Antraptseva, N. M.

Koval, L. B.

Turko, O. V.

BSU Digital Library

 35 
The composition of the products of Co (II) -Zn dihyphosphates heat treatment 
under isothermal conditions  
L. B. Кoval1, N. M. Antraptseva2, O. V. Turko2  
1V.I. Vernadskii Institute of General and Inorganic Chemistry, NAS of Ukraine, Kyiv, Ukraine,  
2National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine  
e-mail: koval@ionc.kiev.ua 
Polymeric phosphates of bivalent metals are widely used as the basis for creating various in-
organic materials. For practical realization of their synthesis by heat treatment of hydrated salts 
the data on their composition, formation temperature and thermal stability of the products of par-
tial and complete dehydration are needed. Such data on the products of Co(II) –Zn dihydrogen 
phosphates heat treatment under isothermal conditions are absent in the literature. Their prepara-
tion is the aim of this work. 
Heat treatment of Со1–хZnх(H2PO4)2 . 2H2O  (0 < x < 1.0) was performed in the range of 
100–350 °С (±5 °С). The sample was held at a predetermined temperature for 0.5, 1.5, 3.0, 5.0 
and 7.0 hours. The total phosphorus content and anionic composition were determined with 
quantifying the percentage of each of the polymeric phosphates in the dehydration products. 
According to our data, at the heat treatment of Со0.5Zn0.5(H2PO4)2.2H2O at 100 °С for 0.5–7 
hours a heterophase mixture of solid and liquid phases containing only monophosphate anion is 
formed. Condensation of the anion in the solid phase begins upon heating up to 150 °С starting a 
crystalline hydrate. It treatment at this temperature for 0.5 hours leads to the formation of 12.6 
wt. % diphosphate and 1.2 wt. % triphosphate. At the increase in the calcination time to 7 hours 
the degree of polycondensation of the phosphate anion (n) rose to 4. The most complex mixture 
of polymeric phosphates with linear structure of the anion (the n value reaches 9) is formed on 
calcining Со0.5Zn0.5(H2PO4)2.2H2O for7 hours at 225°С. 
Phosphate with cyclic anion structure, cyclotetraphosphate (up to 5.8 wt. % in terms of 
P2O5), has been identified  in  the  products  of  Со0.5Zn0.5(H2PO4)2.2H2O  heat  treatment  at 275 
°С for 3 hours. An increase in the calcination time at this temperature to 7 hours results in the 
simplification of the anionic composition of the heat treatment product. It consists of cyclotetra-
phosphate up to 86 % of the total P2O5 content. The solid phase obtained at 350 °С practically 
completely is formed by the condensed phosphate which is СоZnP4O12anhydrous cyclotetra-
phosphate. 
The total percentage of free phosphoric acids in the heat treatment products of 
Со0.5Zn0.5(H2PO4)2.2H2O is maximal, when it is heated for 0.5 hour at 150°С. It presents 8.8 
wt.% of P2O5 in the form of monophosphate acid. Anionic condensation processes begin at pro-
longing the heat treatment to 1.5 hours.  
Besides monophosphate acid, diphosphate acid (up to 6 % of the total P2O5) is formed. The 
similar changes in the anionic composition of the acid component occur at heat treatment in the 
range of 150–185 °С. When the temperature rises to 350 °С the percentage of free phosphoric 
acids decreases. They are absent in the products of thermal treatment of Со0.5Zn0.5(H2PO4)2 . 
2H2O at 350 °С. 
The results obtained make it possible to select the optimum conditions for the synthesis of 
dihydrophosphates Со1–хZnх(H2PO4)2 . 2H2O with different composition and structure of the ani-
on polymeric products of heat treatment. Changing the value of x in the range 0 < x < 1.0 does 
not almost affect on their composition. When increasing the percentage of cobalt(II), the temper-
ature ranges of polymeric products formation shifts by 10–15 °С to higher temperatures. 


The composition of the products of Co (II) -Zn dihyphosphates heat treatment under isothermal conditions

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The composition of the products of Co (II) -Zn dihyphosphates heat treatment under isothermal conditions

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