the required layer-thickness for a specified hardness, porosity, wear and corrosion resistance, sets up the optimal process parameters (voltage/current) by taking the relation of anodic to cathodic currents into account, and establishing the electrolyte content of different dopants.

Abstract: The paper presents some preliminary experimental results dealing with electrochemical synthesis and corrosion behavior of various black layers types onto Al substrates, suitable to be used as selective absorber coatings in the case of thermal energy production from solar energy, involving several different procedures, respectively: (i) electrodeposition of black Ni-Mo alloy after an initial anodizing in nitric acid electrolyte that offers a very good adherence of the further applied coatings; (ii) cathodic deposition of black Mo based layers after an initial double zincating procedure; (iii) black coatings through a.c. electrochemical coloring of aluminum anodic oxides, using AgNO3/H2SO4, NiSO4 based solutions; (iv) black composite polypyrrole films. The obtained black layers are characterized by a good throwing power, homogeneity, smoothness and adherence, as shown by SEM and AFM investigations. Also, they present a good solar absorption and low values of infrared emittance. To evaluate the resistance of black coating layers against corrosion, several accelerated corrosion tests have been performed, respectively: (i) continuous immersion in 0.5M NaCl for 408 hours with intermediary visual examinations and recording of corrosion potential; (ii) potentiodynamic polarization curves in 0.5M NaCl; (iii) impedance spectra in 0.5M NaCl at open circuit potential using a Zahner IM6e potentiostatic equipment. The corrosion performances are discussed taking into account the applied preparation procedures.

Abstract: High strength aluminium alloys are widely used in the civil and military aerospace industry due to their low weight and high mechanical properties, achieved by selected alloying elements and heat treatments. The resulting multiphase alloy system, a solid solution of alloying elements in the aluminium matrix and a variety of second phase material, requires specific anticorrosion measures in order to prevent localized corrosion, which is promoted by microgalvanic coupling between the different metallographic phases. Traditionally, the anticorrosion performances are achieved by chromic acid anodizing (CAA), followed by painting. However, environmental issues and associated costs for the disposal of chromate wastes, require the development of new approaches for anodizing of aluminium alloys. In this work, the potential for tailoring the porous anodic film morphology through the film thickness by controlled variations of the anodizing potential is inspected. The procedure developed is, in principle, applicable to any aluminium alloy in any anodizing electrolyte and results in the generation of innovative graded porous anodic film morphologies which promise improvement of anticorrosion properties and replacement of CAA .

Abstract: The results of a failure investigation performed on a transportation pipeline for oil products (aromatics – water – DEG) are presented. The damage phenomena of the material were attributed to corrosion – erosion, and secondary to stress corrosion cracking. The analysis aims to identify the mechanisms responsible for service failure of an API 5L grade A pipe after about two years and, also, to mitigate further damage phenomena by a proper identification of the contribution of mechanical, metallurgical and environmental factors (focusing both on technological fluids characteristics and inhibition scheme). Expert report conclusion and other field data give premises for re-designing the maintenance, operating and corrosion-monitoring program in order to avoid future hazards.

Abstract: CrN/ZrN (1, 8, 15, and 30) bilayers were deposited onto AISI 420 steel substrates at 250 °C and 6.6x10-3 mbar with gas ratio Ar/N2 50:3.0 as gas mixture and bias -60V were applied. AFM analysis presented different morphologies, showing that the coatings with 15 bilayers had an average grain size of 49 nm; while the 30-bilayer coating exhibited grain sizes of 99 nm. Coating thicknesses were 3 μm, approximately. The Vickers Test revealed that coatings with 8, 15, and 30 bilayers bore better impact resistance than coatings with 1 bilayer. This result is considered, bearing in mind that in many bilayers propagation of fissures is slower, because the presence of layer inter-phases leads to fissures straying in other directions. Slight corrosion specks are present, but mass loss was around 40 mg. in one bilayer, a higher value than for the coatings with 15 bilayers that was near 18 mg. Homogeneity, grain size, fracture resistance, and corrosion resistance of the coatings with 15 and 30 bilayers are suitable for mechanical applications of these types of coatings, as shown in mechanical measurements. These results indicate that for engineering applications under corrosive environments, the use of these types of bilayer coatings on AISI 420 stainless steel is highly recommended.

Abstract: In below-grade buildings and buried structures, such as those constructed as hardened secure facilities and used for munitions storage on U.S. Army installations, water intrusion can cause serious damage and reduce penetration resistance. Inside the building active water and high humidity can result in corrosion of HVAC, electronic equipment, as well as damage or disrupt mission critical electronic equipment. In the adjacent backfill and the structure itself, excessive water can seriously compromise the structural hardening of the facility. Thus, it is vital to Army sustainability to control moisture in below-grade structures and eliminate corrosion of electrical mechanical equipment. This also prevents mold growth on the interior surface of below grade concrete walls and floors. Control of water movement involves both actively removing water in and around a building, and the use of barriers to prevent water from penetrating to interior spaces. A pumping system is typically required with the use of a barrier system to assist in controlling the movement of moisture into the structure. Conventional waterproofing technologies are expensive and often have short service life. A new approach is needed—a cost effective and robust solution—to the pervasive problem of water intrusion. Electro-Osmotic Pulse is a promising alternative solution presented here. Electro-Osmotic Pulse (EOP) technology uses pulses of electricity to reverse the flow of water seepage. The applied voltage causes moisture to flow out of the basement walls and away from the building. The technology works by alternately pulsating a direct electric field with an off period. The first part of the sequence consists of a pulse of positive voltage (as seen from the dry side of the concrete wall), followed by a pulse of negative voltage. This is followed by a period when no voltage is applied. Of the three parts, the positive voltage pulse has the greatest time duration. The amplitude of the positive signal is typically on the order of 20 to 40 Volts DC. This electrical pulse causes cations (e.g., Ca++) and associated water molecules to move from the dry side (anode) towards the wet side (cathode) against the direction of flow induced by the hydraulic gradient, thus preventing water penetration through buried concrete structures. Laboratory and field tests have shown an increase in calcium compounds at the cathode side of test specimens. The negative portion of the pulse increases the efficiency of moisture movement by depolarizing the electrodes. Electro-Osmotic Pulse (EOP) technology has been successfully installed in military structures such as family housing, steel reinforced deep structures, and tunnels. EOP has also been implemented on Civilian structures such as residential structures, D.C. Metro Tunnels, and an underground treasury vault. EOP has been shown to prevent moisture seepage into below-grade structures. It is effective at keeping concrete surfaces at or below 50 percent humidity content, meaning the treated space stays dry, indoor relative humidity stays low, and no mold or mildew can grow. This technology has received the 2002 international NOVA award for innovation in construction, and twice nominated for the CERF Pankow award (1999 and 2004). The ERDC research on this technology has also been recognized by the 2004 Army Research and Development Achievement Award.