High-purity alumina (HPA) refers to alumina powder materials with a purity of 99.99% or higher. Owing to its excellent optical, electrical, thermal, and mechanical properties, it has become a key basic material supporting the development of modern high-tech industries. From LED lighting and lithium battery separators to semiconductor wafers and high-end optical components, high-purity alumina of different purity grades plays an irreplaceable role.
4N High-Purity Alumina
4N high-purity alumina (purity ≥ 99.99%, total impurity content ≤ 100 ppm). Most of the high-purity alumina finished products produced by domestic enterprises are concentrated at the 4N level and can only be used in mid-to-low-end applications, such as integrated circuit substrates, LED phosphors, polishing micropowders, and alumina ceramics.
Rare-Earth Phosphors
4N high-purity alumina is mainly used in rare-earth trichromatic phosphors, a commonly used luminescent material that plays an important role in lighting and display fields. Rare-earth phosphors are composed of activators and a host matrix; the former are rare-earth elements, and the latter are oxides or salts. In industry, the high-temperature solid-phase synthesis method is the main production process for rare-earth phosphors. For aluminate-based products, high-purity alumina is required.
Integrated Circuit Substrates
Substrates made of 99.99% high-purity α-Al₂O₃ have a stable dielectric constant (10), extremely low loss (tanδ < 0.0002), high thermal conductivity (30 W/(m·K)), and insulation withstand voltage > 10 kV/mm. They are used for substrates and hermetic packaging of high-frequency/high-speed chips and power devices, solving heat dissipation and electrical isolation issues. For example, Routao New Materials uses a chemical method to synthesize high-purity nano-alumina powder with high α-phase content, high purity, good sintering activity, small primary crystallite size, and narrow particle size distribution, with product performance comparable to that of the world's leading Japanese high-purity alumina powder companies. In practical use, thin-film ceramic substrates prepared from this powder have a density of 3.93 g/cm³ and a flexural strength as high as 700 MPa, fully comparable to those of Japan's Kyocera.
Alumina for Lithium Battery Separators
Lithium battery separator ceramic coatings have strict requirements for purity, particle size, morphology, surface modification, and product stability, requiring 4N5 or higher purity and nano-scale high-purity ultrafine alumina. During experimental preparation, process parameters need to be adjusted for different application scenarios. For alumina used in lithium batteries, particular attention should be paid to particle size uniformity and surface characteristics. For instance, the battery-specific nano-alumina CY-L30D produced by Zhejiang Jiupeng New Materials has a particle size controlled at 30 ± 5 nm and a purity of 99.99%; this specification can effectively improve battery energy storage performance and safety performance.
Precision Ceramic Components
Alumina ceramic components meet the strength, precision, electrical properties, and corrosion resistance requirements of wafer manufacturing under special physical environments such as vacuum and high temperature, and play a very important role in the wafer manufacturing process. As integrated circuit manufacturing processes advance toward 3 nm and more advanced nodes, the requirements for alumina ceramic components continue to upgrade, and 4N (≥ 99.99%) or higher ultra-high-purity alumina has become standard for etching-grade components. Taking the ESC support ring as an example, after inferring from the product purity requirement, the purity of the alumina powder used usually needs to reach above 99.95%.
5N High-Purity Alumina
Sapphire Substrates for LEDs
Sapphire single crystals, due to their unique crystal structure, excellent optical properties, and strong mechanical and chemical stability, have been widely used as ideal substrate materials in large-scale integrated circuits and superconducting nanostructured films, and their price is also lower than that of SiN substrates. Since the 1990s, LED lighting has been increasingly adopted as a cold light source, and sapphire has been widely used as a substrate material.
High-purity alumina used to prepare sapphire must have high purity, and the moisture content in the raw material must be very low. When melted at temperatures above 2000 °C, the presence of water can cause oxidation of the molybdenum crucible. For example, the 5N high-purity alumina polycrystalline material produced by Taiyate (Ningxia) New Material Technology Co., Ltd. is the sole raw material for sapphire crystal growth. Its high purity ensures that the final sapphire crystals have excellent light transmittance, high hardness (Mohs hardness up to 9, second only to diamond), and good chemical stability.
Next-Generation Battery Materials
Research by Jinghuang Technology indicates that 5N (99.999%) alumina is suitable for high-voltage (≥ 4.5 V) or long-cycle cathodes (such as nickel-rich NCM811) and solid-state electrolyte modification. Higher purity can reduce interfacial side reactions and improve high-temperature stability; for example, α-Al₂O₃ can achieve a capacity retention of 85.1% after 100 cycles at 45 °C.
In high-tech industries such as solid-state batteries, the purity requirements for alumina are higher and more stringent, requiring ≥ 99.995% purity to reduce interfacial impedance, while the particle size needs to be controlled at the submicron level (0.1–1 μm) to improve ionic conductivity.
Transparent Ceramics
High-purity alumina is an important transparent ceramic material, and one of its uses is the manufacture of high-pressure sodium lamp tubes. High-pressure sodium lamps are electric light sources with very high luminous efficiency. During sodium vapor discharge, temperatures above 1000 °C are generated, and the glass lamp tube cannot withstand the strong corrosion. Only after the advent of high-purity alumina transparent ceramics did high-pressure sodium lamps become practically applicable. The nano-alumina transparent body formed from polycrystalline opaque high-purity nano-alumina (VK-L100G, 99.999%) is used in high-pressure sodium lamp envelopes, with luminous efficiency twice that of mercury lamps, thereby opening up a new way to improve lighting efficiency.
Polishing Abrasives
Nano-alumina polishing slurries require extremely high purity of high-purity alumina, typically 4N (99.99%) or above, while high-end precision polishing (such as semiconductor CMP) requires 5N (99.999%) or above. High-purity nano-alumina has the most stable structure, the highest hardness (Mohs 9), strong chemical inertness, and is insoluble in water, acids, and alkalis. It is suitable for grinding and rough polishing of ultra-hard substrates such as sapphire and silicon carbide, providing a high removal rate.