Influence of ionic surfactants under ultrasonic irradiation to reduce the particle size of mechanically alloyed La_1-xSr_x Fe_0.5Mn_0.25Ti_0.25O₃ powders

In this study, nano particles of La_1-xSr_x Fe_0.5Mn_0.25Ti_0.25O₃ (x = 0.25, 0.50, 0.75 and 1.00) were prepared by two successive methods: the mechanical alloying (MA) with a successive sintering and refining of MA powders in a demineralized water containing surfactant under ultrasonic irradiation. It is shown that MA of La_1-xSr_x Fe_0.5Mn_0.25Ti_0.25O₃ powders have a smallest average particle size of slightly less than 6 micron for x=0.50. Additionally, the particle size distribution shown a large size variation. As powders were dispersed into the demineralized water and irradiated by a 40 KHz ultrasonic wave for 7 hours the particle size distribution was improve significantly, it has a narrow distribution with a mean particle size 180 nm. Thus, the particles can be called nanoparticle clusters. The study also indicated the breakup of nanoparticle cluster was no longer effective in a prolonged irradiation time and reagglomeration was also obvserved. However, the latter was not occurred in a disperse media containing surfactants. In this study, four types of surfactants were used and their influences to the particle sizes were evaluated. According to this study, the four types of surfactants could reduce further the particle size but in different pathways. Sodium Dodecyl Sulphate (SDS) as anionic surfactant was able to segregate the particles and reduced the size of nanoparticle clusters to almost 90 nm by one step ultrasonic destruction. It is shown that cationic, non-ionic and amphoteric surfactants promote the gel formation, the nanoparticle clusters were then obtained after heating the gel to the dry powders.