Doctor of Physical and Mathematical Sciences
Federal State Budgetary Institution «High-Mountain Geophysical Institute
Nalchik, Russian Federation
Department of cloud physics
Federal State Budgetary Institution «High-Mountain Geophysical Institute
Nalchik, Russian Federation
LABORATORY STUDIES OF INCREASING THE ICE-FORMING EFFICIENCY OF PYROTECHNIC COMPOSITIONS BASED ON AD-1
Currently, silver iodide AgI is one of the most widely used reagents when exposed to supercooled clouds in order to prevent hail and precipitation. This is primarily due to the fact that the crystal structure of AgI is similar to the structure of natural ice, which ensures its effective interaction with the cloudy environment and the formation of the necessary crystallization centers in its supercooled part. At the same time, the effectiveness of this reagent when interacting with a supercooled cloudy environment at a temperature of minus 6°C and above decreases. Therefore, research related to the creation of new reagents and increasing the efficiency of existing ice-forming reagents are still relevant. A promising direction in this area is the use of various chemical additives leading to the production of particles with a crystal lattice closer to the crystal lattice of ice. It was proposed to use finely ground zinc powder as such an additive, since zinc crystals have a hexagonal packing of atoms, which is very similar to the structure of ice. The article presents the results of laboratory studies to further increase the effectiveness of pyrotechnic compositions used in anti-hail products such as «Alazan-6» and «Alazan-9». The average values of the yield of crystallization nuclei of the ice-forming component of AD-1 with the addition of zinc (6%) were obtained, which are an order of magnitude higher than the specific yield of the pyrotechnic composition of AD-1.
To generate ice-forming aerosols under active influences on clouds, pyrotechnic compositions containing an active reagent (AgI, PbI2, CuS) and iodizing components (KI, NH4J, NH4JO3, C7O2H5J) are used, which contribute to an increase in the ice-forming efficiency of the compositions. Many believe that the high ice-forming activity of AgI is due to the fact that the structure of its crystal lattice is similar to the crystal lattice of ice [1,2,3]. Indeed, under the conditions of the Earth’s atmosphere, ice has a hexagonal crystal structure, in which each H2O molecule is surrounded by four molecules closest to it, located at equal distances from it, equal to 2.76 angstroms and located at the vertices of a regular tetrahedron, as in AgI. The choice of zinc as an additive to the basic composition of AD-1 is due to the fact that the ice-like structure of zinc, like that of AgI, promotes the adsorption of H2O molecules on its surface, the formation of several layers of molecules on its surface, and the formation of a surface water film, followed by its freezing when the critical thickness. In such a film, microvolumes with oriented H2O molecules are formed, acquiring an ice-like structure with supercooling. It should be noted that zinc oxide (zinc is immediately oxidized in air, becoming covered with a thin oxide layer) at a temperature of 913 °C begins to boil and turn into vapor, which contributes to the formation of zinc oxide nanotubes when the fuel charge of anti-hail missiles burns. With a sufficient size, these microvolumes can become the nuclei of ice crystals [3-5]. It is important that the boiling point of zinc lies in the range of the sublimation temperature of the ice-forming aerosol (the generation of the ice-forming aerosol during rocket seeding of clouds is carried out at temperatures from 700 to 1400° C) .
Materials and research methods
This paper presents the results of laboratory studies, the purpose of which was to increase the efficiency of the AD-1 pyrotechnic composition. This domestic pyrotechnic composition is used to create fuel charges for cruise rocket engines filled with a reagent for equipping anti-hail missiles. Despite the fact that the ratios of all components of the composition were optimized, the yield of active ice-forming particles from one gram of the composition remains insufficiently high, which reduces the efficiency of its application in the region of negative temperatures lying near the zero isotherm. The purpose of experimental studies is to increase the yield of ice-forming particles per gram of AD-1 composition in the temperature range from zero and below. To achieve this goal, finely ground zinc powder, with a particle size of 0.01 — 0.05 mm, was used as additives to the existing pyrotechnic composition of AD-1. The choice of this range of size particles was due to the fact that fine particles are more intensively mixed with other components of the composition during the formation of propellant charges of anti-hail missiles. When carrying out laboratory studies, finely ground zinc powder was introduced into the initial pyrotechnic composition of AD-1 in a ratio to its total mass — 3%, 6% and 9%, respectively. In the cloud chamber, the temperature was maintained at a given level in the range from 0° to –17°С. The efficiency of the reagent was evaluated by determining the number of ice crystals formed when a known amount of a pyrotechnic composition was introduced in the form of an aerosol into the supercooled water mist of a large cloud chamber. The work [1,7] presents in detail the method of laboratory experiments to determine the yield of crystallization nuclei of the pyrotechnic composition AD-1 with various additives at temperatures from -5 to 15 °C. The number of crystals in the chamber was determined based on the number of crystals deposited on the substrate.
Research results and their discussion
Table 1 shows the results of experimental studies.
Average values of the yield of nuclei of crystallization of the ice-forming component of AD-1 with the addition of zinc (6%) at different temperatures
According to the data presented in table 1, it can be seen that the average values of the yield of crystallization nuclei of the ice-forming component of AD-1 with the addition of zinc (6%) increases by an order of magnitude compared to the specific yield of the pyrotechnic composition of AD-1. Figure 1 shows the dependence of the yield of ice-forming active particles (n) for various contents of finely dispersed zinc powder in the initial composition of AD-1. Curve 1 characterizes the yield of ice-forming particles from one gram of the initial composition of AD-1 without zinc content, curve 2 — with a zinc content of 3%, curve 3 with a zinc content of 6% and curve 4 with a zinc content of 9%.
The specific yield of reagent particles depending on the concentration of powdered zinc is shown in figure 2. From the presented graph it can be seen that the maximum yield of ice-forming particles is provided in the range of zinc concentrations of 4.7–6.6 wt. %. This area in figure 2 is bounded by vertical lines.
From the above materials, it follows that the presence of fine zinc powder in the composition of the initial ice-forming fuel in a ratio to the total mass of the composition of 6% sharply increases the yield of ice-forming particles in the entire range of accepted temperatures, ranging from zero to minus 14 ° C. Such an increase in the yield of active ice-forming particles is explained by the fact that at a high combustion temperature of the pyrotechnic composition, zinc oxide nanotubes of various modifications and sizes are formed, which actively interact with the supercooled cloud medium in the accepted temperature range. The cloud layer between the levels of isotherms -6 and -10 ° C is favorable for the growth, aggregation and multiplication of crystals, and corresponds to the threshold of the crystallizing efficiency of the applied reagents . The graph (fig. 2) shows that it is in this temperature range that the new reagent AD-1 plus zinc (6%) sharply increases the yield of ice-forming particles. The effectiveness of work on active influences depends on many factors, including the correct choice of the optimal consumption of the reagent [8, 9]. To determine the flow rate of the proposed pyrotechnic composition and develop recommendations for active influences, we use the data given in , where the efficiency of the AD-1 composition at a temperature of -7 ° C is 1012 particles/g. The mass of the AD-1 pyrotechnic composition with zinc additives, which is necessary to ensure the same yield of ice-forming nuclei, can be determined by the formula:
From formula (1) it can be seen that to create the same concentration of crystals in the cloud, the amount of pyrotechnic composition AD-1 with zinc additions is an order of magnitude less than that of AD-1. This will reduce the consumption of anti-hail products during active exposure. For example, consider an object of influence of the IV category: a super-powerful hail convective cell, from which, according to radar data, a hail of catastrophic intensity falls. On seeding one object of influence of this category, on average, 76 pieces of anti-hail products of the type (Alazan-6, Alazan-9) . The rationing of the consumption of anti-hail products for seeding the target is carried out with the expectation that the concentration of ice-forming nuclei in the seeding volume after 3 minutes was at least 107 м-3, and, if possible, reached 108 м-3, which, according to theoretical modeling data [10-13], provides a dramatic increase in seeding efficiency. To ensure this concentration during seeding, an object of influence of category IV and objects of influence close to them in terms of parameters, repeated seeding is carried out with an increased dosage of anti-hail products of the «Alazan-6» type in time and space. If anti-hail products are used, based on the new reagent AD-1 plus zinc, in which the yield of ice-forming nuclei is an order of magnitude higher than the yield of ice-forming nuclei in anti-hail products such as «Alazan-6», it will be possible to reduce anti-hail products several times.
Thus, the presence of finely dispersed zinc powder in the composition of the initial ice-forming fuel in a ratio to the total mass of the composition of 6% sharply increases the yield of ice-forming particles in the entire range of accepted temperatures, ranging from 00С to -140С, is explained by the fact that at a high combustion temperature of the pyrotechnic composition, zinc oxide nanotubes of various modifications and sizes are formed, which actively interact with the supercooled cloud environment in the accepted temperature range. So, for example, at a temperature of -120С (curve 3 on the graph), the yield of ice-forming particles increases by almost an order of magnitude, and in the temperature range from -20С to -40С it almost doubles, which makes it possible to influence the warmer supercooled part of the cloudy Wednesday. An increase in the ice-forming efficiency of the anti-hail products used will lead to an increase in the efficiency of seeding hail clouds and a decrease in the consumption of anti-hail products, which largely depends on the type and ice-forming efficiency of anti-hail products. On the basis of the initial ice-forming fuel AD-1, a method has been developed for obtaining a new effective pyrotechnic composition for equipping meteorological rockets intended for active effects on thunderstorm clouds in order to artificially increase liquid precipitation and combat hail [2,7,11]. This composition can also be used to create promising ground generators for active impacts on supercooled fogs in order to ensure favorable meteorological conditions for the functioning of cosmodromes, airports and road transport communications.
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© Хучунаев Б. М., Геккиева С.О., 2021