Quantitative Analysis of Zinc Vaporization from Manganese Zinc Ferrites

Zinc vaporization of Mn-Zn ferrites was quantitatively characterized in terms of oxygen partial pressure P _O2, temperature, grain size and sample geometry. The amount of zinc loss was measured as a function of time at various temperatures by a thermogravimetric method. The weight loss due to irreversible zinc vaporization showed a linear behavior with time and increased exponentially with temperature. The observed weight loss due to zinc evaporation at 1100°C was small, whereas a significant weight change was detected at 1200°C. The weight loss was even greater in a reducing atmosphere ( P _O2= 5 × 10⁻⁵). Below 1300°C, the diffusion of elemental zinc was sufficiently fast to compensate the zinc loss at the interface region, resulting in a linear dependence on time. At temperatures ≥1400°C, the weight change no longer followed the linear dependence and showed a rather parabolic behavior with a concave upward slope. The core shape and the gas flow around ferrite cores were important factors that affected the rate of zinc vaporization, but not the grain size.