Steatite · grade
Steatite C-221
Properties of the C-221 condition, compared with the other Steatite tempers.
Pick when RF/VHF loss matters: alkali content is minimised so the 1 MHz loss tangent is roughly half that of C-220.
What is Steatite C-221?
Steatite C-221 is Steatite in the C-221 grade — pick when RF/VHF loss matters: alkali content is minimised so the 1 MHz loss tangent is roughly half that of C-220. Steatite C-221 has a tensile strength of 60 MPa (8.7 ksi), weaker than 64% of ceramic grades. Elongation at break is 0% and the elastic modulus is 105 GPa (15.2 Msi). Steatite C-221 has a density of 2.8 g/cm³ (0.101 lb/in³), lighter than 79% of ceramic grades. It melts at 1,450°C (2,642 °F). As Fired is the default condition FabDigit quotes; C-221 is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 94% of ceramic grades
- Lightweight — 2.8 g/cm³ (0.101 lb/in³), better than 79% of ceramic grades
Limitations
- Poor heat conductor — 2.6 W/m·K (1.5 BTU/hr·ft·°F), worse than 80% of ceramic grades
- Hard to polish — 60/100, worse than 80% of ceramic grades
Steatite C-221 properties
Typical room-temperature values for Steatite C-221 — 12 properties are specific to this condition; the rest are grade-level values shared by every Steatite temper. Each bar shows where the value sits among the ceramic grades in FabDigit's library — further right is higher.
Physical3
Steatite C-221 has a density of 2.8 g/cm³ (0.101 lb/in³), lighter than 79% of ceramic grades. It melts at 1,450°C (2,642 °F).
Mechanical12
Steatite C-221 has a tensile strength of 60 MPa (8.7 ksi), weaker than 64% of ceramic grades. Elongation at break is 0% and the elastic modulus is 105 GPa (15.2 Msi).
Thermal5
Steatite C-221 is rated for continuous service to 1,050°C (1,922 °F). It conducts heat at 2.6 W/m·K (1.5 BTU/hr·ft·°F), worse than 80% of ceramic grades. Thermal expansion is 8 µm/m·K (4.44 µin/in·°F).
Electrical5
Steatite C-221 is an electrical insulator with a dielectric strength of 12 kV/mm (304.8 V/mil) and a resistivity of 1×10¹³ Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (87/100), better than 74% of ceramic grades.
Sustainability4
Producing a kilogram of Steatite C-221 takes about 27 MJ of energy and emits 1.9 kg of CO₂ — less than 95% of ceramic grades. Typical recycled content is 2%.
Manufacturability3
Steatite C-221's machinability is not recommended (8/100, better than 70% of ceramic grades).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Steatite tempers and conditions
Steatite is also supplied in 2 other conditions. The full side-by-side table is on the Steatite overview.
- As FiredDefaultStandard dense, zero-porosity steatite as fired — general-purpose low-cost HF insulator and heater/terminal component.60 MPa tensile
- POROUSPick for wire-wound resistor cores, bobbins and burner parts where open porosity aids cement bonding and thermal-shock survival, and strength is secondary.20 MPa tensile
- C-221Pick when RF/VHF loss matters: alkali content is minimised so the 1 MHz loss tangent is roughly half that of C-220.680 HV
Working with Steatite C-221
Is Steatite easy to machine?
Machine in the green/bisque state (drill, turn, mill dry with carbide) allowing ~10–14 % firing shrinkage; fired parts require diamond grinding, lapping or laser/ultrasonic drilling.
Can Steatite be welded?
Not weldable — join by glass frit, ceramic cement, active-metal or Mo-Mn metallizing plus brazing, or mechanical clamping with compliant gaskets.
Can Steatite be formed, bent or molded?
Dry-pressed, isostatically pressed, extruded (tubes/rods) or injection/wet-pressed from talc–clay–flux batches, then fired at 1250–1350 °C; the vitrification window is narrow (~±20 °C), so temperature uniformity controls warpage and porosity.
What surface finishes work on Steatite?
Fired surface is naturally smooth and can be glazed for tracking resistance; ground/lapped for flatness, and Mo-Mn or thick-film Ag metallizing is used for solderable/brazable pads.
Steatite 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 |
|---|---|---|
| SiO2from talc + clay | 55 – 65 | 61 |
| MgOprotoenstatite former | 25 – 32 | 29 |
| Al2O3clay addition | 2 – 8 | 5 |
| BaOflux; BaCO3 used in low-loss C-221 instead of alkali feldspar | 0 – 6 | 3 |
| CaO | 0 – 2 | 0.7 |
| Na2O+K2Okept <0.5 % in low-loss C-221 | 0 – 2 | 0.5 |
| Fe2O3impurity | 0 – 1 | 0.3 |
Steatite C-221 — frequently asked
What is Steatite C-221 used for?
Steatite C-221 is typically used for electrical insulators and bushings, heater coil supports, terminal blocks and fuse bodies, thermostat and switch insulating parts, lamp holders and sockets and extruded insulating tubes and beads. In short: low-cost electrical porcelain.
What is the tensile strength of Steatite C-221?
Steatite C-221 has a typical tensile strength of 60 MPa (8.7 ksi) — weaker than 64% of ceramic grades. Strength varies by condition: see the 3 listed tempers.
Is Steatite C-221 easy to machine?
Not especially — machinability is rated not recommended (8/100, better than 70% of ceramic grades). Machine in the green/bisque state (drill, turn, mill dry with carbide) allowing ~10–14 % firing shrinkage; fired parts require diamond grinding, lapping or laser/ultrasonic drilling.
Can Steatite C-221 be welded?
Not weldable — join by glass frit, ceramic cement, active-metal or Mo-Mn metallizing plus brazing, or mechanical clamping with compliant gaskets.
What surface finishes work on Steatite C-221?
Fired surface is naturally smooth and can be glazed for tracking resistance; ground/lapped for flatness, and Mo-Mn or thick-film Ag metallizing is used for solderable/brazable pads.
Can Steatite C-221 be formed, bent or molded?
Dry-pressed, isostatically pressed, extruded (tubes/rods) or injection/wet-pressed from talc–clay–flux batches, then fired at 1250–1350 °C; the vitrification window is narrow (~±20 °C), so temperature uniformity controls warpage and porosity.
What is the maximum service temperature of Steatite C-221?
Steatite C-221 is rated for continuous use to about 1,050°C (1,922 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in Steatite C-221?
Yes — Steatite C-221 is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM D116 — Standard Test Methods for Vitrified Ceramic Materials for Electrical Applications (grades C-220, C-221) — ASTM International (2016)
- ASM Engineered Materials Handbook, Vol. 4: Ceramics and Glasses — ASM International (1991)
- Steatite technical ceramic property sheets — CoorsTek / CeramTec / Kyocera (2023)
- Technical ceramics property tables (steatite, magnesium silicate) — MatWeb (2024)
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.