The characteristics and uses of different non-metals

Non-metals

The characteristics and uses of different non-metals

What are non-metals?

In chemistry all materials can be grouped into two groups: Metals and Non-metals. There are only few elements in the periodic table that are classified as non-metals while there are over 80 metals. However, most of the service of the earth and the atmosphere are made up of non-metals and, most of the materials that living things are made of are non-metals. Non-metals are important.

Characteristics of non-metals

Here are some of the characteristics that classify a material or element as a non-metal.

Conduction:       Non-metals are not very good conductors of electricity when compared to metals. This is because the structures of atoms of the various elements differ. We already know that everything is made up out of atoms. Atoms can be broken up into smaller particles. The middle of the atom is called the nucleus. The nucleus is made up of particles called protons and neutrons. There are smaller and lighter particles called electrons that spin around the nucleus. (See the simple model of the atom below.)

When atoms are joined together, electrons can move from one atom to another. This is how electricity is conducted through a material. The electrons in metals can move very easily from one atom to another so they can conduct electricity well. However, in non-metals the electrons can’t move very easily from atom to atom so they cannot conduct electricity very easily.

Resistance to heat:         Generally non-metals have a much lower boiling point that metals. This means that you would not be able to use them in places where they would have to withstand high temperatures.

Density:               The relationship between the mass of something and its size or volume. A bucket of bricks will weigh more than a bucket of feathers because the bricks have a higher density than the feathers. Non-metals will usually be less dense than metals. If you compare the same volume of material, non-metals will usually have less mass than metals.

Brittleness:        At room temperature non-metals are either gases like oxygen or solids like carbon. In solid form non-metals are usually a lot more brittle than metals.

Luster:                  The way metals reflects light. Non-metals are usually dull with little or no luster.

Different types of non-metals

Fibreglass:          Fibreglass is also called glass fiber. Made of very thin fibers or strands of glass, fibreglass has the same characteristics as cloth. Fibreglass can bend and flex.

Fibreglass comes in two forms: Glass wool, made by blowing melted glass into a jet of steam.

                                                                Glass strands, made by forcing molten glass through tiny holes. This process is called extrusion.

Fibreglass strands can be woven into a cloth called roving or chopped into short pieces that are laid down in no particular pattern, called chopped strand mat.

Polymers:           Polymers are everywhere. Even your DNA is a polymer. Other polymers are the proteins and starches in our food, the wheels on a skateboard and the tires on trucks and cars. We are surrounded by polymers. Plastics are made from polymers.

Polymers are made of tiny molecules called monomers that are bonder together in long chains. Monomers are made of carbon (C) and hydrogen (H) atoms. Sometimes other elements such as oxygen (O), nitrogen (N), chlorine (Cl) and fluorine (F) are used together with these two as well. The monomer units are joined together by covalent bonds to form polymer chains. The polymer chains are then held together by secondary bonds which are much weaker than the covalent bonds.

There are two groups of polymers:- thermoplastics and thermosetting plastics.

Thermoplastics:               Thermoplastics are materials that soften and melt when you heat them. In this state you can mould them into any shape that you want. When the material is cooled, it hardens and keeps the shape you moulded it into. You can repeat this proses of heating and cooling and change the shape as many times as you want.

Thermosetting plastics:                In thermosetting plastics the polymer chains join together as cross-linked chains or networks. This type of bonding form very strong covalent bonds and all the polymer chains are bonded together very tightly. These cross-linked bond are formed when the polymers are heated and undergoes a chemical reaction. Thermosetting plastics can only be heated and moulded once.

Elastomers:        All plastics are polymers but not all polymers are plastics. Elastomers are another type of polymer. Elastomers are sometimes called rubbers but there is a slight difference between the two materials. An elastomer is a material that will almost, but not completely, recover its size and shape after a load has been removed. On the other hand, a rubber is described as a material that will go back to its original shape almost immediately after a load has been removed.

Many elastomers has cross-linked arrangements as described in thermosetting plastics. The hardness of the elastomer increases with the amount of cross-linking. Once the elastomer is cross-linked it cannot be re-shaped.

When rubbers are cross-linked, it gets harder to stretch the material because it gets harder to pull the polymer chains out of their position.

Ceramics:            Ceramics are compounds (mixtures) of non-metal and metal elements. Ceramics are usually made by heating the ingredients to very high temperatures after it has been shaped or moulded into its required shape or form. The very high temperatures allow chemical reactions to take place in the clay so that it become permanently hard.

Ceramics can be divided into two main classes: Traditional ceramics and advanced ceramics.

Ceramics have many properties that make them useful. They are harder and stiffer than steel, they are more resistant to heat and corrosion than most metals, they are less dense than many metals and the ingredients are found inexpensively in nature.

Ingredients of ceramics. One of the oldest materials for making ceramics is clay, of which kaolinite is the most common. The other main ingredient of ceramics found in nature is flint and feldspar. Flint is a type of rock and feldspar is a group of crystalline materials that are made up of aluminium silicates, as well as potassium, calcium or sodium.

 Oxide ceramics:              There are two types of oxide ceramics:- Alumina and zirconia.

                Alumina is made from a compound called aluminium oxide. You can find aluminium oxide in nature but because of its impurities its reactions are unpredictable. Scientists therefore use only manmade aluminium oxide so the purity can be controlled.

                Zirconia is made of a compound called zirconium oxide. This ceramic is very tough, and is resistant to wear and tear and corrosion. It does not conduct heat very well. In the industry zirconia is used to make refractory bricks and tiles because of its terrific heat resistance.

Cermets:             Cermets is a mixture of ceramics (cer) and metallic (met) materials. As cermets contains less than 20% metal it is classified as non-metal.

Ø  Tungsten carbide and titanium carbide cermets are very hard, strong and wear resistant materials. They are often used to make cutting tools and valves.

Ø  Silicon carbide cermet is very resistant to wear, heat and corrosion. It stay strong, even at very high temperatures. Because of this you can use it in furnaces that get very hot.

Ø  Nitride cermets contain a metal bonded with nitrogen.

Ø  Cubic boron nitride cermet is the second hardest material that we know of (diamond being the hardest. Because it is so hard, it is often used in cutting tools and as abrasives on grinding wheels. This ceramic does not exist in nature and is manmade.

Ø  Titanium nitride cermet is often used as coating on cutting tools to improve the useful life of the tool as it is very resistant to wear and tear.

Ø  Silicon nitride cermet is not really affected by high temperatures and conduct heat well. Because of this it is used in areas where components have to withstand very high temperatures. (car engines and gas turbines)

Glass:                    Glass is an amorphous solid. It is formed when melted materials are cooled to quickly to form regular crystal patterns. We use soda-lime glass in windows and for light bulbs, but there are about 750 different types of glass. Different types of glass have different uses that include window glass, glass for containers, cookware, lightening, glass fibers and glass that has special high temperatures, electrical and corrosion characteristics.

Normally glass contains at least 50% silica also known as silicon oxide. Silica is called a glass former. You can, however, change the properties of glass by adding aluminium oxide, sodium oxide, calcium oxide, barium oxide, potassium oxide, magnesium oxide, boron oxide or lead oxide. These oxide will then be called intermediates or modifiers.

Glass is very brittle and will shatter when bent but it has a very high compressive strength. Glass does not conduct electricity or heat very well.

Diamond:            Diamond is the hardest substance that we know of. Diamonds are mined from the earth but it can also be made. (synthetic diamonds are made) Although synthetic diamonds are exactly the same as natural diamonds they have no impurities and therefore they are more suitable for use in industry.

Because of its properties, diamonds have many important uses such as:

Ø  Cutting tool materials

Ø  Abrasives in grinding wheels for grinding hard materials

Ø  Sharpening the abrasives on grinding wheels

Ø  Coating for cutting tools

Common uses of non-metals

Uses for fibreglass:

Ø  Electrical, sound and heat insulation

Ø  Glass wool is useful for isolation of house ceilings (think pink)

Ø  Fibreglass woven cloth is used to reinforce plastics (cars and boats)

Properties and uses for Polymers:

Ø  Food and drink containers

Ø  Packaging and signs

Ø  Exteriors of computers and monitors and electronic products

Ø  Medical equipment

Ø  Paints

Ø  Pipes, toys, hard hats, safety glasses and car parts.

Polymers have such a wide range of products because of its many properties which includes:

o   Resistance to corrosion and chemicals

o   Poor conductors of heat and electricity

o   Low density

o   Strong and light

o   Noise insulation

o   Made in lots of colours

o   Easy to manufacture

Properties and uses for some plastics:

Ø  Functional and transparent:- Lenses, goggles, safety glazing, signs, laboratory equipment.

Ø  Functional and decorative:- Handles, knobs, cameras, battery cases and pipe fittings

Ø  Heat resistant:- Appliances, cookware and electrical components

Ø  Chemical resistant:- Containers for chemicals, laboratory equipment, food and drink containers.

Ø  Electricity resistant:-  Electrical parts and equipment, appliances

Ø  High friction:- Tires, non-skid surfaces, soles of shoes and flooring

Ø  Low friction:- Sliding services and artificial joints

Ø  Wear and tear resistant:- Gears and bearings

Ø  Mechanically strong:- Gears, valves, fan blades and pistons  

Properties and uses for thermoplastics

Acetyls:                Strong, stiff and abrasion resistant: - machine parts like bearings, gears and pump impellers.

Acrylics:               Quite strong and resistant to chemicals, weather and electricity: - (Perspex and Plexiglas) Used in lenses, furniture, windows, lighted signs, skylights and windshields.

Acrylonitrile butadiene styrene (ABS):  Very stiff and resistant to chemicals, abrasion and electricity and very slippery (low friction): - Pipes, fittings, helmets, tool handles, car parts, luggage and appliances.

Fluorocarbons: resistant to high temperatures, the weather, chemicals, electricity. It’s also very slippery (low friction): - non-stick coatings for pots and pans, electrical insulation for high temperature wires and for low friction surfaces.

Polycarbonates:               Good mechanical and electrical properties and they can be made resistant to chemicals: - safety helmets, medical apparatus, bullet proof windows and roof sheeting.

Polyesters:         Resistant to abrasion and good electrical, mechanical and chemical properties: - Gears, rollers and parts that must support a lot of weight.

Polyethylenes: Good mechanical and electrical properties: - bumpers on cars, bottles, dustbins and packaging materials.

Polystyrenes:    Average properties: - disposable containers and packaging, toys and foam insulation.

Polyvinyl chloride: (PVC)             water resistant, cheap, and can be made rigid or flexible: - Rigid; signs, pipes and conduits. Flexible; wire and cable coatings.

Properties and uses for elastomers:

Natural rubber: Long lasting and resistant to abrasion but not a lot of resistance to sunlight, heat and oil: - Used in tires, heals of shoes and the mounts of engines.

Synthetic rubber:            More resistant to heat, petrol and chemicals: - tires, belts, shock absorbers and seals.

Silicones:            Resistant to the biggest range of temperatures but not so strong and low resistance to wear and tear and oil: - Seals, high temperature electrical switches and heat insulation.

Polyurethane:   good strength, stiffness and hardness properties. It is also very resistant to cutting, abrasion and tearing: - Seals, cushioning and parts of cars.