Non-classical nucleation and crystallization

Resume : The integration of quartz on silicon in thin film form is a challenging issue due to the differences in the crystal structures of these materials. In this regard, this work overcomes the main challenges for the integration of novel functional oxide materials on silicon including (i) epitaxial piezoelectric α-quartz thin films [1] and (ii) 1D single crystalline phases of manganese oxides that share common growth mechanisms [2,3]. The aim of this contribution is to discuss in detail the non classical nucleation and crystallization mechanisms of these materials grown from chemical solutions. Quartz films are crystallized by a confined devitrification of amorphous silica films assisted by a heterogeneous catalysis driven by alkaline earth cations present in the precursor solution. The films are made of perfectly oriented individual crystallites epitaxially grown on (100)-Si. The active influence of the Si substrate mediates the preferential orientation of crystal nuclei, yielding competitive growth and producing a columnar microstructure. Quartz films are piezoelectric and can be used as template for the epitaxial growth of manganese oxide nanowires on silicon. This methodology exhibits a great potential for the design of novel oxide compounds on silicon with unique properties. [1] A. Carretero-Genevrier et al. Science 340, 827 (2013); [2] A. Carretero-Genevrier et al. Chem.Mater. 10.1021/cm403064u (2013) [3] A. Carretero-Genevrier et al. Chem.Soc.Rev. 10.1039/C3CS60288E (2013)

Resume : Recently, substantial attention has been focused on the preparation of porous metal oxides because of their wonderful physicochemical properties and wide potential applications in the areas of catalysis, sorption, chemical and biological separation, photonic and electronic devices, and drug delivery [1, 2]. In the present work, a series of high-surface-area and porous tetravalent metal oxides (TiO2, CeO2, ZrO2) were successfully synthesized using the colloid mill and hydrothermal technique. The key features of this unusual method are a very rapid mixing of reactants and nucleation process in a colloid mill followed by a separate aging process in the presence of NaBH4. Furthermore, the extreme forces to which the nucleation mixture is subjected in the colloid mill prevent aggregation of the nuclei and result in the nuclei having a uniform small size, while NaBH4 added can further induce the formation of porous metal oxide framework. As a result, this approach for the nucleation and crystallization endows a series of tetravalent metal oxides with high surface area, small crystallite size and narrow pore size distribution, which might provide a new platform for the preparation of advanced functional metal oxide materials. Reference [1] X. Wang, D.P. Liu, et al., J .Am. Chem. Soc. 135 (2013) 15864-15872. [2] E. Ortel, S. Sokolov, et al., Chem. Mater. 24 (2012) 3828-3838

Resume : Investigation of the structural relationship of the liquid and solid phases during the formation of Al single crystals on the basis of analysis of AE signals VB Vorontsov, V.K.Pershin , AS Cherepanov Department «Physics and Chemistry» URALS STATE UNIVERSITY of RAILWAY TRANSPORT The results of these and our previous studies [1,2 ] are devoted to the interpretation of the acoustic emission signals AE observed during phase transitions of type II . Emission AE signals during solidification accompanies crystallization of substances having a crystalline structure , therefore the laws of phase transitions from solid to liquid and back on the model material will be repeated in the main terms on any material of given crystalline structure and structure-sensitive properties of substance. In this paper, as a model substance Al ¬ 99,999 is used. Acoustic signals recorded during the experiment, were subjected Fourier analysis of the main parameters : amplitude A, frequency ƒ, separate signal energy E , Σ E of all signals . Given the fact that the method of Fourier analysis is a universal one and differs high sensitivity we decided to apply it to study the kinetics of processes in the melt and at the interface by changing its temperature in the direction of increasing and decreasing from t = 860 ° C to the point of crystallization. The task of the study included: a) analysis of the spectral composition of AE signals and establishing energy connection of all AE signals , with the change of temperature conditions in the melt . b) the study of the nature of AE signals and their manifestation of kinetics process of isothermal heating and cooling of the melt. As a result , on the basis of experimental data , we supposed that in the melt when overheated to t = 800 ° C areas with short-range order of atoms or (clusters) are retained but their size and number are changed during the heating. Prepared integral response melt its structural changes as a reaction to the total energy of these signals with AE melt incrementally heated to 860 ° C and cooled to the crystallization point at the same rate. A correspondence between the dynamics of clusters landing at the interface during the growth of single crystal and generated acoustic signals was set. References 1. V.B.Vorontsov ,V.V. Katalnikov Relationship between acoustic emission during phase transitions of the melt-solid body and the structure of the melt of metallic systems”. Proceedings of the Russian Conference “Structure and Properties of Metal and Slag Melts”. V. 4. 2004. p. 12. 2 . V.B Vorontsov, D.V.Zhuravlev, J.Chem.Chem.Eng.6 2012 p. 358.