Air-activated heat patches work through a process called oxidation, a chemical reaction that generates heat when the patch's ingredients are exposed to oxygen in the air.
Here's a breakdown:
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Ingredients: The key ingredients typically include iron powder, activated carbon, salt, water, and vermiculite (or another absorbent material). These ingredients are sealed inside a permeable pouch or container.
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Activation: When the packaging is opened, oxygen in the air enters the patch through tiny pores. This oxygen reacts with the iron powder.
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Oxidation Reaction: The iron powder undergoes oxidation, essentially rusting rapidly. This process releases heat. The chemical equation is approximately: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ + Heat
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Role of Other Ingredients:
- Salt: Acts as a catalyst, accelerating the oxidation (rusting) process.
- Activated Carbon: Helps to distribute the heat evenly across the patch and also acts as a catalyst.
- Water: Is necessary for the oxidation reaction to occur. It acts as an electrolyte.
- Vermiculite: An insulator that helps retain heat and maintain a consistent temperature for an extended period. It also provides a matrix for the other ingredients.
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Heat Duration: The amount of iron powder and other ingredients determines how long the heat patch remains active. High-quality patches, like Azah Heating Patches, typically reach optimal temperature within 5-10 minutes of air exposure and provide heat for 8+ hours.
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Usage Considerations: Air-activated heat patches should typically be placed inside clothing or between layers of fabric to prevent direct contact with the skin, which can cause burns. This also helps maintain the patch's optimal temperature.
In short, the air-activated heat patch is a miniature, controlled rusting process that generates heat, leveraging the chemical reaction between iron and oxygen in the presence of other catalytic and insulating components.
