The question of whether copper contains nickel depends entirely on the material’s purity and its intended use. Elemental copper, in its refined state, is intentionally free of nickel, but the presence of nickel becomes a defining characteristic in many metal combinations designed for industrial applications. The confusion arises because copper is a base metal for a wide family of alloys, where other elements, including nickel, are deliberately introduced to enhance specific properties.
Composition of Pure Copper
Pure copper, such as the commercially available \(\text{C11000}\) grade, is defined by its high purity level. This material must contain a minimum of 99.90% copper, with the remaining fraction consisting of trace elements and oxygen. Nickel is not an intentional additive in this form, which is primarily valued for its outstanding electrical and thermal conductivity. While minute amounts of nickel may be present, they typically fall below 0.005% alongside other contaminants. Therefore, if the material is specified as pure or elemental copper, it is scientifically considered nickel-free.
Copper Alloys That Contain Nickel
The relationship between copper and nickel changes entirely when manufacturers deliberately combine them to form a new metal with superior characteristics. These engineered materials are known as copper-nickel alloys, or cupronickel, where nickel is a primary alloying element. Nickel is completely soluble in copper, allowing for a wide range of compositions that significantly improve the base metal’s strength, ductility, and resistance to corrosion. The primary reason for nickel addition is to create an alloy that excels in harsh environments, particularly in contact with saltwater. Copper-nickel alloys used in marine applications, such as for seawater piping and heat exchangers, typically contain nickel percentages ranging from 10% to 30%.
Properties and Applications
For example, the common \(\text{C70600}\) alloy contains 90% copper and 10% nickel, along with small additions of iron and manganese for enhanced erosion resistance. Nickel imparts a solid solution strengthening mechanism to the copper’s crystalline structure, which significantly increases the metal’s yield strength. This blend of high strength and excellent corrosion resistance makes these alloys indispensable in shipbuilding and offshore platforms. A well-known example of a high-nickel copper alloy is Monel, which can contain 50% or more nickel. Cupronickel alloys containing about 25% nickel are commonly used in the manufacture of coinage due to their durability.
Nickel Sensitivity and Exposure Risks
The deliberate inclusion of nickel in copper alloys is the reason for public concern regarding skin exposure, particularly for individuals with metal sensitivities. Nickel is a major trigger for allergic contact dermatitis, a delayed-type hypersensitivity reaction affecting a significant percentage of the population. This allergy is a lifelong condition triggered by contact with items that release nickel ions. The mechanism of the allergic reaction involves the corrosion of the metal when it is in prolonged contact with the skin, especially with sweat or moisture. This process causes nickel particles to leach out and penetrate the skin, initiating an immune response that results in an itchy, red rash.
Symptoms may not appear immediately, often presenting 12 to 72 hours after initial exposure. Common items that are the source of exposure often utilize nickel-containing copper alloys, including coins, jewelry components, and metal fasteners on clothing. For those with a known allergy, avoidance of these nickel-containing alloys is the only way to prevent the uncomfortable skin reaction.