Materials.Business Weekly ⚙️

September 28, 2021

Quote of the week:  “The most important thing in life is to stop saying ‘I wish’ and start saying ‘I will’.” Charles Dickens, English writer, (1812 – 1870).

From The Editor's Corner

Revisiting the principles – a little worm enemy

Always, to refresh knowledge about the mechanisms of corrosion and protection of materials is valuable, and most of the time, is also funny. In particular, the revisited subject concerns the ultimate basis of the phenomena. This is the case about filiform corrosion, a type of attack that occurs under films or coatings, with a filament appearance, just microns with, but can grow millimeters per day. The problem arises under metallic coatings such as electrodeposits of tin, silver, and gold, and even under conversion coatings like phosphates, but mainly under polymeric coatings and paints on substrates like steel, aluminum, magnesium, and galvanized steel exposed to the atmosphere. Metallic substrates covered by a lacquer are prone to this kind of attack, it is possible to see the appearance of the changes happening under the film, and to understand the occurrence of a corrosion cell, “live”, and very graphically, is possible. On the other side, such a problem usually has a significant aesthetic impact on interest assets.

Systematic approaches to the study of the issue occurred with the boom in anti-corrosion paints during the Second Industrial Revolution. The 1950s were plenty of scientific reports by colleagues who dealt with anticorrosive paints, such as J.E.O. Mayne in the University of Cambridge, UK. As a result, some of the phenomenological facts around filiform corrosion were understood, and prevention measurements were developed. New efforts by other researchers like Henry Leidheiser at the Lehigh University, in Bethlehem, Pa., USA, were done in the following decades, and knowledge about the phenomenon improved. However, a few years later, significant progress was made, thanks to the leap in electronic instrumentation as part of the Third Industrial Revolution, mainly new spectroscopic and microscopic tools.

As a primary electrochemical corrosion reaction, filiform corrosion is directly related to heterogeneities. This means degradation associated with heterogeneities or defects on the surface of the substrate, the coating, or the interface in between. In the first place, we can mention inclusions, other chemical differences, or finishing imperfections. However, the most influential factors are related to the interface and the coating. Regarding the interface, we can mention the problems of poor adhesion, but above all, the presence of contaminants on the substrate before the application of the coating (e.g., sodium chloride, calcium sulfate, ammonium sulfate, sodium nitrate, flue dust, ash, iron oxide, and carborundum). In the case of the coating, there are also factors that can influence severely the filiform corrosion occurrence like thickness, porosity, permeability through ion channels, scratches, etc. In addition, environmental variables like relative humidity, temperature, and solar radiation have a role. Also, the nature of the interaction, included wet/dry cycles, affects the level of the corrosive attack.

Many anticorrosive developments have been achieved during all the previous decades. More carefully surface preparation procedures, and much better paint and coating systems have led to a considerable reduction of the problems of filiform corrosion. Corrosionists must keep the phenomenon under control. Then, it is good to remember the more relevant facts about filament formation:

● A water concentration gradient can be established in such a weaker point, mainly if the interface shows airborne species affine to water, such as Na+ and Cl-.

● Water diffuses towards the substrate; soluble salt crystallites deliquesce and dissolve into droplets. This solution droplets become retained because of the lesser vapor pressure of the concentrated electrolyte solution than the partial pressure of water vapor in the air.

● Corrosion attack is initiated under electrolyte droplets, leaving circular anodic areas.

● Oxygen acts as the limiting reagent, and a differential aeration cell becomes the driver of the process.

● Other concentration cells are established. In the case of iron contaminated with NaCl, a salt-depleted, extremely acidic, and Cl- enriched zone in front of the filament head has been found.

● Ionic species are displaced along the reaction area. A head and a tail are defined, and there is also a reaction control by mass transport.

● With a pH considerably higher than the head, the larger peripheral area acts as a cathode, proportionally demanding high levels of electrons in a somewhat unfavorable relationship of the cathode to the anode.

● The attack spreads step by step, and the circular zones become elliptic due to the directional demand for electronic current.

● The worm or knotty filament grows in a broken line pattern due to a very efficient, demanding cathodic area against a small-rounded tip or head, driven by an aeration cell but controlled by mass diffusion. Meanwhile, a long tail remains behind the front of the attack.

Filiform corrosion can spoil the appearance of a luxury car, but it can also be the start of the catastrophic deterioration of an anti-corrosion coating. There is no little enemy.

Remember: Protection of materials and equipment is a profitable business!

Prof. Carlos Arroyave, Ph.D. Editor.

Materials Biz News

Potential global risk from Google’s transatlantic cable

According to a statement from the search company Google, he has completed the laying of his giant submarine internet cable Grace Hopper, which pulls a huge area of ​​the Atlantic Ocean from New York to Great Britain before going to Spain. The search giant also announced in August that it had entered into an agreement with Facebook to build a new cable called “Apricot,” which will connect six countries in Southeast Asia using 7,456 miles of cable, the increase in harmful weather events due to climate change can also make submarine cables extremely vulnerable. In 2012, for example, Hurricane Sandy shut down several key exchanges where submarine cables ran between North America and Europe.

Desktop Metal Acquires Aidro

Desktop Metal announced it had acquired Aidro, a pioneer in the mass production of next-generation fluid and hydraulic power systems through metal additive manufacturing across a wide range of industries. , including petroleum, agricultural equipment, aerospace, mobile and industrial machinery, among others, desktop Metal, Inc., headquartered in Burlington, Massachusetts, is accelerating its manufacturing transformation with an expanding portfolio of 3D printing solutions, from rapid prototyping to mass production, the companies provide innovative and customized solutions that leverage the benefits of additive manufacturing such as weight reduction, reinforced assembly and improved performance, to customers across sectors such as oil and gas, industrial, agricultural, aerospace, and mobile and industrial machinery, among others.

Historical price of aluminum makes scrap becomes strategic

The price of this raw material in the international metal market has been increasing rapidly for a year and a half. Scrap trades at the same level as first-generation aluminum from the bauxite ore from which this material was developed. Scrap can sometimes be paid for a few cents more than primary aluminum, the aluminum sector, which is increasingly demanding this raw material. The worldwide shortage of aluminum has also been proven by the Spanish industry, along with these aluminum producers, Spain has a strong recycling industry that uses this metal as a primary source for products, first, in the segment of aluminum elements for the building. Armando Mateos, President of the Spanish Aluminum Association, explains that there are between 17,000 and 20,000 workers among aluminum producers and extrusion plants and activities directly related to them in Spain.


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Networking & Knowledge Exchange

Taking aluminum to new horizons. Virtual

Estal (European Association for Surface Treatment on Aluminum) is offering a two-day conference. The program will consist of the use possibilities of aluminum, the durability aspects of aluminum and the surface technology for aluminum, the conference will be divided on three half-day sessions, the first session will focus on topics related to powder coating, the second will provide presentations about anodizing, the third and final session will address subjects of general interest and also deal with the surface treatment on recycled aluminum, one of the most significant challenges for our industry.

Dates: From Wednesday, October 06th to Thursday, October, 07th of 2021

Control Valves & Actuated On/Off Valves. Virtual

Fleming events is offering a three-day conference to provide an introduction into the key aspects related to actuated valves, actuated valves are commonly used as final elements in control- and safety systems, and play an important role in plant performance, reliability, and safety. You will be attending topics such as:

● Rotary motion valves: Ball, butterfly, and plug valves

● Design aspects: Pressure classes, end connections, gaskets, bonnets, stem seals, seats, backseats, etc.

● Installation and maintenance aspects of control valves

Dates: From Monday, October 25th to Wednesday, October, 27th of 2021

Anti-Corrosion Paint Inspection Fundamentals. Virtual

Electrobras CEPEL is offering a four-day conference presenting good practices in anti-corrosion painting services, helping companies in the electricity sector to deal more successfully with corrosion: a process that can directly affect the life of their assets and generate costs of different magnitudes the course is based on the Electrobras Standards of Anti-Corrosion Painting, being highly sought after by professionals from the Brazilian electricity sector in search of training in the area.

Dates: FromTuesday, October 26th to Friday, October 29th of 2021

Upcoming events

September 2021

September 28th International stainless and special steel conference 2021 (Link)

September 28th Robotic storage tanks inspection (Link)

September 30th Heat recovery and utilization - Defining the foundation industries' sector innovation needs (Link)

October 2021

October 06th Taking aluminum to new horizons** *(Link)​***

October 07th Sensors, controls, and digitalization – Defining the foundation industries’ sector innovation needs (Link)

October 14th Waste utilization and symbiosis – Defining the foundation industries’ sector innovation needs (Link)

October 21st Heat recovery and utilization – Solutions for the foundation industries sector (Link)

October 25st Control Valves & Actuated On/Off Valves (Link)

October 26th 240th Meeting of the Electrochemical Society. (Link)

October 26th Anti-Corrosion Paint Inspection Fundamentals. (Link)

October 28th Sensors, controls, and digitalization – Solutions for the foundation industries sector (Link)

October 30th Blechexpo (Link)

Photo by Jimmy Ofisia on Unsplash