Sunday, 30 October 2016

Magnetic Domains in magnetic particle inspection.

Ferromagnetic materials get their magnetic properties not only because their atoms carry a magnetic moment but also because the material is made up of small regions known as magnetic Domains.  In each domain, all of the atomic dipoles are coupled together in a preferential direction. This alignment develops as the material develop ls it's crystalline structure during solidification from the molten state. Magnetic Domains can be detected using magnetic force Microscopy (Mum)and images of the domains like the one shown below can be constructed.
during solidification, a trillion or more moments are aligned parallel so that the magnetic force within the domain is strong in one direction. Ferromagnetic materials are said to be characterized by spontaneousm magnetization since they obtain saturation magnetization in each of the domains without an external magnetic field being applied.  Even though the domains are magnetically saturated  the bulk material may not show Amy signs of magnetism because the domains.develop themselves and are randomly arrested relative tutor each other. 

The source of magnetism in magnetic particle inspection.

All matter is composed of atoms, and atoms are composed of protons and electrons.The protons and neutrons are located in the atoms nucleus and the electrons are in constant motion around the nucleus. Electrons carry a negative electrical charge and produce a magnetic field as they move through space..A magnetic field is produced whenever an electrical charge is in motion. The strength of this field is called the magnetic moment.
This may be hard to visualize on a subatomic scale but consider electric current flowing through a conductor. When the electrons ( electric current)  are flowing through the conductor, a magnetic field forms around the conductor. The magne field can be detected using a compass. The magnetic field will place a force on the compass needle, which is another example of a dipole. Since all matter is comprised of atoms, all materials are affected in some way by a magnetic field. However, not all materials react the same way. This will be explored more in the next section.