When PTFE is better than PEEK?
By Pawel Jerzy Wojcik, Ph.D.
If you want to cite this blog post use: Wojcik, P.J. (2021). When PTFE is better than PEEK? [online] redox.me Available at: https://redox.me/blogs/good-measurement-practices/when-ptfe-is-better-than-peek [Accessed Date Accessed].
Although PEEK is usually the material of choice for electrochemical cell body, redox.me team often gets questions, whether PTFE would be better for a given experiment. In this short post, we have collected information gathered from the chemical compatibility charts, publications, our own observations, and feedback received from our customers.
PEEK plastic (Polyetherether Ketone) is a tough, strong, and rigid material. It is an excellent material for CNC machining and 3D printing of electrochemical cell and electrode components. PEEK exhibits excellent resistance to a wide range of organic and inorganic chemicals and is compatible with almost any electrolyte used in electrochemical devices. There are just a few chemicals that cause immediate destruction of the electrochemical cell assembly made of PEEK.
PTFE (polytetrafluoroethylene) belongs to the fluoropolymer family, which is distinct from PEEK. The presence of fluorine provides even greater chemical resistance. Both PEEK and PTFE are stable at temperatures up to 260˚C (500˚F). However, PTFE is a much softer material and electrochemical cell elements made of it, such as threads, wear out quickly. This makes it necessary to use metal threaded inserts for plastic, which makes fabrication more difficult and limits the design possibilities. Those metal inserts may also corrode in contact with spilled electrolyte, which will reduce the aesthetic value of the setup but will not affect its functionality.
In conclusion, PEEK is a better material for an electrochemical cell body, as long as you do not use the chemicals listed below:
- Aqua regia - HNO3 + HCl
- Benzenesulfonic acid - aqueous C6H5SO3H
- Bromine (liquid) - pure Br2
- Carbolic Acid (Phenol) - C6H5OH
- Carbon Disulfide - CS2
- Chlorine (aqueous and anhydrous liquid) - Cl2
- Chlorosulfonic acid - pure ClSO3H
- Chromic Acid - aqueous H2CrO4 >50%
- Ethylene bromide (anhydrous) - pure CH2CHBr
- Fuming sulphuric acid (Oleum) - pure H2SO
- Hydrobromic acid - aqueous HBr
- Hydrofluoric acid - concentrated aqueous HF
- Nitric acid - aqueous HNO3 >50%
- Sulphuric acid - concentrated (96%) H2SO4
- Sulphurous acid - aqueous H2SO3
There are also other chemicals that can cause minor changes in the appearance and properties of the PEEK component surface (discoloration, change in roughness, swelling of small features, local delamination, minor deformation). Therefore, if you are using any of the chemicals listed below, make sure the exposure time is short and the concentrations low.
- Boric acid - aqueous H3BO3
- Sulphuric acid - 20-30% H2SO4
- Carbolic acid (phenol, hydroxybenzene) - aqueous C6H5OH
- Chloroethanol (ethylene chlorohydrine) - pure ClCH2CH2OH
- Chromic acid - 30-50% aqueous H2CrO4
- Dichloromethane (methylene chloride) - pure CH2Cl2
- Dimethyl sulfoxide (DMSO) - pure (CH3)2SO
- Ethylene chlorohydrin (chloroethanol) - pure ClCH2CH2OH
- Formaldehyde solution (formalin) - aqueous CH2O
- Formic acid - pure HCOOH
- Hydrochloric acid - aqueous 36% HCl
- Hydroxybenzene (carbolic acid, phenol) - aqueous C6H5OH
- Iodine with potassium iodine - aqueous I2 + KI
- Methylene chloride (dichloromethane) - pure CH2Cl
- Methyl ethyl ketone (2-butanon) - pure CH3COCH2CH3
- Nitric acid - aqueous (40%) HNO3
- Nitrobenzene - pure C6H5NO2
- Nitrotoluenes (o-, m-, p) - pure C6H4(NO3)(CH3)
- Phenol (hydroxybenzene, carbolic acid) – diluted aqueous C6H5OH
- Sodium chromate - aqueous NaCrO4
There is only one chemical known to us that destroys both PEEK and PTFE materials. It is a Fluorine introduced to the system in any form. Please note that variations in chemical behavior during handling due to factors such as temperature, pressure, and concentrations can cause an electrochemical setup to fail, even though it is not listed above.
An electrochemical cell also consists of other components such as O-Rings, gaskets, fittings, tubbing, tripods/stands, handles, metal contacts, cables, metal guides, frits, screws, washers, inserts, glass chambers, and windows. Their chemical resistance and selection rules will be discussed in a separate post.
Please, note that the content of this article is constantly being updated to cover the topic in the possibly most reliable way. At the same time, we are doing our best to keep it in line with the state-of-the-art research.