[6]
For replica method this behavior is suitable, seeing that as subject of an external force the suspension is fluid enough to enter, fill and coat uniformly the surface of template, whereas under static condition, its viscosity is high enough to remain on the surface of replica template. Fig. 1– Flow curves of SY30 with 0-0.5 wt% of CMC in CR mode According to previous rheological analyzes for replica method the following processing parameters are summarized in Table 1. Table 1- Processing parameters for replica method
Solids load (vol%)
pH Binder (wt%) (mPa.s) (Pa)
Thixotropy (Pa.s-1)
30.0
10
0.5
424.0
42.49
7.435
: apparent viscosity at 100s-1 Immersion time (IT ) evaluation in replica method Fig. 2 shows an increasing of the quantity (mass) of NY as a function of IT from 5 to 120min. For times up to 15min the gain of mass was few (54.90%), meaning that the adhesion of the suspension on NC surface was not much efficient. Besides, from 15 to 30 min a significant shift in mass of 62.68% was observed. For further intervals this increasing still went on, although with less intensity. Fig. 2 - Increasing of NYs mass as a function of IT.
Morphology evolution of NY as a function of IT The effect of IT in morphology of sintered yttria nettings (NY) is shown in Fig. 3. For IT≤15min, NYs presented a heterogeneous distribution of struts (thin/ thick), where it was more evident at IT=5min. Even though no cells had been trapped, that confirms the rheological behavior of suspension was suitable, the following result shows that this interval did not supply favorable conditions for suspension cover the surface of NCs uniformly. However, the uniformity of struts was obtained apart from IT=30min. Finally, the thickest strut was formed at IT =120min. These results can be associated with those presented previously in Fig. 2, seeing that at IT =30min a significant gain in mass of NYs was observed. Fig. 3 – NYs produced by replica, whereby IT from 5-120min. Conclusions Yttria nettings (NY) were produced by replica, whereby immersion time (IT) of templates shifted from 5 to 120min was evaluated. A significant gain in mass of NYs (impregnated suspension), associated with homogeneous distribution of cells and thick struts could be gotten with IT from 30min. Thus, even though the rheological behavior of a suspension is an important parameter for replica method, the role of immersion time (IT) is also very significant to control the morphology of cells, and also the thickness and homogeneity of struts. Acknowledgements The authors are gratefully acknowledged to High Degree People of Improvement Coordination (CAPES) for financial scholarship support of the student Silas Cardoso dos Santos. Referencies
Google Scholar
[1]
WOOD, S.,HARRIS, A. T., Porous burners for lean-burn applications, Progress in Energy and Combustion Science, vol. 34, pp.667-684, 2008.
DOI: 10.1016/j.pecs.2008.04.003
Google Scholar
[2]
WANG, W. N., WIDIYASTUTI, W., OGI, T., et al., Correlations between crystallite/particle size and photoluminescence properties of submicrometer phosphors, Chemistry of Materials, vol. 19, pp.1723-1730, 2007.
DOI: 10.1021/cm062887p
Google Scholar
[3]
SCHWARTZWALDER, K.,SOMERS, A. V., "Method of Making Porous Ceramic, " United States of America Patent, 1963.
Google Scholar
[4]
SANTOS, S. C., "Processamento coloidal de componentes cerâmicos para queimadores de gás," Dissertação de Mestrado, Instituto de Pesquisas Energéticas e Nucleares (IPEN), Universidade de São Paulo (USP), São Paulo, 2010.
DOI: 10.11606/d.85.2010.tde-29082011-105822
Google Scholar
[5]
SANTOS, S. C. D., SETZ, L. F. G., YAMAGATA, C., et al., Rheological study of yttrium oxide aqueous suspensions, Materials Science Forum, vol. 660 - 661, pp.712-717, 2010.
DOI: 10.4028/www.scientific.net/msf.660-661.712
Google Scholar
[6]
MEWIS, J.,WAGNER, N. J., Thixotropy, Advances in Colloid and Interface Science, vol. 147-48, pp.214-227, 2009.
DOI: 10.1016/j.cis.2008.09.005
Google Scholar
