In-situ spectroscopy and two-color thermography during microwave irradiation in materials processing

[EN] Concentration of microwave E-field between material particles is considered to cause the enhancement of sintering1 and chemical reaction under microwave irradiation. For example, it is usually required 1700 °C to synthesize AlN by carbothermal reduction method using Al2O3 as a starting material, but microwave processing can proceed this process at 1200 °C2. To understand this phenomenon, it is necessary to understand an occurrence behavior of plasma and a chemical reaction related to radical species generated by a local E-field concentration. In addition, in material synthesis using a raw material powder of several mm, it is suggested that a selective heating in the powder scale occurs. However, to discuss this selective heating behavior on this scale, it is necessary to realize a quantitative temperature measurement system with independent of the emissivity of the material and several mm spatial resolution. In this study, we conducted an in-situ spectroscopy and two-color thermography to verify these non-equilibrium effects during microwave irradiation. For example, in the iron making process, it was investigated that CN plasma was generated, and this CN radical contributed to the reduction reaction (Fig. 1(a))3. In addition, the developed two-dimensional two-color thermography system with a high resolution of 8.8 mm/pixel was enable to discuss local temperature gradients quantitatively (Fig. 1(b)).This work was supported by a JSPS Grant-in-Aid for Scientific Research (S) No. JP17H06156.Fukushima, J.; Takizawa, H. (2019). In-situ spectroscopy and two-color thermography during microwave irradiation in materials processing. En AMPERE 2019. 17th International Conference on Microwave and High Frequency Heating. Editorial Universitat Politècnica de València. 373-377. https://doi.org/10.4995/AMPERE2019.2019.9882OCS37337

Controlling oxygen coordination and valence of network forming cations

Understanding the structure-property relationship of glass material is still challenging due to a lack of periodicity in disordered materials. Here, we report the properties and atomic structure of vanadium phosphate glasses characterized by reverse Monte Carlo modelling based on neutron/synchrotron X-ray diffraction and EXAFS data, supplemented by Raman and NMR spectroscopy. In vanadium-rich glass, the water durability, thermal stability and hardness improve as the amount of P2O5 increases, and the network former of the glass changes from VOx polyhedra to the interplay between VOx polyhedra and PO4 tetrahedra. We find for the first time that the coordination number of oxygen atoms around a V4+ is four, which is an unusually small coordination number, and plays an important role for water durability, thermal stability and hardness. Furthermore, we show that the similarity between glass and crystal beyond the nearest neighbour distance is important for glass properties. These results demonstrate that controlling the oxygen coordination and valence of the network-forming cation is necessary for designing the properties of glass

Size Control of Ti₄O₇ Nanoparticles by Carbothermal Reduction Using a Multimode Microwave Furnace

Utilization of Ti4O7 in applications such as catalyst support calls for control over the size of the Ti4O7 nanoparticles. This can be achieved using a simple process such as carbothermal reduction. In this study, various sizes of Ti4O7 nanoparticles (25, 60, and 125 nm) were synthesized by carbothermal reduction using a multimode microwave apparatus. It was possible to produce Ti4O7 nanoparticles as small as 25 nm by precisely controlling the temperature, heating process, and holding time of the sample while taking advantage of the characteristics of microwave heating such as rapid and volumetric heating. The results show that microwave carbothermal reduction is advantageous in controlling the size of the Ti4O7 nanoparticles

Control of Magnetic Properties of NiMn2O4 by a Microwave Magnetic Field under Air

NiMn2O4 prepared by conventional heating was irradiated with a microwave H-field using a single-mode cavity under air and magnetic properties of the microwave-irradiated material were investigated. X-ray diffraction and transmission electron microscopy demonstrated that the phase and microstructure are not affected by H-field irradiation. Measurements of the magnetization as a function of temperature revealed that the antiferromagnetic sublattice disappeared and electron spin resonance showed the existence of Mn2+, suggesting that Mn3+ is partially reduced. Moreover, the magnetization of NiMn2O4 was controlled from 35.3 to 18.2 emu/g and the coercivity from 140 to 750 Oe by changing the sample temperature during microwave irradiation. The reduction reaction of NiMn2O4 is controlled by microwave H-field irradiation, resulting in control over the magnetic properties