Fluorine (F2) and Fluorine Mixture Recommendations

Tuesday, March 16th, 2021

Fluorine (F2) gas handling is of special concern. F2 is a corrosive, toxic and highly reactive oxidizer requiring special care and handling beyond what is typical for other specialty gases. In semiconductor and related applications, 100% F2 gas and 20% F2/80% N2 mixtures are typically used. 100% F2 and F2 mixtures have different auto-ignition risks and therefore different requirements. Cylinder fill pressure for 100% F2 is generally limited to 30 bar (435 psig, 3 MPa). 20% F2 mixtures are typically available at 100 bar (1,450 psig, 10 MPa) and 140 bar (2,030 psig, 14 MPa), but other filling pressures are possible.

Valve and gas regulator selection is critical for safety and reliability. The AP1900 SHEM gas regulator is recommended for 100% F2 and F2 mixtures. The 1900 SHEM is a tied-diaphragm regulator with a mechanically linked poppet and diaphragm design to allow positive shutoff in case of over pressurization. The 1900 SHEM model includes non-standard options (features not defined on the AP1900 datasheet). Features include internal edges with radius rather than chamfer and removal of internal gross filter. These changes are made to reduce risk of auto-ignition by reducing sharp edges and fine features. Materials such as Monel® (Ni-Cu alloy, UNS N04400) and other high Nickel based alloys such as Hastelloy® C-22® (Ni-Cr-Mo alloy, UNS N06022) have a higher auto-ignition temperature and better heat dissipation than stainless steel. Monel is used for the poppet and nozzle while Hastelloy C-22 is used for the poppet spring and diaphragm. These improvements reduce the ability of the wetted material to ignite. The AP1900 SHEM model with standard PCTFE seat is recommended for source application F2 mixtures up to 20% concentration not exceeding 50 slpm and 150 bar (2,175 psig, 15 MPa). 100% F2 requires more considerations. The AP1900 SHEM with PFA seat (designated “PF” in model number) is recommended for 100% F2, and F2 mixtures up to 69 bar (1,000 psig, 6.9 MPa). Valves upstream of the pressure regulator should have either a metal or PFA seat. Maximum flow again is limited to 50 slpm.

For F2 mixtures up to 20% concentration, standard AP series valves with wetted materials of 316L SS, Hastelloy C-22 (Ni-Cr-Mo alloy, UNS N06022) Monel (Ni-Cu alloy, UNS N04400), and Elgiloy (Ni-Co alloy, UNS R30003), PCTFE or PFA are compatible.

Gas velocity limits are of special concern for 100% F2 and 20% F2 mixes and should be discussed with gas system designer.

100% F2 and F2 mixtures require system passivation. The most common passivation method is to expose the gas system to increasing concentrations and pressures of F2 or F2 mixtures with minimum soak times. Passivation of metal creates a protective film. For example, stainless steel forms a protective chromium fluoride (CrF3) scale which helps prevent reaction with Fluorine. Passivation also ensures that any contaminant in the gas system will react with F2 at lower pressures and concentrations. Please consult your Fluorine gas supplier for passivation procedures and best practices.

If a valve or regulator fails and must be replaced, ensure that the valve or regulator is properly purged -HF gas and aqueous HF can be present. When replacing the component, gas stick or gas panel, ensure that there is positive pressure inert gas exiting all open connections of the gas system at all times. This will reduce moisture ingress. Care must be taken when handling the removed valve or regulator as there may be hazardous and corrosive byproducts of F2 in the used component. After installation of a new valve or regulator and completion of leak and function testing with inert gas, the new component must be passivated with Fluorine before entering service.

For more information about AP Tech valve and regulator solutions for F2 gas applications, please contact your local distributor or AP Tech.

Monel® is a registered trademark of Special Metals Corporation
Hastelloy® C-22® are registered trademarks of Haynes International