Elsevier

Current Applied Physics

Volume 31, November 2021, Pages 151-157
Current Applied Physics

Synthesis of titanium boride nanoparticles and fabrication of flexible material for radiation shielding

https://doi.org/10.1016/j.cap.2021.08.009Get rights and content

Highlights

  • The thermal flow inside of an RF plasma torch was numerically simulated.

  • The titanium boride nanoparticles were synthesized at 42 nm with mean diameter.

  • The half-value layer of titanium boride hydrogel was 2.91 cm for 0.662 MeV γ-ray.

Abstract

A numerical simulation for a radio frequency (RF) thermal plasma torch was carried out to identify the temperature and velocity distributions and determine the optimal design of a plasma system based on the coil turn and torch inner diameter parameters. Then, the optimized conditions of five coil turns and a torch inner diameter of 64 mm were applied to synthesize titanium boride nanoparticles. The major crystal structure of the synthesized titanium boride nanoparticles was TiB2, with TiB as a minor phase and an average particle size of 42 nm. Subsequently, the gamma-ray shielding performance was analyzed using synthesized titanium boride nanoparticles. Flexible shielding materials were fabricated using a hydrogel to load the synthesized nanoparticles. The attenuation coefficient of the titanium boride nanoparticle flexible material was 0.238 cm−1, and the half-value layer was 2.91 cm.

Introduction

Radioactive waste is generated from various industrial applications such as nuclear plant processing, medical isotope production, and nondestructive inspection. In order to treat radioactive waste, many types of radiation shielding materials are used, providing protection from a variety of radiation sources, such as alpha particles, beta particles, gamma-ray, and neutrons [1]. In the case of gamma-ray shielding, materials with high atomic number and density, such as lead, iron, and tungsten, are required owing to the high energy of the electromagnetic wave and it decreases through the interaction with the orbital electrons of the metallic material. In the neutron, on the other hand, low-density material such as polymers, boron, and water are typically used to shield [[2], [3], [4], [5], [6]].

The heavy metal has disadvantage such as crack from external shocks and high transportation costs. To improve these disadvantages, hydrogen-rich polymers and epoxy with high-density polyethylene (HDPE) were developed. Also, these polymers were embedded with high-density elements, such as Fe, Pb, or W [7,8]. However, HDPE is limited by the amount of the material that boron and metal particles can constitute, as increasing this amount weakens the tensile strength and elasticity of HDPE [[8], [9], [10], [11], [12], [13], [14], [15]]. In addition, hydrogel embedded metal oxide was tried to be shielding material and they are flexible and have a Young's-modulus range from 10 kPa to 10 MPa [[16], [17], [18], [19]]. However, it is a disadvantage that the embedded metal oxide will be made with radioactive material by neutrons.

The titanium boride has a high melting point and high strength, electrical conductivity, and hardness. It is an attractive engineering material with radiation shielding ability and wear resistance [[20], [21], [22]]. In order to synthesize titanium boride, high temperature is essential, owing to the high boiling point of raw materials, boron and titanium. Radio frequency (RF) induction thermal plasma has high enthalpy to enhance the high chemical reactivity and a large reactive volume with oxidizing or reducing atmospheres. In addition, it able to synthesize nano-size particles with high purity because there is no metallic electrode to discharge. Particularly, the high quenching rate of the plasma flame with rapid temperature gradient leads to homogeneous nucleation [[23], [24], [25], [26], [27], [28], [29], [30]].

In this study, a flexible shielding material with titanium boride nanoparticles synthesized by RF thermal plasma was fabricated, and its shielding performance was analyzed. First, in order to design an optimum torch structure for the synthesis of titanium boride nanoparticles, we simulated the thermal characteristics of an RF plasma torch based on the number of coil turns and inner diameter of the torch. Second, titanium boride was synthesized in the optimized plasma system, which was revealed by numerical simulation. Then, the flexible shielding material with the synthesized product was fabricated, and its performance in shielding 137Cs gamma-ray (0.662 MeV) was analyzed.

Section snippets

Numerical simulation

Fig. 1 shows a schematic diagram of the RF thermal plasma system for the synthesis of metal boride nanoparticles and the numerical simulation domain of the RF thermal plasma torch. The RF thermal plasma system consists of an RF power supply, plasma torch, reaction chamber, collector, vacuum pump, and powder feeder. The injected plasma-forming gas was exhausted through a cyclone filter as indicated in Fig. 1(a). The numerical simulation dealt primarily with the thermal flow characteristics

Plasma characteristics on the RF thermal plasma torch

Fig. 3 shows the temperature and velocity of plasma inside the RF torch region with increasing coil turn number. In Fig. 3(a), the high-temperature region was extended from the torch center to the exit with increasing coil turns. Fig. 3(b) describes the plasma velocity distribution and streamlines for five coil turns. It was revealed that the plasma velocity reached a maximum of 40 m/s at the RF torch exit, whereas, in the upper part of the coils, a backflow appeared with velocities ranging

Conclusion

The thermal characteristics of an RF plasma torch were analyzed through numerical simulation; then, titanium boride nanoparticles were synthesized in an optimized RF thermal plasma system. In the numerical simulation, the plasma temperature and velocity were investigated with the coil turn number (4–6 turn) and torch inner diameter (64–75 mm) serving as design variables. The optimized conditions for coil turn and torch inner diameter were determined to be 5 turn and 64 mm, respectively.

We

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2015M2B2A9030393 and 2018M3A7B4070992).

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