In this study, a process is developed for 3D printing with alumina (Al₂O₃). First, a photocurable slurry made from nanoparticle Al₂O₃ powder is mixed with hexanediol diacrylate binder and phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide photoinitiator. The optimum solid content of Al₂O₃ is determined by measuring the rheological properties of the slurry. Then, green bodies of Al₂O₃ with different photoinitiator contents and UV exposure times are fabricated with a digital light processing (DLP) 3D printer. The dimensional accuracy of the printed Al₂O₃ green bodies and the number of defects are evaluated by carefully measuring the samples and imaging them with a scanning electron microscope. The optimum photoinitiator content and exposure time are 0.5 wt% and 0.8 s, respectively. These results show that Al₂O₃ products of various sizes and shapes can be fabricated by DLP 3D printing.

Rare earth magnets are the strongest type of permanent magnets and are integral to the high tech industry, particularly in clean energies, such as electric vehicle motors and wind turbine generators. However, the cost of rare earth materials and the imbalance in supply and demand still remain big problems to solve for permanent magnet related industries. Thus, a magnet with abundant elements and moderate magnetic performance is required to replace rare-earth magnets. Recently, a”-Fe₁₆N₂ has attracted considerable attention as a promising candidate for next-generation non-rare-earth permanent magnets due to its gigantic magnetization (3.23 T). Also, metastable a”-Fe₁₆N₂ exhibits high tetragonality (c/a = 1.1) by interstitial introduction of N atoms, leading to a high magnetocrystalline anisotropy constant (K₁ = 1.0MJ/m³). In addition, Fe has a large amount of reserves on the Earth compared to other magnetic materials, leading to low cost of raw materials and manufacturing for industrial production. In this paper, we review the synthetic methods of metastable a”-Fe₁₆N₂ with film, powder and bulk form and discuss the approaches to enhance magnetocrystalline anisotropy of a”-Fe₁₆N₂. Future research prospects are also offered with patent trends observed thus far.

In this study, the effect of the content of MgO-CaO-Al₂O₃-SiO₂ (MCAS) glass additives on the properties of AlN ceramics is investigated. Dilatometric analysis and isothermal sintering for AlN compacts with MCAS contents varying between 5 and 20 wt% are carried out at temperatures ranging up to 1600°C. The results showed that the shrinkage of the AlN specimens increases with increasing MCAS content, and that full densification can be obtained irrespective of the MCAS content. Moreover, properties of the AlN-MCAS specimens such as microhardness, thermal conductivity, dielectric constant, and dielectric loss are analyzed. Microhardness and thermal conductivity decrease with increasing MCAS content. An acceptable candidate for AlN application is obtained: an AlN-MCAS composite with a thermal conductivity over 70 W/m·K and a dielectric loss tangent (tan δ) below 0.6 × 10⁻³, with up to 10 wt% MCAS content.

In this study, MgO–CaO–Al₂O₃–SiO₂ (MCAS) nanocomposite glass powder having a mean particle size of 50 nm and a specific surface area of 40 m²/g is used as a sintering additive for AlN ceramics. Densification behaviors and thermal properties of AlN with 5 wt% MCAS nano-glass additive are investigated. Dilatometric analysis and isothermal sintering of AlN-5wt% MCAS compact demonstrates that the shrinkage of the AlN specimen increases significantly above 1,300°C via liquid phase sintering of MCAS additive, and complete densification could be achieved after sintering at 1,600°C, which is a reduction in sintering temperature by 200°C compared to conventional AlN-Y₂O₃ systems. The MCAS glass phase is satisfactorily distributed between AlN particles after sintering at 1,600°C, existing as an amorphous secondary phase. The AlN specimen attained a thermal conductivity of 82.6 W/m·K at 1,600°C.

Citations

Citations to this article as recorded by  

• Effect of MgO-CaO-Al₂O₃-SiO₂ Glass Additive Content on Properties of Aluminum Nitride Ceramics
  Kyung Min Kim, Su-Hyun Baik, Sung-Soo Ryu
  Journal of Korean Powder Metallurgy Institute.2018; 25(6): 494.     CrossRef