Effect of ball size and powder loading on the milling efficiency of a laboratory-scale wet ball mill

Alumina powder was wet-milled by zirconia balls with varying diameter at varying rotation speed, and the resultant particle size of the milled powder was analyzed. At a given rotation speed, there exists an optimum ball size to yield minimum particle size of alumina. The optimum ball diameter decreases as the rotation speed increases. This result has been interpreted in light of the competition between the reduced kinetic energy of the smaller balls (a negative source for milling efficiency) and the increased number of contact points of the smaller balls (a positive source), which yields the optimum ball diameter at an intermediate size. As the rotation speed increases, kinetic energy of the balls increases, which, in turn, shifts the optimum ball size toward a smaller value. As the powder loading increases from 1 to 35 g at a given rotation speed and ball size, the milling efficiency decreases monotonically.     

Effect of ball milling treatment on the microstructures and properties of Cr2AlC powders and hot pressed bulk ceramics

Ball milling was used on synthesized Cr₂AlC powders, and dense Cr₂AlC bulk ceramics with almost pure phase were fabricated by hot pressing these ball milled Cr₂AlC powders at 1300 °C for 2 h under 30 MPa. The phase compositions and the microstructures of powders and bulk ceramics were characterized. The mechanical properties and dislocation analysis of bulk ceramics were also investigated. Our results indicated that the grain size of powders became uniform and smaller after ball milling, which was also inherited in the bulk ceramics. Moreover, the mechanical properties of hot pressed Cr₂AlC ceramics, including flexural strength, fracture toughness, and Vickers hardness, significantly increased by using ball milled powders treated at speed 200 rpm. The organization of hexagonal dislocation networks during hot pressing and reduction of grain size both had a positive effect on improving mechanical properties.     

Bi-directional freeze casting of porous alumina ceramics: A study of the effects of different processing parameters on microstructure

Highly aligned lamellar ceramic scaffolds were produced using a bi-directional freeze casting technique. A specially designed, sloped copper mould was covered with a polymer to modulate the temperature field. Effects of different processing parameters (cooling rate, mould slope angle, ceramic solid loading and binder concentration) on lamellar orientation were systematically studied. The results showed that freezing under a dual temperature gradient produced highly aligned ceramic scaffolds. Increasing both the cooling rate and the mould slope angle increased the size of the ordered ceramic region. Using different alumina solid loadings in the initial suspension had little effect on the aligned lamellar structure. Increasing the binder concentration affected ice crystal growth in a highly aligned direction. Therefore, freeze casting using a dual temperature gradient can be used to fabricate highly aligned porous materials.     

Parameter effects on wet ultrafine grinding of limestone through slurry rheology in a stirred media mill

Wet ultra-fine grinding of a limestone powder (< 100 μm) has been investigated in a stirred media mill with respect to the effect of slurry rheology. The grinding results obtained by various parameters (i.e., molecular weight of a dispersant, solids concentration, additive dosage, addition method and beads load) are evaluated in terms of energy efficiency and the fineness of a product. A polymeric dispersant called Dispersant S40 with a molecular weight of 5500 gives the best grinding results. For a certain level of beads load, an optimal solids concentration exists. In the case of the additive dosage of Dispersant S40 at 0.1 wt.% or more, a smaller additive amount of Dispersant S40 gives a higher energy efficiency and a smaller median size at a lower level of specific energy input. However, the excessive amount of the dispersant could cause a cushion layer formed on milling beads and thus lowers stress intensities from the collisions of milling beads, leading to an inefficient milling operation. This can be avoided by either the multi-point addition of the dispersant or a higher beads load (≥ 83 vol.%). In addition, it was found that the higher the beads load, the better the cumulative energy efficiency, and the smaller the product size at the same specific energy consumption. For a given solids concentration, the relationships between the specific surface area and the particle size of an FP product and the additive amount of Dispersant S40 are explored, respectively. Furthermore, an empirical particle size-energy model provides a good fit (R² > 0.991) to the grinding results under the experimental conditions investigated.     

The effects of ball milling time on the rheological,optical, and microstructural properties of YAG transparent ceramics

Stable slurries dispersed mixture of commercial Al₂O₃ and Y₂O₃ powders, ammonium poly meta acrylate (Dolapix CE64) as the dispersant, and tetraethyl orthosilicate (TEOS) as the sintering aid were prepared by ball milling process. The effects of the milling time on the fabrication of transparent polycrystalline yttrium aluminum garnet (YAG) ceramics were investigated by slip casting and vacuum sintering. The results showed that the best milling time for the deagglomeration of the powder mixture was 16 hours and the slurry prepared during this time showed a near-Newtonian behavior due to the better deagglomeration and lower viscosity. X-ray patterns also showed that all samples were pure YAG phase. The results also revealed that the sample prepared by 16 hours ball milling time suspensions exhibited higher relative green and final density, as well as the maximum transmittance at 1064 nm (≈ 77%). These samples had a more uniform microstructure too.     

Effect of milling method and time on the properties and electrochemical performance of LiFePO4/C composites prepared by ball milling and thermal treatment

Effects of ball milling way and time on the phase formation, particulate morphology, carbon content, and consequent electrode performance of LiFePO₄/C composite, prepared by high-energy ball milling of Li₂CO₃, NH₄H₂PO₄, FeC₂O₄ raw materials with citric acid as organic carbon source followed by thermal treatment, were investigated. Three ball milling ways and five different milling durations varied from 0 to 8 h were compared. LiFePO₄/C composites could be obtained from all synthesis processes. TEM examinations demonstrated LiFePO₄/C from ball milling in acetone resulted in sphere shape grains with a size of ∼60 nm, similar size was observed for LiFePO₄/C from dry ball milling but in a more irregular shape. The ball milling in benzene resulted in a much larger size of ∼250 nm. The LiFePO₄/C composites prepared from dry ball milling and ball milling in acetone showed much better electrochemical performance than that from ball milling in benzene. SEM examinations and BET measurements demonstrated that the high-energy ball milling effectively reduced the grain size. A ball milling for 4 h resulted in the best electrochemical performance, likely due to the proper amount of carbon and proper carbon structure were created.