Structure and Crystallization of Alkaline-Earth Aluminosilicate Glasses: Prevention of the Alumina-Avoidance Principle
authors Allu, AR; Gaddam, A; Ganisett, S; Balaji, S; Siegel, R; Mather, GC; Fabian, M; Pascual, MJ; Ditaranto, N; Milius, W; Senker, J; Agarkov, DA; Kharton, VV; Ferreira, JMF
nationality International
journal JOURNAL OF PHYSICAL CHEMISTRY B
keywords NUCLEAR-MAGNETIC-RESONANCE; X-RAY-DIFFRACTION; SI-29 MAS NMR; MOLECULAR-DYNAMICS SIMULATIONS; OXIDE FUEL-CELLS; SOLID-STATE NMR; AL-27 NMR; RAMAN-SPECTROSCOPY; MICROSCOPIC ORIGINS; RANGE ORDER
abstract Aluminosilicate glasses are considered to follow the Al-avoidance principle, which states that Al-O-Al linkages are energetically less favorable, such that, if there is a possibility for Si-O-Al linkages to occur in a glass composition, Al-O-Al linkages are not formed. The current paper shows that breaching of the Al-avoidance principle is essential for understanding the distribution of network-forming AlO4 and SiO4 structural units in alkaline-earth aluminosilicate glasses. The present study proposes a new modified random network (NMRN) model, which accepts Al-O-Al linkages for aluminosilicate glasses. The NMRN model consists of two regions, a network structure region (NS-Region) composed of well-separated homonuclear and heteronuclear framework species and a channel region (C-Region) of nonbridging oxygens (NBOs) and non-framework cations. The NMRN model accounts for the structural changes and devitrification behavior of aluminosilicate glasses. A parent Ca- and Al-rich melilite-based CaO-MgO-Al2O3-SiO2 (CMAS) glass composition was modified by substituting MgO for CaO and SiO(2 )for Al2O3 to understand variations in the distribution of network-forming structural units in the NS-region and devitrification behavior upon heat treating. The structural features of the glass and glass- ceramics (GCs) were meticulously assessed by advanced characterization techniques including neutron diffraction (ND), powder X-ray diffraction (XRD), Si-29 and Al-27 magic angle spinning (MAS)-nuclear magnetic resonance (NMR), and in situ Raman spectroscopy. ND revealed the formation of SiO, and AlO4 tetrahedral units in all the glass compositions. Simulations of chemical glass compositions based on deconvolution of Si-29 MAS NMR spectral analysis indicate the preferred formation of Si-O-Al over Si-O-Si and A1-0-Al linkages and the presence of a high concentration of nonbridging oxygens leading to the formation of a separate NS-region containing both SiO, and AlO4 tetrahedra (Si/Al) (heteronuclear) in addition to the presence of Al-[4] O-Al-[4] bonds; this region coexists with a predominantly SiO4 -containing (homonuclear) NS-region. In GCs, obtained after heat treatment at 850 degrees C for 250 h, the formation of crystalline phases, as revealed from Rietveld refinement of XRD data, may be understood on the basis of the distribution of SiO4 and AlO4 structural units in the NS-region. The in situ Raman spectra of the GCs confirmed the formation of a Si/Al structural region, as well as indicating interaction between the Al/Si region and SiO4 -rich region at higher temperatures, leading to the formation of additional crystalline phases.
publisher AMER CHEMICAL SOC
issn 1520-6106
year published 2018
volume 122
issue 17
beginning page 4737
ending page 4747
digital object identifier (doi) 10.1021/acs.jpcb.8b01811
web of science category Chemistry, Physical
subject category Chemistry
unique article identifier WOS:000431723800014
  ciceco authors
  impact metrics
journal analysis (jcr 2019):
journal impact factor 2.857
5 year journal impact factor 2.88
category normalized journal impact factor percentile 50.629
dimensions (citation analysis):
altmetrics (social interaction):



 


Sponsors

1suponsers_list_ciceco.jpg