Sodium acetate (CH₃COONa) ntawm 50% concentration thiab 90℃yog siv rau hauv textile dyeing thiab ua tus neeg sawv cev buffering. Cov tshuaj yog alkaline (pH 8-9). Acetic acid impurity los ntawm hydrolysis los yog paug paug txo cov pH. Thaum pH poob qis dua 5, titanium passive zaj duab xis yuav tsis ruaj khov, thiab cov tshuaj tiv thaiv cathodic hloov ntawm oxygen txo mus rau hydrogen evolution. Atomic hydrogen tuaj yeem xa mus rau hauv titanium lattice thiab tsim molecular hydrogen ntawm cov voids sab hauv, ua rau blistering ntawm qhov chaw. Qhov siab tshaj plaws acetic acid impurity los tiv thaiv hydrogen blistering yog 500 ppm (0.05%). Tshaj li qib no, pH poob qis dua 5, thiab hlwv tshwm sim hauv 100-500 teev.

Lub Mechanism ntawm Hydrogen Blistering hauv Acetate Solutions

Hauv alkaline sodium acetate, cov tshuaj tiv thaiv cathodic yog txo qis oxygen, uas tsis tsim hydrogen atoms. Acetic acid txo cov pH: CH₃COOH → CH₃COO⁻ + H⁺. Thaum pH qis dua 5, cov tshuaj tiv thaiv hydrogen evolution 2H⁺ + 2e⁻ → H₂ ua rau cov thermodynamically haum. Lub atomic hydrogen intermediate (H) yog tsim los ntawm titanium nto. Qee cov atomic hydrogen recombines los ua H₂ roj, tab sis ib feem diffuses rau hauv titanium lattice. Hydrogen atoms tsiv mus rau hauv cov voids, inclusions, los yog grain ciam teb, qhov uas lawv recombine los ua H₂ roj. Cov pa roj ua kom siab, ua rau cov hlwv ntawm qhov chaw tuaj yeem tawg.

Quantitative Blistering ua haujlwm ntawm Acetic Acid Concentration

Kev tswj xyuas hauv 50% sodium acetate nrog txawv acetic acid impurity ntawm 90℃tshaj 500 teev tau tsim cov hauv qab no. Ntawm acetic acid qis dua 100 ppm, pH yog 8.5-9.0, tsis muaj hydrogen evolution tshwm sim, tsis muaj hlwv daim ntawv, thiab saum npoo tseem ci. Ntawm 100-300 ppm, pH yog 6.0-7.5, kab hydrogen evolution yuav tshwm sim, tab sis tsis pom hlwv tshwm sim. Ntawm 300-500 ppm, pH yog 5.0-6.0, qee zaus cov pob me me (<0.5 mm diameter) form after 300–500 hours, and the blister density is 1–5 per cm². At 500–1,000 ppm, the pH drops to 4.0–5.0, moderate blistering occurs with blister size 0.5–2 mm, blister density reaches 5–20 per cm², and blistering initiates within 100–300 hours. Above 1,000 ppm, the pH falls below 4.0, severe blistering occurs with blister size exceeding 2 mm, blister density exceeds 20 per cm², and blistering initiates within 50–150 hours.

Kev cuam tshuam ntawm Kub thiab Oxygen Level ntawm Blistering Threshold

The maximum allowable acetic acid decreases with increasing temperature. At 70°C, the allowable acetic acid is 1,000 ppm (0.1%). At 80°C, it is 750 ppm. At 90°C, it is 500 ppm. At 100°C, it is 300 ppm. At 110°C, it is 150 ppm. Dissolved oxygen level also affects the threshold; deaerated solutions cause blistering at lower acetic acid concentrations because oxygen reduction is not available to compete with hydrogen evolution. Aerated solutions (oxygen >5 ppm) nce qhov tso cai acetic acid los ntawm 30-50%.

Acetic Acid Impurity Control Guide rau Sodium Acetate Heaters

Cov lus hauv qab no muab qhov siab tshaj plaws acetic acid concentrations rau Qib 2 titanium rhaub hauv 50% sodium acetate ntawm 90 degree, raws li qhov xav tau kev pab lub neej thiab blistering kam rau ua.

Engineering Beyond Acetic Acid Control

Qib titanium cuam tshuam rau blistering kuj. Qib 7 (palladium-stabilized) muaj 3-5 npaug siab dua rau acetic acid vim palladium catalyzes hydrogen recombination, txo cov hydrogen uas nkag mus rau hauv cov hlau. Qib 12 muaj kev txhim kho nruab nrab. Phab ntsa tuab tsis tiv thaiv blistering tab sis cov phab ntsa tuab tuaj yeem tiv taus ntau cov hlwv ua ntej xau. Cov tshuaj pH yuav tsum tau saib xyuas txhua lub lim tiam; yog tias pH poob qis dua 7, ntxiv sodium hydroxide los txhawb nws. Nitrogen daim pam kom tsis suav nrog oxygen txo qhov tso cai acetic acid pib. Ntxiv cov oxidant xws li sodium nitrite (100 ppm) nce qhov pib los ntawm kev txhawb nqa cov pa txo qis dua hydrogen evolution.

Ua ib qho kev qhia tshwj xeeb

Rau Qib 2 titanium rhaub siv los ua kom sov 50% sodium acetate ntawm 90 degree, tswj acetic acid impurity qis dua 300 ppm kom muaj kev nyab xeeb qis dua 500 ppm blistering pib. Saib xyuas pH txhua lub lim tiam; Yog tias pH poob qis dua 7, ntxiv 0.1% sodium hydroxide kom rov qab alkalinity. Rau cov ntawv thov uas acetic acid ntau tshaj 500 ppm, qhia Qib 7 titanium lossis ntxiv cov oxidant xws li 100 ppm sodium nitrite. Thaum lub sijhawm ua haujlwm, tshuaj xyuas lub tshuab cua sov rau cov hlwv txhua 3 lub hlis; Yog tias pom muaj cov kab mob hlwv, neutralize cov tshuaj thiab hloov lub rhaub. Los ntawm kev tswj cov acetic acid impurity qis dua 500 ppm, tus engineer tiv thaiv hydrogen blistering ntawm Qib 2 titanium rhaub hauv sodium acetate kev pabcuam.