What is BHC in chemistry



 

As Coercive force (Hc, H for the magnetic field strength and c For coercivity) refers to the magnetic field strength that is necessary to completely demagnetize a ferromagnetic substance so that the resulting total flux or the local flux density is zero. The higher the coercive field strength, the better a magnet retains its magnetization when exposed to an opposing field. The SI unit is like all magnetic field strengths , Occasionally the outdated unit Oe (Oersted) is still used.

If ferromagnetic materials are exposed to a magnetic field, a residual magnetism, the remanence, remains even after the field has been removed. This also applies to ferrimagnetic and all other paramagnetic substances, albeit in a significantly weakened form.

application

A distinction is made between the coercive field strength (bHc) the magnetic flux density and the coercive field strength (jHc) the magnetic polarization. If a permanent magnet is exposed to a field strength bHc, the magnetic flux density in the magnet disappears. However, it is still magnetic after being removed from the field. Only with a demagnetizing field strength jHc does the permanent magnet lose its magnetic polarization and thus its magnetization completely, i.e. the applied field strength causes a magnetic flux density of the size ยต0 * H, so that at this point the material changes with regard to its magnetic properties such as vacuum or behaves roughly like air.

Note the strong temperature dependence of these field strengths, which is to be found not least in the temperature dependence of ferromagnetism.

Practical meaning

The coercive field strength is measured with a so-called Coercimeter, which measures the polarization via induction in a moving coil as a function of an applied external magnetic field strength. Since the magnetizability and thus also the remanence or the coercive field strength depends on the structure of the material, knowledge about the material structure (e.g. degree of deformation) can be derived from the magnetic properties.

values

material Coercive force
in A / m
iron
(technically pure)
10 to 200
Dynamo sheet I 200
Dynamo sheet IV 25 to 60
Cold rolled sheets 20 to 35
Nickel iron
(50% Ni)
3 to 16
MU metal
(76% Ni, 5% Cu, 2% Cr)
0.8 to 5

Category: Magnetism