Chinese suppliers including INNOVACERA, Duratec, Yixing Minghao and Tangzi hold stock programmes across these grades, with 95 Al₂O₃ finished parts (balls, substrates, machined bodies) catalogued as the highest-volume SKU and 99.5%+ runs positioned as specials with longer lead times [S1][S4][S5].
Alumina ceramic (aluminium oxide, Al₂O₃) is a sintered oxide ceramic used both as an electrical insulator and as a wear/refractory body; commercial grades are formulated by blending calcined alumina with binders and sintering aids, then firing above 1600 °C to reach theoretical-density bodies that exceed 3.6 g/cm³ in 99% grades and approach 3.9 g/cm³ in 99.7% Al₂O₃ [S1][S3].
The Al₂O₃ purity tier — controlled by raw bauxite, fused-white alumina, or reactive alumina feedstock — directly sets refractoriness: high-alumina brick at ≥75% Al₂O₃ carries a refractoriness rating of 1770 °C or above, while 95%-99.5% Al₂O₃ bodies reach use temperatures in the 1500-1700 °C band depending on load and atmosphere [S2]. For a deeper mechanical-property primer tied to bearing and seal duty, see the alumina ceramic reference page and the broader industrial ceramic overview.
The Decision Matrix: Wear, Electrical, Thermal
Selection starts with the dominant service driver, not the Al₂O₃ number. Wear duty (lining tiles, hydrocyclones, grinding media) prioritises density and hardness, electrical duty (substrates, spark plugs, feedthroughs) prioritises dielectric strength and surface finish, and thermal duty (furnace furniture, refractories) prioritises refractoriness and thermal-shock resistance [S1][S2][S3].
The general rule holds: as Al₂O₃ climbs from 75% to 99.7%, hardness, compressive strength, dielectric resistivity and chemical inertness rise, while thermal-shock tolerance and unit cost move in opposite directions [S1][S3].
Grade-by-Grade Property Bands
95 Al₂O₃ is the workhorse: density typically 3.6-3.7 g/cm³, hardness around 9 on Mohs, volume resistivity in the 10¹⁴ Ω·cm range at room temperature, dielectric strength commonly cited at 10-15 kV/mm, and a flexural strength band near 300-350 MPa — a balanced mechanical/electrical package that Chinese finishing shops including Yixing Minghao list as their largest catalogue line [S1][S5].
96% Al₂O₃ is the legacy thick-film substrate grade, valued for a smoother as-fired surface (Ra typically below 0.5 µm) and a thermal conductivity near 24-28 W/(m·K), which supports metallisation adhesion for hybrid circuits [S3]. 99% and 99.5% Al₂O₃ push density toward 3.85-3.92 g/cm³, hardness to roughly 9 on the Mohs scale, and dielectric strength above 15 kV/mm, with flexural strength reaching the 350-400 MPa band, which makes them the default for semiconductor insulators, dense mechanical seals, and high-purity feedthroughs [S1][S3].
Comparison Table: 75 / 95 / 96 / 99 / 99.5+ Al₂O₃ Grades
Five commercial bands compared on four decision criteria, drawn from supplier data: [S1]
Decision criteria: Refractoriness / use temperature; typical density; dielectric strength; dominant application.
75% Al₂O₃ (high-alumina brick, refractory): refractoriness ≥1770 °C; density typically 2.5-2.7 g/cm³ for fired brick; dielectric data not the design driver; furnace linings, ladle linings, kiln furniture [S2].
95% Al₂O₃ (general industrial): use temperature roughly 1500-1600 °C; density 3.6-3.7 g/cm³; dielectric strength 10-15 kV/mm; wear tiles, pump/cyclone liners, electrical insulators, ceramic balls [S1][S5].
96% Al₂O₃ (thick-film substrate): use temperature roughly 1500-1650 °C; density near 3.7 g/cm³; smooth as-fired surface; hybrid-circuit substrates, resistor networks [S3].
99% Al₂O₃ (high-purity insulator): use temperature roughly 1600-1700 °C; density 3.85-3.9 g/cm³; dielectric strength above 15 kV/mm; high-voltage insulators, feedthroughs [S1][S3].
99.5%-99.7% Al₂O₃ (semi/special): use temperature approaching 1700 °C; density up to 3.95 g/cm³; lowest dielectric loss; semiconductor chamber parts, dense mechanical seals [S1].
Specification Levers Beyond the Al₂O₃ Number
Three specification levers shift price and lead time as much as the grade itself. Surface finish: as-fired, ground, or polished — polishing for seal faces and bearings can add 20-30% to finished cost and gate 2-3 weeks onto lead time [S1][S5].
Tolerance: pressed-and-sintered bodies land at ±1% on linear dimension; tight-tolerance parts (for example, mechanical seal rings and ball-valve seats) require post-sinter diamond grinding to ±0.01 mm or better, which is what separates commodity tile stock from engineered components [S1][S4]. For bearing-grade rotating components, see the ceramic bearing reference.
Form factor: thin substrates (sub-0.5 mm) in 96% Al₂O₃ require tape casting rather than dry pressing, which routes the order to a different production line and a different price band than tile or rod stock [S3].
Where Alumina Wins and Where It Loses
Alumina wins in acidic and abrasive service, where hardness above 9 on the Mohs scale and chemical inertness outperform mild steel and most polymer liners, and it wins in electrical insulation duty where its 10¹⁴ Ω·cm class volume resistivity at room temperature and 10-15 kV/mm dielectric strength carry the design [S1][S3].
Alumina loses to zirconia in applications with high thermal cycling and impact risk, because a low fracture toughness (typically 3-4 MPa·m^½ for 95% Al₂O₃) makes it prone to brittle fracture under thermal shock or point loading — for those cases, the zirconia ceramic reference documents the higher-toughness alternative. Alumina also loses to silicon carbide in extreme-temperature abrasive service above the practical use envelope of 95% Al₂O₃.
Sourcing Signals, Mid-2026
Chinese alumina ceramic suppliers — INNOVACERA, Duratec (founded 2005, positioned as a global wear-protection and impact-ceramic supplier), Yixing Minghao, and Tangzi New Material — all show active 2026 product and content updates, with 95 Al₂O₃ machined parts, alumina ceramic balls, and steatite/95% substrate bodies listed as in-stock programmes [S1][S4][S5]. Tangzi's technical notes describe alumina ceramic as a material used in thick-film integrated circuits [S3].
For buyers comparing alumina procurement to other industrial-material supply chains, the Nickel Alloy Price & Cost Guide and the Stainless Steel Price & Cost Guide 2026 lay out the same grade-plus-Moq pricing logic across adjacent material families. For decorative or architectural alumina-based surfaces, see the ceramic tile reference.