Solid-state 27Al NMR studies on polycrystalline aluminates of the system CaO-Al2O3

Multiple magnetic field27Al solid-state NMR study of the calcium aluminates CaAl4O7 and CaAl12O19

“…In CA2, Muller et al in 1986 assigned two resonances with C Q s of 6.7 and 13 MHz. 9 However, a very thorough study by Skibsted et al at faster spin rates with multiple fields and analysis of the satellite transitions again revealed two aluminium sites, but with C Q s of 6.25 and 9.55 MHz. 10 Within the quoted errors there is essentially complete agreement between Ref.…”

“…7 Previous 27 Al NMR studies of calcium aluminates have shown complex peak shapes with strongly overlapping resonances. 8 -10 Since the early work, 8,9 there have been great improvements in NMR technology (e.g. higher applied magnetic fields, faster MAS).…”

Application of27Al NMR techniques to structure determination in solids

“…Of partitular note in CaA16010 the two Al(6) sites could be distinguished but the Al(5) site could not be observed and in CaA1407 the large Cq was attributed to some oxygen sites being tri-coordinate [101]. In hydration of calcium aluminates there is a coordination change Al(4) to Al (6).…”

“…For Al(4) Cq and ~/are more sensitive to changes in site symmetry than 6is o With Q1 and Q3 generally giving r/-0 and Cq(Q~ 4) < Cq(Q1,Q2,Q3). Systems studied include LiaO-AI203 [10], CaO-AI203-H2O [58,101,102], BaO-A1203-H20 [103], Y203-A1203 [73], La203-A1203 [104] and CaO-(Eu,La, Y,Pr)203-AI203 [105]. Y4A1209 contains isolated (A1207) 6-groups with two Al(4) connected via a single bridging oxygen and for this unit Cq must be very large as no Al(4) resonance could be observed under MAS.…”

27Al NMR Studies of Aluminosilicate Glasses

“…Q nÀ1 Si conversion [2,4,[84][85][86]. Although early 27 Al NMR studies on crystalline aluminate phases indicated the absence of any correlation between δ iso [4] and the number of BO atoms (n) at the Q Al n tetrahedron [87,88], the data-bank of 27 Al isotropic chemical shifts from phyllosilicate minerals, which comprise sheets of interconnected Q Al 3 (3Si) groups, reveal about 10 ppm higher shifts (typically $ 65-75 ppm) than those of Q Al 4 (4Si) groups ($ 55-70 ppm) in 3D framework structures, such as zeolites [38,41]. Moreover, several MAS NMR studies of Al-bearing aluminate and aluminosilicate glasses manifest weak but consistent 27 Al deshielding effects for increasing network-modifier content of the glass [6,49,60,89].…”