Rough automatic draft, low quality: expect mistakes and awkward wording. It will be replaced by a better translation. Original →
32
LABORATORY “QUANTA”
SNOW
CRYSTALS
A. S. Varpakhovsky, A. N. Vilenkin
Photographs and figure seeds can be found in many physics textbooks in the chapters that talk about symmetry. But until recently, this was the limit of scientists’ interest in sooty crystals. Serious study of the nucleation, growth and structure of soot crystals began not so long ago. Interest in sozh crystals was mainly associated with the study of the formation of jedya and the phenomena that originated in the area. It turned out that most of the djedeva drops begin their life as soot crystals, taloshes, before they fall to the ground. However, only cold, high-altitude cirrus clouds are composed of ice crystals. Basically, clouds are collections of small water droplets that are suspended in the air in the same way as smoke particles. For many years, it remained a mystery how these droplets grew to the size required for them to fall to the ground. It also remained a mystery that often these droplets “refused” to freeze, although the temperature of the cloud was much lower than the normal freezing point of water, that is, below 0 ° C.
We now know that a supercooled cloud remains stable until it contains at least a small number of small ice crystals that originate on particles of earthly dust. Water molecules that fall on an ice crystal form a strong bond with it, which is quite difficult to break. Water molecules that condense on a drop are relatively easy to tear off - the heat of evaporation is less than the energy required to separate a water molecule from an ice crystal. Therefore, the cloud consists of water droplets and ice crystals, and ice crystals grow much faster than drops. Moreover, due to the growth of ice crystals, the humidity of the surrounding air decreases. This causes the water droplets to gradually evaporate and disappear. At the same time, the ice crystals grow to a size large enough for them to fall to the ground. When falling, several crystals can unite, forming a seedling.
Although soot crystals are varied, they can be classified according to their basic shapes; hexagonal recognition columns
34
fluctuates from - 5 ° C to 0 ° C, you can find crystals in the form of hexagonal plates, short prisms and strikingly beautiful stars with a diameter of about several millimeters. These stars are the basis of snowflakes. At temperatures several degrees below zero, the crystals fuse together to form snowflakes.
All this suggests that the shape of crystals is determined mainly by the temperature at which they grow. This was confirmed by experiments on growing ice crystals in the laboratory. Ice crystals are grown in a special chamber in which the temperature and amount of water vapor are strictly controlled. A thin thread was used as a seed. The temperature in the chamber was different in different areas along the thread. figure 3 shows a photograph of a section of thread overgrown with crystals. The size of this area is about 6 cm. On the right at figure the temperature in the chamber is indicated. In the upper part of the thread, mostly tiny hexagonal plates were grown. Below are hexagonal plates, branched stars and again hexagonal plates. At temperatures below - 25° C, hexagonal features are formed again.
Experience has shown that it is the temperature that determines the shape of the crystal. The amount of water vapor affects the growth rate. However, the exact nature of snow crystal growth still remains unclear.
It is very interesting to study the growth of snow crystals on earth. Often in winter, when there is a sharp drop in temperature, tree branches and house walls become covered with frost. The clouds where snowflakes originate are difficult to reach. Frost is easily achieved and can be observed during its formation. Frost usually appears on objects that have a high heat capacity and low thermal conductivity. When res-