NICKEL
CONTROL QUALITY

The process can be summarised as follows:

• The first stage is concentration, which involves a succession of partial firings followed by reductive melting: this involves high temperatures in an oxidising atmosphere, the aim of which is to enrich the raw material with nickel by eliminating impurities as much as possible.
  The material obtained is called: “speiss” if the nickel is combined with arsenic (mixture of nickel, cobalt and arsenic) and “matte” if it is combined with sulphur (mixture of nickel, copper and sulphur). A final firing transforms the materials obtained into oxides.
• The second stage is the treatment of the oxidised ores, which generally involves reducing the oxides combined with the metal or directly reducing the metallic nickel.
  Due to the multitude of oxides present, several processes can be carried out involving either different heat treatments or different chemical solutions, with the aim of reducing specific oxides.

It is very rarely used pure. Nickel is mainly used as an alloying or additive element:

• Stainless steels, addition of nickel to improve corrosion resistance,
• Invar/Kovar, an iron, nickel (and chromium for Kovar) alloy with a very low thermal expansion coefficient, used in watchmaking, topography, measuring devices, etc.
• Cunife and Fernico, an alloy of copper, nickel and iron with the same thermal expansion coefficient as some types of glass.
• Phynox, an austenitic superalloy of cobalt, chromium, nickel, iron and molybdenum used for its very high corrosion resistance,
• Nickel silver, an alloy of copper, nickel and zinc, used for its low oxidation and silvery appearance, in jewellery, musical instruments, precision instruments, watches, etc.
• AlNiCo, an alloy of aluminum, nickel and cobalt used for its ferromagnetic characteristics allowing the manufacture of permanent magnets (AlNiCo magnet),,
• Gold-nickel alloys used in jewellery for their colours and superior mechanical properties, etc.

However, its main unalloyed use is as a coating. Nickel is stainless in the ambient air and associated with its bright and aesthetic appearance, it is used for protection against corrosion, improvement of mechanical properties (resistance to wear, abrasion, friction) and/or to improve appearance.
These coating operations are called “nickel plating”. There are two types: electrolytic nickel plating and chemical nickel plating.

Nickel also benefits from its own alloys (%Ni > 50%), they are practically all used for their corrosion/ oxidation resistance and creep resistance, among them:

• Copper-nickel alloys (Monel), which are more mechanically resistant than non-alloyed nickel and are very resistant to corrosion in chemical environments. They are heat treatable and with the addition of aluminum and titanium, the alloys retain their corrosion resistance and have enhanced mechanical characteristics. Therefore, they are used in the marine industry, oil and gas industry, in the transport of steam and water (fresh and sea water), in chains, cables, etc.
Example of grade: Ni-Cu35 (Monel or Alloy 400); Ni-Cu35AlTi (Monel or Alloy K-500).

• Nickel-chromium alloys, which have high resistivity, very good oxidation resistance and good mechanical strength at high temperatures. Thanks to these characteristics, they are often used for electric heating resistors (electric ovens, toasters, dryers, etc.). Iron can be added to nickel-chromium alloys to increase creep resistance.
Example of grade: Ni-Cr20 (Chromel A); NiCr14Fe6 (Inconel 600).

• Nickel-based superalloys are high-performance alloys, which initially designate alloys developed for turbojet engine parts (aeronautics industry). Today they are also used in the power generation industry, the oil industry, the automobile industry, the chemical industry, the nuclear industry, etc. Their main benefit lies in their excellent mechanical resistance at high temperatures (creep resistance, oxidation/corrosion, ductility, fatigue, etc.). Some alloys also have cryogenic properties. Nickel-based superalloys have a nickel content of more than 50%. A multitude of additive elements can be added and heat treatments can be carried out with the aim of influencing mechanical properties by modifying the microstructure of the alloys.
Example of grade: Inconel (625 or 718); Hastelloy; Nimonic; Rene Alloy.

• Other nickel alloys, such as:
Nickel-titanium alloys (Ni-Ti) called “Nitinol” which benefit from shape memory and super-elasticity properties allowing them to withstand severe deformations but which can recover their initial shape. They are used in the aerospace sector (coupling sleeves, Frangibolt devices, solar panels), the biomedical sector (instrumentation, stents, etc.) and the commercial sector (clothing and sports equipment, etc.).

Permalloy alloys which are nickel and iron based alloys used for their magnetic properties. These include: their high magnetic permeability and magnetoresistance as well as their low coercive field and magnetostriction.

Alumel alloys, consisting of 95% nickel (with manganese, aluminum and silicon), are used to make thermocouples.