With the rapid development of military high technology, the detection, tracking and attack capabilities of defense systems around the world are becoming stronger and stronger, and the survivability of ground military targets and penetration capabilities of weapons systems are increasingly under serious threat.
In order to improve the survivability of ground military targets in national defense system and the penetration and deep strike capability of weapon system, the development and application of stealth technology has become an important direction of national defense system development.
Stealth material is the most important part of stealth technology.
As a result, the research on stealth materials has been booming in recent years.
At present, some new stealth materials have been used and developed, such as wide-band absorbing agent, polymer stealth materials, chiral stealth materials, nano-stealth materials, etc.
In recent years, more and more reports about nanomaterials with high absorption coefficient of electromagnetic wave have aroused great interest of military scientists.
1 application of a new stealth material in the military field
Nanometer zinc oxide is also one of the research hotspots in nanometer stealth materials.
Nanometer zinc oxide is a promising new type of radar absorbent for military applications.
Preparation of nanometer zinc oxide
There are many kinds of chemical preparation methods of nanometer zinc oxide, and new technologies emerge in an endless stream, such as liquid-solid-solution phase transfer and separation method. However, there are mainly precipitation method, sol-gel method, microemulsion method, hydrothermal (solvothermal) method and so on.
1. Precipitation method
Precipitation method is generally divided into direct precipitation method and uniform precipitation method.
By direct precipitation, the precursor of zinc oxide was prepared by adding precipitant to the solution of soluble zinc salt.
Common precipitators are ammonia, ammonium bicarbonate, etc.
The precursors were Zn(OH)2, Zn2(OH)2CO3, etc.
2. Sol-gel method
Sol-gel method is a wet chemical method for preparing ultrafine particles.
The basic principle is to dissolve metal inorganic salt or metal alcohol salt in the solvent to form a uniform solution, solute and solvent hydrolysis or reaction with alcohol, reaction products after aggregation, generally generate nanoscale particles and form sol.
3. Microemulsion method
Microemulsions are thermally stable, isotropic, externally transparent or translucent, with particle size between 1 and 100 nm, formed by two dissimilar solutions under the action of surfactants.
Microemulsions are usually transparent, isotropic, thermodynamically stable systems of surfactants, cosurfactants, oil, and water.
4. Hydrothermal (solvent-thermal) method
Hydrothermal synthesis is a new method for preparing ultrafine particles in liquid phase.
Generally, particle construction and crystal growth at the atomic and molecular levels are achieved at 100-150oc temperature and under high pressure.
Solvent for water called hydrothermal method, for other solvents such as ethanol, isopropanol, known as solvent thermal method.
Figure 2 SEM diagram of nanometer zinc oxide
The basic principle and application of nanometer zinc oxide as stealth material
Stealth materials are used to reduce the detectability of military targets.
The basic principle of material stealth is to reduce the signal intensity emitted or reflected by the target itself.
Or reduce the signal contrast between the target and the environment, making it lower than the threshold value of the detector;
Or the law of object and environment contrast is confused, causing the difficulty of object geometry recognition.
At present, radar still plays a dominant role in various detectors, so radar wave stealth material is the most important and fastest developing stealth material in stealth technology.
Radar wave stealth material basic performance requirements is to absorb radar waves, so this material is also known as radar absorbing material.
Radar absorbing materials absorb and attenuate the incident energy to reduce the reflected energy and reduce the detectability of military targets.
The absorbing principle is usually the following three types: first, when the radar wave ACTS on the material, the material absorbs the energy of the radar wave, and through the generation of conductivity loss, high frequency dielectric loss, hysteresis loss, etc., the electromagnetic energy is converted into heat energy and emitted;
Second, the reflected energy of the radar wave on the surface of the material is dispersed to each part of the target surface to reduce the electromagnetic energy scattered in the direction of the radar receiving antenna.
The third is to make the radar wave on the surface of the material and the reflection wave into the material at the bottom of the superposition interference.
3. Interaction between waves and matter
Zinc oxide (zno) is a new inorganic semiconductor material with direct bandgap and wide bandgap.
At room temperature, the band gap width is 3.37 eV, the exciton binding energy is up to 60 MeV, and it has good piezoelectric properties. It is widely used in ultraviolet emission materials, transparent conductivity, field emission display devices, solar cells and gas sensors, and materials of ultraviolet semiconductor photoelectric devices.
In recent years, it has been found that zno is a good absorbing material, which has aroused great interest.
Nanometer zinc oxide is a new kind of multifunctional inorganic materials, the sound, magnetism, light, electricity, etc, has a number of excellent performance, and now the industrialization in the production of various shapes of nanometer zinc oxide has been implemented, therefore, with the increasingly deepening of research, nano zinc oxide could become a kind of multifunctional composite absorbing materials.