Aluminum nitride (AlN) possesses extremely high theoretical thermal conductivity (~320 W/(m·K)), excellent electrical insulation, low dielectric loss, and a coefficient of thermal expansion matching semiconductor materials. Whether as an ideal material for high-power chip packaging substrates, a core functional filler in thermally conductive greases and gels, or precision ceramic components operating in harsh environments, AlN continues to push performance boundaries. However, AlN powder is highly susceptible to hydrolysis, producing oxygen-containing impurities (e.g., γ-AlOOH, Al(OH)₃, γ-Al₂O₃), which significantly reduce powder purity and degrade the thermal conductivity of final products. More critically, the hydrolysis products directly hinder the development and application of water‑based forming processes for AlN ceramics (e.g., tape casting, gelcasting). Therefore, as the application scenarios of AlN expand-especially the increasing need for contact with high‑humidity environments and aqueous systems-improving the anti‑hydrolysis stability of AlN powder has become a core technical bottleneck to ensure reliable realization of its outstanding properties.
Hydrolysis Mechanism of Aluminum Nitride
Limited by current production processes and environmental sensitivity, the industrial production of high‑purity AlN powder remains challenging. First, when AlN contacts water, hydroxyl groups (–OH) from water molecules interact with nitrogen (N) and aluminum (Al) in AlN, disrupting the crystal structure and forming amorphous intermediate products (AlOOH) and NH₃. The released NH₃ further reacts with water to form ammonium (NH₄⁺) and hydroxide ions (OH⁻), and the exothermic nature raises the system's temperature and alkalinity (pH > 9), facilitating subsequent reactions. Under certain temperatures and alkaline conditions, amorphous AlOOH further reacts with water to produce Al(OH)₃. Ultimately, AlN completely hydrolyzes to Al(OH)₃ and NH₃.
It is noteworthy that this hydrolysis process is not limited to direct contact between AlN powder and liquid water. Exposure to air can also induce hydrolysis by adsorbing atmospheric moisture. Moreover, defects on the AlN particle surface or the presence of other impurities significantly catalyze the hydrolysis reaction. Therefore, surface modification is required to reduce the chemical activity of the powder surface toward water.
Anti‑Hydrolysis Modification Technologies for Aluminum Nitride
To address the hydrolysis issue of AlN, two main modification strategies exist: thermal treatment and surface modification. Surface modification is further divided into inorganic and organic approaches.
01 Thermal Treatment
This method involves high‑temperature treatment of AlN powder under a specific atmosphere, controlling oxygen content, temperature, and oxidation time to form a dense Al₂O₃ film on the surface as a physical barrier, thereby improving the powder's hydrolysis resistance to some extent. Although this method is simple and low‑cost, its core drawback is that the inevitable introduction of Al₂O₃ phase during thermal treatment significantly degrades key properties such as the thermal conductivity of the final AlN ceramics. Thus, it is not considered an ideal anti‑hydrolysis route for high‑quality AlN storage and application.
02 Inorganic Surface Modification
Inorganic surface modification mainly uses inorganic acids such as H₂SiO₃ or H₃PO₄ to protect AlN, forming a thin film‑like layer on the surface that suppresses hydrolysis in solution. Generally, the solubility of the formed film greatly influences the hydrolysis behavior. For example, aluminum silicate has very low solubility in both hot and cold water, while aluminum phosphate has higher solubility in hot water. Therefore, at elevated temperatures, the anti‑hydrolysis effect of H₂SiO₃ is significantly better than that of H₃PO₄. Furthermore, the effectiveness of this modification is related to the particle size of AlN powder. Smaller particles possess higher surface activity and stronger adsorption capacity for inorganic acids, leading to a more pronounced anti‑hydrolysis effect. For larger particles, the coating effect is less effective than for small‑sized ones, so smaller sizes are preferred. In addition to inorganic acid washing, treatment with an Al(H₂PO₄)₃ solution allows phosphate anions to form at least a monolayer of phosphate on the AlN particle surface, preventing water ingress. Hence, using a single high‑temperature Al(H₂PO₄)₃ solution treatment, or combining it with inorganic acid washing, is also an effective anti‑hydrolysis modification approach. Inorganically surface‑modified AlN exhibits good hydrolysis resistance and low cost, making it a practical and promising treatment method.
03 Organic Surface Modification
Organic surface modification typically uses hydrophobic long‑chain organic molecules to coat the AlN powder surface or to perform in‑situ polymerization, thereby preventing water molecules from contacting the AlN surface and thus improving hydrolysis resistance. This approach features simple processing, short treatment time, and significant modification effects, while also improving the dispersibility of AlN powder in liquid suspensions to some extent. Commonly used organic modifiers include organic carboxylic acids and stearic acid. The carboxyl groups in such organic acids can interact and react with hydroxyl groups on the AlN surface, covering the AlN surface with a long organic chain that forms an effective waterproof layer. Additionally, coupling agents-additives that improve interfacial properties between inorganic and organic materials-contain both hydrophilic and hydrophobic groups. The hydrophobic group chemically reacts with or has good compatibility with organic materials, while the hydrophilic group can form chemical bonds with inorganic materials. When used as modifiers for AlN, the hydrophilic group bonds to the AlN surface, while the hydrophobic group is exposed on the AlN surface, imparting hydrophobicity and thus preventing direct contact between water and the AlN surface, thereby improving hydrolysis resistance. However, because organic materials generally have poor thermal stability, this technique has certain limitations in application.