Vim Li Cas Thiaj Muaj Cov Hlau Ions (Fe³⁺) hauv 30% HCl Accelerate PFA Permeation los ntawm Factor 2-3 ntawm 100 degree?

Hauv kev lag luam hydrochloric acid kev pabcuam (xws li cov kab pickling, ntxhia ua, tshuaj ntxuav) yaj hlau ions (Fe³⁺) sib sau ua ferric chloride. Fe3+ accelerates qhov nqus ntawm PFA los ntawm 2-3 zaug piv rau HCl ntshiab ntawm tib qhov concentration thiab kub. Lub tshuab yog catalytic, nyob rau hauv uas, Fe3+ hom permeate rau hauv amorphous feem ntawm PFA thiab hnov ​​​​mob nrog kab ya raws los tsim FeCl3·6H2O. Cov ntsev ntub dej no muaj qhov ntim molecular ntau dua li PFA qhuav, uas ua rau muaj qhov o thiab microvoids. Cov microvoids tsim cov kab uas tsis muaj zog rau kev nthuav dav ntawm HCl thiab dej. Fe3+ kuj catalyses oxidative kev puas tsuaj ntawm PFA saw xaus, ua kom lub ntim dawb. Lub sij hawm rau cov tub ntxhais corrosion raug txo los ntawm 8,000-10,000 teev mus rau 3,000-5,000 teev hauv 30% HCl ntawm 100 degree, nrog 2 hli PFA phab ntsa uas muaj 500 ppm Fe3+. Rau cov ntawv thov tseem ceeb khaws Fe 3+ < 50 ppm thickness .

Mechanism ntawm ceev permeation ntawm hlau ions
Kev nkag mus ntawm HCl los ntawm PFA ua raws li cov kev daws teeb meem -diffusion qauv P=SD, qhov twg S sawv cev rau kev solubility thiab D lub diffusion coefficient. Nyob rau hauv ntshiab HCl, D yog txiav txim los ntawm lub dawb ntim ntawm lub polymer. Fe3+ ions (radius 0.06 nm, hydrated radius 0.43 nm) yog qhov loj heev rau kev nthuav tawm los ntawm PFA tsis zoo. Txawm li cas los xij, Fe3+ muaj nyob rau hauv cov tshuaj raws li complexes nrog FeCl4-, uas yog nruab nrab thiab muaj ib tug tsawg solubility nyob rau hauv fluoropolymer. Cov complexes diffuse mus rau saum npoo ntawm PFA thiab hydrolyse rau Fe (OH) 3 thiab precipitate li nano{17}}particles (5-20 nm). Cov nag lossis daus tus neeg kho tshuab kev nyuaj siab induces microvoids. Kev tsim ntawm microvoids txhim kho qhov zoo diffusion coefficient, txij li HCl tuaj yeem cuam tshuam los ntawm qhov tsis muaj kev sib txuas (gas theem diffusion) tsis yog los ntawm cov polymer matrix. Qhov no void-pab permeation yog 10-100X sai dua matrix diffusion.

Qhov kev txiav txim catalytic nyob ntawm qhov concentration. Fe 3+ tsuas yog soluble ntawm 1,000-2,000 ppm ntawm 100℃(raws li FeCl 3) ntawm 30% HCl. Lub permeation acceleration factor (AF) yog AF=1 + 0.003 × [Fe 3+] (ppm) (rau 1,000 ppm). 500 ppm Fe 3+ AF=2.5 × . 1000 ppm Fe 3+ AF=4 FeCl₃ crystals tuaj yeem ua rau ntawm PFA nto ntawm qhov ntau dua 1,500 ppm, ua rau lub cev ua mob rau lub cev.

Cov ntaub ntawv Permeation: Fe3+ tawm tsam Pure HCl-Contaminated HCl (100 degree, 2 hli PFA phab ntsa)
Fe3+ Concentration (ppm) Steady-State Permeation Rate (g/m2.day) Lub Sijhawm rau 1.0 mm Phab Ntsa Thinning (teev) Lub Sijhawm rau Core Corrosion (teev) Acceleration Factor (vs. pure) Surface Condition
0 (ntshiab) 0.8–1.2 12,000–15,000 8,000–10,000 1.0 × Smooth, pob tshab 50 1.0–1.5 10,000–12,000 6,000–8,000 1.2–1.4 × Slight
100 1.3-1.8 8,000-10,000 5,000-7,000 1.5-1.8x Haze, trace deposits 250 1.8-2.5 5,000-7,000 3,500-5,000 2.0-2.5x Visible white deposits 500 2.5-3.5 3,500-5,{{12},000-5,{12}3},{12},{12},{12}, tain 1,000 4.0-6.0 2,000-3,000 1,500-2,000 4.0-5.0x Crystalline deposit 2,000 (saturated) 6.0-10.0 1,000-1,500 800-1,200 6.0-10.0x Hnyav scaling, cracking
Muaj peev xwm ntawm Fe 3+ hauv HCl
Hlau ions tuaj rau hauv kwj ntawm HCl los ntawm:

Hlau pickling hlau oxide nplai (feem ntau 200-1,000 ppm Fe3+) yaj

Corrosion ntawm upstream carbon steel tanks los yog pipework

Cov txheej txheem catalytic (FeCl3 catalyst hauv chlorinations)

Reclaimed acid (cov kab mob tsis huv HCl)

Fe³+ yog yam tsis muaj nyob hauv cov kab pickling. Qhov concentration nce nrog lub hnub nyoog ntawm da dej. Kev da dej tshiab tuaj yeem yog 0-50 ppm. Kev siv da dej tuaj yeem ncav cuag 2,000-5,000 ppm Fe3+. PFA cov cua sov hauv cov chav da dej uas siv tau muaj lub neej luv dua li cov kua qaub tshiab.

Mitigation Alternatives
Txhawm rau txo qis permeation nrawm los ntawm Fe3+:

Precipitate Fe3+ thiab lim Ntxiv cov nag lossis daus (xws li oxalic acid lossis phosphate) los hloov Fe3+ mus rau insoluble FePO4 lossis Fe2 (C2O4)3. Lim ua ntej lub rhaub. Fe3+ raug txo los ntawm 1000 ppm rau 50-100 ppm.

Siv cov khoom siv hluav taws xob txiab txiab Khiav cov kua qaub hla lub txaj ntawm ion- pauv cov resin (muaj zog acid cation) kom tshem tawm Fe3+. Resin yuav tsum yog HCl tshaj.

Nce PFA phab ntsa thickness: Ob chav lub neej rau 3 hli phab ntsa nrog sib npaug Fe3+ concentration. Phab ntsa 2 hli kav ntev li 2,500-3,500 teev rau 500 ppm Fe3+. Phab ntsa 3 hli kav ntev li 5,000-7,000 teev.

Txo kev khiav hauj lwm kub: Yog hais tias qhov kub thiab txias yog txo los ntawm 100℃mus rau 80 degree, lub diffusivity yog txo los ntawm ib tug ntau ntawm ob. AF los ntawm Fe 3+ kuj txo (ob peb lub microvoids yog tsim los ntawm qhov kub thiab txias).

Siv PFA liner nrog Fe³⁺ txheej txheej. Ib txheej nyias (0.1 hli) ntawm amorphous carbon lossis pob zeb diamond-zoo li carbon (DLC) tiv thaiv qhov sib txawv ntawm Fe³⁺. Muaj los ntawm cov kws tsim khoom tshwj xeeb.

Damage Sensing ntawm Fe³⁺ Trigger
Txheeb xyuas PFA sheath rau:

- Deg deposits, dawb los yog tan (hydrolysis khoom ntawm FeCl₃)

Nto roughness (microvoids pom ntawm 50x magnification)

Increased water absorption (weigh dry sample before and after immersion; weight rise >0.2% qhia microvoiding)

IR spectroscopy - Ib lub teeb liab ntawm 1040 cm-1 qhia Fe-O bonding hauv cov deposits nto.

Yog tias muaj Fe³⁺ deposits, lub rhaub yog twb degraded. Nws raug nquahu kom hloov nws.

Field Case
Steel pickling kab tau ua haujlwm ntawm 100℃nrog 30% HCl thiab 600–800 ppm Fe3+. PFA cov cua sov (qib tus qauv, 2 hli phab ntsa) siv sijhawm 2,000–3,000 teev (3–4 lub hlis). Cov nroj tsuag tsim lub tank crystallisation txias cov kua qaub rau 20℃upstream Fe3+ poob rau 80-120 ppm rau kev tshem tawm cov muaju ntawm FeCl3.6H2O. Lub tshuab rhaub lub neej tau txuas ntxiv mus rau 7,000-9,000 teev (10-12 lub hlis), 3 × ntev dua. Lub crystalliser ($ 20,000) tau them rov qab rau hauv 8 lub hlis los ntawm kev hloov pauv cua sov tsawg dua thiab lub sijhawm poob qis.

Xaus Fe3+ nce PFA permeation los ntawm 2-3 × ntawm 500 ppm
Hauv 30% HCl ntawm 100 degree, cov hlau ions (Fe³⁺) nce PFA permeability los ntawm 2-3 × ntawm 500 ppm thiab mus txog 10 × ntawm 2,000 ppm. Fe 3+ hom permeate rau hauv PFA, precipitate li hydrates, tsim microvoids thiab muab tsis tshua muaj zog diffusion channel rau HCl thiab dej. Qhia kom tuab dua rau cov kev pabcuam HCl nrog Fe3+> 100 ppm PFA phab ntsa (3mm) lossis nruab qhov kev tshem tawm hlau (crystallisation, pom, ion pauv) Kos Fe³+ txhua lub limtiam. Fe³⁺> 500 ppm: kwv yees lub cua sov lub neej ntawm 2,000-4,000 teev tsis hais txog lwm yam. Pure acid tsis ua phem, acid nrog hlau yog. Tswj cov hlau, tswj cov permeation, ua kom lub neej ntev. Lub tshuab cua sov tsis tuaj yeem qhia qhov txawv thiab cov hlau ua kom tsis muaj zog. Tshem tawm, lossis muaj txoj sia tsawg dua. Nws yog kev xaiv nyiaj txiag. xam, ces txiav txim.