Mullite C-620
Grade · default condition
C-620 = 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.
Values for the C-620 condition
Other Mullite tempers and conditions
Mullite is listed in 3 conditions; see the grade overview at Mullite.
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-620DefaultThis page 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 C-620?
Mullite C-620 is Mullite in the C-620 grade — 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. Mullite C-620 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). Mullite C-620 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).
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 C-620 properties
Typical room-temperature values for Mullite C-620; 14 are specific to this condition. Other listed values are Mullite reference data and may not represent this condition. Bars are the position among ceramic grades.
Physical4
Mullite C-620 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 C-620 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 C-620 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 C-620 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 C-620 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 C-620's machinability is not recommended (5/100, worse than 59% of ceramic grades).
Common Calculations4
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Mullite C-620
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.
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.
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) | — |
Mullite C-620 — frequently asked
What is Mullite C-620 used for?
Mullite C-620 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 C-620?
Mullite C-620 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 C-620 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 C-620 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 C-620?
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 C-620 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 C-620?
Mullite C-620 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.