Metal Sheets in Calamansi Juice | No Lacquer Test Part Two

In my previous post. I got two cans, an aluminum can and a tin can. Opened both. Scratched inside with a sand paper to damage the lacquer coatings. Then filled them both with vinegar and did observation for several days. Both showed positive reactions – color change, corrosion and putrid odor.

The reactions observed above vinegar surface were clear signs of oxidation process. They were similar to rusting of ordinary metal. I did a second set of experiment for verification.

I used citric acid this time, natural citric acid of calamansi juice. I mixed extracts of five calamansi and three scoops sugar in 500 ml water. A portion of prepared juice was for the setup, the rest was for me.  Calamansi juice has the clearest complexion among natural fruit juices that allowed easy observation.

I cut out two sheets of metal. About one square inch each. One from aluminum can and one from tin can. Tin from sardine can and aluminum from canned soda. Sanded the edges to remove sharpness. Made few scratches on center.  Color changes on center and edges were the expected point of observation. Placed metal sheets in separate polypropylene bags and filled with the prepared calamansi juice. No oxidation reaction was expected to occur cause the metals were completely submerged in liquid.

aluminum and tin metal sheetsmetal sheets in polypropylene bagsAfter few hours, bubbles started appearing around the metal sheets and on sides of polypropylene bags, for both aluminum and tin. Sign of positive reactions, reactions of citric acid to metals. I never expected it cause I did not see it in previous setup.  Perhaps metal cans reflection interfered with bubbles visibility.

bubbles appearing around metal sheetsBulging canned foods are caused by gas producing bacteria. In high acid foods, defective lacquer coating may also cause bulging. Though it needs more thorough experiment and research.

After six days…

Blackening occurred on tin metal edges, on back side and on scratched lacquer coating. No noticeable change observed on aluminum sheet.  Bubbles were observed clinging in plastic bag sides.

aluminum tin outer sidealuminum tin inner sideDefective tin can lacquer and its complete absence can be detected easily after opening. On the other hand, defective lacquer on aluminum can can be detected but not the complete absence.


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One Comment

  • Hello! I just wanna ask, if you happen to know what is in the calamansi juice that can cause corrotion on aluminum? or doe it corrode the aluminum?

    thanks!

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