Coulometric Titration Method Research Articles

Oxygen nonstoichiometry, defect chemistry and thermodynamic modeling of donor-doped CaMnO3−δ: Effect of disproportionation of Mn3+ ions in nonstoichiometric manganites

The present study concerns the investigation of the oxygen content in the perovskite-type manganite Ca0.6−уSr0.4HoуMnO3−δ (0 ≤ y ≤ 0.15) as a function of temperature (T) and oxygen partial pressure (pO2) in the gas phase since the oxygen nonstoichiometry (δ) has a significant impact on the physicochemical properties of materials applied in a variety of high-temperature devices. The δ value has been determined using thermogravimetry and coulometric titration methods. The resulting pO2 – T – δ diagrams have been accurately described by the defect chemical equilibrium model, that accounts for the oxidation reaction of Mn3+ to Mn4+ in all of the studied samples. Additionally, for the samples containing holmium, the disproportionation reaction of Mn3+ to Mn2+ and Mn4+ has been considered. This is the first study to demonstrate the distinction in Mn3+ disproportionation reactions in stoichiometric and nonstoichiometric Ca0.6−уSr0.4HoуMnO3−δ manganites, resulting from the discrepancy in oxygen coordination of Mn3+ ions at low and high temperatures. The experimental dependencies δ(T, pO2) have been employed in order to calculate the chemical potential of oxygen (ΔμO) in relation to the standard state. Statistical thermodynamic analysis has yielded equations that describe the relationships between the partial molar enthalpy (ΔhO) and entropy (ΔsO) of oxygen with standard enthalpies and entropies of defect formation reactions, Mn3+ ion concentration, and nonstoichiometry δ. The calculated functions ΔhO(y, δ, T) and ΔsO(y, δ, T) have been shown to exhibit a high degree of correlation with the values of ΔhO and ΔsO obtained from the linear dependencies of ΔμO on T.

Determination of phase equilibria in the CuxZryCr1-ySe2 system by the EMF method

Layered materials ZrSe2, CuZrSe2 and CuCr0.8Zr0.2Se2 were synthesized, and the structure of the obtained compounds was determined. The phase states in CuxZrSe2 and CuxZr0.2Cr0.8Se2 systems were determined by coulometric titration and electromotive force methods. An increase in the potential difference in the electrochemical cells Cu|Cu+|CuxZryCr1-ySe2 upon substituting Zr4+ for Cr3+ (0 < x < 0.5) was also noted. The copper diffusion coefficients for CuZrSe2 and CuCr0.8Zr0.2Se2 were estimated to be 10─9 and 10─10 respectively.

Coulometric method with titratable impurity analysis and mass balance method: convert acidimetric purity to chemical purity for SI-traceable highest standard of qNMR (potassium hydrogen phthalate), and verified by qNMR.

In this study, the coulometric method with titratable impurity analysis and the mass balance method were successfully applied in the quantification of the certified reference material of potassium hydrogen phthalate (KHP) with accurate metrological traceability of chemical purity value (99.983% with an expanded uncertainty of 0.024%, k = 2). In contrast to the general coulometric titration method, the coulometric method with titratable impurity analysis enables the conversion of acidimetric purity to chemical purity: The acidimetric purity was determined by coulometric titration method, and then the impurities that may be titrated as principal components were found as far as possible using various methods and the result of deducting these impurities from the acidimetric purity can be considered as chemical purity. The mass balance method also accounted for all possible types of impurities as much as possible to improve the accuracy of the determined result. The accuracy and reliability of the purity results were subsequently verified by a two-step quantitative nuclear magnetic resonance (qNMR) method. This KHP certified reference material was the first hydrophilic internal standard of qNMR (applied in polar solvents) with an expanded uncertainty lower than 0.03%, which will become a major reference standard in the organic chemistry traceable calibration chain, especially when evaluating hydrophilic organic compounds to obtain purity values with very low uncertainty.

Implementation of the Theoretical Coulometric Titration Curve in the Determination of the Amount of Substance of Potassium Hydrogen Phthalate: the Search for a Better Metrological Approach.

In metrology, the certification of potassium hydrogen phthalate (KHP) as a reference material is made using the potential primary method of coulometric titration. Usually, this titration is performed in three steps at constant current, where two endpoint (EP) times are determined from the nonlinear regression that fits the empirical W-function (eWf) to the experimental data. As an alternative, we propose the implementation of the theoretical coulometric titration curve (TC). The TC allowed us to compute the KHP amount of substance, the influence of CO2 in the system, the acid dissociation constants for carbonic and phthalic acids, assuming that those species are the only acids present during titration, and the EP times. The amount of substance of KHP estimated with the EP time and obtained from the TC was compared with the results of the eWf, and no statistical difference was found, while the amount of substance, when estimated directly as a parameter of the nonlinear regression of the TC, was lower. Therefore, the traditional method finds the total acidity of the dissolution, and our method finds the KHP purity. In addition, the acid dissociation constants for H2CO3 and phthalic acid estimated in this work agreed with the data reported in the literature. Finally, the description of the coulometric system using the theoretical TC has a solid and well-known chemical support that is not present in the eWf; this fact is essential for the uncertainty budget and the scientific support for coulometry as a potential primary method.

Method of Identifying Total Sulfur Content in Coal: Geochemical and Geophysical Logging Data from the Upper Paleozoic in North China.

The research of sulfur content and logging parameters in coal seams is of great significance for accurate mining and efficient utilization of coal. Taking 81 coal samples collected from the Upper Paleozoic in North China as an example, coulometric titration and chemical reagent methods were used to determine the contents of total sulfur and morphological sulfur in coal seams, and correlation analysis and multivariate linear fitting methods were used to analyze the relationship between total sulfur in coal and the shape and peak value of logging curve. The results show that the content of total sulfur in the Upper Paleozoic coal seams ranges from 0.19% to 12.36%. The morphological sulfur in coal is mostly pyrite sulfur, followed by organic sulfur and sulfate sulfur. The logging curves of the deep lateral resistivity log (LLD), natural gamma ray (GR), short-distance gamma gamma (CGS), and spontaneous potential (SP) in coal seams from Shanxi Formation are funnel-shaped, tooth-shaped, box-shaped, and flat-shaped, respectively. The shapes of LLD corresponding to a few coal seams with a sulfur content of less than 3.0% are finger-shaped and bell-shaped, and GR is finger-shaped. The GR, CGS, acoustic (AC), and density (DEN) curves corresponding to Taiyuan Formation coal seams with a total sulfur content more than 3.0% (St,d ≥ 3.0%) are mainly box-shaped, and the LLD curve corresponding to high-sulfur coal seams is mostly tooth-shaped. The LLD, GR, CGS, and AC curves are second only to funnel-shaped, and the DEN curve is tooth-shaped. The LLD, GR, AC, CGS, and DEN curves of coal seams with a total sulfur content less than 3.0% are mainly box-shaped. GR, AC, and DEN curves are next to tooth-shaped, LLD is bell-shaped, and CGS curve is finger-shaped. The total sulfur content in coal has a negative correlation with LLD and CGS values and a positive correlation with GR, AC, DEN,and SP values. The prediction model of total sulfur in coal is established by using a multivariate linear fitting method through geophysical logging parameter values, which can provide a method for comprehensively quantifying the change of total sulfur content in coal seams.

Application of direct and indirect methods for determining the mass fraction of the main component in flotation potassium chloride

The article is devoted to the comparison of two approaches to determining the purity of metal salts on the example of a complex in composition object - flotation potassium chloride. The results of determining the mass fraction of the main component (potassium chloride) in flotation potassium chloride obtained by direct (using the coulometric titration method with correction for anions titrated with the determined chloride ion and an excess of cations) and indirect (according to the scheme 100% minus the amount of impurities with regard to their species) methods. It is shown that direct and indirect methods give well consistent results: (96.08 ± 0.17) % and (96.11 ± 0.12) %, respectively. Also, the measurement results obtained using the standard installations considering the uncertainty are well consistent with the certified value of the mass fraction of potassium chloride (96.11 ± 0.11) %, obtained based on an interlaboratory experiment in laboratories that perform measurements in accordance with GOST 20851.3. The feature of the direct and indirect methods implemented in this work is the construction of a model of the chemical composition of the analysed object based on a priori and experimental data using two basic principles when summing up the content of impurities: the conditions of material balance and the principle of electroneutrality.

Размер и содержание органических частиц в копролитах Aporrectodea caliginosa и Lumbricus rubellus

Размер и содержание органических частиц в копролитах Aporrectodea caliginosa и Lumbricus rubellus

Specific interrelations of magnetic, thermodynamic and structural properties in highly non-stoichiometric PrBaMnFeO6−δ double perovskite

The complex oxide PrBaMnFeO6−δ (PBMF) was successfully synthesized through the organo-metallic precursor’s combustion. At high temperatures the obtained perovskite was shown to crystallize either in cubic or in tetragonal phase depending on external conditions applied. Magnetic studies additionally confirmed the significant difference of these phases. The coulometric titration method was carefully implemented in order to define the equilibrium values of oxygen content in PBMF as a function of oxygen partial pressure in a 973–1223 K temperature region. The obtained data revealed the existence of the transitory area between cubic and tetragonal phases enabling their mutual presence in a narrow range of oxygen partial pressures. The comprehensive analysis of defect structure was carried out by the development of independent thermodynamic models involving different sets of defect formation processes. As a result, the defect structure of the tetragonal phase was shown to be governed by averaged B-site cation reduction and oxygen disordering while independent iron and manganese reduction reactions occur to be dominant in the highly-symmetric cubic oxide. Based on the obtained data the equilibrium concentrations of point defects, as well as thermodynamic functions of weakly-bonded oxygen were calculated. Defect concentrations determined were further used to explain chemical deformation of manganites studied which revealed a positive impact of iron doping on lattice expansion of PBMF at reduction. A combination of elevated stability of the reduced phase and high values of stored heat compared to analogous oxides suggests PBMF can be considered as perspective oxygen and energy storage material.

Determination of phenolic compounds in medicinal preparations by galvanostatic coulometry

In this work, the possibility of using reactions of electrogenerated titrants with phenolic compounds was studied and a method for their coulometric determination in medicaments by galvanostatic coulometry was developed. The research objects were: rutin, salicylic acid and drugs containing phenolic compounds such as «Ascorutin», «Salicylic Paste» and «Salicylic Ointment» of Russian manufacture. Electrogenerated halogens (Cl2, Br2 and I2) and hexacyanoferrate(III)-ions were used as titrants. It was found that for the quantitative determination of phenolic acids, the optimal reagent is electrogenerated bromine, for rutin - electrogenerated bromine and iodine, and for ascorbic acid - any of the studied electrogenerated titrants (Cl2, Br2, I2 and [Fe(CN)6]3-). The correct definition was checked by the «entered-found» method, the error does not exceed 2%. As experimental studies have shown, our method of coulometric titration with electrogenated bromine and iodine is characterized by good reproducibility of results, expression, accuracy and can be used to determine phenolic compounds in drugs, for example, «Ascorutin» tablets. It should be noted that by our procedure it is possible to determine the spectrum of phenol-containing compounds (rutin, ascorbic and salicylic acids) in drugs without their preliminary separation. Therefore, the coulometric method using electrogenerated titrants can be recommended for the determination of salicylic, ascorbic acids and rutin in dosage forms. The proposed method is accurate and eliminates the experiment error in comparison with the Pharmacopoeic method.

(Invited) Oxygen Defects in Oxide-Based Lithium Ion Battery Cathodes: Formation and Influences on Electrochemical Properties

IntroductionDemands on high energy density batteries increase to exploit renewable energies efficiently and develop zero-emission vehicles [1]. Among technological issues for next-generation batteries, we focus on the development of cathode active materials. So far, oxide-based cathode materials have been used in lithium ion batteries because of their excellent electrochemical properties. However, the formation of oxygen defects like oxygen vacancy is inevitable in oxides. There are two important motivations for the study of oxygen defect formation in oxide-based cathodes, one is the safety of batteries and the other is the battery performance. For the safety, it was reported that the reaction between organic liquid electrolytes and released oxygen from oxide-based cathodes is exothermic and cause abnormal heat generation [2]. To prevent catastrophic thermal runaway of battery systems, understanding oxygen release mechanism is important. For the influence on battery performance, it was reported that preliminary reduction treatments for Li-rich cathodes improved capacity, rate capability and capacity retention [3]. To establish the guideline for the oxygen defect engineering for advanced battery materials, it is necessary to understand influences of oxygen defects on electrochemical properties. In the presentation, oxygen vacancy formation behavior in oxide-based cathodes and influences of oxygen vacancy on battery performances are discussed.ExperimentalLi1.2Mn0.6Ni0.2O2 and Li1.2Ni0.13Co0.13Mn0.54O2 were synthesized by solid state reaction of carbonate precursors and LiOH·H2O. The oxygen vacancy formation was evaluated by thermogravimetry and the coulometric titration using yttria stabilized zirconia. The absolute oxygen content of the sample was determined by iodometric titration. Samples with different oxygen vacancy concentration were also prepared by the coulometric titration method. Influences of oxygen vacancy on crystal and electronic structures were evaluated by X-ray diffraction (XRD) and soft X-ray absorption spectroscopy (XAS). Charge/discharge measurements were performed on the pristine and the oxygen-deficient cathodes.Results and discussionFigure 1 shows the variation of the oxygen content in Li1.2Mn0.6Ni0.2O2 and Li1.2Ni0.13Co0.13Mn0.54O2. In the figure, the vertical axis, O/M, represents the molar ratio of oxygen in and metal components (Li, Ni, Co and Mn) in the target material, meaning that O/M = 1 represents the oxygen stoichiometric composition for Li1.2Mn0.6Ni0.2O2 and Li1.2Ni0.13Co0.13Mn0.54O2, and the horizontal axis represents the equilibrium P(O2) for each oxygen content. With decreasing O/M, P(O2) decreased and reached a constant value regardless of the relative oxygen content. The oxygen nonstoichiometric data in Figure 1 can be roughly classified into two regions depending on the slope of the curve. In the higher P(O2) region where the O/M vs. log P(O2) curve showed a certain slope, meaning both oxygen content and P(O2) changes simultaneously. In the lower P(O2) region, on the other hand, P(O2) is almost invariant regardless of O/M. The high P(O2) region is the oxygen deficient nonstoichiometry region where the oxygen vacancies were randomly distributed in the oxide-based cathodes. On the contrary, the low P(O2) region is the multiphase co-existing region where the sample is decomposed by the electrochemical oxygen extraction and co-exist with the decomposition phases. In this case, the equilibrium P(O2) is fixed with that of the multiphase co-existing state regardless of apparent O/M. The reduction stability of Li1.2Mn0.6Ni0.2O2 and Li1.2Ni0.13Co0.13Mn0.54O2 were also confirmed by XRD. The reduction stability limit of Li1.2Mn0.6Ni0.2O2 and Li1.2Ni0.13Co0.13Mn0.54O2 were log(P(O2)/bar) = -17.7 and -20.7, respectively. From these evaluations, it can be concluded that Li1.2Mn0.6Ni0.2O2 and Li1.2Ni0.13Co0.13Mn0.54O2 can accept oxygen vacancy up to about 2 mol% and about 3 mol%, respectively. The results of XRD, XAS and battery tests will be shown in the presentation, and influences of oxygen defects on crystal and electronic structures and electrochemical performance will be discussed.

Determination of water content of crude oil by azeotropic distillation Karl Fischer coulometric titration

The determination of water content in crude oil is important for oil transportation, refining, and trade. However, the sensitivity and accuracy of the conventional azeotropic distillation (AD) method are inadequate. Karl Fischer titration methods may give false high results because of the reducing sulfur compounds in crude oil. The present study developed an azeotropic distillation Karl Fischer coulometric titration (AD-KFCT) method which required a modified instrument and a new calibration procedure. The method was modified to decrease the interference caused by reducing sulfur compounds. A certified reference material for water content in liquid was used to determine the recovery of water mass achieved using the AD-KFCT method. The effect of the sample polarity on the method accuracy was assessed. The relative error and relative standard deviations of the water content in three crude oils containing known amounts of water were -7.5% to 2.9% and 0.4% to 6.0%, respectively. The interference by reducing sulfur compounds was studied. The crude oil containing 1-propanethiol was measured using a sulfur dioxide-free anolyte, and the amount of iodine consumed by the distilled 1-propanethiol was determined. The contribution of 1-propanethiol was then subtracted from the water content measured using the normal Karl Fischer reagent. Finally, the relative error of the modified water content in the crude oil samples containing 1-propanethiol was -4.4% to 0.7%. Therefore, the modified AD-KFCT method is accurate and convenient for crude oil.

Determination of Low Chlorine Content in Organic Compounds and Polymers Using an Expert-006 Coulometer

A method of visual mercurimetric titration of chloride ions is widely used in elemental microanalysis for determination of chlorine content in organic substances after their combustion in an oxygen-filled flask. However, when the chlorine content is less than 0.5%, the mercurimetric method fails to provide sufficient accuracy, and a more sensitive method of chlorine coulometric titration by electrogenerated silver ions appears preferable. We consider the possibility of determining microgram contents of chloride ions in solutions using a digital coulometric analyzer (Expert-006 produced by Econics-Expert (Moscow)) supplemented with an electrolytic cell with silver electrodes. The coulometer was tested in different operating modes to select the optimal electrochemical parameters of ion chloride titration and develop a technique for coulometric determination of chloride ions which in combination with the preliminary burning of the analyzed substances in an oxygen-filled flask provides determination of the residual chlorine in organic matrices at a level of 0.1–0.5%. The proposed technique was used to determine the residual chlorine in a number of polymers. The relative error did not exceed 5% at chlorine concentrations of 0.16–0.28%.

Development of a reference material for the composition of 0.1 m potassium dichromate solution. Certified reference material GSO 10992-2017

This paper describes key stages in the development and investigation of a high-precision certified reference material (CRM) for the composition of potassium dichromate solution. The proposed reference material (RM) exhibits metrological traceability to the units of the International System of Units (SI). Not requiring additional preparation before use, the CRM is convenient for use as a titrant in redox titration. The metrological characteristics of the developed CRM were determined by the direct primary method of coulomet-ric titration using the State Primary Standard GET 176. The interval of permissible certified values of the molar concentration of potassium dichromate in the CRM under study is found to vary from 0.098 mol/dm 3 to 0.102 mol/ dm 3 . The relative expanded uncertainty (k = 2) of the certified value ofpotassium dichromate molar concentration is calculated to be 0.024 %, with relative standard uncertainties caused by long-term and short-term instability each being equal to 0.0044 %. The shelf life of the developed CRM is found to be 1 year, provided that storage conditions are ensured. A procedure for measuring the molar concentration ofpotassium dichromate is described, along with the equipment used. A comprehensive uncertainty budget for the measurements is assembled. The developed CRM is included into the State Register of Certified Reference Materials under the number GSO 10992-2017. The CRM can be used for transferring the mass (molar) concentration unit of a component to RMs and chemical reagents via oxidation-reduction reactions; the verification and calibration of measuring instruments (MI), as well as control of metrological characteristics during MI trials including type approval; MI graduation; validation of measurement procedures; control of measurement results when determining the mass (molar) fraction and mass (molar) concentration of components in liquid and solid substances and materials.

Development and Certification of Formononetin Reference Material for Quality Control of Functional Foods and Botanical Supplements

Background: Formononetin is a common soy isoflavonoid that can be found abundantly in many natural plants. Previous studies have shown that formononetin possesses a variety of activities which can be applied for various medicinal purposes. Certified Reference Materials (CRMs) play a fundamental role in the food, traditional medicine and dietary supplement fields, and can be used for method validation, uncertainty estimation, as well as quality control. Methods: The purity of formononetin was determined by Differential Scanning Calorimetry (DSC), Coulometric Titration (CT) and Mass Balance (MB) methods. Results: This paper reports the sample preparation methodology, homogeneity and stability studies, value assignment, and uncertainty estimation of a new certified reference material of formononetin. DSC, CT and MB methods proved to be sufficiently reliable and accurate for the certification purpose. The purity of the formononetin CRM was therefore found to be 99.40% ± 0.24 % (k = 2) based on the combined value assignments and the expanded uncertainty. Conclusion: This CRM will be a reliable standard for the validation of the analytical methods and for quality assurance/quality control of formononetin and formononetin-related traditional herbs, food products, dietary supplements and pharmaceutical formulations.

Electrochemical behavior of Th(IV) on the bismuth electrode in LiCl–KCl eutectic

The electrochemical behavior of Th(IV) on a bismuth electrode in LiCl–KCl eutectic was investigated by various electrochemical techniques, aiming at in-depth elucidation of basic electrochemical and thermodynamic properties of Th in molten salt. The results of cyclic voltammetry and coulometric titration indicated that the reduction of Th(IV) on a liquid Bi electrode occurred at −0.92 V (vs. Ag/AgCl) and was a one-step process with four electrons transferred. In addition, thermodynamic properties of Th in liquid Bi medium were evaluated by coulometric titration method in the temperature range from 723 to 798 K. The redox peaks of Bi2Th intermetallic compound were detected at −1.13 and −1.05 V, and the corresponding Gibbs free energy of formation was measured by open circuit chronopotentiometry (OCP). Finally, galvanostatic electrolysis (GE) was conducted on a liquid Bi electrode to extract Th from molten salt at 773 K. X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) were applied to characterize the composition and morphology of the products, and revealed the formation of Bi2Th intermetallic compound.

Water content in biodiesel for diesel fuel blends: measurement using centrifuge and coulometric titration method

Biodiesel nowadays is being used as a blend with diesel fuel to promote the renewable fuels. One of the critical parameters of biodiesel is water content, both free and soluble water is covered. Water presence in biodiesel is limited by the specification to prevent fouling in storage and handling facilities and to avoid trouble in fuel system of engine. Currently in Indonesia, the measurement of water in biodiesel use the centrifuge method that measure both of water and sediment content. Refer to diesel fuel specification, water content is measured separately from sediment content. In order to prepare higher biodiesel percentage in diesel blends (up to 30%) as the Government of Indonesia planning in 2020, water content measurement in biodiesel need more accurate method. In this study, we present the measurement of water content in 20 biodiesel samples using 2 methods: the centrifuge and coulometric titration method. The result show that all biodiesel samples having different water content vary from 173.36 ppm to 968.12 ppm, while all water and sediment content from 20 biodiesel samples are mostly nil, only 1 sample has 0.05 vol % water and sediment.

Determination of Trace Amounts of Hydrofluoric Acid in Non-Aqueous Solutions by the Coulometric Titration Method.

For monitoring of trace amounts of hydrofluoric acid in the organic fluorine chemical industry, a facile method for determination of the hydrofluoric acid in an ethanol solution of lithium chloride, by coulometric titration, was proposed. Relying on homemade acid–base coulometric autotitrator, the electrolyte was 0.50 mol·L−1 LiCl ethanol solution and the constant current intensity was 0.2–2 mA. As for the working electrode pair, a platinum plate was used as a working electrode, and a platinum wire was used as an auxiliary electrode. The indicating electrode was the pH composite glass electrode and the titration endpoint was pH 5.50. The results showed that the relative standard deviation was below 2.0%, as the content of the hydrofluoric acid was between 2 μg to 100 μg. The recovery rate was 99.0–102.0%. This proposed route has the advantages of simplicity, convenience, quickness, accuracy, and automation, which can be applied to the accurate determination of trace amounts of hydrofluoric acid, in non-aqueous solutions.

High-precision determination of potassium hydro phthalate content by a method of coulometric titration in a horizontal type of electrochemical cell

The main aim of the work was high-precision determination of potassium hydrophthalate content by coulometric system with horizontal type cell. The coulometric system was developed for functioning of the State primary standards of pH GET 54-2011 and pX GET 171-2011 ions activities in liquid media. The coulometric system is necessary to ensure the procedures for monitoring the purity of chemical reagents used in the production of high-cleaning reference substances, which used as working standards. High-clean substances are used to prepare mixtures and solutions for metrology area, particularly they are used in the State primary standards key comparisons, as well as, to direct transfer of units of quantify characteristics of chemical substances used in the calibration or verification procedures of measuring instruments, in certification of standards, in control of precision of measurement methods.

Determination of low chlorine content in organic compounds and polymers using an «Expert-006» coulometer

A method of visual mercurimetric titration of chloride ions is widely used in elemental microanalysis for determination of chlorine content in organic substances after their combustion in an oxygen-filled flask. However, when chlorine content is less than 0.5%, the mercurimetric method fails to provide essential accuracy, and a more sensitive method of chlorine coulometric titration by electrogenerated silver ions appeared favorable. We consider a possibility of determining the microgram content of chloride-ions in solutions using a digital coulometric analyzer («Expert-006» produced by «Econics-Expert» (Moscow)) supplemented with an electrolytic cell with silver electrodes. The coulometer was tested in different operation modes to select the optimal electrochemical parameters of ion chloride titration and develop a technique for coulometric determination of chloride ions which in combination with the preliminary burning of the analyzed substances in an oxygen-filled flask provides determination of the residual chlorine in organic matrices at a level of 0.1 – 0.5%. The proposed technique was used to determine the residual chlorine in a number of polymers. The relative error did not exceed 5% at chlorine concentrations of 0.16 – 0.28%.

Thermochemical CO2 dissociation using Ce0.8Zr0.15Sc0.05O2-δ

Two-step thermochemical cycle for CO2 splitting has been studied using cerium oxide (CeO2-δ) as a redox material. Since oxygen release capacity of CeO2-δ increases by doping ZrO2, a lot of studies have been conducted on CeO2-ZrO2 solid solutions as state of the art redox materials for this cycle. In this study, further doping of Sc3+ into CeO2-ZrO2 solid solution was attempted with an expectation to increase amount of available oxygen vacancies which could improve redox kinetics. Scandium was chosen since the ionic radius is close to Zr4+and oxygen vacancy is introduced by the aliovalent doping. Oxygen nonstoichiometry of Ce0.8Zr0.15Sc0.05O2-δ was investigated by a coulometric titration method and chemical diffusion coefficient and surface reaction rate constant by an electrical conductivity relaxation method. Oxygen vacancy formation of Ce0.8Zr0.15Sc0.05O2-δ upon reduction was similar to that of Ce0.8Zr0.2O2-δ, while chemical diffusion coefficient in a high oxygen partial pressure region became larger by introducing Sc3+. Those were discussed in correlation with the reaction kinetics in the thermochemical cycle.