Electromagnetic Properties And Calefactive Mechanism Of High-carbon Ferrochrome Powders Decarburized In Solid Phase Via Microwave Heating

It is possible for microwave heating, as the second anthropic flame, to bean important technology for mineral treatment and metal smelting in the futuremetallurgical industry on account of its advantages, including volumetric andselective heating. The ability of microwaves to interact with materials andgenerate heat is closely related to the electromagnetic properties of materials.During solid-phase decarburization, the mutative electromagnetic properties ofmetallurgical materials not only reflect the variation degree of materialcomponents, but also affect the whole process of microwave heating. However,there have been few comprehensive reports on the electromagnetic propertiesand solid-phase decarburization of metallurgical materials.In this paper, high-carbon ferrochrome powders were decarburized withcalcium carbonate powders as the decarburizer through controlling heatingtemperature and holding time under the condition of microwave heating. Thevector network analyzer and the carbon-sulfur analyzer are used tosystematically probe the interrelation between the electromagnetic properties ofthe decarburized materials and the process of solid-phase decarburization. The calefactive characteristics of microwave heating are experimentally andtheoretically studied to concretely analyze the internal laws of the microwaveheating process of the powdered materials and the effect of the mutativeelectromagnetic properties on the microwave heating process. Furthermore, thequantum mechanics and the related theories are employed to go deep into themicro mechanism of microwave heating of transition metal carbides and theinterrelation between the density of states and microwave heating.As the geometry size of high-carbon ferrochrome reduces to mesoscopicsize, the powdered materials are affected by polarization relaxation and resonantresponse. At mesoscopic size,4s and4p electrons of ferrochrome carbidesweaken the delocalization due to quantum confinement effect, which benefits tomicrowave heating. Compared with bulk high-carbon ferrochrome, the ability ofhigh-carbon ferrochrome powders to absorb microwaves enhances distinctly andthe maximum microwave absorption rate is53.89%. During solid-phasedecarburization, magnetic loss and dielectric loss, which transform mutually, areclosely related with many factors, including carbon content, C-vacancies andcrystal structure of the powdered materials. Moreover, the microwave heatingprocess of the powdered materials at mesoscopic size is the volumetric heatingprocess, which includes two elementary reactions, namely microwaveabsorption and energy conversion. If taking the larger energy loss of broadsideand underside edge into account, the temperature field distribution of thepowdered materials is axisymmetrical distribution, whose central temperature is larger than broadside and underside temperature. Differences exist in theelectromagnetic properties of the powdered materials in radial direction,thus influencing the whole process of microwave heating.With heating temperature elevating, the relative permittivity of thedecarburized materials increases firstly and then decreases, whereasthe variation tendency of the relative permeability is exactly contrary to that ofthe relative permittivity. As heating temperature and holding time increase, therelative complex permittivity ultimately tends to be stable, demonstratingtransformation of ferrochrome carbides to chromium ferrite. In the decarburizedmaterials, the relative permittivity and dielectric loss factor tend to decreasewhile the relative permeability and magnetic loss factor tend to increase,corresponding to the maximum mean velocity of decarburization. Duringmicrowave heating, the calefactive curves of the powdered materials all accordwith the cubic function whether chemical reaction heat exists or not. Withoutchemical reaction heat, the heating rates are in good agreement with the derivedfunction of the cubic function. The interaction of microwaves with the powderedmaterials is that microwave photons increase the confusion degree ofmicroscopic particles, presenting as vibration at the molecular level. In thesecarbides, the interband transition of3d electrons is apt to take place inmicrowave field, resulting in the increment of the atomic thermal vibration.It is hoped that the results of this paper may be beneficial to furthercomprehend the interaction of microwaves with the powdered materials, thereby throwing light on the microwave heating mechanism of transition metal carbidesand serving as a theoretical foundation for widespread use of microwavemetallurgy and quantum metallurgy.