High Temperature Magnet – The Ultimate Guide

A high-temperature magnet is an elevated version of ordinary magnets improved to retain magnetic properties even at extremely high temperatures. The composition and structure of its magnetic material allow optimal performance at temperatures beyond 100 degrees.

Benefits of High Curie Temperature Magnets

High Temperature Dics Shaped Magnets
High Temperature Dics Shaped Magnets

Magnets have developed to become the cornerstone of most technological and mechanical appliances. However, their application in various devices and environments has been limited by extreme temperature variations.

To overcome this challenge, numerous solutions have been invented to ensure there are powerful magnets with high curie temperature thresholds for hot temperature applications. Their advantages include:

Stability at High Temperatures

Ordinary magnets tend to lose some magnetic properties when operating under extreme heat or beyond their curie temperature point. However, high temperature magnets are specifically engineered to operate under heat without suffering thermal demagnetization. Their magnetic capabilities remain unhinged and this makes them perfect for use in motors and other devices often subjected to heat.

Improved Performance Under Tough Conditions

Most applications that involve the use of magnets are prone to harsh conditions that include extreme heat, dust, and moisture. High curie temperature magnets are manufactured using robust materials to boost tolerance against the said harsh conditions.

For instance, in car motors fitted with typical magnets inefficiencies and premature damage can be experienced due to heat and dust. But by deploying high temperature Alnico magnets with a maximum operating temperature of 525 °C, these challenges are averted.

Energy Efficiency

High-circuit temperature magnets facilitate efficient energy use by reducing the need for coolers. When using typical magnets in hot conditions, cooling systems may be needed and this translates into higher energy bills. However, when using magnets designed for high-temperature uses the need for cooling systems is eliminated resulting in efficient energy use.

Extended Operational Range

Ordinary magnets are likely to become demagnetized when utilized under hot conditions repeatedly. This limits their application fields.

High-temperature magnets, on the contrary, are more accommodating of applications that may be subject to harsher conditions. They can be used in energy-generating industries and automotive industries despite the high temperatures they are exposed to.

Strong Magnetic Field

Materials used to make magnets resistant to hot temperatures are often endowed with strong magnetic properties. They include neodymium, which is rated as the best material for making strong magnets. High-temperature magnets can create independent magnetic fields that are profoundly strong even without electrical energy.

High Curie Points

In addition to demonstrating excellent operating temperatures, these magnets also exhibit unmatched curie temperature points. For instance, Alnico magnets boast of an exemplary curie point at approximately 800°C. This means that the deployment of high-temperature magnets in very hot environments is feasible. It also means that the magnets will continue to provide exceptional services without the risk of demagnetization.

Examples of High-Temperature Magnets

There are varying materials exploited to produce magnets with all kinds of properties. These distinct materials often demonstrate different levels of thermal resistance. However, there are four types of magnets renowned for their high operating temperatures as well as their high curie points.  They are:

High-Temperature SmCo Magnets

High-temperature SmCo magnets are essentially named after the elements they are made from, Samarium and Cobalt.

The Sm1Co5 version of these magnets has a maximum operating temperature of 250°C while the Sm2Co17 version has a maximum operating temperature of 350°C. The curie point of the Sm1Co5 high-temperature magnet is approximately 700°C while the curie point of the Sm2Co17 high-temperature magnet is roughly 800°C.

High Temp SmCo Magnets
High Temp SmCo Magnets

Neodymium High-Temperature Magnets

Also referred to as NdFeB magnets, neodymium magnets exhibit the lowest level of thermal resistance compared to fellow high-temperature magnets. However, their strongest suit lies in their magnetic strength.

Their maximum operating temperature ranges from 80-200°C depending on the grade. High temperature-resistant NdFeB magnets exhibit a maximum operating temperature of 200°C. Their curie temperature is approximately 310-400°C.

NDFeB Magnets
NDFeB Magnets

Alnico High-Temperature Magnets

Alnico magnets are known for their composition, which includes components such as aluminum and cobalt amongst others. When it comes to thermal resistance, they are the most robust.

Alnico high-temperature magnets boast of a maximum operating temperature of roughly 525°C and a curie temperature of approximately 800°C. Owing to these outstanding properties, Alnico magnets have been tremendously exploited in the past and their uses today are mainly centered on high temperature applications.

High Temp Alnico Magnets

High-Temperature Ferrite Magnets

They also go by the name ceramic magnets. Their composition includes iron oxide and traces of metallic elements which give them a maximum operating temperature of 250°C. Higher caps can be obtained if the grade of the material is improved. High-temperature ferrite magnets begin to lose magnetism when the 450°C mark is surpassed.

high temperature Ferrite Magnets
High-temperature Ferrite Magnets

This is their curie point.

Here is a summary of the distinct curie temperatures and maximum operating temperatures of high temperature magnets.

High Temperature Magnet Curie Temperature in (°C) Maximum Operating Temperature in (°C).
Alnico magnet 800°C 525°C
Sm1Co5 magnet

Sm2Co17 magnet

700°C

800°C

250 °C

350°C

Ferret magnet 450°C 250°C
Neodymium magnet 200°C 80-200°C

 

Factors Affecting High Curie Temperature Magnets

Harnessing the true potential of high-temperature magnets is often impeded by numerous factors including;

Material Type and Composition

High temperature magnets can be manufactured using varying ingredients and the composition of these ingredients may also differ. These magnetic materials and their respective compositions exhibit distinct levels of resistance to thermal demagnetization as well as magnetic field strength.

For instance, Alnico magnets demonstrate higher thermal resistance in comparison to neodymium magnets. Neodymium magnets, on the other hand, demonstrate stronger magnetic forces compared to Alnico magnets. To improve thermal resistance, magnetic materials can be injected with additives, which elevate the operating temperature point.

Temperature Stability

Extreme fluctuations of temperature from hot to cold or vice versa can greatly impact the performance of high-temperature magnets. Even though these magnets are uniquely designed to function optimally under high temperatures, exceeding certain points can damage the magnets. Similarly, subjecting the magnets to low temperatures can also lead to reduced effectiveness. For example, at -190°C, Alnico high curie temperature magnets may experience irreversible magnetic losses of up to 10%.

Magnetic Field Strength

If a high-temperature magnet is operating in an environment infiltrated by stronger external magnetic fields, inefficiencies in performance may be experienced. This is because stronger magnetic forces cause disruptions within the magnet domains.

In cases where the external magnetic field is emitting opposing magnetic forces, the high-temperature magnet may end up demagnetized. This is because of the disorientation suffered by the existing magnetic domains.

Mechanical Stress

Exerting physical or mechanical stress on a high curie temperature magnet can result in numerous fatalities. First, the magnet’s strength and resistance to heat may be lost due to the disoriented magnetic domains. Secondly, the high-temperature magnet may suffer permanent damage and 100% demagnetization in case of a fatal breakage.

Design and Manufacturing Techniques

Magnetic materials can be designed distinctly and distinct designs often mean different levels of thermal resistance. Designs can differ in terms of the magnetic domain alignment or the physical design.

Bar magnetisms, for instance, are known for having stronger magnetic capabilities compared to magnetic strips. High temperature magnets with uniformly aligned magnetic domains also exhibit stronger thermal resistance and magnetic force.

Effects of Excessive Temperatures on Magnets

Despite being suited for high-temperature applications; high curie temperature magnets can suffer various kinds of damage when subjected to excessive heat.

Here are the three types of damages a high-temperature magnet is likely to suffer when exposed to extreme temperatures.

Reversible Damage

When a high-temperature magnet suffers reversible damage, it has simply lost certain magnetic properties momentarily. This kind of damage is experienced once a magnet is subjected to slightly extreme temperatures. Upon cooling or the return of optimal temperatures, the magnet regains its optimum magnetic properties.

An excellent example of reversible magnet damage is the magnetic weakening experienced in car motors. The loss is typically occasioned by the heating of the motors as the vehicle moves. The slightly hot temperatures impact the magnet but upon cooling of the motors, the magnets regain their prime magnetic capabilities.

Irreversible Damage

Irreversible damage is experienced once a high-temperature magnet is subjected to hot conditions that supersede its maximum temperature point. However, the heating must be below its curie point.

Irreversible damage means that the magnet does not regain its optimal magnetism after cooling.

To make up for the lost capabilities, demagnetization can be undertaken but this is rarely recommended. This is because remagnetization can be quite expensive. A ceramic magnet with a maximum operating temperature of 250°C and a curie point of 450°C will suffer irreversible loss when exposed to temperatures as high as 300°C.

Permanent Damage

Permanent damage is a consequence of continuous exposure to temperatures well above a magnet’s given curie temperature point. Simply put, the high temperature magnet gets fully demagnetized.

At this point, its magnetic domains are completely disarranged. This can be illustrated by a SmCo high-temperature magnet exposed to temperatures well beyond 900°C over a period of time. Having surpassed its curie point, the magnet will become permanently damaged and cannot be remagnetized.

Applications of High-Temperature Magnets

Heat Resistant Magnets for Oven Doors

Neodymium high-temperature magnets coated with nickel are extensively fitted into oven doors to help keep the doors tightly shut during operation.

Nuclear Reactors

Most nuclear reactors use SmCo high-temperature magnets in their sensors and control rod actuators because of their great thermal stability.

Aerospace

Aircraft and satellites in the aerospace industry rely profoundly on magnets and Alnico high-temperature magnets are the most favored. This is because they have the strongest thermal demagnetization resistance.

Electric Vehicle Motors

Utilizing neodymium magnets in electric vehicle motors results in higher performances and range of the electric motors due to the magnet’s high energy density. They are also immune to the heat generated by the motors.

MRI Machines

High-temperature magnets are also highly depended on in medical equipment like MRI machines because of their robust and stable magnetic properties.

Geothermal Applications

With their high resistivity against high temperatures, high-temperature ferrite magnets are exploited in geothermal power generation systems.

Generators

Alnico magnets are capable of maintaining optimal magnetic even under hot temperatures and this is why they are installed in generators to aid in energy conversion.

FAQs

Is Loss of Magnetization at High Temperature Reversible?

Magnets exposed to high temperatures can lose magnetism at varied degrees; reversible, irreversible, and permanent. Reversible magnetism loss is experienced when a magnet is subjected to slightly hotter temperatures. Irreversible loss is suffered when a magnet is exposed to heat that exceeds its maximum operating temperature. Permanent loss is experienced when a magnet is subjected to extreme heat exceeding the magnet’s maximum operating point as well as curie point.

Can Magnets Handle High Heat?

Yes.

However, it depends on the type and composition of the magnet. High temperature magnets like Alnico, SmCo, and neodymium magnets can handle varied degrees of heat.

However, each magnet has a maximum operating temperature and a curie point, which when bypassed can lead to loss of magnetism.

Is Magnet Curie Temperature the same as Maximum Operating Temperature?

No.

Magnet curie temperature is a point in which a magnet gets demagnetized due to extreme temperatures. Maximum operating temperature, on the other hand, is a point at which the magnet can function reliably.

When a magnet is subjected to heat above its maximum operating temperature, it suffers irreversible damage. However, when the heat surpasses its curie point, it suffers permanent damage.

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