Generation of Engineered Aerosol Stainless Steel Nanoparticles using a Spark Discharge Generator

Abstract: This diploma work has shown that it is possible to generate engineered stainless steel nanoparticles using a spark discharge generator (SDG) with a selectable size in the size range 20-70 nm in diameter. The generated particles have similar composition as the electrodes used, although further studies are needed to verify if this is true for all particles generated. If this is true, it would be possible to produce nanoparticles of any type of stainless steel alloy - the only prerequisite is that it exists in bulk form. The most suitable operating parameters for the generation have been determined to: 2 mm gap distance between the electrodes and 10 mA charging current when the capacitance was 21 nF. The compaction temperature was determined to be approximately 1200$^{\circ}$C when 50 nm agglomerates were compacted in nitrogen. It is still uncertain whether it exists a protective chromium oxide layer surrounding each particle and making it corrosion resistant. The chromium content in the particles indicates that there might be and the particles are stable in air but more research is needed to conclude this. A complete study on engineered stainless steel nanoparticles has not been performed and more research needs to be done, different types of carrier gas need to be tested to optimize for higher concentration, lower compaction temperature and avoiding possible nitride formation and oxidation. Also, more TEM and XEDS studies need to be performed in order to determine the average composition of the nanoparticles. An experiment when these nanoparticles were used to enhance sintering behavior of a micro-powder was initiated but not completed and needs to be investigated further. The results in this work can be used as a base for further studies on engineered stainless steel nanoparticles.