Untitled

Effects of cation field strength on the structure of aluminoborosilicate glasses: High-resolution 11B, 27Al and 23Na MAS NMR

“…Similar boron coordination number changes were found in a variety of borosilicate, aluminoborate and aluminoborosilicate glasses [3,11,42,54,65]. 17 O NMR studies have shown that NBO in such systems is most commonly bonded to Si, but that some NBO on borons are present in Ca-rich glasses [42,50]. We also note that higher field strength modifier (or 'charge compensating') cations will also help to stabilize the types of bridging oxygens that have the greatest concentration of negative charge, for example [4] Al-O- [4] Al and [4] B-O- [4] B, whose abundances are generally minimized in systems dominated by large, monovalent cations, as seen directly by 17 O NMR [42,66,67].…”

“…17 O NMR studies have shown that NBO in such systems is most commonly bonded to Si, but that some NBO on borons are present in Ca-rich glasses [42,50]. We also note that higher field strength modifier (or 'charge compensating') cations will also help to stabilize the types of bridging oxygens that have the greatest concentration of negative charge, for example [4] Al-O- [4] Al and [4] B-O- [4] B, whose abundances are generally minimized in systems dominated by large, monovalent cations, as seen directly by 17 O NMR [42,66,67]. This effect might tend to stabilize [4] B, a trend opposite of what is seen in most borosilicate systems and in the results presented here.…”

“…Many studies have documented the close relationships between physical properties and structure of boron-containing glasses [11][12][13][14][15][16][17][18]. Extensive efforts have also been made to model the effects of composition on properties [19][20][21], many of which are based on structural speciation reactions [22][23][24][25][26][27].…”

“…As discussed in recent studies that included 17 O NMR, oxygen speciation is closely linked to the network structure [41,43,44]. In a simple silicate melt, NBOs are formed stoichiometrically on addition of modifier oxide to silica (assuming negligible 'free' O 2À ions), as expressed by the structure 'reaction':…”

“…In the types of compositions studied here, most of the NBO are associated with Si instead of with B as shown directly by 17 O NMR [42,50], but a complete thermodynamic formulation would of course include both types of species. At low contents of modifier oxides in boron-rich glasses, these reactions are nearly complete [24,28,29].…”