MANUFACTURING METHOD OF ARTIFICIAL SNOW, AND PRODUCT FOR IMPLEMENTING THIS METHOD

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES

[0001] The present invention relates to the field of artificial snow production.

[0002] It relates more particularly to a snowmaking process consisting of incorporating particles of nucleating agent into water and projecting said water containing said particles of nucleating agent into an environment whose temperature is below 0°C, by means of a device adapted for the production of snow.

[0003] The invention also relates to a particular product, in the form of a powder, intended to be incorporated into water to serve as a nucleating agent in the implementation of the aforementioned snowmaking process.

[0004] It also relates to the use of a product in powder form to serve as a nucleation agent in the implementation of the snowmaking process. TECHNOLOGICAL BACKGROUND

[0005] In general, it is known to manufacture artificial snow, particularly on ski slopes, in order to compensate for a lack of natural snow.

[0006] Artificial snow is manufactured using snow production devices (also called "snow cannons"), supplied by pressurized water pipes and possibly pressurized air.

[0007] These devices spray water into the cold ambient air in the form of droplets that freeze or crystallize to produce snow.

[0008] The possibilities for snow production, as well as the quality of the snow produced, depend on the atmospheric conditions present.

[0009] Generally speaking, the colder the ambient air, the easier it is to produce good quality artificial snow. Conversely, producing good quality snow is not easy under the fairly frequent conditions of sub-zero temperatures close to 0°C.

[0010] Snowmaking devices may include a pole fixed securely in the ground, which carries pressurized water and pressurized air via separate supply lines to a snowmaking head located at its free end, several meters or even ten meters high.

[0011] The snowmaking head often includes a plurality of spray nozzles whose pressurized water and pressurized air supply is regulated by one or more valves, in order to optimize the amount of artificial snow to be produced according to weather conditions.

[0012] We also know of snow production devices comprising water spray nozzles associated with a fan structure whose airflow is adapted to ensure the dispersion in the ambient air of the water droplets produced.

[0013] In both cases, if we are content with this spraying of water, the drops do not freeze in flight but only upon impact with the ground, creating a sheet of ice. This is due to the phenomenon known as "supercooling", which prevents pure water from freezing naturally before several tens of degrees Celsius below zero.

[0014] Thus, it has been demonstrated that in order to freeze water at relatively high temperatures, it is necessary to initiate the process by means of one or more foreign bodies, called "nucleating agent(s)".

[0015] To achieve this, it is common practice to inject ice cores into the main jet of the aforementioned snowmaking devices, using one or more devices called "nucleators" associated with the water spray nozzles.

[0016] This process is effective, but it requires the production of cold, generally through a violent expansion of compressed air, and therefore consumes a significant amount of energy. The impact on the cost of a snowmaking system is thus considerable.

[0017] Nucleation can also be achieved by impacting the water, particularly with ultrasound. However, the equipment used for this is complex and energy-intensive; moreover, without compressed air, the nucleating agents are not evenly distributed in the jet, and the power required becomes greater than that needed for conventional compressed air nucleation.

[0018] Document US-4 200 228 proposes another solution to increase the temperature from which snowmaking devices can be implemented under good conditions and to produce snow without compressed air.

[0019] To achieve this, it is planned to incorporate into the water particles acting as nucleation agents which come in the form of fragments of cells derived from microorganisms and containing a protein capable of initiating crystallization, when this water is sprayed into the air in fine droplets.

[0020] The corresponding product, in powder form, is marketed by the company SNOMAX, under the name SNOMAX (registered trademark).

[0021] This product works below -2.8°C and is the best industrial nucleation agent produced to date.

[0022] Its presence also has other advantages, such as making the snow easier to work with and therefore saving grooming time.

[0023] However, the production of this biological product for the manufacture of artificial snow is relatively expensive.

[0024] Furthermore, it requires specific cold storage conditions, and its implementation necessitates a restrictive operating procedure that takes into account its biological nature.

[0025] Other, more efficient nucleation agents exist, for example metaldehyde, which is active at -0.4°C, but they are unusable in the context of snow production, particularly because of their toxicity.

[0026] Document AT 509 864 A4 describes silicate particles between 0.05 and 5 µm, intended for nucleation in snowmaking. The document ZHIPING HUO ET AL: "Synthesis of zeolite NaP with controllable morphologies", MICROPOROUS AND MESOPOROUS MATERIALS, ELSEVIER, AMSTERDAM, NL, vol. 158, March 12, 2012, pages 137-140, (XP028489673) describes synthetic zeolite particles having microcavities on their surface.

[0027] There is therefore a need to propose a new type of nucleation agent for the manufacture of artificial snow that is inexpensive, easy to implement and not very polluting. SUBJECT OF THE INVENTION

[0028] In order to remedy the aforementioned drawback of the prior art, the present invention proposes a method for manufacturing snow according to claim 1.

[0029] According to another characteristic, at least 10% of said silicate particles have at least one microcavity opening through a surface opening and delimited by a lateral wall which defines its internal volume, which at least one microcavity is capable of initiating the birth or generation of ice in its internal volume when said water projection is carried out in an environment whose temperature is between -4°C and -0.5°C.

[0030] Advantageously, the process consists of using a silicate particle base, in which at least 80% of the particles have a unit equivalent sphere diameter of less than 15µm, and preferably less than 5µm.

[0031] The concept of equivalent sphere diameter refers to the diameter of a sphere having the same volume as that of a nucleating agent particle.

[0032] Interesting results were obtained with silicate particles selected from the group consisting of feldspars, tectosilicates, inosilicates, and phyllosilicates. In particular, the silicate is advantageously a microcline-type feldspar and / or an orthoclase-type feldspar.

[0033] In particular, it was thus possible to crystallize water droplets on a cold plate above -2.8°C and down to -0.3°C.

[0034] Depending on other non-limiting and advantageous characteristics of the process, taken individually or in all technically possible combinations: for the manufacture of snow, silicate particles are incorporated into the water in a number between 5 x 10⁵ and 2 x 10¹⁰ particles per liter of water, preferably between 5 x 10⁵ and 7 x 10⁸ particles per liter of water; said projection of the water containing said silicate particles consists of a spraying of the water in the form of droplets whose size is between 100 and 700µm; the silicate particles are incorporated into the water so as to obtain between one silicate particle for 10 water droplets and ten silicate particles per water droplet;

[0035] The process according to the invention provides for subjecting said particles to at least one activation treatment prior to their incorporation into water, which at least one activation treatment is the creation of microcavities on the surface of said particles, allowing to increase the temperature at which said particles are able to initiate the formation of ice.

[0036] This creation of microcavities (or pores, or orifices) can consist either of creating microcavities that did not exist before the treatment applied, or of updating (or revealing) pre-existing microcavities that were at least partially blocked previously.

[0037] The microcavity(ies) in question open through a surface opening and are delimited by a lateral wall, their depth being advantageously greater than the diameter of the disk equivalent to the surface of said surface opening (called equivalent diameter).

[0038] In this context, one or more of the following treatments are advantageously applied: Application to the particles, previously impregnated with water, of at least one cold treatment, and preferably of at least two successive cold treatments, separated by a warming phase. This cold treatment(s) advantageously consist of cooling the particles below -7°C for at least 10 minutes, followed by warming them above 0°C for at least 10 minutes. Immersion of the particles in an aqueous potassium hydroxide solution; this activation treatment advantageously includes the step of immersing the particles in an aqueous potassium hydroxide solution for at least 20 minutes at a temperature between 0°C and 90°C. Application to the particles of a cleaning and separation step using ultrasound; this ultrasonic treatment step is advantageously carried out in an aqueous medium before one of the treatments mentioned above.exposure of said particles to an ozone atmosphere in a suitable reactor, preferably for at least 20 minutes, at a temperature between 0°C and 300°C. exposure of said particles to an oxygen plasma in a suitable reactor, preferably for at least 10 minutes at a temperature between 0°C and 300°C.

[0039] The invention also provides a product according to claim 13.

[0040] In this product, preferably, at least 10% of the silicate particles comprise at least one microcavity opening through a surface opening and delimited by a lateral wall; preferably, the depth of said at least one microcavity is greater than the equivalent diameter of its surface opening.

[0041] This surface opening of said at least one microcavity preferably has an equivalent diameter between 100 and 1000nm and a depth between 700nm and 3 µm.

[0042] The invention further proposes the use of such a product in powder form to serve as a nucleation agent in the implementation of the artificial snow manufacturing process described above. Preparation of silicate powder

[0043] To obtain the silicate particles, blocks of rock of the type chosen from the feldspar, tectosilicate, inosilicate, and phyllosilicate groups are used. These blocks are dry-ground using a mill (e.g., a jaw crusher or a roller mill) until a powder of particles is obtained, at least 80% of which have a unit equivalent sphere diameter of less than 15 µm, preferably less than 5 µm. For example, at least 80% of the particles obtained have a unit equivalent sphere diameter between 1 and 7 µm.

[0044] One or more treatments are applied to the particles during or after grinding.

[0045] These treatments may be intended for: sort the particles according to their size, select the most active particles, improve the activity of the particles. Tests illustrating the effectiveness of a material on the initiation of crystallization

[0046] Since full-scale tests of the effectiveness of a nucleating agent are lengthy and expensive to implement, the inventors used a known method, feasible in the laboratory, based on the cooling of a plate or wafer and the small-scale observation of the temperature at which the crystallization of a calibrated water droplet is initiated. Protocol No. 1:

[0047] A thin section, or platelet, of the silicate material to be tested is prepared, with a thickness of approximately 0.5 to 1 mm, on which a drop of distilled water is deposited.

[0048] This preparation is placed on a Peltier effect plate type cooling system whose temperature is controlled to the tenth of a degree between -20°C and +20°C (Linkam type Peltier effect refrigerated plate with precision 0.1°C).

[0049] The system is placed in an enclosed environment under controlled humidity conditions to prevent condensation.

[0050] The temperature is lowered rapidly to a few degrees above 0°C and then slowly (on the order of 1°C / min.) while visually assessing the freezing of the drops under an optical microscope.

[0051] And we record the temperature at which freezing was triggered for each droplet.

[0052] For this protocol #1, since the temperature of the drops is higher than the temperature of the Peltier effect plate, the temperatures measured on the Peltier plate must be increased by a certain value to obtain the desired nucleation temperature.

[0053] The precise difference is subject to prior calibration using a thermocouple introduced into the drop. Protocol No. 2:

[0054] The silicate powder is used as prepared above and is suspended in distilled water at a volume concentration of approximately 0.01% to 1%.

[0055] Drops of such a suspension are deposited on a glass support slide, of the type classically used in microscopy and whose inert appearance on the nucleation is checked beforehand.

[0056] The glass strip thus prepared is placed on a Peltier effect plate cooling system whose temperature is controlled to the tenth of a degree between -20°C and +20°C (Linkam type Peltier effect refrigerated plate with precision 0.1°C).

[0057] The system is placed in an enclosed environment under controlled humidity conditions to prevent condensation.

[0058] The temperature is lowered rapidly to a few degrees above 0°C and then slowly (on the order of 1°C / min.) while visually assessing the freezing of the drops under an optical microscope.

[0059] And we record the temperature at which freezing was triggered for each droplet.

[0060] It should be noted that the higher the freezing temperature, the more transparent the drops remain, which makes detection by other means, especially automatic ones, very uncertain.

[0061] For this protocol #2, since the temperature of the drops is higher than the temperature of the Peltier effect plate, the temperatures measured on the Peltier plate must be increased by a value of around 1.5°C to obtain the desired nucleation temperature. Results :

[0062] Numerous tests have been carried out to test silicate particles, according to protocol no. 2 above, the results of which appear in tables 1 and 2 below (divided in two for better readability). Table 1 Sample Mineral Source Family Maximum temperature (°C) Minimum temperature (°C) Average Temp. (°C) Snomax Reference Snomax Organic -2,5 -5,5 -2,9 AZ-B1 Amazonite Brazil-Minas Gerais Tectosilicate -1,5 -11,5 -4,5 AZ-K1 Amazonite Russia-Kola Tectosilicate -1,5 -7,5 -3,8 OM1 Microdine Malawi-Mt Malosa Tectosilicate -0,5 -6,7 -2,6 IFK1 Microdine India-Rajahstan Tectosilicate -13 -13,5 -4,4 IF8 Microdine India-Rajahstan Tectosilicate -1 -14,8 -3,9 ORI1 Orthodase India-Rajahstan Tectosilicate -2 -13 -4,3 ORP Orthodase Madagascar Tectosilicate -1,5 -10 -2,8 AEG1 Aegirine Malawi-Mt Malosa Inosilicate -1,4 -7,5 -4,1 Thor Thorite USA-El Paso NM Nesosilicate -2,5 -6,2 -3,6 IF5 K-Mica Spain Phyllosilicate -3 -14,5 -6,9 Table 2 Sample Number of experiments % Very High temp. % High temp. Snomax 28 86% 96% AZ-B1 17 65% 71% AZ-K1 11 55% 73% OM1 124 80% 92% IFK1 144 40% 69% IF8 146 65% 78% ORI1 29 52% 83% ORP 58 38% 66% AEG1 44 57% 84% Thor 21 76% 90% IF5 46 22% 30%

[0063] In the rest of this text, we will speak of very high crystallization temperatures when they are greater than or equal to -3°C and of high crystallization temperatures when they are between -4°C and -3°C.

[0064] For the different referenced samples, these tables 1 and 2 mention the type of mineral, its origin (source), its family, the maximum and minimum crystallization temperatures obtained, the number of experiments carried out, the percentage of very high crystallization temperatures obtained and the percentage of high crystallization temperatures obtained.

[0065] Since the best known nucleation agent is the SNOMAX product (registered trademark), the nucleation temperature of this agent on a glass slide is the reference against which the different products are compared in all results.

[0066] A first series of tests on the SNOMAX product (registered trademark) made it possible to film the different phases of the freezing of a drop and to calibrate the nucleation temperatures.

[0067] From an initial series of coarsely ground minerals, it was found that a particular feldspar: amazonite (ref. AZ-B1), had performance as good as the SNOMAX product (registered trademark).

[0068] However, these performance levels only appeared after several freeze / melt cycles, as shown by the curve of the figure 1 .

[0069] This curve of the figure 1 represents the freezing temperature of the same drop (Tfdrop(°C)) placed on an Amazonite plate ref. AZ-B1 (according to protocol no. 1 above), as a function of the number of freeze / melt cycles (the protocol of which is detailed later in the description).

[0070] In this figure, we can see that the crystallization temperature, initially -6.2°C, improves as a function of the number of freezing cycles, reaching -2.5°C after 15 cycles.

[0071] To understand this phenomenon, amazonite platelets or thin sections were prepared to implement protocol #1 above. Observation of the droplet crystallization under an optical microscope showed that the ice originated from beneath the platelet surface when the nucleation temperature was highest.

[0072] The same observations were made under an electron microscope; a mapping of the nucleation sites was carried out, and the only remarkable element highlighted was the presence of microcavities on the surface at which the ice crystals originated.

[0073] Furthermore, the application of one or more freeze / melt cycles has been shown to cause microcracks and new microcavities to appear.

[0074] THE figures 2a and 2b These correspond to two electron microscope images showing the effect of freezing a water droplet placed on the surface of a thin plate of material ref. AZ-B1. figure 2a shows the surface state of the water before freezing and the figure 2b shows the surface condition after freezing.

[0075] In the circled areas, which correspond to the same surface zones, very fine new cracks accompanied by new holes (in black) are clearly visible in white (after freezing); on the figure 2b , bottom right, the cracks initiate the detachment of a 2µm grain of material.

[0076] On the other hand, it has been noted that the disappearance of microcavities is associated with a decrease in nucleation temperature.

[0077] Since amazonite has the disadvantage of being a semi-precious stone, other microcline feldspars were tested, whose high-temperature performance proved to be similar to and even better than that of amazonite.

[0078] This is notably the case of a microcline from Mount Malosa in Malawi, referenced as OM1 in the tests.

[0079] It was indeed possible with this variety to crystallize water at -0.5°C and this from the first freezing.

[0080] However, the source of this mineral is difficult, and there are no exploitable feldspar mines in the region.

[0081] It has been shown that this mineral has numerous microcavities on the surface opening through a surface opening and delimited by a lateral wall which defines its internal volume.

[0082] As the repeatability is remarkable, it was possible to photograph under electron microscope, in the presence of water vapor, the birth or generation of ice in the internal volume of these microcavities on a microcline plate ref. OM1.

[0083] This birth of ice is illustrated in four stages by the photographs of figures 3 to 6 attached.

[0084] Other varieties (ref. IFK1 and IF8), from known mines in Rajasthan, India, require several freezings before reaching their best nucleation temperatures.

[0085] In the case of these 2 microclines acting at very high temperatures (ref. IFK1 and IF8), the presence of microcavities was observed and is at the origin of the nucleation of part of the nucleation zones.

[0086] These "active" microcavities were characterized under the microscope by their depth being greater than the largest dimension of their surface opening, and preferably by their depth being greater than or equal to the equivalent diameter of their opening surface.

[0087] Tests on material particles (grains) have shown that there are more active grains at very high temperatures when the number of such microcavities is greater.

[0088] By extending the search to other feldspars, it was shown that several orthoclases have a relatively high nucleation temperature, including 2 very high ones, comparable to microclines.

[0089] One of them comes from India (ref. ORI1), and the other from Madagascar (ref. ORP).

[0090] By extending the search further, the inventors found 2 minerals unrelated to feldspars which also act at high temperature: Aegirine (ref. AEG1) and Thorite (ref. Thor).

[0091] Although they have no direct application in snowmaking, these minerals demonstrate that the capacity for nucleation at high temperatures is not limited to feldspars and that the phenomenon is broader. This is the case, for example, with certain potassium micas (ref. K-Mica).

[0092] It has also been shown that not all microclines function at high temperatures and that other varieties have nucleation temperatures comparable to the less efficient microclines.

[0093] By examining the Thorite sample under the electron microscope, microcavities of significant depth compared to the equivalent diameter of their surface opening were highlighted, a characteristic which therefore appears to be essential for nucleation in silicates.

[0094] This characteristic can therefore be taken into account for the choice by the person in the trade of the base material to be used, with a view to the preparation of active particles as a nucleation agent in the production of artificial snow.

[0095] Without this being deduced from any theory, the particular confinement of the water may allow ice to form and reach critical size at very high temperature, then to extend out of the microcavity, up to several degrees above the surface nucleation temperature.

[0096] The number of active grains depending on the grinding is also an important parameter since, for a mineral powder added to water to be economically viable, its quantity must not be too large.

[0097] In theory, one particle per droplet is sufficient for nucleation. In practice, given the interactions between drops, it is not necessary for every droplet to contain a particle. One particle per 10 drops is sufficient.

[0098] Furthermore, the size of this particle must not exceed 15 µm to remain suspended in the droplet, which has a size between 100 and 500 µm, during its flight time. And it must not be smaller than 2 µm to exhibit at least one microcavity.

[0099] This results in mineral quantities of around 100g to 2kg per 380m3 of water.

[0100] It is understood that for an application in artificial snow the proportion of grains active at very high temperatures is essential.

[0101] In this context, to improve the nucleation temperature and increase the number of active grains, the inventors had the idea of ​​trying to create new microcavities on the material particles, or to free (or "clean") existing microcavities of at least some of the material that could clog them.

[0102] Several treatments have proven effective in this regard: treatment by cold (for the creation of new microcavities), and treatment by ultrasound (sonification), by potash, by ozone and / or by oxygen plasma (for the cleaning of microcavities). Activation treatment(s) of silicate particle powder

[0103] A / Cold treatments: The powder from grinding is mixed with water and subjected to one or more freezing cycles.

[0104] The mixture is frozen either by spraying onto a cold surface or in bulk in a suitable container.

[0105] The freezing temperature TC is lowered below -7°C; the temperature decrease is from ambient temperature at a rate of 1 to 20°C / minute.

[0106] After freezing, the mixture is kept at temperature TC for at least 10 minutes.

[0107] The mixture is then thawed at a TD temperature between +0.1°C and +4°C.

[0108] Once the mixture has completely thawed, after 10 minutes, another cycle can begin.

[0109] Between 1 and 15 cycles can be performed in this way.

[0110] At the end of the last cycle, the powder is extracted from the mixture, for example by filtration, and then dried.

[0111] It has been observed that this treatment leads to the creation of new active microcavities (whose depth is greater than the equivalent diameter of their surface opening) and the figure 1 demonstrates the effectiveness of such treatment on increasing the nucleation temperature.

[0112] As mentioned above, the curve of the figure 1 represents the freezing temperature of the same drop placed on an Amazonite plate ref. AZ-B1 (according to protocol no. 1 above), as a function of the number of freeze / melt cycles.

[0113] We observe that the first freezing takes place at -6.2°C, that after 7 cycles it rises to -3.1°C to reach a maximum of -2.5°C after 15 cycles.

[0114] B / Oxygen plasma treatment: The powder is rinsed with pure water and then dried completely.

[0115] A second drying process is carried out using dry nitrogen.

[0116] Disperse the powder in a thin layer on an inert substrate (e.g., a silica glass plate).

[0117] Place the powder-covered plate in an airtight chamber.

[0118] Close the chamber and pull a vacuum (air pressure less than 20mbar).

[0119] Fill the chamber with dioxygen up to a pressure of approximately 200mbar.

[0120] Run the plasma generator for 20 to 30 minutes.

[0121] Restore atmospheric pressure and stir the powder.

[0122] Repeat the cycle 2 or 3 times.

[0123] Efficacy tests of this oxygen plasma treatment were carried out on silicate platelets ref. OM1, according to protocol no. 1.

[0124] THE figures 7 and 8are electron microscope photographs showing the surface condition of the corresponding platelet before and after oxygen plasma treatment, at a first magnification; and the Figures 9 and 10 These are electron microscope photographs that show the surface condition of the same platelet, always before and after treatment with oxygen plasma, according to a second magnification, greater than the first.

[0125] We then notice a greater number of microcavities on the surface of the figure 8 compared to that of the figure 7 .

[0126] On the other hand, the Figure 10 shows the disappearance of debris or particles from the microcavities compared to the figure 9 and also the presence of sharper angles.

[0127] There figure 11represents the effect of oxygen plasma treatment on the freezing temperature of a set of water droplets deposited on a silicate plate ref. IFK1, according to protocol no. 1.

[0128] The vertical axis represents the cumulative percentage of frozen droplets. The horizontal axis represents the temperature of the water in the droplet.

[0129] On this graph, we notice that before treatment (IFK1 curve) 40% of the drops freeze above -3°C, while 100% of the drops are frozen at -3°C after treatment with oxygen plasma (IFK1 PLASMA curve).

[0130] C / Potash treatment: The powder from grinding is mixed with a potassium hydroxide solution of concentration between 10 and 100% for 20 to 60 minutes.

[0131] Then it is washed with pure water so that the pH becomes less than 8. Then the powder can be dried or stored in water.

[0132] Numerous tests were carried out on the same minerals, both with and without the above treatment with potash.

[0133] Without treatment with potassium hydroxide, nucleation was obtained at very high temperature in 37% of cases, and at high temperature in 53% of cases.

[0134] Whereas with potassium treatment, nucleation was obtained at very high temperature in 63% of cases and at high temperature in 48% of cases.

[0135] There figure 12 represents the effect of 10% potassium treatment on the freezing temperature of a set of water drops containing IFK1 powder (particles less than 15µm) deposited on a glass slide and tested according to protocol no. 2 (IFK1 KOH curve).

[0136] By comparison, we show the curve of IFK1 ground manually immediately before testing (fresh IFK1 curve).

[0137] The vertical axis represents the cumulative percentage of frozen droplets. The horizontal axis represents the temperature of the water in the droplet.

[0138] It is observed that before treatment less than 30% of the drops freeze above -3°C, whereas more than 60% of the drops are frozen above -3°C after treatment with potassium hydroxide.

[0139] It should also be noted that 100% of the drops are frozen at -5°C after processing, whereas it is necessary to reach -8°C to obtain this result with the freshly ground raw product.

[0140] D / Ozone treatment: The powder is rinsed with pure water and then dried completely.

[0141] A second drying process is carried out using dry nitrogen.

[0142] Disperse the powder in a thin layer on an inert substrate (e.g., a silica glass plate).

[0143] Place the powder-coated plate in a chamber.

[0144] Close the chamber and fill it with oxygen.

[0145] Circulate the oxygen for at least 5 minutes.

[0146] Start the ultraviolet lamp which transforms dioxygen into ozone.

[0147] Leave the powder exposed to ozone for 20 to 30 minutes.

[0148] Turn off the lamp and open the room.

[0149] Rinse the powder with clean water.

[0150] Optionally, let it dry.

[0151] Optionally, repeat the cycle several times.

[0152] Results showing the effectiveness of this ozone treatment appear on the figure 13 attached, commented on below.

[0153] E / Ultrasonic treatment (sonification): Microcavities tend to clog naturally; in particular, during grinding, the finest particles adhere to surfaces and obstruct pores. Impurities present during the various stages of product development can also play the same role. These impurities are often organic. The use of ultrasound makes it possible to detach any biofilm or grains retained by surface effect and to break down certain impurities. Treatment applied:

[0154] The raw powder or powder mixed with water is placed in a container which is itself immersed in an ultrasonic tank.

[0155] The tank operates with a 40kHz frequency generator and the exposure lasts a minimum of 10 minutes.

[0156] One variation involves immersing an ultrasound generator in the powder container.

[0157] Results showing the effectiveness of this ultrasound treatment appear on the figure 13 presented below.

[0158] This figure13 represents the effect of ozone and sonication treatments on the freezing temperature of a set of water droplets (TGoutte(°C)) containing IFK-1 powder, tested individually according to protocol 2.

[0159] The same batch of IFK1 powder was used for all 4 series of tests.

[0160] The vertical axis represents the cumulative percentage of frozen droplets. The horizontal axis represents the temperature of the water in the droplet.

[0161] On this figure 13 : The "IFK1 raw" curve illustrates the results obtained without treatment, the "IFK1 US" curve illustrates the results obtained with ultrasound treatment (sonification), the "IFK1 O3 20Min." curve illustrates the results obtained with ozone treatment (for 20 minutes), and the "IFK1 US + O3" curve illustrates the results obtained with ultrasound treatment followed by ozone treatment.

[0162] We can observe the different effects of ozone (O3) treatment, sonication (US) and the two combined.

[0163] It is observed that the first drops containing untreated IFK1 powder freeze at -5.7°C and represent only 12% of the drops. To have 100% of the drops frozen, a temperature of -8.9°C must be reached.

[0164] The sonication treatment (IFK1 US) improves the initial freezing temperature and the percentage of drops frozen at the highest temperature, with 32% of the drops frozen at -3.7°C. It should also be noted that 100% of the drops are frozen at -5.2°C.

[0165] Treatment with ozone alone (IFK1 O3) further improves the freezing temperature of the first drops: 17% froze at -2.7°C. 100% of the drops froze at -7.3°C, which is better than the raw product but not as good as sonication treatment.

[0166] By combining the two treatments, a significant increase in the number of active grains at high temperature is obtained since 60% of the drops are frozen at -3.7°C and 100% at -5.2°C.

[0167] It should be noted that the various treatments mentioned above can be implemented individually or in combination. In particular, a sonification treatment is advantageously implemented before any other treatment. Operating procedure for the production of artificial snow

[0168] Silicate particles preferably activated by one or more of the aforementioned treatments are incorporated into the feed water of the snowmaking devices, in a number between 5 x 10⁵ and 2 x 10¹⁰ particles per liter of water, preferably between 5 x 10⁵ and 7 x 10¸ particles per liter of water, so as to obtain between one silicate particle for 10 water droplets and ten silicate particles per water droplet, knowing that the desired size of the droplets to be produced is between 100 and 700µm.

[0169] The projection of droplets into the ambient air for the production of snow is carried out by any known device for the production of artificial snow.

[0170] As an alternative, part of the snow production device in contact with the water flow can be made of silicate, with the water flow then removing the necessary quantity of particles by erosion.

[0171] This process can also be used to manufacture ice, for example in an ice rink or in a crushed ice machine, by projecting water containing a nucleating agent in the form of silicate particles against a cold surface (temperature less than or equal to 0°C). In these cases, the high nucleation temperature allows the use of higher water temperatures, and therefore higher refrigerant temperatures, thus improving efficiency.

Claims

1. A snow making method consisting in incorporating nucleation agent particles into water and in spraying said water containing said nucleation agent particles onto a surface or into an environment whose temperature is lower than 0°C, by means of a device for producing snow or ice, said nucleation agent particles comprising silicate particles whose unit equivalent spherical diameter is lower than 15 µm, preferably lower than 5 µm, wherein the method consists also of subjecting said particles to at least one activation treatment before their incorporation into water, characterized in that said at least one activation treatment comprises the creation of at least one micro-cavity on the surface of said particles.

2. The method according to claim 1, characterized in that it consists in using a base of silicate particles, in which base at least 80% of the particles have a unit equivalent spherical diameter lower than 15 µm, and preferably lower than 5 µm.

3. The method according to claim 1 or 2, characterized in that the silicate is chosen among the group consisting of the feldspars, tectosilicates, inosilicates and phyllosilicates.

4. The method according to claim 3, characterized in that the silicate is a feldspar of the microcline type and / or a feldspar of the orthoclase type.

5. The method according to claim 1, characterized in that the silicate particles are incorporated into the water in a number comprised between 5 x 105 and 2 x 1010 particles per litre of water, preferably between 5 x 105 and 7 x 108 particles per litre of water.

6. The method according to claims 1 to 5, characterized in that said spraying of the water containing said silicate particles consists in spraying the water in the form of droplets whose size is comprised between 100 and 700 µm, and wherein the silicate particles are incorporated into the water so as to obtain between one silicate particle for 10 water droplets and ten silicate particles per water droplet.

7. The method according to any of the claims 1 to 6, characterized in that it consists in creating at least one micro-cavity on the surface of said particles, wherein said micro-cavity opens through a surface aperture and is delimited by a lateral wall, the depth of said at least one micro-cavity being greater than equivalent disk diameter of the area of said surface aperture.

8. The method according to any of the claims 1 to 7, characterized in that said at least one activation treatment consists in applying to the previously water impregnated particles at least one cold treatment, preferably said at least one activation treatment consists in applying to the previously water impregnated particles at least two successive cold treatments, separated by a warming phase.

9. The method according to any of the claims 1 to 7, characterized in that said at least one activation treatment consists in exposing said particles to an ozone atmosphere in a suitable reactor, preferably during at least 20 minutes, at a temperature comprised between 0°C and 300°C.

10. The method according to any of the claims 1 to 7, characterized in that said at least one activation treatment consists in exposing said particles to an oxygen plasma in a suitable reactor, preferably during at least 20 minutes, at a temperature comprised between 0°C and 300°C.

11. The method according to any of the claims 1 to 7, characterized in that said activation treatment comprises the step consisting in immersing said particles into an aqueous solution of potash during at least 20 minutes and at a temperature comprised between 0°C and 90°C.

12. The method according to any of the claims 1 to 11, characterized in that said at least one activation treatment comprises a step of ultrasound cleaning and separation of said particles.

13. A powdery product obtained by grinding rock blocks chosen among the group consisting of feldspars, tectosilicates, inosilicates and phyllosilicates, comprising silicate particles which have a unit equivalent spherical diameter lower than 15 µm, wherein said particles have been subjected to an activation treatment to create at least one micro-cavity on the surface of said particles, wherein at least 10% of said silicate particles comprise at least one micro-cavity opening through a surface aperture and delimited by a lateral wall which defines its internal volume, which product is intended to be incorporated into water to serve as a nucleation agent in the context of the implementation of the snow making method according to any one of claims 1 to 12.

14. The product according to claim 13, characterized in that at least 10% of said silicate particles comprise at least one micro-cavity opening through a surface aperture and delimited by a lateral wall, the depth of said at least one micro-cavity being greater than the maximum dimension of said surface aperture.

15. The product according to claim 14, characterized in that the surface aperture of said at least one micro-cavity has an equivalent diameter comprised between 100 and 1000 nm and a depth comprised between 700 nm and 3 µm.

16. Use of a product in powdery form according to any one of claims 13 to 15, as a nucleation agent within the framework of the implementation of the snow making method according to any one of claims 1 to 12.