Teflon's remarkable chemical resistance stems from its unique molecular structure, primarily its strong carbon-fluorine bonds and the shielding effect of fluorine atoms. This makes it inert to most acids, bases, and solvents, though it has limitations with extreme chemicals like hydrofluoric acid or molten alkali metals. Its stability under harsh conditions makes it invaluable for lab equipment and industrial applications where contamination or reactivity must be avoided.
Key Points Explained:
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Molecular Structure of polytetrafluoroethylene teflon
- Composed of long carbon chains surrounded by fluorine atoms, creating a dense "shield" that repels other molecules.
- Carbon-fluorine bonds are among the strongest in organic chemistry (485 kJ/mol), resisting breakage by most chemicals.
- The symmetrical fluorine coverage prevents reactive sites, unlike polymers with hydrogen atoms (e.g., polyethylene).
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Inertness to Common Chemicals
- Acids/Bases: Resists concentrated sulfuric acid, nitric acid, and sodium hydroxide due to non-reactive fluorine shielding.
- Solvents: No known industrial solvent dissolves PTFE at room temperature—unlike rubbers that swell in hydrocarbons.
- Exceptions: Degrades in hydrofluoric acid (HF), which attacks the carbon backbone, and molten alkali metals that strip fluorine atoms.
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Temperature and Mechanical Limits
- Stable up to 260°C (PFA variant), but prolonged exposure above 200°C (FEP) may cause gradual decomposition.
- Cold flow (creep) under sustained pressure can compromise seals, though this is a physical, not chemical, limitation.
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Industrial vs. Lab Applications
- Piping/Valves: Preferred for corrosive chemical transport (e.g., chlorine gas) where metals would corrode.
- Labware: Used in stir bars, flask linings, and syringe parts to prevent sample contamination or reaction byproducts.
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Trade-offs with Specialty Chemicals
- Vulnerable to fluorinating agents (e.g., chlorine trifluoride) that "over-fluorinate" the structure, breaking bonds.
- Ketones/amines may cause slow surface degradation, limiting use in certain pharmaceutical processes.
For purchasers, Teflon’s resistance justifies its higher cost in corrosive environments, but alternatives like PEEK may be needed for extreme temperatures or mechanical stress. Always verify compatibility charts for specific chemical exposures.
Summary Table:
| Key Feature | Explanation |
|---|---|
| Carbon-Fluorine Bonds | Extremely strong (485 kJ/mol), resisting chemical attacks. |
| Fluorine Shielding | Dense fluorine coverage prevents reactive sites. |
| Acid/Base Resistance | Inert to concentrated sulfuric acid, nitric acid, and sodium hydroxide. |
| Solvent Immunity | No industrial solvent dissolves PTFE at room temperature. |
| Temperature Limits | Stable up to 260°C (PFA variant), but degrades above 200°C (FEP). |
| Exceptions | Vulnerable to hydrofluoric acid (HF) and molten alkali metals. |
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