Theoretical Calculations Of Microwave Dielectric Properties And Study On The Mechanism Of Microwave Heation Of High-carbon Ferrochrome Powders

In the transformation process of the microwave metallurgy from the experiment to the industry, it is not enough to study the interaction mechanism between microwave and the substance, which mainly includes the study of the dielectric properties of the material, resulting in currently controlling microwave energy to industrial inefficiently. It is difficult to achieve a wide range of applications. The issue of the study is high-carbon ferrochrome(HCFC) metal powder. We research microwave dielectric properties of materials by the theoretical calculating and experimental study, proposing series of theory on microwave dielectric response of materials, and further study the interaction characteristics and mechanism between microwave and substance.The electronic structure and microwave dielectric properties of Fe-doped o-Cr7C3were studied theoretically based on first-principles calculations. The3d,4s and4p orbits of Cr atoms in o-Cr7C3are hybridised. The electrons of these orbits pair up with electrons of the non-equivalent sp3hybrid orbits of C atoms into delocalisation electron-deficient covalent bonds, leading to the formation of a covalent bond net consisting of Cr-C-Cr chains in the metallic matrix. Fe-doping can substantially improve the microwave dielectric properties of o-Cr7C3. The microwave dielectric properties of Fe-doped o-Cr7C3are closely related to the strength of covalent bonds and metallic anti-bonding. The electrons in the covalent bonds and metallic anti-bonding in the microwave field are apt to be polarised because the effect of the positive ions cores on the delocalised electrons is relatively weak. Precise knowledge of the electronic structure of Fe-doped o-Cr7C3will facilitate better understanding of its microwave dielectric properties.On the other hand, we researched the heated state of high-carbon ferrochrome metal powder at2.45GHz of microwave frequencies and the variation of dielectric constant in the2-18GHz microwave frequency range. Meanwhile, the vibration frequency of Cr7C3and Fe-doped Cr7C3, the main substance of HCFC, is studied theoretically based on first-principles calculations. We studied the impact of the particle size of high-carbon ferrochrome powder to the microwave dielectric properties of the metallic high-carbon ferrochrome powder from the lattice dynamics, and obtained the microwave dielectric mechanism of metallic HCFC. From the analysis of the curve on relative permittivity varied with microwave frequency, microwave formation mechanism of HCFC powder contains resonant dispersion mechanisms and space charge polarization mechanism. The former formed the electron-deficient covalent bond C-M or metallic anti-bonding. The latter formed the charge polarization of the powder particle surface. The electron-deficient covalent C-M and metallic anti-bonding forming the resonant dispersive has the nature of weakly bound on electrons, effectively absorbing the microwave energy. The particle surface tension also have the same effect weakly bound on electrons, which makes electronics of the materials in powder state absorb microwave energy. This should be due to the electronic energy levels of the metal particles changed on the surface tension. The real and imaginary parts of the theoretical calculated permittivity of the block Cr7C3is very high. But as the free electron has no stable level after absorption of microwave energy, it immediately releases the microwave energy, thereby forming the shielding effect to the microwave of the materials. Meanwhile, the powder state of the material makes the resonance dispersion frequency shift from the infrared region to the relatively low frequency of the microwave band, and it has been validated by kinetic calculation. The microwave heating on metallic carbon ferrochrome powder realising body heating effect of microwave heating, makes the temperature gradient of the material is low and the energy of particles is relatively uniform. By the Maxwell Boltzmann distribution, this will make the number of particles equal to or greater than the activation more relative to traditional heating. That is to say reaching a certain number of the particles, the activation energy of reactions requires low energy of microwave heating than conventional heating. The low activation energy of microwave heating ultimately reduce the temperature of chemical reaction.