Alloy

Pure Metals Atom Arrangements

Most metals are solid. Pure metal is soft and anemic. They also have similar size , shape and are arrange closely but still there is gap between the atoms. The arrangement of atoms in metals furnish the metals ductile and malleable properties.

when force is applied to pure metals , the atoms slide along one another easily. This properties causes pure metal to be ductile, that is , it can be stretched into wire.

When knocked or hammered, metal atoms slide along one another to fill spaces between the metal atoms. This property causes pure metal to be malleable, that is , it can be knocked or pressed into various desired shapes.

What is the meaning of alloy?

Alloy is a mixture of two or more elements with a certain fixed composition in which the major component is a metal. The process of forming alloy is called alloying

What are the purposes in making alloy?

there are few purposes such as :

>make the metal harder and stronger

>prevent corrosion and rusting of the metal

>to improve the appearance of the metal

other than that, changing the physical properties of the base metal

For instance, carbon and chromium are added to iron to make "stainless steel", which resists staining and corrosion, making it a good choice for knives, bolts, watch straps, etcetera.

Likewise, you can mix pure gold with copper and silver to get "yellow gold" for jewelry. Yellow gold is cheaper than pure gold, and since it's harder than pure gold, jewelry made from yellow gold won't bend as easily.

why alloy is harder, stronger, less ductile and less malleable than its pure metals.

Alloys are strong and hard. not easily bent. Layers of atoms cannot slide over each other easily as extraneous atoms of different sizes and intrude the orderly arrangement of metal atoms.

whereas ,

pure metals are soft and easily bent ( malleable) because layers of atom ( of same size) can slide over each other easily. This sliding process is call Slip.

Alloy atoms arrangement                                        Pure metal atoms arrangement

source: Google images (bbc.co.uk)

Comparing the hardness

Aim : To study the hardness and strength of an alloy as compared to a pure metal.

Problem Statement : Is brass (copper alloy) harder then copper?

Hypothesis : Diameter of depression on brass is smaller than diameter of depression on pure copper.

Variables : Manipulated:Type of metal block

Responding :Diameter of depression

Constant :Height of metal ball

Material : Copper block, brass block, metal block, metal ball (steel), cellophane tape, thread.

Apparatus : Metre rule, 1 kg weight, retort stand.

Apparatus to study the hardness and strength of an alloy
source: Longman Essential Chemistry SPM

Procedure :

1. A steel ball is stuck to a brass block using cellophane tape.
2. A weight of 1 kg is hung at a height of 50 cm from the top of the brass block.
3. The weight is released so that it falls on the metal ball.
4. The diameter of depression formed on top of the brass block is measured using a metre ruler and the measurement is recorded in Table 9.5
5. Steps 1 to 4 are repeated twice on different spots on the brass block to obtain an average of the diameter
6. The experiment is repeated using a pure copper block.

Results :

Block	Diameter of depression
	1	2	3	Average diameter (mm)
Brass
Copper

Analysis :

1. The depression made on the brass block is smaller than the depression made on the pure copper block.
2. Alloy can be defined operationally as a material which is harder because the depresssion produced is smaller.

Conclusion :

1. Alloys are harder than pure metals.
2. The hypothesis made is accepted.

The rate of rusting of iron, steel and stainless steel

Aim: To compare the rate of rusting of iron, steel and stainless steel

Problem Statement: How does the rate of rusting of iron, steel and stainless steel differ?

Hypothesis: Iron rust faster that steel and steel rust faster than stainless steel.

Variables: manipulated variable: Different type of nails

responding variables: Intensity and amount of blue colour

constant variables: size of nails

Materials : Iron nails, stainless steel nails, agar, potassium hexacyanoferrate(|||) solution.

Apparatus : Test tube, test tube rack.

Apparatus to study the rates of corrosion of iron and stainless steel nails
source: Longman Essential Chemistry SPM

Procedure :

1. Hot agar solution is prepared and poured into two test tubes.
2. A little potassium hexacyanoferrate(|||) solution is added.
3. Iron nails are placed in one test tube and stainless steel nails in the other.
4. The apparatus is left for several days.
5. A change in colour is observed in the test tubes.

Observation :

Experiment	Observation
Iron nails	Dark blue spots form
Stainless steel nails	No dark blue spots

Analysis :

1. If iron corrodes (rust), iron(||) ions form. Potassium hexacyanoferrate(|||) solution can detect the presence of iron(||) by forming a dark blue colour.
2. If the nails corrode (rust), dark blue spots form in the agar.
3. Dark blue spots form only in the test tube containing the iron nails, so we can conclude that iron corrodes but not stainless steel.
4. Alloy can be defined operationally as a material which is resistant to corrosion becauseno dark blue spots are produced.

Conclusion :

1. Iron corrodes (rust) faster than steel.







2. The hypothesis made is accepted.

USES OF ALLOY

STEEL

composition: 99% iron , 1% carbon

properties: hard and strong , withstand corrosion

uses: vehicles , building skeleton , bridges

source: ramblingsfromtheleft.wordpress.com

Bronze

composition: 90% copper , 10% tin

properties: hard and strong , has shiny surfaces , withstand corrosion

uses: medals , statues , bells

source: rusticwoods.com

Stainless steel

composition: 74% iron, 8% carbon, 18% chromium

properties: shiny , strong , does not rust

uses: cook wear , forks and spoons, tongs

source: dennisflood.com

Brass

composition: 70%copper , 30 % zinc

properties: strong, shiny, harder than copper

uses: keys , musical instruments, ornaments

source: simoncotter.com

Duralumin

composition: 93% aluminium , 3%copper , 3% magnesium , 3% manganese

properties: light, strong , withstand corrosion

uses: the body of aeroplane and racing bycicle.

source: z-bycicles.com

Pewter

composition: 96% tin, 3% copper, 1% antimony

Properties: lustre, shiny surface , strong

uses: picture frames, trophies

source: budgettrophies.net