HRTEM Analysis and Magnetic Properties Study of Surface Oxidizing and Nitriding of Nanocrystalline Iron Particles

• Main Authors: Tsai,Kuen Rong, 蔡坤榮
• Other Authors: Lin, Hong Ming
• Format: Others
• Language: en_US
• Published: 1993
• Online Access: http://ndltd.ncl.edu.tw/handle/26302346331702818839

碩士 === 大同工學院 === 材料科學(工程)研究所 === 81 === Ultrafine particles of Fe were produced by using gas condensation method. Pure oxygen, air and nitrogen were introduced into the as-evaporate particles before they were taken out from chamber. Change atmosphere produces different layer structure around Fe. The crystal structure was identified by using high resolution electron transmission microscope( HRTEM) and image analysis technique. The conventional transmission electron microscope (TEM) was also use to check the result from the HRTEM. The average particle size was carried out by using BET nitrogen adsorption method and magnetic properties will be determined by VSM. The results indicate that the mean particle size of Fe increases as the absolute He pressure increasing. When the pressure changed from 1 mbar to 100 mbar, the mean particle of Fe varied from about 13 nm to 40 nm and a maximum value of coercivity about 1262 Oe was observed at the critical mean particle size of 20 nm. A layer of amorphous structure was formed initially. After the annealing under the electron irradiation this layer crystallized into ferrosoferric oxide or gamma-ferric oxide if the atmosphere was pure oxygen or air, but it formed a passivated layer of zeta-iron nitride when nitrogen was introduced. In attempt to investigate the effect of oxide on magnetic properties, a hydrogen reducing process was employed to remove the oxide layer. It was found that the clean surface leads to the increasing of the coercivity and magnetization at room temperature, but the change is not significant. However, the field required to saturate the particles without the oxide layer increases.