Type 1 ultrapure water is so pure that it is actually corrosive to some materials. This is because ultrapure water has an extremely high resistivity (typically 18.2 megohm-cm at 25°C) and lacks any dissolved ions, which means it has a strong tendency to absorb ions and impurities from any material it comes into contact with. This can cause corrosion or degradation in materials that aren’t specifically designed to handle such high-purity water, such as certain metals and even some types of glass or plastics. Because of its aggressive nature, ultrapure water is often used in semiconductor manufacturing, pharmaceuticals, and other applications where even the slightest contamination can have significant consequences.
Some of the recommended materials that can be used for handling and processing ultrapure water include.
1. Polytetrafluoroethylene (PTFE)
- Properties: Excellent chemical resistance, low extractables, high purity, and non-reactive.
- Applications: Tubing, seals, gaskets, and fittings.
2. Perfluoroalkoxy Alkane (PFA)
- Properties: High purity, excellent chemical resistance, and maintains clarity and flexibility.
- Applications: Tubing, fittings, and valves.
3. Polyvinylidene Fluoride (PVDF)
- Properties: Good chemical resistance, high purity, and mechanical strength.
- Applications: Piping, fittings, and valve components.
4. Polypropylene (PP)
- Properties: Good chemical resistance, low cost, and suitable for DI water at lower purity levels.
- Applications: Piping, tanks, and valve bodies.
5. High-Purity Polyethylene (HDPE)
- Properties: Good chemical resistance and high purity.
- Applications: Tubing, containers, and fittings.
6. Polyetheretherketone (PEEK)
- Properties: Excellent chemical resistance, high strength, and low extractables.
- Applications: Tubing, fittings, and pump components.
7. Quartz (Silica)
- Properties: Extremely high purity and inertness.
- Applications: Piping and containers, often in semiconductor processing.
8. Stainless Steel (316)
- Properties: High corrosion resistance, often electropolished for ultra-high purity applications.
- Applications: Piping, valves, and fittings, usually for non-corrosive DI water applications.
- Avoid using 304 grade stainless and ensure all welds have been polished and passivated.
9. Borosilicate Glass
- Properties: High resistance to chemical leaching, but less durable than plastic options.
- Applications: Laboratory containers and some piping systems
Read the next article on ‘Why is ultrapure water corrosive?‘ to find out more.