The heating principle of heat packs is mainly based on the oxidation reaction between iron powder and oxygen in the air, which releases heat.
Specifically, heat packs contain iron powder, activated carbon, water, and salt. When exposed to air, the iron powder reacts with oxygen to form iron oxide and release heat. Activated carbon adsorbs moisture to ensure the oxidation process proceeds smoothly; it also conducts heat, allowing for uniform heat distribution.
Salt (usually sodium chloride) acts as a catalyst, promoting the corrosion of the iron powder. Vermiculite serves as a thermal insulator to prevent skin burns.
The main chemical reaction equation for heat generation in heat packs is:4Fe + 3O₂ → 2Fe₂O₃ (iron oxidation)
Under the action of salt, water helps accelerate the reaction. As the temperature rises, water evaporates. This process helps stabilize the temperature of the heat pack until the iron powder is completely oxidized or the reaction stops.
In addition, the temperature regulation mechanism of the heat pack and the oxygen permeability of the breathable membrane also affect the heating effect, ensuring continuous heat release while preventing overheating.
When using, avoid direct contact with the skin to prevent low-temperature burns, and do not apply it to the same area for a long time.
