HUANG Huichao ¹, LI Kaiqin ², ZHA Yue ¹, SHI Hua ², HUANG Wenlong ²,

LAI Dongsheng ², LIU Guihua ³, YANG Yulong ³, CHANG Qibing ³, FU Ling ²

(1. Ceramic Research Institute of Light Industry of China, Jingdezhen 333000, Jiangxi, China; 2. Jingdezhen Jinghua Special Ceramic Co., Ltd., Jingdezhen 333403, Jiangxi, China; 3. Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended abstract:

[Background and purposes] Alumina ceramics are widely applied in critical fields, including electronic information, aerospace and high-end equipment manufacturing, owing to their excellent high-temperature stability, wear resistance and dielectric properties. Dry pressing has become the mainstream forming technology for alumina ceramics, due to its high machining precision, simple operation, low equipment requirement and high production efficiency. However, this method still faces two core bottlenecks: insufficient green body strength and high incidence of mold adhesion and corner breakage during forming, which severely restrict product yield and production continuity. Single-component binders commonly used in existing studies tend to cause uneven atomization, nozzle clogging and particle agglomeration during spraying drying, thus further leading to defects, such as closed pores and cracks during sintering. Although polyethylene glycol (PEG) and hydroxypropyl methyl cellulose (HPMC) have shown potential in improving powder lubricity and granulation quality, the synergistic effect of composite additive system combined with spraying drying and dry pressing process remains insufficiently studied. This study was aimed to systematically optimize the composite binder formulation, spraying pressure and forming parameters, to enhance the green body strength of alumina ceramics, eliminate mold adhesion and corner damage and provide technical support for the large-scale production of high-performance alumina ceramics.

[Methods] α-Al₂O₃ powder was used as the raw material, with polyvinyl alcohol (PVA), starch, PEG2000 and HPMC as composite additives. An L9(3⁴) orthogonal experiment was employed to study the effects of PVA (0.7–1.3 wt.%), starch (0.8–2.0 wt.%) and PEG2000 (0.3–0.9 wt.%) on flexural strength of the green bodies, so as to optimize the optimal binder formulation. The slurry was mixed by using planetary ball milling, granulated by pressure spray dryer and then formed into green bodies through dry pressing. The effects of spraying pressure (2.00–4.25 MPa) and forming pressure (8–18 MPa) on powder morphology, green body microstructure and mechanical properties were systematically studied. Flexural strength of the green bodies and sintered bodies was tested by using the three-point bending method, microstructure of the granulated powder and green body was characterized by using scanning electron microscope (SEM), and the moisture content, bulk density, tap density and water absorption of samples were measured.

[Results] Range analysis of the orthogonal experiment showed that PEG2000 and starch had stronger influence on green body strength than PVA. The optimal composite binder formulation was 1.3 wt.% PVA, 2.0 wt.% starch, 0.9 wt.% PEG2000 and 0.3 wt.% HPMC. The optimal spraying pressure was 3.5 MPa, under which the alumina powder obtained a Hausner ratio of 1.145. The green body strength was positively correlated with forming pressure in the range of 8–14 MPa, reaching the peak value of 2.90 MPa at the optimal forming pressure of 14 MPa. Excessive forming pressure over 14 MPa caused internal cracks in the green body, due to elastic after effect, leading to strength reduction. After sintering at 1700 ℃, the optimized sample achieved a flexural strength of 320 MPa, along with lower firing shrinkage (13.60%), lower water absorption (0.02%) and higher bulk density (3.68 g·cm⁻³).

[Conclusions] A synergistic optimization strategy of composite additive system, spray drying and dry pressing process for high-performance alumina ceramics was established. The optimized composite binder system effectively eliminated mold adhesion, while significantly improving the green body strength. 3.5 MPa spray pressure endowed the powder with excellent fluidity and compact granule structure, while 16 MPa forming pressure achieves the optimal balance between green body density, strength and structural integrity. The optimized process not only solved the common industry problems of low green body strength and high defect concentration in dry pressing of alumina ceramics, but also significantly improved the mechanical properties and densification of sintered bodies, providing a reliable theoretical basis and technical route for the large-scale industrial production of high-performance alumina ceramics.

Key words: alumina ceramics; dry pressing; spaying drying; green body strength