What is metal?
All kinds of objects are made from metals. Metals combine with other elements to form compounds and in nature compounds of metals are found in the form of ores. To obtain metals from ore, various processes such as extraction, refining etc. have to be done, due to which impurities and metals are separated. At present metals are used in almost all engineering industries. Each metal has its own properties which reveal their nature.
physical properties of metals
Those properties of a metal, which can be known by just touching or seeing without destroying the metal, are called physical properties of metals. These properties of metals are permanent. They cannot be changed. In other words, the natural properties of metals are called physical properties. These are as follows-
Each metal has its own distinctive colour. It is because of this color that it can be easily recognized; For example, yellow metal can be brass, while red metal can be copper etc.
The structure of each metal is different. By looking at the broken piece of metal, its structure can be identified. Some metals such as – wrought iron, linear motion of particles in aluminum and some metals; For example, the particles in cast iron and bronze have a crooked motion.
(iii) Weight/Specific Gravity
The gravitational force of the Earth pulls every object towards its (earth’s) centre. Therefore, the force with which the earth pulls an object towards its center is called the weight of the object.
Note: Except mercury, all other metals are solid because mercury is found in liquid state.
(iv) Relative Density
The ratio of the density of water to the density of a given object is called relative density.
Every metal has a certain density. The density of any substance is directly proportional to the mass of that substance and inversely proportional to the space or volume occupied by it. There are metals with high density such as lead, gold etc., and metals with low density such as aluminum, silicon etc.
The property of metals due to which they are attracted to magnets is called magnetism. This property is found in ferrous metals.
Every metal melts at a certain temperature, this temperature is called the melting point of that metal. The melting point of each metal is different.
The property of metals, due to which they allow heat and electricity to pass from one end to the other, is called conductivity.
All metals are good conductors of heat and electricity. Due to the conductivity property, on heating one end of a metal rod, after some time the other end of the rod also gets heated, whereas on heating the end of a non-metal rod, its other end is not heated. That is, metals are good conductors of heat and electricity, while non-metals are insulators of heat and electricity.
The property of opacity is found in all metals. That is, it cannot be seen through metals.
mechanical properties of metals
The properties which show the reaction of a metal under the influence of different types of forces are called mechanical properties. These are as follows-
The property due to which metals resist wear, cut and corrode, that property is called hardness. Some metals are soft, which can be easily corrode, such as tin and lead etc. And some metals are more hard, which cannot be easily cut or scraped, such as steel or titanium etc.
The property due to which metals break into pieces when they are injured, that property is called brittleness. For example, if there is an injury on glass, cast iron and silicone etc., then they get broken into pieces.
The property due to which wires can be made by stretching metals, that property is called ductility. Wires can be made of almost all metals, such as iron, brass, aluminum, copper, gold, silver and platinum etc.
The thinner the metal wire that can be made, the more ductile that metal is said to be.
Note- This quality is found more in gold, silver and platinum.
The property due to which metals tolerate shock and do not break easily on bending, breaking or twisting, that property is called toughness. Some chisels are metals like tungsten, copper, gold etc.
This property is opposite to brittleness. The chisel sinks into the workpiece when struck by a hammer because of its sharpness. So it tolerates the trauma easily.
When a force is applied on a metal, its shape changes but when the force is removed, it regains its former shape. This property is called elasticity. By using this property, springs of metals are made.
The property of elasticity in metals remains to a certain extent. If deformed beyond this limit, metals do not regain their former state even after removing the force and take their changed shape forever.
This property of metals is called ductility or plasticity. Due to this property, we convert sheets of metals into different types of utensils.
The property due to which metals expand when they are struck or rolled, is called malleability. This property can be used to convert a metal cable into a sheet. Gold is the most malleable.
The property due to which metals do not break when pulled or pressed, that property is called tenacity.
(ix) impact resistance
The property of a metal, which prevents it from breaking due to sudden injury to the metal, is called impact resistance.
The property of metals, due to which less force is required to cut and separate a small part of the job, is called machinability. Metals that are brittle require less force to machine them, and more force is required to machine or cut ductile metals. Therefore brittle metals have high machinability.
(xi) fatigue resistance
The property of metals, which prevents them from breaking down to the ultimate strength due to continuous shocks, is called fatigue resistance. This property is found in gray cast iron.
The property of a metal due to which the metal exerts pressure to a certain extent Feather Pressing, but not bursting, is called compressibility. By applying a pressure-force to the length of the metal, its width increases and by applying a pressure-force to the width or thickness, its length increases.
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