# Caustic soda: Characteristics

Why rayon and battery makers check salt and iron

Source page: https://www.materialinsights.org/chemicals/caustic_soda/characteristics/

What this tab covers The physical and chemical properties that set its grade, price and uses, with the commercial grades and the standards that define them.

Caustic is traded on a dry metric tonne (dmt, 100% NaOH) basis whether sold as 32%, 50% solution or 98% flake. Salt, chlorate and iron content matter to rayon, food, pharmaceutical and battery users. Membrane-grade caustic commands a small premium over diaphragm-grade.

#### Properties that matter commercially

| Property | Value / specification | Why it matters | Source |
|---|---|---|---|
| **Concentration** | liquid 48-50% or 32%; flakes 98-99% | sets freight cost and handling | IS 252 (indicative) |
| **Sodium chloride** | membrane grade below about 0.01%; diaphragm grade about 1% | chloride corrodes equipment and spoils rayon and battery uses | indicative |
| **Freezing point** | about 12 C for 50% solution | requires heated storage and tanks | standard property |

#### Commercial grades

- Rayon grade (low salt, low iron) for viscose
- Membrane grade 50% lye
- Diaphragm grade 50% lye
- Flakes and prills 98-99%
- Food and pharma grade

## Other sections

- [Summary](https://www.materialinsights.org/chemicals/caustic_soda/index.md)
- [Overview](https://www.materialinsights.org/chemicals/caustic_soda/overview/index.md)
- [Correlation](https://www.materialinsights.org/chemicals/caustic_soda/correlation/index.md)
- [Production route](https://www.materialinsights.org/chemicals/caustic_soda/routes/index.md)
- [Production](https://www.materialinsights.org/chemicals/caustic_soda/production/index.md)
- [Feedstocks](https://www.materialinsights.org/chemicals/caustic_soda/feedstocks/index.md)
- [Cycles](https://www.materialinsights.org/chemicals/caustic_soda/cycles/index.md)
- [Trading](https://www.materialinsights.org/chemicals/caustic_soda/trading/index.md)
- [Movement](https://www.materialinsights.org/chemicals/caustic_soda/movement/index.md)
- [Regulation](https://www.materialinsights.org/chemicals/caustic_soda/regulation/index.md)
- [Emissions](https://www.materialinsights.org/chemicals/caustic_soda/emissions/index.md)
- [Relationships](https://www.materialinsights.org/chemicals/caustic_soda/links/index.md)