Crystallization of barium magnesium phosphate glasses determined by differential thermal analysis and X-rays diffraction

The scope of this work is to determine the crystalline phases of devitrified barium magnesium phosphate glasses and the glass composition which presents the best resistance to crystallization. Barium magnesium phosphate glasses with composition xMgO center dot (1 - x)(60P(2)O(5) - 40BaO) mol% (x = 0, 0.15, 0.3, 0.4, 0.5, and 0.6) were analyzed by differential thermal analysis (DTA) to evaluate the thermal stability against crystallization, and X-ray diffraction (XRD) to identify the crystalline phases formed after devitrification. The glass transition temperature (T-g) increases as the MgO content increases. The maximum temperature attributed to the crystallization peak in the DTA curve (T-g) increases when x increases in the range 0 <= x <= 0.3, and it decreases for x > 0.3. The most thermally stable glass composition against crystallization is for x = 0.3. After the devitrification, the number of coexisting crystalline phases increases as the MgO content increases. For x = 0.3 there is the coexistence of gamma Ba(PO3)(2) and Ba2MgP4O13 phases for devitrified glasses. The trend of the T-c is explained based on the assumptions of changes in the Mg2+ coordination number and the amphoterical features of MgO. (c) 2008 Elsevier B.V. All rights reserved.