Emf Values Research Articles

High temperature thermodynamic stabilities of RCoO 3 (R=Nd, Sm, Eu, Gd or Dy) using solid oxide-electrolyte emf technique

Solid oxide-electrolyte emf measurements were carried out on the test electrodes Pt, RCoO 3, R 2O 3, CoO (R = Sm, Eu, Gd or Dy) as well as on Pt, Nd 4CO 3O 10, NdCoO 3, CoO and Pt, Nd 4CO 3O 10, Nd 2O 3, CoO against air, Pt as the reference electrode by using a 15 mol% calcia stabilized zirconia tube as the electrolyte in a two compartment cell assembly. These emf values were used to derive the standard change for the reaction (Δ G° R) 1/2R 2O 3(s)+CoO(s)+1/4O 2(g)→RCoO 3(s) A systematic trend in the Δ G R 0 values at 1100 K could be observed for the above reaction as a function of atomic number as well as σ, the distortion from perovskite structure.

Influence of nonionic surfactants on the potentiometric response of ion-selective polymeric membrane electrodes designed for blood electrolyte measurements.

The effect of the nonionic surfactants Brij 35 and Triton X-100 on the selectivity of neutral carrier-based ion-selective electrodes (ISEs) commonly used for measurements of electrolytes in whole blood is investigated. Studies are conducted with plasticized PVC membranes doped with several neutral ionophores commonly employed to prepare clinically useful potassium, calcium, and sodium ISEs. An observed increase in the electrodes' EMF values upon the addition of surfactant to the test solution suggests a change in the ion selectivity of the polymeric membranes in the presence of Brij 35 or Triton X-100. For membranes doped with K(+)-selective valinomycin, the effect of nonionic surfactants is relatively small. However, in the case of calcium-selective membranes prepared with ETH 1001 and ETH 129, nonionic surfactants, especially Triton X-100, decrease the selectivity for calcium over potassium cations by nearly 1 order of magnitude. Such behavior is even more dramatic for sodium-selective membranes, with the degree of surfactant-induced loss of ion selectivity dependent on the specific sodium ionophore employed, the lipophilic tetraphenylborate derivative content of the membrane, and the surfactant type. A detailed theoretical model is presented to explain the effect of nonionic surfactants on the EMF response function of cation-selective polymeric membrane electrodes. Experimental results are in good agreement with theoretical predictions based on known binding constants for ionophores and surfactants with given cations.

Molar Gibbs Energy of Formation of BaMo2O7(s) Using the Solid Oxide Galvanic Cell Method

ΔfG°(BaMo2O7,s,T) has been determined using the emf technique. The cell used was: (−)Pt/(BaMo2O7(s)+BaMoO4(s)+MoO2(s))//CSZ//air (p(O2(g)=21.21 kPa)/Pt(+). The observed emfs in the temperature range 828–985 K could be represented byE=0.7663−4.953×10−4T(±0.001) V. The standard molar Gibbs energy of formation of BaMo2O7(s) was evaluated from emf values and the ΔfG°(T) of BaMoO4(s) and MoO2(s). The corresponding expression is given as ΔfG°(BaMo2O7,s,T)=−2269.7+0.6173T(±5.1) kJ mol−1. Using the required literature values, the ΔfH°(BaMo2O7,s, 298.15 K) was calculated by the second-law method and the corresponding value is −2291.2 kJ mol−1. The present study is the first experimental work for the determination of ΔfG°(BaMo2O7,s,T).

Solid electrolyte HC sensor on gasoline engines

A sensor for detecting CH 4 in exhaust gases from gasoline engines has been constructed from two Pd | YSZ | Au cells, which are attached to each other with their Pd electrodes in the interior side of the assembly. When the sample gases consisting of CH 4, O 2 and H 2O were fed to the sensor element at 750°C, EMF values were generated from the one cell and then compensated by pumping O 2 electrochemically from the other cell. Currents applied to the latter cell linearly increased with CH 4 concentration, but were not influenced by changing O 2 concentration.

Thermodynamic studies on Cs 4U 5O 17(s) and Cs 2U 2O 7(s) by emf and calorimetric measurements

The oxygen potentials over the phase field: Cs 4U 5O 17(s)+Cs 2U 2O 7(s)+Cs 2U 4O 12(s) was determined by measuring the emf values between 1048 and 1206 K using a solid oxide electrolyte galvanic cell. The oxygen potential existing over the phase field for a given temperature can be represented by: Δ μ(O 2) (kJ/mol) (±0.5)=−272.0+0.207 T (K). The differential thermal analysis showed that Cs 4U 5O 17(s) is stable in air up to 1273 K. The molar Gibbs energy formation of Cs 4U 5O 17(s) was calculated from the above oxygen potentials and can be given by, Δ f G 0 (kJ/mol)±6=−7729+1.681 T (K). The enthalpy measurements on Cs 4U 5O 17(s) and Cs 2U 2O 7(s) were carried out from 368.3 to 905 K and 430 to 852 K respectively, using a high temperature Calvet calorimeter. The enthalpy increments, ( H 0 T − H 0 298), in J/mol for Cs 4U 5O 17(s) and Cs 2U 2O 7(s) can be represented by, H 0 T − H 0 298.15 (Cs 4U 5O 17) kJ/mol±0.9=−188.221+0.518 T (K)+0.433×10 −3 T 2 (K)−2.052×10 −5 T 3 (K) (368 to 905 K) and H 0 T − H 0 298.15 (Cs 2U 2O 7) kJ/mol±0.5=−164.210+0.390 T (K)+0.104×10 −4 T 2 (K)+0.140×10 5(1/ T (K)) (411 to 860 K). The thermal properties of Cs 4U 5O 17(s) and Cs 2U 2O 7(s) were derived from the experimental values. The enthalpy of formation of (Cs 4U 5O 17, s) at 298.15 K was calculated by the second law method and is: Δ f H 0 298.15=−7645.0±4.2 kJ/mol.

Thermodynamic stabilities of Cs 2CrO 4(β), Cs 3CrO 4 and M 2Cr 2O 7(l) (where M = Na, K or Cs) by solid electrolyte emf method

The emf of the galvanic cells with Pt, Cs 2CrO 4 (α or β)|Cr 2O 3|Cs 3CrO 4 (cell I) and Pt, s 2CrO 4(β)|Cr 2O 3|Cs 2Cr 2O 7(l) (cell II) against air|Pt reference electrode using 15 mol% calcia stabilized zirconia as the electrolyte were measured to be E I(a)(mV) = (1345.88 ± 3.68) − (0.53174 ± 0.03376) T(K); (860–967 K) E I(b) (mV) = (1266.47 ± 1.50) − (0.45345 ± 0.04351) T(K); (1052–1097 K) E II (mV) = (344.42 ± 1.84) − (0.25715 ± 0.0079) T(K); (1025–1189 K). Using the literature data for the standard Gibbs energies of formation of α-Cs 2CrO 4 and Cr 2O 3 together with the above numerical expressions for the emf values of cell I, the transition temperature and the standard enthalpy of α-to-β phase transformation in Cs 2CrO 4 were found to be 1014 K and 12.8 kJ mol −1. In addition, the Δ G f 0 (Cs 3CrO 4) was derived to be as follows: (Δ G f 0 (Cs 3CrO 4) ± 2.0) (kJ mol −1 = −1531.72 + 0.38044 T(K). The emf results from cell II led to the expression (Δ G f 0 (Cs 2Cr 2O 7,1 ± 3.35) (kJ mol −1) = − 2066.47 + 0.55062 T(K). By making emf measurements on galvanic cells with Pt, M 2CrO 4 (β)|Cr 2O 3|M 2Cr 2O 7 (l) (where M = Na or K) against air|Pt as the reference electro configuration identical with cell II, the following expressions for Δ G f 0 of M 2Cr 2O 7(l) were derived. (Δ G f 0(Na 2Cr 2O 7,1 ± 2.0) (kJ mol −1) = −1942.68 + 0.51289 T(K), (Δ G f 0(K 2Cr 2O 7,1 ± 2.5) (kJ mol −1) = −2037.35 + 0.5406 T(K). The third law treatment of the emf data on cells I and II yielded the values of −1549.8 ± 1.4 kJ mol −1 and −2108 ± 4 kJ mol −1 r for the standard enthalpies of formation, Δ H f298 0 of Cs 3CrO 4(s) and Cs 2Cr 2O 7(s).

Obtaining High Output in an Electromagnetic Tachometer

Electromagnetic tachometers (EMTs) are used with products from many different industries. Evaluation of their performance requires magnetic field analysis. We simulated the electromotive force (emf) dependence on the yoke in circular cone shape and the thickness of the cylindrical permanent magnet, using the simpler emf calculation method with the finite element method. As a result, the value of emf/ (coil turns) in this simulation was 380% of that for the current yoke shape. Next, we compared the emf of an Al-Ni-Co magnet with that of a Sm-Co magnet. For the current magnet thickness (12 mm), the emf values of the magnets were close. For smaller magnet thicknesses, (3-9 mm), however the emf of the Sm-Co magnet was higher than that of the Al-Ni-Co magnet Therefore, EMTs can be made smaller and with higher emf than current models.

Suspension effect in gels in view of its new concept

The suspension effect (SE) observed in potentiometric measurements in gels is in accordance with the suspension effects measured in heterogeneous suspensions. The SE depends on processes at the indicator electrode (PWSE) and on the consequences of the imperfection of the reference electrode (OSE). Together, these represent the originally defined suspension effect (ODSE). The PWSE is considered to be due to the change of the potential forming mechanism of the indicator electrode in the real solution (simple electrode) compared to the different one in a suspension or a sediment (double electrode). The PWSE, expressed as a change of voltage, has only small values, whether measured in organic or inorganic gels. OSE values (as voltage changes) are greater but still several times smaller than in the suspensions of ion exchangers. OSE were obtained from the Donnan emf, measured according to the common practice, neglecting the junction potential of the sce immersed in the equilibrated supernatant solution. In this case the Donnan emf is identical with the “anomalous liquid junction” potential, which in our SE concept is considered as the potential of the “leaky membrane”. The Donnan potential at the equilibrium solution/sediment interface is regarded as negligible or zero. This is argued from the negligible Donnan emf values obtained when the “anomalous liquid junction” is destroyed by agitation of the sce salt bridge, immersed in the sediment of the Donnan cell. From this point of view some recent opinions declaring the Donnan potential to be the main contributor to the SE are discussed. Another mode of Donnan emf measurement, specified by the reversed flow of KCl solution in sce salt bridges, shows zero voltage values. A detailed galvanic cell diagram must be used for a valid unambiguous interpretation of these voltage values.

Preparation of iridium clusters by MOCVD and their electrochemical properties

Iridium-carbon (Ir-C) cluster films were prepared by metal organic chemical vapor deposition (MOCVD) using an acetylacetonate precursor. The Ir-C cluster films consist of Ir clusters (1 to 3 nm in diameter) and amorphous carbon layers which surround each Ir cluster. The Ir-C cluster films had excellent electrochemical performance as a reversible electrode for zirconia solid electrolyte particularly at low temperatures. The electrode/electrolyte interface conductivity of the Ir-C cluster films was about 100 times greater than that for other conventional platinum electrodes below 773 K. The emf values of the oxygen cell constructed from the Ir-C cluster film electrodes and zirconia electrolytes showed the Nemstian theoretical values even at 573 K.

Solid state galvanic cell studies of interdiffusion between NiO and CoO-doped MgO

In the present work, interdiffusion between NiO and CoO-doped MgO has been investigated by the solid state galvanic cell method in the temperature range 1273–1439 K. The compositional as well as temperature effects of doping on the rate of interdissolution were examined during the measurements. Evaluation of the interdiffusivity data from the cell EMF values required a knowledge of the activity of NiO in the ternary oxide system CoOMgONiO. An assessment of the thermodynamics of this system was made from the literature data on the relevant binary systems using a two sublattice model. From the EMF values and the thermodynamic information, the interdiffusivities were calculated using a theoretical model developed in the division earlier. The results indicate that, at low concentrations of the dopant, the changes in the interdiffusivities are not significant. On the other hand, at 10 mol% CoO in the starting CoOMgO solid solution in contact with 50 mol% NiO, an increase in the rate of diffusion was noticed.

1000 h stability test of the Au/Pd thermocouple at 1000 °C

A newly developed Au/Pd thermocouple has shown very high reproducibility and good immersion characteristics. A stability test of the Au/Pd thermocouple has been conducted for 1000 h at 1000 °C in air to assess its suitability for practical application. Two thermocouples from two manufacturers were fabricated and their emf values were checked in a silver freezing-point cell before and after the soaking at 1000 °C. It was found that the high-temperature stability of the Au/Pd thermocouple is within ±30 mK (2σ) throughout the test time. This result implies that the Au/Pd thermocouple possesses characteristics which may make it suitable for use as a secondary high-temperature thermometer in industry.

Measurements of standard Gibbs energies of formation of Sb 2O 3, MgSb 2O 4 and Ca 4Sb 2O 7 by an EMF method

Magnesium and calcium antimonites, which can coexist with MgO and CaO, respectively, were synthesized by a phase-equilibration technique and identified by X-ray diffraction to be MgSb 2O 4 and Ca 4Sb 2O 7. To determine the standard Gibbs energies of formation of those antimonites, emf values of the following galvanic cells have been measured: Pt, Re/Sb (s,ℓ), Sb 2O 3(s,ℓ)/ZrO 2 + CaO(or Y 2O 3)/air, Pt Pt, Re/Sb (ℓ), MgSb 2O 4(s), MgO (s)/ZrO 2 + CaO/air, Pt Pt, Re/Sb (ℓ), Ca 4Sb 2O 7(s), CaO(s)/ZrO 2 + CaO/air, Pt. The following free energies of formation were determined: Δ G 0/kJmor −1 ±0.4 = −687.7+0.2425 T (773-904K), for 2 Sb(s) + 3/2 O 2(g) = Sb 2O 3(s) Δ G 0/kJmor −1 ±0.3 = −730.2+0.2895 T (904-929K), for 2 Sb(ℓ) + 3/2 O 2(g) = Sb 2O 3(s) Δ G 0/kJmor −1 ±0.2 = −683.1+0.2385 T (929-1095K),for 2 Sb(ℓ) + 3/2 O 2(g) = Sb 2O 3(ℓ) Δ G 0/kJmor −1 ±0.7 = −78.9 + 0.0495 T (929-1101 K), for Sb 2O 3(ℓ) + MgO(s) = MgSb 2O 4(s) Δ G 0/kJmor −1 ±0.7 = −134.7+0.0017 T (972-1101 K), for Sb 2O 3(ℓ) + 4CaO(s) = Ca 4Sb 2O 7(s).

Stabilized zirconia-based sensor using oxide electrode for detection of NO x in high-temperature combustion-exhausts

New type NO x sensors were newly designed by using stabilized zirconia and an oxide sensing electrode. Among the various oxides examined for the sensing electrode, CdMn 2O 4 was found to be the most excellent material. Both planar and tubular devices attached with a sputtered CdMn 2O 4 layer could respond well to NO 2 as well as NO in air at higher temperature, such as 500 °C. The EMF values of the devices were almost linear to the logarithm of NO x concentration with a positive slope for NO 2 and a negative slope for NO. A NO x sensing mechanism involving mixed potential was proposed based on the measurements of polarization curves.

Influence of nonionic surfactants on the potentiometric response of hydrogen ion-selective polymeric membrane electrodes.

The influence of poly(ethylene oxide)-based nonionic surfactants (i.e., Triton X-100 and Brij 35) in the sample phase on the response properties of hydrogen ion-selective polymeric membrane electrodes containing mobile (lipophilic amines) or covalently bound (aminated-poly-(vinyl chloride)) hydrogen ion carriers is reported. In the presence of these nonionic surfactants, membrane electrode response toward interfering cation activity (e.g., Na+) in the sample phase is increased substantially and the pH measuring range shortened. The degree of cation interference for pH measurements is shown to correlate with the basicity of the hydrogen ion carrier doped within the membrane phase. The observed deterioration in selectivity arises from the partitioning of the surfactant into the membrane and concomitant extraction of metal cations by the surfactants in the organic phase. The effect of nonionic surfactants on pH electrodes prepared with aminated-PVC membranes is shown to be more complex, with additional large shifts in EMF values apparently arising from multidentate interactions between the surfactant molecules and the polymeric amine in the membrane, leading to a change in the apparent pKa values for the amine sites. The effects induced by nonionic surfactants on the EMF response function of hydrogen ion-selective polymeric membrane electrodes are modeled, and experimental results are shown to correlate well with theoretical predictions.

Mixed Potential Type NO x Sensor Based on Stabilized Zirconia and Oxide Electrode

A new solid‐state sensor operative at high temperature was designed using stabilized zirconia and an oxide sensing electrode. Among the various oxides examined, was found to be the most excellent material for sensing at 500°C. The EMF values of the sensor were almost linear to the logarithm of concentration with a positive slope for and a negative slope for NO. A, sensing mechanism involving mixed potential was proposed based on the measurements of polarization curves.

Salt Flux and Electromotive Force in Concentration Cells with Asymmetric Ion Exchange Membranes and Ideal 2:1 Electrolytes

The previously proposed Nernst−Planck−Donnan description (J. Phys. Chem. 1996, 100, 7623) of the salt flux and the emf in concentration cells with asymmetric ion exchange membranes is generalized to encompass ideal 2:1 electrolytes (doubly charged cation and singly charged anion). Any point in the membrane may be considered to be in Donnan equilibrium with a given external salt concentration. The profile of this salt concentration through the membrane determines the ion concentrations, the local salt flux, the profile of electric field strength, and the immediate value of the emf. The Donnan potential and ion distribution are found as the unique, positive and real root of a third-degree polynomial. In this paper we focus on the stationary state rather than the initial state. For this purpose, the stationary state nonlinear differential equation for the salt concentration profile is solved numerically by the “shooting method”. We consider salt concentration profiles, ion concentration profiles, and field strength profiles in three different cases: (1) a very weak cation exchange membrane (VWC), (2) a weak anion exchange membrane (WA), and (3) a strong anion exchange membrane (SA). The membranes are asymmetric with spatial dependence of the Nernst distribution coefficient for the salt, of the fixed charge density, and of the ion diffusion coefficients. We study both directions of stationary flow through the membranes. The emf is a functional of the salt concentration profile and is found by numerical integration. The overall behavior of the VWC is almost Fickian with respect to diffusion of salt in both direction, and there is practically no diffusion asymmetry. However, there may be considerable differences in the stationary state emf values for the two directions of diffusion. The WA is close to Fickian for the diffusion in one direction, but strongly non-Fickian with reversed diffusion flux. There is a large diffusion and emf asymmetry for stationary state diffusion in the two directions for large differences of concentration. The order of magnitude found for the calculated stationary state emf asymmetry corresponds to observed values for various membranes. The SA is strongly non-Fickian, but there is practically no diffusion asymmetry. The SA is almost an ideal anion exchange membrane because of the Donnan exclusion from the membrane of the doubly charged cation. Thus, the emf measured with electrodes reversible to the anion should be zero, and so it is found within numerical uncertainty.

Thermodynamic properties of aqueous mixtures of LiCl and Li2SO4 at different temperatures

Emf measurements were made on the cell without liquid junction: Li−ISE LiCl(m1), Li2SO4(m2) Ag/AgCl. The performances of the electrode pairs constructed in our laboratory were tested and exhibited near-Nernstian behavior. The mean activity coefficients of LiCl for the system Li+−Cl−−SO 4 2− −H2O have been investigated by the emf values at temperatures of 0, 15, 35°C and constant total ionic strengths of 0.05, 0.1, 0.5, 1.0, 2.0, 3.0 and 5.0 mol·kg−1. The activity coefficients decrease with increasing temperature and the ionic strength fraction of Li2SO4 in the mixtures. The thermodynamic properties are interpreted by use of Harned's empirical equations and Pitzer's ion interaction approach including the contribution of higher order electrostatic terms. The experimental results obey Harned's rule and are described by using Pitzer equations satisfactorily. The activity coefficients of Li2SO4, the osmotic coefficients and the excess free energies of mixing for the system in the experimental temperature range were reported.

Application of hydrogen sensor using proton conductive ceramics as a solid electrolyte to aluminum casting industries

A galvanic cell type of hydrogen sensor was developed using CaZrO 3-based proton conductor as a solid electrolyte. It was clear that the hydrogen sensor could be used for the accurate determination of hydrogen concentration in molten aluminum alloys. The sensor probe exhibited stable EMF values and a fast response when the hydrogen concentration in the melt was changed. The application of this sensor to the real aluminum foundry was also investigated. This sensor could work very stably even when the flow rate of the liquid metal was very fast. In situ measurement was possible using this sensor anywhere in the casting shop, such as melting furnace, holding furnace, the degassing station, etc.

Determination of Aluminum Concentration in Molten Zinc by the E.M.F. Method Using Zirconia Solid Electrolyte.

Control of the dissolved aluminum concentration in a hot dip galvanizing bath is of great importance for producing galvannealed steel sheets. Since aluminum has much greater affinity for oxygen than zinc, the oxygen potential of Zn-Al-O bath may be determined only by the following equilibrium reaction; Al2O3(s)=2Al(in Zn)+3O(in Zn) when the aluminum concentration in the bath is relatively low. Aluminum sensor based on the emf method using the zirconia solid electrolyte has been devised by utilizing the above equilibrium relation.In this paper, emf measurements have been carried out in Zn-Al-O baths having aluminum concentration of 0.02-0.50 mass% under an air atmosphere by using some of the most appropriate combinations of zirconia solid electrolyte and liquid reference electrode for Zn-O baths.From the analysis of such emf values at temperatures between 450-500°C, the following relationships between aluminum concentration and cell emf for two reference electrodes were obtained; E/mV=57.19 ln[Al]/mass%+506.4, 0.02≤[Al]/mass%≤0.30 (In-In2O3 as ref. electrode)E/mV=68.27 ln[Al]/mass%+270.4, 0.05≤[Al]/mass%≤>0.20 (Zn-ZnO as ref. electrode)The external AC voltage applied on these sensors immediately after immersion into the bath showed to be effective to their responsibility and stability. The emf measurements were also carried out in Zn-Mn-O and Zn-Cr-O baths, respectively, and it has been ascertained that the sensors work much better in these baths, even though the partial oxygen pressure PO2 of the bath is as low as 10-40 Pa at 450°C. The posssibility of the present aluminum sensor has been ascertained experimentally.

Determination of Aluminum Concentration in Molten Zinc by E.M.F. Method Using Calcium Fluoride Solid Electrolyte

Calcium fluoride solid electrolyte has been extensively used in galvanic cells for the measurement of fluorine potential to obtain the activity of alloys and compounds, because the ionic transference number of the electrolyte is about unity even at P F2 /P 0 = 10 -62 above 550°C. So far there were no literature data available for the measurement below 500°C by use of the calcium fluoride solid electrolyte. The purpose of this work is to develop the sensors for the control of aluminum concentration in a hot dip galvanizing bath, which is of industrial importance for producing high quality galvannealed steel sheets. In this report, a trial has been made to measure the fluorine potential in a molten zinc bath artificially equilibrated with ZnF 2 at the temperatures between 450 ∼ 500°C using CaF 2 cells with some kinds of reference electrode. By use of Bi, BiF 3 or Zn, ZnF 2 as the reference electrode, the cells respond quickly and stable emf values which agree fairly well with the literature data are obtained. Subsequently, a trial has been made to measure the fluorine potential in molten Zn-Al baths artificially equilibrated with AlF 3 at the temperatures between 450-500°C using CaF 2 cells with the above reference electrodes. The initial response of these cells after immersion of the cells into these baths is relatively slow. However, once emf of the cell becomes stable, each cell responds quickly to the aluminum concentration change. The response time is not longer than 5 min. From the analysis of such emf measurements, the emf values are found to increase linearly with the logarithm of the aluminum concentration. The possibility of the present method has been ascertained in Zn-Al baths.