Abstract:
Stable isotopes are currently widely used in medical, biological, agricultural, environmental, industrial manufacturing, scientific research and other fields. There are three isotopes of silicon in nature, namely
28Si,
29Si, and
30Si, with natural abundances of 92.22%, 4.69%, and 3.09%, respectively.
28Si isotopes are mainly used in the semiconductor field and also have certain applications in quantum computing and metrology. Silicon crystals made from pure
28Si isotope with an abundance of over 99% have a perfect lattice structure, which can reduce phonon scattering, improve thermal conductivity, lower gate voltage, increase switching speed, and increase chip frequency.
28Si can be used to manufacture high-speed CPUs, high-power devices, high-performance sensors, and more. Different experimental studies have shown that using
28Si materials with an abundance of over 99.85% to prepare semiconductor components can increase their thermal conductivity by 10%-60% compared to Si materials of natural abundance at room temperature. High abundance
28Si is a key material for preparing long spin coherent time devices in the field of quantum information, which can remove interference from
29Si. Silicon quantum bit is a promising quantum computing platform with advantages such as long coherence time, small device size, and compatibility with industrial manufacturing technology. In addition,
28Si isotope can also be applied in metrology to define the exact values of the Avogadro constant and kilogram units. With SiH
4 as the medium, the separation of
28Si isotope was studied by gas diffusion method in this paper. At present, research on the separation of silicon isotopes using cryogenic distillation methods (SiH
4, SiCl
4, or SiH
3CH
3 systems), gas centrifugation methods (SiF
4 or SiHCl
3), chemical exchange methods (systems of SiF
4 and different complexing agents), laser methods (Si
2F
6, SiF
4), and electromagnetic methods (SiH
4) has achieved certain results both domestically and internationally. However, industrial production of silicon isotopes has not yet achieved breakthroughs. The cryogenic distillation method for silicon isotopes has a smaller separation coefficient, while the gas centrifugation method has a lower efficiency in separating light gases. The laser separation method has a low yield and high cost, and its economic viability for industrial production is poor. Nowadays, low-cost and high-quality polymer organic membranes have been widely applied in industry. A high-speed maglev compressor used under negative pressure conditions can effectively compress SiH
4 gas. Compared to other potential separation media, SiH
4 has a relatively small molecular weight and a relatively large gas diffusion separation coefficient. The overall separation factor of SiH
4 can reach 1.010 measured through a 4-stage diffusion cascade experiment. Using multicomponent separation theory for cascade analysis and calculation, with natural SiH
4 as raw material, the
28Si isotope abundance in light fractions can be concentrated to over 99% through a matched abundance ratio cascade (MARC) of no more than 300 stages. This study verifies the feasibility of diffusion separation of
28Si isotope with SiH
4 as the medium.