Galaxy Technology Empire

Huang Junjie flipped through the information on ion generation and photon generation one by one. Many of these materials are theoretical papers. Of course, there are still many practical applications of ion generation.

Milijia, Sun Nation, and the Western Continent Alliance all have ion-generated satellites or detectors. Especially for deep space detectors, plutonium isotope batteries can only fly for decades if they are combined with ion generators.

Otherwise, those detectors that have been flying for decades would not be able to use chemical fuel engines.

After looking at it for a long time, there are still very few useful ones that solve the heat problem of nuclear fusion miniaturization.

However, ion hair and photon hair still have great potential. Huang Haojie asked Zhong:

"I remember if we had an ion engine research institute?"

[Yes, the Ion Engine Research Institute is in Keelung City. The director is Zhou Botong and the chief engineer is Mishima Ji. ]

"Zhou Botong?" Huang Junjie raised his head curiously.

［╭(′ o ′)╭ is a scholar who is knowledgeable and talented. ]

"Uh..." Huang Haojie suddenly felt awkward and quickly changed the topic:

"Send the small reactors No. 5, 6, and 7 in my laboratory to the Ion Engine Research Institute and let them study the ion engine for nuclear fusion. By the way, they will also be given the task of the photon engine."

[OK. ]

After Huang Haojie ordered this matter, he focused his attention on thermoelectric power generation, which is a simple and direct power generation technology.

There is no need for complicated equipment, just a special material called "thermoelectric material", which imposes a temperature difference on both ends - for example, one end is 27 degrees Celsius cold water, the other end is 100 degrees Celsius boiling water, this is a temperature difference of 73 degrees Celsius , this material can be made to emit a certain amount of electrical energy.

Since this power generation technology has so many advantages and huge potential, why are there so few applications of it?

Because thermoelectric power generation has a fatal flaw—the efficiency is too low.

The thermal efficiency of the best existing thermoelectric power generation materials is less than half that of conventional thermal power plants, and even lower than that of geothermal power generation (geothermal power generation efficiency is about 6 to 18%). With such low thermal efficiency, those capitalists are not stupid. Damn, how could you do such a loss-making business?

However, when Huang Haojie read a paper published in Nature, he found that this paper gave him a lot of inspiration.

This paper was published by a research team led by Professor Ernst Bauer from the Western Continental Alliance - Technical University of Vienna, Austria.

The data in the paper shows that they have achieved a doubling of the thermoelectric figure of merit (ZT value), a key performance indicator of thermoelectric power generation materials.

The thermoelectric materials they developed have a thermoelectric figure of merit as high as 5 to 6, while the best previous materials generally only had about 2.5 to 2.8.

Huang Haojie immediately focused his attention and asked Zhong to collect the team's information on thermoelectric materials. After a while, a lot of information appeared in his holographic computer.

If thermoelectric power generation wants to improve thermoelectric efficiency, it is necessary to increase the ZT value of the thermoelectric material. Only when the ZT value reaches or exceeds 4 can this technology have commercial value. However, more than 100 years have passed since the discovery of the thermoelectric effect, and it is still difficult for scientists to achieve even 3.

Why is it so difficult to increase the ZT value of thermoelectric materials? This starts with the physical principle on which thermoelectric power generation technology relies - the thermoelectric effect itself.

There are a certain number of carriers (such as electrons or holes) inside metals or semiconductors, and the density of these carriers changes with temperature. If one end of the object has a high temperature and the other end has a low temperature, Different carrier densities will appear in the same object.

As long as the temperature difference between the two ends of the object can be maintained, carriers can continue to diffuse, thus forming a stable voltage. This is the principle of thermoelectric power generation.

The efficiency of thermoelectric power generation depends on three important characteristics of thermoelectric materials:

First, the Seebeck coefficient (the ability of a material to generate electromotive force when there is a temperature difference). The higher the Seebeck coefficient, the higher the electromotive force generated under the same temperature difference, which means more electricity can be emitted.

Second, conductivity (the conductivity of the material). The higher the conductivity, the easier it is for electrons to diffuse inside the material.

Third, thermal conductivity (thermal conductivity of the material). The higher the thermal conductivity, the faster the heat can be transferred from the hot end to the cold end, so that the temperature difference that thermoelectric power generation relies on disappears, and the electromotive force disappears. .

Obviously, for thermoelectric materials, the stronger the first two abilities, the better, while the weaker the latter ability, the better.

The thermoelectric figure of merit ZT is the set of these three parameters: the higher the Seebeck coefficient, the higher the electrical conductivity, and the lower the thermal conductivity, the higher the ZT value and the higher the efficiency of the material in thermoelectric power generation.

Therefore, the key to the research on thermoelectric materials is how to improve the ZT value of the material, that is, to obtain low thermal conductivity while achieving high Seebeck coefficient and electrical conductivity.

However, it is very difficult to optimize these three parameters at the same time. Because these three properties are interrelated, improving one property is often accompanied by a weakening of the indicators of another, or even two properties.

Generally speaking, increasing the Seebeck coefficient of a material will decrease its conductivity. This interrelated nature of the three parameters has made the development of thermoelectric materials progress slowly.

However, the relationship between the three parameters of "all losses and prosperity" among the three parameters is not completely absolute.

This "community of interests" also has a "traitor" - thermal conductivity, or more precisely, a part of thermal conductivity. The thermal conductivity of a material includes two parts, namely electronic thermal conductivity and phonon thermal conductivity.

Among them, the former is closely related to electrical conductivity and is a member of the "community of interests"; but phonon thermal conductivity is the only one among the various parameters that determine the properties of thermoelectric materials that has no impact on all other parameters in the ZT value. parameters.

The research idea of ​​this University of Vienna team is to reduce the overall thermal conductivity by reducing the phonon thermal conductivity without affecting the electronic thermal conductivity of the material.

Specific to the microscopic level of the material, it is to enhance the scattering of phonons through some special structures without affecting the electron transport, thereby only reducing the phonon thermal conductivity of the material without changing other parameters.

After years of research starting in 2013, they discovered a material that can achieve both high electronic thermal conductivity and low phonon thermal conductivity.

Using a layer of alloy material composed of iron, vanadium, tungsten and aluminum elements covering the silicon crystal, a ZT value as high as 5 to 6 is achieved, doubling the ZT value compared to the current best level.

Under normal circumstances, the structure of this alloy composed of four elements: iron, vanadium, aluminum, and tungsten is very regular. For example, there must be only iron atoms next to vanadium atoms, and the same is true for aluminum atoms, while two adjacent ones of the same element The distance between atoms is also always the same.

However, when scientists combined a thin layer of this material with a silicon substrate, something magical happened.

Although the atoms still maintain their original cubic structure, the mutual positions of the atoms have drastically changed.

Where a vanadium atom should have appeared before, it may now be an iron atom or an aluminum atom; and next to an aluminum atom, there should be an iron atom, but now it may still be an aluminum atom, or even a vanadium atom.

Moreover, this change in position between atoms is completely random and has no rules.

This combination of ordered and disordered crystal structure gives the material unique properties:

Electrons can still have their own special path and "freely" shuttle in the crystal, so that the electrical conductivity and electronic thermal conductivity are not affected; however, the phonon migration that relies on heat conduction is blocked by the irregular structure, resulting in phonon thermal conductivity. rate dropped significantly.

In this way, the temperature difference between the hot and cold ends is maintained, and the resulting potential difference does not disappear.

The University of Vienna team has also achieved the coveted goal of keeping the electronic thermal conductivity of thermoelectric materials unchanged and reducing the phonon thermal conductivity, thus significantly increasing the ZT value to 6.

In their theory, if the topological structure of related conceptual materials can be changed, a ZT value of 20 will no longer be just a dream.

When the ZT value reaches 6, the thermal efficiency will reach about 12%. If the ZT value can be increased to 20, the thermal efficiency can be comparable to that of a steam turbine.

Compared with steam turbines, the structure of thermoelectric power generation equipment is extremely simple. For example, the plutonium isotope battery mentioned above is a thermoelectric power generation battery.

However, in terms of materials science, Huang Haojie was not as good as the orthodox Li Xiang and others. He quickly sent a research project to the Materials Research Institute, asking the Materials Research Institute to develop a thermoelectric material with a ZT value of about 20.

This is an extra update today! The ominous chapter number was skipped.