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Influence of Fluorine and Nitrogen on the IR Transmission of Glasses
C. M. Crowley a and S. Hampshire a ,
a Department of Materials Science and Technology, University of Limerick, Ireland
b Department of Chemical and Environmental Sciences, University of Limerick, Ireland
Clare.Crowley@ul.ie
Abstract
The influence of glass chemistry and firing conditions
on the thermomechanical properties and IR
transmission of aluminosilicate, sialon, fluorinated
aluminosilicate and fluorinated sialon glasses has been
examined. Improvements in the thermomechanical
properties were achieved with increasing nitrogen
content while a concomitant improvement in IR
transmission was achieved under specific firing
conditions.
Introduction
Glass is commonly used as a medium to transmit
infrared (IR) radiation in applications. Glasses,
however, normally contain water impurities in their
atomic structure which are efficient absorbers of IR
radiation leading to energy loss and heat generation in
the glass. Commercial producers of IR glasses
overcome this by employing expensive processes and
ultra pure materials. The incorporation of nitrogen into
rare-earth aluminosilicate glasses has previously been
shown to enhance infrared transmission due to the
reduction in the formation of silanols in the glass
network [1]. However, the production cost of rare-earth
sialon glasses, fired under reducing conditions, is not
commercially viable. In this study the feasibility of
using nitrogen-based glasses to reduce the occurrence
of ‘water’ impurities in alkali-earth sialon glasses has
been examined.
Materials and Methods
Glass compositions
Glass compositions (Figure 1) were prepared using high
purity (99.9 %) reagents which were melted for 1 hr at
1500 - 1600°C under nitrogen at a pressure of 0.1 MPa.
The glass melts were annealed in a muffle furnace at Tg
- 30°C for 1 hr.
0.8
0.6
0.4
0.2
6Ca
0.0 1.0
2+
1.0 0.0
0.0 0.2 0.4 0.6 0.8 1.0
4Al 3+
3Si 4+
Figure 1: Vertical triangular plane of the Janecke
triangular prism for Ca-sialon glasses examined
0.8
0.6
0.4
0.2
173
Materials characterisation
Powder X-ray diffraction (XRD) was performed
between 10 to 70 degrees 2 with a CuKα radiation
source at 35mA, 40kV ( = 1.540566) (Phillips X’Pert
diffractometer) to confirm that the samples were
amorphous. FTIR spectra (Perkin Elmer Spectrum 100)
of the glass slices (thickness = 1.06 ± 0.1 mm; polished
to 1m) were collected between 4000 – 450 cm -1
(resolution = 1 cm -1 , number of scans = 50).
Results
Sialons and fluorinated sialons, with different modifier
cations (Mg, Ca, Sr and Ba) have been produced that
show improved thermomechanical properties, compared
with their oxide/oxyfluoride counterparts, and
improved infrared transmission in the 2.5 – 5 m range
compared to a boro-aluminosilicate standard (Figure 2).
Transmission (%)
100
90
80
70
60
50
40
30
20
3588cm -1
2.8m
10
0
2703 cm
1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
-1
3.7 m
Wavelength (m)
Aluminosilicate standard
Series 6 N5 F1 Al20Ca24
Series 2 N5 F1 Al24Ca20
Figure 2: Comparison of the FTIR transmission of
F1N5 glasses (High purity) and the boro-aluminosilicate
standard (Glass slices 1.06 ± 0.1 mm thickness)
Discussion
For the Ca-oxyfluoronitrides examined there was an
increased incidence of transparent glasses produced
when the Al content = 20 eq.%. Transparency may
therefore be related to the number of bridging oxygens
per tetrahedra (BO/T) as no transparent glasses were
obtained when the BO/T > 3.33 for the base oxide. This
may be related to a shift in Si from Q 3 to Q 4 following
the addition of nitrogen and is currently being examined
by Raman spectroscopy.
References
[1] E. Dolekcekic, M.J. Pomeroy, S. Hampshire (2007)
Structural characterisation of Er–Si–Al–O–N glasses by
Raman spectroscopy. J. European Ceramic Society27(2-3):
893-898.