Till now the ice quality and its sliding characteristics after ice preparation were considered to be invariable and equal for all speed skaters. An analysis has shown that the resistance force to a skate sliding had changed greatly in time and had a pronounced extremal character. The methods to control the parameters of ice that provided all skaters with equal sliding conditions were elaborated. The searches of groups of matters, the addition of which reduced greatly a skate friction, were carried out. The study of physical origin of such a phenomenon at the molecular level gave the possibilities to create the composites of organic origin, the introduction of which lead to ice sliding properties' improvement by 50-60% in comparison with ice without such additions. The investigations were performed at the indoor skating rink "Krylatskoe" in Moscow; the results of investigations were partially applied during the Olympic Games-2006 in Turin.
1. INTRODUCTION. TASK DESCRIPTION
Sportsmen are enabled to improve world records and to achieve absolutely best results ever shown in a certain distance. In speed skating setting a new world record reflects not only physical and psychological form of a sportsman, his talent, but also a scientific and technical level of an ice palace in general and it's ice preparation technology in particular.
Since the indoor ice palaces have become centers of trainings and competitions (the 80s of XX century), we got for the first time the possibility to influence the crystal lattice of ice and therefore to optimize the sliding conditions.
However, what the notion "super-high-speed ice" means? It means the ice surface, which physical and mechanical qualities ensure the minimal resistance force to sliding of a sportsman's skate on ice. Summarizing and synthesizing information found by scientists from Russia and other countries allow formulating the technical demands to physical and mechanical qualities of ice corresponding to the best sliding characteristics. Ice surface should have not only the minimal constant of friction µ, but also the minimal sliding resistance force F, which is proportionate to the product of µ and practical area of contact of a skate and ice S (µ x S). In other words, ice should be equally slippery (minimum µ) and hard: in that case the edge of a skate doesn't penetrate deep into the ice and doesn't get stuck in ice.
1.1. The influence of temperature on frictional drag
The dependence of friction resistance F on ice temperature is already well explored and analyzed. The decrease of ice temperature provokes the increase of a constant of friction µ, but in that case ice becomes harder and a practical area of contact of a blade and ice S is reduced. The reverse action of these factors determines an extremal character of the dependence F=f(µ,S) . The research made by the scientists of the Faculty of Human Movement Sciences (The Free University in Amsterdam, the Netherlands) have shown that the optimal diapason of ice temperature is -6°C - -8°C.
2. PHYSICAL MODEL OF "SUPER-HIGH-SPEED ICE"
Our method to improve the sliding characteristics of ice and to keep its hardness is based on creating two-ply ice. The lower layer is extremely hard in order to exclude a too deep penetration into the ice. The upper layer (Δ maximum 1 mm thick) is extra soft owing to specially introduced components for better sliding (Figure 1):
Figure 1 - Physical model of "super-high-speed ice"
To solve the first problem (creating hard ice) it is necessary to refine water by all the kinds of admixtures (coarse, minute, punctual admixtures) and to repair structural defects (hydroxide ions, hydroxonium, Bierrum orientational defects). We use the following measures:
For the first time the technology was used in December 2004 at the indoor Ice Palace "Krylatskoye" during the European Junior Championship. It was appreciated by sportsmen, coaches, experts. The obtained ice massif was clear and hard (much harder then ice, frozen according to a traditional technology). Measurements were taken without destruction of ice surface, which is more proper than the indenters' introduction.
At different distances (between 500m and 5000m) 74% of sportsmen (both ladies and men) have bettered their personal bests, e.g. 99 records in 133 heats! In addition, these impressive results were shown at the beginning of the season, when the overwhelming majority of skaters is not still in the best form yet. One more major breakthrough was a setting of two junior world records in team pursuit (women and men).
2.1. The influence of time after ice preparation on sliding characteristics of ice
Till 2005 the ice quality and its sliding characteristics after ice preparation were considered to be invariable and equal during all the heats for all speed skaters. For the experiments was constructed a special apparatus - "an iron sportsman". It models the sliding of a skater and its run length after a constant shock impulse defines sliding resistance force F or else ice slipperiness. A part of the apparatus form professionally sharpened modern racing skates. The unit load on a blade is corresponding with the pressure of an average statistical skater on ice. The measurements of the run length were taken every 1.5 minutes after ice preparation.
A theoretical analysis and an experimental research have shown that the resistance force to a skate sliding and therefore ice slipperiness changed greatly in time and had a pronounced extremal character. Our results are shown as a sliding curve in Figure 2. The sliding curve has four zones. Zone #1 corresponds to the period of the best sliding, disappearing of liquids from the surface of ice and forming of a quasi liquid layer. The resistance of a hydraulic film is negligible and the intensity of molecular interaction (work of adhesion) between a blade and ice is also insignificant. This state of ice is similar to a crystalline structure of a solid, but with weaker molecular links.
At zone #2 ice slipperiness is worse. Ice temperature gradually falls, the action of quasi liquid layer decreases, a constant of friction increases. The next zone #3 is "a plateau". At this juncture the temperature of ice surface approaches the temperature of the massif and sliding characteristics are constant. Zone #4 is characterized by deterioration of sliding qualities. The surface of ice is damaged by condensate, roughness etc.
So it is evident that equal conditions for all skaters may be created only in the zone of "a plateau" if all the necessary climatic requirements are observed.
The character of sliding zones depends on the following factors:
Rise in temperature of water leads to a later beginning of the best sliding qualities of ice and to an increase of its absolute value (Figure 2a). Rise in thickness of the poured water layer leads to the same consequences (Figure 2b). What is really important is that the values of the run length in the zone of "a plateau" are higher when water temperature (tw) is higher. In other words, the slower the crystallization is, the better velocity conditions of ice after freezing are. The zone of the best sliding can be purposefully transferred to a certain moment or the average conditions during the heats after an ice preparation can be better/worse than after previous preparation. In such a way, changing thermal physic conditions may be used as an instrument to manipulate ice slipperiness and consequently the sportsmen's results.
As a result of our research we have elaborated the techniques to control the ice preparation and to exclude unfair manipulations. We have given a report to the International Skating Union (ISU). Our principles were partially tested at the Olympic Games-2006 in Turin. As a result, ISU Council has made a decision to change the Speed Skating competitions Rules and, particularly, to introduce an obligatory ISU control of the process of ice pouring.
Figure 2 - Sliding curves:
a - Influence of water temperature on ice quality, its sliding.
2.2. The influence of the additives on sliding characteristics of ice
The second task (an extra soft upper layer of ice) of our research was to find out the groups and combinations of chemical matters which purposefully influence the ice characteristics and to elaborate the techniques how to introduce it. A physical model of the optimal ice structure has been worked out. It consists of a thin layer of water ice crystals with dissemination of dissolved chemical agents surrounded by hydrate coverings (so-called "bound water"). In that case a sliding blade traverses canals of bound water and gets additional grease even when the temperature is lower than the temperature of pure water freezing. The efficacy of this kind of ice surface structure is confirmed by electron-microscope investigations and by an X-ray microanalysis.
Let's mention the basic requirements to the introduced compositions:
Introduction of surface-active materials reduces the surface tension and leads to decrease of the cohesive resistance both of ice and of a liquid film. So it is necessary to spend less energy to tear the molecular links, in other words, sliding resistance force falls. The surface activity increases when the length of a hydrocarbon chain grows. That's why we choose as additives high-molecular compounds, whose place is higher in homologous series. Our techniques are based exceptionally on using micro doses of introduced additions. Overdosing leads to the softening and the loosening of the upper layer of ice. A blade penetrates too deep into ice. Total sliding resistance force increases and it practically brings a positive effect of additions to nothing. To sum up, using micro doses of special additions considerably improves the sliding characteristics of ice, but it is well to remember that the slightest overdosing can make worse the quality of ice.
The comparison of sliding curves for different ice modifications is represented in Figure 3.
Figure 3 - Sliding curves:
The best results were obtained on ice previously treated by organic compounds. An average run length on such an upper layer exceeds normal results by 50-60%. The property of this curve is a wider and platter zone of maximum and a high "plateau". Here a concentration of organic additions didn't exceed 0.5-1.0 ppm. The environmental safety of the additions is beyond question moreover, it is compatible with human blood and plasma. They are used as a component of medicines (including children's). The novelty of our researches is admitted and by now we have taken three patents out.
3. SURFACE DEFECTS AND THE WAYS OF THEIR ELIMINATION
Unfortunately, introducing the additions even in micro doses may distort the relief of ice surface and bring to the appearance of plait-shaped micro asperities (Figure 4a). But vibration and lack of smoothness provokes sportsmen's psychological aversion and complaints of coaches and organizers. When the crystallization is completed, the appearance of the asperities is caused first of all by the system's tendency to equilibrate the thermodynamic instability whose reason is the deliverance of free energy on movement of a solidifying interface. So it is "better" for the system to modify its state in order to decrease the area of contact of ice and the liquid. Then the liquid curdles and the blemishes the form.
An in-depth study of this effect has helped to determine the chemical substances which prevent ice from appearing of surface defects and keep high velocity qualities. These grading substances represent a fine-dispersed aqueous suspension. They are also introduced in micro doses (≤1 ППm). Independently the grading substances also augment the run length, but together with surface-active materials they improve the results of an "iron sportsman" by 50-60% and keep its smoothness (Figure 4b).
Fig. 4. Ice surface:
a - without grading substances;
1. As a result of the research we have plotted using "an iron sportsman" a curve expressing the dependence of ice qualities on time after ice preparation. We have determined the factors which influenced the absolute value and the location of the sliding zones on an axis of time.
2. We have worked out the ways to control thermal physic conditions of water during ice preparation in order to exclude any manipulations with ice quality.
3. We have revealed and experimentally tested a complex of chemical additives and its concentrations which contribute to the improving of the results by 50-60%.
PRINCIPES PHYSIQUES DE LA CRÉATION DE LA GLACE ARTIFICIELLE
Jusqu`à nos jours la qualité de la glace était considérée comme invariable et identique pour tous les coureurs. L'analyse effectuée a mis en évidence que la force résistante au mouvement de la lame changeait beaucoup et que le graphique portait un caractère d'une fonction extrémale. Le groupe des chercheurs et des ingénieurs du Centre technique de réfrigération a élaboré la méthode pour contrôler les conditions identiques pour tous les coureurs. La recherche des substances chimiques permettant de réduire le coefficient de friction a été faite. Des études profondes de ce phénomène au niveau moléculaire ont donné la possibilité de relever des composés organiques qui amélioraient le glissement du patin à 50-60% par rapport à la glace sans additifs. Les investigations étaient réalisées dans le Palais de la Glace "Krylatskoe" à Moscou. Les résultats ont été déjà partiellement appliqués pendant les Jeux Olympiques-2006.