Alloys

Goal of the class To introduce alloys and their uses Question of the day: Why is carbon added to iron? Previous Answer: Long chains of carbon atoms make up the backbone of crude oil constituents. Previous question: What is the main component of crude oil?

What is an Alloy? Alloy is a mixture of two or more elements with a certain fixed composition in which the major component is a metal. Examples include: Stainless steel Bronze Solder An alloy is a mixture of either pure or fairly pure chemical elements, which forms an impure substance (admixture) that retains the characteristics of a metal. An alloy is distinct from an impure metal, such as wrought iron, in that, with an alloy, the added impurities are usually desirable and will typically have some useful benefit. Alloys are made by mixing two or more elements; at least one of which being a metal. This is usually called the primary metal or the base metal, and the name of this metal may also be the name of the alloy. The other constituents may or may not be metals but, when mixed with the molten base, they will be soluble, dissolving into the mixture.

Why Make Alloys? To increase the hardness and strength of a metal To prevent corrosion or rusting To improve the appearance of the metal surface Hardened steel, like in bicycle locks.

Bronze Bronze is an alloy consisting primarily of copper and the addition of other metals, usually tin. A very important advancement in human history (Bronze Age). Used for 3rd place medals. The discovery of bronze enabled people to create metal objects which were harder and more durable than previously possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were harder and more durable than their stone and copper ("Chalcolithic") predecessors. Initially, bronze was made out of copper and arsenic, forming arsenic bronze, or from naturally or artificially mixed ores of copper and arsenic.[6] It was only later that tin was used, becoming the major non-copper ingredient of bronze in the late 3rd millennium BC.[7] Tin bronze was superior to arsenic bronze in that the alloying process could be more easily controlled, and the resulting alloy was stronger and easier to cast. Also, unlike arsenic, tin is not toxic. Used to make swords too

Properties of Bronze Hard and Strong Doesn’t corrode easily Has shiny surface The discovery of bronze enabled people to create metal objects which were harder and more durable than previously possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were harder and more durable than their stone and copper ("Chalcolithic") predecessors. Initially, bronze was made out of copper and arsenic, forming arsenic bronze, or from naturally or artificially mixed ores of copper and arsenic.[6] It was only later that tin was used, becoming the major non-copper ingredient of bronze in the late 3rd millennium BC.[7] Tin bronze was superior to arsenic bronze in that the alloying process could be more easily controlled, and the resulting alloy was stronger and easier to cast. Also, unlike arsenic, tin is not toxic. Hard and Strong Doesn’t corrode easily Has shiny surface Used to make swords too

Steel Steel is composed of 99% iron and 1% carbon. It is very hard and strong and used in the construction of buildings and bridges. Talk about adding carbon in furnance Steels are alloys of iron and carbon, widely used in construction and other applications because of their high tensile strengths and low costs. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the crystal lattices of iron atoms.

Steel The viaduct La Polvorilla, Salta Argentina.jpg

Stainless Steel Contains the following: 74% iron 8% carbon 18% chromium Stainless steel is strong, shiny and corrosion resistant. Stainless steel does not readily corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments.[2] There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and corrosion resistance are required.

Stainless Steel Stainless steel does not readily corrode, rust or stain with water as ordinary steel does. However, it is not fully stain-proof in low-oxygen, high-salinity, or poor air-circulation environments.[2] There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and corrosion resistance are required.

Nickel Titanium Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium Nitinol alloys exhibit two closely related and unique properties: shape memory superelasticity Smart alloys have unusual properties. Nitinol is an alloy of nickel and titanium, and is known as a shape memory alloy. If nitinol is bent out of shape, it returns to its original shape when it is either heated or an electric current is passed through it. This property makes it useful for making spectacle frames - they return to their original shape if they are put in hot water after bending them.

Amalgam In dentistry, amalgam is an alloy of mercury with various metals used for dental fillings. It commonly consists of mercury (50%) silver (~22–32% ) tin (~14%) copper (~8%) other trace metals Smart alloys have unusual properties. Nitinol is an alloy of nickel and titanium, and is known as a shape memory alloy. If nitinol is bent out of shape, it returns to its original shape when it is either heated or an electric current is passed through it. This property makes it useful for making spectacle frames - they return to their original shape if they are put in hot water after bending them.

Aluminium Alloys Duralumin, used in aircraft manufacture, is 96 percent aluminium and 4 percent copper and other metals. Used for its low density

Aluminium Alloys Used for its low density

Atomic Arrangements When force is applied, layers of atoms in pure metal slide. So, metals are ductile. There are empty space between the atoms. When it is knocked, the shape of the metal changes. So, metals are malleable.

Atomic Arrangements The presence of atoms of other metals that are of different sizes disturb the orderly arrangement of atoms in the metal. This reduces the layer of atoms from sliding. Thus, an alloy is stronger and harder than its pure metal.

Homework Please complete Chemical Building Blocks workbook page 53-54 http://phet.colorado.edu/en/simulation/build-an-atom