I was shocked when I opened a door and was shocked by the metal handle... I took off a sweater at night and sparkled with lightning... Even when I petted a cat, it crackled with sound effects... It's the season when static electricity, an old friend, comes to visit. When talking about static electricity, we usually think of two things first - one is frictional electrification, and the other is that static electricity is really annoying.
However, static electricity is actually more than just frictional electrification, and in some situations, the harm caused by static electricity is far more than just annoying. However, if used properly, static electricity can serve human beings. Let’s talk about it in detail next.
Frictional electrification is not simple
The most common static electricity in life is frictional electrification, and it is also the one that usually tortures everyone the most. Everything from the crackle of a handshake to the rumble and crackle of lightning are all due to it.
Historically, this is also one of the earliest electrical phenomena noticed and recorded by humans: In Greek, ἤλεκτρον (pronounced electron) is a synonym for amber, and amber is prone to electricity and dust. It was recorded by the ancient Greek philosopher Thales in the 6th century BC.
Although triboelectricity has long been a household name, scientists have not fully understood this phenomenon...because its behavior is quite unstable and its causes are complex and diverse. For example, the general impression we get when we go to school is that whoever can grab electrons more will be negatively charged. If we only consider materials, there is supposed to be a final boss who will come out on top in the game of grabbing electrons.
But in reality, for some materials, the competition for electrons through triboelectrification is not a game where the strong take all. It's more like playing rock, paper, scissors: silk loses to paper, paper loses to cotton, cotton loses to glass, glass loses to zinc, and zinc loses to silk at the beginning!
It can be seen that material properties are not necessarily the only factor. After research, it is currently recognized that some influencing factors include: the properties of the material itself, surface structure and direction, local roughness, friction intensity, environmental humidity, etc.
Static electricity is not just caused by wiping it out
Friction can generate static electricity, but it does not rely solely on friction. Another type of static electricity is piezoelectricity, represented by quartz and tourmaline (also called tourmaline).
What is the principle of piezoelectricity? To use an imprecise analogy, it's like a bus. When there are not many passengers, people are standing facing any direction. As the bus becomes more and more crowded, people will involuntarily move in one direction. When viewed from one side, the piezoelectric material appears to be a front face, and from the other side, it appears to be a back. This phenomenon is called polarization, and a positive charge appears at one end of the piezoelectric material, while a negative charge appears at the other end. Because heating will also cause stress in the crystal lattice, some piezoelectric materials also have a pyroelectric effect.
There is another type of static electricity that is more likely to appear in space. When the high-energy ultraviolet rays and X-rays in sunlight hit an object, they drive electrons out, leaving a layer of positive charge in their place. For example, on the surface of the moon, dry and finely divided lunar soil particles all carry positive charges and repel each other. They rise from the ground and float several meters high, forming a layer of lunar dust "atmosphere" (not a gas). Once lunar dust encounters foreign objects, it is easy to adsorb.
Readers who have removed foam plastic packaging must have a deep understanding of this. Electrostatically suspended moon dust greatly interferes with lunar exploration equipment. Our first Yutu had a power problem just over a month after it went up (the second day on the moon). It was probably caused by the failure of moon dust entering the interior. The same principle applies to the dust raised by the Apollo lunar rover that persists for a long time, and is not the effect of a ground studio.
Yutu lunar rover from Wikipedia
How harmful is static electricity?
Most static electricity is harmful and annoying. Although there are various causes of static electricity, the main theme is still the word "static". If charge is generated but does not flow, it may accumulate and cause disaster.
In the winter in the north, the house is heated and the environment is dry. If a humidifier is not used (although using it may not help), the static electricity generated when walking around or changing clothes is difficult to dissipate and accumulates on the body surface, waiting for an opportunity to vent. The voltage of small sparks like those that usually make our fingers numb can reach tens of thousands of volts. This number sounds scary, but the physical formula behind it is this:
Charge = Capacitance x Voltage
It can be seen that capacitance and voltage are inversely proportional, the smaller one is, the larger the other is. When we shake hands, there is a very small capacitance between our hands, so only a small amount of charge can generate a high voltage that breaks down the air, forming that small arc that makes us tremble. But don’t be afraid. It is the current, not the voltage, that is really lethal. The charge of static electricity in daily life is very small, so the current is also very weak and will not cause death or disability.
But everyone should be careful. If this small arc that can penetrate the air is placed in a dangerous situation, it may cause catastrophe. For example, if a tanker truck is not fully filled, the oil sloshing in the tank may cause friction and electrification, causing an explosion. Early oil tank trucks were equipped with an iron chain hanging from the rear of the truck to the ground, in order to send static electricity to the earth in a timely manner.
Nowadays, anti-static measures are more and more reliable: the iron chain is replaced with conductive rubber to ensure that it is pressed against the ground at all times without intermittent or sparks. The tire material also uses conductive rubber. An oil barrier is placed in the oil tank to reduce the impact and bump of the oil.
As for gas stations, there are many measures to prevent static electricity from loading and unloading oil to refueling for car owners, such as discharging before refueling, etc. There are also industries with serious dust such as flour mills. In addition to open flames, they are also strictly guarded against static electricity, because static electricity may cause terrible dust explosions and affect the normal production of flour.
Friends who like to install their own computers know very well that if they touch the computer motherboard or memory chip with bare hands, the machine may become "bricked". The reason is the same as the above formula. The high voltage generated by static electricity breaks down the chip. Therefore, electronic equipment sent by manufacturers is usually wrapped in bags that can slow down or conduct static electricity.
When we dismantle and assemble these equipment, we must first touch the wall or hold the metal casing of the large machine with the other hand. Masters who specialize in circuit maintenance always have a piece of grounded conductive rubber on their desks and conductive "handcuffs" on their wrists.
The author's real shot of anti-static packaging outside electronic equipment
In the semiconductor industry, the upstream of electronic equipment production, static electricity is a serious enemy. Wearing ultra-clean clothes in the factory not only covers the whole body to prevent skin flakes from falling off, but also has conductive filaments woven into the clothes, and the soles of the shoes are mixed with carbon conductive rubber. Wear anti-static slippers even when walking in the "grey area" outside the workshop.
The author has been wearing these slippers for several years. They are soft and hard, and are durable. It is said that if you have a set at home, you can happily pet your cat. but! Wearing these slippers will greatly increase the risk of electric shock! (Leave it to the reader to think: Why?) Let’s weigh it up and put up with the crackling.
Friends who often fly may notice that there are many pointed thorns on the wings.
They are not communication antennas, nor can they increase power, but are used to release static electricity, known as electrostatic brushes. The high-speed friction between aircraft and air will inevitably generate static electricity, but there is no way to use mopping equipment like oil tankers, so these small spikes were installed based on the principle that static electricity will be released into the air in sharp-shaped parts.
The largest electrostatic discharge phenomenon that can be experienced in daily life is probably lightning, but this topic is too big, so I won’t go into details.
Make good use of static electricity
Although most static electricity is harmful and useless, if we can induce it to act according to our will, it can create value.
The most successful use case for static electricity is probably the copier. It first fills the semiconductor with static electricity, and then irradiates the area where the words should not be with light, turning the semiconductor here into a conductor, eliminating the static electricity here, leaving the unirradiated static area to absorb toner.
By introducing and constraining a large amount of charge at the position we designed to form a strong electric field, we can accelerate charged particles and study basic physics and many related disciplines. Compared with cyclotrons, this kind of electrostatic accelerator has low cost and small footprint, and is widely used in the world.
Electrostatic accelerator from Wikipedia
Quartz resonators can be made by allowing the static electricity generated by the piezoelectric effect to flow. This is the core component of quartz watches, which has brought great convenience to people's lives (but with the popularity of mobile phones, watches seem to be just clothing).
In the spraying industry, the principle of homogeneous mutual repulsion of static electricity can be used to evenly disperse mist droplets. And when they are close to the spray target, they can be attracted by electrostatic induction. This scene is actually very familiar. It is basically the principle of how moon dust destroys the lunar rover, but when used in the right place, it has another effect.
Therefore, it seems to be an unbreakable truth that a lot of understanding can turn enemies into friends!
Planning and production
This article is a work of Popular Science China-Starry Sky Project
Produced by Science Popularization Department of China Association for Science and Technology
Producer｜China Science and Technology Press Co., Ltd., Beijing Zhongke Galaxy Culture Media Co., Ltd.
Author丨Qu Jiong popular science author
Review丨Liu Qian, researcher at Beijing Planetarium
Planning|Ding'ao
Editor丨Ding Er