I. Origin: Bauxite

Aluminium-bearing minerals and rocks are widely distributed in nature, including bauxite, shale, alunite, nepheline syenite, clay, coal gangue and fly ash. All of these can serve as raw materials for aluminium extraction. However, only bauxite has commercial mining value to date. Bauxite is defined as ore containing gibbsite, boehmite or diaspore as its primary constituents.

Global bauxite reserves are concentrated in Guinea (7.4 Gt), Australia (6.2 Gt), Brazil (2.6 Gt) and Jamaica (2.0 Gt). These four countries account for approximately 65% of the world's total proven reserves of 28 Gt. China has bauxite reserves of 0.98 Gt, distributed mainly across four provinces: Shanxi (41.6%), Guizhou (17.1%), Henan (16.7%) and Guangxi (15.5%).

II. Conversion: Alumina

Alumina extraction from bauxite is an established chemical process. Currently, 95% of global alumina production uses the Bayer process, invented by Austrian engineer Karl Josef Bayer in 1887. The process principle is as follows: concentrated sodium hydroxide solution converts hydrated aluminium oxide in bauxite to sodium aluminate. Upon dilution and addition of aluminium hydroxide seed crystals, aluminium hydroxide re-precipitates. The remaining sodium aluminate solution (mother liquor) is recycled to treat subsequent batches of bauxite.

The main impurities in alumina are silicon, iron and sodium. Some originate from the bauxite ore, while others are introduced during extraction. Sodium is a notable process-derived impurity.

Subsequently, alternative processes have been developed to accommodate varying bauxite grades, including the sintering process and combined Bayer-sintering processes.

Alumina is a critical base material in modern industry. More than 90% of alumina is used as feedstock for aluminium smelting via the Hall-Héroult process (cryolite-alumina molten salt electrolysis) to produce metallic aluminium.

The remaining 10% of alumina is used in specialised applications due to its versatile properties, including ceramics, high-temperature refractories, adsorbents and catalysts, thermal management, and optics.

III. Advancement: Spherical Alumina

The dense crystal structure of α-alumina provides excellent thermal conductivity and electrical insulation. Spheroidised alumina in particular has become a primary material for thermal conduction and dissipation.

Unlike alumina for electrolytic applications, thermal-grade alumina has stricter limits on sodium impurities. Calcined low-sodium alumina (sodium content <300 ppm) is therefore preferred. Via high-temperature flame melting, alumina particles are rapidly melted and contracted into spherical microparticles. Subsequent classification, washing and drying produce spherical alumina products suitable for the electronics industry.

The core technologies in spherical alumina production are powder spheroidisation and control of particle size and ionic impurities. Spheroidisation efficiency directly affects application viscosity. Particle size distribution affects the stability of thermal conductivity in thermal formulations. Ionic impurities interfere with formulation viscosity and reaction behaviour.

Bestry is an early entrant in spherical alumina R&D and focuses on the development and production of high-quality spherical alumina. With mature processes, a broad product portfolio and strong market recognition, Bestry is a reliable supplier of thermal conductive materials.