Methods of preparing magnets, molecular theory of magnetism, demagnetization

Some magnets can be created using any of the following ways below.

Induction
Stroking
Using electricity

Since these magnets can be made, they are usually referred to as temporary magnets. Electromagnets are magnets made using electricity and so are called temporary magnet since they only show their magnetic influence when there is electricity passing through it.

Magnets made by induction and stroking are also temporary magnets. This is because; they will lose their magnetic influence when the inducing or stroking magnets are removed. This means that magnets that always exhibit their magnetic influence and characters are known as permanent magnets.

Permanent magnets are usually made from steel while temporary magnets are made from iron. Iron nails become temporary magnets when they are attached to magnets. The nails lose their Magnetism when the magnet is taken away. Materials such as steel are able to retain their magnetism for a long time.

Induction

The material to be magnetized such as an iron nail is attached to a bar magnet for some period of time. After some time, some pins are brought close to the iron nails.

It is seen that the pins become attracted to the iron nails. The iron nails is now behaving like a magnet as a result of its attachment to the bar magnet. Conclusion: Magnet can also be made by induction.

Making a Magnet by Stroking

A nail is placed on a flat surface and is stroke repeatedly in the same direction with the North Pole of the magnet. The pole is slide along the nail from end to the other and then lifted away from the nail in a large circle. It is returned to the starting end of the nail. A pin is brought close to the nail.

It is seen that the nail attracts the pin to itself.

This shows that the nail has now been magnetized because of the stroking by the bar magnet so it now shows magnetic influence on the pin. Magnet can also be made by stroking with a bar magnet.

Using Electricity

A wire is wound around a card board tube to form what is called a solenoid. Leave the ends of the wire so that, they can be connected to a source of power such as a battery in an electrical circuit. The material to be magnetized is placed in the solenoid and the current is switched on for a short time. The needle is then taken out and some pins are brought close to it.

The pins become attracted to the needle for some time. This shows that the needle becomes magnetized so, the pins were attracted. Magnets can also be made using electricity.

Molecular theory of magnetism

A popular theory of magnetism considers the molecular alignment of the material. This is known as Weber’s theory. This theory assumes that all magnetic substances are composed of tiny molecular magnets. Any unmagnetized material has the magnetic forces of its molecular magnets neutralized by adjacent molecular magnets, thereby eliminating any magnetic effect. A magnetized material will have most of its molecular magnets lined up so that the north pole of each molecule points in one direction, and the south pole faces the opposite direction. A material with its Molecules thus aligned will then have one effective north pole, and one effective south pole. An illustration of Weber’s Theory is shown in figure above, where a steel bar is magnetized by stroking. When a steel bar is stroked several times in the same direction by a magnet, the magnetic force from the north pole of the magnet causes the molecules to align themselves.

Demagnetization

After conducting a magnetic particle inspection, it is usually necessary to demagnetize the component. Remanent magnetic fields can:

Affect machining by causing cuttings to cling to a component.
interfere with electronic equipment such as a compass.
create a condition known as “arc blow” in the welding process. Arc blow may cause the weld arc to wonder or filler Metal to be repelled from the weld.
cause abrasive particles to cling to bearing or faying surfaces and increase wear.

Removal of a field may be accomplished in several ways. This random orientation of the magnetic domains can be achieved most effectively by heating the material above its curie temperature. The curie temperature for a low carbon steel is 770oC or 1390oF. When steel is heated above its curie temperature, it will become austenitic and loses its magnetic properties. When it is cooled back down, it will go through a reverse transformation and will contain no residual Magnetic Field. The material should also be placed with it long axis in an east-west orientation to avoid any influence of the Earth’s magnetic field.

It is often inconvenient to heat a material above its curie temperature to demagnetize it, so another method that returns the material to a nearly unmagnetized state is commonly used. Subjecting the component to a reversing and decreasing magnetic field will return the dipoles to a nearly random orientation throughout the material. This can be accomplished by pulling a component out and away from a coil with AC passing through it. The same can also be accomplished using an electromagnetic yoke with AC selected. Also, many stationary magnetic particle inspection units come with a demagnetization feature that slowly reduces the AC in a coil in which the component is placed.

A field meter is often used to verify that the residual flux has been removed from a component. Industry standards usually require that the magnetic flux be reduced to less than 3 gauss after completing a magnetic particle inspection.

Table of Contents

Methods of preparing magnets

Magnets are materials that have a permanent magnetic field. They are used in a variety of applications, including motors, generators, and loudspeakers. There are several methods of preparing magnets, including casting, sintering, powder metallurgy, electroplating, and chemical vapor deposition.

Casting

In casting, a molten metal is poured into a mold and allowed to cool and solidify. The mold can be made of a variety of materials, including sand, plaster, and metal. The shape of the magnet is determined by the shape of the mold.

Sintering

In sintering, a powder of magnetic material is heated until it fuses together. The powder can be made of a variety of materials, including iron, nickel, and cobalt. The shape of the magnet is determined by the shape of the mold.

Powder metallurgy

In powder metallurgy, a powder of magnetic material is compacted and then sintered. The powder can be made of a variety of materials, including iron, nickel, and cobalt. The shape of the magnet is determined by the shape of the die.

Electroplating

In electroplating, a thin layer of magnetic material is deposited on a non-magnetic substrate. The substrate can be made of a variety of materials, including plastic, paper, and metal. The shape of the magnet is determined by the shape of the substrate.

Chemical vapor deposition

In chemical vapor deposition, a thin layer of magnetic material is deposited on a substrate by Chemical Reaction. The substrate can be made of a variety of materials, including plastic, paper, and metal. The shape of the magnet is determined by the shape of the substrate.

Molecular theory of magnetism

The molecular theory of magnetism is a theory that explains the magnetic properties of materials. The theory is based on the idea that the electrons in a material can have two different spin states, up and down. When the electrons are all in the same spin state, the material is said to be ferromagnetic. When the electrons are in different spin states, the material is said to be paramagnetic.

The exchange interaction is a force that causes the electrons in a material to align their spins. The exchange interaction is stronger in ferromagnetic materials than in paramagnetic materials.

Spin-orbit coupling is a force that causes the electrons in a material to interact with the magnetic field of the nucleus. Spin-orbit coupling is stronger in paramagnetic materials than in ferromagnetic materials.

Crystal field theory is a theory that explains the electronic structure of materials in crystals. The theory is based on the idea that the electrons in a material are attracted to the nuclei of the atoms in the crystal. The crystal field theory can be used to explain the magnetic properties of materials.

Demagnetization

Demagnetization is the process of removing the magnetic field from a magnet. There are several methods of demagnetization, including thermal demagnetization, field demagnetization, irreversible demagnetization, and Barkhausen effect.

Thermal demagnetization

Thermal demagnetization is the process of demagnetizing a magnet by heating it. When a magnet is heated, the electrons in the material move faster. The faster the electrons move, the more difficult it is for them to align with the magnetic field.

Field demagnetization

Field demagnetization is the process of demagnetizing a magnet by applying a magnetic field in the opposite direction to the magnetic field of the magnet. When a magnetic field is applied in the opposite direction, the electrons in the material are forced to align in the opposite direction.

Irreversible demagnetization

Irreversible demagnetization is the process of demagnetizing a magnet by applying a strong magnetic field in the opposite direction to the magnetic field of the magnet. When a strong magnetic field is applied in the opposite direction, the electrons in the material are forced to align in the opposite direction. The alignment of the electrons is permanent and cannot be reversed.

Barkhausen effect

The Barkhausen effect is the noise that is produced when a magnet is demagnetized. The noise is caused by the movement of the domain walls in the material. The domain walls are regions of the material where the magnetic field is aligned in different directions. When the magnet is demagnetized, the domain walls move and produce noise.

Methods of preparing magnets

What are the different methods of preparing magnets?

There are many different methods of preparing magnets, but the most common are:

Powder metallurgy: This involves mixing powdered iron or other magnetic materials with a binder, then pressing and sintering the mixture to form a solid magnet.
Injection molding: This involves melting a magnetic material and injecting it into a mold to form a desired shape.
Electromagnetic forming: This involves applying an electric current to a coil of wire, which creates a magnetic field that attracts a piece of magnetic material. The magnetic material is then shaped by the magnetic field.
What are the advantages and disadvantages of each method?

The advantages and disadvantages of each method of preparing magnets vary depending on the specific material and application. However, some general advantages and disadvantages include:

Powder metallurgy: This method is relatively inexpensive and can be used to produce a wide variety of shapes and sizes of magnets. However, it can be time-consuming and the magnets may not be as strong as those produced by other methods.
Injection molding: This method is relatively fast and can be used to produce complex shapes of magnets. However, it can be expensive and the magnets may not be as strong as those produced by other methods.
Electromagnetic forming: This method is relatively fast and can be used to produce strong magnets. However, it can be expensive and the magnets may not be as uniform as those produced by other methods.

Molecular theory of magnetism

What is the molecular theory of magnetism?

The molecular theory of magnetism is a theory that explains the magnetic properties of materials in terms of the alignment of the magnetic moments of individual atoms or molecules.

What are the different types of magnetic moments?

There are two main types of magnetic moments: orbital magnetic moments and spin magnetic moments. Orbital magnetic moments arise from the motion of electrons around the nucleus of an atom. Spin magnetic moments arise from the intrinsic spin of electrons.

How are magnetic moments aligned in a magnet?

In a magnet, the magnetic moments of individual atoms or molecules are aligned in the same direction. This alignment creates a net magnetic field.

What are the different types of magnets?

There are two main types of magnets: permanent magnets and temporary magnets. Permanent magnets retain their magnetism even when there is no external magnetic field present. Temporary magnets lose their magnetism when there is no external magnetic field present.

Demagnetization

What is demagnetization?

Demagnetization is the process of removing the magnetism from a material.

What are the different methods of demagnetization?

There are many different methods of demagnetization, but the most common are:

Heating: Heating a magnet can cause the magnetic moments of the individual atoms or molecules to become disordered, which results in the loss of magnetism.
Applying an external magnetic field: Applying an external magnetic field in the opposite direction to the magnetic field of the magnet can cause the magnetic moments of the individual atoms or molecules to become disordered, which results in the loss of magnetism.
Mechanical shock: Mechanical shock can cause the magnetic moments of the individual atoms or molecules to become disordered, which results in the loss of magnetism.
What are the advantages and disadvantages of each method?

The advantages and disadvantages of each method of demagnetization vary depending on the specific material and application. However, some general advantages and disadvantages include:

Heating: Heating is a relatively simple and inexpensive method of demagnetization. However, it can be time-consuming and it can damage the material if it is heated too high.
Applying an external magnetic field: Applying an external magnetic field is a relatively fast and efficient method of demagnetization. However, it can be expensive and it can damage the material if the magnetic field is too strong.
Mechanical shock: Mechanical shock is a relatively simple and inexpensive method of demagnetization. However, it can be time-consuming and it can damage the material if the shock is too severe.

Which of the following is not a type of magnet?
(A) Permanent magnet
(B) Temporary magnet
(C) Electromagnet
(D) Diamagnet
Which of the following is the most common type of magnet?
(A) Permanent magnet
(B) Temporary magnet
(C) Electromagnet
(D) Diamagnet
What is the most common material used to make permanent magnets?
(A) Iron
(B) Nickel
(C) Cobalt
(D) All of the above
What is the most common material used to make temporary magnets?
(A) Iron
(B) Nickel
(C) Cobalt
(D) None of the above
What is the most common material used to make electromagnets?
(A) Iron
(B) Nickel
(C) Cobalt
(D) Copper
What is the difference between a permanent magnet and a temporary magnet?
(A) A permanent magnet retains its magnetism after the external magnetic field is removed, while a temporary magnet does not.
(B) A permanent magnet is made of a ferromagnetic material, while a temporary magnet is made of a diamagnetic material.
(C) A permanent magnet is made of a ferrimagnetic material, while a temporary magnet is made of a paramagnetic material.
(D) A permanent magnet is made of a ferromagnetic material, while a temporary magnet is made of a non-magnetic material.
What is the difference between an electromagnet and a permanent magnet?
(A) An electromagnet is made of a ferromagnetic material, while a permanent magnet is made of a diamagnetic material.
(B) An electromagnet is made of a ferrimagnetic material, while a permanent magnet is made of a paramagnetic material.
(C) An electromagnet is made of a ferromagnetic material, while a permanent magnet is made of a non-magnetic material.
(D) An electromagnet is made of a conductor, while a permanent magnet is made of an insulator.
What is the principle behind the operation of an electromagnet?
(A) When an electric current is passed through a conductor, it creates a magnetic field.
(B) When an electric current is passed through a conductor, it creates an electric field.
(C) When an electric current is passed through a conductor, it creates a heat field.
(D) When an electric current is passed through a conductor, it creates a Light field.
What is the most common application of electromagnets?
(A) Motors
(B) Generators
(C) Transformers
(D) All of the above
What is the most common way to demagnetize a magnet?
(A) Heating it
(B) Cooling it
(C) Hitting it
(D) Exposing it to a magnetic field of opposite polarity