Surface growth mechanisms and structural faulting in the growth of large single and spherulitic titanosilicate ETS-4 crystals |
| |
Authors: | Peter Q. Miraglia Bilge Yilmaz Juliusz Warzywoda Albert Sacco Jr. |
| |
Affiliation: | Chemical Engineering Department, Center for Advanced Microgravity Materials Processing, 147 Snell Engineering Center, Northeastern University, Boston, MA 02115, USA |
| |
Abstract: | Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to 110, 010 and 001 directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on 1 0 0 and 0 0 1 surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on 1 0 0 surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred. |
| |
Keywords: | A1. GADDS, A1. Growth models, A1. Surface structure A2. Single crystal growth B1. ETS-4 B1. Titanosilicates |
本文献已被 ScienceDirect 等数据库收录! |
|