Empty

The empty (from the Latin vacīvus) is the total absence of matter in a certain space or place, or the lack of content inside a container. By extension, the condition of a region where the density of particles is very low, such as interstellar space, is also called a vacuum; or that of a closed cavity where the pressure of air or other gases is less than atmospheric.

It can exist naturally or be artificially caused, it can be for technological or scientific uses, or in daily life. It is used in various industries, such as food, automobile or pharmaceutical.

The quality of a partial vacuum refers to how close it is to a perfect vacuum. Other things being equal, lower gas pressure means a higher quality vacuum. For example, a typical vacuum produces enough suction to reduce air pressure by about 20%. But higher quality vacuums are possible. Ultravacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10^-12) of atmospheric pressure (100 nPa), and can reach about 100 particles/cm³. Outer space is an even higher quality vacuum, with the equivalent of only a few hydrogen atoms per cubic meter on average in intergalactic space.

The void has been a frequent topic of philosophical debate since ancient Greece, but it was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories on atmospheric pressure. A Torricellian vacuum is created by filling a tall glass container closed at one end with mercury, then inverting it into a bowl to hold the mercury (see below).

Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and tubes vacuum, and since then there is a wide range of vacuum technologies. The development of manned spaceflight has raised interest in the impact of vacuum on human health and life forms in general.

A large vacuum chamber

Definition of emptiness

According to the definition of the «American Vacuum Society» or AVS (1958), the term refers to a certain space filled with gases at a total pressure less than atmospheric pressure, so the degree of vacuum is increases in direct relation to the decrease in residual gas pressure. This means that the more the pressure is lowered, the greater the vacuum will be obtained, which allows the degree of vacuum to be classified in correspondence with increasingly lower pressure intervals. Each interval has its own characteristics.

Etymology

The word empty comes from the Latin “an empty, null space”, a substantive use of the neuter of vacuus, which means "empty", related to with vacare, meaning "to be empty".

Vacuum is one of the few words in the English language that contains two consecutive letters u.

Historical interpretation

Historically, there has been much discussion about whether a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or nothing, in the context of atomism, which posited the vacuum and the atom as fundamental explanatory elements of physics. Following Plato, even the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, by itself, provide additional explanatory power beyond the physical volume with which it was commensurate. and, by definition, it was literally nothing at all, that could not be said to exist. Aristotle believed that no void could occur naturally, because the surrounding denser material continuum would immediately fill in any incipient oddities that might give rise to a void.

In his Physics, Book IV, Aristotle offered numerous arguments against a vacuum: for example, that motion through an unimpeded medium could continue ad infinitum, there being no reason for something to come to rest in any particular place. Although Lucretius defended the existence of the void in the I century B.C. C. and Heron of Alexandria unsuccessfully attempted to create an artificial vacuum in the I century AD. C.

In the medieval Muslim world, the physicist and Islamic scholar, Al-Farabi (Alfarabio, 872-950), conducted a small experiment concerning the existence of a vacuum, in which he investigated hand plungers in water. He concluded that the volume of air can expand to fill the available space, and suggested that the concept of a perfect vacuum was incoherent. According to Nader El-Bizri, the physicist Ibn al-Haytham (Alhazen, 965-1039) and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, and supported the existence of a void. Using geometry and mathematics, Ibn al-Haytham demonstrated that place (al-makan) is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al- Bīrūnī also states that "there is no observable evidence to rule out the possibility of a vacuum." The suction pump was described by the Arab engineer Al-Jazari in the 13th century, and later appeared in Europe from XV century.

European scholasticism, such as Roger Bacon, Biagio Pelacani and Walter Burley in the 13th and 14th centuries, focused on issues relating to the concept of emptiness. Ultimately following Stoic physics in this case, scholars from the 14th century onwards increasingly departed from the Aristotelian perspective. in favor of a "supernatural void" beyond the confines of the cosmos itself, a conclusion widely recognized by the 17th century, which helped segregate natural and theological concerns.

Nearly two thousand years after Plato, René Descartes also proposed an alternative theory of atomism based on geometry, without the problematic dichotomy of vacuum and atom. Although Descartes agreed with the contemporary position that the vacuum does not occur in nature, the success of his eponymous coordinate system and, more implicitly, the body-spatial component of his metaphysics would come to define the notion philosophically. modern representation of empty space as a quantified extension of volume. However, by the old definition, directional information and magnitude were conceptually distinct.

Torricelli's mercury barometer produced one of the first sustained gaps in a laboratory.

Medieval thought experiments on the idea of a vacuum considered whether a vacuum existed, even for an instant, between two flat plates when they were being pulled apart rapidly. plates or, as Walter Burley postulated, whether a "heavenly agent" prevented the vacuum from occurring. The widely held view that nature abhorred a vacuum was called horror vacui. There was even speculation that even God could not create a vacuum if he wanted to, and the 1277 Paris condemnations of Bishop Etienne Tempier, demanding that there be no restrictions on God's powers, led to the conclusion that God could create a vacuum if he wanted to. I wanted it. Jean Buridan reported in the 14th century that teams of ten horses could not pull open bellows when the port was sealed.

The Crookes tube, used to discover and study cathodic rays, was an evolution of the Geissler tube

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The first attempts to quantify measurements of partial vacuum occurred in the 17th century. Evangelista Torricelli's Mercury 1643 barometer and Blaise Pascal's experiments demonstrated a partial vacuum.

In 1654, Otto von Guericke invented the first vacuum pump and carried out his famous Magdeburg hemispheres experiment, showing that due to atmospheric pressure outside the hemispheres, teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved upon Guericke's design and with the help of Robert Hooke further developed vacuum pump technology. Thereafter, partial vacuum research waned until August Toepler invented the Toepler Pump in 1850 and in 1855 when Heinrich Geissler invented the mercury displacement pump, achieving a partial vacuum of about 10 Pa (0.1 Torr).. A series of electrical properties become observable at this level of vacuum, which renewed interest in further research.

While outer space provides the rarest example of a natural partial vacuum, the heavens were originally thought to be filled with a rigid, indestructible material called aether. Borrowing something from the pneuma of Stoic physics, the ether came to be regarded as the rarefied air from which it took its name. The first theories about light postulated an ubiquitous terrestrial and celestial medium through which light propagated. In addition, the concept served as the basis for Isaac Newton's explanations of refraction and radiant heat. The experiments of the 19th century on this luminiferous ether they tried to detect a tiny drag in Earth's orbit. Although the Earth does indeed move through a relatively dense medium compared to interstellar space, the drag is so minuscule that it could not be detected. In 1912, astronomer Henry Pickering commented: "Although the interstellar absorbing medium may simply be the ether, [it is] characteristic of a gas, and free gaseous molecules are certainly there."

Later, in 1930, Paul Dirac proposed a model of the vacuum as an infinite sea of particles possessing negative energy, called the Dirac sea. This theory helped refine the predictions of his earlier Dirac equation, and successfully predicted the existence of the positron, confirmed two years later. Werner Heisenberg's uncertainty principle, formulated in 1927, predicted a fundamental limit within which instantaneous position and momentum, or energy and time, can be measured. This has far-reaching consequences on the "vacuum" of the space between the particles. At the end of the XX century, the so-called virtual particles that arise spontaneously from empty space were confirmed.

Vacuum measurement

Atmospheric pressure is the pressure exerted by the atmosphere or air on Earth. At room temperature and normal atmospheric pressure, a cubic meter of air contains approximately 2× 10²⁵ molecules moving at an average speed of 1600km/h. One way to measure atmospheric pressure is with a mercury barometer; its value is expressed in terms of the height of the mercury column of unit cross section and 760 mm high. Based on this, one standard atmosphere is said to be equal to 760 mmHg. For convenience, the unit torricelli (symbol, Torr) will be used as a measure of pressure; 1 Torr= 1 mmHg, so 1 atm= 760 Torr; therefore 1 Torr= 1/760 of a standard atmosphere, or 1 Torr = 1.316 × 10^–3 atm.

Low pressure measurement

One of the best known methods for measuring low pressures is the method developed by Pirani. It consists of a Wheatstone bridge where a resistance of the bridge is exposed to the vacuum to be measured. The resistance of this sensor element will vary as the pressure changes, because at vacuums close to atmospheric pressure the filament will be in contact with more molecules, generating a drop in temperature and consequently a drop in its resistive value. As the vacuum improves, this filament will find fewer molecules to dissipate its heat, therefore its temperature will increase. This increase in temperature will produce an increase in its resistive value, generating an imbalance in the Wheatstone bridge. This imbalance is measured with a microammeter. Then it only remains to interpolate the microamps generated by the Wheatstone bridge with the vacuum values. These values are transferred to a table with which a scale is drawn, where, for example, in CINDELVAC vacuum gauges, there will be 0 microamps when the sensor is in high vacuum and 50 microamps at atmospheric pressure. The Wheatstone CINDELVAC bridge response table is as follows:

Ionization measurements

They have the same foundation as ionization bombs, to the point that the latter can be considered as a consequence of the former. When it comes to measuring very low vacuum pressures, the variants proposed by Bayard-Alpert of those devices capable of supplying pressures up to 10^{–12 with great accuracy are used.} Torr.

Air is made up of various gases; the most important are nitrogen and oxygen, but it also contains gases such as carbon dioxide, argon, neon, helium, krypton, xenon, hydrogen, methane, nitrous oxide and water vapor in lower concentrations.

Applications of vacuum techniques

History

Torricelli mercury barometer, which produced the first vacuum in a laboratory.

Throughout all of Antiquity and until the Renaissance, the existence of atmospheric pressure was unknown. They could not therefore give an explanation of the phenomena due to vacuum. In Greece, therefore, two theories clashed. For Epicurus and especially for Democritus (420 BC) and his school, matter was not a continuous whole but was made up of small indivisible particles (atoms) that moved in an empty space and that with their different ordering gave rise to the different physical states. On the contrary, Aristotle excluded the notion of a vacuum and to justify the phenomena that his own Physics could not explain he resorted to the famous aphorism according to which "Nature is horrified by a vacuum" (a theory that was dominant during the Middle Ages and until the discovery of vacuum). of pressure).

This term horror vacui was even used by Galileo himself at the beginning of the XVII century by not being able to explain to his disciples the fact that a column of water in a tube closed at its end does not come off, if the tube has been inverted while its free end is submerged in water. However, he knew how to transmit to his disciples the concern to explain the previous fact and associated with it, why the suction-impeller pumps (a hydraulic organ invented by the Alexandrian Ctesibius, a contemporary of Archimedes) could not raise the water from the wells to higher than 10m.

In 1630 Giovanni Battista Baliani sent a letter to Galileo Galilei notifying him that he could not get the water in the siphons to rise higher than 10 m. Galileo proposed that the explanation was that the vacuum was not strong enough to lift that amount of water. In 1640, the Italian Gasparo Berti, trying to explain what happened with the siphons, carried out the first experiment with a vacuum. He created what is primarily a water barometer, which turned out to be capable of producing a vacuum.

By analyzing Berti's experimental report, Evangelista Torricelli clearly grasped the concept of air pressure, which is why he designed, in 1644, a device to demonstrate pressure changes in air. He built a barometer that used mercury instead of water, and in this way, without meaning to, he verified the existence of a vacuum.

Torricelli's barometer consisted of a container and a tube filled with mercury (Hg) closed at one end. Inverting the tube into the container created a vacuum at the top of the tube. This was somewhat difficult to understand at the time, so an attempt was made to explain it by saying that this region of the tube contained mercury vapor, an argument that was not acceptable since the level of mercury in the tube was independent of the volume of the tube used in the experiment.

The concept of vacuum was accepted when in 1648, Blaise Pascal raised a barometer with 4 kg of mercury up a mountain at 1000 meters above sea level. Surprisingly, when the barometer was at the top, the level of the Hg column in the tube was much lower than at the bottom of the mountain. Torricelli assured the existence of air pressure and said that because of it the Hg level in the container did not drop, which meant that the size of the mercury column remained constant inside the tube. Thus, as the air pressure decreased at the top of the mountain, the Hg level in the container rose and in the column inside the tube immediately fell (it was partially emptied).

The final step that Torricelli took was the construction of a mercury barometer that contained another barometer in the empty part of the tube to measure the air pressure in that region. Many measurements were made and the result was that there was no column of mercury in the tube of the small barometer because there was no air pressure. This clarified that there was no mercury vapor in the empty part of the tube. Thus, the air pressure was revealed and, most importantly, the production and existence of a vacuum.

So, after several experiments, the operation of Torricelli's barometer can be well explained: the atmosphere exerts a pressure, which prevents the mercury from leaving the tube and the container; that is, when the atmospheric pressure equals the pressure exerted by the column of mercury, the mercury will not be able to leave the tube. When air is heavier, it supports a larger column of mercury; and when it weighs less, it is not able to withstand the same column of mercury, so a little mercury escapes from the tube.

Vacuum Applications

On many occasions, in modern laboratories, there are situations in which a container full of a gas must be emptied. Evacuation must be the first step in creating a new gaseous environment. During the distillation process, gas must be continuously removed as the process progresses. Sometimes it is necessary to evacuate the container to prevent air from contaminating a clean surface or interfering with a chemical reaction. Atomic particle beams must be treated in a vacuum to prevent loss of momentum through collisions with air molecules. Many forms of radiation are absorbed by air and can therefore only be propagated over long distances in a vacuum. A vacuum system is an essential part of laboratory instruments such as mass spectrometers and electron microscopes. Simple vacuum systems are used for vacuum dehydration and vacuum freezing. Nuclear particle accelerators and thermonuclear devices require very sophisticated and massive vacuum systems. In modern industrial processes, most notably semiconductor manufacturing, carefully controlled vacuum environments are required.

Vacuum systems

The pressure and composition of waste gases in a vacuum system vary considerably with its design and history. For some applications a residual gas density of tens of billions of molecules per cubic centimeter is tolerable. In other cases, no more than a few hundred thousand molecules per cubic centimeter constitute an acceptable vacuum.

For pressures below atmospheric, vacuum is usually categorized as follows:

The composition of the gas in a vacuum system changes as the system evacuates because the efficiency of vacuum pumps is different for different gases. At low pressures the molecules on the container walls begin to be desorbed and residual gas forms. Initially, the bulk of the gas leaving the walls is water vapor and carbon dioxide; at very low pressures, in containers that have been fired, you have hydrogen.