Activated carbon heater
Activated charcoal warmers are aids for generating chemical heat and are used, for example, in disposable hand warmers .
They consist of iron powder , table salt , activated charcoal , water and vermiculite surrounded by a soft, gas-permeable membrane. After opening an airtight outer packaging, the iron is slowly oxidized with atmospheric oxygen. When combined with oxygen, the iron oxidizes in an exothermic reaction, and the heat of reaction released is released into the environment:
with a reaction enthalpy of ΔH ° = −853.68 kJ per mol of iron.
The maximum temperature can be up to 70 ° C; the heat is given off over a period of 6 to 24 hours. Salt and water fulfill catalytic tasks, activated charcoal and other organic components serve as water storage and sometimes also as a catalyst. Airtight packaging, i.e. sealing against atmospheric oxygen, can stop the reaction and the heat emission can be continued at a later point in time. Heat pillows with the functionality of the disposable hand warmers are particularly widespread in Asia. The pillows are often equipped with an adhesive surface on one side and can be glued to the thigh or back, for example. Shoe insoles based on this principle are also available.