Modeling and Selection of RF Thermal Plasma Hot-Wall Torch for Large-Scale Production of Nanopowders

Progress in Preparation of ZrB2 Nanopowders Based on Traditional Solid-State Synthesis

ZrB₂ is of particular interest among ultra-high temperature ceramics because it exhibits excellent thermal resistance at high temperature, as well as chemical stability, high hardness, low cost, and good electrical and thermal conductivity, which meet the requirements of high-temperature components of hyper-sonic aircraft in extreme environments. As raw materials and basic units of ultra-high temperature ceramics and their composites, ZrB₂ powders provide an important way for researchers to improve material properties and explore new properties by way of synthesis design and innovation. In recent years, the development of ZrB₂ powders’ synthesis method has broken through the classification of traditional solid-phase method, liquid-phase method, and gas-phase method, and there is a trend of integration of them. The present review covers the most important methods used in ZrB₂ nanopowder synthesis, focusing on the solid-phase synthesis and its improved process, including modified self-propagating high-temperature synthesis, solution-derived precursor method, and plasma-enhanced exothermic reaction. Specific examples and strategies in synthesis of ZrB₂ nano powders are introduced, followed by challenges and the perspectives on future directions. The integration of various synthesis methods, the combination of different material components, and the connection between synthesis and its subsequent application process is the trend of development in the future.

RF Thermal Plasma Synthesis of Ultrafine ZrB2-ZrC Composite Powders

Ultrafine ZrB₂-ZrC composite powders were synthesized via a radiofrequency (RF) thermal plasma process. Numerical simulation and thermodynamic analysis were conducted to predict the synthesis process, and experimental work was performed accordingly to demonstrate its feasibility. The as-prepared samples were characterized by XRD, FESEM, particle size analyzer, nitrogen/oxygen analyzer, Hall flowmeter, and the Brunner-Emmet-Teller (BET) measurements. The thermodynamic analysis indicated that ZrB₂ was preferentially generated, rather than ZrC, and numerical simulation revealed that the solid raw materials could disperse well in the gaseous reactants, and experimental work showed that free carbon particles were easily removed from the products and the elements of Zr, B, C, and O exhibited a uniform distribution. Finally, ZrB₂-ZrC composite powders with a particle size of about 100 nm were obtained, the surface area of which was 32.15 m²/g and the apparent density was 0.57 g/cm³.

RF-ICP Thermal Plasma for Thermoplastic Waste Pyrolysis Process with High Conversion Yield and Tar Elimination

This paper demonstrates an RF thermal plasma pyrolysis reaction apparatus that achieves 89 wt.% reaction conversion yield with no tar content. The demonstrated experimental apparatus consists of a 1100 W RFVII Inc. (104 Church St, Newfield, NJ 08344, United States) @ 13.56 MHz RF thermal plasma generator, a Navio matching network, intelligent feedback controller, and an 8-turn copper RF-ICP torch embedded in a 12 L thermochemical reactor. The intelligent feedback controller optimizes the thermal performance based on feedback signals from three online gas analyzers: CO, CO2 and NOx. The feedback controller output signal controls the RF thermal plasma torch current that provides real-time temperature control. The proposed reaction system achieves precise temperature profiles for both pyrolysis and gasification as well as increases end-product yield and eliminates undesired products such as tar and char. The identified hydrocarbon liquid mixture is 90 wt.% gasoline and 10 wt.%. diesel. The 8-turn RF-ICP thermal plasma torch has an average heating rate of +35 °C/min and a maximum operating temperature of 2000 °C and is able to sustain stable flame for more than 30 min. The reaction operating parameters are (550–990 °C τ = 30 min for pyrolysis and (1300 °C τ = 1 sec) for the gasification process. The identified hydrocarbon liquid products are 90 wt.% of a n-butyl-benzene (C6H5C4H9) and oluene (C7H8) mixture with less than 10 wt.% decane diesel fuel (C10 H22). Comsol simulation is used to assess the RF-ICP thermal plasma torch’s thermal performance.