Silicon carbide (SiC) heating elements are the workhorse of industrial high-temperature furnaces up to roughly…
MoSi2 Heating Elements: Complete Specs, Grades & Selection
MoSi2 Heating Elements: Complete Specs, Grades & Selection
Molybdenum disilicide (MoSi2) heating elements are the standard choice when a furnace has to run hot — really hot. If you are spec’ing a new furnace or replacing worn elements, the single most useful thing is a clean spec sheet you can actually compare against your process. This guide pulls together the grades, diameters, surface-load limits and selection rules we use every day at HeatingDriver, so you can pick the right element instead of guessing.
If you are new to the material itself, start with our introduction to MoSi2 heating elements first — this page is about the numbers.
Temperature grades: EQ1700, EQ1800, EQ1850
MoSi2 melts at about 2030°C, but the element is not run at its melting point. Instead, manufacturers rate elements by the maximum continuous element temperature in air. HeatingDriver supplies three production grades:
| Grade | Max element temp (air) | Furnace chamber temp | Typical use |
|---|---|---|---|
| EQ1700 | 1700°C | up to ~1650°C | General high-temp firing, ceramics, heat treatment |
| EQ1800 | 1800°C | up to ~1750°C | Dental zirconia sintering, technical ceramics, glass |
| EQ1850 | 1850°C | up to ~1800°C | Lab research, advanced materials, highest-temperature needs |
The grade you need is set by the hottest temperature your chamber must hold, not the peak it hits for a few minutes. Always leave a margin: choose EQ1800 if your process sits at 1700°C, so the element is never at its limit.
Diameter and size options
MoSi2 elements are made as a hot zone (thin, high-resistance) and cold ends (thicker, low-resistance) joined into a U. The diameter pair is written as hot / cold in mm:
| Hot / cold diameter | Surface area | Common application |
|---|---|---|
| Φ3/6 | Smallest | Compact furnaces, low-power zones, dental units |
| Φ4/9 | Small | Dental sintering furnaces (e.g. Sirona HTC Infire), small chambers |
| Φ6/12 | Medium | General box/tube furnaces, most common size |
| Φ9/18 | Large | High-power furnaces, large chambers, fast heat-up |
See our Φ6/12 U-type elements and Φ4/9 elements for dental sintering furnaces. Shank space (the cold-end spacing) is chosen to match your furnace wall thickness and terminal layout.
Surface load (W/cm²) limits
“Surface load” is the power per unit heated area. It is the real limiter on life: too high and the element runs too hot locally. Approximate maxima for the heated zone:
| Element temp | Φ3/6 | Φ4/9 | Φ6/12 | Φ9/18 |
|---|---|---|---|---|
| 1700°C | ~10 | ~12 | ~14 | ~16 W/cm² |
| 1800°C | ~8 | ~9 | ~11 | ~13 W/cm² |
| 1850°C | ~6 | ~7 | ~8 | ~10 W/cm² |
These are planning values. The exact number for your geometry comes from the element datasheet, and we confirm it during ordering. Lower surface load = longer life, so when in doubt, go one size up.
Current, resistance and the cold-start rule
MoSi2 has a positive temperature coefficient: its resistance is low when cold and rises sharply as it heats. A Φ6/12 element is typically rated near 170 A at working temperature. Because the cold resistance is only a fraction of the hot resistance, switching full mains voltage straight onto a cold element causes a large inrush current that can damage terminals and the element.
The standard fix is the 1/3-voltage start: bring the element up on roughly one-third of rated voltage, let it heat into its high-resistance state, then ramp to full. Most modern controllers handle this automatically. We cover the procedure in our maintenance and lifespan guide.
How to select the right element
- Temperature: pick the grade by your hold temperature + margin (EQ1700 / EQ1800 / EQ1850).
- Atmosphere: air and oxidising are ideal; reducing gases cut the usable limit (see our atmosphere notes).
- Power: size the diameter so surface load stays in the table above.
- Fit: match the U-bend reach, leg length and shank space to your furnace drawing.
- Quantity: because of the PTC behaviour, new and old elements can share a circuit and self-balance current.
Why HeatingDriver
We have supplied MoSi2 and SiC elements to dental, ceramics and research labs for nearly 20 years, with no minimum order (1 piece) and Industry 4.0 fast turnaround. Every element is matched to your furnace drawing before it ships.
Related guides
- Molybdenum disilicide heating elements
- Silicon carbide heating elements
- MoSi2 vs SiC heating elements guide
- W-type MoSi2 heating elements
- Silicon carbide heating elements complete guide
Why specify with HeatingDriver
Why specify with HeatingDriver — HeatingDriver is a manufacturer and exporter of MoSi2 (molybdenum disilicide) heating elements with nearly 20 years of experience. We supply EQ1700U / EQ1800U / EQ1850U grades for 1700–1850°C, free drawing review, custom sizes and shapes, and technical support for furnace builders worldwide. Browse our MoSi2 heating elements.
What are the main MoSi2 temperature grades?
The main grades are EQ1700U (1700°C), EQ1800U (1800°C) and EQ1850U (1850°C), each matched to a furnace temperature range.
What diameters are standard for MoSi2 elements?
Common hot-zone/cold-end diameter series include Φ 3/6, Φ 4/9, Φ 6/12, Φ 9/18 and larger, selected by power and furnace size.
How is surface load specified?
MoSi2 elements are typically rated at 4–9 W/cm² surface load, chosen with furnace volume and atmosphere.
What atmosphere is required?
MoSi2 needs an oxidising atmosphere (air/oxygen); the protective silica layer forms only there, so vacuum is not recommended.
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