If two pieces of metal come into contact in space, they will fuse together. Why?

This phenomenon exists. It is called "cold welding" in academic and technical terms. Although it is not clear whether humans have ever done such an experiment in space, such a thing has happened in space. Happened. This happened to a probe launched by the Americans. This probe was originally intended to detect several major planets. After detecting Venus and Mercury, its antenna rotation axis was cold welded. There was no way. The backup antenna had to be activated, but its efficiency was only one percent of the main antenna.

So why does this happen? In fact, the reason is very simple. When two identical pieces of metal come into contact in the vacuum environment of space, there is no obstruction between the atoms on the surface of the two contact surfaces. Then the atoms on the two surface layers will grab each other when they come into contact. Live each other and make them one. This is how the cold welding phenomenon occurs. The reason why the American detector is in that situation is because the metal connection of its rotating axis is too simple. After the detector enters space, after a period of use, the oxide layer on it is worn away. When used, cold welding occurs.

So why is this phenomenon rarely seen on this earth? In fact, there are two main reasons. The first is that the exposed surface of the metal will oxidize rapidly to form an oxide layer. In this way, when two pieces of metal are brought together, cold welding will not occur due to the barrier of the oxide layer. The other reason is that on the earth The presence of air will cause a barrier between the two pieces of metal, so it is difficult for the metal atoms of the two pieces of metal to be directly connected, so of course the cold welding phenomenon is not easy to occur.

But this phenomenon does not absolutely never happen on the earth. If the surface layers of the two pieces of metal are not oxidized and there is no air or other things between them, put them together and squeeze them. If the atoms on the contact surface are fully in contact, cold welding will also occur.

This phenomenon is very important in space exploration. In fact, there is a scientific term to describe this phenomenon, "cold welding". Traditional welding requires high temperature to melt two pieces of metal waiting to be welded. The metals in the molten state diffuse and fuse together, and then solidify and join together after cooling down.

Cold welding refers to the phenomenon of two pieces of metal melting into one after being brought together at room temperature or even low temperature. Feynman once jokingly described this phenomenon: Because the atoms in the two metals couldn't figure out which metal they belonged to, they simply fused together.

This is naturally a joke. Atoms are not conscious, but the diffusion of metal atoms does happen. Normally we cannot observe this phenomenon because the earth's surface is full of atmosphere. If two pieces of metal are put together, there will still be a barrier between them, such as an oxide layer or an air layer. These layers prevent the free diffusion of metal atoms, making it impossible for two pieces of metal to automatically merge into one. But in space, there is no barrier between the oxide layer and the gas layer. The atoms of the two pieces of metal can diffuse freely. After they are seamlessly connected together, the phenomenon of "cold welding" will occur.

This phenomenon has a great impact on space exploration. For example, the Galileo Jupiter probe launched by the United States in the last century was due to cold welding, which prevented the antenna from being opened as planned, greatly affecting signal transmission. Therefore, in order to prevent this phenomenon from happening, oil or other substances are used to separate the folding device and the transmission device from each other to prevent the two separate pieces of metal from fusing together and affecting normal functions.

It’s like this. When two pieces of metal meet in space, they may be welded together if certain conditions are met.

This phenomenon is called cold welding. Cold welding is the phenomenon of varying degrees of adhesion between solids and solid surfaces when they come into contact with each other in an ultra-high vacuum environment.

Why does this happen?

Regarding the cold welding phenomenon, Richard Phillips Feynman, the first physicist to propose the concept of nanometers, once compared it in a lecture introducing friction: In a vacuum, When two pieces of metal come into contact, because there is nothing between the atoms on both sides of the metal contact surface to block them, they cannot tell which side they are originally from. The atoms on both sides diffuse into each other, and gradually the two pieces The metal atoms fuse together, and eventually the two pieces of metal are welded together. But if there are other non-similar atoms such as air or an oxide layer, these metal atoms will realize that they belong to different parts and will not fuse together.

In summary, in an ultra-vacuum environment, the surfaces of two materials reach atomic level cleanliness. Through contact or under a certain pressure, adhesion occurs or fuses into one, which is cold welding. Because air can be said to be everywhere on the earth, it is difficult to see the cold welding phenomenon.

Example

Everyone knows that a broken mirror cannot be reunited, but there is a situation that I don’t know if you have ever encountered. A piece of mirror or glass is on the verge of breaking, but it still They are stuck together, and a crack extending from the crack can be clearly seen on the surface. When you find a good angle and compress the mirror or glass in the vertical direction of the crack, the crack on it will miraculously become smaller. This can actually be explained by the principle of cold welding, because there are no impurities between the two contact surfaces at the end of the crack, and a certain force can make the cracks "stick" together again.

There are also ancient blacksmithing techniques. For example, a hero's knife broke and he came to the blacksmith shop. The blacksmith heated the broken part of the knife red, and at the same time prepared another piece of iron that was also hot red. After beating it repeatedly, he finally helped the hero to connect the knife. By heating the metal, the atoms move more violently, and by beating to increase the pressure, the two pieces of metal are finally forced to stick together. This is embarrassing!

The impact of cold welding on aerospace

There is no air in space, so it is easier for metals to undergo cold welding. When the U.S. Galileo spacecraft carried out its Jupiter exploration mission, the communication antenna was retracted by default during the first long-term flight. However, after a year of flight, when scientists wanted to open the antenna for data transmission, they found that it could not be opened. . It is because of the cold welding phenomenon that the antennas are stuck together and cannot be opened.

Summary

Today, cold welding technology is a newly developed technology, which plays an important role in some scenarios that traditional welding technology cannot satisfy.

The most significant advantage of cold welding is that it has the same welding strength as the raw material itself, and will not have a thermal impact on the connected parts. Traditional welding is generally high-temperature welding, which has sparks, dust and other effects. . The cold welding process is fast and without deformation, and the operation is simple.

However, cold welding itself also has many limitations. The requirements for cold welding materials are generally ductile metals, no excessive hardening, clean surfaces, regular welding surface shapes, etc. Therefore, cold welding cannot be widely used.

This is called cold welding. When two pieces of metal come into contact in a vacuum, they stick together without any heating or liquid phase. But to do this, make sure that both metal surfaces are smooth. Since space is a vacuum, cold welding can fuse two pieces of metal.

In the vacuum environment of the universe, two bare pieces of similar metals will bond to each other after contact, as if they were welded together. This phenomenon is called "Cold Welding".

Richard Feynman, the most humorous physicist in history, once vividly explained that this phenomenon occurs because "in a vacuum, there are no atoms between the metal atoms on both sides of the contact surface." No substance separates them, so these metal atoms "can't know" that they actually belong to two separate pieces of metal.

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In the atmospheric environment, due to the presence of air and the presence of oxides on the metal surface, two pieces of metal will not stick together even after contacting each other.

First of all, there is no absolute vacuum, including the high orbit around the space station, so no one has ever done or witnessed this so-called welding in a vacuum. An important task of the space station is space experiments including metallurgy, breeding, biological hybridization, etc. Some special alloys are processed using suitable processes found on the space station. The mechanism of this phenomenon you mentioned is still just speculation. The point is not vacuum, but low pressure and low temperature. When exposed to the background temperature of the universe, many properties of metals change. Do you remember that freezing metal with liquid nitrogen makes it brittle? The universe is such a low temperature, and if the pressure is low, I really can’t imagine what kind of metal would be like this. Will the air-tight openings of the docking door of the space station be welded together and inseparable?

In space, if two similar metals come into contact with each other, they will easily stick together. The reason for this phenomenon is that cold welding occurs between the metals. The various welding we usually see basically uses high temperature to melt metal, and the solidified metal is integrated and then welded, such as electric welding, gas welding, friction welding, etc. Cold welding can be performed at room temperature, which reflects the meaning of the word "cold". How does the cold welding phenomenon occur?

The environment in space is different from that on earth. In space, objects are not affected by gravity, and there is no air around them. The factor that affects the occurrence of cold welding is air. . Space is basically a vacuum environment. When two objects come into contact with each other, since there is no gas barrier between them, the metal atoms can be said to be really in contact.

On Earth, if we press two pieces of metal together, there will actually be a very thin gas layer between the metals to separate them, because the object itself has a strong impact on the gas molecules. There is adsorption, and it is difficult for us to completely get rid of them, so cold welding will not occur under normal circumstances on the earth, unless we give a lot of pressure to the two metal plates to completely squeeze out the gas in the middle. At this time They are likely to stick together.

So how are two metal plates that are in complete contact with each other welded together? This is mainly due to the diffusion of metal atoms. When talking about diffusion, we will quickly think of gases and liquids, because these two types of substances are fluids, and we can easily see the diffusion of substances in this state in life. In fact, diffusion also occurs in solids, but it is not as obvious compared to gas and liquid states, so it is not easy for us to observe.

In a vacuum, atoms between two metals that are in complete contact will diffuse and fuse with each other, thus continuously generating new metallic bonds, causing the two pieces of metal to be "welded" together. Some scientists have specifically studied the phenomenon of cold welding, using gold nanowires to come into contact in a vacuum state, and found that it only takes about two minutes for the two nanowires to start to adhere.

Since the diffusion rate is related to pressure, the greater the pressure, the faster the diffusion rate of atoms, and the more obvious the effect of cold welding will be. At the same time, the smaller the size of the object, the faster the cold welding phenomenon occurs.

In addition, metals in space are not prone to oxide layers. Without the barrier of the oxide layer, atoms will more easily diffuse and cause cold welding. NASA's Galileo probe encountered cold welding problems

In 1989, the United States launched a Galileo probe to detect Jupiter. Since it was a long way to reach Jupiter, it designed a The larger signal receiver, and to protect the receiver from damage from solar radiation, is planned to be deployed in a year and a half. But then a problem arose. Ground scientists sent commands to Galileo to deploy the signal receiver, but found that it could not be deployed. After layers of investigations, they finally found that several antenna brackets were bonded due to cold welding, so the antenna could not be deployed. Fortunately, there is a very small secondary antenna on the detector. Although the bandwidth of the secondary antenna is only a few hundredths of that of the main antenna, a large number of scientific research tasks were successfully completed by relying on it.

A small cold welding phenomenon almost wiped out the billions of dollars that the United States invested in Galileo.

During the flight of the detector, the vibration of the instrument will also promote the occurrence of cold welding. The vibration process causes friction and impact between different metals, providing the energy barrier required for diffusion. It promotes the diffusion of atoms, so when current equipment enters space, it is necessary to fully consider the issue of cold welding to prevent unnecessary trouble.

I have answered similar questions in detail before, so I will briefly say a few words here.

First of all, if two pieces of metal are just in contact in space, they will not be "welded together".

There is no oxygen in space, which will not produce an oxide film on the metal surface. Some people think that cold welding must occur. In fact, this is not the case. The oxide film is not the only obstacle to metal bonding.

Metals are crystals (don’t be surprised). The atoms are linked together according to a crystal lattice to form a whole. This crystal lattice is repellent to the addition of other atoms.

In order for the lattice to accept new atoms, it needs to be given additional energy. Such as applying pressure, heating, electricity or friction.

Therefore, the occurrence of cold welding requires external conditions, and it cannot be accomplished by being close together. The mere drift of free electrons does not cause atoms to hold hands.

A cold welding accident occurred in the Galileo detector launched by the United States before. The surface of its main antenna was plated with gold. During the launch process, the gold vibrated and rubbed against each other, causing cold welding. The antenna was launched into the Unable to deploy behind the orbit, ground operators tried many methods but failed. In the end, they had to use a small antenna to replace the main antenna, which greatly reduced the transmission efficiency. Note that gold is the most susceptible metal to cold welding and it also requires friction to stick together.

There is no oxide layer on the surface of gold. Have you ever heard that the gold bars in the vault are stuck together and cannot be separated? No!

In space, two smooth and flat pieces of iron that have not been oxidized will soon become one piece of iron when put together. This phenomenon is called "cold welding", which means it can be welded without heating. The reason for welding together is also very simple. When two iron blocks are close to each other, the iron atoms of the two pieces attract each other. Since the distance between the atoms of the two pieces is close enough, the iron atoms on the contact surface can Grasping each other, the two pieces of iron eventually become a whole.

However, this phenomenon only occurs in metal objects, because there are a large number of free electrons in metals, and metals have no fixed microstructure. All metals are like a bunch of atomic nuclei swimming inside. In the ocean of electrons, although most metals are solid, in fact they are actually just stagnant liquids, and metal atoms are also in motion. As long as high temperatures are applied to them, the metal can easily become liquid. Many metals will change shape under high pressure, but their essence will not change. For example, an iron block under a hydraulic press is often changed in shape like mud, but no matter how it is changed, it is still iron, which shows the ductility of metal. Mostly good too.

When two pieces of iron come into contact in space, the iron atoms on the contact surface will first contact at the level of free electrons, and the exchange of free electrons makes the two become one body. The free electrons of the atoms will not distinguish whether the iron nuclei they are in contact with belong to two pieces of iron. This is because the internal structure of the metal is chaotic and does not reflect a certain crystal pattern, so the metal atoms will not always stay in a fixed position. Moreover, the physical and chemical properties of the same metal elements are the same, the electrons and atomic nuclei are also the same, and the movement patterns are the same, which makes them easily integrated when in contact. If it is a non-metallic substance with a crystal structure, this cold welding phenomenon will not occur.

Gibbs free energy G= H-T S, theoretically the reaction is possible as long as G is not greater than 0.

In a vacuum environment, when two pieces of metal become one, it should be from disorder to order. S is less than zero, but the vacuum is close to absolute zero, so T is close to 0. Then it only depends on H. This is related to the system composed of vacuum and metal. At present, It seems it can still be achieved. So cold welding is actually feasible.

In other words, under the action of pressure and temperature, atoms undergo diffusion motion, and the binding force between particles becomes smaller. In turn, in the space environment, when the pressure and temperature are low, the binding force on the particles becomes smaller. will be enhanced. When the smooth surfaces of the same metal are in contact, the distance between the particles can be very close enough for the inter-particle force to take effect, and they will naturally be bound together, which macroscopically manifests as the so-called cold welding