About Nickel
About Nickel
Nickel
Commercially pure or low-alloy nickel has characteristics that are useful in several fields, notably chemical processing and electronics. Nickel is highly resistant to various reducing chemicals and is unexcelled in resistance to caustic alkalis. Compared with nickel alloys, commercially pure nickel has high electrical and thermal conductivity.
Nickel 200
Nickel 200 is commercially pure (99.6%) wrought nickel. It has good mechanical properties and excellent resistance to many corrosive environments. Other useful features: high thermal and electrical conductivities, low gas content and low vapour pressure. The corrosion resistance of Nickel 200 makes it particularly useful for maintaining product purity in the handling of foods, synthetic fibres and caustic alkalis; and in structural applications where resistance to corrosion is a prime consideration.
High Temperature Properties
Nickel 200 is normally limited to service at temperatures below 315°C. At higher temperatures Nickel 200 products can suffer from graphitisation, which can result in severely compromised properties. For applications above 315°C, Nickel 201 is preferred.
Corrosion Resistance
Water
The resistance of Nickel 200 to corrosion by distilled and natural waters is excellent. Nickel 200 effectively resists water containing hydrogen sulphide or carbon dioxide. Nickel 200 has good resistance in seawater.
Acids
Sulphuric
Nickel 200 can be used with sulphuric acid at low or moderate temperatures.
Hydrochloric
Nickel 200 may be used in hydrochloric acid in concentrations up to 30% at room temperature. Increasing temperature will accelerate corrosion. If oxidising salts are present at less than 0.5% concentration, the material can be used satisfactorily up to 150°-205°C.
Hydrofluoric
Nickel 200 has excellent resistance to anhydrous hydrofluoric acid even at elevated temperatures. In aqueous solutions however, usage is usually limited to below 80°C.
Phosphoric
Nickel 200 has limited usefulness in commercial phosphoric acid solutions as these usually contain impurities such as fluorides and ferric salts that accelerate corrosion.
Nitric
Nickel 200 should be used in nitric acid only in solutions of up to 0.5% concentration at room temperature.
Organic
Nickel 200 has excellent resistance to organic acids of all concentrations.
Alkalis
Nickel 200 is its resistance to caustic soda and other alkalis. Ammonium hydroxide is an exception. Nickel 200 is not attacked by anhydrous ammonia or ammonium hydroxide in concentrations of 1%. Stronger concentrations can cause rapid attack.
Nickel 200 has excellent resistance to caustic soda in all concentrations. Below 50%, rates are negligible, even in boiling solutions. As concentration and temperature increase, corrosion rates increase very slowly. A major factor contributing to Nickel 200 in highly concentrated caustic soda is a black protective film that forms during exposure.
This film – nickel oxide – results in a marked decrease in corrosion rates over long exposure under most conditions. The presence of chlorates in caustic increases corrosion rates significantly, every effort should be made to remove as much of them as possible.
Salts
Nickel 200 is not subject to stress-corrosion cracking in any of the chloride salts and has excellent resistance to all of the non-oxidising halides. Oxidising acid chlorides such as ferric, cupric and mercuric are very corrosive and should be used with alloy 200 only in low concentrations. Stannic chloride is less strongly oxidising, and dilute solutions at atmospheric temperature are resisted. The maximum safe limit for use of Nickel 200 in oxidising alkaline chlorides is 500 ppm available chlorine for continuous exposure. In bleaching, sodium silicate (1.4 specific gravity) can be used as an inhibitor to corrosion; as little as 0.5 ml/liter of bleach has been found to be effective. Some very reactive and corrosive chlorides – phosphorus oxychloride, phosphorus trichloride, nitrosyl chloride, benzyl chloride and benzoyl chloride – are commonly contained in Nickel 200. It has excellent resistance to neutral and alkaline salt solutions.
Fluorine and Chlorine
Fluorine and chlorine are strong oxidisers that react with metal as a result Nickel 200 can be used successfully in such environments under certain conditions. At room temperature, Nickel 200 forms a protective fluoride film and is considered satisfactory for handling fluorine at low temperatures. Nickel 200 effectively resists dry chlorine at low temperatures. Hydrogen chloride when dry behaves similarly towards the metal. In wet chlorine at low temperature or wet hydrogen chloride at temperatures below the dew point, Nickel 200’s performance is somewhat as in hydrochloric acid.