What Does Induction Time Mean?
Induction time refers to a period of time that is necessary to initiate a reaction. Induction time allows a chemical reaction to reach a necessary stage. In paint, it is the duration that must elapse after mixing fresh paint material before starting a satisfactory application. In pitting corrosion, it is the time interval necessary for initiating the first pit.
Induction time also called "sweat-in time."
Corrosionpedia Explains Induction Time
Induction time is the time interval needed to start a reaction or further action. For example, an induction period is necessary for a precatalyst to undergo a transformation to form the active catalyst, before the catalyst can take effect in a catalytic reaction. In an auto-catalytic reaction, the rate of reaction remains slow until sufficient products have formed to catalyze the reaction.
Heat is normally used to accelerate reactions. In the case of an exothermic reaction, the rate of the reaction is initially very low; heat is generated along the reaction and the rate of reaction increases. A time interval is needed for the reaction to reach full re-activity. This time interval is regarded as induction time.
Insufficient induction times in coatings or paints cause coating failures. For example, many epoxy coatings require a fixed time interval in order to make the epoxy resin and hardener fully compatible. When this pre-reaction time is not met, it will produce poor a film appearance and poor coating performance. Induction time will usually increase with low temperatures and/or high humidity.
In coating industries, improperly inducted epoxies will lead to:
- A reduced gloss (than expected)
- Polyamide/amine blushing
- Poor color appearance
- Lower corrosion and chemical resistance
- Poorer film
The induction time of pitting is not the same for all steel. It varies from steel to steel and depends on the environment. In pitting, the induction time mainly depends on the concentration of chloride ion (Cl-) in the solution. The higher the concentration of Cl-, the less the induction time. Induction time also increases with the decreasing of the potential.