Metals, Alloys and Smart Alloys Learning Objectives: To understand that the uses for certain metals relate to their specific properties. To understand that the properties of metals can be improved by producing alloys. To recall that some of the latest alloys, called ‘Smart Alloys’ can alter their properties on demand.

Metals and Alloys

Metallic bonding Metals form a special form of giant lattice structure Metal atoms are packed closely together in a regular arrangement Since they are so close together, the valence electrons tend to move away from their atomic nuclei A ‘sea’ of free delocalised electrons is formed surrounding a lattice of positively charged metal ions The positive ions are held together by their strong attraction to the mobile electrons which move in between the ions Let’s watch a video!

Remember those properties of metals? Most (not all group 1) metals have high melting and boiling points It takes a lot of energy to weaken the strong forces of attraction between metal ions and delocalised ions in the lattice…

Metals are good conductors of heat and electricity When a voltage is applied, the delocalised electrons move through the metal lattice towards the positive pole of the cell

In pure metals the atoms arrange themselves closely together into regular patterns. This makes them dense and also gives them many of their other useful properties.

Metals are malleable and ductile The layer arrangement of the atoms allows the metals to change shape if a force is applied. The layers can slip over each other. This can be useful if you want to shape the metal but not so useful if you want it to resist the force and be strong.

What is an alloy? An alloy is a special mixture of two or more metals or one or more metals with a non-metal An alloy is NOT just a mixture of metal crystals In fact, the atoms of the second metal form part of the metal crystal lattice

Structure of an alloy

Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal. It is more difficult for layers of atoms to slide over each other in alloys

Why use alloys? Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, alloys are often harder than the metal they contain.

Common alloys Alloy Main metal in alloy Uses Properties Amalgam mercury Dental fillings ‘smart’ amalgam Brass Copper and zinc Hinges and plugs, musical instruments Stronger than copper but still malleable Solder Lead and tin Joining metals Very tough Bronze (5000 BC!) Copper and tin Machines, statues, bells Stainless steel Iron +chromium + nickel Cutlery, surgical instruments Doesn’t rust

By mixing two or more metals together the regular arrangement of the atoms is disrupted. This prevents the atoms forming layers and makes it harder for the atoms to slide over each other. The alloy is stronger than the pure metals. Metal A Metal B

Steel is an alloy. Pure iron is not strong enough to be used in structures. Steel contains a small amount of carbon. This disrupts the layers of atoms in the metal and increases the strength of the metal considerably. Although it is very strong steel will corrode (rust) easily and it has to be constantly protected from the effects of water and air.

Stainless steel is an alloy that contains other metals such as Nickel and Chromium. Stainless steel has the strength of steel combined with the corrosion resistance of nickel and the shininess of chromium. This makes it a useful material in applications where you need strength combined with beauty and corrosion resistance..

Smart alloys Nickel-titanium spectacles have ‘memory’! These are alloys that can ‘remember’ their original shape. If they are deformed they can return to their original shape. Nickel-titanium spectacles have ‘memory’!

Smart alloys: your braces! Cobalt nickel titanium OR multiple memory materials

Smart alloys – blood vessel stents Vascular stents are made of platinum-chromium or cobalt-chromium

Metals, Alloys and Smart Alloys Learning Objectives: To understand that the uses for certain metals relate to their specific properties. To understand that the properties of metals can be improved by producing alloys. To recall that some of the latest alloys, called ‘Smart Alloys’ can alter their properties on demand.

Metal Properties Uses Aluminium Copper Gold Steel Copy the table below. Working with a partner, complete as much of the table as you can. Metal Properties Uses Aluminium Copper Gold Steel Low density, strong, resistant to corrosion, good conductor of electricity Lightweight structures, aircraft, drinks cans, high voltage cables. Electrical wiring, water pipes. Good conductor of electricity, resistant to corrosion, easily shaped, flexible Jewellery. Shiny, very resistant to corrosion, very unreactive, soft, easily shaped Very strong, very dense. Large structures and heavy duty engineering such as bridges, trains, cars etc.