Optical in situ diagnostics of iron nanoparticle aerosols in microwave plasma

Microwave plasma synthesis of iron nanoparticles is a complex process involving nucleation and growth of particles, and phase transitions. Accurate diagnostics are essential for understanding this process. In this study, we employ optical in situ diagnostics, including line-of-sight attenuation, optical emission spectroscopy, and two-color thermometry, to investigate the synthesis process. We evaluate the effects of different nanoparticle sizes and phases on the diagnostics. Our results demonstrate that while the nanoparticle phase has a limited effect on pyrometric temperature measurements, size variations can introduce significant errors in volume fraction measurements. We observe that an increase in precursor flow rate yields a higher nanoparticle count but results in smaller nanoparticle size, lower nanoparticle temperature, and a more strongly focused nanoparticle stream. The observed thermal radiation indicates successful nanoparticle generation within the plasma zone. This research contributes valuable insight into the process of iron nanoparticle formation and the associated diagnostics. • Iron nanoparticles are synthesized within a low-pressure microwave plasma reactor. • Temperature and volume fraction distribution of nanoparticles are measured. • Effects of optical properties on diagnostics are evaluated.