Ashmyanskaya, E. I.

Dudkina, E. N.

Ogorodnikova, T. G.

Polyachenok, L. D.

Polyachenok, O. G.

Voitenko, S. I.

BSU Digital Library

 28 
Synthesis  and  thermal  stability  of  lanthanum chloride 
  and  sulfate  lowest  hydrates  
O. G. Polyachenok, T. G. Ogorodnikova, S. I. Voitenko, E. I. Ashmyanskaya,  
E. N. Dudkina, L. D. Polyachenok 
Mogilev State University of Food Technologies, Mogilev, Belarus,  
e-mail: polyachenok@mogilev.by 
Different methods are used for drying air, other gases and organic liquids. Certain ad-
vantages give the methods based on the use of chemical water absorbents, especially anhydrous 
salts, such as chlorides and sulfates often having high hygroscopic properties. It was shown [1] 
that the drying power of these salts depends on their lowest hydrates thermal stability; thus the 
temperature dependence of these hydrates water pressure is necessary to describe the desiccant 
properties of anhydrous salts.  
The aim of this work was to obtain this information for lanthanum chloride and sulfate low-
est hydrates. A derivatographic method with a special vessel having a thin capillary was used to 
determine the decomposition temperature of the lowest hydrates at the atmospheric pressure. 
Then the temperature dependence of water vapor was derived [2] by use of the approximate de-
composition entropy (146,8 ± 4 J/mol·K [3]). This functional dependence (Fig.) is not very pre-
cise, but it is sufficient for the evaluation of drying power of the salts concerned. 
The highest hydrates of these salts (LaCl3∙7H2O and La2(SO4)3∙5H2O) were obtained by 
crystallization from their water solutions. The latter does not liquefy on heating in our condi-
tions, but the chloride melts incongruently at about 90 °С to give a sintered product showing too 
high decomposition temperatures of trihydrate and monohydrate. Therefore the lower hydrate 
LaCl3∙3H2O was obtained with a method of controlled isothermal drying at the temperature 80 
°С. This intermediate hydrate shows no liquefying on heating and thus the minimal kinetic inhi-
bition of the decomposition process is achieved.  
 
Fig. Water pressure of hydrates:LaCl3 tri- (1) and mono-(2), La2(SO4)3 penta- (3) and mono- (4) 
 
References 
1. E.I. Ashmyanskaya, E.N. Dudkina, O.G. Polyachenok, L.D. Polyachenok. Chemical dryers of gases 
and liquids // Int. conf. collected papers. Mogilev: MSU of Kuleshov (2013) 219. 
2. O.G. Polyachenok, T.G. Ogorodnikova et al. Thermodynamics of the lowest hydrates of lanthanum 
chloride and sulfate // Conf. RCTS–14 materials.  Kazan (2014) 2: 243. 
3. O.G. Polyachenok, L.D. Polyachenok. Herald of the MSU of Kuleshov, (2001)  2–3: 126. 


Synthesis and thermal stability of lanthanum chloride  and sulfate lowest hydrates

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Synthesis and thermal stability of lanthanum chloride and sulfate lowest hydrates

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