Mullite
Mullite is an aluminosilicate ceramic offering good high-temperature strength, low thermal expansion and creep resistance, supplied here in the C-610, C-620 and POR conditions of the silicate ceramic family.
Reference datasheet — Mullite is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the C-620 condition
Mullite tempers and conditions
Mullite is supplied in 3 conditions, soft to hard. C-620 is the default FabDigit quotes; the values on this page are for it.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Mullite/aluminous porcelain, 50–65 % Al₂O₃ | Lower-alumina, glass-bonded mullite body: cheapest, good electrical insulation and thermal shock, but lower strength and creep limit — insulators, burner parts, kiln furniture to ~1300 °C. | 60 | 850 HV | 3 W/m·K | ||
C-620Default Dense sintered mullite, 65–80 % Al₂O₃ | Standard engineering mullite near stoichiometric 3Al₂O₃·2SiO₂ — best combination of high-temperature strength, creep resistance and thermal-shock life for protection tubes and furnace components. | 80 | 1,100 HV | 5 W/m·K | ||
Porous mullite refractory | Choose for insulating and thermal-shock-cycled refractory shapes where low weight and high spalling resistance matter more than strength. | 2 W/m·K |
What is Mullite?
Mullite is an aluminosilicate ceramic offering good high-temperature strength, low thermal expansion and creep resistance, supplied here in the C-610, C-620 and POR conditions of the silicate ceramic family. It is chosen for furnace and refractory hardware where dimensional stability under thermal cycling matters, and is produced as slip-cast shapes, extruded tubes, pressed blocks and injection-moulded parts. Typical values are density 2.9 g/cm³, tensile strength 80 MPa, elastic modulus 150 GPa, thermal conductivity 5 W/m·K and service to 1550 °C, with a corrosion resistance score of 80. Strength and hardness are well below alumina or ZTA, and the material is not weldable and only diamond-machinable after firing. Mullite has a density of 2.9 g/cm³ (0.105 lb/in³), lighter than 76% of ceramic grades. It melts at 1,840°C (3,344 °F). Mullite has a tensile strength of 80 MPa (11.6 ksi), weaker than 53% of ceramic grades. Elongation at break is 0% and the elastic modulus is 150 GPa (21.8 Msi).
What is Mullite used for?
- kiln furniture
- refractory linings
- thermocouple protection tubes
- high-temp insulators
- burner nozzles
Advantages
- Low embodied carbon — 3.2 kg CO₂/kg, better than 84% of ceramic grades
- High service temperature — 1,550°C (2,822 °F), better than 83% of ceramic grades
- Lightweight — 2.9 g/cm³ (0.105 lb/in³), better than 76% of ceramic grades
Limitations
- Hard to polish — 60/100, worse than 79% of ceramic grades
Mullite properties
Typical room-temperature values for Mullite-C-620; bars are the position among ceramic grades.
Physical4
Mullite has a density of 2.9 g/cm³ (0.105 lb/in³), lighter than 76% of ceramic grades. It melts at 1,840°C (3,344 °F).
Mechanical13
Mullite has a tensile strength of 80 MPa (11.6 ksi), weaker than 53% of ceramic grades. Elongation at break is 0% and the elastic modulus is 150 GPa (21.8 Msi).
Thermal5
Mullite is rated for continuous service to 1,550°C (2,822 °F). It conducts heat at 5 W/m·K (2.89 BTU/hr·ft·°F), worse than 62% of ceramic grades. Thermal expansion is 4.5 µm/m·K (2.5 µin/in·°F).
Electrical5
Mullite is an electrical insulator with a dielectric strength of 12 kV/mm (304.8 V/mil) and a resistivity of 1×10¹² Ω·m.
Chemical & Environmental2
Corrosion resistance is very good (80/100), better than 56% of ceramic grades.
Sustainability4
Producing a kilogram of Mullite takes about 45 MJ of energy and emits 3.2 kg of CO₂ — less than 84% of ceramic grades. Typical recycled content is 5%.
Manufacturability3
Mullite's machinability is not recommended (5/100, worse than 59% of ceramic grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the ceramic family
Yield strength against density for every ceramic grade FabDigit runs. Mullite is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Mullite
Is Mullite easy to machine?
Green/bisque machining is preferred; after firing only diamond grinding, lapping or laser/ultrasonic machining — allow ~1–2 % firing shrinkage tolerance.
Can Mullite be welded?
Not weldable; join by glass frit, active-metal brazing (Ti/Ag-Cu) or ceramic cements rated for the service temperature.
Can Mullite be formed, bent or molded?
Slip casting, extrusion (tubes), isostatic or dry pressing and injection moulding, then sintering at 1550–1750 °C; large sections need slow burnout to avoid cracking.
Mullite chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Al2O3stoichiometric 3Al2O3·2SiO2 = 71.8 % Al2O3 | 65 – 80 | 71.8 |
| TiO2from bauxite/kyanite raw materials | ≤ 1.5 | 0.4 |
| Fe2O3 | ≤ 1.5 | 0.5 |
| CaO+MgOfluxes; lower is better for creep | ≤ 1 | 0.3 |
| K2O+Na2Oalkalis degrade high-temperature strength | ≤ 0.8 | 0.2 |
| SiO2balance, part as glassy phase | ≥ 19 (balance) |
What surface finishes work on Mullite?
As-fired surfaces can be glazed for gas-tightness; ground/lapped surfaces reach Ra ≈ 0.2–0.4 µm, metallising (Mo-Mn) possible for hermetic seals.
Equivalent designations
Standards and trade names that resolve to Mullite in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Also called
- 3Al2O3-2SiO2
How much does Mullite cost?
Mullite is a premium-cost ceramic ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Mullite — frequently asked
What is Mullite used for?
Mullite is typically used for kiln furniture, refractory linings, thermocouple protection tubes, high-temp insulators and burner nozzles. In short: low-expansion high-temperature ceramic; creep-resistant kiln furniture body; 1550 °C service capability.
What is the tensile strength of Mullite?
Mullite has a typical tensile strength of 80 MPa (11.6 ksi) — weaker than 53% of ceramic grades. Strength varies by condition: see the 3 listed tempers.
Is Mullite easy to machine?
Not especially — machinability is rated not recommended (5/100, worse than 59% of ceramic grades). Green/bisque machining is preferred; after firing only diamond grinding, lapping or laser/ultrasonic machining — allow ~1–2 % firing shrinkage tolerance.
Can Mullite be welded?
Not weldable; join by glass frit, active-metal brazing (Ti/Ag-Cu) or ceramic cements rated for the service temperature.
What surface finishes work on Mullite?
As-fired surfaces can be glazed for gas-tightness; ground/lapped surfaces reach Ra ≈ 0.2–0.4 µm, metallising (Mo-Mn) possible for hermetic seals.
Can Mullite be formed, bent or molded?
Slip casting, extrusion (tubes), isostatic or dry pressing and injection moulding, then sintering at 1550–1750 °C; large sections need slow burnout to avoid cracking.
What is the maximum service temperature of Mullite?
Mullite is rated for continuous use to about 1,550°C (2,822 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does Mullite cost?
Mullite is a premium-cost ceramic ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- IEC 60672-3 Ceramic and glass insulating materials — Part 3: Specifications for individual materials — IEC (1997)
- Engineered Materials Handbook Vol. 4: Ceramics and Glasses — ASM International (1991)
- Refractories Handbook (mullite and high-alumina refractories) — CRC Press (2004)
- Technical ceramics material data (mullite / silicate ceramics) — CoorsTek / Kyocera / Ceramtec (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.