Journal of the society of powder technology Japan
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At dispersion of agglomerated nanoparticles to mono particles by a bead mill, large-sized beads give excess impact power to the agglomerated nanoparticles, resulting in crushing and re-agglomeration of the particles. Recentely a new process have been developed (new bead mill), capable of using microbeads (down to 0.03mm), and its dispersion performance for agglomerated ferrite nanoparticles to get the monodispersed nanoparticles was investigated under varios operating conditions in this study. Ut is shown that the impact force generated by the beads during the dispersion can be controlled by varying the bead size and that hence the adverse effect of impact force on the crystallinity and the surface of particles can be prevented. As a result, ferrite nanoparticles with diameter down to 50nm (close to the diameter of primary particles) and sharp size distributions were obtained. The present study of dispersion operation by microbeads is expected to be directly applicable to the development of nano-dispersion of novel materials.
Reflecting a strong demand for nanoparticle materials dispersed down to several tens of nano meters in the field of eletronic materials, dispersion process for nanoparticle agglomerate using a bead mill has become an important issue. In addition, it is frequently demanded that nanoparticle agglomerate be dispersed down to the mono particles without damaging them.
However, the two technical requirements conflict, therefore, it has become necessary to determine optimum dispersion power that will satisfy the both requirements as much as practicable. Although varios attemps for optimum dispersion power were made eith convencional continuous bead-mills, it was difficult to reduce the diameter of a vead used in the processing. Large beads which generate large bead impact energy tended to cause a problem of re-agglomeration due to particle destruction and damages. In such circumstances, it was an important challenge to develop a new technology to disperse nanoaprticle down to the mono particle.
Meanwhile, a new system has developed a new bead mill, capable of using 0.3mm beads which were never usable in the conventional bead mills. In the present research, we also used 0.05mm and 0.1mm beads to make a comparative study betwee these and 0.03mm beads, Furthermore, the experimentation was conducted under different rotor speeds for bead agitation to investigate and empirically determine optimun operating conditions in which dispersion down to the primary particles with minimum influence on the particle´s crystaline properties and surface properties is possible. In the analysis of the results, we focused on impact energy applied to particles by the beads to evaluate the minimum impact energy required for agglomerates dispersion as well as the relationship between said impact energy and optimum operating conditions.
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Regards,
Tarik Della Santina Mohallem
R&D Director
Nanum Nanotecnologia SA
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