What is Metal?
A metal is a type of element that possesses a shiny appearance. It is also characterised by its ductility and malleability. Ductility is the property that allows a metal to be drawn into wires, whereas malleability refers to a substance’s ability to be shaped into thin sheets. Metals contain free electrons, which make them good conductors of heat and electricity.
Metals also have a high melting point allowing them to maintain a solid structure at room temperature. However, some metals exist as liquids at room temperatures, e.g. Cesium, Gallium, Mercury and so on.
A metal is also more durable and less likely to degrade at high temperatures. As a result, metals are used in many applications that subject a material to forces and pressures.
Properties of Metals
The properties of any substance can be divided into three main types: physical, mechanical and chemical. Let us look at some characteristic properties of metals.
Physical Properties
The properties that can be observed without the application of force are known as physical properties. Some examples of physical properties include color, density, appearance, weight, luster, melting point, and boiling point.
Most metals exist in dark shades with shiny surfaces. Except for lithium, sodium, and potassium, all metals are denser than water causing them to sink in it. They are also characterised by high melting point and boiling points necessitating the use for furnaces and other heat sources when making items out of them.
Mechanical Properties
Mechanical properties are those that can only be observed through the application of forces. Some examples include hardness, ductility, malleability, tensile strength, compressive strength, and shear strength.
Atoms of a metal are closely packed together. This makes them capable of handling higher forces than metals and, as a result, they exhibit higher values when it comes to properties such as strength and hardness. Due to this, most heavy machines that require high strength from components are made out of metals.
Chemical Properties
Chemical properties are those that are observed when a substance reacts with other elements in its vicinity. These properties include corrosion resistance, oxidation, and reactivity among many others. Metals are generally inert in most chemical reactions but continued exposure to corrosive elements like salt water and soil can cause them to react and degrade over time.
Types of Metals
Metals can be divide into various categories depending on the property we use for classification. They may be classified as ferrous and non-ferrous, magnetic and non-magnetic, pure metal and alloys, atomic structure, phase at room temperature, and so on. Let us start with the ferrous vs non-ferrous classification as it is the most common method of classifying metals.
Ferrous Metals
Ferrous metals are those that have a significant ratio of iron in their composition. Examples of ferrous metals are cast iron, wrought iron, stainless steel, high carbon steel, etc. Ferrous metals may also contain some percentage of carbon. A higher carbon content generally makes them vulnerable to rust and brittleness. Lower carbon content makes the iron softer and more elastic.
Ferrous metals are also typically magnetic making them useful for motor and electrical applications. They can often be found in many applications in the construction, manufacturing, and automotive sectors.
Non-Ferrous Metals
Non-ferrous metals are those that do not contain iron as their main constituent. Examples of non-ferrous metals include copper, aluminum, zinc, and silver. Non-ferrous metals are typically non-magnetic and find use in applications such as plumbing, electrical wiring, and consumer goods.
Types of Ferrous Metals
The list of ferrous metals is very long. By varying the concentration of carbon and other alloying elements, we can form many different grades of carbon steel and other ferrous alloys. They can cover a range of properties.
In this section, let us explore some common ferrous metals, their properties and applications in the industry. We shall cover the following metals:
- Iron and Steel
- Carbon steel (Low, medium and high carbon steel)
- Alloy steel
- Cast iron
Iron and Steel
Iron is the backbone of all industries on earth. Its use started with rudimentary implements such as daggers as far back as 3000 BC. Through constant research and advancements, we can use iron more effectively by mixing it with other elements to imbibe or eliminate properties as needed. For example, we can improve its hardness and strength by adding silicon while the addition of chromium can eliminate iron’s natural vulnerability to corrosion. The most common use of iron is in the form of steel — a mixture of iron, carbon, and other trace elements.
Steel is the most used metal in the world because it is strong, durable and versatile. Steels can be of two main types: carbon steel and alloy steel.
Carbon Steel
Carbon steel is made by extracting iron from ore and adding carbon and other elements. It contains low carbon content between 0.008% and 2.14%. Based on the carbon percentage, carbon steels are divided into three main types: low-carbon steels, medium-carbon steels, and high-carbon steels.
Low-carbon steels contain carbon between 0.008% and 0.30%. Medium-carbon steels contain between 0.30% and 0.60% carbon. The remaining steels that contain more than 0.60% carbon are referred to as high-carbon steels. With increasing carbon content, steel increases in strength and hardness.
Alloy Steel
Alloy steel is steel that has chemical elements other than carbon in sufficient quantity to obtain special properties. They are used for high-intensity applications that require niche properties from steel. Stainless steel is an example of high alloy steel that contains a minimum of 10.5% chromium, less than 1.2% carbon, and other alloying elements. The addition of chromium imparts excellent corrosion resistance making it suitable for corrosive environments. Other examples of alloy steel are nickel steel, molybdenum steel, vanadium steel, and tool steel.
Cast Iron
Cast iron are iron alloys that have between two and four percent carbon content. The higher carbon content gives cast iron different properties such as higher compressive strength, greater machinability, and a lower melting point.
On the basis of composition, cast iron is mainly divided into five parts:
- White cast iron
- Gray cast iron
- Mottled cast iron
- Malleable cast iron
- Ductile cast iron
Non-Ferrous Metals
Non-ferrous metals refer to metals that do not contain any iron. They can be pure metals such as aluminum and copper or alloys such as brass. Non-ferrous metals are comparatively light weight and do not rust as easily as ferrous metals. They are also usually non-magnetic. Non-ferrous metals can also be recycled much more easily than ferrous metals.
In this section, let us review some popular non-ferrous metals. We shall cover the following:
Aluminum
Aluminium is the most abundant metal in the earth’s crust and also the most commonly used non-ferrous metal. It is also the third most abundant element of all elements after oxygen and silicon. It is a silvery white metal but may also develop a dull gray colour depending on the surface roughness.
Properties of Aluminum
The pure form of aluminum is soft and lacks strength. However, its alloys have very high strength and other desirable properties such as corrosion resistance, conductivity, lightweight characteristics, ductility, heat conduction and recyclability.
Uses of Aluminum
Their higher strength-to-weight ratio has given them an edge over traditional metals in weight sensitive industries such as aerospace and automotive. Aluminum is also used extensively for everyday products. Most appliances and electronics use aluminium components. It is used in smartphones, laptops and televisions because of its lower weight, shiny appearance, and durability.
However, there are also applications where aluminium may not be the best option. Aluminum is a reactive metal and, when used in cooking, can react with salts and acids in the presence of heat and leach into the food. While the amount of aluminum that leaches during cooking is generally considered safe, sensitive individuals may face side effects from long-term exposure.
Limitations of Copper
Other disadvantages such as higher prices, lower melting point, toxicity to aquatic animals, and susceptibility to corrosion can further limit the use of aluminum in some products.
Copper
Copper is a reddish, non-ferrous metal with excellent heat and electrical conductivity properties. As a result, it is used extensively in electrical and heat conduction applications.
Properties of Copper
Advantageous properties of copper include ductility, corrosion resistance, fire resistance, machinability, durability, and 100% recyclability. Strength and hardness can be enhanced by cold working.
Uses of Copper
Copper’s properties such as ease of use and high electrical conductivity make it ideal for use as a heat and electrical carrier in products. Consequently, most motor and heater windings are made out of copper. The use of electrical motors in modern vehicles as a prime mover has increased the use of copper in the automotive sector.
Copper’s unique combination of properties makes it ideal for use in solar cells, medical instruments, electromagnets, printed circuit boards (PCBs), heat exchangers, jewelry, musical instruments,
Because of its aesthetic appeal, copper finds cosmetic applications in architecture for gutters, wall cladding and roofing, and rain water spouts. Its high corrosion resistance makes it suitable for service environments susceptible to corrosion such as water piping in domestic appliances. Its antibacterial properties are ideal for use in medical devices. Copper T, for instance is a 99% effective intra-uterine device to prevent pregnancies.
Copper alloys like beryllium copper find use in specialized applications in aerospace, automotive and robotics sectors.
Limitations of Copper
Copper is more expensive than aluminum and some other metals. This limits its use in applications where cost is a major driver. Its higher weight can make it unfeasible in certain electrical applications such as overhead wires.
It also has lower strength rating making it unsuitable for demanding applications. Copper is also susceptible to corrosion which may lead to degradation over time causing issues such as performance drop, reduced lifespan and safety risks. Copper toxicity is also a serious issue for infants and patients suffering from Wilson’s disease.