Electron-beam (e-beam) treatment of PFA creates low levels of cross-linking between polymer chains (0.5–2% cross-link density). A lightly cross-linked PFA heater can exhibit 40–60% lower permeation to chlorine gas (Cl₂) at 1 bar and 80°C compared to uncross-linked PFA of the same thickness. The cross-links reduce the free volume of the amorphous regions, creating a more tortuous diffusion path for Cl₂ molecules (kinetic diameter 0.32 nm). Cross-linking also suppresses the swelling that normally occurs when Cl₂ dissolves into PFA, which would otherwise increase free volume. However, excessive cross-linking (>5%) ua rau PFA nkig thiab nquag tawg. Rau cov kev pab cuam chlorine gas, maj mam hla - txuas PFA (e-beam koob tshuaj 50–150 kGy) muab qhov zoo sib npaug: qis permeation yam tsis muaj embrittlement. Kev kho mob ntxiv 10-20% rau cov nqi tsim khoom tab sis txuas ntxiv lub neej ntawm cov khoom siv tshuaj chlorine los ntawm 2-3 ×.
Hla -Txoj kev cuam tshuam ntawm Permeation
Chlorine permeation ua raws li kev daws teeb meem - qauv diffusion: P=D × S, qhov twg D yog diffusivity thiab S yog solubility. Nyob rau hauv uncrosss -linked PFA, amorphous regions muaj dawb ntim uas tso cai rau Cl₂ molecules diffuse kuj yooj yim. Hla -txuas txuas ua raws li lub cev tsis muaj zog, yuam cov molecules mus rau txoj kev ntev dua (tortuosity factor τ nce ntawm 1 txog 2–3). E-Beam kev kho mob kuj txo cov solubility ntawm Cl₂ vim cov polymer yog tsawg dua plasticizable. Cov nyhuv ua ke txo P los ntawm 40-60%.
Kev sim cov ntaub ntawv rau 1 hli PFA zaj duab xis ntawm 80 degree, 1 bar Cl₂:
| Hla -Txoj kev ceev | E-Beam Dose (kGy) | Permeation Rate (g / m²) hnub | Kev txo qis vs. Tsis hla - txuas | Tensile zog (MPa) | Elongation ntawm Break (%) |
|---|---|---|---|---|---|
| 0% (tsis hla- txuas) | 0 | 2.5–3.5 | 0% | 28 | 320 |
| 0.5% | 50 | 1.5–2.0 | 40% | 29 | 280 |
| 1.0% | 100 | 1.2–1.6 | 50% | 30 | 240 |
| 1.5% | 150 | 1.0–1.3 | 60% | 30 | 200 |
| 2.0% | 200 | 0.8–1.1 | 70% | 29 | 150 |
| 3.0% | 300 | 0.6–0.8 | 75% | 25 | 80 |
| 5.0% | 500 | 0.4–0.5 | 85% | 18 | 30 |
Qhov zoo tshaj plaws rau kev pabcuam chlorine yog 1–2% hla-kev sib txuas (dose 100–200 kGy). Elongation tseem nyob saum 150%, kom ntseeg tau yooj yim.
Vim li cas Hla-Txuas Kev Pab Tshwj Xeeb rau Chlorine
Chlorine molecules yog polarizable thiab muaj kev sib cuam tshuam nrog fluoropolymer. Nyob rau hauv uncrosss -linked PFA, Cl₂ ua o (0.5–1.5% ntim nce), uas ntxiv tsub kom dawb ntim thiab accelerates permeation (auto-catalytic). Hla - txuas PFA tiv thaiv qhov o vim tias tus ntoo khaub lig covalent - txuas txwv txoj hlua txav. Qhov o yog txo rau<0.2%, eliminating the auto-catalytic effect.
Chlorine kuj reacts maj mam nrog PFA saw xaus (ua -COCl pab pawg). Hla -txuas txuas txo tus naj npawb ntawm cov saw hlau xaus (chains tau khi ua ke). Tus nqi degradation yog txo los ntawm 30-50%.
Kev lag luam -Offs thiab txwv
Yooj yim hla- txuas PFA muaj ntau qhov tsis zoo:
Txo elongation: Ntawm 2% hla- txuas, elongation poob los ntawm 300% mus rau 150% - tseem siv tau rau feem ntau cov ntawv thov.
Tsawg thermal stability: Cross-linked PFA degrades faster at >220°C (starts to char). Not suitable for high-temperature service (>200 degree).
Nce hardness: Ntug D nce ntawm 66 txog 70–72. Tsawg yoog raws, yooj yim dua rau tawg hauv qab ntse khoov.
Tus nqi siab dua: E-kev kho kab teeb ntxiv 10–20% rau cov nqi cua sov.
For chlorine gas service below 100°C, the benefits outweigh the drawbacks. For hot chlorine (>120°C) or high pressure (>5 bar), hla - txuas PFA tseem degrades; siv quartz los yog hlau.
Kev kuaj pom ntawm Hla-Txuas
Hla -link ceev tuaj yeem ntsuas los ntawm:
Kev kuaj o: Raus hauv xylene ntawm 80℃rau 24 teev. Uncross-txuas PFA swells 10–15%; hla -txuas PFA swells 2–5% (los ntawm qhov hnyav).
DSC (differential scanning calorimetry): Hla-txuas txuas txo qhov chaw melting endotherm (qis crystallinity pom tseeb). Tsis ncaj.
Kev kuaj elongation: Txiav 1 cm strip; stretch. Hla -linked PFA muaj qis elongation.
Piv txwv teb
Lub tshuab hluav taws xob chlorine dioxide siv PFA cov cua sov hauv 1 bar Cl₂ roj ntawm 70 degree. Txheem PFA cov cua sov ua tsis tiav tom qab 12-18 lub hlis (permeation corrosion ntawm cov tub ntxhais). Cov nroj tsuag hloov mus rau e-beam kho PFA (1.5% cross-txuas, 150 kGy). Lub tshuab rhaub lub neej txuas ntxiv mus rau 48+ hli. Qhov ntxiv $100 rau ib lub rhaub tau them rau nws tus kheej hauv 8 lub hlis.
Xaus: Lub Teeb Hla-Txuas (1–2%) Txo cov tshuaj chlorine permeation los ntawm 50–60%
Lightly cross-linked PFA (e-beam treated, 1–2% cross-link density, 100–200 kGy) shows 40–60% lower permeation to chlorine gas at 1 bar compared to uncross-linked PFA. The cross-links reduce free volume, suppress swelling, and create a more tortuous diffusion path. For chlorine gas service up to 100°C, specify lightly cross-linked PFA. The 10–20% cost premium extends heater life by 2–3×. Do not over-cross-link (>3%): cov khoom ua nkig. Qhov nyiaj tshuav yog qhov tseem ceeb. Chlorine permeates PFA; hla - txuas thaiv chlorine. Kho nrog electrons, thaiv cov roj, txuas lub neej. Rau cov tshuaj chlorine, hla - txuas maj mam. Rau qhov kub siab, tsis txhob hla - txuas. Xaiv kom zoo.
