The core criteria for determining if color-changing silica gel is aging are: inability to restore color, particle breakage or pulverization, and a significant decrease in adsorption capacity, which does not improve even after proper regeneration.
1. Three Visual Signs of Aging
Judgment Indicators Normal State Aging Signs
Color Recovery Ability Can completely return to blue or orange after heating Only partially recovers or remains unchanged (e.g., grayish-white, dark red, brown)
Physical State Particles intact, hard texture Cracks, breakage, pulverization, or softening and clumping appear
Moisture Absorption Performance Slowly changes color when placed in a humid environment (blue → pink) Extremely rapid color change or no change at all indicates that the microporous structure has collapsed.
Key Note: If the color cannot be completely restored after heating, it can be basically determined that the indicator function is malfunctioning. Even if some adsorption capacity is still present, it is not recommended for use in critical moisture-proof scenarios.
2. Auxiliary Judgment Methods
Method Operating Instructions Aging Signs
Regeneration Test Heating according to standard procedure (baking at 100–120℃ for 1–2 hours) No color change or only partial recovery
Usage Duration and Number of Uses Check if it has been regenerated ≥5 times or used for more than 1 year. Performance degradation accelerates after exceeding the limit.
Environmental Exposure Test Place the cooled silica gel in a sealed, humid container for 24 hours. No color change → No response; rapid complete color change → Adsorption out of control, both are abnormal.
In the laboratory, "adsorption capacity decreases by more than 30% after 5 regenerations" is often used as the aging and elimination standard.
3. Causes of Aging and Prevention Recommendations
Main Causes:
Excessively high regeneration temperature (>120℃) leads to cobalt chloride oxidation;
Failure to promptly treat multiple deep moisture absorptions;
Clogged micropores by oil and organic matter;
Long-term exposure to high temperature and high humidity environments.
Precautions:
Control the regeneration temperature between 100–120℃; Regenerate when the color change reaches 1/3 to avoid complete saturation; Ensure cleanliness and freedom from contamination before regeneration; Record the number of regenerations, and strengthen monitoring after a cumulative total of ≥5 regenerations.
Practical suggestions: Aging silicone should be labeled "Invalid" and stored separately to avoid misuse in precision equipment such as cameras and hearing aids. Protect from moisture.
