First Day of Winter –a pair of these will keep your hand warm via an exothermic reaction that, in essence, creates rust.
For winter sports enthusiasts, hand warmers can mean the difference between calling it a day early and playing outside for as long as possible. In fact, anyone who braves cold temperatures might be tempted to try the little pouches that emit warmth within seconds of being exposed to air.
Hand warmers date back centuries to when the Japanese would use hot stones to warm their hands, says Keiko Ishikawa, a marketing manager of hand-warmer maker Mycoal USA. Portable hand warmers filled with hot ash were the version that followed, she says.
These days, disposable hand warmers turn up the heat in your mittens by means of an exothermic reaction that, in essence, just creates rust. Each pouch typically contains iron powder, salt, water, an absorbent material, and activated carbon. When the pouch is removed from its outer packaging, oxygen drifts across the pouch’s permeable covering. With salt and water present, the oxygen reacts with the iron powder located inside to form iron oxide (Fe2O3) and release heat.
The absorbent material can be vermiculite, pulverized wood, or a superabsorbent polymer such as polyacrylate. It helps retain the moisture so that the reaction can occur. The activated carbon helps to evenly disperse the heat produced, which can average 135 °F.
Visit “What’s That Stuff” to read more about hand warmers.
Excerpted with permission, Chemical & Engineering News
Copyright © 2010 American Chemical Society