Available online at www.sciencedirect.com
Journal of the European Ceramic Society 29 (2009) 1477–1484
Spark plasma sintering of lead phosphovanadate Pb
3
(VO
4
)
1.6
(PO
4
)
0.4
L. Campayo
a,∗
, S. Le Gallet
b
, Yu. Grin
c
, E. Courtois
a
, F. Bernard
b
, F. Bart
a
a
CEA Marcoule, DTCD/SECM/LDMC, BP 17171, 30207 Bagnols sur Ceze Cedex, France
b
Institut Carnot de Bourgogne, UMR 5209 CNRS-UB, 9 Av. Alain Savary, BP 47870, 210780 Dijon Cedex, France
c
Max-Planck-Institut für Chemische Physik fester Stoffe Nötnitzer Strasse 40, 01187 Dresden, Germany
Received 23 July 2008; received in revised form 11 September 2008; accepted 11 September 2008
Available online 26 October 2008
Abstract
Lead phosphovanadates can be used as reactants for the synthesis of iodoapatite. Because of its high chemical durability, iodoapatite has considerable
potential interest for immobilizing radioactive iodine. Iodine-bearing compounds must be synthesized and consolidated at low temperatures to avoid
iodine volatilization. Spark plasma sintering (SPS) thus appears to be a suitable sintering process because of its short processing time. This paper
deals with spark plasma sintering of lead phosphovanadate powder prepared mechanically by attrition and planetary ball milling. The influence of
sintering parameters such as the heating rate, temperature, and holding time on the degree of densification and the microstructure of bulk materials
is discussed. The bulk characteristics were directly correlated with the shrinkage curves. The powder characteristics were determined (grain size
and size distribution, specific area, crystallite size, etc.) to explain the singular sintering behavior of the attrited powder; we also investigated
whether the latter exhibited the same singular behavior during conventional sintering and hot pressing.
© 2008 Elsevier Ltd. All rights reserved.
Keywords: Lead phosphovanadate; Spark plasma sintering; Attrition; Iodine conditioning
1. Introduction
Lead phosphovanadates Pb
3
(VO
4
)
2(1-x)
(PO
4
)
2x
(x = 0 or 0.2)
were used as reactants for synthesizing apatites Pb
10
(VO
4
)
6(1-x)
(PO
4
)
6x
I
2
1
with good water leaching resistance.
2
These
apatites are potentially of interest for immobilizing radioactive
iodine arising from nuclear fuel reprocessing.
2,3
They are syn-
thesized by calcining stoichiometric quantities of lead iodide
and lead phosphovanadate according to the following equation:
3Pb
3
(VO
4
)
2(1-x)
(PO
4
)
2x
+ PbI
2
→ Pb
10
(VO
4
)
6(1-x)
(PO
4
)
6x
I
2
Confined process conditions are necessary to prevent iodine
volatilization above 500
◦
C. For this purpose, additional lead
phosphovanadate was used to form an impermeable jacket
around a 3Pb
3
(VO
4
)
2(1-x)
(PO
4
)
2x
+ PbI
2
core.
4
This requires
closure of the open porosity in the jacket prior to the beginning of
iodine release, which occurs at about 450–500
◦
C (based on ther-
mogravimetric analysis of the resulting iodine apatite
1–5
). This
relative low temperature requires unconventional sintering tech-
∗
Corresponding author.
E-mail address: lionel.campayo@cea.fr (L. Campayo).
niques for densification of the jacket. Previous work on pressure-
less consolidation of attrition-milled Pb
3
(VO
4
)
2(1-x)
(PO
4
)
2x
powder (S
BET
(N
2
) = 7.0 m
2
/g)
6–8
showed that a temperature of
at least 650
◦
C is necessary to exceed a relative density of 92%,
the value above which open porosity is generally considered to
have been eliminated. However, because of a phase transfor-
mation at 100
◦
C for Pb
3
(VO
4
)
2
(P 2
1
/c → R 3m), the pellets
with the composition Pb
3
(VO
4
)
2
remained brittle and this is
why the present study was carried out with lead phosphovana-
date Pb
3
(VO
4
)
1.6
(PO
4
)
0.4
for which the allotropic temperature
is -50
◦
C.
9–11
In addition, to reduce the sintering tempera-
ture while allowing high heating rates, spark plasma sintering
(SPS)
12–14
was found here to be an appropriate tool. This article
aims at describing an experimental investigation of spark plasma
sintering of lead phosphovanadate Pb
3
(VO
4
)
1.6
(PO
4
)
0.4
.
2. Experimental procedures
2.1. Powder synthesis and characterization
Pb
3
(VO
4
)
1.6
(PO
4
)
0.4
powder was obtained by mixing and
calcining the stoichiometric powder mixture of PbO (99.3%
purity, Prolabo, France), V
2
O
5
(99.2% purity, Alfa Aesar,
0955-2219/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jeurceramsoc.2008.09.003