Phase Transitions in Antimony Oxychloride Glasses
Robin Orman, Diane Holland Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
Alex Hannon ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
Abstract
Introduction
An investigation of the phase transitions of Sb2O3 (senarmontite) and vitreous
Sb2O3:Cl has been carried out using thermal analysis techniques. A glass
transition temperature of 280±6°C has been measured and similarities between
the phase transitions of the two materials are apparent. However, factors such
as atmosphere, particle size, sample age and chlorine content (of the glass)
have also been identified as variables potentially affecting the behaviour of the
systems. Further thermal and structural investigations are planned.
Whilst past attempts to form pure antimony oxide glass by melt-quenching have proven difficult, there has been some
success at forming a chlorine-stabilised specimen [1,2]. Since heavy metal antimony oxychloride glasses have already been
considered for potential use in infra-red transmission [3], and other antimony oxyhalide glasses appear to show similar
optical characteristics [4], further study of the properties of this chlorine-stabilised antimony oxide glass seems justified.
Thermal analysis techniques have been used to examine phase transitions of the material with comparisons drawn to those
of the crystalline Sb2O3 system; further investigations utilising other techniques are ongoing.
Simultaneous differential thermal analysis and thermogravimetric analysis were conducted on crystalline Sb2O3 identified by x-ray
diffraction to be initially in its low-temperature cubic form, senarmontite. Samples were run under air or argon flowing at 250ml/min at
heating rates ranging from 10°C/min to 160°C/min with quartz as a reference material.
Heating
Cooling
Oxidation
Exo
Melting
Quartz
Recrystallisation
Quartz
Exo
10
0
Exo
-10
-20
?
Quartz
O
20 C/min
-30
1
-40
O
40 C/min
2
O
-50
80 C/min
-60
O
120 C/min
160 C/min
Endo
Endo
400
450
500
550
600
650
700
750
500
800
-70
Senarmontite-Valentinite
transition?
O
525
550
575
600
Melting
625
650
675
Endo
550
o
Figure 2 – Differential thermal analysis of Sb2O3 under Argon
at a heating/cooling rate of 10°C/min.
When run under an atmosphere of flowing air (Fig 1),
it was observed that the oxidation of Sb2O3 to Sb2O4
could be suppressed by increasing the heating rate to
reveal an endotherm due to melting; mass loss was
also increased from 6% at 20°C/min to 68% at
160°C/min, as more unoxidised Sb2O3 volatilised.
Thermal analysis under a flowing argon atmosphere allowed a
slower heating rate to be used (Fig 2) revealing a second
endotherm prior to the melting peak, probably from the transition to
the other crystalline phase of Sb2O3, valentinite, which consists of
chains of [SbO3] trigonal pyramids.
650
700
750
O
Temperature ( C)
Figure 1 – Differential thermal analysis of Sb2O3 in
air at various heating rates.
600
-90
800
Temperature ( C)
o
Temperature ( C)
-80
3
500
700
Figure 3 – Simultaneous differential thermal and
thermogravimetric analysis of Sb2O3 under Argon at a
heating rate of 20°C/min.
Further examination at a higher heating rate (Fig 3) resolved
a third endothermic peak in the same region, with
corresponding changes in mass loss of the sample. Peaks 1
and 2 are believed to be either the senarmontite-valentinite
transition followed by valentinite melting, or the melting of
small particulate senarmontite prior to the phase transition
and general melting at peak 3.
Vitreous Sb2O3:Cl
Under Air
Under Argon
A 50g batch was prepared from 50 mol% Sb2O3 (99.6%, Alfa Aesar)
and 50 mol% SbCl3 (99.9+%, Aldrich). A lidded alumina crucible
containing the mixed powders was placed into a furnace preheated to 1000°C, held at temperature for 5-10 minutes until molten
and fuming, then agitated and splat-quenched between two cooled
copper plates.
A sample of the Sb2O3:Cl
glass formed by splatquenching. Energy dispersive x-ray analysis
suggests that the glass
contains 6-18 at.% Cl.
The resulting glass was ~1mm in thickness, pale yellow in colour
and translucent with some evidence of deposits (presumably
chlorine-rich) on or near the surface.
Crystallisation
Exo
Start of
oxidation
Glass
transition
3
1
Endo
2
Sb2O3
Oct'04 Glass
Sep'03 Glass
Quartz
Exo
-Sb2O3 - -Sb2O3
transition
Melting
peaks
Endo
500
525
550
575
600
625
650
% Weight Change
Thermal Analysis of Sb2O3
675
700
O
Temperature ( C)
Figure 5 – Comparison of differential thermal analysis
patterns for Sb2O3 and Sb2O3:Cl glasses at 20°C/min under
Argon.
250
Differential thermal analysis of the newly-made (October 2004) glass
and an older sample (September 2003) was performed under the
same conditions used for the commercial Sb2O3 powder.
The results show (Fig 4) that the onset temperatures of phase
transitions appear to be affected by atmosphere (more specifically,
the presence of oxygen). This relationship was not observed in the
crystalline Sb2O3, where oxidation also began at a higher
temperature.
300
350
400
450
500
550
4
600
650
700
O
Temperature ( C)
Figure 4 – Comparison of differential thermal analysis
patterns at 20°C/min for Sb2O3:Cl glass under different
atmospheres. Peaks 1 & 2 are thought to be the crystalline
phase transition with peaks 3 & 4 corresponding to melting.
Comparisons between the two glasses and senarmontite (Fig 5)
demonstrate that the crystal phase change and melting endotherms
occur both earlier and more widely separated when Sb2O3 is
crystallised from vitreous material. These features may be the result
of factors such as the chlorine content, sample age and particle size
(Table 1). The shapes of the endotherms also indicate that several
features are overlapping one another, suggesting a similar spread of
peaks to those found in Sb2O3.
The glass transition temperatures were determined to be 277±3°C
for the September 2003 glass and 283±3°C for the October 2004
sample. These values were independent of the atmosphere used
for the analysis.
Sample
Mean particle
size / μm
Approx. Cl
content / at.%
Sb2O3
(senarmontite)
4
–
Sb2O3:Cl glass
(Sep ’03)
7.5
8
Sb2O3:Cl glass
(Oct ’04)
15
12
Table 1 – Some physical parameters of the
samples investigated.
References
Conclusions and Further Work
1. J A Johnson, D Holland, J Bland, C E Johnson, M F Thomas, J. Phys.: Condens. Matter 15 (2003), 755-764.
Thermal analysis of the vitreous Sb2O3:Cl system has shown that it has phase transitions
similar to those of crystalline Sb2O3 (senarmontite), although apparently influenced by factors
including the presence of oxygen in the surrounding atmosphere, and potentially particle size,
sample age and chlorine content. Further thermal analysis studies to determine the impact of
these variables is planned, together with Raman and NMR/NQR structural investigations.
2. A C Hannon, R G Orman, D Holland, J. Non-Cryst. Solids (in preparation).
3. M R Sahar, M M Ahmed, D Holland, Inst. Phys. Conf. Ser. 111 (1990), 449-458.
4. B Dubois, H Aomi, J J Videau, J Portier, P Haggenmuller, Mater. Res. Bull. 19 (1984), 1317-1323.