Introduction
An alloy is a substance which is formed when two or more metals are combined. They can also be formed when metals are combined with other elements. However, the properties which alloys exhibit are different from the individual properties of these elements. When you compare it to the pure metals, alloys are stronger and harder. Alloy examples include red gold which is made by combining gold and copper together. Another example of alloy includes white gold which is an amalgamation of silver and gold. Today, we will learn about what is an alloy in chemistry, alloy definition and constituents of alloy.
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Alloy Definition
Let us now learn what alloy means in chemistry.
An alloy refers to a combination of two or more metals, or a metal combined with one or more elements. The resulting alloy has different properties than the original elements altogether, like increased strength and hardness. For example, when elemental iron is combined with non-metallic silicon or carbon, it yields steel or silicone steel.
Constituents of Alloy
Now that you have learned about what the meaning of alloy is, let us look at what the constituents of alloy are. An alloy consists of two or more elements, either as a compound or a solution. The components of alloys are generally metals. However, carbon is an exception to being a non-metal and an important constituent of steel. Alloys are usually produced when the mixture of its constituents is melted.
Properties of Alloy
When you have learnt about what is meant by alloy, learning the properties of alloy becomes easier.
An alloy is a substance that has metallic properties and is composed of two or more elements, out of which at least one is a metal. A metal, having metallic properties, is a material, which, when freshly made, fractured, or polished, demonstrates a lustrous appearance. It also conducts heat and electricity as well.
Metals are generally malleable, which means that they can be easily hammered into thin sheets. They are also ductile, meaning that they can be drawn into wires as well. A metal can either be a chemical element like iron, or an alloy like stainless steel. Most of the pure metals are either very brittle, soft, chemically reactive to be practically used. When different ratios of metals are combined as alloys, it modifies the original properties of metals to give desirable characteristics. Alloys are generally made to keep them less brittle, corrosion-resistant, harder, or even have a more desirable luster and color.
Therefore, alloying of metal helps us to use the metal in daily life application. This process also helps in making different types of metals perfect for use (by modifying its properties ).
Alloy Examples
Let us now look at some of the alloy examples.
Steel
Steel is an alloy of carbon and iron. It is a popular alloy because of its low cost and higher tensile strength. However, many different types of steels consist of different amounts of carbon along with several other elements like manganese, phosphorus, sulfur, chromium, copper, nickel, and molybdenum. Primarily, the composition of iron is accounted for by iron, which is at least 75% of the total alloy’s weight. It also consists of different amounts of carbon and many other elements depending on the type of steel. Since steel has higher tensile strength and affordability, it is used in the infrastructure and construction of buildings, bodies of vehicles and electrical appliances.
Bronze
Bronze is known to be an alloy of tin and copper. It is commonly used in heavy tools and gears, coins, medals, trophies and even in different forms of electrical hardware. The strength of bronze varies depending on the alloys that are used in the alloying. You must know that bronze is much superior compared to pure copper when it comes to hardness. It is also more ductile and machineable compared to pure copper.
Nichrome
Nichrome is an alloy of chromium and nickel. However, it is also common for the nichrome alloys to consist of iron and other similar elements. Nichrome is primarily used in resistance wires. It also has its application in several electrical appliances like bread toasters and space heaters. Nichrome alloys are also used in dental fillings.
Brass
It is a very common and useful alloy of copper. In this, the quantity of zinc is kept at 45%. Along with zinc, metals such as Sn, Mn , Al , Fe,Pb etc are also added in a small amount to obtain some special properties. There are many types of brass. These all have varying compositions of copper. For example - muntz brass, naval brass, aluminum brass, german silver, ordinary brass, Cap copper etc. These alloys have great strength, durability and machinability as compared to normal copper. Also, their melting point is lower than copper and zinc. These alloys are also corrosion, water resistant and have a good lifespan. Brass is used in making jewelry , forgings, rivets, screws. The cartridge brass is mostly used for making sheets and tubes. These alloys are also used in making decorative articles and marine propeller shafts.
Types of Alloy
Alloys are classified as :
On the Basis of Principle Metal in the Alloy : Examples are copper alloy, iron alloy, lead alloy. A copper alloy has copper as a major constituent, i.e, Bronze.
On the Basis of Phases : There can be single phase alloys (consist of a uniform face) and double phase alloys ( consist of two different phases). Example of single phase alloy is brass which has 30% Zn + 70 % Cu. Example of Double phase alloys is muntz metal which has 60% Cu + 40% Zn.
On the Basis of Iron Content : On the basis of iron content, Alloys are classified as ferrous alloys and non ferrous alloys. The alloys which contain Fe as a constituent are known as ferrous alloys whereas the non-ferrous alloys do not contain Fe as a constituent. Example of ferrous alloys is Stainless steel made of Fe + Cr. Example of non-ferrous alloys is Solder which has Pb + Sn.
FAQs on What is an Alloy?
1. What do you mean by Alloy?
An alloy is an amalgamation of a metal or metals and other elements. Several metals or elements can be added to the existing metal for enhancing their properties. For example, pure aluminum and pure copper are relatively softer metals. However, when copper and aluminum are alloyed together, the resulting alloy has greater strength than the metals in their original states. This way, alloys add or enhance specific properties like strength, luster or color to the existing parent metals.
The two or more elements to be alloyed are mixed together in their molten state. This mixture is then allowed to solidify in a sand mold or a metal. The resultant alloy is stronger and more practically useful than the pure elements or metals due to their properties.
2. How are Alloys formed?
An alloy of a metal is formed when it is combined with one or more elements. The most common and one of the oldest methods to alloy a metal is carried out by heating the metal beyond its melting point. The solutes are then dissolved into the molten liquid. This is possible even when the melting point of the solutes is much greater than that of the metal. For example, titanium in its liquid state is quite a strong solvent that is capable of dissolving most elements and metals. Also, it readily absorbs gasses such as oxygen and burns in nitrogen presence. This, in turn, increases the chances of contamination from surfaces, and hence must be melted in special copper crucibles that are water-cooled and have vacuum induction-heating capacity.
3. What are the Needs of Making an Alloy?
The needs for making alloys are:
Improve the Hardness of Metal - Alloy making increases the hardness of metal. For ex : when we convert soft gold into hard gold, alloying makes it harder and usable to wear. If we alloy 1% carbon to metal, it's tensile strength increases by ten times.
For Lowering the Melting Point of Metal - Alloying of metal makes the metallic system easily fusible. Therefore, molding becomes easy.
Alloying increases the casting properties of the metal. This makes the alloyed metal fit for making other objects out of the primary metal.
To Modify the Color - By alloying, we can also change the color of the metal we are alloying. For example, red copper and silver with white zinc produces brown brass alloy after alloying. Here, change in color is being observed.
To Resist Corrosion - Alloying of two or more metal makes it stronger and resist corrosion. The alloying of Fe, C , Ni with Cr makes 'stainless steel' which doesn't corrode in moist environments.
4. Write a Short Note on the Following :
(i) Alnico
(ii) Solders
(i) Alnico - Alnico is also known as aluminum nickel-cobalt steel. This alloy is made up of Aluminum (10 to 12%), Nickel (15 to 20%) and Cobalt (40 to 60%). The aluminum nickel-cobalt steel is commonly used in permanent magnets in motors. This alloy is highly magnetic. Hence, it is also used for making powerful magnets. The permanent magnets in the galvanometer are also made by alnico.
(ii) Solders - These are the alloy of tin and lead which has a low melting nature. Following are the types of solders :
Soft Solders : This contains Pb, Sn and Sb as ( 37-67%), (31-60%), (0.12 -0%) respectively.
Silver Solders : This contains Ag, Cu, Zn as (10-80%), (15-42%) and (4-48%) respectively.
5. What is the Heating Treatment of Steel? Explain the Processes Involved in Heat Treatment of Steel.
In heat treatment of steel, steel is heated or cooled according to a strictly determined temperature schedule. The heat treatment helps in:
Altering the magnetic properties of steel.
Structural changing of the steel.
To make it more resistive to heat and water corrosion.
To make the steel more useful.
To increase its strength and hardness.
Steel Goes Through the Following Processes During 'Heat Treatment' :
Annealing - This makes the steel soft (so that it is easy to work on it with the help of machines).
Case-hardening - In this, carbon content at the surface of the specimen is increased which makes it harder then the other parts of the specimen.
Cementing Process - In this, steel's skin is saturated with carbon and heated between the temperature of 8800 C – 9500C .
Hardening - This process is opposite of the annealing process. In this, steel is hardened (by cooling the steel at a controlled rate).
Nitriding - In this, the surface layer of steel is saturated with nitrogen by heating. It increases its resistance to corrosion, wear and damage.
Normalizing - After going through so much change in the state of steel, this process restores the steel structure to normal conditions. It also makes the specimen more ductile.
Tempering - This process is used to get the required proportion of hardness and ductility from the heated metal. This process also increases the stress capacity of metal.