Vacuum is a space in which there is no matter. In applied physics and technology, it means a medium in which a gas is contained at a pressure less than atmospheric pressure. What were rarefied gases when they were first discovered?
History Pages
The idea of emptiness has been a point of contention for centuries. Rarefied gases tried to analyze the ancient Greek and Roman philosophers. Democritus, Lucretius, their students believed: if there were no free space between the atoms, their movement would be impossible.
Aristotle and his followers refuted this concept, in their opinion, there should be no "emptiness" in nature. In the Middle Ages in Europe, the idea of "fear of the void" became a priority, it was used for religious purposes.
The mechanics of Ancient Greece, when creating technical devices, were based on air rarefaction. For example, water pumps that functioned when a vacuum was created above the piston appeared at the time of Aristotle.
The rarefied state of gas, air, has become the basis for the manufacture of piston vacuum pumps, which are currently widely used in technology.
Their prototype was the famous piston syringe of Heron of Alexandria, created by himto draw out pus.
In the middle of the seventeenth century, the first vacuum chamber was developed, and six years later, the German scientist Otto von Guerick managed to invent the first vacuum pump.
This piston cylinder easily pumped air out of a sealed container, creating a vacuum there. This made it possible to study the main characteristics of the new state, to analyze its operational properties.
Tech vacuum
In practice, the rarefied state of gas, air is called technical vacuum. In large volumes, it is impossible to obtain such an ideal state, since at a certain temperature the materials have a non-zero saturated vapor density.
The reason for the impossibility of obtaining an ideal vacuum is also the transmission of gaseous substances through glass, metal walls of vessels.
In small quantities it is quite possible to obtain rarefied gases. As a measure of rarefaction, the free path of gas molecules that randomly collide, as well as the linear size of the vessel used is used.
Technical vacuum can be considered a gas in a pipeline or vessel with a pressure value less than in the atmosphere. A low vacuum occurs when the atoms or molecules of a gas stop colliding with each other.
A fore vacuum is placed between the high vacuum pump and atmospheric air, which creates a preliminary vacuum. In the case of a subsequent decrease in the pressure chamber, an increase in the path length of gaseous particles is observed.substances.
When the pressure is from 10 -9 Pa, an ultra-high vacuum is created. It is these rarefied gases that are used to conduct experiments using a scanning tunneling microscope.
It is possible to obtain such a state in the pores of some crystals even at atmospheric pressure, since the diameter of the pores is much smaller than the free path of a free particle.
Vacuum based appliances
The rarefied state of the gas is actively used in devices called vacuum pumps. Getters are used to suck gases and obtain a certain degree of vacuum. Vacuum technology also includes numerous devices that are necessary to control and measure this state, as well as to control objects, to carry out various technological processes. The most complex technical devices that use rarefied gases are high-vacuum pumps. For example, diffusion devices operate on the basis of the movement of residual gas molecules under the action of a working gas flow. Even in the case of an ideal vacuum, there is little thermal radiation when the final temperature is reached. This explains the main properties of rarefied gases, for example, the onset of thermal equilibrium after a certain time interval between the body and the walls of the vacuum chamber.
Rarefied monatomic gas is an excellent thermal insulator. In it, the transfer of thermal energy is carried out only with the help of radiation, thermal conductivity and convection are notare observed. This property is used in Dewar vessels (thermoses), consisting of two containers, between which there is a vacuum.
Vacuum has found wide application in radio tubes, for example, magnetrons of kinescopes, microwave ovens.
Physical vacuum
In quantum physics, such a state means the ground (lowest) energy state of the quantum field, which is characterized by zero values of quantum numbers.
In this state, a monatomic gas is not completely empty. According to quantum theory, virtual particles systematically appear and disappear in the physical vacuum, which causes zero oscillations of fields.
Theoretically, several different vacuums can exist simultaneously, which differ in energy density, as well as other physical characteristics. This idea became the basis for inflationary big bang theory.
False vacuum
It means the state of the field in quantum theory, which is not a state with a minimum energy. It is stable over a certain time period. There is a possibility of "tunneling" a false state into a true vacuum when the required values of the main physical quantities are reached.
Outer space
When discussing what a rarefied gas means, it is necessary to dwell on the concept of "cosmic vacuum". It can be considered close to the physical vacuum, but existing in the interstellarspace. The planets, their natural satellites, many stars have certain attractive forces that keep the atmosphere at a certain distance. As you move away from the surface of a stellar object, the density of rarefied gas changes.
For example, there is the Karman line, which is considered a common definition with outer space of the planet's boundary. Behind it, the value of the isotropic gas pressure decreases sharply in comparison with solar radiation and the dynamic pressure of the solar wind, so it is difficult to interpret the pressure of a rarefied gas.
Outer space is full of photons, relic neutrinos that are difficult to detect.
Measurement features
The degree of vacuum is usually determined by the amount of substance that remains in the system. The main characteristic of the measurement of this state is the absolute pressure, in addition, the chemical composition of the gas and its temperature are taken into account.
An important parameter for vacuum is the average value of the path length of the gases remaining in the system. There is a division of vacuum into certain ranges in accordance with the technology that is necessary for measurements: false, technical, physical.
Vacuum forming
This is the manufacture of products from modern thermoplastic materials in hot form using low air pressure or vacuum action.
Vacuum forming is considered a drawing method, as a result of which sheet plastic is heated,located above the matrix, up to a certain temperature value. Next, the sheet repeats the shape of the matrix, this is due to the creation of a vacuum between it and the plastic.
Electrovacuum devices
They are devices that are designed to create, amplify, and convert electromagnetic energy. In such a device, air is removed from the working space, and an impermeable shell is used to protect against the environment. Examples of such devices are electronic vacuum devices, where the electrons fit in a vacuum. Incandescent lamps can also be considered vacuum devices.
Gases at low pressures
A gas is called rarefied if its density is negligible, and the length of the molecular path is comparable to the size of the vessel in which the gas is located. In such a state, a decrease in the number of electrons is observed in proportion to the density of the gas.
In the case of a highly rarefied gas, there is practically no internal friction. Instead, external friction of the moving gas against the walls appears, which is explained by the change in the momentum of the molecules when they collide with the vessel. In such a situation, there is a direct proportionality between the speed of particles and the density of the gas.
In the case of low vacuum, frequent collisions between gas particles in full volume are observed, which are accompanied by a stable exchange of thermal energy. This explains the phenomenon of transfer (diffusion, thermal conductivity), is actively used in modern technology.
Obtaining rarefied gases
The scientific study and development of vacuum devices began in the middle of the seventeenth century. In 1643, the Italian Torricelli managed to determine the value of atmospheric pressure, and after the invention of a mechanical piston pump with a special water seal by O. Guericke, a real opportunity appeared for conducting numerous studies of the characteristics of a rarefied gas. At the same time, the possibilities of the impact of vacuum on living beings were studied. Experiments carried out in a vacuum with an electric discharge contributed to the discovery of a negative electron, X-ray radiation.
Thanks to the heat-insulating ability of vacuum, it became possible to explain the methods of heat transfer, to use theoretical information for the development of modern cryogenic technology.
Using a vacuum
In 1873 the first electrovacuum device was invented. They became an incandescent lamp, created by the Russian physicist Lodygin. Since that time, the practical use of vacuum technology has expanded, new methods for obtaining and studying this state have appeared.
Various types of vacuum pumps have been created in a short period of time:
- rotational;
- cryosorption;
- molecular;
- diffusion.
At the beginning of the twentieth century, academician Lebedev managed to improve the scientific foundations of the vacuum industry. Until the middle of the last century, scientists did not allow the possibility of obtaining a pressure less than 10-6 Pa.
BCurrently, vacuum systems are built all-metal to avoid leakage. Vacuum cryogenic pumps are used not only in research laboratories, but also in various industries.
For example, after the development of special evacuation means that do not pollute the object used, new prospects for the use of vacuum technology have appeared. In chemistry, such systems are actively used for the qualitative and quantitative analysis of the properties of pure substances, the separation of a mixture into components, and the analysis of the rate of various processes.
