In a Titanium Heat Rod Installed in a Tank of 50% Lithium Hydroxide at 90°C, How Does the Dissolved Carbon Dioxide Level (0 ppm vs. 50 ppm) Alter the Passivation Time and Steady-State Corrosion Rate?

Titanium is stable in 50% lithium hydroxide (LiOH) at 90°C to generate a passive layer of lithium titanate (Li 2 TiO 3 ). Dissolved carbon dioxide (CO2) interacts with LiOH to lithium carbonate (Li2CO3) that precipitates on the surface. Li 2 CO 3 is porous and less protective than Li 2 TiO 3 . At 0 ppm CO₂, the passivation time is 10–20 hours and the steady state corrosion rate is 0.005–0.010 mm/year. The passivation times are increased to 50-100 hours at 50 ppm CO2 and the steady state corrosion rates increase to 0.020-0.040 mm/year.

Quantitative CO₂ Effect on Corrosion

Dissolved CO₂ (ppm) Passivation Time (hours) Steady-State Rate (mm/year)Scale Composition Li 2 TiO 3 0 <10-20 0.005-0.010 Li 2 TiO 3 10 10-20 0.010-0.020 Mixed 25 20-40 0.015-0.030 Li 2 TiO 3 + Li 2 CO 3 50 30-60 0.020-0.040 Li 2 CO 3 dominating 100 >100 0.040-0.080 Li 2 CO 3 only
CO2 Control Guide

CO₂ Level (ppm) Recommended Action Heater Life (1.5 mm wall) <10 None >20 years
10–25 Nitrogen blanketing 15-20 years
25-50 CO2 scrubber on vent 8-12 years > 50Alternate alternative 4-6 years
Engineering Tips

For 50% LiOH at 90°C cover the tank with nitrogen to keep dissolved CO₂ below 10 ppm. The engineer adjusts the CO2 level such that passivation is rapid and the steady state corrosion rate is low.