Preliminary results of the study of condensation properties of zinc oxide nanoparticles

Weather modification in order to regulate precipitation is one of the urgent tasks of meteorology. To solve this problem, it is necessary to develop effective reagents that affect microphysical processes in clouds

Therefore, one of the ways to increase the activity of reagents is to synthesize reagents in the form of nanoparticles

Modern scientific research in the field of weather modification is characterized by the study of hygroscopic reagents, which is an urgent task. The beginning of the research on condensation properties was given in

An instrument base for conducting experiments

The large cloud chamber (Fig. 1, a) is a rectangular container with thermally insulated walls. The chamber is cooled using three refrigerating units. The temperature control system in the chamber maintains temperature conditions from +5 to +30 °C. The chamber is covered with a thermal insulation film to reduce the temperature gradient and has four fans for mixing the air. The camera has a sensor for monitoring relative humidity. An artificial mist generator is connected to the chamber through a pipe, a fan is installed in the chamber to create a stream of moist air, and a device for sublimating the reagent is located.

The concentration of aerosol particles in the chamber was measured by a Lasair III meter (Fig. 1, b). During the experiment, the meter was installed in the camera, and the data was printed from a printer built into the meter. The aerosol particle counter takes a measurement from the camera every 20 seconds.

An AmScope microscope with a video camera was used to photograph the droplet area (Fig. 1, c).

Figure 1 - Equipment for performing experiments

Note: a) Cloud chamber: 1 – control panel; 2 – window for reagent application; 3 – viewing window; b) The Lasair III aerosol particle counter; c) Data analysis system: AmScope microscope; video camera; computer

DOI:10.60797/IRJ.2025.159.74.1

In recent years, many methods have been developed for the synthesis of zinc oxide nanoparticles

[12]

,

[13]

,

[14]

. We used the arc discharge method, which was used to produce nanoparticles in

[15]

. The sublimation was carried out in a vacuum chamber on a graphite substrate. Pieces of zinc measuring 0,4 × 0,4 cm were placed in a cuvette of graphite 0,5 cm thick, 7-9 cm long and 2 cm wide, and graphite powder weighing 8 % of the weight of zinc was poured into it. The first one serves as a catalyst for the growth of zinc oxide nanoparticles. The current was 80–150 A, the voltage was 30–40 V, and the substrate temperature was measured with a pyrometer and reached 2200 °C. The arc discharge was maintained from 2 to 5 minutes. The particles were collected on glass substrates, which were examined under an optical microscope. The samples were deposited on a carbon film for examination under an electron microscope.

The analysis of the substrates showed that zinc oxide nanoparticles were formed under the action of an arc discharge (Fig. 2). They are shaped like tubes, plates, and balls. The tubes have a diameter of 7–10 microns, and the plate has a thickness of several tens of microns. There are many "fluffy" balls on micron tubes.

Figure 2 - Nanotube ball (a) and zinc oxide plate (b)

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As can be seen, the balls consist of many nanotubes (Fig. 2, a). The plates (Fig. 2, b) consist of nanotubes of the same length arranged parallel to each other.

Let's estimate how many times the effectiveness of a zinc oxide reagent increases when dispersed in the form of nanotubes. Let's assume that the reagent particles in the first case have a spherical shape with a diameter of 5×10-6 cm, in the second case they have the shape of nanotubes with an outer diameter of 5×10-7 cm and an inner diameter of 3×10-7 cm. The mass of one spherical particle M =Vp, where V=3,8×10-16 cm3 is the volume of the spherical particle; p=5,6 g/cm3 is the density of the reagent. The number of particles per gram is N=2,6×1015.

Let's perform a similar calculation for nanotubes. We will find the length of the nanotube from the equality of the surface areas of the spherical particle and the nanotube. This approach is justified by the fact that the critical particle size of the reagent is determined by the surface area of the particle.

By performing elementary calculations, we obtain that the length of the nanotube is L = 2,5×10-5 cm. The mass of one nanotube particle is Mt=1×10-17, and the number of particles per gram is N=5,5×1016. A comparison of the calculation results shows that the specific yield of the reagent in the form of nanotubes is on average an order of magnitude higher than that of spherical particles.

In fact, the reagent particles are not spherical, so the difference will be smaller. In any case, their specific yield from the reagent when dispersed in the form of nanotubes will be greater.

To study the condensation properties, substrates with zinc oxide nanoparticles were kept in a humid environment.

Figure 3 - Glass substrate with nanoparticles

Note: a – after deposition; b – after exposure at a humidity of 100 %

DOI:10.60797/IRJ.2025.159.74.3

As can be seen from Figure 3, after exposure to a humid environment, the nanotubes increased in size due to condensed moisture and became visible in the field of an optical microscope. Figure 4 shows a glass substrate after exposure in a cloud chamber. The substrate was kept at a temperature of +5 °C and a relative humidity of 100 % for 15 minutes. Such conditions are close to real ones — the sowing of clouds for artificial precipitation.

Figure 4 - Glass substrate with nanoparticles after exposure in a humid environment

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As shown by experimental studies, when the glass substrate is exposed to a cloudy environment before the reagent is applied, the background droplet concentrations are significantly lower than the droplet concentrations on zinc oxide nanoparticles (Fig. 5). The graph shown in Figure 6 clearly demonstrates a rapid increase in droplet concentrations after the reagent is applied. The excess of quantitative concentrations is 2 times during the entire period of the experiment.

Figure 5 - Glass substrate with droplets

Note: a – background values; b – after reagent sublimation

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Figure 6 - The concentration spectrum of water droplets of different sizes

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During the preliminary experiments, all droplets in the size range from 0,3 to 25 microns were taken into account. The above data are the average results for the experiments. In particular, some large water droplets have fallen outside the focus of the microscope and cannot be fixed on the image.

It has been found that the amount of condensed water is much greater than the number of nanotubes. However, in order to effectively use the condensation properties of nanotubes to affect cloud processes, they must be obtained in an environment that should be affected, since moisture condenses on nanotubes during storage.

A method for synthesizing nanotubes for weather modification has been developed. Preliminary studies show that under the action of an arc discharge, zinc oxide nanoparticles are formed, which have the shape of tubes, plates and balls.

The tubes have a diameter of 7–10 microns, and the plates are several tens of microns thick. The specific yield of the reagent in the form of nanotubes is on average an order of magnitude higher than that of spherical particles.

After exposure to a humid environment, the nanotubes increase due to condensed moisture. Under the action of reagent particles, the concentration of droplets increases rapidly and their number is on average 2 times higher than the background values of the droplet spectrum.

The use of nanotechnology in meteorology can give an impetus to understanding the initial mechanisms of water phase transitions in the real atmosphere and contribute to the development of more effective means of weather modification.

This is an important step to test the effect of rain-causing reagents before conducting field work on cloud seeding from the air. Preliminary results have shown that a reagent based on zinc oxide nanoparticles can be used for cloud seeding.