For a Titanium Heat Rod Operating in a 50% Potassium Carbonate Solution at 110°C, How Does the Dissolved Oxygen Level (0.5 ppm vs. 5 ppm) Change the Stability of the Titanate Passivation Layer?

In 50 % potassium carbonate (K2CO3) at 110 °C a protective coating of potassium titanate (K2TiO3) is formed on the titanium surface. Dissolved oxygen (DO) is a key element of titanates production. At low DO (0.5 ppm) the titanate layer is thin (0.1–0.5 µm), porous and offers inadequate protection. At high DO (5 ppm) layer is thicker (1-3 µm) and dense decreasing corrosion rate by 5-10×.

Quantitative Stability of Passivation Layer vs. Dissolved O2

50% K 2 CO 3 110°C 1,000 h:

DO (ppm) Titanate Layer Thickness (µm) Corrosion Rate (mm/year)Effect of Temperature on DO Requirement Surface Condition 0 (deaerated) 0.05-0.1 0.15-0.30 Dark, porous 0.5 0.1-0.3 0.08-0.15 Grey, mild 2 0.5-1.0 0.03-0.08 Light grey 5 1.0-2.0 0.01-0.03 Bright, protective 10 2.0-3.0 0.005-0.015 Bright, steady

Temperature (°C) Minimum DO for Stable Passivation (ppm)Suggested DO (ppm) 80 1 3 100 2 5 110 3 6 120 4 8 Dissolved oxygen management guide

DO (ppm) . Titanate Layer Stability .Recommended Action >5 Excellent No 3-5Good Monitor weekly 1-3 Marginal Sparge air
0.5–1 Bad Increase aeration <0.5 Unstable Redesign; add oxidiser
Engineering Advice

50% K.sub.2CO.sub.3 at 110.degree. C. keep dissolved oxygen >5 ppm by air sparging The engineer's control of DO supports a steady protective potassium titanate layer.