Recent Patents on Corrosion Science - Volume 3, Issue 2, 2013

Corrosion affects the quality of the environment, the durability of the infrastructure assets and industrial equipments. Therefore, it is crucial using corrosion engineering control methods and techniques, in particular safe "green" e.g. environmental friendly corrosion inhibitors that will extend the life of the infrastructure saving large expenses in materials equipment and structures. This review presents an analysis of patents on corrosion inhibitors developed for aqueous systems, steel reinforced concrete, acid pickling operations, oil industry and additives in the formulation of protection coatings.

Ferrous based-metals, e.g., iron metal and metal alloys containing iron (mild steel), and steels are routinely used in the construction of cooling systems and in other fields due to their low cost and availability. Environmental considerations have been of paramount importance. Corrosion resistant stainless steel or “super alloys” have been used in applications where prevention of corrosion of steel structures or pipes was absolutely essential. These materials are expensive and more difficult to produce than conventional steel materials. Iron and steels undergo inhibition, passivation and corrosion protection treatments to make these materials economical and durable for variety of applications. Numerous techniques are available in the literature to provide these treatments. Heavy metals, chromates, phosphates and fluorides are employed as effective materials for inhibition, passivation and corrosion prevention. A lot of research is underway to remove these materials due to their toxicity. In Europe rules have been established to limit the Chromium content (due to its toxicity) for easy and safe recycling of the materials. There still exists a need for finding out economical, efficient processes and materials which will reliably adhere to the surface being treated in chemically adverse or saline environment and can provide protection against corrosion. For these reasons tremendous efforts are being made to develop/invent new processes for inhibition, passivation and corrosion protection.

The use of Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) thin coatings has become a widespread practice in the design of components subject to an aggressive environment. Corrosion in an aggressive environment can be critical for the design of structural components under constant and fatigue loads, due to the presence of Stress Corrosion Cracking (SCC) and fatigue corrosion. The protection from aggressive environments granted by the use of thin coatings is desired also in nonstructural, electrochemically active components, such as medical implants and fuel cells. In the present work, a review of the most recent industrial patents related to the application of PVD and CVD coatings developed in the last decade for the reduction of the detrimental effects of corrosion is presented. The article illustrates some selected patents which deal with the corrosion protection of components subject to fatigue loads and to static corrosion. Regarding dynamically loaded parts the reviewed papers describe thin coatings adopted to screen out turbine blades and disks from pitting corrosion, erosion and oxidation. A method to protect sliding parts of compressors using Hydrofluoroolefin refrigerant is also reported. In the latter part of the work, technical solutions for components under static corrosion are investigated, by presenting patents related to the coating of Implanted Medical Devices (IMD) and fuel cells, thus providing shielding from the external aggressive environment. Finally, a patent which proposes a multilayer finishing to improve the corrosion protection of common PVD treatments is presented.

This paper intends to review the main systems of monitoring the degradation of reinforced concrete structures with steel that have been patented in the last 10 years. Given that the degradation process in the large majority of cases is an electrochemical corrosion process of the reinforcement caused by chemical actions on the structure, the systems are generally systems that determine electrochemical greatnesses. The systems are essentially sets of electrodes with different arrays that allow the implementation of different electrochemical techniques such as linear polarization resistance, electrochemical impedance spectroscopy, electrochemical noise, ionic conductivity, in order to obtain information about reinforcement potentials and corrosion rates and penetration speeds of aggressive agents.

The electrochemical corrosion properties of bulk nanocrystalline 304 stainless steel produced by severe rolling technique and its conventional polycrystalline 304 stainless steel were studied by immersion test for 20 days in 0.5 mol/L HCl solution at room temperature. The corrosion rate of bulk nanocrystalline 304 stainless steel was less than that of conventional polycrystalline 304 stainless steel. The electronic structures and compositions of the two oxide films on bulk nanocrystalline 304 stainless steel and conventional polycrystalline 304 stainless steel in 0.5 mol/L HCl solution for 20 days’ immersion at room temperature were also studied by X-Ray Photoelectron Spectroscopy (XPS). The pitting corrosion resistance of bulk nanocrystalline 304 stainless steel was also simultaneously enhanced in comparison to conventional polycrystalline 304 stainless steel. These results were attributed to the better chemically stable, more compact and thicker oxide film on bulk nanocrystalline 304 stainless steel. The better chemical stability of oxide film on bulk nanocrystalline 304 stainless steel was due to the larger binding energies of Fe3+2p3/2, Fe2+2p3/2 and Cr3+2p3/2 in the oxide film on bulk nanocrystalline 304 stainless steel.