What determines the magnetic strength of NdFeb pot magnets?

What determines the magnetic strength of NdFeb pot magnets?

There are a number of factors that determine the strength of a pot magnet. One of these factors is the Curie temperature. This is a temperature at which the flux is lost irreversibly. Another factor that determines the magnetic strength of a pot magnet is the magnetic properties of the materials used to make it like Alnico magnets.

Source:https://i.pinimg.com

Samarium-cobalt

A samarium-cobalt alloy is an important magnetic alloy for the production of permanent magnets. Compared to other permanent magnets, samarium-cobalt magnets have a high magnetic strength and high temperature resistance. However, they are easily demagnetized. If you need to produce a samarium-cobalt permanent magnet, you should consult a magnet expert to design and manufacture a reliable magnetic product.

Samarium-cobalt (SmCo) magnets are used in applications with extreme temperatures, such as headphones for personal stereo systems. They are also characterized by a stable magnetic field and good corrosion resistance. As a result, they are highly suitable for spot-welding machines.

Neodymium iron boron (NdFeB) is another rare earth permanent magnetic material for Samarium cobalt (SmCo) magnets. It is one of the most powerful magnets available today. But they are extremely expensive due to the cost of raw materials. In addition, their operating temperature is limited to about 80 degrees C. These magnets are not oxidation-resistant, and their coercivity is relatively low.

SmCo magnets are especially suitable for use in spot-welding machines. They can also be used in various applications with temperatures up to 350 deg C. Despite their great thermal stability, SmCo magnets are relatively expensive to manufacture. So, it is a good idea to look for cheaper alternatives when working with these magnets.

NdFeB pot magnets are available in a variety of forms. Those with a permanent magnet core are commonly referred to as round magnets. Moreover, they can be asymmetric or rectangular, and the shapes can be flat or U-form. Depending on the application, they can be used for holding thin metal sheets or for simple handling.

Shallow pot magnets have a magnetic core of samarium-cobalt or neodymium. They have a steel or stainless steel housing, and a non-magnetic separating layer that creates a shielded system. The magnetic core is protected by a rubber protective jacket. This increases the coefficient of friction, and doubles the magnet's shear force. Other versions of shallow pot magnets are characterized by threaded pins or internal threads.

Norelem disc magnets are also produced. These magnets are made from neodymium and aluminum, and they are screwed down.

Source:https://i.pinimg.com

Ceramic

A study of the effect of magnetic materials on the magnetic strength of NdFeB as well as Neodymium magnets pot magnets was conducted. The results showed that the properties of the materials vary due to different microstructures. This variation is also reflected in their mechanical properties.

Magnetic strength of the Nd-Fe-B pot magnets was measured in two ways. One was the bending strength of the material. Another was the permeability coefficient. It is a ratio of the permeability of the specific medium to free space.

To improve the corrosion resistance of the Nd-Fe-B magnets, a coating technique was applied. In this process, a coating of copper was applied to the surface of the sintered magnet.

After applying this coating, the surface of the sintered magnet was observed using the scanning electron microscope. Corrosion morphology was also evaluated.

The study concluded that the higher grade of the material showed classical eddy currents, while the lower grade showed hysteresis losses. The weight loss of the magnet was also determined after brushing off corrosion products.

The temperature coefficient was found to be nearly unchanged after the addition of Mg. Moreover, the corrosion current density was lower in the magnets with the addition of Mg.

The intrinsic coercive force was found to be 17 kOe for the magnets with the larger particles. In contrast, the distribution of the Nd-rich phase was homogenous for the smaller ones.

These findings suggest that the distribution of the Nd-rich phase is influenced by the size of the particles. For the large particles, the Nd-rich phase is distributed at triple junctions. However, the small ones exhibit isotropic grains on the c-plane side.

An electrochemical method was then used to evaluate the corrosion resistance of the magnets. The results showed that the corrosion rate of the Nd-Fe-B was slower than the constant humid-heat test.

These results suggest that the temperature stabilization technique may be beneficial in removing irreversible flux losses. Further, the corrosion resistance of the Nd-Fe-B can be improved by the double coating protection technique. Finally, the study suggests that the corrosion resistance of the sintered magnets can be compared to those of commercial superconducting wire.

Irreversible flux loss

NdFeB pot magnets have remarkable magnetic properties. However, they are prone to corrosion. Several factors may contribute to the corrosion process. Some studies have attempted to improve corrosion resistance. Among these are: reducing corrosion current density and improving humidity-heat resistance. In addition, coatings on the magnets have also been tried.

The reversible temperature coefficient describes the loss of flux density with temperature changes. The magnitude of the coefficient depends on the temperature. Higher values indicate better temperature stability.

Inductive and residual magnetism are important properties of magnets. Generally, magnets with a large B-H value have a stronger magnetizing force. Similarly, a high BHmax means a small magnet is required for application.

For pressless processed fine grained Nd-Fe-B sintered magnets, backscattered electron images led to the identification of four different types of Nd-rich phases. These phases have different microstructures, which can be observed by scanning electron microscopy.

Corrosion-heat resistance of the Nd-Fe-B magnets has been improved through the partial substitution of Dy for Nd. A scanning electron microscope equipped with energy dispersive x-ray analysis system was used to study the corrosion process and to identify the microstructure of the magnet.

The results of this study reveal that the magnetic and mechanical properties of the magnets vary, mainly because of the presence of several phases at grain boundaries. There are two major groups of Nd-Fe-B magnets: radial magnets and the non-radial types. Radial magnets are particularly unique because their morphologies differ from that of the non-radial magnets.

An interesting aspect of this study is that the remanent field strength BR remains, despite the fact that Weiss domains have not returned to their original state. This indicates that demagnetization of a magnet is reversible.

Another significant result of this study was that the microstructure of the magnets consisting of larger particles showed a higher coercivity. Magnets with a broader range of particle size have a higher magnetic saturation, which is the maximum magnetic energy that can be stored in the magnet. Moreover, it was noted that the distribution of the Nd-rich phase at triple junctions has become homogenous, a prerequisite for the development of a high coercivity.

Curie temperature

When a magnet is heated up to the Curie Temperature, it loses its ferromagnetism. This process is called demagnetization. At this point, the magnet cannot be remagnetized.

The intrinsic coercive force of sintered Nd-Fe-B magnets is increased with increasing annealing temperatures. However, this increase is accompanied by a decrease in its maximum usable temperature for Bonded NdFeB magnets.

The influence of sintering temperatures on the magnetic properties of sintered Nd-Fe-B pot magnets is complex. They were investigated using the Kerr microscopy. High grade material showed hysteresis losses, whereas low grade material had classical eddy currents. Moreover, the remanence point of these two magnets were found to be different.

In order to increase humidity-heat resistance of these magnets, minor Co was added. These results are interesting. Besides, phosphorous Nd at grain boundaries showed passivation pretreatments.

However, these findings are not consistent with calculations. Consequently, the effect of the microstructure on the mechanical properties was considered to be more sensitive than the magnetic properties.

Another interesting finding is the presence of different phases at the grain boundaries of these magnets. This is believed to be related to the heterogeneity of these magnets.

It is important to note that in order to maintain the high magnetic coercivity of these magnets, homogeneous distribution of the Nd-rich phase is essential. Four types of Nd-rich phases were identified through backscattered electron images.

It has been shown that the optimum magnetic properties of the sintered Nd-Fe-B are obtained at 540 AdegC. The coercivity of this material is 17 kOe.

This study shows that the Nd-rich phase distribution at the triple junctions becomes homogeneous with the increase in the particle size. Moreover, the surface of these magnets shows multiple domain grains.

Therefore, the Nd-rich phase is easily oxidized. These magnets have poor corrosion resistance. Nevertheless, the presence of the rare-earth rich phases has facilitated their use in several applications.

A general mechanism of corrosion of these magnets is attributed to the presence of different phases at the grain boundaries. Furthermore, a coating may be required in very harsh environments.

In addition, the corrosion potential of the magnets with higher Mg additions is higher. The resulting corrosion current density is lower.