Yuav ua li cas muaj cov kab mob fluoride Ions nyob rau hauv Phosphoric Acid Solutions Hloov Qhov Kev Nyab Xeeb Kev Ua Haujlwm Kub Ceev rau Qib 2 Titanium Sheaths?

Concentrated phosphoric acid (H₃PO₄) 30-85% yog ib qho nruab nrab hauv kev tsim cov chiv, kev kho hlau thiab kev ua tshuaj. Qib 2 titanium tau txais kev txhim kho corrosion nyob rau hauv cov ntshiab phosphoric acid txog li 80-100 degree, nyob ntawm qhov concentration. Phosphate pob zeb ores siv nyob rau hauv kev tsim cov phosphoric acid, txawm li cas los xij, muaj fluorapatite ua cov khoom siv ntuj tsim thiab ua rau cov kab mob fluoride ions (F⁻) mus rau cov kua qaub kawg ntawm qhov ntau ntawm 100 thiab 2,000 ppm. Fluoride ions yog heev hostile rau passive zaj duab xis ntawm titanium. Cov tshuaj fluoride ntawm cov kab ntau ntau ua rau txo qis kev nyab xeeb kev ua haujlwm kub txwv. Kev nkag siab txog qhov kev hloov pauv no yog qhov tseem ceeb kom tsis txhob muaj kev puas tsuaj tsis txaus ntseeg ntawm titanium immersion heaters hauv daim ntawv thov phosphoric acid.

Mechanism ntawm passivity breakdown los ntawm fluoride

Hauv cov ntshiab phosphoric acid TiO2 txheej ua rau titanium ruaj khov. Cov yeeb yaj kiab no cuam tshuam los ntawm fluoride ions los ntawm kev sib txawv ntawm cov tshuaj chlorides. Titanium ions tsim fluoride complexes nrog soluble hexafluorotitanate hom (TiF₆²⁻). Cov txheej txheem no tshem tawm titanium los ntawm cov zaj duab xis passive ncaj qha yam tsis tas yuav tsum tau ua cov yeeb yaj kiab tawg. Cov tshuaj tiv thaiv yog TiO₂ + 6F⁻ + 4H⁺ → TiF₆²⁻ + 2H₂O. Cov tshuaj tiv thaiv no nce nrawm dua ntawm qhov kub siab dua. Thaum cov tshuaj fluoride tau txais los ntawm cov txheej txheem passive lub hauv paus titanium hlau dissolves thiab sim repassivate. Txawm li cas los xij, fluoride txuas ntxiv mus rau txoj kev tshiab titanium ions, inhibiting ruaj khov zaj duab xis reconstruction. Yog li, kev hloov pauv ntawm tus cwj pwm tsis zoo mus rau qhov muaj zog corrosion tshwm sim ntawm qhov ntsuas kub uas txo qis nrog cov ntsiab lus fluoride. Corrosion tus nqi qis dua qhov pib no yog qis dua 0.1 hli / xyoo. Cov nqi tuaj yeem siab tshaj 1.0 hli / xyoo siab tshaj qhov pib rau 10-20℃kub nce.

Kev nyab xeeb kev khiav hauj lwm kub txwv kom muaj nuj nqis hloov

Kev nyab xeeb kev ua haujlwm kub txwv rau Qib 2 titanium (txhais tias tus nqi corrosion tsawg dua 0.1 hli hauv ib xyoos) tau tsim los ntawm kev ntsuas hluav taws xob hluav taws xob hauv 50% phosphoric acid nrog ntau yam fluoride concentrations:

Fluoride tsis kuaj pom (<10 ppm) Safe working limit 95° C. Titanium possesses a stable passive film at all practical temperatures of heater operation.

Fluoride ntawm 50 ppm: Kev nyab xeeb kev ua haujlwm txwv qis qis rau 82 degree. Lub caij nplooj zeeg ntawm 13 degree. Ntawm lub zog ib txwm muaj zog (20 W / cm2), cov cua sov saum npoo tuaj yeem ncav cuag qhov kev txwv no txawm tias cov kua qaub ntau ntawm 70 degree.

Fluoride 200 ppm: Cov kev pab cuam txo qis rau 65 deg.C. 30℃poob. Feem ntau ntawm cov khoom siv phosphoric acid heaters khiav ntawm cov txheej txheem txheej txheem kub (75-85 degree) yog nyob rau hauv lub active corrosion regime.

Fluoride 500 ppm: Txo kev nyab xeeb kev txwv rau 52℃. 43 degrees C txias dua. Cov txheej txheem txheej txheem kub yog 20-30℃siab tshaj qhov txwv thiab yuav ua tsis tau sai hauv lub lis piam.

Fluoride ntawm 1,000-2,000 ppm: Kev nyab xeeb kev ua haujlwm txwv txo qis rau 35-40 degree. Qib 2 titanium yuav tsis muaj txiaj ntsig rau txhua daim ntawv thov thaum cua sov. Lwm cov ntaub ntawv (zirconium, siab silicon cam khwb cia hlau) yuav tsum tau txiav txim siab.

Hloov nyob rau hauv Kub txwv tshaj phosphoric acid Concentrations

Qhov cuam tshuam fluoride yog cuam tshuam nrog qhov concentration ntawm phosphoric acid. Cov kua qaub ntau dua (70-85%) ua rau muaj kev txo qis hauv ib puag ncig thiab txo qis dej dawb uas tseem txo cov fluoride aggression rau qee yam. Cov lus hauv qab no yog cov lus qhia txog kev txwv kev nyab xeeb ua tiav.

Phosphoric Acid Concentration Fluoride Concentration (ppm F-) Kev Nyab Xeeb Kev Txwv rau Qib 2 TitaniumCommon Damage Mechanism
30–40% <50 ppm 85°C Uniform passive thinning (<0.05 mm/yr)
30–40% 50–200 ppm 60°C Accelerated uniform corrosion with pitting 30–40% >200 ppm Not recommended High active corrosion (>1 hli / xyoo)
50-65% <50 ppm 95°C Passive with occasional metastable pitting 50-65% 50-200 ppm 70°C Fluoride complexation dominates surface chemistry
50-65% 200-500 ppm 55℃Fragile kev pabcuam yuav tsum tau kuaj xyuas
70-85% <50 ppm 100 C Cov ntaub ntawv ua haujlwm zoo tshaj plaws
70-85% 50-200 ppm 75℃Haum rau ntau daim ntawv thov chiv
70-85% 200-500 ppm 60℃Lub neej ua haujlwm luv (feem ntau 6-12 lub hlis)
70–85% >500 ppm 45℃Qib 2 tsis tsim nyog, xav txog qib 7 lossis zirconia
Cov kev cuam tshuam rau kev ua haujlwm ntawm lub rhaub

Qhov kev hloov pauv ntawm qhov kub thiab txias ua haujlwm muaj kev cuam tshuam ncaj qha rau lub rhaub dej kub. Lub tshuab cua sov ntsuas rau 85℃bulk acid kub yuav muaj qhov kub thiab txias ntawm 15℃siab dua (vim cov cua sov flux), ncav cuag 100℃ntawm titanium-kua interface. Ntawm 200 ppm fluoride nyob rau hauv cov kua qaub, lub interface kub yog 35℃siab tshaj qhov kev nyab xeeb txwv ntawm 65 degree, thawb lub rhaub kom zoo rau hauv lub active corrosion regime. Txo lub zog ceev ntawm lub rhaub kom txo tau qhov kub thiab txias delta. Rau cov tshuaj fluoride-muaj phosphoric acid, kev siv cov watt ntom ntom (10-12 W / cm2 piv rau 20-25 W / cm2) ua rau lub raj nplaim ze rau qhov kub thiab tej zaum tseem tshuav tsis tau. Xwb, ua cov txheej txheem ntawm qhov kub thiab txias (xws li . 65℃es tsis txhob 85℃) rov qab tau cov npoo kev nyab xeeb rau cov fluoride nruab nrab.

Tsim kom muaj kev paub tshwj xeeb

Thaum xaiv qib 2 titanium sheath rhaub rau kev pabcuam phosphoric acid, thov los ntawm lub chaw kuaj pom muaj cov tshuaj fluoride ntawm cov txheej txheem acid. Raws li cov kev ua haujlwm nyab xeeb saum toj no, Qib 2 puas tsim nyog? Yog tias qib fluoride yog 100–300 ppm, siv Qib 7 titanium (palladium-stabilized). Cov hlau noble nce qhov kev txwv tsis pub ua haujlwm nyob ib puag ncig 25-30℃saum qib 2, vim nws ua catalytically hauv cov txheej txheem cathodic. Yog hais tias cov fluoride cov ntsiab lus nyob rau hauv kub phosphoric acid ntau tshaj 300 ppm, xav txog zirconium heaters uas yog deb tshaj fluoride complexation dua titanium. Saib xyuas phosphoric acid rau drift nyob rau hauv fluoride concentration thaum sib txawv ore batches nkag mus rau hauv tus txheej txheem. Lub tshuab cua sov uas muaj kev nyab xeeb tsuas yog ob peb lub lis piam ua ntej tuaj yeem ua tsis txaus yog tias qib nce ntawm 150 ppm txog 350 ppm. Kev siv cov tshuaj fluoride concentration raws li tus qauv tsim tseem ceeb hloov pauv txuag tus kws ua haujlwm xav tsis thoob hauv ib qho ntawm feem ntau tseem tsis tau muaj tshuaj lom neeg siv cua sov rau cov khoom siv titanium.