A novel triple-cathode plasma torch with hot-wall nozzle for YSZ spherical thin-walled hollow-shell powder preparation

Abstract

Yttria-stabilized zirconia spherical thin-walled hollow-shell powder (YSZ-STHS) is a highly promising ceramic top-coat materials used in thermal barrier coatings with good homogeneity, a low thickness and no continuous flaws. However, the current technologies for preparing yttria-stabilized zirconia hollow spherical powder (YSZ-HOSP), such as spray drying, inductively coupled plasma spheroidization, and arc plasma spheroidization, face challenges in producing YSZ-STHS due to thick shell thickness and low hollow powder ratio. The triple-cathode plasma torch (TCPT) has characteristics such as high enthalpy and axial powder feeding, making it a promising tool for YSZ-STHS preparation. However, the plasma torch nozzle is often clogged due to powder deposition on the cold anode wall, limiting its application. To address this issue, a novel spheroidization method using a TCPT with hot-wall nozzle is proposed to achieve low shell thickness and high hollow powder ratio in YSZ-STHS powder preparation. Experiments were carried out to investigate the electro-thermal characteristics of the TCPT. The results indicated that the TCPT displayed a high mean enthalpy ranging from 2.37×107 J/kg to 3.36×107 J/kg and a low arc voltage fluctuation of ±1 V, indicating that the proposed TCPT is capable of producing a stable plasma jet with a high temperature. Additionally, experiments and numerical simulations were conducted to reveal the effect of the hot-wall nozzle. The results revealed that the hot-wall nozzle increased the inner wall temperature, decreased the radial temperature gradient of the plasma jet, reduced the nozzle clogging, and extends the high-temperature region and maximum temperature inside the nozzle. Finally, YSZ-STHS preparation by TCPT with hot-wall nozzle was demonstrated through experiments. The results showed that YSZ-STHS with a high spheroidization ratio close to 100%, a high hollow powder ratio of 93.4%, a thin shell thickness with an average value of 3.63 μm, and fully tetragonal phase was successfully prepared, demonstrating the effectiveness of the proposed TCPT with hot-wall nozzle for the preparation of YSZ-STHS.