Conductivity refers to how easily heat or an electric charge can pass through a material. Metals are known for their electrical and thermal conductivity, as the molecular structure of metals makes them effective conductors. The electrical conductivity of metals lets an electrical current move about with little resistance. Thermal conductivity translates to how fast heat gets transferred through metals through physical contact.
Below, we discuss the conductivity of metals, whether or not there are any nonconductive metals, and why some metal alloys are less conductive than metals.
What Causes Thermal and Electrical Conductivity in Metals?
The presence of free-flowing electrons in metals makes them conductive to heat. As temperature increases, the delocalized and free electrons gain more energy and vibrate more quickly. These molecules, in turn, bump into nearby particles and transfer some of their energy to them. The process continues, eventually passing energy from the hot end to the colder end of the metal. Silver, copper, and aluminum are some of the metals with the highest thermal conductivity value. The high thermal conductivity of silver is utilized in various industrial and manufacturing processes including brazing, welding, or soldering. The thermal conductivity of copper makes it best suited for heat sinks, heat exchangers, and even cookware bottoms. Aluminum has slightly lower thermal conductivity than silver and is the preferred material for microelectronics such as laser diodes and LEDs.
The free-moving delocalized electrons also contribute to the electrical conductivity of metals. When electric voltage is applied, the electric field triggers the movement of electrons within the metal and makes them move towards the positive terminal. Thermal and electrical conductivity are closely related. That is why metals that are good thermal conductors are also good electrical conductors.
The high electron mobility in metals such as copper, silver, aluminum, and gold makes them the best conductors of electricity. As silver and gold are expensive metals, they are used exclusively for specialized equipment such as satellites or circuit boards. Even though copper has relatively low electrical conductivity compared to silver and gold, it is cheaper and widely used for soldering and wrapping into wires in household appliances. Aluminum is more conductive than copper but forms an electrically-resistant oxide surface, causing an electrical connection to overheat. That is why it is used for high-voltage transmission lines that are further encased in steel.
Are There Any Nonconductive Metals?
Technically, all metals conduct heat and electricity—some more effectively than others. Under normal conditions, no metal displays infinite resistance and is conductive up to a certain extent. Conductivity is a defining characteristic of metals that sets them apart from non-metal elements. In contrast to free-moving delocalized electrons in metals, electrons are tightly bound in non-metals that offer extremely high resistance to the flow of charge or heat through them. Most non-metals are poor conductors of heat and electricity and are often used for insulation.
What Are the Least Conductive Metals?
Bismuth, tungsten, lead, and titanium are some examples of the least conductive metals. Bismuth is least conductive to heat and electricity and is used in fuses to detect an electrical surge. Tungsten, a rare metal, is nonconductive to electricity under standard temperatures. However, it has a high melting point, and that is why it‘s often used in electric bulbs. Pure lead is a good conductor of electricity, but when it reacts with atmospheric oxygen, it forms a layer of lead oxide that does not let electricity or heat pass through. Though titanium is a transition metal, it has very low electrical and thermal conductivity as compared to other transition metals. As a poor conductor, titanium can withstand extreme environmental conditions and is used as an insulator in the manufacturing of aircraft components.
Why Are Some Metal Alloys Less Conductive Than Pure Metals?
Several factors impact the conductivity of metals including impurities, temperature, electromagnetic fields, frequency, and crystal structure and phases. Adding an impurity to a pure metal decreases its conductivity. For example, stainless steel is an alloy of iron, carbon, chromium, and other alloying elements. It has significantly lower thermal and electrical conductivity when compared to silver, copper, or aluminum and is widely used across industries. Similarly, bronze—an alloy of copper and tin—displays very low thermal conductivity when compared to its base elements.
So, are there any nonconductive metals? The simple answer is no. However, for specific applications that require nonconductive materials, metals such as titanium can be used as insulators. Some alloy metals can also be used as nonconductive materials.
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