Some Properties of Tungsten Technetium Alloys for Use in Putative Fusion Reactors. [View all]
It is obviously true that the development of fusion energy did not come in time to address extreme global heating, since extreme global heating is here now, and fusion powerplants, um, aren't.
Oh well, then. I don't have anything against the concept of fusion power, except that it's not here; it has a Sisyphean element to it. If it works some day, well great, but it isn't working now, and the collapse of the planetary atmosphere is taking place now.
Over the Thanksgiving break I had a chat with my son about a fission reactor design that popped into my head which would feature grids of the synthetic element technetium, a fission product available from used nuclear fuels that does not occur on Earth other than as a trace element found from spontaneous fission in uranium ores. (The concentrations are too small for recovery from these ores.) An issue in the design I discussed with my son would concern the mechanical strength of technetium metal, specifically the shear modulus.
I looked up the shear modulus of technetium metal, which is rather high, stronger than steel, and in the process, I came across this paper, concerning tungsten-technetium alloys for potential use in fusion reactors, should workable models ever be built: Li Xue, Xunjie Wang, Fei Xue, Xilin Zhou, Fangfang Guo, Diyou Jiang, Structural, mechanical, electronic properties and Debye temperature of tungsten-technetium alloy: A first-principles study, Fusion Engineering and Design, Volume 168, 2021, 112433,
The introduction begins with "As we all know..."
As we all know, pure tungsten (W) is considered to be the most promising plasma facing materials for magnetic confinement fusion devices. This is due to the attractive engineering properties, such as high melting point (about 3410 °C), high temperature high strength, low sputtering yield, excellent thermal conductivity, and low thermal expansion coefficient [[1], [2], [3]]. In addition, pure tungsten as a shielding component or divertor plate is also used in fusion power reactor and other systems related to nuclear fusion reactor [4]. However, pure tungsten is known as a poor radiation stability, low elongation and low reduction of area, fracture toughness and low-temperature brittleness, with high yield strength, low ductility, with high ductile-brittle transition temperature (DBTT). Therefore, it is necessary to improve the ductility and brittleness of pure tungsten as plasma facing materials.
The engineering properties of pure tungsten can be improved by alloying. For example, alloying with other elements can improve the thermodynamic properties of pure tungsten [[5], [6], [7]]. At the same time, the ductility of pure tungsten can be improved by adding rhenium (Re), technetium (Tc), molybdenum (Mo), titanium (Ti), hafnium (Hf), vanadium (V), zirconium (Zr) and tantalum (Ta) to tungsten [[8], [9], [10], [11], [12], [13], [14]]. In particular, rhenium reduces the ductile-brittle transition temperature and improves the ductility of W-Re alloy significantly [8]. Technetium belongs to group VIIB together with rhenium and manganese. The electrochemical properties of technetium are between rhenium and manganese, which is closer to Rhenium. So far, however, there are few reports on the influence of technetium concentration on the mechanical properties of pure tungsten, especially theoretical reports. On the other hand, due to the high cost and time-consuming design of traditional experimental alloys, first-principles methods can be used to study alloy structure-performance relationships and design materials. Computer simulation can study the properties of specific alloys and greatly reduce the amount of preparation and characterization of parts, such as multi-scale calculation methods, diffusion mechanisms, lattice dynamics, crystal structure, electronics, mechanical, thermodynamics and surface properties of materials [[15], [16], [17], [18], [19]].
In the present study, we investigated the structural stability, electronic structures, mechanical properties and Debye temperature of W-Tc alloy in detail by first principles method according to density functional theory. Therefore, we calculated some related parameters, such as the formation energy (Ef), phonon dispersion curve, lattice constant and cell volume (V), melting point and hardness, elastic constant, etc. The ductile/brittle properties of W-Tc alloy are determined based on the B/G ratio and Poisson’s ratio (v) . Besides, the Cauchy pressure (C' ) and anisotropy of W-Tc alloy are also evaluated. These results provide an effective help for the optimization of W-Tc alloy and a useful database for the application of PFMs...
As we all know...
The shear modulus of pure technetium is 132 GPa, compared to a shear modulus of steel of around 79 GPa. Pure technetium is stronger than steel.
A table of data from the paper, concerning tungsten-technetium alloys, where the technetium is substituted for more expensive (and rarer) rhenium:
Nobody has built a fusion reactor that can provide exergy. It is already too late for one to prevent extreme global heating, since we are now experiencing it.
If someday, someone does design one capable of exergy recovery, and it has a tungsten/technetium alloy, the neutrons resulting from fusion (which are much higher energy, by an order of magnitude than fission neutrons) will slowly transmute technetium into valuable ruthenium and even more valuable rhodium, over a longer period, should fusion reactors have a reasonably long lifetime, something that is not entirely clear. Tungsten will, in turn, be transmuted into rhenium, osmium, and iridium, also extremely valuable elements.
Other material properties are also given:
Some conclusions from the paper:
Based on the first principles method, the crystal structure, mechanical properties, electronic properties and Debye temperature of tungsten-technetium alloy are investigated. The main conclusions are summarized as follows:
1)
The tungsten-technetium alloy still maintains the cubic lattices. The lattice constant of tungsten-technetium alloy decreases with the increase of technetium concentration.
2)
In tungsten-technetium alloys, W15Tc1, W14Tc2, and W12Tc4 alloys all have strong bond interactions, while W8Tc8 alloy bond interactions is the weakest.
3)
When the concentration of technetium is below 25 %, the doping of technetium element has little effect on the mechanical strength, melting point and hardness, and Debye temperature of tungsten-technetium alloy. However, when the technetium concentration reaches 50 %, these properties are significantly reduced.
4)
Doping concentration of less than 25 % technetium can improves the anisotropy of pure tungsten. However, Doping technetium can always improves the ductility of pure tungsten.
Have a nice day tomorrow.
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