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Abstract

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal (heat treatment) history. Alloys usually have different properties from those of the component elements.

The term alloy is used to describe a mixture of atoms in which the primary constituent is a metal. The primary metal is called the base, the matrix, or the solvent. The secondary constituents are often called solutes. If there is a mixture of only two types of atoms, not counting impurities, such as a copper-nickel alloy, then it is called a binary alloy. If there are three types of atoms forming the mixture, such as iron, nickel and chromium, then it is called a ternary alloy. An alloy with four constituents is a quaternary alloy, while a five-part alloy is termed a quinary alloy.

Because the percentage of each constituent can be varied, with any mixture the entire range of possible variations is called a system. In this respect, all of the various forms of an alloy containing only two constituents, like iron and carbon, is called a binary system, while all of the alloy combinations possible with a ternary alloy, such as alloys of iron, carbon and chromium, is called a ternary system. The purpose of this project is to determine qualitatively, the contents of samples of Brass and Bronze

Theory:

i) To modify chemical reactivity :-

When sodium is used as reducing agent it is too reactive to be used but its alloy with mercury, called sodium amalgam can be safely used as reducing agent.

ii) To increase hardness :-

Hardness of gold is increased by adding copper to it. Also zinc is added to copper to make copper hard in form of brass.

iii) To increase tensile strength :-

Nickeloy, an alloy of Nickel (1%), Copper (4%) and aluminium (95%) has high tensile strength.

iv) To lower the melting point :-

Solder metal which is an alloy of Sn(30%) and Pb(70%) has very less melting point as compared to melting points of Sn and Pb.

v) To modify the colour :-

Aluminium bronze an alloy of Cu and Al has a beautiful golden colour.

vi) To resist corrosion:-

Iron gets rusted and corroded. Its corrosion takes place with time but for stainless steel, an alloy of iron (98%) and carbon (2%) to not get rusted.

Aim : To analyze a sample of brass qualitatively

Requirements

China dish, test-tube funnel, filter paper and common laboratory reagents.

Theory :

Brass is an alloy of copper and zinc. with the following.

Composition :

Cu = 60-90% and Zn. = 10-40%.

Thus Cu and Zn. form the main constituents of brass. Both these metals dissolved in 50% of nitric acid due to formation of nitrates which are soluble.

3Cu + 8HNO 3 à 3Cu(NO 3 ) 2 + N 2 O + 5H 2 O

4Zn + 10HNO 3 à 4 Zn (NO 3 ) 2 + N 2 O + 5H 2 O

The solution is boiled to expel the oxides of nitrogen and the resulting solution is tested for Cu2+ and Zn+2 ions.

Procedure :

1. Place a small piece of brass in a china dish and heat this with minimum quantity of 50% HNO 3 so as to dissolve the piece completely.

2. Continue heating the solution till a dry solid residue is obtained.

3. Dissolve the solid residue in dil. HCl and filter. Add distilled water to the filtrate.

4. Pass H 2 S gas through the filtrate. A black precipitate of copper sulphide is obtained. Separate the black ppt. and keep the filtrate for the test of Zn +2 ions Dissolve black ppt. by heating them with 50% HNO 3 . To this solution add ammonium hydroxide solution. Appearance of deep blue colouration in the solution shows the presence of copper ions in the solution.

5. To test Zn+2 ions, boil the filtrate to remove H2S gas, then add solid NH4Cl to this and heat to dissolve NH4Cl. Add excess of NH4OH so that a solution is ammoniacal. Now pass H2S gas through this ammoniacal solution. Dirty white or grey precipitation indicate zinc. Separate the precipitates and dissolve it in minimum amount of dil. HCl. Boil to expel H 2 S gas and add potassium Ferro cyanide solution, white or bluish white ppt. confirm Zn+2 ions in the solution.

Result :

The given sample of brass contains copper and zinc. metals as the main constituents.

Aim : To analyze a sample of bronze qualitatively

Requirements

China dish, test-tube funnel, filter paper and common laboratory reagents.

Theory :

Bronze is an alloy of copper and tin with the following.

Composition :

Cu = 88-96% and Sn. = 4-12%.

Thus copper and zinc. form the main constituents of bronze. Both these metals dissolved in nitric acid.

Cu + HNO3 à Cu2+ + NO + H2O

Sn + HNO3 à H2SnO3 + NO2 + H2O

(Conc. acid) (Metastannic Acid)

Excess of nitric acid is removed by heating the solution. The resulting solution now would contain Cu+2 ions and metastannic acid. This solution is acidified with dil. HCl and H2S gas is passed when the sulphides of copper and tin are formed.

Cu 2+ + S 2 à CuS (Black ppt.)

H 2 SnO 3 + 2H 2 S à SnS 2 (Black ppt.) + 3H2O

The sulphides are separated by boiling the ppt. with yellow ammonium sulphide when SnS2 goes into solution as thiostannate where as CuS is not affected.

SnS 2 + (NH 4 ) 2 S à (NH 4 ) 2 SnS 2 (Soluble)

Ammonium thiostannate.

CuS + (NH 4 ) 2 S à CuS (Unaffected)

Black ppt.

The soluble black ppt. is tested for Cu+2 ions and the solution is tested for Sn2+ ions as in elementary qualitative analysis.

Procedure :

1. Take about 1g. of small pieces of bronze in a china dish and add to it 5-10 ml. of dil. HNO 3 .

2. Heat the contents slowly to dissolve copper and tin completely and then boil the contents to a paste to remove excess of HNO 3 . All this is carried out in cup board.

3. Dissolve this dry mass in distilled water containing HCl (1:1) to get a clear solution.

4. Transfer the solution in a test tube and pass H2S in excess i.e. till the precipitation is complete. Filter and reject the filtrate.

5. Take the black ppt. in a test tube and add to it 2-3 ml. of yellow ammonium sulphide and heat. Filter the contents. Black residue is tested for Cu+2 ions and filtrate is tested for Sn+2 ions.

6. Analysis of black residue :

Transfer a little of the black ppt. into a test tube. Add to it 2-3 ml. of 50%. HNO3 and boil the contents of the tube. A light blue or green sol. indicates the presence of Cu+2. Divide this sol. into two parts.

(a) To one part add excess of NH4OH a deep blue colouration confirms the presence of Cu+2 ions.

(b) Acidify the second part with acetic acid and add K4 [Fe (CN)6] i.e. potassium ferrocyanide solution. A reddish brown ppt. confirms the presence of Cu+2 ions.

7. Analysis of filtrate :

Boil the filtrate with 1 ml. of dil. HCl. A yellow ppt. is obtained. Dissolve in 1 ml. conc. HCl. To this solution add 0.5 g. of zinc. dust and boil it for 2-3 minutes. Filter and to filtrate add 1-2 ml. of mercuric chloride solution. A white ppt. turning grey on standing confirms the presence of Sn+4 ions.

Result :

The given sample of bronze contains - Copper and Tin as the main constituents.