Corrosion Awareness Month
24 April was officially designated Corrosion Awareness Day by the World Corrosion Organization and the European Federation of Corrosion. It is the occasion of many initiatives in the scientific community to raise awareness about corrosion and corrosion protection around the world. As a member of this community, I decided to contribute through daily postings to my professional network of pictures of corroded plates and impressions, to illustrate how a threat that costs 3% of the GDP of industrial countries can contribute to create nice artworks.
This page collects all postings sent between 24 April 2022 and 24 May 2022 on this occasion.
On the occasion of the Corrosion Awareness Day, I would like to illustrate how corrosion can also be used in Art. Indeed, the etching technique also called Aqua Forte consists in drawing designs onto a varnished metal plate, followed by the application of a strong acid to corrode the unprotected parts of the metal. This plate can then be used as a stamp to print multiple copies of the same picture. Rembrandt, the famous Dutch artist of the 17th century, is known as one of the most prolific etcher. Later on, other artists such as Pierre Soulages moved from figurative to abstract art, leaving a great place to chance in the final picture.
In the coming weeks, I will illustrate the bright sides of corrosion by daily postings of printings of corroded coupons and plates.
Day 1 - 9 coupons printed in Yellow Ochre and Red Carmin
As a starter, I share a print of 9 corrosion coupons (Hastelloy C22, Inconel 625, Superduplex 2507, duplex 2205, 904L, 316L) saved from the laboratory after a few weeks of exposure in 12% FeCl3 solution at 60 to 100 °C.
Here, carmin red was used first to fill pits and holes. Yellow ochre was then applied atop to reveal the uncorroded or uniformly corroded surfaces.
Day 2: recto verso impression in gold & black
For this second day, the coupons already presented yesterday (Hastelloy C22, Inconel 625, Superduplex 2507, duplex 2205, 904L, 316L exposed to hot FeCl3) were printed recto verso, using bronze colour to reveal the corroded areas and carbon black elsewhere. My printing technique was still nascent at this time but more mature impressions will be presented soon.
Day 3: Pits trio
This second series still sheds the light on pitting corrosion. Three 316L coupons were simultaneously exposed to dilute FeCl3 at ambient temperature for 10 days.
The first image shows a photo collage to illustrate the printing process. Steel plates with extensive pitting appear to the left of the picture, while the printed image is shown to the right. Full pictures of the three coupons and the impression are then also presented.
Day 4: the quintessence of pitting
After recycling corrosion coupons from laboratory experiments, I started to elaborate my own corroded plates at home. Ferric chloride being quite easy to manipulate (of course never forget to wear protection gloves, glasses and a blouse), I kept working with this type of solution and stainless steel plates. The corrosiveness of FeCl3 is the result of a highly oxidative power due to the Fe(3)/Fe(2) redox couple, and the high concentration of chloride ions that can affect the stability of the passive layer of stainless steels. It is not a surprise that this corrosive environment was chosen to elaborate a standard test method to qualify the pitting and crevice corrosion resistance of stainless steels (ASTM G48).
The next example shows a huge pitting attack onto a 20 cm x 17 cm 304L plate. Through wall (1 mm thick) pits were obtained after 40 days exposure to a 20 g/L FeCl3 solution at ambient temperature. Nice streaks were also seen near some of the pits. This was seen only at the metal face exposed downwards, and it is probably associated with local acidification due to corrosion reactions and/or to the accumulation of gases close to the pit. Interestingly, the part of the plate that was immersed at a greater depth suffered the strongest attack. If you wish to see a nice impression obtained with this plate, you will need to wait for another day.
Day 5: The quintesence of pitting
As promised yesterday, two more pictures of the 304L plate with huge pits. The first one shows the inked plate. Bronze nicely fills all corroded areas, while Prussian blue was applied anywhere else. The second picture shows the resulting impression onto a BFK Rives paper (250 g).
Day 6: Waterline & uniform corrosion
Two plates (304L and 316L) were exposed to the same corrosive solution composed of FeCl3. The concentration was slightly higher than the previous plate (Quintessence of pitting). They were installed in the test solution with a slope, so that the upper part of the plates was not immersed.
The pictures illustrate different types of attack: as previously seen, pitting corrosion is still present. However, corrosion at the waterline is now observed, as well as uniform active corrosion for the 304L.
The impression of these plates was done simultaneously on the same paper. The first layer of ink was Carbon Black (filling holes), while Yellow Ochre was applied on top. It has to be noted that the printed image presents the 304L to the left and 316L to the right.
As previously observed, this plate shows nice pits, and a severe attack at the bottom part. The waterline is also clearly visible with deeper metal loss. Apart from the pits, the main surface of the plate remained unaffected.
In comparison to 316L, this 304L plate looks surprisingly less corroded. The pits are smalled, and there is no severe attack at the bottom. However, a closer look shows a uniform attack, revealing a complete loss of passivity.
Day 7: When crevice corrosion comes into play
Yesterday I presented the case of a 316L plate with pits and waterline attack after several days exposure in FeCl3. The printed picture corresponded to the face of the plate that was oriented upward. Today, I show what the downward face of the same plate looks like. To maintain a slope, this plate was set on a rigid support. This contact region formed a very nice crevice that eventually corroded the full thickness (1 mm) of the plate at one end. The impression of this plate was obtained by filling the holes with black ink and yellow ochre elsewhere. The crevice is perfectly visible as a straight black line on the picture.
This pate corresponds to the reverse side of the plate already presented on Day 6. A nice crevice (straight line) can be seen at the top half of the plate. It corresoinds to the location where the plate was set up against a rigid support in the corrosive solutions.
This impression was obtained by applying black ink in the holes and yellow ochre atop.
Day 8: Playing with colors
Following yesterday's post, I show here different impressions of the same 316L plate with uniform corrosion, pitting and crevices. The first impression was obtained with yellow ochre. It is followed by bronze, burnt sienna, and ultramarine blue.
Day 9: Pitting, waterline and crevices
This 304L plate (21 cm x 21 cm) was partially immersed in FeCl3 at ambient temperature. Since the solution was not concentrated enough at the beginning of the exposure, FeCl3 powder was added periodically, resulting in light attacks of the top part of the plate that was not immersed. Indeed, FeCl3 is highly hygroscopic and the particles that were deposited on the metal were eventually hydrated, leading to localised corrosion with nice patterns. Below the waterline, two areas suffered strong localized attack looking like crevices. These were likely associated with solid deposits of FeCl3 that did not dissolve immediately and created crevices. The more severe attack at the waterline is also clearly visible.
The pictures below show the metal plate and an impression obtained with Bronze inside the holes and Prussian Blue atop.
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Day 10 - 3 minutes to turn a corroded plate into an impression
This 304L plate was corroded through 3 successive immersions in FeCl3. Some parts of the plate were protected by adhesive tape resulting in pitting, crevices, and uniform corrosion.
This video illustrates the whole printing process from inking until the printing press.
Day 11 - A patchwork of corrosion mechanisms
This one was also obtained with a 304L plate (25 cm x 25 cm) showing various types of corrosion. the third left of the plate was highly corroded with pits and uniform attack. The waterline was nearly completely dissolved. The third right was also exposed to the corrosive environment (still FeCl3), but both the duration and the concentration of the solution were reduced. Here, the main corrosion patterns are pitting and crevices due to a dead weight that was placed on the plate. Two impressions were obtained from this plate: either with Burnt Sienna (reddish color) or Sienna (yellow). Black ink was applied in the holes.
Day 12 - La rouille c'est cool
For this last post, no new corrosion mechanisms or test solution (still FeCl3), but another type of cause. In order to protect the backside of the 304L plate during exposure, I used adhesive tape to mask the surface. On the top right and bottom left corners, application of the tape was not meticulous, and folds formed in certain locations. This created areas where the solution could accumulate near the metal, forming natural crevices. These appear as black lines on the impression. In the middle of the plate, the adhesive was better installed. However, several pits that initiated on the other (unprotected) side of the plate eventually crossed the thickness of the plate reaching the adhesive tape. The bottom of these throughwall pits also formed crevices that created craters. At certain locations, the attack was so severe that several cm² of metal were lost.