When A Titanium Immersion Heater Is Installed In A 10% Sodium Metasilicate Solution At 80°C, Why Does The Silicate Ion Form A Protective, Non-Porous Film Only At PH >11, Thiab Yuav Ua Li Cas Thaum PH 9?
Tso lus
In sodium metasilicate (Na₂SiO₃) solutions at 80°C, silicate ions polymerize on titanium surfaces. At pH >11, silicate tsim ib qho txuas ntxiv, tsis yog - ntxeem tau, tiv thaiv zaj duab xis nrog lub thickness ntawm 0.5-2 µm. Ntawm pH 9, zaj duab xis yog ntxeem tau, tawg, thiab tsis yog - tiv thaiv, cia chloride los yog lwm yam aggressive hom nkag mus thiab ua rau pitting. Qhov sib txawv tshwm sim los ntawm lub xeev polymerization ntawm silicate ions. Thaum pH siab, silicate tshwm sim raws li monomeric SiO₄⁴⁻ ions uas tsim cov duab ntom ntom, iav. Nyob rau hauv qis pH, silicate polymerizes rau hauv colloidal chains uas tsim ib tug ntxeem tau, tawg qauv.
Lub Mechanism ntawm pH-Dependent Silicate Film Formation
The polymerization of silicate ions follows: SiO₄⁴⁻ + H₂O → HSiO₄³⁻ + OH⁻. At high pH (>11), qhov sib npaug txaus siab rau monomeric ions, uas tso ua ib daim duab ntom ntom amorphous silica. Ntawm pH 9–10, cov ions polymerize rau hauv cov saw hlau-zoo li cov qauv uas tsim kom muaj qhov ntxeem tau. Cov yeeb yaj kiab kuj suav nrog sodium ions, tsim cov iav sodium silicate. Kev tiv thaiv zoo yog txiav txim siab los ntawm qhov ntom ntawm cov yeeb yaj kiab thiab qhov tsis muaj micro- tawg.
Quantitative Film Quality raws li kev ua haujlwm ntawm pH
Kev tswj xyuas hauv 10% Na₂SiO₃ ntawm 80℃tshaj 500 teev tau tsim cov hauv qab no rau Qib 2 titanium. Ntawm pH 8, zaj duab xis thickness yog 0.1-0.3 µm, zaj duab xis porosity siab, tus nqi corrosion yog 0.15-0.30 hli ib xyoo, thiab pitting yog tam sim no. Ntawm pH 9, lub thickness yog 0.2-0.5 µm, lub porosity siab, tus nqi corrosion yog 0.08-0.20 hli ib xyoo, thiab pitting yog qee zaus. Ntawm pH 10, lub thickness yog 0.5-1.0 µm, lub porosity yog nruab nrab, tus nqi corrosion yog 0.04-0.10 hli ib xyoo, thiab pitting yog tsawg. Ntawm pH 11, lub thickness yog 1.0-1.5 µm, lub porosity yog tsawg, tus nqi corrosion yog 0.02-0.05 hli ib xyoo, thiab tsis muaj pitting tshwm sim. Ntawm pH 12, lub thickness yog 1.5-2.5 µm, lub porosity tsawg heev, tus nqi corrosion yog 0.01-0.03 hli ib xyoo, thiab tsis muaj pitting tshwm sim. Ntawm pH 13, lub thickness yog 2.0-3.0 µm, lub porosity tsawg heev, tus nqi corrosion yog 0.005-0.015 hli ib xyoo, thiab tsis muaj pitting tshwm sim.
Kev cuam tshuam ntawm qhov kub thiab txias ntawm pH xav tau
Qhov tsawg kawg nkaus pH yuav tsum muaj rau cov yeeb yaj kiab tiv thaiv nce nrog qhov kub thiab txias. Ntawm 60 degree, pH tsawg kawg yog 10.5, thiab pH pom zoo yog 11.0. Ntawm 80 degree, qhov tsawg kawg nkaus yog 11.0, thiab qhov pom zoo yog 11.5. Ntawm 100 degree, qhov tsawg kawg nkaus yog 11.5, thiab qhov pom zoo yog 12.0. Ntawm 120 degree, qhov tsawg kawg nkaus yog 12.0, thiab qhov pom zoo yog 12.5. Kev kub siab dua txhawb silicate polymerization, yuav tsum muaj pH siab dua los tswj lub xeev monomeric.
pH Control Guide rau Sodium Metasilicate Service
Cov lus hauv qab no muab cov lus pom zoo rau pH tswj kom muaj kev tiv thaiv silicate zaj duab xis ntawm Qib 2 titanium rhaub hauv 10% sodium metasilicate ntawm 80 degree.
| Ua haujlwm pH | Zaj duab xis zoo | Corrosion Rate (mm / xyoo) | Pitting Risk | Pom zoo ua |
|---|---|---|---|---|
| >11 | Tiv thaiv | <0.05 | Tsis muaj | Tsis muaj |
| 10–11 | Marginal | 0.05–0.10 | Tsawg | Nce pH nrog NaOH |
| 9–10 | pluag, ntxeem tau | 0.10–0.20 | Nruab nrab | Add NaOH to raise to >11 |
| 8–9 | Tsis yog- tiv thaiv | 0.15–0.30 | Siab | Rov tsim kho dua |
| <8 | Tsis ruaj khov | >0.30 | Mob hnyav | Tsis tau |
Engineering Tshaj pH Control
Qib titanium cuam tshuam rau pH qhov xav tau. Qib 7 (palladium-stabilized) tsim cov yeeb yaj kiab tiv thaiv silicate ntawm pH 10.5–11.0, qis dua qib 2 me ntsis. Qib 12 muaj tus cwj pwm zoo sib xws rau Qib 2. Phab ntsa tuab muab kev tiv thaiv corrosion yog tias cov yeeb yaj kiab tsis tiv thaiv tag nrho. Lub silicate concentration cuam tshuam rau kev tsim cov yeeb yaj kiab; ntawm 5% Na₂SiO₃, pH yuav tsum yog 11.5. Ntawm 15% Na₂SiO₃, pH xav tau yog 10.5. Lub xub ntiag ntawm chlorides (los ntawm impurities) nce pH qhov xav tau los ntawm 0.5-1.0 units. Cov tshuaj yuav tsum tau saib xyuas nrog pH meter calibrated rau siab -pH daws.
Ua ib qho kev qhia tshwj xeeb
Rau lub titanium immersion rhaub hauv 10% sodium metasilicate ntawm 80 degree, tswj pH saum 11.0 los ntawm kev ntxiv sodium hydroxide. Nruab lub pH maub los nrog lub tswb teeb ntawm 10.8 thiab kev cuam tshuam ntawm 10.5. Rau cov tshuab uas twb muaj lawm nrog pH qis dua 11, ntxiv NaOH kom nce pH mus rau 11.5. Yog tias pH tsis tuaj yeem tsa tau, siv Qib 7 titanium lossis txo qhov kub ntawm 60 degree. Thaum lub sijhawm ua haujlwm, tshuaj xyuas lub tshuab cua sov rau pitting; Yog tias pitting pom, nce pH tam sim ntawd. Los ntawm kev tswj cov pH saum toj no 11, tus kws ua choj ua kom muaj kev tiv thaiv, tsis yog - ntxeem tau silicate zaj duab xis ntawm titanium.
