The most conductive metals are silver, copper, and gold. Silver has the highest conductivity, but copper is widely used for electrical appliances as it is cost-effective. Metals' effectiveness in conducting heat or electricity depends on their crystalline nature, variations in temperature, and impurities present in the metals.
This article discusses the most conductive metals and the factors that affect their conductivity.
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Most Conductive Metals in Order (High to Low)
The conductivity of a metal is defined by its ability to conduct electricity or heat.
The following table lists the most conductive metals and their corresponding thermal and electrical conductivity values.
| Metals | Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|---|
| Silver | 62.1 | 420 |
| Copper | 58.7 | 386 |
| Gold | 44.2 | 317 |
| Aluminum | 36.9 | 237 |
| Zinc | 16.6 | 116 |
| Brass | 15.9 | 150 |
| Nickel | 14.3 | 91 |
| Iron | 10.1 | 72 |
| Bronze | 7.4 | 85 |
Silver
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 62.1 | 420 |
The most conductive metal is pure silver. The presence of free electrons in the lattice structure of silver makes it highly conductive.
Silver tarnishes and oxides when exposed to sulfur gases in the air. This affects its appearance and conductive properties.
Since silver is an expensive metal, it is not an ideal choice for most conductivity-based applications.
Copper
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 58.7 | 386 |
Like silver, copper also has a free-moving electron, allowing the metal to conduct heat and electricity with less resistance.
In addition to being conductive, copper has good machinability and ductility.
This enables copper to be drawn into wires (for electrical wiring) and fabricate copper stampings.
Gold
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 44.2 | 317 |
Gold exhibits high conductivity and is very efficient. It does not tarnish or oxidize like silver and copper.
Being conductive, gold has good flexibility and corrosion resistance properties. Thus making it suitable for fabricating connectors, circuits, and semiconductors.
However, being a rare and valuable metal, using gold is only economical if functionality is of utmost importance, for example, in space research applications.
Aluminum
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 36.9 | 237 |
Besides being light and abundantly available, aluminum offers good thermal and electrical conductivity.
Characteristics like ductility and good strength-to-weight ratio allow aluminum to be used as raw material in manufacturing kitchenware.
Aluminum forms a natural oxide layer over its surface, protecting the material from corrosion.
Zinc
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 16.6 | 116 |
Zinc is a fair conductor of heat and electricity. It exhibits good durability and is relatively inexpensive.
Though brittle at room temperature, zinc is malleable at higher temperatures.
Zinc offers resistance to corrosion and is, therefore, primarily used as a protective coating for iron.
Brass
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 15.9 | 150 |
An alloy of copper, brass has less conductivity than copper due to alloying metals like zinc and phosphorous.
Copper in brass offers good conductivity compared to other alloying elements.
When tensile strength and machinability are needed for an application, brass is chosen over copper.
Brass is commonly used in making relays, connectors, etc., as it offers non-magnetic properties, thereby not interfering with the transmissions.
Nickel
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 14.3 | 91 |
In addition to good strength and durability at high temperatures, pure nickel has moderately good thermal and electrical conductivity.
Nickel is commonly used as a protective coating for metals prone to rust.
Iron
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 10.1 | 72 |
The presence of free electrons in its crystalline structure offers iron the ability to conduct heat and electricity.
Iron exhibits the least resistance to the flow of electrons. Hence, it is a good conductor.
Bronze
| Electrical Conductivity 106 (S/m) | Thermal Conductivity (W/mK) |
|---|---|
| 7.4 | 85 |
Similar to brass, bronze is an alloy of copper and nickel. Though brass and bronze conduct heat and electricity, bronze may melt at higher temperatures.
Bronze coils have significant applications in automotive industries, especially in electric cars. This is due to its resistance to wear under high stress and pressure conditions.
Factors That Affect Conductivity in Metals
Addition of Impurities
The addition of impurities is when other elements are added to pure metal.
In general alloying metals act as impurities reducing the overall conductivity of the pure metal.
This is because the presence of impurities hinders the free movement of the electrons, reducing their conductivity.
Temperature
The thermal conductivity of a metal is dependent on the working temperature.
Higher temperatures tend to excite the atoms, which leads to increased resistance to the free movement of the electrons.
The higher the resistance lower will be the heat/electric current passed through the metal, thereby reducing the overall conductivity of the metal.
Frequency
The frequency of the alternating current passed through the metal impacts its conductivity. The phenomena "skin effect" explains the reason for this variation.
Skin effect demonstrates that at higher frequencies, the current tends to surround or distribute around the metal rather than flow through it. Thus affecting the conductivity of a metal.
Using direct current eliminates this effect on the conductivity of a metal.
Crystalline structure
Different states or phases of metal have a significant impact on the conductivity of the metal.
This is because of variations in the flow rates of the electrons in a lattice structure.
The conductivity of the metal also changes when it is being processed.
Electromagnetic fields
A current-carrying metal develops a magnetic field perpendicular to the direction of current flow.
The magnetic field generated, in turn, creates resistance to the current flowing through the metal. This effect thereby reduces the conductivity of the metal.
Final Thoughts
Conductivity is a property that showcases the ability of a metal to let heat or electric current pass through.
Silver is the most conductive metal, but being expensive, it is replaced by copper, which is relatively inexpensive in most applications.
Temperature variation, changes in the crystalline structure, and the presence of impurities all affect the conductivity of metals.
Further, the conductivity values can be improved through the heat treatment processes.
Frequently Asked Questions
Can the conductivity of metal be improved?
Yes, heat treatment processes like annealing help improve a metal's conductivity. Heating and holding the metal at high temperatures (preferably below the melting point) and cooling slowly to room temperature improves its conductivity.
Is it desirable to have metals with high-conductive values?
Generally, extremely high conductivity values are not desired as the electrical conductivity tends to make the surrounding environment corrosive. Thus leading to deterioration or failure of the metal parts.
Does thermal conductivity depend on the thickness of the metal?
Yes, thermal conductivity depends on the thickness of the metal. The rate of heat flow through the material is proportional to the thickness of the part.
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