​Production of Ultra-Fine Aluminum Oxide Using Zirconia Oxidation via Ball Milling Method

Ultra-fine aluminum oxide possesses excellent properties such as high-temperature resistance, corrosion resistance, abrasion resistance, high strength, high hardness, large surface area, and good insulation. It finds widespread applications in areas like bioceramics, surface protective coatings, chemical catalysts, integrated circuit chips, aerospace, infrared-absorbing materials, and humidity-sensitive sensors. Ball milling is a common and cost-effective method for producing ultra-fine aluminum oxide powder. This chapter explores the preparation of ultra-fine aluminum oxide powder using an industrial-grade aluminum oxide as the starting material and varying the size of zirconia balls through a ball milling process. An orthogonal experimental design is used to investigate the impact of ball milling time, ball-to-material ratio, milling speed, and grinding aids on particle size.

Experimental ReagentsThe specifications and sources of the reagents used in the experiments are listed in Table 2.1. Zirconia balls of various sizes (10mm, 6mm, 4mm, 2mm) were employed as grinding media, as shown in Figure 2.1.

Experimental InstrumentsThe primary instruments used in the experiments and their sources are detailed in Table 2.2.

Experimental Procedure(1) Determination of Zirconia Ball RatiosIndustrial-grade aluminum oxide with an average particle size of 79.26µm (7g) was combined with zirconia balls (28g) in an alumina milling jar. The ball-to-material ratio was set at 4:1, milling speed at 500r/min, and milling time at 30min in a planetary ball mill. Different sizes of zirconia balls (10mm, 6mm, 4mm, 2mm) were used to investigate the resulting particle size.

(2) Orthogonal ExperimentsTo investigate the impact of milling time, milling speed, and ball-to-material ratio on particle size, 7g of industrial-grade aluminum oxide (average particle size: 79.26μm) was milled with 4mm and 2mm zirconia balls (mass ratio 1:3) in an alumina milling jar, following specified conditions. The orthogonal experimental factor levels are shown in Table 2.3.

(3) Wet Ball Milling7g of industrial-grade aluminum oxide with an average particle size of 79.26μm was milled with 4mm and 2mm zirconia balls (mass ratio 1:3) in an alumina milling jar. Milling conditions included a milling time of 30min, milling speed of 500r/min, and a ball-to-material ratio of 6:1 in a planetary ball mill. The influence of grinding aids on particle size and morphology was investigated by varying the amount of grinding aid added.

Experimental Characterization(1) Scanning Electron Microscopy (SEM)Microscopic morphology of aluminum oxide powder was examined using a TM3000 scanning electron microscope produced by Hitachi under standard conditions with an accelerating voltage of 15kV.

(2) Laser Diffraction Particle Size AnalysisParticle size analysis of milled powders under different process conditions was performed using a BT-9300S laser particle size analyzer produced by Dandong Bait Instrument Co., Ltd. The analysis provided data on median particle size, particle size distribution, and specific surface area. Testing conditions included a measurement range of 0.1-716μm, repeatability error <1%, light obscuration range of 10-15%, and water as the dispersant. Three measurements were taken, and the average results were recorded.

Experimental Results and Discussion(2.3.1) Influence of Zirconia Ball Size on ProductThe impact of zirconia ball size on product was examined under various conditions. Before milling, industrial-grade aluminum oxide powder exhibited a narrow particle size distribution, with an average particle size of 79.26µm. After milling with zirconia balls of different sizes (10mm, 6mm, 4mm, 2mm) under specific conditions (milling speed: 500r/min, milling time: 30min, ball-to-material ratio: 4:1), the particle size distribution of the resulting powder widened, and particle sizes decreased significantly. However, when zirconia ball size decreased further to 2mm, the particle size tended to stabilize due to reduced impact force. The smallest median particle size of 11.41µm was achieved using 4mm zirconia balls.

(2) Influence of Two Zirconia Ball RatiosUnder constant milling conditions (milling speed: 500r/min, milling time: 30min, ball-to-material ratio: 4:1), using a combination of 4mm and 2mm zirconia balls produced powder with a narrower particle size distribution and smaller median particle size (10.66µm) compared to using 4mm balls alone (11.41µm).

(3) Influence of Three Zirconia Ball RatiosWhen three different zirconia ball sizes were used for milling under specific conditions (milling speed: 500r/min, milling time: 30min, ball-to-material ratio: 4:1), the resulting powder exhibited a narrow particle size distribution and smaller median particle size (68.09µm) using 10mm, 4mm, and 2mm zirconia balls. This indicates effective particle disaggregation and dispersion.

In conclusion, the choice of zirconia ball size and ratio significantly influences the particle size and distribution of the milled aluminum oxide powder, affecting its suitability for various applications.