Application of spherical magnesium oxide in the field of heat conduction

Magnesium oxide (MgO) is a very widely used chemical material.

Generally, magnesium oxide is a flaky crystal, but some special morphology of magnesium oxide has been found to be very effective in many aspects

↑↑Spherical magnesium oxide

Type of thermally conductive filler

The thermal conductivity of high molecular polymer materials is generally low.

Thermally conductive fillers are mainly divided into three types: carbon-based materials, metallic materials and non-metallic inorganic materials.

1.

The thermal conductivity of some carbon-based materials is significantly higher than that of metallic materials and inorganic non-metallic materials.

↑↑Graphite thermal conductive sheet

2.

Metal materials are recognized as good conductors of heat.

However, the density of metal materials is relatively large, and it is difficult to mix them uniformly with polymer materials, which restricts its application in polymer materials and thermally conductive fillers

3.
Inorganic non-metallic materials

Inorganic non-metals mainly rely on phonons to conduct heat.
Generally, the thermal conductivity is lower than that of carbon-based materials and metal materials, but they have better insulation
.
Divided into metal nitride and a metal oxide, metal nitride fillers include: BN, AlN and the like; a metal oxide filler comprising: MgO, Al203 and the like
.

Among them, the nitride exists in the form of crystals, the structure is regular and compact, and the resistance of phonons to propagate in the crystal is small, so the heat can be transferred more effectively
.
But the higher the purity of the nitride, the higher the price
.
Although metal oxides have low thermal conductivity, they are cheap and have a wide range of materials, so they are widely used
.

The most commonly used oxides are alumina and magnesia.
The thermal conductivity of alumina is relatively low, but the cost is not high, so it is widely used
.
Although the thermal conductivity of magnesia is lower than that of boron nitride, it is higher than alumina, 36W/m·K, and the cost is lower, so the application of thermally conductive filler has attracted more and more attention
.

The influence of different filler morphology on thermal conductivity

Generally, rod-shaped and sheet-shaped structural fillers with a certain aspect ratio are easier to form a thermally conductive network chain in the polymer material, thereby improving the thermal conductivity of the composite material, but such fillers will be oriented during processing.
That is, the rod-shaped structure has different directions, which will cause anisotropy in the thermal conductivity of the composite material, and the thermal conductivity in the processing direction is much higher than the thermal conductivity in the vertical processing direction
.

↑↑Flake filler

Therefore, when designing and producing the shape of the filler product, try to make the filler orientation direction consistent, so as to improve the thermal conductivity of the composite material
.

In contrast, due to the isotropy of the spherical structure, the spherical filler has more advantages in improving the thermal conductivity of the composite material than the rod-shaped or sheet-shaped structure
.
At the same time, the particle size of the spherical powder is small and uniform, the surface morphology is regular, and the bulk density of the powder is significantly increased, which can greatly improve the fluidity and dispersibility of the powder and minimize the impact of agglomeration.
The defects inside the powder are improved
.

Development status of spherical magnesium oxide

For spherical magnesium oxide products, due to the application of high-performance chip technology, the technology of spheroidization of magnesium oxide is highly confidential in foreign countries.
International procurement of products is difficult, and complete technical parameters and professional manufacturing equipment of the products cannot be obtained
.
According to relevant literature reports, currently only a few technologically developed countries such as Japan, the United States, and Israel have mastered the synthetic manufacturing technology of this product in the world
.

Physical and chemical methods of powder spheroidization

▲▲▲

At present, spherical magnesium oxide is mainly prepared by two methods:

1) Using magnesium salt as a raw material, a precursor for preparing spherical magnesium oxide is first obtained, and the precursor is heat-treated to obtain spherical magnesium oxide.
Generally, the precursor is spherical basic magnesium carbonate or spherical magnesium hydroxide or spherical basic magnesium oxalate
.

2) After mixing the magnesium oxide powder with the solvent and the binder, the spherical magnesium oxide is obtained by mechanical molding, and the spherical magnesium oxide product is obtained after heat treatment
.

However, in the exploration of industrialization, the spheroidization of magnesium oxide is more dependent on the accumulation of technology based on spherical alumina and spherical silica powder.
On a global scale, Denka is currently at the forefront, and there are also some domestic spherical powder companies in the process.
Production line layout
.
It is believed that with the boom in emerging markets such as 5G and new energy vehicles, spherical magnesia, which is regarded as the “next-generation thermally conductive filler” connected to baseball-shaped alumina, can also be mass-produced as soon as possible to realize localized substitution and start large-scale production.
Application promotion
.