Zircon formation from amorphous powder and melt in the silica-rich region of the alumina–silica–zirconia system

Mineralogy and Microstructure of Hydrated Phases During the Pozzolanic Reaction in the Sanitary Ware Waste/Ca(OH)2 System

“…These bands not clearly detected on the infrared spectrum for the waste, which exhibited only a wide should at around 618 cm -1 . 29 This finding confirmed the small percentage of this phase in the starting material (on the order of ppm).…”

“…26 The intense overlapping adsorption bands in the 1170-1000 cm À1 frequency interval, characteristic of T-O and Si-O-T (T = Si, Al) bond vibrations, have also been observed by other authors. 26,27 More specifically, the band at 1082 cm À1 was associated with the Si-O-Si or Si-O-Al asymmetrical stretching vibrations in amorphous aluminosilicates, [28][29][30] while the shoulder at 1164 cm À1 was attributed to the Si-O asymmetrical vibrations in mullite and orthoclase. 28,31,32 Of the several bands present in the 530 to 680 cm À1 range, characteristic of the AlO 6 vibrations in mullite, 27,30 the one at 553 cm À1 was the most intense.…”

“…The 29 Si MAS NMR spectra, in turn, contained a series of wide and scantly resolved signals in the À84 to À120 ppm range, likewise characteristic of amorphous compounds. Silicon environments whose second coordination sphere contains aluminium are described in 29 Si NMR as Q n (mAl) units, where m ≤ n, Q represents the SiO 4 tetrahedra, m the number of AlO 4 units bound to those tetrahedra, and n the number of oxygen atoms connecting each tetrahedron, i.e., the number of oxygen atoms shared with the adjacent Si atoms (known as tetrahedral connectivity). 33 Hence, Q 4 (1Al) units have one SiO 4 tetrahedron coordinated with three SiO 4 tetrahedra and one AlO 4 À tetrahedron; Q 4 (2Al) units have one SiO 4 tetrahedron coordinated with two SiO 4 and two AlO 4 tetrahedra, and so on.…”

“…The structure of the SW waste and its hydrated phases (C-S-H gels) was determined with NMR and Fourier transform infrared spectroscopy (FTIR). MAS NMR experiments were conducted on a Bruker Avance-400 (9.4 T) spectrometer operating at a frequency of 79.4 MHz for 29 Si and 104.3 MHz for 27 Al. The samples were packed into 4-mm zirconium rotors scanned under the following conditions for 29 Si and 27 Al, respectively: 5-and 2-ls p/2 pulses, 10-and 5-s relaxation delays, spinning rates of 6 and 10 kHz, and 400 and 360 scans.…”

“…MAS NMR experiments were conducted on a Bruker Avance-400 (9.4 T) spectrometer operating at a frequency of 79.4 MHz for 29 Si and 104.3 MHz for 27 Al. The samples were packed into 4-mm zirconium rotors scanned under the following conditions for 29 Si and 27 Al, respectively: 5-and 2-ls p/2 pulses, 10-and 5-s relaxation delays, spinning rates of 6 and 10 kHz, and 400 and 360 scans. Kaolin and AlC 13 Á6H 2 O solutions (d = 91.5 mm and 0 relative to TMS for 29 Si and 27 Al, respectively) were used as external standards for the chemical shifts.…”