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Thermodynamic information on aqueous nickel species is systematized. The reactions between various species are discussed. The activity – pH diagram for NiII species and the revised potential – pH diagram of Ni – H2O system at 25ºC, 1 bar and a[Ni] = 10–8 mol l–1 are plotted.
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УДК 544.653:544.016:544.313.2.031
THE POTENTIAL pH DIAGRAM FOR Ni H2O SYSTEM
P. A. Nikolaychuk
Chelyabinsk State University, Chelyabinsk, Russia. E-mail: npa@csu.ru
Thermodynamic information on aqueous nickel species is systematized. The
reactions between various species are discussed. The activity pH diagram for
NiII species and the revised potential pH diagram of Ni H2O system at 25ºC, 1
bar and a[Ni] = 108 mol l1 are plotted.
The variants of Pourbaix
diagram for nickel, available in
literature [1–3], don’t correspond
to each other and don’t reflect the
nonstoichiometry of nickel oxide.
This study proposes the revised
version of this diagram.
Nickel oxides form a series
of solid solutions, which can be
treated as a continuous phase
NiOx with variable composition,
1 < x < 2 [4].
Figure 1. The activity pH diagram for NiII species.
Table 1. The standard Gibbs energies of
formation of nickel species.
Compound
o1
f 298
G ,Jmol
Reference
NiOx (s)
2
155 912
367 342
x
x


[46]
Ni2H (s)
11 800
[8]
Ni2+ (aq)
46 400
[3,9]
NiOH+ (aq)
226 300
[3,9]
2
HNiO
(aq)
350 000
[3,9]
(aq)
62 900
[4]
Table 2. The basic chemical and electrochemical equilibria in Ni H2O system.
Electrode reaction
E, V (s. h. e.) or pH of the solution
+2
2
NiOH H Ni H O


+
2
NiOH
Ni
pH 9,856 lg a
a

+
22
HNiO 2H NiOH H O


2
+
HNiO
NiOH
pH 10,030 0,5 lg a
a
 
22
NiO 2H Ni H O


2
Ni
pH 6,319 0,5 lg a
 
+
NiO H NiOH
+
NiOH
pH 2,781 lg a
22
HNiO H NiO H O


2
HNiO
pH 17,270 lg a

2
Ni 2e Ni (fcc)

2
Ni
E 0,240 0,0295 lg a
 
2
NiOH H 2e Ni (fcc)+H O
 

NiOH
E 0,095 0,0295 pH
0,0295 lg a
 

22
HNiO 3H 2e Ni (fcc)+2H O
 

2
HNiO
E 0,644 0,0887 pH
0,0295 lg a
 

22
NiO 2 H 2( 1)e
Ni H O
xxx
x

 
2
2
Ni
0,808 0,674 0,240
Ex1
0,0591 0,0295
pH lg
11
xx
xa
xx
 

 

2
NiO (2 1)H 2( 1)e
NiOH ( 1)H O
xxx
x

   

2
NiOH
0,808 0,674 0,051
E1
0,0295 (2 1) 0,0295
pH lg
11
xx
x
xa
xx
 


 

2
2
HNiO (3 2 )H 2(1 )e
NiO +(2 )H O
x
xx
x
 
 
2
2
HNiO
0,808 0,674 0,648
E1
0,0295 (3 2 ) 0,0295
pH lg
11
xx
x
xa
xx
 

 
 

2
4
2
NiO 2(4 )H 2(3 )e
NiO +(4 )H O
x
xx
x
 
 
2
4
2
NiO
0,808 0,674 5,240
E3
0,0591 (4 ) 0,0295
pH lg
33
xx
x
xa
xx
 


 

+2
2Ni (fcc) H e Ni H

E 0,122 0,0591 pH 
The standard Gibbs energies of formation of nickel species are
listed in Table 1. The expression for
o
f 298
G (NiO )
x
was estimated using
the modified Gorichev’s method [4–7]. Thermodynamic properties of
basic chemical and electrochemical equilibria in system are summarized
in Table 2. Figure 1 presents the predominance diagram of NiII species.
Calculations show that in diluted solutions, when a[Ni] < 107 mol
l1, nickel monoxide NiO isn’t formed and nickel has no passivity
domain in the area of electrochemical stability of water. A phase NiOx
becomes thermodynamically stable above the potentials of oxygen
electrode. The following order of oxidation is possible depending on ion
activities:
lg a[Ni] > 7,085:
Ni2+ (aq) → NiO (s) →
2
HNiO
(aq);
7,085 > lg a[Ni] > 7,244:
Ni2+ (aq) NiOH+(aq) NiO (s)
2
HNiO
(aq);
lg a[Ni] < 7,244:
Ni2+ (aq) → NiOH+(aq) →
2
HNiO
(aq).
Figure 2. The potential pH diagram for Ni H2O system.
The revised potential pH diagram of Ni H2O system at 25ºC, 1
bar and a[Ni] = 108 mol l1 is presented at Figure 2. Dashed lines
represent the hydrogen and oxygen electrodes and border the domain of
electrochemical stability of water at atmospheric conditions.
Nickel can be electrochemically reduced to nickel hydride Ni2H
[6], however, the domain of its thermodynamic stability lies outside the
area of electrochemical stability of water.
The corrosion properties of nickel are strongly determined by the
concentration of ionic speices in solution. In concentrated solutions
nickel can be passivated by formation of nickel monoxide and higher
nickel oxides. Contrary, in diluted solutions the domain of stability of
the oxide phases vanishes and nickel becomes very vulnerable to
corrosion.
REFERENCES:
1. Atlas of Eh-pH diagrams: Intercomparison of thermodynamic databases. Open
file report 419. National Institute of Advanced Industrial Science and
Technology, 2005.
2. Brookins, D. G. Eh-pH diagrams for geochemistry. Berlin: Springer, 1987.
3. Schweitzer, G. K., Pesterfield, L. L. The aqueous chemistry of the elements.
Oxford: Oxford University Press, 2010.
4. Tyurin, A. G. Termodinamika khimicheskoy I elektrokhimicheskoy
ustoychivisti tvyordykh splavov zheleza, khroma i nikelya [Thermodynamics of
chemical and electrochemical stability of solid alloys of iron, chromium and
nickel]. Chelyabinsk: Publishing House of Chelyabinsk State University, 2011 [In
Russian].
5. Nikolaychuk, P. A., Tyurin, A. G. Thermodynamics of chemical and
electrochemical stability of copper-nickel alloys. Physical Chemistry of Surfaces
and Protection of Metals, 2012. Vol. 48. No. 4. P. 462 476.
6. Nikolaychuk, P. A., Tyurin, A. G. Thermodynamic assessment of chemical and
electrochemical stability of nickel silicon system alloys. Corrosion Science,
2013. Vol. 73. P. 237 244.
7. Nikolaychuk, P. A., Tyurin, A. G. Method of estimating the standard Gibbs
energies of formation of binary compounds. Abstracts of the XVIII International
Conference on Chemical Thermodynamics in Russia (RCCT-2011). Vol. 2.
Samara: Samara State Technical University, 2011. P. 16 17.
8. Baranowski, B., Bocheńska, K. The Free Energy and Entropy of Formation of
Nickel Hydride. Zeitschrift für Physikalishe Chemie Neue Folge, 1965. Bd. 45.
Heft 3 4. S. 140 152.
9. Wagman, D. D. et al. The NBS tables of chemical thermodynamic properties.
Selected values for inorganic and C1 and C2 organic substances in SI units. Journal
of Physical and Chemical Reference Data, 1982. Vol. 11. Suppl. 2.
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Book
Most fields of science, applied science, engineering, and technology deal with solutions in water. This volume is a comprehensive treatment of the aqueous solution chemistry of all the elements. The information on each element is centered around an E-pH diagram which is a novel aid to understanding. The contents are especially pertinent to agriculture, analytical chemistry, biochemistry, biology, biomedical science and engineering, chemical engineering, geochemistry, inorganic chemistry, environmental science and engineering, food science, materials science, mining engineering, metallurgy, nuclear science and engineering, nutrition, plant science, safety, and toxicology.
Chapter
The Eh-pH diagram for scandium species is shown in Fig. 64. The thermodynamic data for important scandium species are given in Table 49.
Termodinamika khimicheskoy I elektrokhimicheskoy ustoychivisti tvyordykh splavov zheleza, khroma i nikelya [Thermodynamics of chemical and electrochemical stability of solid alloys of iron
  • A G Tyurin
Tyurin, A. G. Termodinamika khimicheskoy I elektrokhimicheskoy ustoychivisti tvyordykh splavov zheleza, khroma i nikelya [Thermodynamics of chemical and electrochemical stability of solid alloys of iron, chromium and nickel]. Chelyabinsk: Publishing House of Chelyabinsk State University, 2011 [In Russian].
The Free Energy and Entropy of Formation of Nickel Hydride. Zeitschrift für Physikalishe Chemie Neue Folge
  • B Baranowski
  • K Bocheńska
Baranowski, B., Bocheńska, K. The Free Energy and Entropy of Formation of Nickel Hydride. Zeitschrift für Physikalishe Chemie Neue Folge, 1965. Bd. 45. Heft 3 -4. S. 140 -152.