Technical snow. We have already touched on this topic several times. We have already mentioned several times that technical or artificial snow, in short, so-called man-made snow, is not actually real snow. Today we will take a closer look at the specifics and unique properties of this human creation.
Artificial snow is produced by using a pressure pump to drive a stream of water to a sprayer, where it is broken into small water droplets of approximately 0.1 mm in size. The droplets of the broken water must not be much larger or much smaller than 0.1 mm. Larger droplets risk not freezing sufficiently, while smaller droplets risk evaporating after contact with cold air or being blown away by the wind outside the snow-covered area.
As soon as a droplet of sprayed water hits cold air, the temperature of which should not be higher than about -2.5 degrees C when using chemically untreated water, a kind of ice shell or ice coating first forms on the surface of the water droplet, which seals the rest of the liquid water inside. As soon as this ice shell starts to fall towards the ground, the liquid enclosed inside has approximately 1 second to freeze due to the cold air.
If this does not happen, it is necessary to let the artificial snow "ripen" or "freeze out" in piles on the ground, where the freezing out already occurs much more slowly and due to the insulating properties of the snow and the increasing temperatures towards the ground, part of the internal water can remain in a liquid, i.e. unfrozen, state.
It is this possible proportion of liquid water inside the ice grains that causes artificial snow to often be wetter or more humid than natural snow under comparable conditions.
The relatively small size of the so-called seed droplets of technical snow (the optimal size is about 0.1 mm) is the reason for the second characteristic property of technical snow, which is its high density and bulk density. Small droplets of dispersed water form small ice grains with an average size of 0.1 to 0.8 mm, which are also very round or rounded. These small round grains fit tightly together and leave almost no space for air between them, which greatly complicates the process of snow freezing after it hits the ground, where the access of cold ambient air ensures the complete freezing of the ice grain.
The last important characteristic of artificial snow is the round or spherical shape of the small grains. This third – characteristic – characteristic of artificial snow, which so significantly distinguishes it from natural snow, is caused by the opposite direction of freezing of artificial and natural snow. While natural snow grows from the core towards the surface (air moisture condenses on the germ of dirt or dust somewhere high in the clouds), artificial snow freezes from the surface to the core (when a water droplet comes into contact with cold air, a kind of ice shell is first formed, which encloses the remaining still liquid water, which then – during a short flight towards the ground – must freeze to the center or core of the grain, if this does not happen, there is a real risk that the center of the ice crystal will remain filled with liquid water).
Repetition is the mother of wisdom. Let us therefore repeat the basic characteristic properties of artificial snow. Artificial snow is made up of small ice grains with an average size of 0.1 to 0.8 mm. Ice grains are primarily round or rounded, without sharp edges or facets. Technical snow therefore has a high density and bulk density (shortly after production it reaches a weight of about 500 kg/m3). If technical snow is produced at higher temperatures or the broken droplets have a very short flight path in cold air before hitting the ground, it tends to be significantly wetter or moister than natural snow under similar conditions, which is caused by the liquid or unfrozen center of the ice crystals.
The above specification suggests that man-made snow should cause a relatively low level of abrasion or mechanical stress on the ski base. The grains are round, moist, small, without sharp edges and facets, higher humidity blocks electrostatic charge... But in fact, the opposite is true. Anyone who has even the slightest experience with servicing skis, especially cross-country skis, knows that artificial snow is enormously aggressive and abrasive and causes enormously rapid wear or even "abrasions" of even the most tenacious waxes. In other words: technical snow is much more abrasive than practically any natural snow, including aggressive and abrasive firns or angular-grained snows deep below freezing point...
But how can we explain this? Where does this high level of abrasion and aggressiveness come from, when technical snow should be anything other than aggressive and abrasive due to its shape, humidity and details.
The explanation is very simple and at the same time deeply hidden. As we mentioned above, technical snow freezes from the surface to the center. A kind of shell or ice shell first forms on the surface of the water droplet, inside which the remaining part of the liquid water remains closed. This liquid water then freezes from the surface to the center. We all know what happens if we forget a bottle of beer or wine in the freezer, which we put there for the purpose of rapid cooling and which we eventually forgot about. Yes, that's right. The beer or wine tears the packaging, usually a glass bottle. Why, liquids increase their volume when changing from liquid to solid. The force that acts on a glass beer bottle is so great that the bottle eventually breaks.
However, when the ice droplets of artificial snow gradually freeze, the shell or ice cover does not burst, and all the energy of the gradual increase in volume, which must fit into the same space, is reflected in the "densification" or "compaction" of the locked water in the ice grain. Yes, the molecular lattice of the frozen water changes, which is then much stronger, denser and much less subject to temperature fluctuations and melting processes.
Yes, that's right, the ice grains of artificial snow are ice grains of compacted water, which are enormously strong, enormously hard, enormously stable, and therefore enormously aggressive and abrasive in relation to other materials, such as ski bases. The ice grains of compacted water are also much less subject to temperature influences and melting processes, which is why technical snow can withstand even relatively high temperatures above freezing, where natural snow would have melted completely long ago.
As we know, a significant part of the World Cup competitions in all possible skiing disciplines are already taking place mainly or primarily on artificial or technical snow. With regard to the progressing climate changes and the retreat of the natural snow line to ever higher positions, it can be assumed that skiing on technical snow, and not only on the summit, will become an increasingly frequent and common phenomenon.
However, skiing on artificial snow places significantly higher demands on the chemical, but especially mechanical properties of the ski base than skiing on natural snow. In terms of the chemical properties of the base, this is mainly hydrophobicity and dirt-repellency (as we have repeatedly mentioned above, technical snow is much wetter and at the same time much dirtier), in terms of mechanical properties, this is mainly hardness, toughness and abrasion resistance (as we know, technical snow is very aggressive and abrasive and its hardness often exceeds the own hardness of the base, which is manifested by the so-called effect of plowing the base with ice crystals).
It is a big question whether standard hydrocarbon waxes, even supplemented with various additives, are and will be able to meet these increasing demands for hydrophobicity, dirt-repellency, but above all hardness, toughness and abrasion resistance. Perhaps the time and space have come to completely abandon wax technology, or at least supplement it with new, more promising and effective alternatives...