Molten PbCl2 Research Articles

Efficiency of Electrochemical Methods of Purification and Control over the Oxide Concentration in Halide Melts: PbCl2

The purification of molten salts from admixtures as well as the effective control of admixture concentration has attracted researchers’ interests. In the present paper, the possibility of the electrochemical purification of PbCl2 from PbO and the effective control over the oxide ions concentration in molten PbCl2 is studied at the temperature of 520 °C. The PbCl2 melt with the initial addition of 0.5 wt% of PbO was used as a molten salt sample. The method of potentiostatic electrolysis was used to remove the oxide additions from the melt; the linear and square-wave voltammetry dependencies were recorded, and the melt samples were taken for analysis. Based both on the results of the electrochemical measurements and the analysis of oxygen concentration in the electrolyte, we built linear empirical dependencies of the anode peak current of the oxidation of oxygen-containing electroactive anions on the PbO concentration in the studied melt. We demonstrated that the obtained dependencies may be used for direct electrochemical nondestructive in-situ control over the concentration of PbO dissolved in the PbCl2 melt containing up to 0.5 wt% of PbO. The deep electrochemical purification of the chloride PbCl2 melt from molten oxide (up to 0.044 wt% PbO or to 0.007 wt% of oxygen) was achieved by the potentiostatic electrolysis.

Conductivity of Some Molten Chlorides at Elevated Temperatures I. Experimental and Calculation Techniques for BeCl2, ZnCl2, and PbCl2

A cell for the electrical conductivity measurements of molten salts at the elevated temperatures and vapor pressures of several tens of atmospheres was constructed. The electrical conductivities of molten BeCl2, ZnCl2, and PbCl2 were measured up to temperatures of (823, 1421, and 1320) K, respectively. The melts density was estimated, and molar conductivities at the same temperatures were calculated.

Evaporation Kinetics of the Molten PbCl2-ZnCl2 System from 973 to 1073 K

The clarification of chlorides evaporation behavior from chloride or oxychloride melts is quite important for the treatment and recycling of fly ash generated from incineration processes of municipal solid waste. In the present study, the evaporation rate of the molten PbCl2–ZnCl2 binary chloride system was measured at 973, 1023 and 1073 K. The effects of temperature, composition of the melt and the oxygen partial pressure of atmosphere on the evaporation rate of molten chloride were investigated. The ZnCl2 in chloride melt evaporated preferentially, but the evaporated amount of PbCl2 was negligibly small. Calculated activation energy of ZnCl2 evaporation was 194±4 kJ/mol and that evaporation rate was smaller than that estimated from ZnCl2 activity for the PbCl2–ZnCl2 system. Therefore, the evaporation is considered to be controlled by the slower chemical reaction step than the interfacial evaporation reaction. The evaporation rate increased with increasing oxygen partial pressure in the atmosphere, which might be due to the effect of oxychloride formation.

Raman spectra and structure of PbCl 2–ACl (A = K, Cs) melts

Quantitative Raman spectra of molten PbCl 2–ACl (A = K, Cs) mixtures have been measured at different compositions and at temperatures up to 680 °C. Spectral changes upon melting the Cs 4PbCl 6, CsPbCl 3, KPb 2Cl 5 and PbCl 2 solids have been also measured. All spectra of melts are mainly characterized by an isotropic (polarized) ν P and an anisotropic (depolarized) ν D band. The intensity and position of the ν P (∼237 ± 2 cm −1) and ν D (∼113 ± 3 cm −1) bands remain practically constant at X PbCl 2 ⩽ 0.5 indicating that the structure is predominated by coordination polyhedra of the type Pb n Cl 3 n n - ( n ⩽ 4). With increasing PbCl 2 mole fraction the ν P and ν D bands shift to the “red” and the “blue”, respectively, reaching the corresponding values of 215 and 132 cm −1 in pure molten PbCl 2. Furthermore, the intensity ratio of the anisotropic to isotropic spectra increases indicating contributions to the scattering intensity arising from dipole–induced-dipole interactions in these melts.

X-ray structural analysis of molten PbCl 2

The structure of molten PbCl 2 was investigated by using high temperature X-ray diffraction(XRD) and X-ray absorption fine structure (XAFS) analysis techniques. It is concluded from the Fourier transformation and Debye scattering analyses of the XRD data and the curve fitting analysis of the XAFS function that the nearest Pb 2+–Cl − pair consists of relatively rigid 4-fold coordination and additional loose 2&3 coordination structures.

Molten-salt synthesis of Ba 1− xPb xTiO 3/BaTiO 3 composites with controlled compositions

Ba 1− x Pb x TiO 3/BaTiO 3 composite particles with a core-shell structure were prepared by the reaction between BaTiO 3 and molten PbCl 2. The composition of the shell region of the resulting composite particles was controlled by changing the mole ratio of PbCl 2 BaTiO 3 . By using a sintered BaTiO 3 compact, a bulk Ba 1− x Pb x TiO 3/BaTiO 3 composite was formed. This contained compensational concentration gradients of Ba and Pb in the ~ 20 μm thick Ba 1− x Pb x TiO 3 layer, of which the outer region had the composition Ba 0.1 Pb 0.9 TiO 3.

Electrical conductivity of field-assisted ion-exchanged glass with molten PbCl2 salt

Field-assisted ion-exchange was carried out between soda-lime-silica glass tubes and molten PbCl2 at 823 ‡K for 2 h under constant potential of 12 V. The field-assisted ion-exchange leads to the formation of a lead-exchanged layer underneath the glass surface. The influence of the exchange on the bulk d.c. and a.c. electrical conductivity was investigated and compared with that of the glass before ion-exchange. The d.c. conductivity of the exchanged glass showed an activation energy higher than that of the glass before ion-exchange. The higher activation energy was attributed to the lower mobility of lead cations in the exchanged layer in comparison with that of sodium cations. The a.c conductivity of the exchanged glass showed an increase in the dielectric constant and a decrease in the dielectric loss. These findings suggest that lead cations enter the glass network in modifying positions in the exchanged glass. The results also support the data previously obtained that one lead cation from the molten PbCl2 replaced two sodium cations from the glass.

Activities of Lead Chloride in Molten PbCl<SUB>2</SUB>–KCl–NaCl and PbCl<SUB>2</SUB>–KCl–LiCl Ternary Systems

Activities of Lead Chloride in Molten PbCl<SUB>2</SUB>–KCl–NaCl and PbCl<SUB>2</SUB>–KCl–LiCl Ternary Systems

Activities of Lead Chloride in Molten PbCl2–KCl–NaCl and PbCl2–KCl–LiCl Ternary Systems

AbstractThe vapour pressures of pure PbCl2 and of PbCl2 over the ternary systems PbCl2–KCl–NaCl and PbCl2–KCl–LiCl were measured by a transportation technique over the temperature range 873–1073 K. From the obtained data, PbCl2 activities were calculated. Negative deviation from ideality was observed over a range of compositions in both ternary systems except for the composition region close to the PbCl2–LiCl binary system. Over the temperature range studied, the effect of temperature on the PbCl2 activities in the ternary systems was small. Prediction of activities in ternary systems based on a simple additivity expression of the two binary systems is discussed. The use of these ternary systems as possible electrolytes for the electrowinning of lead is evaluated.

Purification of lead chloride for USE as high-temperature solvent in the growth of crystals of II-VI compounds

A process for removing oxygen impurities from PbCl 2 is described which consists of three steps: Chlorination with gaseous SiCl 4, high-temperature filtration of the molten PbCl 2 and directional solidification into largely monocrystalline ingots of defined diameters.

Surface tension and density of the molten PbCl2–KCl–NaCl ternary system

The maximum bubble pressure method was used to determine the surface tension and density of melts within the PbCl2–KCl–NaCl system. The temperature range of this study was from 450 to 800 °C. In all cases, the surface tension was found to decrease with increasing temperature. At constant molar ratios of KCl to NaCl, a minimum in the surface tension was observed at approximately 40 mol% PbCl2. The ternary surface tension values were found to obey the simple additivity expression of the binary surface tensions of PbCl2–KCl and PbCl2–NaCl. Based on these findings, constant surface tension contours have been drawn.The density obtained in the present study agree well with the previously determined densities using a bottom-balance Archimedean technique reported by this laboratory.

Structural analysis of molten PbCl2

The structure of molten PbCl2 has been re-examined by X-ray diffraction analysis. In molten PbCl2, each Pb atom is surrounded by three Cl atoms at an average distance of 2.63 A as well as four Cl atoms of 3.14 A. The average Pb—Pb interaction within 10 A is similar to a distorted f.c.c. arrangement.

Oxidation of lead sulphide in molten PbCl2 + KCl: electrolysis and visible spectrophotometry

Controlled potential electrolyses of lead sulphide solutions, coupled with visible absorption spectrophotometry have shown: (a) the exchange of two moles of electrons per mole of sulphide ion, whatever the electrolysis potential is on the two oxidation steps of PbS; (b) the formation of an intermediate polysulphide during electrolyses on the first step.

AC impedance measurements in molten PbCl 2—KCl: In(III) reduction and lead sulphide oxidation

Impedance measurements have been performed in molten PbCl 2—KCl at 400°C to investigate the mechanism of In(III) reduction and sulphide ion oxidation. In(III) reduction is purely diffusion controlled and represented by a Warburg impedance. The diffusion coefficient obtained for In(III) is D = 0.49 × 10 −5 cm 2s −1. The first oxidation step of sulphide is rapid and also diffusion controlled.

Oxidation of lead sulphide in molten PbCl 2+KCl: Electrolysis and visible spectrophotometry

Controlled potential electrolyses of lead sulphide solutions, coupled with visible absorption spectrophotometry have shown: (a) the exchange of two moles of electrons per mole of sulphide ion, whatever the electrolysis potential is on the two oxidation steps of PbS; (b) the formation of an intermediate polysulphide during electrolyses on the first step.

Structural analysis of some molten materials by X-ray diffraction. Part 5.—LiCl, PbCl2 and their mixtures

The molten structure of PbCl2, LiCl and their mixtures were examined by X-ray diffraction analysis. In molten Pbcl2, each Pb atom is surrounded by about eight Cl atoms at a distance of 2.92 A, which is near to the sum of the ionic radii of Pb2+ and Cl–. It is expected that only very few rigid complex anions will be present in molten PbCl2. The results of X-ray diffraction analysis in molten PbCl2 are consistent with those of Raman spectroscopy. The average Pb–Pb interaction in the molten state should be intermediate between a b.c.c. and an s.c. arrangement and the s.c. arrangement takes precedence with increasing LiCl concentration.

Darstellung von HfCl 4 und HfBr 4 durch umsetzung von hafnium mit geschmolzenen metallhalogeniden

Abstract Molten metal halides like PbCl 2, PbBr 2, CuCl, CuBr, AgCl and AgBr react with metallic hafnium to form volatile HfCl 4 and HfBr 4, respectively. The reactions of Hf with molten PbCl 2 and molten PbBr 2, carried out in a closed vacuum system, lead to pure HfCl 4 and HfBr 4 with high yields and are of preparative interest, therefore.

Electric Conductivity and Viscosity of the Molten PbCl<SUB>2</SUB>–ZnCl<SUB>2</SUB> Binary System

Electric Conductivity and Viscosity of the Molten PbCl<SUB>2</SUB>–ZnCl<SUB>2</SUB> Binary System

溶融PbCl<SUB>2</SUB>-ZnCl<SUB>2</SUB> 2成分系の電気伝導度および粘性係数

溶融PbCl<SUB>2</SUB>-ZnCl<SUB>2</SUB> 2成分系の電気伝導度および粘性係数

Vapour phase composition and activities for the molten PbCl2 + NaCl system

Vapour pressures of molten PbCl2 + NaCl mixtures have been measured a.t 1071 K by a transpiration method. The vapours have also been investigated by mass spectrometry and the complex NaPbCl3 has been established. The enthalpy of formation of this complex from NaCl(g) and PbCl2(g) has been determined and the equilibrium constant for its formation has been estimated. Enthalpies of vaporization of NaCl and PbC12 and the enthalpy of dimerization of NaCl(g) agree with published results. The mass spectrometry results have enabled corrections to be made to measured activities of PbCl2 from the transpiration results, for errors due to the NaPbCl3 complexes. The activity values so determined are compared with those for other molten binary systems involving lead and alkali chlorides. The PbCl2 + NaCl system (like the other PbCl2 + alkali chloride systems except PbCl2 + LiCl) does not behave as regular solutions.