Structure and Physical Properties of Strontium Borophosphate Glasses with High
Chemical Durability
Maria D. Anastasopoulou*, Konstantinos C. Vasilopoulos, Demetrios K. Papayannis
and Michael A. Karakassides
Department of Materials Science and Engineering, University of Ioannina, GR-45110 Ioannina, Greece
*[email protected]
Durability of glass or its resistance to weathering and chemical reagents has generally been recognized as one
of the most important features in glass technology and its literature is probably greater than that of any other
property of glass1, 2. Generally, phosphate and borate glasses have poor chemical durability in aqueous solutions.
Therefore the practical applications of these glasses are often limited by their high dissolution rate (DR). The
present work aims to study the structure, density and chemical durability of strontium borophosphate glasses
(SrBP glasses). The combination of the two glass-formers, P2O5 and B2O3 and their effect on the structure and
physical properties of resulting glasses is an intrinsically interesting subject of study. The correlation of
dissolution behavior and density with borophosphate network structure is studied by weight loss and Raman
spectroscopy.
Strontium borophosphate glasses of composition xSrO·(1-x)·[0.68B2O3·0.32P2O5], with 0.40 ≤ x ≤ 0.68,
were prepared using analytical reagent grades of SrCO3, B2O3 and H6NO4P. The batches were melted for 15min
from 1500 to 1600oC depending on the SrO content. The SrBP glasses were obtained by pouring the melts onto a
stainless steel plate and immediately quenched by pressing with another plate. The density of the glass samples,
ρ, was determined at room temperature by the Archimedes Method, with water as the immersion liquid. The
chemical durability of the glasses was evaluated from their dissolution rate in distilled water at 90°C. The glass
samples were put in distilled water for 6 days. The dissolution rate, DR, was calculated from the expression
DR=ΔW / S·t, where ΔW is the weight loss (g), S is the sample area (cm2) before the dissolution test and t is the
dissolution time (min).
Fig.1 shows the Raman spectra of glasses together with the
spectra of two strontium phosphate crystalline compounds,
2SrO∙P2O5 (2:1) and 3SrO∙P2O5 (3:1) having compositions at
x=0.67(pyrophosphate) and 0.75 (orthophosphate) respectively,
and the ab initio theoretical calculated spectrum of Sr2BP2O9unit (a) for comparison purposes. As it is shown, the whole
frequency profile of the SrBP glass series spectra appears to be
more or less a convolution of the corresponding spectra of
strontium borophosphate moieties. This suggests that the glasses
contain mostly structural units (or variations) such as those in the
corresponding crystalline compounds. These spectra exhibit
bands which are mainly attributed to vibrations of ortho (Q0) and
pyro (Q1) phosphate units or to vibrations of the more
complicated borophosphate structural units3-6. Especially the
bands at 1084 cm-1 and 764 cm-1 are assigned to the symmetric
stretching of the P–O- bonds and to the O–P–O bending modes of
the vibrations of the pyrophosphate P2O74- units (Q1), while the
band at 940 cm-1 to the symmetric stretching of the P–O- bonds
of the orthophosphate PO43- units (Q0) and the band at 980cm-1 is
attributed according the ab initio theoretical calculations to
symmetric stretching of the P–O- bonds of Sr2BP2O9- units. It is
also evident that increasing SrO content the borophosphate
network is gradually depolymerized. The bands at 1385 and
1180cm-1 are attributed to B-O- vibrations of triangular borate
Fig.1: Raman spectra of glasses, crystalline units (x=0.68).
compounds (2:1, 3:1) and theoretical (a).
The chemical durability of the studied
glasses is closely associated with their SrO
content.
This
behavior
undoubtedly
corresponds to some changes in the nature of
the bonding in the structural network. The
dissolution rate for these glasses (Fig.2 (a))
steeply increases within the range of x = 45%
mol to 62% mol. The decrease in the
dissolution rate, DR, as the SrO content is
decreased up to 68% mol is accompanied by
an increase in chemical durability (logDR).
This finding provides evidence for the
increasing strength of the glass network due
to the formation of P-O-B bonds. It is
important to notice that the calculated values
Fig.2: (a) Dissolution rate (DR) and (b) density for SrBP glasses.
of chemical durability (logDR) of these SrBP
glasses has a great tendency to approach and reach for high oxide compositions, the chemical durability of the
resistant silicate oxides (~10-7). Fig.2 (b) shows dependence of density by the content of strontium oxide for
SrBP glasses. The observed minimum in density values for 0.48 ≤ x ≤ 0.56 can be attributed to an increase of the
depolymerization degree of borophosphate network, leading us to a less compact structure. By further increase of
the strontium oxide up to 68% mol, density increases again, leading us to a more stable structure.
The structural and physical properties of the SrBP glasses have been studied. Raman spectroscopy results and
ab initio theoretical calculations have revealed the features of the network structure of these glasses which are
correlated with the observed changes in their physical properties. The dissolution rate of glass at 90°C in distilled
water decreases by increases the SrO content up to 68% mol, meaning enhanced chemical durability.
References
[1] Dimbleby, V. and Turner, W. E. S., Glass Tech., 1926, 10, 304±363.
[2] Newton, R. G., The durability of glass - a review. Glass Tech., February 1985, 26, (1).
[3] M.A. Karakassides, A. Saranti, I. Koutselas, J. Non-Cryst. Solids 347(2004) 69.
[4] R.K. Brow, D.R. Tallant, T.M. Sharon, C.C. Phifer, J. Non-Cryst.Solids 191 (1995) 45.
[5] B. Tischendorf, J.U. Otaigbe, J.W. Wiench, M. Pruski, B.C. Sales, J.Non-Cryst. Solids 282 (2001) 147.
[6] L. Koudelka, P. Mosner, J. Non-Cryst. Solids 293 (2001) 635.
Acknowledgements
This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national
funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference
Framework (NSRF) - Research Funding Program: Heracleitus II. Investing in knowledge society through the
European Social Fund.