Interfaces and Surfaces NSF REU Site
Department of Materials Science and Engineering, Clemson University
May-August 2013
PROCESSING CHALLENGES IN WET CHEMICAL SYNTHESIS OF BARIUM OXIDE
K. Tontodonato1, C. Kucera2, J. Furtick2, J. Ballato2, and L. Jacobsohn2
Department of Materials Science & Engineering, Virginia Tech, 24060
2
Center for Optical Materials Science and Engineering Technologies (COMSET) and
Department of Materials Science and Engineering, Clemson University, 29634
1
Introduction: Scintillators are materials that when struck with ionizing radiation, emit light in the visible
spectrum which can then be measured using photomultiplier tubes. Scintillators find application in radiation
detection and measurement. Single crystal materials are typically used due to the demanding property
requirements necessary for these applications, but they are quite costly. Polycrystalline, or ceramic, materials
could provide a cheaper alternative. The objective of this study is to investigate the feasibility of the synthesis of
barium oxide via a wet chemical route followed by calcination for the purpose of subsequent doping of the
precursor solutions with rare earth elements for scintillator applications. The use of a wet chemical method
provides control of purity and doping of the final product; this process is used for other rare earth doped ceramics.
Barium oxide has a band gap of 4.8 eV and a rocksalt cubic structure that could allow for the fabrication of
transparent ceramics. Barium oxide has not attracted attention as a host of luminescent species.
Materials and Methods: Barium nitrate and barium carbonate precipitates were obtained via a wet chemical
route and subsequently calcined under various conditions. An antisolvent crystallization process was used to
form barium nitrate precipitates from a barium nitrate and ammonia water solution with an ethanol antisolvent.
The precipitates were separated by centrifuge, washed once with ethanol, and dried in a desiccator. Barium
nitrate precipitates were calcined at 400°C, 600°C, and 1000°C for 2 hours under oxygen flow. Barium carbonate
precipitates were obtained from solutions of barium nitrate and ammonium bicarbonate. The precipitates were
separated by centrifuge, washed twice with water and twice with ethanol, and dried in a desiccator. These
precipitates were calcined at 850°C and 1000°C for 1 hour in air, and at 1000°C for 12 hours in air.
Results and Discussion: Barium nitrate precipitates calcined at 400°C did not thermally decompose; there was no
weight loss observed in the sample and x-ray diffraction indicated that the sample was still barium nitrate.
Barium nitrate precipitates calcined at 600°C and 1000°C both reacted with the fused silica crucible to form
barium silicates, a result confirmed by x-ray diffraction studies. Figure 1 below is a sample of this data. The
formation of barium silicate is likely due to the production of NOx gases during the decomposition of the nitrate,
which promote interaction with the crucible material. In previous work, barium nitrate precipitates were shown to
also react with platinum foil, alumina crucibles, and zirconia crucibles. Barium carbonate precipitates calcined at
850°C and 1000°C for 1 hour, and 1000°C for 12 hours also did not thermally decompose, as confirmed by x-ray
diffraction. Literature cites the decomposition temperature of barium carbonate as 1300°C. Reaching the
necessary temperature was not feasible in this laboratory setting due to two factors: fused silica crucibles cannot
be used safely above 1200°C, and even though platinum or molybdenum foil could be used to protect another
crucible material, these foils were too expensive to take the risk of a reaction with them.
Interfaces and Surfaces NSF REU Site
Department of Materials Science and Engineering, Clemson University
May-August 2013
Intensity, arbitrary units
Figure 1. X-ray diffraction results (shown in blue)
for barium nitrate precipitates calcined at 1000°C
indicate a reaction with the fused silica crucible,
showing the presence of barium silicates (shown in
red, corresponding to PDF card no. 00-026-1403).
2θ, degrees
Conclusions: In this study, barium nitrate and barium carbonate precipitates were successfully synthesized using
a wet chemical process. Further studies are necessary to determine the proper firing conditions for thermal
decomposition to barium oxide. Due to equipment limitations, these conditions may or may not be feasible in this
lab at this time. Barium nitrate is likely not the best candidate precursor for barium oxide due to production of
NOx gases during its thermal decomposition which promote interaction with any crucible or foil materials;
however, further studies could enable the use of barium carbonate for this purpose due to its less reactive nature.
Future Work: Barium carbonate could be thermally decomposed above 1300°C in an alumina crucible with
molybdenum or platinum foil under nitrogen or inert gas flow. Barium carbonate mixed with carbon black could
also be thermally decomposed at 1100°C in a fused silica crucible in vacuum. An alternative method could be
solution combustion synthesis (SCS) of barium oxide using an organic fuel such as HMT or urea.
Acknowledgements: The authors thank Diane Folz, Jaclyn Schmitt, Laura Hill, and Colin McMillen for their
contributions to this work. This work was supported by the National Science Foundation’s REU program under
grant number 1062873 and the Center for Optical Materials Science and Engineering Technologies (COMSET).
References:
[1] C. Greskovich et al. Annu Rev Mater Sci. 1997. 27 (69-88).
[2] L. Wen et al. Opt Mater. 2006. 29 (239-245).
[3] C. Satterfield et al. AICHE J. 1959. 5 (122-124).
[4] V. Orante-Barrion et al. J Lumin. 2011. 131 (1058-1065).