Structural Origins of Crack Resistance on Magnesium Aluminoborosilicate Glasses Studied by Solid-State NMR

The beneficial effect of magnesium oxide upon the performance of crack-resistant oxide glasses has been explored in a series of aluminoborosilicate glasses with the compositions 60SiO2–(20 – x)Al2O3–xB2O3–20Na2O and 60SiO2–(20 – x)Al2O3–xB2O3–10Na2O–10MgO. The simultaneous presence of both boron and aluminum oxides in these glasses produces a synergetic effect upon crack resistance (CR), whose structural origins are being explored by detailed 11B, 23Na, 27Al, and 29Si single and double resonance solid-state NMR studies. Aluminum is exclusively four-coordinated, whereas boron is found in both three- and four-coordination. Substitution of B2O3 with Al2O3 and Na2O with MgO leads to a dramatic reduction of N4, the fraction of four-coordinate boron, accompanied by an increase in CR. 11B/27Al double resonance NMR studies show only weak interactions between the boron oxide and aluminum oxide components, giving no evidence of the formation of new structural units not already realized in the ternary aluminosilicat...