Metals: The Most Widely Used Material in the World

This materials science basics topic is the second oldest class of materials, metals.

The materials science basics topic last week was about ceramic materials and this week we are talking about metallic materials. If you want a recap on exactly what material science you should check out the what is materials science post.

Brief History of Metal Materials

The name metal comes from the Greek word μέταλλον (metallon) which means mine, quarry, or metal. The oldest use of metals dates back to 9000 BC. The copper artifacts were small copper beads excavated from a settlement called Çayönü Tepesi. The first known functional use of metals dates back to the stone age. During the stone age people made tools for hunting and gathering out of raw copper.

Since their first use, we have learned so much about metals and use them in even more applications today.

Properties of Metallic Materials

Metals are opaque and lustrous elements that are good conductors of heat and electricity. Additionally, metals are malleable and ductile. This means they have some flexibility. The ductility of metals can be attributed to the type of bonding present. Metallic materials use metallic bonding.

In metallic bonding, the positively charged nuclei of the element condense at a central point becoming positive ions, and all of their electrons form a cloud around that positive central point. This orientation of the electrons in metallics bonding is often referred to as delocalized electrons. The delocalized electrons are not held rigidly by one molecule, which makes heat and electricity transfer through the materials easier. This is why metallic bonding makes metallic materials good conductors of heat and electricity

Uses of Metals

Metals can be used in elemental or alloyed forms. Materials made from elemental metal means that there is only one metallic element present in the material (with the absence of impurities). Metals can also be alloyed together to create new materials. Some examples of metal alloys that are commonly used today include brass which is an allow of copper and zinc,

Another example of a metal alloy is steel. Steel is an alloy of iron and carbon, and stainless steel which is an alloy of iron, carbon, and chromium. As a fun fact, chromium is the component of the stainless steel alloy that gives it its shiny color because the chromium on the outer layer of the alloy is reacting with oxygen in the air to form chromium oxide, which is actually a ceramic material. So stainless steel is a metal alloy, but it has a thin ceramic layer that makes it corrosion resistant and easy to clean.

Processing Metals

When we discussed ceramics we talked about their brittle nature making their processing unique. The ductility and malleability of metals make their processing very different compared to ceramics. Explained very simplistically, processing metals involves making them molten then pouring them into a mold. Everything that happens subsequently is nuance for the application.

Metallic materials are polished or secondary processed to alter their properties after the initial pour. The application of chemical treatments gives metals a better surface finish. To alter properties processes called hot-working or cold-working are used.

Hot-Working

Hot-working is a type of secondary processing which means they are formed or molded while still hot. This process can be preferential because the metals are more malleable. The size and shape of the parts can be altered while keeping the metal formable after it hardens. This is a good secondary processing technique when the metal needs to remain ductile. Ductility is a property that describes how easy it is to bend a material. For metals, this processing technique is important in the automotive, aerospace, and plumbing industry.

Cold-Working

Cold-working is another broad category of secondary processing. During the cold-working process, the shape and size of the part are changed at lower temperatures. This creates dislocations in the microstructure to prevent fracturing. Dislocations are small microscopic defects in the microstructure of the material that toughen the material and make it harder to break. For metals, this processing technique is important in the building industry.

Applications of Metals

Roughly 50% of the Earth’s crust is composed of metals and semi-metals. Due to their prevalence, it makes sense metals are the most widely used material in the world. It would take pages and pages to talk about applications of metals, but to give a brief overview we will talk about a few.

Steel is a staple building material that is used to make tall structures like skyscrapter. They are also critical to the electronics industry due to their conductivity. Magnesium alloys are one of the most important components in batteries. Lastly, the automotive industry uses aluminum alloys because they are lightweight and still have good strength to make the car safe with a lower fuel economy. These are just a few applications of metals.

If you want to learn more about metals you can check out the metals contents repository!