Nickel - the corrosion resistant one

 Nickel - the corrosion resistant one

Nickel is one of the metals that aren't hard to find in everyday life, but are infinitely more common in the form of thin coatings or alloys. Addition of nickel in steels helps stabilize austenitic microstructure in room temperature, which, together with chromium, can make steels resistant to corrosion in some of the most problematic acids, like nitric or dilute sulfuric acid.

Pieces of nickel anode.

Relatively pure nickel sheet can be bought as sacrificial anodes for electroplating. I got such anode in the form of a small strip, which I divided into smaller pieces that could fit my sample jar. In such form, the interesting yellowish tinge of nickel metal is easily visible.

Nickel spheres.

Pure nickel metal can be also bought in the form of small spheres produced through decomposition of nickel tetracarbonyl gas on heated nickel seeds (Mond process). Such spheres make for a really nice sample and can range anywhere from under a gram to impressive, cluster-like rounds weighing in hundreds of grams.

Brass coins plated chemically with Ni.

As mentioned before, nickel is used to plate everything, ranging from steel parts (such as barbells, shackles or jewellery), through neodymium magnets, to even polymer items, like car bumpers. It is most often utilized paired with a thicker copper coating beneath to improve the adhesion - that's why many nickel plated items, when subjected to everyday wear, tend to go more into the copper's color range.

Such plating can improve the corrosion resistance, structural integrity (in the case of brittle ceramics), and overall looks of the item.

Nickel coatings can be made through electrochemical and chemical (electroless) processes, with the main differences being the use of direct current and the composition of plating baths. Electroplating also utilizes sacrificial anodes, such as the one I cut into pieces (or bigger Mond rounds).

The quality of plating on the steel plate seen below can teach one crucial lesson regarding any form of surface engineering - correct preparation of the plated surface is the only way to achieve a well adherent, aesthetic plating.

Crudely electrochemically plated steel.

Ni coating on NdFeB magnets.

316L austenitic steel.