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Synthesis of NiTi Nanoparticles by Electrical Discharge Method

Sabzehparvar, Milad | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48443 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Sadrnezhad, Khatiboleslam
  7. Abstract:
  8. Nickel-titanium nanoparticles showing shape memory properties at nanoscale, have recently attracted much attention as nanoactuators in the field of nano-electro-mechanical systems. So, spark discharge method was utilized in this study for synthesis of NiTi nanoparticles. First step was to design and build a suitable set-up for synthesis of nanoparticles with high qualities at a high production rate. Nextly, NiTi nanoparticles were synthesized from prealloyed electrodes at a positive pressure and were characterized by the EDS, XRD, SEM and DSC methods. The obtained product was as agglomerated nanoparticles having sizes of around 40nm with primary particle size of <10nm. Chemical composition of the product was the same as the composition of the electrodes materials, and Ni, NiTi and TiO2 phases were characterized. Results of DSC analysis showed a very weak peak at temperatures around 65 to 70℃ relating to martensitic transformation of NiTi phase. Next, the effect of Ar gas pressure was studied by keeping other operational parameters constant and the EDS, XRD and SEM characterization methods were utilized for this purpose. The EDS analysis showed that by synthesizing nanoparticles from prealloyed electrodes, the chemical composition of the electrodes is maintained. The XRD analysis showed that the gas pressure doesn`t have any direct effect on the obtained phases, but it can affect on detection of phases with a low volume fraction as a result of an enhanced production rate and a much greater amount of sample obtained at high gas pressures. Calculating the crystallite size by scherrer equation showed that the crystallite size of nanoparticles lowers from 13.7nm to 9.6nm with increasing the gas pressure, but SEM analysis showed that the agglomerated size of nanoparticles increases with pressure. The next step in this study was to synthesis nanoparticles from elementaly pure Ni and Ti electrodes and evaluating the effect of gas pressure on their formation. The EDS and XRD characterization methods were utilized for this purpose. The EDS analysis showed that at low gas pressures, the ablation rate of Ti electrode is much lower than Ni electrode and increases with the gas pressure. The XRD analysis in accordance with the EDS analysis, showed an increase in the amount of Ni-rich phases in the samples with increasing the gas pressure. Calculating the crystallite size by scherrer equation showed that the crystallite size of nanoparticles decreases with increasing the gas pressure. Then, the effect of the third element e.g. Ag, Au, Pt, Mo and Cu on the formation of NiTi nanoparticles from NiTi prealloyed electrodes was investigated. The EDS and XRD characterization methods were utilized. Results showed that using elements with high solubility for Ni and Ti elements, e.g. Au, Pt, Mo and Cu as an electrode material facing to the NiTi electrode, the Ni and Ti elements enter to the lattice of the third element and form an alloyed solid solution phase, instead of co-consendation and formation of NiTi nanoparticles. But using the Ag element resulted to air-stablized NiTi nanoparticles as a result of its low solubility for Ni and Ti elements. Finally, the synthesized NiTi nanoparticles were deposited on nickel foam substrates by the spark discharge method. SEM analysis showed a uniform distribution for nanoparticles with sizes smaller than 10nm on the surface
  9. Keywords:
  10. Shape Memory Alloy ; Solubility ; Spark Discharge ; Titanium NanoParticles ; Nickel-Titanium Shape Memory Alloy ; Nanoactuators ; Prealloy Electrode ; Elementary Pure Electrode

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