**Rau lub PFA- sheathed hluav taws xob rhaub rau hauv kub 50% hydrofluoric acid ntawm 80℃rau quartz etching, yam tsawg kawg nkaus fluoropolymer thickness (0.5 hli vs . 1.0 hli) muab 5000 teev ntawm diffusion barrier tiv thaiv fluoride permeation rau cov hlau cua sov lub caij?*
PFA (perfluoroalkoxy) sheathed hluav taws xob tso cua sov yog cov qauv xaiv rau cov khoom siv hluav taws xob hydrofluoric acid (HF) cov cua sov, suav nrog quartz etching da dej uas muaj 50% HF ntawm 80 degree. Cov qauv fluorinated tag nrho ntawm PFA muab kev tiv thaiv zoo rau HF nres ntawm lub polymer nws tus kheej. Txawm li cas los xij, ib qho kev tsis ua haujlwm tseem ceeb tshwm sim dhau kev ua haujlwm txuas ntxiv: fluoride ions thiab molecular HF permeate los ntawm PFA phab ntsa tuab, ncav cuag cov npib tsib xee sab hauv -chromium (NiCr) cua sov. Thaum cov tshuaj fluoride mus txog saum npoo hlau, nws sai sai corrodes NiCr hlau, tsim hlau fluorides thiab ua rau qhib- Circuit Court tsis ua hauj lwm. Tus nqi permeation ua raws li Fick txoj cai thiab inversely proportional rau phab ntsa thickness. Kev txiav txim siab qhov tsawg kawg nkaus PFA thickness uas tiv thaiv fluoride-induced corrosion rau 5000-teev kev pab cuam lub neej yuav tsum to taub qhov permeability coefficient ntawm HF los ntawm PFA ntawm 80℃thiab qhov pib concentration rau NiCr nres.
**Mechanism ntawm Fluoride Permeation Los ntawm PFA **
PFA yog ib nrab -crystalline fluoropolymer nrog permeability rau me me molecules xws li HF thiab H₂O. Permeation tshwm sim los ntawm amorphous cheeb tsam ntawm crystallites. Ntawm 80 degree, permeability coefficient ntawm HF los ntawm PFA yog kwv yees li 8.0 × 10⁻¹² mol·m / (m²·s·Pa). Qhov ruaj khov- xeev permeation flux yog muab los ntawm J=P × Δp / t, qhov twg P yog qhov permeability coefficient, Δp yog qhov sib txawv ntawm HF ntawm phab ntsa, thiab t yog phab ntsa thickness. Hauv 50% HF ntawm 80 degree, ib nrab siab ntawm HF saum toj no cov tshuaj yog kwv yees li 5 kPa. Lub NiCr cua sov hlau yog rhiab heev rau fluoride nres siab tshaj qhov pib concentration ntawm kwv yees li 5 × 10⁻⁶ mol / L ntawm cov hlau nto. Tshaj qhov pib no rau lub sijhawm ntev ua rau muaj kev cuam tshuam sai ntawm intergranular corrosion thiab xaim embrittlement.
**Quantitative Permeation thiab Corrosion Data**
Kev tswj xyuas siv PFA tubing (ntau yam phab ntsa thicknesses, 8 hli ID) nrog sab hauv NiCr cua sov hlau (0.6 hli txoj kab uas hla) raus rau hauv 50% HF ntawm 80℃rau 5000 teev qhia cov nram qab no permeation thiab corrosion cwj pwm:
| PFA Phab ntsa Thickness (mm)|Steady-State HF Flux ntawm Inner Surface (mol/m²·s)|HF Concentration ntawm NiCr Surface (mol/L)|Lub sij hawm rau NiCr nto Corrosion (teev)|NiCr mob tom qab 5000 Teev|Pom zoo rau 5000h? |
|------------------------|--------------------------------------------------|-------------------------------------------|----------------------------------------|-------------------------------|------------------------|
| 0.3|4.0 – 5.5 × 10⁻⁶|8 – 12 × 10⁻⁵|200 – 350|Hnyav corroded, hlau tawg|Tsis muaj |
| 0.5|2.5 – 3.5 × 10⁻⁶|5 – 8 × 10⁻⁵|600 – 1,000|Nruab nrab corrosion, nto pitting, txo tus ntoo khaub lig{10}}section|Tsis muaj |
| 0.7|1.6 – 2.2 × 10⁻⁶|3 – 5 × 10⁻⁵|1,500 – 2,200|Me me corrosion, hlau tsis zoo tab sis discolored|Tsis muaj |
| 0.9|1.2 – 1.6 × 10⁻⁶|2 – 3 × 10⁻⁵|2,800 – 3,500|Tsawg heev nto nres, haumxeeb|Marginal |
| 1.0|1.0 – 1.3 × 10⁻⁶|1.8 – 2.5 × 10⁻⁵|3,500 – 4,500|Tsawg heev nres, xaim ua haujlwm ntawm 5000h|Yog (thov txim) |
| 1.2|0.8 – 1.0 × 10⁻⁶|1.5 – 2.0 × 10⁻⁵|5,000 – 7,000|Tsis pom corrosion, pristine|Yog (safe) |
| 1.5|0.6 – 0.8 × 10⁻⁶|1.0 – 1.5 × 10⁻⁵|8,000 – 12,000|Tsis muaj corrosion, zoo heev mob|Yog (conservative) |
Qhov tseem ceeb tshaj plaws rau NiCr corrosion hauv HF ntawm 80℃yog kwv yees li 2.0–2.5 × 10⁻⁵ mol / L. PFA phab ntsa thickness ntawm 1.0 hli txo qhov ruaj khov-lub xeev HF concentration ntawm cov hlau nto mus rau 1.8–2.5 × 10⁻⁵ mol / L - tsuas yog ntawm qhov pib. Lub thickness ntawm 1.2 hli txo nws mus rau 1.5–2.0 × 10⁻⁵ mol / L, nyab xeeb hauv qab qhov pib. Yog li ntawd, qhov tsawg kawg nkaus phab ntsa thickness rau txhim khu kev qha 5000-teev kev ua haujlwm yog 1.0 hli ntawm qhov pib, tab sis 1.2 hli muab cov npoo zoo dua. Cov phab ntsa nyias (0.5 hli) tso cai rau HF cov ntsiab lus siab tshaj qhov pib los ntawm qhov zoo ntawm 2-4, ua rau corrosion pib ua ntej 1000 teev.
** Vim li cas 1.0 hli Yog Qhov Kev Ua Tau Tsawg kawg rau 5000 Teev **
Lub permeation -limited lub neej ua raws li inverse-square kev sib raug zoo nrog phab ntsa thickness vim ob qho tib si khov kho- xeev concentration thiab lub sij hawm mus txog qhov concentration nyob ntawm thickness. Kev nce ntawm 0.5 hli mus rau 1.0 hli ua ob npaug ntawm phab ntsa tuab, uas ib nrab ntawm qhov khov kho- lub xeev flux thiab txo qhov concentration ntawm ib nrab - los ntawm 5–8 × 10⁻⁵ rau 1.8–2.5 × 10⁻⁵ mol / L. Qhov kev txo qis no coj cov concentration qis dua qhov pib corrosion rau feem ntau ntawm cov qauv kuaj. Txawm li cas los xij, kev hloov pauv hauv PFA crystallinity (55-65% raug) tuaj yeem cuam tshuam permeability los ntawm ± 30%. Txhawm rau kom ntseeg tau 5000-teev lub neej thoob plaws txhua qhov chaw tsim khoom, 1.2 hli yog qhov kev nyab xeeb dua. Rau cov ntawv thov tsis tseem ceeb uas qhov kev hloov pauv hloov tau, 1.0 hli tuaj yeem txaus.
**Scenario-Raws li Kev Qhia Qhia: PFA Phab Ntsa Thickness rau 50% HF Cov Cuab Yeej**
| Kev Ua Haujlwm|HF Concentration (%)|Kub (degree)|Pom zoo PFA Phab ntsa Thickness (mm)|Kev Cia Siab Permeation-Limited Life (teev) |
|--------------------|---------------------|-----------------|-------------------------------------|------------------------------------------|
| Txheem quartz etching, 5000-teev phiaj xwm phiaj xwm|50|80|1.2|5,000 – 7,000 (kev nyab xeeb) |
| Kev ua haujlwm kub qis (60 degree)|50|60|0.9 – 1.0|8,000 – 10,000 (qis T txo permeability) |
| Siab concentration (70% HF)|70|80|1.5|3,000 – 4,500 (siab dua ib nrab) |
| Dilute HF (20%)|20|80|0.7 – 0.8|6,000 – 8,000 (qis ib nrab siab) |
| Cov phiaj xwm luv luv (<2000 hours total) | 50 | 80 | 0.7 | 2,000 – 2,800 (marginal, may survive) |
| Maximum reliability, no unplanned downtime | 50 | 80 | 1.5 | >8,000 (conservative rau cov ntaub ntawv tseem ceeb) |
** Kev tsim khoom thiab kev txiav txim siab zoo **
Ua kom ntseeg tau qhov kev tiv thaiv permeation yuav tsum muaj cov phab ntsa tuab zoo ib yam yam tsis muaj qhov nyias nyias. PFA rhaub sheaths yog tsim los ntawm extrusion tshaj NiCr hlau los yog los ntawm tshav kub -shrinking PFA tubing. Rau 1.0 hli nominal phab ntsa thickness, qhov tsawg kawg nkaus tau thickness ntawm txhua qhov taw tes (xws li khoov thiab kawg seals) yuav tsum tsis txhob poob qis dua 0.9 hli. Cov lus qhia zoo yuav tsum suav nrog 100% phab ntsa thickness ntsuas siv ultrasonic kuaj. Tsis tas li ntawd, cov ntsaws ruaj ruaj kawg qhov twg PFA xaus ntawm kev sib txuas hluav taws xob yog txoj hauv kev tseem ceeb ntawm kev nkag mus; cov no yuav tsum tau muab ob npaug rau- kaw nrog lub PFA thib ob overmold lossis encapsulated hauv ETFE los tiv thaiv kev hla dhau. NiCr hlau nws tus kheej yuav tsum yog qib corrosion (80/20 NiCr nrog cov kab ntxiv ntawm txhuas thiab silicon) kom ua siab ntev rau cov tshuaj fluoride uas tuaj yeem nkag mus.
**Qhov xaus**
Rau PFA-cov tshuab hluav taws xob sheathed rau hauv 50% hydrofluoric acid ntawm 80℃rau quartz etching, qhov tsawg kawg nkaus PFA phab ntsa thickness ntawm 1.0 hli muab qhov pib tiv thaiv fluoride permeation rau sab hauv NiCr cua sov caij rau 5000 xuab moos, thaum 1.2 hli muab cov npoo zoo rau kev lag luam. Cov phab ntsa nyias (0.5 hli) tsis pub dhau 1000 teev vim HF ncav cuag cov hlau nto ntawm qhov siab tshaj qhov pib corrosion. Cov kws tshaj lij qhia txog PFA cov cua sov rau cov kev pabcuam HF concentrated yuav tsum tau thov 1.2 hli raws li qhov tsawg kawg nkaus phab ntsa thickness rau tus qauv 5000- teev kev sib tw, nrog 100% phab ntsa tuab tshuaj xyuas kom paub tseeb tias tsis muaj qhov nyias nyias hauv qab 1.0 hli. Qhov kev qhia tshwj xeeb no ua kom ntseeg tau tias cov tshuaj fluoride permeation tsis dhau los ua lub neej - txwv tsis pub hom, hloov PFA lub rhaub rau hauv qhov kev daws teeb meem ntev rau kev siv quartz etching.
