Materials Science · 2024-02-20 · 6 min read
What Is Borosilicate Glass?
Borosilicate glass is a type of glass that contains boron trioxide (B₂O₃) as a key component, typically 12-15% by weight. The most common industrial grade is borosilicate 3.3, which refers to its coefficient of thermal expansion of 3.3 × 10⁻⁶/K.
Key Properties
Low Thermal Expansion
The most important property of borosilicate glass is its low coefficient of thermal expansion (CTE) of 3.3 × 10⁻⁶/K, compared to 9 × 10⁻⁶/K for soda-lime glass. This means borosilicate glass expands much less when heated, making it highly resistant to thermal shock.
Chemical Resistance
Borosilicate glass offers excellent resistance to most chemicals, including:
- Acids (except hydrofluoric acid)
- Alkalis at moderate concentrations
- Water and steam
- Most organic solvents
High Temperature Performance
Borosilicate glass can withstand continuous operating temperatures up to 500°C, with short-term exposure up to 600°C.
Optical Clarity
High optical clarity allows accurate visual inspection of liquid levels and process media.
Why DIN Standards Specify Borosilicate Glass
DIN 7081 (reflex gauge glass) and DIN 7080 (flat gauge glass) both specify borosilicate glass 3.3 as the required material. This is because:
- **Safety** — Low thermal expansion reduces risk of glass failure due to thermal cycling
- **Reliability** — Chemical resistance ensures long service life in aggressive environments
- **Accuracy** — Optical clarity enables precise level readings
Borosilicate vs. Soda-Lime Glass
| Property | Borosilicate 3.3 | Soda-Lime |
|---|---|---|
| CTE (×10⁻⁶/K) | 3.3 | 9.0 |
| Max Temperature | 500°C | 300°C |
| Chemical Resistance | Excellent | Good |
| Thermal Shock | Excellent | Poor |
| Cost | Higher | Lower |
Conclusion
For industrial gauge glass applications, borosilicate glass 3.3 is the clear choice. Its combination of thermal stability, chemical resistance, and optical clarity makes it the safest and most reliable material for level measurement in demanding industrial environments.