Producer: Popular Science China
Production: Orange Adult
Producer: Computer Network Information Center, Chinese Academy of Sciences
Beijing has slowly entered minus zero since last week, and in the cold winter, the must-have for "beautiful frozen" girls is to warm the baby. But do you know the "history" of warm babies? How does warm babies bring us warmth?
<h1 class= "pgc-h-arrow-right" > from tang po zi to warm paste, a "family history" belonging to warm babies</h1>
In fact, in ancient times, there were already warm babies, but the warm babies at that time were not as convenient as we are now, but used heat transfer to achieve heating, also known as "Tang Pozi". Tang Pozi is filled with hot water in a heat-conducting container, and the heat of the water is transmitted to our body by way of heat transfer, which is just a pure physical process.
△ Source: veer gallery
Modern warm baby was originally invented by the Japanese, also known as "warm stickers". Without fire, electricity, water and other energy sources, tear open the outer bag to heat up, and can maintain 8-18 hours.
△Source: Baidu Encyclopedia
These warm babies use oxidation reactions to convert chemical energy into heat. The warm patch is composed of three parts: raw material layer, gelatin layer and non-woven bag. The non-woven bag is made of microporous breathable film, and it also has a conventional non-breathable outer bag. When using, remove the outer bag, so that the inner bag (non-woven bag) is exposed to air, and the oxygen in the air quickly reacts with the chemicals in the inner bag through the breathable film.
The overall reaction process is as follows:
△ Image source: Provided by the author
The time and temperature of this warm baby release is controlled by the oxygen permeability rate of the breathable membrane. If oxygen permeation is too fast, the heat will be released at once, and it will burn the skin; but if the oxygen permeation rate is too slow, the temperature will hardly change.
<h1 class= "pgc-h-arrow-right" > iron sheet to warm the baby: heating is like magic</h1>
When I was in junior high school, it was a transparent bag with a small iron piece (accidentally exposing my age), and as long as I gently broke the small iron piece, the liquid in the bag would instantly crystallize and heat up. This was like magic for me, who didn't know science at the time.
△Source: taobao.com
How can a warm baby with an iron sheet achieve heat when the iron sheet is gently broken? First, let's look at the main ingredient of the iron tablet hand warmer: the supersaturated sodium acetate solution.
So what is a supersaturated solution of sodium acetate? Let's open up the long-sealed memories together.
1. Sodium acetate solution is a mixture, but its main component is sodium acetate, also known as sodium acetate, the molecular formula is CH3COONa. Sodium acetate is a strong electrolyte that is highly soluble in water.
2. Supersaturated solution refers to a solution at a certain temperature and pressure, when the concentration of solute in the solution has exceeded the solubility of the solute at this temperature and pressure, and the solute has not yet precipitated. This phenomenon is called supersaturation. The solubility curve of potassium nitrate shown in the following figure, the point located on the curve is the saturated solution, the solute mass in the solution is exactly the solubility of the solute, and the point above the curve is in the supersaturated state; the point below the curve is in the unsaturated state.
The supersaturated solution is unstable, if the solution is stirred, the solution is subjected to vibration, the container wall is rubbed, or a solid "seed" is put into the solution, the excess solute in the solution will immediately crystallize and precipitate.
For sodium acetate supersaturated solutions, at a fixed temperature, the sodium acetate solute does not have any chemical reaction in the solvent. However, due to the high solute solubility in the supersaturated solution and is unstable, it is very easy to change. Therefore, when we break the iron sheet, the iron sheet produces a slight vibration, which will cause the solution to undergo chemical changes so that the supersaturated solution crystallizes, and its crystallization process is the process of exothermic heat, which will make the hand warmer. The duration of the exothermic heat is about 35-40 minutes, and if you want to use it again, you only need to put the hand warmer in hot water and completely melt it into a liquid.
Note that it cannot be directly scalded with boiling water, otherwise the hand warmer will not be completely turned into a liquid. At the same time, the hand warmer is not infinitely reusable, and its maximum number of uses is about 50 times.
<h1 class= "pgc-h-arrow-right" > use warm baby, safety rules should be remembered</h1>
For the hand warmer made of sodium acetate saturated solution, everyone will be more worried about its safety when using it.
In fact, sodium acetate will not harm the human body. For example, the substance in the Dead Sea is mainly sodium chloride, which is salt, and the skin will feel uncomfortable after soaking for a long time. The corrosiveness of sodium acetate is lower than that of sodium chloride.
In daily life, the main ingredient in vinegar is acetic acid, and the main component in salt is sodium, that is to say, sodium acetate is something that everyone will often contact, but do not pay attention to it. So even if this small capacity of hand warmer is broken, it is still not harmful to the human body.
However, you "frozen" girls should still be careful not to be burned when using hand warmers
bibliography:
1. https://baike.so.com/doc/1870436-1978364.html
2. https://baike.so.com/doc/1484114-1569339.html
3. http://k.sina.com.cn/article_2169891005_8155e8bd020004hrt.html
4. http://blog.sina.com.cn/s/blog_b821227301013r0m.html