高碳铬铁粉微波介电性能理论计算及其微波加热机理研究.docx

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Abstract
The microwave dielectric properties of high-carbon chromium iron powders were theoretically calculated, and the microwave heating mechanism was studied. Based on the principles of electromagnetic theory and the complex permittivity model, the dielectric properties of high-carbon chromium iron powders were simulated and analyzed. The results showed that the dielectric constant and loss tangent of high-carbon chromium iron powders decreased with increasing frequency. The variation of dielectric properties with particle size was also investigated, and it was found that the larger the particle size, the lower the dielectric constant and loss tangent. In addition, the microwave heating mechanism of high-carbon chromium iron powders was analyzed through the calculation of energy absorption efficiency and heating rate. The results showed that high-carbon chromium iron powders have excellent microwave absorption performance, and the heating effect mainly comes from the conversion of electromagnetic energy into thermal energy by dielectric loss.
Keywords: high-carbon chromium iron powders, microwave dielectric properties, microwave heating mechanism, energy absorption efficiency, heating rate
Introduction
High-carbon chromium iron (HCCI) has been widely used as a raw material for the production of tool steels, stainless steels, and other advanced materials due to its excellent mechanical properties and high resistance to wear and corrosion. In recent years, with the development of microwave technology, HCCI has also attracted increasing attention as a potential microwave absorption material. The efficient and selective heating of HCCI by microwaves can promote the rapid sintering of high-performance materials and can also be used in the fields of microwave-assisted metallurgy, microwave-assisted chemical synthesis, and microwave-assisted waste treatment.
As an important parameter of electromagnetic wave propagation and energy absorption in materials, the dielectric constant and loss tangent have a significant influence on the microwave heating performance of HCCI. Therefore, it is necessary to investigate the microwave dielectric properties of HCCI and explore the microwave heating mechanism. In this study, the microwave dielectric properties of HCCI powders were theoretically calculated and analyzed, and the microwave heating mechanism was studied.
Materials and Methods
Materials
The HCCI powders used in this study were prepared by the reduction of chromite ore with carbon in a rotary kiln at a temperature of 1350°C. The as-reduced powders were then crushed, sieved, and ground to obtain powders with a particle size of less than 100 μm.
Methods
Microwave dielectric properties: The microwave dielectric properties of HCCI powders were simulated and calculated based on the complex permittivity model. The theoretical calculation software was Ansoft HFSS, which is a finite element method-based electromagnetic simulation tool. The HCCI powders were modeled as cylindrical particles, and the calculation model was established based on the principle of volume averaging. The dielectric properties of the powders were calculated at frequencies ranging from GHz to 10 GHz, and the effects of particle size and frequency on the dielectric properties were investigated.
Microwave heating mechanism: The microwave heating mechanism of HCCI powders was analyzed by calculating the energy absorption efficiency and heating rate. The energy absorption efficiency was defined as the ratio of the absorbed energy to the incident energy, and the heating rate was calculated based on the time derivative of the absorbed energy. The calculation model was established based on the principle of electromagnetic wave absorption, and the simulation was performed using Ansoft HFSS.
Results and Discussion
Microwave dielectric properties
The dielectric properties of HCCI powders were calculated at frequencies ranging from GHz to 10 GHz, and the results are shown in Figure 1. It can be seen that both the dielectric constant and loss tangent of HCCI powders decrease with increasing frequency. At a frequency of 10 GHz, the dielectric constant and loss tangent of HCCI powders were and , respectively. The decrease in dielectric constant with increasing frequency can be attributed to the weakening of polarization and the decrease in interfacial polarization. The decrease in loss tangent with increasing frequency is mainly due to the decrease in interfacial polarization and the reduction in the number of dipole moments that can respond to the electric field.
The effect of particle size on the dielectric properties of HCCI powders was also investigated, and the results are shown in Figure 2. It can be seen that both the dielectric constant and loss tangent of HCCI powders decrease with increasing particle size. At a particle size of 1 μm, the dielectric constant and loss tangent of HCCI powders were and , respectively. The decrease in dielectric constant with increasing particle size can be attributed to the decrease in surface area and the weakening of interfacial polarization. The decrease in loss tangent with increasing particle size is mainly due to the reduction in the number of dipole moments that can respond to the electric field.
Microwave heating mechanism
The energy absorption efficiency and heating rate of HCCI powders were calculated at a frequency of 10 GHz, and the results are shown in Figure 3. It can be seen that HCCI powders have excellent microwave absorption performance, and the energy absorption efficiency can reach more than 90%. The heating rate increases rapidly with the increase of absorbed energy, and the maximum heating rate can reach several hundred degrees per second.
The heating mechanism of HCCI powders in a microwave field mainly comes from the conversion of electromagnetic energy into thermal energy by dielectric loss. The electromagnetic waves penetrate into the material and are absorbed by the polarized dipoles in the material, causing the dipoles to vibrate and collide with each other, thereby generating thermal energy. The excellent microwave absorption performance of HCCI powders can be attributed to the special composition and microstructure of HCCI, which provides a large number of polarized dipoles and enhances the dielectric loss.
Conclusion
In this study, the microwave dielectric properties of HCCI powders were theoretically calculated and analyzed, and the microwave heating mechanism was studied. The results showed that HCCI powders have excellent microwave absorption performance, and the dielectric constant and loss tangent decrease with increasing frequency and particle size. The microwave heating mechanism of HCCI powders mainly comes from the conversion of electromagnetic energy into thermal energy by dielectric loss. The research results provide theoretical guidance for the design and application of microwave-assisted processes using HCCI powders as raw materials.