Plastics and Metals

8/6/2019 Plastics and Metals

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materials


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Plastics

Plastic materialsdisplay properties that are unique when

compared to other materials and havecontributed greatly toquality of our everyday life.Name 3 way how

plastic has contributed to your quality of life.


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M any natural plastics exist, such as rubber,asphalt, and cellulose ; however, it is man'sability to synthetically create a broad range of materials demonstrating various useful

properties that have so enhanced our lives.Plastics are used in our clothing, housing,

automobiles, aircraft, packaging, electronics,signs, recreation items, and medical implantsto name but a few of their many applications.

Plastics


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Plastics

P lastics are made from organic compounds. P lasticscan exhibit different properties base on theirmethod of synthesis.

These can be low- melting to high temperatureresistant plastics.P lastics are very poor conductor of heat and do notconduct electricity, but can be used as insulators.P lastics do not corrode and can be tough anddurable. They are relatively cheap and can be madefrom by- products of the petroleum industry.P lastics are readily available.


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There are different types of plastics:

1. T hermo- plastics: includes Polythene:

And Poly Vinyl Chloride (P.V.C.)2 . Thermo se tting plastics


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Thermosetting plastics

Becomes permanently hard once they beenheated and mould into form, they cannot bereheated and mould into form. They areheat resistant and can resistant temperatureof 450 degrees celcius

M e la m in e , which is used to make work surfaces,spoons and ovenware. B

ake

lite,

is used to

make door handles and telephone (in the lastcentury.


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T hermo- plasticscan resist high heat up to 450 0C, canbe used to line pots. Thermoplasticsbecome soft when heated. They canbe easily moulded and remouldedwithout significant degrading.Thermoplastics consist of long

molecular chains with no regularstructure (or very little regularstructure).There are many thermoplasticsavailable:P olyethyleneP olystyreneP olycarbonateNylonAcrylicAcetal


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Polythene


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Poly Vinyl Chloride

Po lyvinyl c h lor id e , commonly abbreviated PVC, isa thermoplastic polymer . It is a vinylpolymer constructed of repeating vinyl

groups (ethenyls) having one of their hydrogens replaced with a chloride group.

P olyvinyl chloride is the third most widely producedplastic, after polyethylene and polypropylene . PV Cis widely used in construction because it is cheap,P olyvinyl chloride ( PV C) is recyclable durable, andeasy to assemble.


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Poly Vinyl Chloride


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A dvantag e s

A dvantag e s of using plastics rather than metals:

1. P lastics are cheaper2

.P

lastics are readily available3. P lastics are easily shaped

4. P lastics can be rolled into thin sheets

5.P

lastics are non-corrosive


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D isadvantag e s

D isadvantag e s of using plastics rather thanmetals:

1.P

lastics are easily combustible2 . P lastics give off toxic fumes contributing toair pollution

3.P

lastics are non-biodegradeable


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M e tals

These are very good conductors of heat makingthem suitable for making pots and pans.They make good ornaments because they have a

shine when polished.This high polish makes it able to keep foods hot.Metal are strong.

This quality makes it useful in making burglarbars, windows and door frames.Metals are ductile and malleable making it ableto be drawn into wires and roll into sheets.


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PROPERTIES OF METALS

MALLEA BILITY-metals can be hammered into sheets.DU CTILITY -metals can be drawn into wires.

LUS TRE -metals can reflect light.H IGH DENS ITY -most metals have high density except for

lithium.H IGH MEL TIN G AND BOILIN G POIN T -most metals have

highmelting and boiling points.

GOO D CONDU CTORS -metals are good conductors of heatand electricity because of free electrons.


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This property of metals enables it to change itsform through compression without cracking or

breaking that is, a metal can be made into sheets..A solid gold sheet can bemade into an ornament..

MALLEABILITY


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It refers to a material's ability to deform under tensilestress; this is often characterized by the material's abilityto be stretched into a wire..

Coil of silver wire

DUC TILITY


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Metallic lustre refers to the shiny coating or coveringpossessed by various metals. It means that the metal and its

surface have light-reflective qualities..

L US TRE


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D EN S ITYThe density of a material is defined as itsmass per unit volume. The density of metals is very high except for lithium

Lithium (low density) Iridium (high density)


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CO N DUC TIVITYConductivity of metal is the ability or power toconduct or transmit heat, electricity.

Aluminum is used to make pots Copper Is used to make electric wires


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H IG H MELTING AN D B O ILING P O INT

Most metals have high melting and boiling

points because in metals there is a very strongintermolecular force of attraction and it needsa lot of energy to melt or to boil


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Alloy

in nature, most metals occur as alloys , as mining depositstypically contain multiple metals.The desired metal must be extracted from other metals

and waste materials, after which it is refined, leaving apure metal.Manufacturers create alloys, which are two or more puremetals combined together, by using heat to blend themtogether.

Both alloys and pure metals have advantages anddisadvantages, depending upon their application.


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Advantages of using alloy

Alloys will have different property than puremetals. So, you can have an alloy with- higher strength- better corrosion resistance- lower cost- different melting point (higher or lower than

any of its constituent in some extreme cases


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P ure metals also tend to be more prone to corrosion,where the metal is slowly eaten away by acid. Copper isespecially vulnerable to corrosion.When creating brass , manufacturers add 5 to 45percent zinc, which has anti-corrosive properties,making this material ideal for wet areas, such askitchen cabinet handles and sink and bathtub faucets.manufacturers add chromium to steel to create an

alloy known as stainless steel. Through the addition of more than 11 percent chromium this material, inaddition to nickel, prevents steel from rusting.

Advantages of using alloy


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Cle aning H ou seho ld M e tal A pplianc e s

Metals and metal appliances will tarnish overtime. The tarnish can be removed by cleaningthe metal with an abrasive substance, forexample silvo which is used to clean silver, orBrasso which is used to clean copper andcopper alloys or steel wool can be used to

clean a number of surfaces.


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Corro sio n

It is a spontaneous process by which asubstance generally a metal is deterioratedforming a compound of that substance.Corrosion results in loss of metallic property,bringing it back to it natural state as ores of the metal.


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Corro sio n

There are two methods of corrosion, whichdepends on the environmental conditions.D ry ox idati o n- this metal corrodes in a water free evironment, such as the oxidation of aluminum to from the protective aluminiumcondition.W e t ox idati o n this takes place when air andwater is present. Examples are the corrosion of iron (known as rusting) and the formation of green deposits on copper or brass.


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rusting


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Corrosion of Iron (Rusting)

For rusting to occur, air and water have to bepresent.

Iron is oxidized by oxygen and water to formhydrated iron(III) oxide, or iron (III) hydroxide(rust).

The presence of electrolytes, acids and heatspeed up the rusting of iron.


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R usting occurs when oxygen comes in long-term contact with certain metals.

Over time, the oxygen combines with themetal, forming a new compound called anoxide and weakening the bonds of the metalitself.

rusting


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If the base metal is iron or steel, the resultingrust is properly called iron oxide .R

usted aluminum would be called aluminumoxide, copper forms copper oxide and so on.

rusting


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Co nditi o ns W h ich Cau se Ru sting

1. Water and air and iron combines2. Iron atoms go into solution giving up iron ions3 . Oxygen dissolves in water forming hydroxyl ions4 . Iron and hydroxyl ions combine to form an

insoluble substance called iron hydroxide5 . Iron hydroxide is rapidly oxidized to iron oxide

(rust).6 . The rust that is formed is porous and flakyallowing more air and water to attack the iron.


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Fact or s t h at Aff e ct t he Rat e o f Ru sting

The presence of hydrogen sulphide, sulphurdioxide and some soluble salts in combinationwith water form acids that react with iron andsteel forming iron salts of these acids.

These dissolved salts increase the rate atwhich iron rusts. Sea water also increasesrusting. High temperatures increase rusting.


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Ru st p re ve nti o n


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1 . PaintingThe paint provides a waterproof layer to the metal preventing the entry of air and water.

2 . Oil or GreasingThe oil coating keeps out water and oxygen. Imported motor vehicles areusually covered with grease to protect it from sea spray.

3. ElectroplatingCoating the metal with a non-corrosive metal by the process of electrolysis.

4 . GalvanizingSteel is covered with a layer of zinc. Zinc forms a protective covering forthe steel.

Plastics and Metals

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