This is the parametric wall of South Korea's "Modern Exhibition Hall". It is so dark that even the three-dimensional structure has disappeared. Even if you turn on the light on the wall, it is difficult to see the existence of the wall. Instead, it looks like a dotted network of dots. The universe gives people the feeling of walking in space.
We know that except for black holes, any material on the earth will reflect light, but the intensity is different. But as long as there is light, we can basically see it with the naked eye. Could this wall be as capable as a black hole? Devour the light?
A black hole is a celestial body with very strong gravity in the universe. It can swallow up all matter including light. Since it neither emits light nor reflects light, the black hole is surrounded by darkness. That's why it's called a black hole.
A black hole is the final stage of stellar evolution. The conditions for its formation are very harsh. Even the sun cannot evolve into a black hole because its mass is too small. At the end of its life, it will first turn into a red giant, and the red giant will swallow it. Most of the planets, including the Earth, will fall away, and then begin to collapse inwards under the influence of gravity. Due to the small mass and small gravity, they can only shrink into white dwarfs.
The life of the sun is at least a few billion years away. Maybe humans at that time have long since perished, or maybe technology is advanced enough to allow the earth to escape the solar system, so there is no need to worry about the end of the world.
Although black holes cannot exist on the earth, scientists can develop new materials whose light-absorbing effects can be infinitely close to those of black holes. The black walls of South Korea’s modern exhibition hall are also coated with a light-absorbing material made of Developed by Nanosystems Company in Surrey, UK
The English abbreviation is Vantablack, which means vertically arranged carbon nanotube array.
When Vanta Black was first introduced, it was known as the blackest substance on earth and the closest thing to a black hole in the universe. If it is used to make a piece of clothing, the person wearing this piece of clothing may Being treated like a monster. Because only the head and limbs can be seen, the body is a dark void, and even the outline of the body cannot be seen.
Wearing black clothes in the summer will obviously make you feel hotter when standing in the sun, while wearing white clothes will make you much cooler. This is because the darker the object, the stronger its ability to absorb light.
Light is actually a high-speed moving photon. Their speed reaches 300,000 kilometers per second. Once it shines on an object, it will inevitably collide with and reflect particles. Only some of the photons will be converted into heat and absorbed. Unless the light is relatively dark, black objects are not easy to detect.
Vanta Black also reflects light, but its surface uses a carbon nanotube structure. The diameter of these carbon nanotubes is only one ten thousandth of that of a hair. If you put it under a microscope and observe it , you will find countless vertical black tubes on its surface. These small carbon tubes can change the reflection path of light.
When light enters these tubes, the carbon nanotubes will first absorb most of the light. After countless refractions, the remaining light will gradually be converted into heat absorption by the carbon nanotubes, and only very little light can be absorbed. Reflected out.
The principle seems quite simple. To give a simple example, if you quickly pour a basin of water on the cement floor, it will definitely splash. If you replace the cement floor with grass, it will only splash. Tiny water droplets. Moreover, carbon nanotubes also have ultra-high thermal conductivity, absorbing light like a sponge absorbing water.
Therefore, Vanta Black can only reflect 0.35 of light, reaching the point where it cannot be observed by the naked eye. In 2014, it entered the Guinness Record for the darkest color in the world. However, this record was canceled in 2019. MIT team breaks down.
Professor Brian Wald of the team promoted that they have created a material that is 10 times darker than Vanta Black. This material is also made of carbon nanotubes, but the diameter of the carbon nanotubes is It is only one 50,000th the size of a human hair, so it can only reflect 0.005 of the light, making it the blackest material in history.
Professor Brian did not think of using carbon nanotubes to make extremely black materials at the beginning. In addition to excellent thermal conductivity, carbon nanotubes also have good mechanical properties. Their density is only 1/6 of steel. However, The tensile strength is 100 times that of steel, and its hardness is equivalent to diamond.
If other engineering materials and carbon nanotubes are made into composite materials, they can show good strength, elasticity, and fatigue resistance, which will greatly improve the performance of composite materials.
Russian scientists once placed carbon nanotube composite materials under water pressure of 1011Mpa, which is equivalent to the pressure of 10,000 meters in the deep sea. The composite carbon nanotubes were crushed by the huge pressure and recovered instantly after the pressure was removed. In its original state, this good toughness is an excellent material for making springs.
In addition, the electrical conductivity of carbon nanotubes is 10,000 times that of copper. Professor Brian originally planned to grow carbon nanotubes on the surface of aluminum to improve its electrical conductivity and thermal properties. An oxide film will form in it, which is very corrosion-resistant.
Moreover, oxides generally have an insulating effect and will reduce the electrical and thermal conductivity of aluminum, so chlorine ions must be used to erode the surface of aluminum. This etching technology is very common in metal processes.
Due to the small radius and strong penetrating ability of chlorine ions, it is most likely to penetrate the very small pores in the oxide film, reach the surface of the aluminum metal and form soluble compounds with it, causing the structure of the oxide film to change. It is slowly etched away, and finally the etched aluminum is heated in a microwave oven, and then carbon nanotubes are grown through chemical vapor deposition.
This method is also called hydrocarbon gas pyrolysis. Gaseous hydrocarbons will decompose at a high temperature of 1,000 degrees to form carbon nanotubes, which are then attached to the aluminum foil under the action of catalyst particles.
Professor Brian finally found that the combination of carbon nanotubes and aluminum foil achieved the expected experimental purpose, and the thermal and electrical conductivity of the composite material was significantly improved. But the most surprising thing was that the material was so dark that it was unbelievable, so another optical reflectivity test was conducted.
Test results show that this material can absorb 99.995% of incident light from all angles, which is second only to black holes in the universe. Regardless of whether its surface is uneven or has other morphological features, it cannot be seen by the naked eye. It is just a void of darkness.
Professor Bryan and his team have applied for a patent for this technology, but they plan to let artists use it for free for non-commercial art creation. There was a rich man who coated a diamond worth 2 million US dollars with aluminum carbon nanotube material, so that the originally shiny diamond took on a completely opposite state, becoming so black that it disappeared. It was named "Vanity Salvation" ”, on display at the New York Stock Exchange.
BMW also used Vanta Black as a paint, and specially designed an X6 SUV car for display. This car can be used at night or during the day, no matter how strong the light you shine on it. , it also looks almost as black. If it weren't for the fact that the windows, lights and other components still have some sheen, you would even think that this car was painted on the wall, because you can't see the edges and lines on its surface at all.
This is because the designer was merciful and reserved a light reflectivity of 1, so that the outline of the car can barely be seen, lest it look similar to a piece of paper, which is just right for this. The trolley looks luxurious and connotative in appearance, full of mystery and nobility.
However, this car cannot be driven on the road because due to technical limitations, Vanta Black is easy to peel off as a paint. If the paint peels off, there is no way to repaint it. And some netizens joked that it is estimated that The paint is more expensive than the car, so you can only buy it for viewing.
So besides bringing the ultimate visual effect, what practical uses does this ultra-black material have?
Nobel Prize-winning astrophysicist John Mather said that this ultra-black material can improve the sensitivity of optical instruments and can eliminate interference light from space telescope lenses.
For example, the infrared space telescope being developed in the United States has its main mission to conduct wide-field imaging and surveys of the infrared sky and solve basic problems in the fields of dark energy and infrared astrophysics.
But this type of space optical instrument must get rid of unnecessary glare, so a "star-shading umbrella" must be designed to block the stray light in space, and it must also withstand the high temperature generated by rocket launches. Aluminum foil carbon nanotubes With super light absorption and high temperature resistance, it is undoubtedly the best basic material for manufacturing star-shading umbrellas.
Since aluminum foil carbon nanotubes cannot reflect light, they can hide the contours of undulating objects and are an ideal camouflage coating material, so they have a lot of application space in the field of military weapons. Japan will launch a black pigment with a light absorption rate of 99.4 in 2020, which can easily make objects flat, elevated, frosted, and even invisible.
Secondly, it also has excellent electrical and thermal conductivity properties, as well as efficient photon absorption, so aluminum foil carbon nanotubes can be used in heat dissipation systems, power transmission, and photovoltaic new energy fields.
However, whether it is Vanta Black or aluminum foil carbon nanotubes, due to the difficulty of preparation, it is currently impossible to leave the laboratory, let alone large-scale mass production and use.
Finally, to sum up, carbon nanotube extreme black materials currently have problems of difficulty in preparation and high production costs, and cannot be quickly promoted and applied to related industries. But it does have broad application prospects and deserves further research by scientists.
Just like when the steam engine was first invented, it was expensive and the benefits it produced were not as good as manual labor. However, after Watt improved the steam engine, human society quickly entered industrial civilization.
Maybe one day, when technology becomes more advanced, humans can also use "black" to change the world.