SURFACE MODIFICATION OF Al2O3 FIBER WITH NANOPARTICLES USING A DRY MECHANICAL COATING TECHNIQUE
N. Coowanitwong, C-Y Wu, J. Nguyen, M. Cai, M. Ruthkosky, J. Rogers, L. Feng, S. Watano, and T. Yoshida
Assistant Professor, US
Keywords: surface modification, fiber, binary nanoparticles, degree of dispersion, homogenous distribution, crystalline phase, performance activity, and dry mechanical coating technique
Nanoparticles are of great interest to many industries due to their unique properties. One of the well-known properties is high surface area, which is critically essential to enhancing performance activity  and greatly vital to environmental, chemical and materials industries such as to synthesize useful materials or to decompose pollutants. Nanosized powders, however, always exist as agglomerates although the applications usually require dispersion for better property . Good dispersion becomes more challenging when two or more types of nanoparticles are involved. Incorporating nanoparticles into the composite can be potentially accomplished by a dry mechanical coating process. This technique applies high shear and compression force to adhere materials onto substrates [3, 4]. With the intensive shear force and compression, good dispersion of nanoparticles on the substrates can be achieved .
While a dry coating process can possibly be applied to fabricate a composite particle, several questions still remain to be answered. Since high forces are applied to achieve coating, the size and morphology of the materials may very well change due to the forces. Most of past studies focused on spherical particles . How the coating process affects the morphology of non-spherical materials such as fiber has seldom been investigated. The coating performance (i.e., how much feed is actually coated on the non-spherical substrates) is another important question. Moreover, the quality of the coating (i.e., the dispersion of nanoparticles on the substrates) is another critical key. Since mechanochemistry at high mechanical conditions , may result in the formation of materials with undesired properties, the preservation of material properties is also of great concerned.
In this study, nanosized Al2O3 particles were deposited on Al2O3 fiber substrates using Theta Composer. Operating parameters including initial loading of nanoparticles and processing time were varied to study their effects on the coating characteristics and product properties. To evaluate the impact of the processing time on fiber length and morphology, fiber without nanoparticles was processed at several processing time. Figure 1 (a) showed the SEM images of fiber after the process indicating the reduction in length while maintaining smooth surface and a long aspect ratio. To access the effect of nanoparticles on fiber length and surface area, nanoparticles with various initial loadings were coated on the fiber. Results showed that fiber length was independent to the nanoparticle loading while the surface area increased with the initial loading. However, as the initial loading increased, the coating efficiency (ratio of coated feed to initial loading) decreased. To investigate the effects of processing time and nanoparticles on dispersion, various nanoparticle loadings were coated on the fiber at different processing time. Figure 1 (b) showed that at a very low loading, nanoparticles were well dispersed. As the loading increased, large agglomerates started to appear as shown in Figure 1 (c). However, Figure 1(d) suggested that the dispersion improved as the processing time increased. Figures 2 and 3 confirmed that the dispersion of nanoparticles also improved (i.e., higher mean with lower standard deviation) as the processing time increased when the mixture of Al2O3 and CuO nanoparticles were deposited on Al2O3 fiber substrates. In addition, the homogeneity of Al2O3 with CuO nanoparticles improved as the processing time increased as shown in Figure 4. Experimental results clearly indicated the preservation of the nanoparticle properties under the conditions studied in this work.
NSTI Nanotech 2003 Conference Technical Program Abstract