Huang Haojie flipped through the information on ions and photons one by one. Many of these materials are theoretical papers. Of course, there are still many practical applications of ions.
Milijia, Sun Country, and Western Continent Alliance all have ion satellites or detectors. Especially for deep space detectors, plutonium isotope batteries can only fly for decades if they are combined with ions.
Otherwise, those detectors that often fly for decades would not be able to use chemical fuel engines.
I have been looking at it for a long time, but there are still very few useful ones to solve the heat problem of nuclear fusion miniaturization.
However, ions and photons still have great potential. Huang Haojie asked Zhong:
"I remember if we had an ion motivation research institute?"
[Yes, the Ion Motive Research Institute is located 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 knowledgeable and talented doctor.]
"Uh..." Huang Junjie suddenly felt awkward and quickly changed the topic:
"Send the small reactors No. 5, 6, and 7 in my laboratory to the Ion Motive Research Institute and let them study the ion motive for nuclear fusion. By the way, they will also be given the task of photon motive."
[OK.]
After Huang Junjie ordered this matter, he focused his attention on thermoelectricity, which is a simple and direct electrical 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 used to produce a certain amount of electrical energy.
Since electrical technology has so many advantages and huge potential, why are there so few applications of it?
Because thermoelectric electricity has a fatal flaw - its efficiency is too low.
The thermal efficiency of the best existing thermoelectric materials is less than half that of conventional thermal power plants, and even lower than that of geothermal electricity (the efficiency of geothermal electricity is around 6-18%). With such low thermal efficiency, those capitalists are not stupid.
, how could you do such a loss-making business?
However, when Huang Haojie flipped through a paper listed in nature, he found that this paper gave him a lot of inspiration.
This paper was presented 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 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 thermoelectricity wants to improve the 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, the thermoelectric effect is now 1oo years later, and scientists are still 3
Difficult to achieve.
Why is the zT value of thermoelectric materials so difficult to increase? This starts with the physical principle on which thermoelectric 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 will change with changes in 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 thermoelectricity.
The efficiency of thermoelectricity 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 come out.
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 on which thermoelectricity depends is lost, and the electromotive force is also lost.
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Obviously, for thermoelectric materials, the stronger the first two abilities, the better, while the weaker the latter ability, the better.
The thermoelectric merit coefficient zT is the set of these three parameters: the higher the Seebeck coefficient, the higher the electrical conductivity, the lower the thermal conductivity, the higher the zT value, and the higher the efficiency of the material in thermoelectricity.
Therefore, the key to the research on thermoelectric materials is how to improve the zT value of the material, that is, while achieving high Seebeck coefficient and electrical conductivity, obtain low thermal 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 reduce its electrical conductivity. This interrelated nature of the three parameters has made the research on thermoelectric materials progress slowly.
However, the relationship between the three parameters of "all suffer losses and all prosper" is not completely absolute.
This "community of interests" also has a "traitor" - thermal conductivity, more precisely, it is a part of thermal conductivity. The thermal conductivity of a material includes two parts, namely electronic thermal conductivity and phonon thermal conductivity.
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Among them, the former is closely related to electrical conductivity and is a member of the "community of interests"; but phonon thermal conductivity, among the various parameters that determine the properties of thermoelectric materials, is the only one that has no effect 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.
Starting in 2013, after years of research, they discovered a material that can simultaneously achieve 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 of up to 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 always the same.
However, when scientists combined a thin layer of this material with a silicon substrate, something magical happened.
Although these atoms still maintain their original cubic structure, the mutual positions of the atoms have changed drastically.
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 end and the cold end is maintained, and the resulting potential difference will 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 2o 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 2o, the thermal efficiency can be comparable to that of a steam turbine.
Compared with steam turbines, the structure of thermoelectric equipment is extremely simple. For example, the plutonium isotope battery mentioned above is a thermoelectric battery.
However, in terms of materials science, Huang Haojie was not as good as the orthodox Li Xiang and others. He quickly submitted a research project to the Institute of Materials, asking the Institute of Materials to specialize in a thermoelectric material with a zT value of about 2o.