Vim li cas Qhov Nto Carbon Contamination Los Ntawm Kev Tsim Lubricants Txo Cov Passivation Range Ntawm Titanium Hluav Taws Xob Rhaub Hauv Kev Pabcuam Nitric Acid?
Tso lus
Nitric acid yog qhov muaj zog oxidizing ib puag ncig qhov twg titanium nthuav tawm cov kev tiv thaiv corrosion zoo tshaj qhov muaj peev xwm ntau. Cov zaj duab xis passive tseem nyob ruaj khov ntawm kwv yees li 0V mus rau tshaj 1.8V vs. SCE. Txawm li cas los xij, cov pa roj carbon monoxide deg- tau qhia thaum lub sij hawm kos duab, khoov, los yog vuam los ntawm cov roj nplaum uas seem, cov khoom ua kom txias, lossis cov ntawv cim kos npe - ua rau cov kab mob kis tau zoo heev. Carbonaceous residues decompose ntawm qhov kub thiab txias, tsim kev txo qis hauv cheeb tsam ntawm titanium nto. Cov cheeb tsam txo qis no tsis tuaj yeem tswj hwm TiO₂ zaj duab xis passive, hloov lub peev xwm hauv zos mus rau hauv kev ua haujlwm corrosion. Qhov tshwm sim yog nrawm nrawm, feem ntau tshwm sim raws li kev sib cais etched bands lossis thaj chaw pitted sib haum rau cov qauv sib kis. Kev nkag siab txog cov txheej txheem no yog qhov tseem ceeb rau kev pabcuam nitric acid qhov twg cov cua sov kev ntseeg tau nyob ntawm qhov chaw huv si, tsis sib xws.
Mechanism ntawm Carbon-Induced Passivity Breakdown
Kev tsim cov roj nplua nyeem feem ntau muaj cov hydrocarbons, chlorinated paraffins, fatty acids, thiab siab heev - siab additives. Thaum lub sij hawm ib txwm tuav, nyias zaj duab xis ntawm cov tebchaw nyob rau hauv titanium nto txawm tias tom qab degreasing. Thaum lub rhaub dej rau hauv kub nitric acid (piv txwv li, 40-65% HNO₃ ntawm 80-100 degree), muaj ob yam tshwm sim. Ua ntej, nitric acid oxidizes carbon residues, ua carbon dioxide thiab dej. Txawm li cas los xij, hauv cheeb tsam hauv cheeb tsam uas cov pa roj carbon tuab, ib nrab oxidation ua rau carbon monoxide thiab organic acids. Cov khoom no siv nitric acid hauv zos thiab txo qis oxidation peev xwm. Thib ob, exothermic oxidation ntawm cov pa roj carbon monoxide nce qhov kub thiab txias hauv cheeb tsam, ua kom cov nitric acid decomposition rau nitrogen oxides. Kev sib xyaw ua ke ntawm kev txo qis hauv zos oxidizing lub zog thiab qhov kub siab ua rau ib puag ncig microenvironment qhov twg titanium nto muaj peev xwm poob qis dua qhov chaw pib passivation (kwv yees li 0.2V vs. SCE). Kev ua haujlwm corrosion pib ntawm cov pa roj carbon-cov chaw muaj kab mob, tsim cov pits lossis trenches.
Kev txo qis hauv Passivation Range los ntawm Carbon Contamination
Kev ntsuas hluav taws xob hluav taws xob hauv 50% HNO₃ ntawm 85℃tau tsim cov kab hauv qab no passivation rau Qib 2 titanium nrog cov pa roj carbon sib txawv:
Ntxuav qhov chaw (<0.1 mg/cm² carbon, properly degreased and acid pickled): Passivation range from 0.1V to >2.0V vs SCE. Corrosion tus nqi qis dua 0.01 hli hauv ib xyoos thoob plaws txhua qhov muaj peev xwm ua tau. Tsis muaj pitting tom qab 1,000 teev.
Lub teeb paug (0.1-0.5 mg / cm² carbon, feem ntau ntawm ib qho degreasing dhau): Passivation ntau yam txo rau 0.2–1.6V vs. SCE. Ntawm qhov muaj peev xwm siab dua 1.6V (ib txwm rau cov concentrated nitric acid), kev sib tsoo hauv zos pib ntawm cov chaw carbon. Pitting qhov tob ntawm 20-50 µm tom qab 500 teev.
Kev sib kis nruab nrab (0.5-2.0 mg / cm² carbon, los ntawm kos cov roj ntsha residue): Passivation ntau ntxiv txo mus rau 0.3–1.2V vs. SCE. Tshaj li 1.2V, active corrosion tshwm sim ntawm qhov chaw tsis huv. Corrosion tus nqi ntawm carbon me ntsis ntawm 0.5-1.0 mm ib xyoo. Pitting nkag mus 1.0 hli phab ntsa hauv 500-1,000 teev.
Heavy contamination (>2.0 mg / cm² carbon, pom smudges lossis ntiv tes): Passivation ntau nqaim mus rau 0.4–0.8V vs. SCE. Ntawm qhov muaj peev xwm nitric acid ib txwm (1.0-1.4V), qhov saum npoo yog nquag corroding ntawm cov cheeb tsam tsis huv. Kev nrawm nrawm hauv cheeb tsam nrog kev nkag mus ntau dua 2 hli ib xyoos.
Carbon Contamination Control Guide for Nitric Acid Service
Cov lus hauv qab no muab cov txheej txheem kev txiav txim siab rau kev qhia meej txog kev tu cov txheej txheem raws li nitric acid concentration thiab kev ua haujlwm kub:
| Kev Pabcuam Nitric Acid | Yuav tsum tau Surface Carbon Limit | Pom zoo txheej txheem ntxuav | Kev Tshawb Fawb |
|---|---|---|---|
| 40-50% HNO₃, 60-80 degree, kev pabcuam txheem | <0.5 mg/cm² | Alkaline degreasing (60 degree, 10 min) + dej kub yaug | Kev ntsuas dej tawg (nruam zaj duab xis) |
| 50-70% HNO₃, 80-100 degree, oxidizing tej yam kev mob | <0.2 mg/cm² | Alkaline degreasing + nitric / citric acid passivation (20% HNO₃, 50 degree, 30 min) | Cov kuab tshuaj extraction + gravimetric tsom xam (ib qho qauv rau ntau) |
| 70-90% HNO₃, 100-120 degree, liab fuming acid | <0.05 mg/cm² | Vapor degreasing (trichloroethylene lossis lwm txoj hauv kev) + ultrasonic tu hauv dej deionized + nitric acid pickling | X-ray photoelectron spectroscopy (XPS) rau cov pa roj carbon monoxide |
| Kev sib cuam tshuam ntawm nitric acid raug (tsuas yog tu lub voj voog xwb) | <0.3 mg/cm² | Txheem alkaline degreasing txaus | Visual soj ntsuam rau daim ntawv dej |
| Daim ntawv thov tseem ceeb uas ib qho pitting tsis tuaj yeem lees txais (semiconductor- qib acid) | <0.02 mg/cm² | Plasma tu los yog lub tshuab nqus tsev ci - tawm (300℃, 2 teev) tom qab degreasing | Auger electron spectroscopy (AES) nto tsom xam |
Engineering Beyond Carbon Tshem Tawm Ib leeg
Lub raj phab ntsa tuab muab qhov muaj kev nyab xeeb thaum cov pa roj carbon -induced pitting tshwm sim. Lub phab ntsa 1.5 hli nrog lub teeb paug tuaj yeem muaj sia nyob 1,000 teev ua ntej qhov nkag mus, thaum phab ntsa 0.8 hli tsis dhau 300 teev. Lub hauv paus hlau qib kuj hloov pauv qhov raug: Qib 7 titanium (0.15% Pd) nthuav tawm qhov dav dav ntawm qhov chaw huv, tab sis qhia tau hais tias cov pa roj carbon zoo sib xws -induced nqaim. Yog li, palladium ntxiv tsis them rau kev tu tsis zoo. Qhov chaw uas muaj kev phom sij tshaj plaws yog vuam cua sov- cov cheeb tsam cuam tshuam qhov twg cov roj nplaum tuaj yeem ua rau ntawm qhov chaw thaum vuam. Tom qab-welding tu nrog stainless hlau hlau txhuam (mob rau titanium nkaus xwb) tshem tawm cov pa paug ntawm cov welds. Kev tuav tom qab ntxuav yuav tsum siv cov hnab looj tes huv si los tiv thaiv cov roj ntiv tes, uas muaj cov pa roj carbon thiab chlorides.
Ua ib qho kev qhia tshwj xeeb
Thaum qhia txog lub tshuab hluav taws xob titanium rau cov kev pabcuam nitric acid, suav nrog qhov yuav tsum tau ua kom huv si hauv qhov kev qhia tshwj xeeb. Yuav kom tag nrho cov titanium Cheebtsam yog alkaline degreased ua raws li acid pickling (20% HNO₃ + 2% HF rau 5 feeb, ces yaug kom huv si). Rau cov ntsiab lus nitric acid siab tshaj 70% ntawm qhov kub siab, qhia meej tias tus neeg muag khoom ua qhov kev kuaj xyuas passivation: raus tus neeg sawv cev daim coupon rau hauv qhov npaj nitric acid ntawm kev ua haujlwm kub rau 24 teev, tom qab ntawd tshuaj xyuas microscopically rau ib qho pitting. Thaum lub sij hawm commissioning, sau lub kaw lus nrog 20% HNO₃ ntawm 50℃thiab ncig rau 2 teev kom passivate txhua qhov chaw thiab tshem tawm cov pa roj carbon seem. Saib xyuas cov xim nitric acid; yellowish xim qhia tias nitrogen oxide tsim los ntawm carbon oxidation, signaling tsis txaus tu. Los ntawm kev tswj cov pa roj carbon monoxide nto raws li qhov tseem ceeb, tus kws tshaj lij xyuas kom meej tias lub tshuab cua sov titanium ua tiav nws qhov kev ua tiav tag nrho thiab muab kev pabcuam txhim khu kev qha hauv cov cheeb tsam oxidizing nitric acid.
