Copper | About, Extraction, Properties, Alloys, and Applications

A vital component of our everyday lives. Known for its distinct reddish-orange hue and remarkable conductivity, copper has been utilized by human civilizations for thousands of years. From ancient times, where it was crafted into tools and ornaments, to the modern era, where it plays a crucial role in advanced technologies, copper continues to be an essential material in various industries.

Copper metal

Copper is a chemical element with the symbol Cu (from the Latin cuprum) and atomic number 29. It is a reddish-brown metal that is soft, malleable, and ductile. Copper is an excellent conductor of heat and electricity, making it a popular choice for electrical wiring and plumbing. It is also found in many alloys, such as brass and bronze.

Extraction of copper

Copper is primarily sourced from copper ores, which are found in various geological formations around the world. The most common copper ores include chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄), chalcocite (Cu₂S), and malachite (Cu₂CO₃(OH)₂). These ores typically occur in association with other minerals such as iron, sulfur, and sometimes precious metals like gold and silver.

The extraction of copper from its ores involves several steps:

1. Mining

The first step in copper extraction is mining. This involves the excavation of the ore-bearing rock from underground mines or open-pit mines, depending on the depth and accessibility of the ore deposit.

2. Crushing and Grinding

Once the ore is extracted, it is crushed and ground into fine particles to increase the surface area for chemical reactions. This process facilitates the subsequent separation of copper minerals from the gangue (unwanted rock and minerals).

3. Concentration

Copper ores are typically low-grade, meaning they contain relatively small amounts of copper. To extract the copper efficiently, the crushed and ground ore is subjected to a process called flotation or froth flotation. In this process, chemicals known as collectors are added to the water along with air bubbles. The collectors selectively bind to the surface of the copper minerals, causing them to float to the surface as a froth while the gangue particles sink. The froth containing the copper concentrate is then skimmed off.

4. Smelting

The next step is smelting, where the copper concentrate undergoes high-temperature treatment in a furnace. During smelting, the copper sulfide minerals are converted to liquid copper matte along with iron sulfide and other impurities. This process separates the copper from the sulfur and other elements present in the concentrate.

5. Conversion

The copper matte obtained from smelting is further processed in a converter furnace or another similar vessel. This step involves blowing air or oxygen through the molten matte to oxidize the remaining sulfur, iron, and other impurities. The resulting product, known as blister copper, typically contains around 98-99% copper along with small amounts of impurities.

6. Refining

The final step in copper extraction is refining, which removes the remaining impurities to refined electrolytically to produce 99.95% electrolytic tough-pitch (ETP) copper. This is often accomplished through electrolysis or electrorefining, where an electric current is passed through the blister copper, causing copper ions to migrate to the cathode and pure copper to deposit on the cathode. The impurities settle as sludge or are collected as gases.

Note that:

• Like aluminum, copper is recyclable without any loss of quality, both from raw state and from manufactured products. In volume, copper is the third most recycled metal after iron and aluminum.

• ETP copper has a nominal oxygen content of 0.04%. Oxygen is almost insoluble in ETP copper and forms interdendritic Cu₂O when copper is cast. For most applications, the oxygen in ETP copper is an insignificant impurity. However, if ETP copper is heated to a temperature above about 400°C in an atmosphere containing hydrogen, the hydrogen can diffuse into the solid copper and react with the internally dispersed Cu₂O to form steam according to the reaction:

Properties of copper

Copper possesses high ductility, and it  is known for its high malleability. It exhibits moderate tensile strength and good fatigue resistance. Copper has excellent creep resistance and low hardness. In addition to its high density, copper stands out for its exceptional electrical conductivity. Furthermore, the metal boasts excellent corrosion resistance.

Mechanical properties

Copper is highly ductile, meaning it can be easily drawn, stretched, or formed into various shapes without fracturing. This property makes copper ideal for applications such as electrical wiring, where it needs to be drawn into thin wires without breaking.

Similar to its ductility, copper is also highly malleable, allowing it to be hammered or rolled into thin sheets or foils without cracking.

While copper is not as strong as some other metals like steel or titanium, it still possesses good strength, especially in its alloyed forms. Copper alloys, such as brass and bronze, can exhibit higher strength levels while retaining many of copper's desirable properties.

Copper has a moderate tensile strength (110–128 GPa), meaning it can withstand pulling or stretching forces without breaking. The tensile strength of copper can be further improved by alloying it with other metals or by cold working processes.

Copper exhibits good fatigue resistance, allowing it to withstand repeated loading and unloading cycles without experiencing failure. This property is particularly important in applications where copper components are subjected to cyclic stresses, such as in machinery and equipment.

Copper has excellent creep resistance, meaning it can withstand prolonged exposure to high temperatures without undergoing significant deformation. This property makes copper suitable for use in high-temperature applications such as heat exchangers and electrical contacts.

Pure copper is relatively soft (35-45 BHN), but its hardness can be increased through alloying or cold working processes. Copper alloys, such as beryllium copper, can exhibit higher hardness levels while maintaining good electrical conductivity.

Physical properties

Copper has a relatively high density, with a density of approximately 8.96 grams per cubic centimeter (g/cm³) at room temperature.

Copper has a relatively high melting point of around 1,083 degrees Celsius (1,982 degrees Fahrenheit). This high melting point makes copper suitable for high-temperature applications, such as electrical wiring and plumbing.

The boiling point of copper is approximately 2,567 degrees Celsius (4,653 degrees Fahrenheit). While copper is not commonly used in applications requiring resistance to extreme heat, its high boiling point reflects its thermal stability.

Copper is an excellent conductor of electricity and heat. It has the second highest electrical conductivity (59.6×10^6 S/m), second only to silver, making it indispensable in electrical wiring, electronics, and power transmission.

The thermal conductivity of copper is approximately 400 watts per meter kelvin (W/m·K) at room temperature, making it highly efficient at conducting heat. This means that copper can rapidly transfer heat from one point to another with minimal resistance, making it ideal for applications where efficient heat transfer is crucial.

Unlike some other metals such as iron and nickel, copper is non-magnetic (diamagnetic).

Chemical properties

Copper is a moderately reactive metal. It reacts slowly with oxygen in the air to form a thin layer of copper oxide on its surface, which gives copper its characteristic reddish-brown color. This oxide layer protects the underlying metal from further corrosion.

Copper can undergo redox reactions, where it can exist in two oxidation states: +1 and +2. In its +1 oxidation state, copper forms compounds known as cuprous compounds, while in its +2 oxidation state, it forms cupric compounds. For example, copper(II) oxide (CuO) is a common cupric compound.

Copper is an excellent catalyst for various chemical reactions. It is used as a catalyst in the oxidation of alcohols to aldehydes or ketones and in the hydrogenation of unsaturated hydrocarbons.

Copper readily forms alloys with other metals, leading to the creation of numerous useful materials. For example, brass is an alloy of copper and zinc, while bronze is an alloy of copper and tin.

Note that:

• Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air. This is due to the low plasma frequency of the metal, which lies in the red part of the visible spectrum, causing it to absorb the higher-frequency green and blue colors.

• The crystal structure of copper at room temperature is FCC (Face-centered cubic).

Classification of copper alloys with applications

Copper alloys in the United States are classified according to a designation system administered by the Copper Development Association (CDA). In this system, the numbers C10100 to C79900 designate wrought alloys and the numbers from C80000 to C99900 designate casting alloys.

Wrought Copper Alloys

Wrought copper alloys are those that are mechanically worked into their final shapes, typically through processes like rolling, forging, extrusion, or drawing. These alloys are known for their excellent combination of properties, including high electrical and thermal conductivity, corrosion resistance, and ease of fabrication.

C10000-C19999 Series (Pure Copper)

C20000-C29999 Series (Copper-Zinc Alloys)

C30000-C39999 Series (Copper-Zinc-Lead Alloys)

C40000-C49999 Series (Copper-Tin Alloys)

C50000-C59999 Series (Copper-Aluminum Alloys)

C60000-C69999 Series (Copper-Nickel Alloys)

Cast Copper Alloys

Cast copper alloys are those that are produced by casting molten copper-based alloys into molds to form the desired shapes. These alloys are known for their excellent combination of properties, including high thermal and electrical conductivity, corrosion resistance, and ease of casting.

C80000-C81100 Series (Copper-Tin Alloys)

C81200-C81300 Series (Copper-Zinc Alloys)

C81400-C81500 Series (Copper-Silicon Alloys)

C81600-C81700 Series (Copper-Nickel Alloys)

C81800-C82900 Series (Other Copper Alloys)

C83000-C84900 Series (Nickel Silver Alloys)

Is copper cookware safe for health?

Copper cookware can be safe for health when used properly and in moderation, while being prized for its excellent heat conductivity. However, it poses safety concerns due to its reactivity with acidic foods, which can lead to copper leaching into the food and potential health risks such as nausea and copper toxicity. Additionally, copper cookware can corrode over time, requiring regular maintenance and potentially exposing harmful compounds.