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In the analytical laboratory, nickel crucibles offer high resistance to dilute alkalies at a very low cost per crucible. In some instances, nickel crucibles are preferable to zirconium: for instance, sodium peroxide fusions in which zirconium itself is to be determined; also in analysis for columbium (niobium), tantalum or low phosphorus.
Although significant amounts of nickel can be introduced into samples, it can be removed easily by several ammonia separations. Life expectancy of a nickel crucible is from 4 to 6 fusions. They present an advantage, other than cost, if small amounts of zirconium are present, or if its removal with Mandelic Acid is unsuccessful. If small amounts of phosphorus are to be determined because of extremely low solubility of zirconium phosphate, then nickel must be used.
Corrosion Resistance of Nickel
Nickel is completely resistant to phosphoric acid as well as being highly resistant to the corrosive effect of the strongest alkalies. Nickel, however, is less than satisfactory when used for salt solutions containing oxidants such as ferric chloride or solutions of mineral acids containing oxidizing salts.
Nickel should not be used for:
1. Hypochlorite solutions when available chlorine is over 3 gram/liter
2. Strongly oxidizing acids such as nitric acid
3. Sulfurous acid and ammonium hydroxide in concentrations over 1%.
Wet and dry gases
No dry gases are actively corrosive to nickel at atmospheric temperature. Nickel is also resistant to dry hydrogen chloride, hydrogen fluoride, and chlorine up to about 535C. Nickel is not affected by steam at temperatures usually encountered. It is corroded by gases containing sulfur.
NICKEL FORMS A TIGHTLY ADHERING OXIDE FILM AT 400C IN OXIDIZING ATMOSPHERES AT TEMPERATURES TO 600C.
In choosing crucibles for laboratory work, nickel can be effective with regard to cost per crucible, and for use in fusions where zirconium or other metals cannot be used.