This document describes a muffle furnace, which heats materials indirectly by surrounding them with hot gases or electric coils rather than exposing them directly to combustion. It discusses two main types - gas-fired muffle furnaces, where hot gases circulate outside the muffle wall to heat it uniformly, and electric muffle furnaces using resistance coils or radiant elements. Muffle furnaces are used to extract metals from ores without contaminating them with fuel, and to test the purity of precious metals like gold and silver. They allow for better temperature control to prevent scaling during processes like annealing.

1. Muffle Furnace
-BY D.C.DHARUN MUGHILAN
1ST BSc. Chemistry(Aided)
20UCH01

2. Introduction
A metallurgical furnace, more commonly referred to as a furnace, is
a device used to heat and melt metal ore to remove gangue, primarily
in iron and steel production. The heat energy to fuel a furnace may be
supplied directly by fuel combustion, by electricity such as the electric
arc furnace, or through induction heating in induction furnaces. There
are several different types of furnaces used in metallurgy to work with
specific metal and ores.
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In Muffle furnace the material to be heated
does not come in the contact with the fuel or
flames. A muffle is a chamber made of
refractory material and is surrounded by
flames and hot gases on all sides. The
products of combustion are removed
through a door provided in the furnace
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TYPES OF
MUFFLE
FURNACES

5. Gas fired muffle furnace
◉ The gas is burnt outside the muffle, and the heating
is effected by the hot gases which are made to
circulate through the ring like space between the
interior-wall and the exterior-muffle wall.
◉ The products of combustion of the gas do not enter
the heating chamber, and thus, the atmosphere of
the furnace can be controlled, and thus, scaling of
the components can be prevented. Also, such a
furnace gives reasonable uniformity of temperature
distribution. The figure illustrates such a furnace
schematically.
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R
e
d

6. Electric Muffle Furnace
◉ Commonly, electrically heated muffle furnaces are
extensively used for the heat treatment of small sized
components. In an electric muffle furnace the chamber is
surrounded by resistance coils.
◉ This figure illustrates heating element like nichrome or
kanthal wire wound around the muffle, or are placed in the
ring-like space to heat the muffle with its contents.
◉ For high temperatures, electric muffle is heated by glow
bars, or radiant elements, where the steel gets heated by
a direct radiations.
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Muffle
Furnace
A MODERN MUFFLE FURNACE

8. APPLICATIONS
◉ Muffle furnace is used for the extraction of zinc,
preparation of red lead, Pb3O4 and for testing
the purity of precious metals like silver and
gold.
◉ A Muffle furnaces are used for bright annealing,
nitriding, a carburising, bright hardening.
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QUESTIONS FOR YOU:
1. Muffle furnace is used to extract gangue and metal from the ores. Say whether it is true
or false.
2. What is the advantage of using muffle furnaces over other furnaces?
3. Gas fired muffle furnace was surrounded by fuel gas then what is the electric furnace
surrounded of?
4. What is the advantage of gas fired furnace over electric one ?
5. The muffle furnace shown as a photograph contained an external door so what type of
muffle furnace is it?
6. Which of the following’s purity cannot be checked by Muffle furnace?
A. Gold
B. Silver
C. Zinc
D. None of these

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Answers for the questions:
1. FALSE because muffle furnace is used for extracting metals from ores by removing
gangue.
2. Other furnaces like blast furnace include heating of metals with the fuels which
makes it harder to again separate the fuel and the metal. But muffle furnace do not
include the fuel to get mixed with the purified ore. Also this makes the temperature
to be in control which helps in prevention of scaling of components.
3. Resistance coils or by radiant elements.
4. In the gas fired the heat is spread uniformly all over the furnace but in electric one it
may not be.
5. It is an electric muffle furnace we can see the schematic diagram of it.
6. C)Zinc is extracted using this method But it’s purity is not checked by this.

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