When it comes to thermal materials in our daily life, most people think of metal materials for the first time, because most metal materials are excellent conductors of heat. This paper mainly introduces the current mainstream non-high thermal metal materials, especially various non-metal thermal materials dominated by oxides.
At present, the most widely used non-metal thermal conductive materials are aluminum oxide (AL2O3), silicon oxide, zinc oxide, aluminum nitride, boron nitride, silicon carbide, graphite, etc. In the industries of electronic circuits and thermally conductive polymer materials, micro-alumina and silicon micro-powders are the main bodies, nano-alumina and nitrides are used as filling powders in the field of high thermal conductivity; while zinc oxide is mostly used as thermal paste (thermal grease) For filling.
The following is a list of thermal conductivity of some non-metallic materials (this table is the measured value under the same conditions, the test value of the same material will be different in different environments):
|Name||Conductivity (W/MK)||Name||Conductivity (W/MK)||Name||Conductivity (W/MK)|
|GaAs||46||Medium Density Silicone||0.17||Pure Copper||401|
|Beryllium oxide||270||PP+25% glass fiber||0.25||Cast iron||42~90|
|Boron nitride||125||Glass||0.5~1.0||Cement sand||0.9~1.25|
|Zinc Oxide||29||Foam||0.045||Stainless Steel||17|
The following is a brief introduction to the advantages and disadvantages of several commonly used non-metallic thermally conductive materials:
Advantages: The thermal conductivity is very high, the thermal expansion coefficient is small, and it is a good heat-resistant thermal shock material. At present, it is mostly used as a heat exchanger material for high temperature structural parts. The thermal conductivity of single crystal can be as high as 275 W/M·K
Disadvantages: Expensive, usually more than 150$ per kilogram. After the aluminum nitride absorbs moisture, it will react with water and hydrolyze AlN+3H20=Al(OH)3+NH3. The Al(OH)3 generated by the hydrolysis will interrupt the thermal conduction path, thereby affecting the transfer of phonons, so it is made into products. The thermal conductivity is low. Even with silane coupling agent for surface treatment, 100% filler surface coverage cannot be guaranteed. Simply using aluminum nitride can achieve high thermal conductivity, but the viscosity of the system increases greatly, which severely limits the application field of the product.
Boron Nitride (BN)
Advantages: Excellent thermal conductivity and stable properties. BN not only its structure but also its properties are very similar to graphite, and it is white, so it is commonly known as: white graphite. The hardness is second only to diamond, and it is a superhard material.
Disadvantages: The price is relatively high, and the market price ranges from tens of dollars to thousands of dollars (depending on the quality of the product). Although the use of boron nitride can achieve high thermal conductivity, similar to aluminum nitride, a large amount of filling The viscosity of the post-system is greatly increased, which seriously limits the application field of the product. I heard that some foreign manufacturers produce spherical BN, which has large particle size, small specific surface area, high filling rate, not easy to increase viscosity, and extremely high price.
Advantages: Silicon carbide (SiC) is made from raw materials such as quartz sand, petroleum coke (or coal coke), and wood chips (salt is required to produce green silicon carbide) through high temperature smelting in a resistance furnace. Good oxidation resistance and stable chemical properties.
Disadvantages: The carbon and graphite produced in the synthesis process are difficult to remove, resulting in low product purity and high electrical conductivity, which are not suitable for electronic glue. The density is high, and it is easy to precipitate and stratify in the silicone rubber, which affects the application of the product. It is more suitable for epoxy glue.
Advantages: The most stable phase of all aluminas. The crystal size distribution is uniform, the purity is high, and the dispersion is high. It has a low specific surface and is inert to high temperature. Affordable.
Disadvantages: Low addition amount. In liquid silica gel, the maximum addition amount of ordinary acicular alumina is generally about 300 parts, and the thermal conductivity of the obtained product is limited.
Advantages: The filling amount is large. In the liquid silica gel, the spherical alumina can be added to a maximum of 600~800 parts, and the obtained product has a high thermal conductivity.
Disadvantages: more expensive, but lower than boron nitride and aluminum nitride.
Zinc oxide (ZnO)
Advantages: Good particle size and uniformity, suitable as a raw material for the production of thermal grease.
Disadvantages: Low thermal conductivity, not suitable for producing high thermal conductivity products; light weight, strong viscosity, not suitable for potting.
Quartz Powder (Crystalline)
Advantages: High density, suitable for potting; low price, suitable for mass filling, reducing cost.
Disadvantages: Low thermal conductivity, not suitable for the production of high thermal conductivity products. Density is higher and delamination may occur.
Through the above detailed description, you should know that different fillers have their own characteristics. When choosing fillers, you should make full use of the advantages of each filler, and use several fillers for mixed use to play a synergistic effect, which can not only achieve high thermal conductivity, but also Effectively reduce costs, while ensuring the compatibility of fillers and polymers.