G. Ren et al. / Journal of Alloys and Compounds 467 (2009) 120–123
123
powder dried from LaCl3 aqueous solution at different tempera-
◦
ture and found that the phase at 300 C is simple LaCl3, and from
5
◦
◦
00 C to 800 C the progressive oxidation of LaCl3 to LaOCl
is going on [8]. Here the oxidation temperature of LaCl3 crystal
in air is much lower than that in H2O. This may be caused by
the more active chemical properties of oxygen than water.
In addition, based on the characteristic that LaOCl is not
dissolved in water, six parts of LaCl3 powder were heated to
◦
◦
◦
◦
◦
temperature of 90 C, 135 C, 165 C, 200 C and 230 C in
an atmosphere and then kept at the above temperature for 2 h.
The powders were then dissolved in water, some substance
will deposit from the solution. After being filtered, dried and
weighed, the deposit was proved to be LaOCl phase by XRD
(Fig. 7a) and its mass is proportional to the temperature (Fig. 7b).
It can be found that the lowest temperature at which LaOCl
appears is 135 C, much lower than that we got from Fig. 6.
Fig. 6. XRD patterns of LaCl3 crystals measured at different temperatures.
◦
This means that the oxidation of LaCl3 in air is really much
easier than that in moist atmosphere.
4. Conclusions
Lanthanum chloride is a kind of hygroscopic compound.
XRD pattern proves that there are three or seven crystallized
water molecules in every LaCl3 formula, and LaCl3·3H2O
can transform into LaCl3·7H2O in aqueous solution. With the
increase of temperature, the scheme of dehydration can be
described in four stages: 7 → 6 → 3 → 1 → 0. During crys-
tal growth, transmission loss phenomenon can appear in some
crystals, its cause is related to the oxidation of LaCl3 at high tem-
perature, and the temperature at which the oxidation takes place
in atmosphere is much lower than that at nitrogen atmosphere.
Therefore, the favorite condition for dehydration reaction should
be limited in an atmosphere without oxygen.
Acknowledgement
This work was supported by National Scientific Foundation
of China (NSFC) with number of 50672109.
References
[
[
[
1] O. Guillot-Noel, J.T.M. De Haas, P. Dorenbos, C.W.E. Van Eijk, K. Kramer,
H.U.J. Gudel, J. Lumin. 85 (1999) 21–35.
2] E.V.D. van Loef, P. Dorenbos, C.W.E. van Eijk, K. Kramer, H.U. Gudel,
Trans. Nucl. Sci. 48 (2001) 341–345.
3] K.S. Shah, J. Glodo, M. Klugerman, L. Cirignana, W.W. Moses, S.E.
Dorenzo, M.J. Weber, Nucl. Instrum. Methods Phys. Res. A 505 (2003)
76–81.
[
4] W.M. Higgins, J. Glodo, E. Van Loef, M. Klugerman, T. ZGupta, L. Cirig-
nana, P. Wong, K.S. Shahet, J. Cryst. Growth 287 (2006) 239–242.
5] H. Chen, P. Yang, C. Zhou, C. Jiang, J. Alloys Compd. 449 (2008) 172–175.
6] V.V. Hong, J. Sundstrom, Thermochim. Acta 307 (1997) 37–43.
7] Y. Pei, X. Chen, D. Yao, G. Ren, Radiat. Meas. 42 (2007) 407–412.
8] A. Marsal, E. Rossinyol, F. Bimbela, C. Tellez, J. Coronas, A. Cornet, J.R.
Morante, Sensors and Actuators B 109 (2005) 38–43.
Fig. 7. XRD pattern of LaOCl deposit (a) and its dependence on the temperature
b).
(
[
[
[
[
transform into LaOCl. Chen et al. proposed that this reaction,
LaCl3 + H2O → LaOCl + HCl, will take place at temperature of
◦
3
65 C [5]. Marsal et al. once measured the XRD of the calcined