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Descriptions and properties of common materials such as wood, metal, glass, plastics, ceramics and paper.
Everything we make is made up of one or more materials. Different materials have different properties. Because of these different properties, they can be used to make many kinds of objects. Materials can be soft or hard. They can be flexible or stiff. They can be delicate or very strong. Let’s take a look at some examples of different materials.
Wood can be classified as either hardwood or softwood.
Hardwood comes from deciduous trees. These are trees that lose their leaves in the fall. Hardwood is usually used to make furniture and in construction projects that need to last for a long time. Examples of hardwoods are oak, maple, and walnut.
Softwood comes from coniferous trees. Coniferous, or evergreen trees, keep their needles all year round. Most timber, or wood that is prepared for construction, is made from softwood trees. Softwood is usually used in parts of buildings, like windows and doors. It is also used in some kinds of furniture. Examples of softwoods are pine, fir, and spruce.
The terms “hardwood” and “softwood” do not refer to how hard the wood in a tree is. These terms refer to how the tree reproduces. Coniferous (softwood) trees reproduce through seeds in cones. Deciduous (hardwood) trees reproduce through seeds that come from a fruit or flower.
Different types of trees produce wood with different properties. But all types of wood have some physical characteristics in common. First, wood is strong. Its strength depends on its grain. Grain is the natural direction of growth of the fibres in the wood. Wood is very resistant to compression when force is applied in the direction of the grain. But it can break easily if force is applied against the grain.
Wood also has an interesting relationship with water. It is a very buoyant material. This means it can float. This is why wood is often used to make ships and boats. But wood is also hygroscopic. This means that it can absorb water. Some types of wood can absorb and hold a lot of water. It is important to consider this characteristic when choosing wood for a project. If a wood contains too much water it may eventually rot. When wood rots, it breaks down.
Did you know?
Balsa wood is one of the lightest and least dense woods, but it’s technically considered a hardwood because the trees that produce it create seeds!
Metals are some of the most important materials used in manufacturing and building. Some examples of metals are iron, aluminum, copper, zinc, tin, and lead. Many metals we use today are alloys. Alloys are made by combining two or more metals. They can also combine a metal with a nonmetal material. Alloys are made to give the metal new characteristics. Things like increased hardness or strength. For example, steel is an alloy of iron that contains a small amount of carbon.
All metals share three main characteristics:
- Lustre: they are shiny when cut or scratched
- Malleability: although they are strong, they can be bent or shaped with the right amount of heat and force
- Conductivity: they conduct heat and electricity
But individual metals have different properties. Metals and metal alloys are usually chosen for objects based on their properties. Many types of metals are used in household objects, from copper to steel, even gold!
Many metals are likely to corrode. Corrosion is a chemical reaction where metal reacts with oxygen. Sometimes this is good because it strengthens the metal. But when iron or steel react with oxygen, rust is created. Corrosion can eventually make metal break down entirely into rust.
Ceramics are often defined by what they’re not. They are nonmetallic and inorganic solids. This means they aren’t made of metal, wood, plastics, or rubber. They are made by baking clay, sand, and other natural materials at very high temperatures.
A few examples of ceramics are bricks, tiles, and concrete. Ceramic materials are used to make everything from the homes we live in to the pots we cook food in to dental implants for our teeth. It is even used to make the insulating tiles on space shuttles! Glass (see below) is also a ceramic. So, you are surrounded by ceramics and you may not know it!
The main properties of ceramics are:
- They are usually hard
- Heat resistant: they have a high melting point
- Resistant to chemical corrosion
- They do not conduct heat or electricity: this means they make good insulators
Some types of ceramics, like glass and porcelain, can also be brittle (they can be broken easily). Nonetheless they can last a very long time.
Glass is one of the most versatile materials created by humans. Glass is made mostly of sand, which is made up of silicon dioxide. When sand is heated to a very high temperature (about 1700°C) it becomes a liquid. When it cools again, it undergoes a complete transformation and becomes a clear solid.
The glass we are most familiar with today is called soda-lime-silica-glass. It is made mostly of sand, but some other ingredients as well. Soda ash, which is made up of sodium carbonate, reduces the sand’s melting point. This means it doesn’t have to be heated to as high a temperature before it turns into a liquid. But soda ash also makes the glass water-soluble. This means it can dissolve in water! Limestone, or calcium carbonate, is added to stop this from happening.
When the liquid glass mixture is cooled a bit, it can be used in many different ways. It can be poured into a mould to create things like bottles or lightbulbs. It can also be “floated” to create perfectly flat sheets that will become windows or mirrors. The mixture is then allowed to cool and become solid.
The main properties of glass are:
- transparency: you can see through it
- heat resistance: it doesn’t melt easily
- hardness: inability to break
You may not think glass is particularly strong. But the objects you’re familiar with, like lightbulbs and water glasses, are made of very thin pieces of glass. If you had a very thick piece of glass (think of a brick made of glass) it would be very strong!
When people make glass objects, they can add different ingredients to give the glass new properties. For example, oven-proof glass like Pyrex contains boron oxide. Glass used to make decorative crystal objects, like vases and figurines, contains lead oxide. This allows it to be cut more easily. Stained or coloured glass has different colours because metals are added when it’s in its liquid form!
Plastics come in many different forms. They are used to make a wide variety of products. Plastic molecules are made up of long chains. These molecules are called polymers.
Did you know?
The word “plastic” comes from the Greek “plastikos” which means “able to be shaped”.
Most plastics are either thermoplastics or thermoset plastics. Thermoplastics are heated and then moulded into shape. They can be reheated later and reshaped. Most plastic bottles are thermoplastic. Thermoset plastics can only be heated and shaped once. Thermoset plastics are used to make things like electrical insulation, dinner plates and automobile parts.
Plastics have many useful properties. They are:
- Usually easy and low-cost to manufacture
- Strong and durable
- Resistant to electricity and water
- Resistant to many types of chemical corrosion
But this durability and resistance to damage can be a problem as well. Plastics can take a very long time to break down. Plastic bottles take about 450 years to break down. Plastic shopping bags can take as long as 10,000 years! This is why it is important to recycle plastics. Thermoplastics are recyclable, but thermoset plastics are not. When possible, it’s better to choose thermoplastics over thermoset plastics so the plastic can be given a new life after use.
The word textiles originally referred to woven fabrics. Now it usually refers to all fibres, yarns, and fabrics. Textiles can be made from natural materials like wool and cotton, or from synthetic materials like polyester. Textiles are used to make clothing, carpet, and many other products.
Did you know?
The earliest-produced textiles have been traced back to about 5000 BCE. Some of the oldest forms of textile production include net-making and basket-weaving.
Textiles are made up of many tiny parts called fibres. Textile fibres must have specific properties in order to be spun into yarn or made directly into fabrics. They must be strong, flexible, elastic, and durable. Fibres with these properties can be made into yarns and fabrics with similar properties.
But not all fibres have the same properties. Some are warmer, some are more durable, some are softer or more comfortable. Sometimes it takes a mix of fibres to achieve the desired properties of a finished textile product!
Traditional leather is made from animal skins. Synthetic, or faux leather is manufactured. Leather is used to make everything from car seats to furniture to footballs to handbags. It is durable and has a natural finish. These properties are difficult to recreate with synthetic materials.
Did you know?
About 65% of leather comes from cows. The other 35% comes mostly from sheep, pigs, and goats.
Cowhide is often used to make traditional leather. It is thick and durable, and is often used to make jackets, coats, and furniture. Sheepskin is usually tanned with its soft fleece still attached to the skin. It is used to make jackets, rugs, and slippers. Pigskin makes a comfortable and water-resistant leather. It is used to make shoes, gloves, and some sports equipment. Goat skin is very soft and malleable. It is often used to make bags, gloves, and rugs. Skins from other animals, like snakes, alligators, crocodiles, ostriches, and even fish can be used to make leather too.
Faux leather is usually made of a mix of natural and synthetic fibres that are coated with a plastic polymer. This material mimics the properties of genuine leather. Like genuine leather, faux leather is soft to the touch and water-resistant. Although it is not as durable as traditional leather, faux leather is difficult to cut or tear. As a result, it’s often used to make furniture.
There are ethical concerns about traditional leather because it is an animal product. But because traditional leathers are made of a natural material, they can biodegrade, or break down naturally. Faux leather behaves more like plastic and takes a very long time to break down.
Paper and Boxboard
Paper is an important material that many people use every day. From reading newspapers to drawing pictures to wrapping presents, you probably don’t realize how often you use paper. Paper can also be used to make other materials, like cardboard.
Paper is made from a material called pulp. Pulp is made from wood fibres mixed with water. These fibres usually come from softwood trees like spruce and pine. To make paper, trees are cut up and the bark is removed. Then the wood is ground into tiny pieces and mixed with water to create pulp. The pulp is chemically treated then pressed flat and dried.
Cardboard is made up of several layers of paper combined. Corrugated cardboard is made up of two sheets of flat paper that have a third sheet of paper corrugated or bent to form a wave shape between them. The final product is stiff, strong, and very lightweight. This cardboard can be folded up and glued to create boxes or other packing materials.
There are two main types of rubber: natural rubber and synthetic rubber. Natural rubber is made from latex, which is produced by plants. Synthetic rubber is made using a mix of chemicals. Synthetic rubber has many of the same characteristics as natural rubber. It can be used in tires, hoses, belts, flooring and more.
Did you know?
If you’ve ever picked a dandelion, you may have seen the milky white fluid on the inside of the stem. This is latex!
Almost 99% of the world’s natural rubber is made from the latex of a plant called Hevea brasiliensis. This plant is commonly known as the rubber tree. Latex undergoes a number of different processes to be made into the versatile, springy material we think of as “rubber”. First, it is “chewed up”, then chemicals are added to it. Next, it is squeezed and stretched, and then cooked at about 140°C so that it holds its shape. The final product is strong, stretchy, elastic, durable, and waterproof. It can be used to make products ranging from pencil erasers to running shoes to wetsuits!