Diploma in Engineering (Common to all branches) II-Semester, Applied Chemistry (BCH-201)
By: Dr. M. Mujahid Ali Khan In-Charge Chemistry Lab Assistant Professor (Chemistry) UNIT-III (Alloys and Fuels)
Alloy: Alloy may be defined as homogeneous mixture of two or more elements. One of the elements in the alloys is essentially a metal, while the other element or elements may be metals or non-metals like carbon, silicon, sulphur or boron.
Alloy = Metal + metal/non-metal(C, Si, S, B)
Pure metals have poor mechanical properties. Hence, they are not used in their pure form in industry.
Their properties are modified by adding other elements.
Some important alloys:
Name of the Alloy Composition Uses
Brass Cu: 80%
Zn: 20%
In making of utensils, pipes and radiator statues etc
Bronze Cu: 90%
Sn: 10%
In making of coins, ornaments, utensils and statues
Stainless steel Fe: 82%
(Ni + Cr): 18
In making of surgical instruments, watches and utensils etc
Magnalium Al: 95%
Mg: 5%
In making light articles and physical balance etc Duralumin
Al: 95%
Cu: 4%
Mn: 0.5%
In making parts of aeroplane and ship etc
Alnico
Al: 8-12%
Ni:15-26%
Co: 5-24%
Cu: 6%
Remaining: Fe, Tl
It is useful in making of magnets
German silver
Cu: 60%
Zn: 20%
Ni: 20%
It is useful in electroplating and making of utensils
Gun metal
Cu: 88%
Sn: 10%
Zn: 2%
It is useful in making of guns, machine parts and canons..etc
Solder metal Pb: 50%
Sn: 50%
It is mainly useful to join electric wires
Amalgams:
Alloys of mercury with other metals like sodium, potassium,gold and zinc...etc are called amalgams.
Silver-tin amalgams are useful for the dental cavities.
Amalgams stored in iron bottles as iron cannot form amalgam with mercury.
Uses of Alloys in Daily Life:
Alloying elements addition for specific design and materials can often be accomplished without major reductions in the attributes associated with pure metals, like conductivity, ductility and resistance against corrosion.
If two or more metals are mixed in the liquid state to produce a final solution the resulting alloy is called a binary alloy. In case of superalloys where the utility could be within microwave cooker or baking oven as many as ten alloying elements may be used to obtain the desired performance.
The use of alloy in daily life is now irrevocable and if the good factors like high tensile strength, hardness are taken into consideration then materials like gas burners, microwave utility vessels, modern-day pressure cooker, pressure valve, washing machine tub, grinder blades, and other simple daily use materials like vehicular parts of bikes and cars etc are produced.
The metals nickel and copper completely dissolve into each other in a liquid state and retain their complete solubility in each other on freezing to form a series of alloys.
When one type of metal is alloyed with another kind either substitutional or interstitial solid solution are usually formed. Substituted solid based solutions are considered for those where the atoms of both solute and solvent are of nearly the same size and the solute atoms simply substitute for atoms of solvents on the crystalline lattice.
Interstitial solid solutions are those in which the solute atoms are found to be much smaller and fit within the spaces between the existing solvent atoms in the crystalline structure.
The only solute atoms small enough to fit in the interstices of metal crystals are hydrogen, nitrogen, carbon and boron.
Common Uses of Alloys:
A typical metal is hard and shiny, tough as well as strong. It helps in conducting or carries electricity and heat very well. Metals have thousands of uses in daily life and are often mixed or combined with other metals or substances to form alloys.
Almost any machine or device which are used for precision instrumentation has at least one metal in it and as the most widely used form is iron we can see the use of steel by using a little amount of non-metal carbon. The use of steel is universal and the day begins with utensils made of steel. The next very common kitchen vessel is aluminium and its alloys.
The next daily use or rather universally used metal is gold which is worn by almost everyone. The ornaments made up of pure gold is never used by the general public as they are found to be very soft and hence the use of copper or doping with copper makes it little wearable. The doped gold is relatively strong and doesn’t bend as easily as the pure form.
The door locks and doorknobs are again made up of brass which is again an alloy form of zinc and copper.
High-performance blades of jets or washing tub or heating elements of microwave and water heater are again nothing but a doped form of the pure metals.
The common saucepans made up of aluminium never last long but if doped with little magnesium, copper or silicon makes it tough enough to withstand high temperature and do not deform.
The aircraft body made up of main aluminium is composed of doping with copper, magnesium and manganese which makes it tough, corrosion-free, lightweight and is widely used in aviation industries.
Introduction of Fuels:
In this present age of rapid industrial development, the power requirement is increasing day-by- day. Heat energy is the main source of power. Burning of carbon, an exothermic reaction produces heat energy. Hence, the carbon compounds have been used as the main source of heat energy.
Fuel: A fuel is a substance, which on proper burning gives large amount of heat energy on combustion. It is used for domestic and industrial purposes. They contain carbon as a main constituent.
Fossil fuel: The main sources of fuels are coal and petroleum oils available in earth’s crust and they are called fossil fuels.
The other sources of fuels are (i) Radioactive elements and (ii) Sunlight
Calorific value of a fuel: Calorific value of a fuel is the total quantity of heat liberated when a unit mass or volume of the fuel is completely burnt.
Unit of heat: Heat energy is measured in terms of calorie or kilocalorie. Calorie is the quantity of heat required to raise the temperature of 1 gram of water through 1° Centigrade (1 kcal = 1000 calories).
Classification of fuels: Fuels are classified into natural or primary fuels and artificial or secondary fuels. Each type is further subdivided into solid, liquid and gaseous fuels.
S.N0 State of fuel Natural Artificial
1. Solid Wood, peat, lignite, coal Wood charcoal, coke
2. Liquid Crude petroleum Kerosene, petrol, diesel,
alcohol
3. Gas Natural gas Water gas, producer gas,
biogas, coal gas, LPG
Wood: It is a low-grade fuel. Freshly cut wood contains 25-50% moisture. Moisture may be reduced to 25% on air-drying. The composition of moisture free wood is C = 55%; H2 = 6%; O2
= 43% and ash = 1%. The calorific value of dried wood is 3500 to 4500 kcal/kg. It burns with a long and non-smoky flame. It is used as a domestic fuel.
Coal: Coal is a natural fuel formed by the slow carbonization of vegetable matter buried under the earth some thousands of years ago. It is classified into four kinds based on the carbon content and the calorific value.
1. Peat 2. Lignite
3. Bituminous coal 4. Anthracite coal
Peat: It is the first stage of formation of coal from wood. It is brown, fibrous jelly-like mass. It contains 80-90% moisture. The composition of peat is C = 57%; H2 = 6%; O2 = 35% and ash = 2.5%. The calorific value of peat is 5400 kcal/kg. It is a low-grade fuel due to high water content.
Uses:
It is used as fertilizer.
It is used as packing material.
Lignite: Lignite is immature form of coal. It contains 20-60% moisture. Airdried lignite contains C = 60-70% and O2 = 20%. It burns with a long smoky flame. The calorific value of lignite is 6500-7100 kcal/kg.
Uses:
It is used as a domestic fuel.
It is used as a boiler fuel for steam production.
It is used in the manufacture of producer gas.
Bituminous coal: It is a high quality fuel. Its moisture content is 4%. Its composition is C
= 83%; O2 = 10%; H2 = 5% and N2 = 2%. Its calorific value is 8500 kcal/kg.
Uses:
It is used in metallurgy.
It is used in steam production.
It is used for making coal gas.
It is also used for domestic heating.
Anthracite coal: It is the superior form of coal. It contains C = 92-98%; O2 = 3%; H2 = 3% and N2 = 0.7%. It burns without smoke. Its calorific value is 8700 kcal/kg.
Uses:
It is used for steam production and house hold purposes.
It is used for direct burning in boilers and in metallurgy.
It is used in thermal power plant.
It is used in coal tar distillation.
It is used in glass furnaces.
CNG: (Compressed natural gas) CNG is a good alternative fossil fuel. It mainly contains methane.
CNG is made by compressing natural gas which is found in oil deposits landfills and waste water treatment plants to less than 1% of its volume, it occupies at standard atmospheric pressure.
It is stored and distributed in hard containers at a pressure of 2900-3600 psi.
Advantages:
It is cheaper than petrol or diesel.
It emits fewer pollutants like CO2, CO, etc. In New Delhi, it is used as a fuel for entire city bus fleet, taxis and three wheelers.
It is safer than other fuels. In the event of a spill, it disperses quickly in air because, it lighter than air.
LPG: (Liquefied petroleum gas)
It is a mixture of propane and butane.
It is stored in steel cylinder under high pressure.
When the cylinder is opened, it comes out in the form of gas.
Commercially, it is supplied under various trade names.
Its calorific value is 27,800 kcal/m3.
Uses:
It is mainly used as a domestic fuel.
It is used as a fuel in diesel engines.
It is used as a motor fuel.
