Solid-State ³¹P/²⁷Al and ³¹P/²³Na TRAPDOR NMR Investigations of the Phosphorus Environments in Sodium Aluminophosphate Glasses

Abstract

Solid-state 31 P/ 27 Al and 31 P/ 23 Na TRAPDOR NMR experiments have been used to investigate the spatial distribution of aluminum and sodium cations with respect to the phosphate backbone for a series of sodium aluminophosphate glasses, xAl 2 O 3 ‚50Na 2 O‚ (50-x)P 2 O 5 (0 e x e 17.5). From the 31 P/ 27 Al and 31 P/ 23 Na TRAPDOR data gathered, information about the medium-range order in these glasses was obtained. The expanded data allow for better identification and interpretation of the new resonances observed in the 31 P MAS NMR spectra with the addition of aluminum. The results of these experiments show that the sodium phosphate distribution remains relatively unchanged for the glass series and that the addition of aluminum occurs primarily through the modification of the phosphate tetrahedral backbone in the melt.

The structure of aluminophosphate glasses revisited: Application of modern solid state NMR strategies to determine structural motifs on intermediate length scales

“…Increasing the alumina content of the glass samples leads to a reduction in the amount of six-coordinated aluminium, accompanied by an increase in the fraction of tetrahedrally coordinated aluminium, which constitutes the dominating species at high alumina content. This trend is in good agreement with previous studies of the aluminium speciation in aluminophosphate glasses [6][7][8][9][10]. At low Al 2 O 3 content the phosphate network is mainly formed by Q 1 -species and charge balancing of the aluminophosphate network favors the AlO 6 coordination (as in the KAlP 2 O 7 structure [23]); at higher Al 2 O 3 content, the phosphate network is mainly constituted by isolated orthophosphate species (Q 0 ) and The error on the T g values is estimated to ±10°C.…”

“…For the highest Al 2 O 3 contents (glasses KAlP_17.5 and KAlP_20), two resonances at 3 and À6 ppm are observed. This limited spectral resolution, especially in the spectra of the glass samples of medium alumina content, impedes a detailed analysis of the structural changes in the phosphate network upon alumina incorporation based on the 31 P-MAS NMR spectra alone and we have to resort to heteronuclear correlation techniques (as described in [8,9,11]) to increase the spectral resolution. 27 Al}-CP-HETCOR NMR 31 P{ 27 Al}-CP-HETCOR NMR experiments for glass samples KAlP_5, KAlP_7.5, KAlP_10, KAlP_15 and KAlP_20 are compiled in Fig.…”

“…The incorporation of alumina to the phosphate glasses is supposed to induce some cross-linking between the phosphate chains via the formation of Al-O-P linkages, hence increasing the stiffness of the glass network. Although a large number of papers has been devoted to the structural characterization of aluminophosphate glasses [6][7][8][9][10][11] a concise structural model is still lacking. In the majority of the published data, solid state Nuclear Magnetic Resonance (NMR) spectroscopy has been utilized as the analytical tool.…”

Identification of the hydrate gel phases present in phosphate-modified calcium aluminate binders

“…In studies of Ca-free sodium aluminophosphate glasses, Zhang and Eckert [53] reported 31 P chemical shifts of ~1.6 and -4.6 ppm, which they also assigned to Q 1 units with 0 and 1 bonded aluminium units respectively, in agreement with the results of Lang et al [54].…”

Synthesis of Aluminophosphate and Sodium Aluminophosphate Gels and Glasses

“…Previous investigation on the solution of aluminum lactate and sodium The 31P spectra ( Figure 2) are composed of four species around 0, -7, -12 and -17 ppm, respectively. We will designate the phosphorus species in aluminophosphate materials using a Qn(mAl) notation [20][21][22], where n is the number of P next-nearest-neghbor (NNN) per P tetrahedron and m is the number of Al NNN per P. Note that this notation makes no distinction as to the species of aluminum. It's readily to assign 0 and -7 ppm to free orthophosphate (i.e.…”