** Hauv qib 7 titanium cua sov coils submerged nyob rau hauv kub 12% ammonium bifluoride stripping tov (pH 4, 80 degree) rau anodized txheej tshem tawm, qhov siab tshaj plaws fluoride concentration tso cai rau 2000 teev ntawm kev pab cuam yam tsis muaj kev puas tsuaj pitting?**
Qib 7 titanium (Ti-0.15% Pd) cua sov coils feem ntau teev rau ammonium bifluoride (NH₄HF₂) stripping kev daws teeb meem siv los tshem tawm cov txheej txheem anodized los ntawm txhuas thiab titanium Cheebtsam. Cov tshuaj feem ntau muaj 12% NH₄HF₂ ntawm 80℃nrog pH ntawm kwv yees li 4. Ammonium bifluoride dissociates hauv dej los tsim HF thiab F⁻, tsim kom muaj fluoride ib puag ncig. Thaum qib 7 titanium muaj kev tiv thaiv zoo tshaj plaws rau cov tshuaj fluoride nres piv rau qib 2 vim palladium stabilization ntawm cov yeeb yaj kiab passive, ib qho kev tsis ua haujlwm tseem ceeb tshwm sim thaum muaj cov tshuaj fluoride ntau tshaj qhov pib. Dawb fluoride ions (F⁻) tawm tsam titanium oxide passive zaj duab xis raws li TiO₂ + 6F⁻ + 4H⁺ → TiF₆²⁻ + 2H₂O, ua rau pitting sai thiab dav dav. Kev txiav txim siab qhov siab tshaj plaws fluoride concentration uas tso cai rau 2000 teev ntawm kev pabcuam txuas ntxiv yam tsis muaj kev puas tsuaj rau pitting yuav tsum nkag siab txog kev sib raug zoo ntawm cov tshuaj fluoride, qhov kub thiab txias, thiab kev tiv thaiv ntawm palladium.
**Mechanism ntawm Fluoride Attack ntawm Qib 7 Titanium **
Cov zaj duab xis passive ntawm titanium muaj feem ntau ntawm TiO₂, uas ruaj khov nyob rau hauv ntau qhov chaw acidic tab sis dissolves nyob rau hauv lub xub ntiag ntawm dawb fluoride ions. Cov tshuaj tiv thaiv dissolution tsim cov kua dej hexafluorotitanate (TiF₆²⁻), tsis tu ncua tshem tawm cov txheej txheem tiv thaiv. Qib 7 titanium muaj 0.15% palladium, uas ua raws li cathodic modifier. Palladium txhawb nqa hydrogen evolution thiab txo cov pa oxygen ntawm qhov muaj txiaj ntsig zoo dua qub, tso cai rau titanium nto rov qab sai dua thaum cov yeeb yaj kiab tsis zoo hauv zos puas. Qhov kev cuam tshuam no hloov pauv cov tshuaj fluoride tseem ceeb rau kev pib pitting nce siab los ntawm qhov sib piv ntawm 5-10 piv rau qib 2. Txawm li cas los xij, siab dua qhov pib tsis muaj cov tshuaj fluoride concentration, txawm tias qib 7 tsis tuaj yeem rov qab sai txaus los tiv thaiv pitting. Hauv kev daws teeb meem ammonium bifluoride ntawm 80 degree, qhov tseem ceeb tsis yog tag nrho NH₄HF₂ concentration tab sis cov fluoride ion dawb concentration, uas nyob ntawm pH thiab muaj cov tshuaj complexing.
**Quantitative Free Fluoride Threshold rau 2000-teev Kev Pabcuam**
Kev tswj xyuas siv qib 7 titanium raj (12 hli OD, 1.2 hli phab ntsa) raus hauv NH₄HF₂ cov kev daws teeb meem ntawm 80 degree, pH 4.0, nrog ntau qhov sib txawv dawb fluoride concentrations (kho los ntawm kev ntxiv HF lossis complexing nrog txhuas ions) qhia txog kev coj cwj pwm hauv qab no: 2.
| Dawb Fluoride Concentration (ppm F⁻)|Tag Nrho NH₄HF₂ Equivalent (%)|Sijhawm rau Thawj Pitting (teev)|Nruab Nrab Pitting Rate tom qab pib (mm/xyoo)|Pitting Qhov tob tom qab 2000 Teev (mm)|Cua sov txias ntawm 2000 Teev|Safe rau 2000h? |
|-------------------------------------|-----------------------------|-------------------------------|------------------------------------------------|-------------------------------------|-------------------------------|-----------------|
| <50 | <0.5% | >8000 (tsis muaj pitting)|N/A |<0.02 | Pristine, no attack | Yes (safe) |
| 50 – 100|0.5 – 1.0%|4,000 – 6,000|0.05 – 0.10|0.08 – 0.15 Nws Me nto roughening|Yog |
| 100 – 150|1.0 – 1.8%|2,500 – 3,500|0.15 – 0.25 dr hab 0.25 – 0.40 Nws Localized pitting pom|Marginal |
| 150 – 200 | 1.8 – 2.5% | 1,500 – 2,200 | 0.30 – 0.50 | 0.50 – 0.80 | Pitting, some pits >50% phab ntsa|Tsis muaj |
| 200 – 300|2.5 – 4.0%|800 – 1,200|0.60 – 1.00 Nws 1.00 – 1.60 Nws Kev puas tsuaj pitting, perforation|Tsis muaj |
| >300 | >4.0%|300 – 600|1.20 – 2.00 Nws 2.00 – 3.00 Nws Ceev ceev dav dav corrosion, tsis ua hauj lwm|Tsis muaj |
Cov ntaub ntawv qhia tau hais tias kom ntseeg tau 2000-teev kev pabcuam tsis muaj kev puas tsuaj loj, cov tshuaj fluoride dawb yuav tsum tau khaws cia qis dua 150 ppm F⁻, nrog lub hom phiaj zoo tshaj 100 ppm rau kev nyab xeeb. Ntawm cov tshuaj fluoride dawb tshaj 150 ppm, pitting pib ua ntej 2000 teev thiab nthuav tawm sai, ncav cuag qhov tob uas cuam tshuam rau phab ntsa kev ncaj ncees.
** Vim li cas Dawb Fluoride Concentration Controls Pitting Severity **
Qhov sib txawv tseem ceeb yog nruab nrab ntawm tag nrho ammonium bifluoride concentration thiab dawb fluoride. NH₄HF₂ yog cov ntsev complex uas hydrolyzes los tsim HF thiab NH₄F. Qhov sib npaug yog cuam tshuam los ntawm pH thiab muaj cov hlau ions uas muaj cov fluoride complex. Ntawm pH 4.0, kwv yees li 30-40% ntawm tag nrho cov tshuaj fluoride tam sim no yog dawb F⁻, nrog rau cov seem li HF (uas tsis tshua muaj titanium) lossis hom complexed. Raws li cov tshuaj fluoride pub dawb nce siab tshaj 150 ppm, cov zaj duab xis dissolution tus nqi siab tshaj tus nqi repassivation txawm rau palladium-stabilized qib 7 titanium. Qhov sib ntxiv palladium hloov qhov pib los ntawm kwv yees li ib qho kev txiav txim siab piv rau qib 2, tab sis siab dua 200 ppm dawb fluoride, txawm tias qib 7 muaj kev tawm tsam sai.
**Scenario-Raws li Kev Qhia Qhia Kev Xaiv: Dawb Fluoride txwv rau Qib 7 Titanium Heaters**
| Kev Ua Haujlwm|Dawb Fluoride Concentration (ppm)|Tag Nrho NH₄HF₂ Concentration (%)|Pom Zoo Ua|Cia siab rau kev pab lub neej (teev) |
|--------------------|----------------------------------|-------------------------------|--------------------|-------------------------------|
| Zoo- tswj da dej, tsis muaj fluoride, lub hom phiaj 2000-teev kev pabcuam |<100 | <1.0% | Grade 7 titanium, 1.2 mm wall | >5000 (kev nyab xeeb) |
| Txheem stripping tov, raug kev khiav hauj lwm ntau|100 – 150|1.0 – 1.8%|Qib 7 titanium, 1.5 hli phab ntsa, saib xyuas txhua lub limtiam|3,000 – 4,000 |
| Da dej txhoj puab heev, siab fluoride ze txwv|150 – 200|1.8 – 2.5%|Qib 7 titanium, 2.0 hli phab ntsa, lossis hloov mus rau PFA-coated|2,000 – 2,500 (marginal) |
| Free fluoride exceeds 200 ppm | >200 | >2.5%|Tsis pom zoo rau titanium – siv PFA los yog quartz rhaub |<1500 |
| Da dej muaj cov tshuaj fluoride-cov tshuaj ua kom nyuaj (Al³⁺, Fe³⁺)|Variable (txo los ntawm complexation)|Txog li 5% tej zaum yuav tau txais|Qib 7 titanium nrog 1.2 hli phab ntsa, txheeb xyuas cov tshuaj fluoride dawb txhua lub lim tiam|4,000 – 6,000 |
** Cov Tswv Yim Txog Kev Tswj Xyuas Tsis Muaj Fluoride Concentration **
Peb txoj hauv kev ua kom muaj cov tshuaj fluoride dawb hauv qab 150 ppm qhov pib. Ua ntej, ntxiv aluminium sulfate (Al₂(SO₄)₃) mus rau lub stripping da dej ntawm molar ratio ntawm Al: F ntawm 1: 6. Aluminium ions complex tsis muaj fluoride li AlF₆³⁻, txo cov aggressive free fluoride concentration yam tsis txo tag nrho NH₄HF₂. Thib ob, tswj pH ntawm 4.0 thiab 4.5 siv ammonia lossis acetic acid; qis pH nce dawb fluoride li HF, thaum pH siab dua precipitates titanium hydroxides. Thib peb, saib xyuas cov tshuaj fluoride dawb txhua lub limtiam uas siv cov tshuaj fluoride ion- xaiv cov electrode thiab kho cov tshuaj chemical hauv da dej thaum cov concentrations mus txog 120 ppm. Rau cov chaw uas tswj tsis tau cov fluoride dawb hauv qab 200 ppm, PFA-coated los yog quartz heaters raug pom zoo hla titanium.
**Qhov xaus**
Rau qib 7 titanium cua sov coils submerged nyob rau hauv 12% ammonium bifluoride stripping tov ntawm 80℃(pH 4), qhov siab tshaj plaws dawb fluoride concentration tso cai rau 2000 teev ntawm kev pab cuam yam tsis muaj kev puas tsuaj pitting yog 150 ppm F⁻, nrog kev pom kev nyab xeeb txwv ntawm 100 ppm. Dawb fluoride qib siab tshaj 150 ppm ua rau pitting pib ua ntej 2000 teev, nrog pitting tus nqi siab tshaj 0.30 hli / xyoo ua rau phab ntsa perforation hauv 1.2 hli hlab. Cov kws tsim qauv qhia cov titanium rhaub rau kev tshem tawm cov txheej anodized yuav tsum xyuas kom meej cov tshuaj fluoride tsis pub siv cov ion- xaiv cov electrode ntsuas, tswj qib qis dua 100 ppm los ntawm dilution lossis aluminium complexation, thiab xav txog PFA-coated lossis quartz sheaths rau da dej tshaj 200 ppm dawb Qhov kev qhia tshwj xeeb ntawm cov tshuaj fluoride pub dawb no hloov pauv qhov siab - qhov pheej hmoo pitting ib puag ncig rau hauv qhov kev xav tau, tswj tau qhov kev pabcuam rau qib 7 titanium rhaub.
