Metals

Prevention of rusting

- Rust resistant alloys - Design: Proper planning during the design stage can minimize water penetration and reduce the risk of rust. Cavities and crevices should be avoided. Joints should be welded not bolted. Drainage holes for water should be considered if appropriate. The design should allow air to freely circulate. For large structures, adequate access should be enabled to allow for regular maintenance. - Galvanization: The process of galvanization involves coating the surface with an external layer of metallic zinc. This is accomplished through hot-dip galvanizing or electroplating. The zinc layer prevents corrosive substances from penetrating further into the metal. In addition the zinc acts as a sacrificial anode which means that the damaging oxidation process of rust will be transferred to the zinc layer. - Bluing: Bluing is a useful technique which offers limited protection against rust for small steel items. The term "bluing" comes from the blue-black appearance of the finish when using this technique. Blueing is often used in firearms manufacture to provide a degree of corrosion resistance. It's also used in fine clocks and other metal work. Bluing is accomplished by immersing the steel parts into a solution of potassium nitrate, sodium hydroxide and water. - Organic coating: Organic coatings such as paint are a cost effective way to protect against rust. Organic coatings form a barrier against corrosive elements. Oil based coatings are ideal for preventing penetration of water and oxygen. Typical organic coatings are 15 to 25 micrometers thick. - Powder coating:A dry powder is evenly applied to a clean surface. Next, the object is heated, turning the powder into a thin film. There are a wide range of powders available including acrylic, polyester, nylon, vinyl, epoxy and urethane. Powders are commonly applied using an electrostatic spray process. The electrically conductive object is sprayed with a charged, non-conducting powder. The charged particles are attracted the object and cling to its surface. The object is placed in a hot oven which fuses the particles into a continuous film. The film is typically between 25 and 125 micrometers. - Regular maintenance: Regular maintenance is advised to stop rust forming and halt the progress of any rust that occurred. It's essential to remove any rust that has formed. A razor blade can be used for small areas. Next any surface grime should be removed using warm water and soap. Lastly a rust resistant coating should be applied to the surface

Thermite reaction

A thermite reaction is basically iron oxide (rust) reacting with aluminum to produce molten iron. The reaction is initiated by the heat from burning magnesium ribbon which is placed in the iron oxide/aluminum mixture. This reaction is highly exothermic and produces molten metal at about 3000°c. Fe2O3 + 2Al --> Al2O3 + 2Fe used in wielding train tracks

Alloys

An alloy is formed when different metals are mixed together (though one important alloy, steel is a mixture of metal and a non-metal.) Alloys can be made because metal atoms of one type will happily sit amongst metal atoms of another, fitting easily into the lattice which is likely to be almost identical to their own. The reason they are made is that the allow will have desirable properties which can make it more useful than the pure metals from which it is made.

Metal Oxide Solubility

Grp 1 oxides are insoluble Grp 2 + transition metal oxides are insoluble (water)

Rusting

Iron reacts with oxygen and water to from a red-brown solid, which is hydrated iron (iii) oxide (Fe2O3) which is commonly known as rust.

Magnesium and steam

Magnesium burns in steam to produce white magnesium oxide and hydrogen gas. Mg + H2O -> MgO + H2

Reactivity of metals

Metals react to form ionic compounds. In these compounds the metal forms cations (positive ions) by the loss of electrons. Therefore we can relate the reactivity of metals to the ease with which they lose their valence shell electrons i.e. the more reactive the metal, the more readily it will lose the valence electron.

Reactivity series

Potassium Sodium Lithium Calcium Magnesium Aluminium CARBON Zinc Iron Tin Lead HYDROGEN Copper Silver Gold Platinum

Structure and bonding in metals

The bonding in metals can be described as a regular arrangement of atoms surrounded by a 'sea' of delocalised electrons. The properties of metals can be explained in terms of the bonding and structure. i.e. Metals are good conductors of electricity because of the delocalised electrons which can carry the charge/current. Metals are good conductors of heat energy because of the close packing of the atoms means that energy is easily transferred between them. Metals are malleable and ductile because the layers of metal atoms can slide past one another easily to form new shapes yet the 'environment' each atom finds itself in will be the same.

Pewter

Typical composition: 30% lead, 70%, a little antimony Properties: malleable, ductile, tough Uses: plates + goblets, ornaments

Brass

Typical composition: 65% copper, 35% tin Properties: harder than Cu, high density, good conductor Uses: electrical conductors (plug), door furniture, ornaments

Stainless steel

Typical composition: 74% iron, 18% chromium, 8% nickel Properties: corrosion resistant, hard Uses: surgical equipment, cutlery, utensils, sinks, taps ...

Bronze

Typical composition: 90% copper, 10% tin Properties: Malleable, ductile, corrosion resistant, tough Uses: statues, castings

Hard steel

Typical composition: 99% iron, 1% carbon Properties: tough Uses: drill bits, chisels, razor blades

Mild steel

Typical composition: 99.5% Iron, 0.5% carbon Properties: malleable Uses: car bodies

Magnesium and cold water

Very clean magnesium ribbon has a very slight reaction with cold water. After several minutes, some bubbles of hydrogen form on its surface, and the coil of magnesium ribbon usually floats to the surface. However, the reaction soon stops because the magnesium hydroxide formed is almost insoluble in water and forms a barrier on the magnesium preventing further reaction. Mg(s) + 2 H2O(l) -> Mg(OH)2 + H2

Metal oxides dissolve in water to form...

alkali solution If non metal dissolves they form acidic solution

Metal + Acid

salt + hydrogen

metal oxide + acid

salt + water

Metal carbonate + acid

salt + water + carbon dioxide

metal ion reactions

when a metal reacts with the ions of a second metal, and replaces it within a compound it is called a displacement reaction Zinc + Copper (II) Sulphate -> copper + Zin sulphate Zn(s) + Cu2+(aq)SO4 2-(aq) -> Cu(s) + Zn2+(aq)SO4 2-(aq) The sulphate ions are spectator ions