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, cov silicate ua rau tsis tu ncua, tsis yog - ntxeem tau, tiv thaiv zaj duab xis (thickness 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.
Quantitative Film Quality vs. pH
Hauv 10% Na₂SiO₃ ntawm 80℃rau 500 teev:
| pH | Zaj duab xis Thickness (µm) | Zaj duab xis Porosity | Corrosion Rate (mm / xyoo) | Pitting Present? |
|---|---|---|---|---|
| 8 | 0.1–0.3 | Siab | 0.15–0.30 | Yog lawm |
| 9 | 0.2–0.5 | Siab | 0.08–0.20 | Qee zaus |
| 10 | 0.5–1.0 | Nruab nrab | 0.04–0.10 | Tsis tshua muaj |
| 11 | 1.0–1.5 | Tsawg | 0.02–0.05 | Tsis muaj |
| 12 | 1.5–2.5 | Tsawg heev | 0.01–0.03 | Tsis muaj |
| 13 | 2.0–3.0 | Tsawg heev | 0.005–0.015 | Tsis muaj |
Cov nyhuv ntawm qhov kub thiab txias ntawm pH xav tau
| Kub (degree) | Yam tsawg kawg pH rau cov yeeb yaj kiab tiv thaiv | Pom zoo pH |
|---|---|---|
| 60 | 10.5 | 11.0 |
| 80 | 11.0 | 11.5 |
| 100 | 11.5 | 12.0 |
pH Control Guide rau Silicate Service
| Ua haujlwm pH | Zaj duab xis zoo | Pom zoo ua |
|---|---|---|
| >11 | Tiv thaiv | Tsis muaj |
| 10–11 | Marginal | Nce pH nrog NaOH |
| 9–10 | pluag, ntxeem tau | Add NaOH to raise to >11 |
| <9 | Tsis yog- tiv thaiv | Rov tsim kho dua |
Kev pom zoo engineering
Rau kev pabcuam sodium metasilicate ntawm 80 degree, tswj pH saum 11 siv sodium hydroxide ntxiv. Los ntawm kev tswj pH, tus kws ua choj ua kom muaj kev tiv thaiv, tsis yog - ntxeem tau silicate zaj duab xis ntawm titanium.
