Page 84 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 4
Table 4.4 gives a comparison of processing parameters between microplasma method and bulk plasma approaches. It is clearly shown that bulk plasma processes always associate with high temperature and low-pressure operation. Therefore, not only extra cooling systems are necessitated to protect reactors, but also vacuum equipment is required to maintain stable plasma in large spatial scale. In some cases, ammonia was used as the precursor, which is toxic, relatively expensive and unsafe. The plasma powers vary with the reactor type and power supply, generally are in kW scale. The particle size also differs in a wide range, from several nanometers to several microns. On the contrary, in this study TiN nanoparticles are produced under atmospheric pressure, without any vacuum equipment or cooling system. The microdischarge power is extremely low (6 W), several orders of magnitude smaller than needed to sustain bulk plasma. In other words, nitride nanomaterials can be directly synthesized at plasma power of several watts, by using nitrogen as the N source in the microplasma process. This may open new application possibilities such as well localized direct plasma printing of nanostructures. However, precursor and energy efficiency of this process are still to be investigated and optimized. It is also important to note, that the confined spatial scale plasma also results in short residence time and uniform RTD, ensuring fine nanoparticles with narrower size distribution.
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