Alumina slurry, as a key material, plays an irreplaceable role in numerous cutting-edge fields. From high-frequency circuit boards in electronic substrates to abrasives, refractory materials, and transparent ceramics like sapphire windows, alumina slurry is ubiquitous. Its performance directly impacts the quality and performance of these products.
However, dispersion challenges have long plagued the industry during the preparation and use of alumina slurry. For example, α-Al₂O₃ particles have a rich surface rich in hydroxyl groups. These hydroxyl groups readily interact through hydrogen bonds, forming hard agglomerates. These agglomerates are extremely stable, making them difficult to effectively disaggregate using traditional stirring methods. The direct consequence is a significant increase in the slurry's viscosity and poor fluidity. In processes like tape casting, this can lead to significant variations in green body thickness, severely impacting product consistency. More critically, after sintering, the presence of agglomerates results in uneven density and significantly increased porosity. For electronic substrates, this reduces thermal conductivity and affects heat dissipation. For transparent ceramics, increased porosity severely impairs light transmittance, making them unable to meet the demanding requirements of optical applications.
Fortunately, the emergence of ultrasonic technology offers hope for resolving this challenge. When ultrasonic waves propagate through liquid media, they produce a unique cavitation effect. This cavitation instantaneously generates shock waves with pressures reaching thousands of atmospheres and powerful shear forces. This energy precisely targets micron-sized agglomerates, breaking them apart. After ultrasonic treatment, alumina particles are successfully dispersed to submicron or even nanometer levels, uniformly suspended in the slurry. This change is evident in a significant reduction in slurry viscosity. For example, at a solids content of 50%, the slurry viscosity can be significantly reduced from over 10,000 cP to less than 3,000 cP. Furthermore, the thickness deviation of tape-cast green bodies can be controlled to less than 5%, significantly improving the quality of the finished product.
In addition to breaking up agglomerates, ultrasonic waves also have a positive effect on the sintering process of alumina slurries. Ultrasonic dispersion results in a uniform slurry with significantly improved density after sintering. Due to the uniform particle dispersion, porosity can be reduced by 30%-50%. In electronic substrates, this allows thermal conductivity to approach theoretical values, significantly improving heat dissipation efficiency and ensuring stable operation of electronic devices. For transparent ceramics, such as (Y,Gd)₂O₃:Eu scintillating ceramics, ultrasonic dispersion can achieve a transmittance exceeding 80%, achieving high transparency and meeting the requirements of high-end optics.
Ultrasonic technology, with its significant advantages in breaking down agglomerates and promoting sintering, provides a powerful boost to improving the performance of alumina slurries. With the continuous advancement of technology, we believe that ultrasonic technology will play an even more important role in alumina slurries and related fields, driving the industry forward.
