The heating principle of the hand warmer is usually that the iron powder is gradually oxidized and undergoes an exothermic reaction.
The self-heating principle of the hand warmer is mainly to use the primary battery to speed up the chemical reaction, thereby converting the chemical energy inside into heat energy, while using the insulation material to maintain the heating time.
Open the package of the hand warmer when using it, and the material inside will react with the oxygen in the air through the outer breathable membrane, which will generate more heat, which is controlled according to the function of the breathable membrane. Usually iron powder is gradually oxidized, so the exothermic reaction is continuous and slow, and it will not burn violently like magnesium powder. The black powder in the hand warmer non-woven bag is harmless to the human body, and the iron oxide produced after the iron powder is oxidized is harmless to the human body, so the hand warmer is safer.
Chemical formula of the reaction occurs in a hand warmer is
2Fe + O2 + 2H2O=2Fe(OH)2
Negative electrode: Fe-2e-=Fe2+,
Positive electrode: O2 + 2H2O + 4e-=4OH-,
The total reaction: 2Fe + O2 + 2H2O=2Fe(OH)2,
4Fe(OH)2 + 2H2O + O2=4Fe(OH)3↓2Fe(OH)3 ==== Fe2O3+3H2O.
It is recommended that diabetics, children, the elderly and other people who are not sensitive should use it with caution to prevent being scalded by low temperature.