When a Grade 7 Titanium Heat Rod Is Exposed to a 0.2% Hydrogen Peroxide Solution at 60°C, How Does the Catalytic Decomposition Rate of H₂O₂ Change as the Palladium Surface Becomes Covered with Oxygen Bubbles?

The grade 7 titanium alloy contains 0.12-0.25% of palladium, which is a good catalyst for the decomposition of hydrogen peroxide: 2H 2 O 2 → 2H 2 O + O 2 . The initial rate of decomposition at 60°C is high so that bubbles of oxygen are produced, and they stick to the palladium-rich surface. Bubbles block active catalytic sites, and the breakdown rate decreases by 50–80% within 24 h. The palladium surface passivation with oxygen bubbles is reversible after cleaning.

Time vs. Quantitative Decomposition Rate

On titanium grade 7 in 0.2% H₂O₂ at 60°C:

O2 Evolution Rate (mL/cm2.hour) Relative Catalytic Activity (%) 0.5 2-5 100 2 1.5-3 70 6 1-2 50 12 0.5-1.5 30 24 0.3-1 20 48 0.2-0.8 15 Effect of H2O2 Concentration and Temperature

H 2 O 2 (%)Temperature (°C)Initial Rate (mL/cm 2 .hour)Rate after 24 hours (mL/cm 2(hour) Deactivation Factor 0.1 60 1~3 0.2~0.6 5× 0.2 60 2~5 0.3~1 5× 0.5 60 5~10 0.8~2 5× 0.2 40 1~2 0.2~0.5 5× 0.2 80 5~10 1~2 5× Oxygen Bubble Management Guide

Required H2O2 Stability Recommended Action Catalyst Activity Maintained
High (minimise decomposition)Grade 2 (no Pd) Use N/A
Moderate (some disintegration is OK) Grade 7 – tolerate deactivation 20 % after 24 h
Periodic cleaning Wipe or rinse surface of heaterBack to full strength
Continuous, high stability H₂O₂ inhibited by phosphoric acid80% reduction in decomposition
Recommendation for Engineering

Use Grade 2 titanium instead of Grade 7 in H2O2 solutions where breakdown is undesirable. If Grade 7 is needed, frequently wipe the surface to remove oxygen bubbles. From knowing palladium-catalyzed breakdown and bubble deactivation the engineer picks the right grade of titanium.