What Does Magnetization Mean?
Magnetization is the density of magnetic dipole moments that are induced in a magnetic material when it is placed near a magnet. A material's magnetic effects can also be induced by passing an electrical current through the material; the magnetic effect is caused by the motion of electrons in atoms, the spin of the electrons or the nuclei.
Magnetization is also known as magnet polarization.
Magnetic fields are known to affect electrochemical reactions—more so for mass transport rates and for metallic materials in aqueous solutions. The effects of magnetic fields on the electron transfer process in the electrode-solution systems are largely studied. The effect of a magnetic field applied on an electrochemical system is additional forces on the ions in the electrolyte. Lorentz force can also be used and is the most generally accepted. Lorentz force is a paramagnetic gradient force that drives convection in respect to the three effects of magnetic field on the electrochemical behavior of metals and their various alloys.
When a material is influenced by a magnetic field and is then subjected to an aggressive or harsh environment, its corrosion rate accelerates compared to when its corrosion rate is not influenced by the magnetic field. A more positive or negative shift in the corrosion potential may also be expected to occur when comparing metal that is under the influence of a magnetic field and in a magnetic field-free environment.
Corrosionpedia Explains Magnetization
When a magnetized material, or any magnetic field-generating materials, are brought into contact with an electrochemical reaction process, it affects the reaction by changing the mass transport of ions in the solution.
Corroded materials generally tend to have a higher magnetic field generation, which results in further decomposition or an accelerated corrosion rate. However, this is not always true. Sometimes the magnetic field may slow the corrosion process, depending on the geometry of the material experiencing the corrosion.
Neodymium magnets (NdFeB) are permanent magnets that highly favor corrosion due to the presence of a reactive Nd-rich phase. If a droplet of dilute hydrochloric acid is placed on the surface of a piece of NdFeB, vigorous corrosion will take place along with the release of hydrogen. If the sample is in its magnetized state, the droplet will rotate. The direction of rotation is reversed if a droplet is placed on the opposite pole of the magnet. No rotation is observed for demagnetized samples.
Oxidation may change a material's magnetic properties strongly, but the reverse does not occur; magnetization cannot change the rate of oxidation. Magnetite and hematite are the oldest magnetic materials and are the two iron oxides in which oxygen makes the iron more magnetic as when it is in an atomic form. This is because the oxygen creates a spinel structure that allows an important magnetic anisotropy to form as well as a local crystal field, which is the interaction between magnetic metal and oxygen.
Oxides are known insulators. They and have a valence band derived from filled oxygen level, and a conduction band derived from unoccupied metal orbitals. Therefore it is easy to see how oxidation is a chemical process due to this electronic exchange. Contrarily, magnetization is fundamentally in alignment to Hund's Rule, whose application to get magnetic products is quite rare in nature as it accounts for much lower energy that is often used.
One study looked at the effects of an external magnetic field on the electrochemical nature of materials in 3.5% sodium chloride (NaCl) solution. More specifically, it looked at active-passive nature in near-seawater solution (i.e., 3.5% NaCl solution) to understand and analyze magnetic field effects on ferromagnetic and non-magnetic materials. Potentiodynamic polarization and corrosion potential vs time studies were done for analyzing corrosion behavior in 3.5% NaCl solution.
In this study, corrosion test results were obtained with and without the influence of an external magnetic field. The effect of an external magnetic field on corrosion potential and corrosion rate is evident when conducting electrochemical analysis in both conditions in 3.5% NaCl solution. In 416 stainless steel and 1018 carbon steel, which are ferromagnetic, a cathodic shift of the corrosion potential and increase in the corrosion rate was observed. Whereas, for ferrous but non-magnetic and passivating material —like 304 grade stainless steel, there was no effect of the magnetic field. This lack of effect can be attributed to 304 grade stainless steel's non-magnetic nature and its stable oxide formation tendency. Similarly, no effect was observed on the non-ferrous alloys like titanium alloy Ti6Al4V and zinc.