Galvanic Cell Technique Research Articles

High temperature thermo-chemical properties evolution of NaF-NiF2 system

In Molten Salt Reactor (MSR), Ni based alloys are more suitable for handling of the molten fluoride salts because of formation of corrosive resistive NiF2 layer over the structural material components. A ternary mixture of LiF-NaF-KF (FLiNaK) can be used as coolant salt for transfer of heat from the reactor core. NiF2 layer of the Ni-based alloys shows reactivity towards NaF at reactor operating temperature. NaNiF3(s) is the single complex ternary compound in the NaF-NiF2 system. The compound has been synthesized and characterized. The thermodynamic stability of NaNiF3(s) has been experimentally measured in terms of Gibbs energy of formation using Galvanic cell technique and its measured ΔfG°m(T) was obtained as.ΔfG°m(T) [NaNiF3(s)]/kJ mol−1 = (−1242.9 ± 2.3) + (0.2312 ± 0.0039) × (T/K).The heat capcity and high temperature enthalpy increment was also experimentally measured using DSC and high temperature calorimetric technique, respectively and the values were obtained as.Cp,m(J·mol−1·K−1) = 117.74 + 0.0498 × T −1.07351 × 106/T2(303 ≤ T/K ≤ 828).(HT-H298)(J·mol−1) = −40270.6 + 120.4 × T + 0.0234 × T2+717669.7/T.Effect of oxygen impurity over the stability of the compound has been investigated by calculating the chemical potential diagram of Na-Ni-F-O system. The binary phase diagram of NaF-NiF2 system and the ternary phase diagram of Na-Ni-F2 system has been calculated based on Gibbs energy minimization technique using the experimental thermodynamic data.

Determination of the thermodynamic properties of the Li2CaThF8 in Li-Ca-Th-F system by the solid-state electrochemical cell method

In the present paper, we have reported the standard molar Gibbs energy of formation for Li2CaThF8(s) measured by solid electrolyte galvanic cell technique with CaF2 as solid electrolyte. The heat capacity, Cp, of the compound has been measured using the differential scanning calorimetric technique. Based on the experimentally obtained thermodynamic parameters, thermodynamic functions for Li2CaThF8(s) have been generated.

Thermodynamic studies on lithium ferrites

Thermodynamic studies on ternary oxides of Li–Fe–O systems were carried out using differential scanning calorimetry, Knudsen effusion mass spectrometry, and solid-state electrochemical technique based on fluoride electrolyte. Heat capacities of LiFe 5O 8(s) and LiFeO 2(s) were determined in the temperature range 127–861 K using differential scanning calorimetry. Gibbs energies of formation of LiFe 5O 8(s) and LiFeO 2(s) were determined using Knudsen effusion mass spectrometry and solid-state galvanic cell technique. The combined least squares fits can be represented as Δ f G m o(LiFe 5O 8,s, T)/kJ mol −1 (±6)=−2341+0.6764( T/K) (588≤ T/K≤971) Δ f G m o(LiFeO 2,s, T)/kJ mol −1 (±3)=−708+0.1656( T/K) (569≤ T/K≤1021) The temperature independent term of the above equations represents Δ f H o m( T av) and temperature dependent term represents negative change in entropy of the respective compounds. Thermodynamic analysis shows that LiFe 5O 8(s) is more stable compared to LiFeO 2(s).

High-Temperature Determination of Surface Free Energy of Copper Nanoparticles

The experimental study of the thermodynamic properties of nanoparticles at high temperatures is still a challenge. In this work we report the experimental determination of the surface free energy, γ, of copper nanoparticles in the temperature range from 750 to 950 K. The solid electrolyte galvanic cell technique makes it possible to study the system under strict equilibrium conditions. The experiment was designed to avoid nanoparticle coalescence, which is one of most severe obstacles to the attainment of reliable results. The surface free energy (in J m−2) of 20 nm Cu nanoparticles changes with temperature according to the equation γ = 60.97 − 0.234T + 3.09 × 10−4 T2 − 1.37 × 10−7 T3. At the lowest explored temperature, i.e., 750 K, a surface free energy of 1.70 ± 0.03 J m−2 was found. This value is in good agreement with numerical simulation data for copper nanoparticles previously reported in literature. A theoretical model is also proposed that accounts for the behavior of the surface energy on temperature.

Study of Chromium Activity in the Cr-Fe-N System by Galvanic Cell Method

In the present work, the Cr-Fe-N alloys with different compositions were synthesized by nitriding the Cr-Fe powder mixtures in the purified nitrogen gas (101,325 Pa) at 1473 K for 2 weeks. The phase relationships in the synthesized alloys and the alloys equilibrated at 1173 K were carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The nitrogen content in the alloys equilibrated in the nitrogen gas (101,325 Pa) at 1173 K was analyzed using the inert-gas fusion thermal conductivity (IGFTC) method. The thermodynamic activities of Cr in Fe-Cr-N alloys were measured in the temperature range 973 to 1123 K using the solid-state galvanic cell technique with CaF2 single crystal as the solid electrolyte. Based on the measured EMF values, the chromium activities in the alloys were calculated with respect to pure Cr with bcc structure as the standard state. The effect of nitrogen on Cr activities in the Cr-Fe-N system was examined by comparing the experimental results of the Cr activities in the Cr-Fe and Cr-Fe-C systems.

Analysis of galvanic cell deposition process in preparation of BaMoO4 films

The galvanic cell method has been used for the synthesis of BaMoO4 double oxide film in barium hydroxide aqueous solutions. This method could resolve the repulsion of the electric field on the anode and favor the mass transfer of cations. The crystal growth in the solution is easier compared with the traditional electrochemical deposition with applied power. The deposition process of the galvanic cell technique has been investigated by deposition time, pH, and ion concentration, and the basic features of this method are discussed.

Thermodynamic studies on LnCoO 3(s) (Ln = Dy, Ho) by solid-state electrochemical cells

Ternary oxides, DyCoO 3(s) and HoCoO 3(s) have been synthesized by citrate–nitrate gel combustion method and characterized by X-ray powder diffraction method. The standard molar Gibbs energies of formation of DyCoO 3(s) and HoCoO 3(s) have been measured using solid oxide galvanic cell technique employing yttria-stabilized zirconia (YSZ) and calcia-stabilized zirconia (CSZ) as solid electrolyte tubes, respectively. The standard molar Gibbs energies of formation of DyCoO 3(s) and HoCoO 3(s) were calculated from the measured e.m.f. data and are given as: Δ f G m ° ( DyCo O 3 , s , T ) kJ mo l − 1 ( ± 4 ) = − 1211.3 + 0.2449 ∗ ( T K ) , ( 1013 K ≤ T ≥ 1167 K ) , Δ f G m ° ( HCo O 3 , s , T ) kJ mo l − 1 ( ± 4 ) = − 1237.8 + 0.2590 ∗ ( T K ) . ( 964 K ≤ T ≥ 1102 K ) , A set of self consistent thermodynamic functions for LnCoO 3(s) (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho) has been computed from available experimental data in the literature.

Synergistic use of Knudsen effusion quadrupole mass spectrometry, solid-state galvanic cell and differential scanning calorimetry for thermodynamic studies on lithium aluminates

Three ternary oxides LiAl 5O 8(s), LiAlO 2(s) and Li 5AlO 4(s) in the system Li–Al–O were prepared by solid-state reaction route and characterized by X-ray powder diffraction method. Equilibrium partial pressure of CO 2(g) over the three-phase mixtures {LiAl 5O 8(s)+Li 2CO 3(s)+5Al 2O 3(s)}, {LiAl 5O 8(s)+5LiAlO 2(s)+2Li 2CO 3(s)} and {LiAlO 2(s)+Li 5AlO 4(s)+2Li 2CO 3(s)} were measured using Knudsen effusion quadrupole mass spectrometry (KEQMS). Solid-state galvanic cell technique based on calcium fluoride electrolyte was used to determine the standard molar Gibbs energies of formations of these aluminates. The standard molar Gibbs energies of formation of these three aluminates calculated from KEQMS and galvanic cell measurements were in good agreement. Heat capacities of individual ternary oxides were measured from 127 to 868 K using differential scanning calorimetry. Thermodynamic tables representing the values of Δ f H 0(298.15 K), S 0(298.15 K) S 0( T), C p 0( T), H 0( T), { H 0( T)– H 0(298.15 K)}, G 0( T), Δ f H 0( T), Δ fG 0( T) and free energy function (fef) were constructed using second law analysis and FACTSAGE thermo-chemical database software.

The system Ag-Au-Se: Phase relations below 405 K and determination of standard thermodynamic properties of selenides by solid-state galvanic cell technique

The existence of the only ternary compound, Ag 3 AuSe 2 (fischesserite), in the Ag-Au-Se system was confirmed by solid-state annealing method. The selenium analog of petrovskaite (AgAuS) was not observed under the experimental conditions (in the temperature range of 350-773 K and own vapor pressure). The solid-state reactions 2Ag(cr) + Se(s) = Ag 2 Se(cr) Ag(cr) + Ag 3 AuSe 2 (cr) = 2Ag 2 Se(cr) + Au(cr) 3Ag(cr) + 2AuSe(s) = Ag 3 AuSe 2 (cr) + Au(cr) were studied by the electromotive force (EMF) technique in all solid-state galvanic cells with Ag 4 RbI 5 as a solid electrolyte. The experiments were run in a dry argon gas flow at atmospheric pressure. The following standard thermodynamic properties of the stable phases were determined at 298.15 K and 1 bar (10 5 Pa): ΔfG°(Ag 2 Se, low naumannite) = -49470 (±130) J/mol, S°(Ag 2 Se, low naumannite) = 149.99 (±0.56) J/(K·mol); ΔfG°(Ag 2 Se, high naumannite) = -47430 (±290) J/mol, S°(Ag 2 Se, high naumannite) = 169.01 (±0.78) J/(K·mol); ΔfG°(Ag 3 AuSe 2 , fischesserite) = -86450 (±320) J/mol, S°(Ag 3 AuSe 2 , fischesserite) = 290.80 (±1.26) J/(K·mol); ΔfG°(β-AuSe) = -4110 (±1300) J/mol; S°(β-AuSe) = 75.49 (±3.55) J/(K·mol). The phase transition point for low naumannite-high naumannite was determined at T trs = 405.4 K, with the enthalpy of transition of Δ trs H = -7713 (±550) J/mol.

Thermodynamic studies of pyrrhotite–pyrite equilibria in the Ag–Fe–S system by solid-state galvanic cell technique at 518–723 K and total pressure of 1 atm

The reaction FeS 2(cr) + 2Ag(cr) = ‘FeS’(cr) + Ag 2S(cr) was studied by measuring the temperature dependence of the electromotive force (EMF) of the all-solid-state galvanic cell with common gas space: ( - ) Pt | Ag | AgI | Ag 2 S, ‘ FeS ’ , FeS 2 | Pt ( + ) The measurements were carried out in the flow of argon at atmospheric pressure to prevent oxidation. AgI was used as a solid electrolyte. From the measurements of EMF as a function of temperature, two linear (Δ r C p = 0) trends were obtained, which characterize the equilibrium hexagonal pyrrhotite + pyrite (po + py) and the β–γ first-order phase transition in hexagonal pyrrhotite (Δ trs H m(γ–β) = (4020 ± 200) J mol −1) at (601 ± 2) K. The latter is presumably related to the γ-paramagnetic-β-antiferromagnetic Neel’s transition. For these measurements, the lower temperature limit (518 K) corresponds to the equilibrium sulfides + metallic silver ( E = 0); and the upper temperature limit (723 K) is determined by the upper temperature at which the contribution of electron conductivity to AgI ion conductive properties may be significant. From experimental results of this study and literature data for Ag 2S, the temperature dependence of the gaseous sulfur activity was determined in the following equilibria: pyrite + high-temperature hexagonal pyrrhotite (γ + py), pyrite + low-temperature pyrrhotite (β + py): log a S 2 ( γ + py ) = ( 15.64 ± 0.035 ) - ( 15455 ± 23 ) · T - 1 , ( 601 < T , K < 723 ) log a S 2 ( β + py ) = ( 14.95 ± 0.05 ) - ( 15040 ± 28 ) · T - 1 , ( 518 < T , K < 601 ) The temperature dependence of the FeS activity in hexagonal pyrrhotite ( a FeS po ) calculated for the pyrrhotite–pyrite equilibrium a FeS po ( γ ) = ( 0.528 ± 9.23 × 10 - 3 ) + ( 2.489 × 10 - 7 ± 1.485 × 10 - 5 ) · T , ( 601 < T , K < 723 ) indicates that the value a FeS po = ( 0.528 ± 0.005 ) remains almost constant in the mentioned temperature range. At temperatures below 601 ± 2 K, a FeS po ( β ) and the Fe/S ratio in β-po decreases with decreasing temperature, which also correlates with the appearance of magnetic order. The compositional extremum (on a T– x diagram) where hexagonal pyrrhotite is in equilibrium with pyrite results in a significant and obvious geological consequence. In all the mineral assemblages that contain hexagonal pyrrhotite and pyrite and that have reached equilibrium at a temperature below (601 ± 2) K, the same pyrrhotite composition will correspond to two different temperatures. However, the minimal temperature principle is acceptable for natural parageneses; and in many cases, the pyrrhotite geothermometer can still be very useful.

Activity of titanium in Fe-Cr melts

The activity of titanium in Fe-Cr melts was measured using a galvanic cell technique. By measuring the activity of oxygen in equilibrium with the molten metal and solid titanium oxide, in conjunction with the analysis of the samples for titanium, the activity coefficient of Ti was measured at 1873 K. Oxygen cells, comprised of a thoria-yttria electrolyte with a Cr-Cr2O3 reference electrode and an Al2O3 (ZrO2)-Mo cermet tipped molybdenum lead wire, were used to take the electromotive force (EMF) measurements. The measured values of γ°Ti and eTiCr were 0.018 and 0.1032, respectively.

Thermodynamic investigations of the Mn–Ni–C–N quarternary alloys by solid-state galvanic cell technique

In view of the important applications of carbides and nitrides of transition metals in the hard materials industries, the thermodynamic activities of manganese in Mn–Ni–C–N alloys have been studied by solid-state galvanic cell technique with CaF 2 as the solid electrolyte. The phase compositions and microstructure of various alloys have been analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Nitrogen was introduced into the alloy by equilibrating with N 2 gas. It was established during the experiments that the solubility of nitrogen in the alloys was affected by the carbon content. A (Mn,Ni) 4(N,C) nitride was formed during the nitriding procedure in the alloys. The electromotive force (EMF) measurements were carried out in the temperature range 940–1127 K in order to determine the activities of Mn in the alloys. The activities of manganese were calculated and compared with those of the corresponding Mn–Ni–C ternary alloys.

Thermodynamic investigations of the C-Cr-Fe system by galvanic cell technique

In view of the applications of intermetallic carbides in the hard materials industries, the thermodynamic properties of the C-Cr-Fe system have been measured by the use of the solid-state galvanic cell technique with CaF2 as the solid electrolyte. The thermodynamic activities of chromium have been calculated from the results of the electromotive force (EMF) measurements. For the calculations, pure bcc-Cr was used as the standard state. X-ray diffraction (XRD) and scanning electron microscopy were used to identify the stable phases present in each investigated sample, as well as for establishing the phase compositions. The experimental results obtained were compared with data calculated by the use of the TCFE3 database available with the Thermo-Calc software.

Phase relationships and thermodynamic properties in the Mn-Ni-C system

In the present work, phase relationships in selected phase regions of the Mn-Ni-C system have been investigated at 1073 and 1223 K by use of an equilibration technique. Alloys of Mn-Ni-C were prepared from pure Mn, Ni, and C powders by the powder metallurgy method. The phase identification of the heat-treated samples was carried out by scanning electron microscope (SEM) and transmission electron microscope (TEM). The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). The experimental results show that the site fraction of Ni in the metallic sublattice of the carbides M23C6, M7C3, and M5C2 is quite low and the value is around 0.02 to 0.03. The thermodynamic activities of manganese in 16 different Mn-Ni-C alloys have been studied by solid-state galvanic cell technique with single-crystal CaF2 as the solid electrolyte in the temperature range 940 to 1165 K. The results are discussed in light of the available thermochemical information.

Study of Mn activities in Mn–Ni–C alloys by EMF measurements

The activities of manganese in Mn–Ni–C alloys have been studied by solid-state galvanic cell technique with CaF2 as the solid electrolyte. The measurements of electromotive force (EMF) have been carried out in the temperature range 920–1240 K. The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). It was established that the substitution of Mn by Ni in the (MnNi)23C6 carbide was limited, that the lattice parameter decreased slightly with increase in the Ni content and that a solid solution is formed between Mn and Ni. It was also found that the activity of manganese decreases with increase in the nickel content when the ratio of C/(Mn+C) is less than 8.3 wt.%, and that the negative effect of Ni on the activity of Mn in Mn–Ni–C ternary system decreases as the carbon content increases. However, when the ratio of C/(Mn+C) is equal to 8.3 wt.% or more, the activity of manganese is independent of the nickel content.

An electrochemical investigation of the thermodynamic properties of the NaCl-AlCl3 system at subliquidus temperatures

The phase relations in the NaCl-AlCl3 system ( $$0.3 \leqslant N_{AlCl_3 } \leqslant 0.65$$ ) have been determined in the temperature range from 373 to 623 K by isothermal equilibration, electrical conductivity, and electromotive force measurements. Only one ternary compound, NaAlCl4, was found to be stable, with a melting point of 426 K. The standard Gibbs energy of formation of NaCl and NaAlCl4 has been measured in the temperature range from 423 to 623 K by a novel galvanic cell technique involving in-situ electrogenerated chlorine electrode in the Na/β″-alumina/NaCl, NaAlCl4/Cl2,C and Al/NaCl, NaAlCl4/Cl2,C cells along with the Na/β″-alumina/NaCl,NaAlCl4/Al cell. The Δ f G NaCl( )/o and $$\Delta _f G_{NaAlCl_4 (l)}^ \circ $$ values have been calculated as −412.4+0.095 T (±1) kJ mol−1 and −1117.5+0.2460 T (±2) kJ mol−1, respectively. The standard entropy of NaAlCl4 (s) at 298 K, computed from the results of the study and the auxiliary information from the literature (184 J K−1 mol−1), show good agreement with the estimated JANAF value (188.28 J K−1 mol−1). The enthalpy of formation of NaAlCl4 (l) from NaCl (s) and AlCl3 (s) at 550 K obtained in the present study (−1850 J mol−1) is in agreement with that computed from the heat-capacity measurements (−1910 J mol−1). The present measurements are unique, as a new electrochemical technique is employed in a cell with low-melting sodium chloroaluminate electrolyte to obtain the thermodynamic properties of NaCl and NaAlCl4 at significantly low temperatures. The Gibbs energy of formation of NaCl (s) is, thus, measured at temperatures as low as 423 K by an electrochemical technique for the first time, in this work.

Thermodynamic Properties of Sr‐Doped LaMnO3 Perovskite in the La‐Sr‐Mn‐O System

Thermodynamic properties of Sr‐doped perovskite‐type lanthanum manganites (LSM) were generated by measuring the electromotive force (EMF) of test materials, using the solid galvanic cell technique. The cell consisted of an anode , an electrolyte ( or ) and a cathode . Two types of cells were tested in which type I used a electrolyte and type II used a electrolyte. The activity of SrO substituting into various LSM compositions was calculated using the measured EMF. The Sr content was varied from 0.16 to 0.6 mol, and the temperature of interest varied from 700 to 1000°C. It was found that the SrO activity decreased with increasing temperature (at fixed composition) and increased with increasing Sr content (at fixed temperature). © 1999 The Electrochemical Society. All rights reserved.

Determination of the activities in {xCaO + (1−x)NiO} by solid-electrolyte galvanic cells in the temperature range 1123 K to 1313 K

The activities of CaO and NiO in {xCaO+(1−x)NiO} have been determined in the temperature range 1123 K to 1313 K by the solid-electrolyte galvanic cell technique. The solubility limits of CaO in NiO and of NiO in CaO have been estimated. The solutions exhibit strong positive deviations from ideal behaviour.

Measurement of the standard potential of the Ce/Ce 3 +couple in (lithium chloride + potassium chloride) eutectic melt

The standard electrochemical potential of he Ce/Ce 3 +couple in fused (lithium chloride + potassium chloride) eutectic was measured as a function of temperature in the range 673 K to 773 K by a high-temperature galvanic cell technique using the reversible concentration cell: Ta Ce ∥ x(CeCl 3) + (1 − x)(0.59 LiCl + 0.41 KCl) ∣ y(AgCl) + (1 − y)(0.59 LiCl + 0.41 KCl) ∥Ag, Ta. The molar Gibbs free energy of formation of CeCl 3and the activity coefficient of CeCl 3at infinite dilution of CeCl 3in the (lithium chloride + potassium chloride) eutectic melt were calculated form the e.m.f. results and auxiliary information from the literature. The results obtained agree satisfactorily with the reported values.

An electrochemical investigation of the thermodynamic properties of cerium stannide (CeSn 3) and liquid tincerium alloys

The thermodynamic properties of the intermetallic compound CeSn 3 and the tin-rich liquid tincerium alloys in equilibrium with CeSn 3 were studied by a high-temperature galvanic cell technique using the reversible concentration cell Ta, Ce∥CeCl 3, LiClKCl (eutectic)∥CeSn (two-phase alloy), Ta in the temperature range 723–873 K. The standard Gibbs energy of formation of CeSn 3 from pure solid cerium and pure liquid tin varies with temperature according to the equation ΔG f(CeSn 3) 0 = −260.08 + 0.0476 T (±2) kJ mol −1 The activity coefficients, excess partial molar free energies, enthalpies and entropies of cerium in the saturated liquid alloys have been computed from the e.m.f. data obtained in this study and the data for the solubility of cerium in liquid tin. The activity coefficients of cerium in liquid tin with reference to solid cerium can be expressed as G Ce xs = RT ln τ Ce = −249 + 0.059 T (±2) kJ mol −1