Concentration and temperature both essential:
🔬 Sulfuric Acid Compatibility vs. Diaphragm Materials
1. Low Concentration (<30%)
Corrosion behavior: Highly aggressive due to strong ionization
Recommended materials:
PTFE (Teflon-lined diaphragm)
Hastelloy C-276
Why: Dilute sulfuric acid is often more corrosive than concentrated acid
2. Medium Concentration (30–70%)
Corrosion behavior: Still aggressive, especially with rising temperature
Recommended materials:
Hastelloy C-276
Tantalum (excellent but costly)
Caution: Standard stainless steel (316L) may fail quickly
3. High Concentration (>70%)
Corrosion behavior: Becomes less reactive at lower temperatures due to passivation
Recommended materials:
316L Stainless Steel (only if temperature is low and stable)
Alloy 20
Key risk: Corrosion rate increases sharply with temperature rise
🌡️ Temperature Matters—A Lot
Even compatible materials can fail if temperature increases
Example:
98% H₂SO₄ at ambient temperature → 316L may work
98% H₂SO₄ at >80°C → Severe corrosion risk → upgrade to Tantalum or PTFE-lined solution
⚙️ Practical Selection Tips
✔ For strong corrosion + uncertainty → Go with PTFE-lined diaphragm seals
✔ For high-end reliability → Tantalum is almost universal for sulfuric acid
✔ Avoid “borderline selections” based on lab data only—real processes fluctuate
💡 Final Thought
In corrosive applications like sulfuric acid, process variation (temperature swings, dilution, impurities) is often the hidden failure driver—not just nominal conditions.
Choosing the right diaphragm material is not about meeting specs—it’s about surviving reality.
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