Carbon In Sodium Research Articles

Elucidating electrochemical intercalation mechanisms of biomass‐derived hard carbon in sodium‐/potassium‐ion batteries

AbstractHard carbon materials are characterized by having rich resources, simple processing technology, and low cost, and they are promising as one of the anode electrodes for commercial applications of sodium‐/potassium‐ion batteries. Simultaneously, exploring the alkali metal ion storage mechanism is particularly important for designing high‐performance electrode materials. However, the structure of hard carbon is more complex, and the description of energy storage behavior is quite controversial. In this study, the Magnolia grandiflora Lima leaf is used as a precursor, combined with simple pyrolysis and impurity removal processes, to obtain biomass‐derived hard carbon material (carbonized Magnolia grandiflora Lima leaf [CMGL]). When it is used as an anode for sodium‐ion batteries, it exhibits a high specific capacity of 315 mAh/g, and the capacity retention rate is 90.0% after 100 cycles. For potassium‐ion batteries, the charge specific capacity is 263.5 mAh/g, with a capacity retention rate of 85.5% at the same cycling. Furthermore, different electrochemical analysis methods and microstructure characterization techniques were used to further elucidate the sodium/potassium storage mechanism of the material. All the results indicate that the high potential slope region represents the adsorption/desorption characteristics on the surface active sites, whereas the low‐potential quasiplateau region belongs to the ion insertion/extraction in the graphitic microcrystallites interlayer. It is noteworthy that potassium ion is randomly intercalated between the graphitic microcrystallite layer without forming a segmented intercalation compound structure.

Corrosion behavior of surface treated steel in liquid sodium negative electrode of liquid metal battery

While liquid metal batteries are attractive options for grid-scale energy storage applications as they have flexible siting capacities and small footprints, the compatibility between structural materials such as current collectors and negative electrode such as sodium is one of major issues for liquid metal batteries. Non-metallic elements such as carbon, oxygen, and nitrogen in the liquid sodium influence the material behaviors of the cell construction materials in the battery system. In this study, the compatibility of structural materials with sodium is investigated in high temperature liquid sodium, and electrochemical impedance spectroscopy (EIS) is used to monitor in-situ the corrosion behavior at the surface of materials in sodium. Chemical vapor deposition (CVD) coatings of SiC and Si3N4 are applied as protective barriers against dissolution and corrosion on the steel surface. The results show that CVD coating of Si compounds can delay corrosion of steel in high temperature liquid sodium comparing to the result of as-received specimens, while SiC coating is more durable than Si3N4 coating in high temperature liquid sodium.

Correlation between carbon activity and carbon content in α-iron in liquid sodium negative electrode of liquid metal battery

Non-metallic elements such as carbon, oxygen, and nitrogen in liquid sodium exert a significant effect on the material behaviour of cell construction materials in liquid metal battery systems. Austenitic Fe-18%Cr-8%Ni foil and α-iron foil are equilibrated at 550 °C in sodium, and, subsequently, the concentration of carbon in the foils is analysed. A new relationship has been obtained between carbon activity and carbon concentration in α-iron foil, and is compared with the previously developed ones involving 304 SS foil reference samples. An equilibrium method has been developed to measure the activity of carbon in liquid sodium by using α-iron with this new expression. The results show similar values to those obtained with the 304 SS foil reference samples.

An electrochemical meter for measuring carbon potential in molten sodium

Thermodynamic analysis and electrochemical investigations were carried out to evaluate the chemistry and electrode kinetics of a molten carbonate based electrochemical carbon meter for monitoring carbon in molten sodium. Based on the results of investigations a procedure was standardized for assembling the cell. The response of the cell thus assembled could be correlated to the carbon activity in sodium. Impedance studies established that mass transfer at iron membrane was the rate limiting step. Meters were extensively tested in both static and dynamic sodium for evaluating the stability and reproducibility in long term conditions.

Development of Sensors for On-Line Monitoring of Nonmetallic Impurities in Liquid Sodium

Sensors for on-line monitoring of hydrogen and carbon in sodium and hydrogen in argon cover gas circuits over sodium have been developed. The performance of these sensors in fast breeder test reactor (FBTR) and large sodium facilities is evaluated. A sensor for monitoring oxygen in sodium is under development. The in-sodium electrochemical hydrogen sensors are found to detect about 10 ppb increase in hydrogen concentration over a background of 50 ppb. The cover gas hydrogen monitoring sensor system is found to sense hydrogen down to 2 vppm in argon over sodium systems. Electrochemical carbon sensors are capable of detecting down to 1 ppm of carbon in sodium.

Determination of carbon in solidified sodium coolant using new ICP-OES methods

AbstractNew methods for the determination of carbon in sodium using laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) and ICP-OES with pneumatic nebulisation (PN-ICP-OES) were developed. The determination was required for the study of the carbon dioxide reaction with molten sodium at high temperatures (300–600°C). After exposition to CO2, the solidified sodium sample was subjected to direct solid analysis by LA-ICP-OES and to solution analysis. For the determination of carbon in the sodium sample surface layer by LA-ICP-OES, three different matrices containing sodium were tested (NaCl, NaF, and Na2B4O7 · 10H2O) as calibration pellets. The calibration dependences were improved using sodium as the internal standard. Average carbon content in the sodium bulk sample was determined by PN-ICP-OES after the sample dissolution by water vapour.

Development of Sensors for On-Line Monitoring of Nonmetallic Impurities in Liquid Sodium

Sensors for on-line monitoring of hydrogen and carbon in sodium and hydrogen in argon cover gas circuits over sodium have been developed. The performance of these sensors in fast breeder test reactor (FBTR) and large sodium facilities is evaluated. A sensor for monitoring oxygen in sodium is under development. The in-sodium electrochemical hydrogen sensors are found to detect about 10 ppb increase in hydrogen concentration over a background of 50 ppb. The cover gas hydrogen monitoring sensor system is found to sense hydrogen down to 2 vppm in argon over sodium systems. Electrochemical carbon sensors are capable of detecting down to 1 ppm of carbon in sodium.

An electrochemical meter for measuring carbon activity in liquid sodium

This paper reports the development of an improved electrochemical carbon meter which gives better long term performance compared to similar meters described by earlier workers. The initial problem of the meter was identified to be due to decarburization of the Fe/Fe 3C reference electrode. The new reference electrode consisting of a graphite-filled nickel capsule was found to give satisfactory performance. However, the test in commercial grade sodium did not give the expected temperature dependance of emf values. This is attributed to the influence of carbon bearing impurity species present in commercial grade sodium. Experiments with purified sodium gave emf response with change in temperature in accordance with the established solubility relationship of carbon in sodium. The long term test of performance of the meter in liquid sodium is described. Its utility for measuring the carbon activities of various metal carbide systems is also pointed out.

Design and Testing of an Electrochemical Carbon Meter for Sodium

An electrochemical carbon meter using liquid Na/sub 2/CO/sub 3/-Li/sub 2/CO/sub 3/ eutectic contained in a thin-walled iron membrane cup was constructed. A reference electrode was kept immersed in the electrolyte. The membrane cup assembly was dipped into static sodium for analysis. Carbon in sodium equilibrates with the iron membrane. An electromotive force was developed across the electrolyte due to the presence of a carbon activity difference and this was measured using a high impedance digital volt meter. The measured electromotive force was dependent on the type of reference electrode used in the probe. Further characterization of the reference electrodes is needed for the reliable operation of this type of carbon meter for sodium. However, graphite seems to fit best the requirements of materials for use as the reference electrode.

Electrochemical techniques for monitoring dissolved carbon, hydrogen and oxygen in liquid sodium

Potential chemical problems associated with the use of liquid sodium as a coolant for fast reactors have led to the need for special analytical techniques, in particular, for dissolved carbon, hydrogen and oxygen. Consideration of the chemical monitoring requirements involved shows methods based on electrochemical cells to be particularly suitable. After a summary of the relevant background phenomena, the development and operational experience of specific electrochemical carbon, hydrogen and oxygen meters are described.

Carbon and nitrogen transfer in Fe-9 Cr-Mo ferritic steels exposed to a sodium environment

Kinetics of carburization/decarburization of five commercial and two high-purity Fe-9 Cr-1 to 2.5 Mo feiritic steels have been studied in a sodium environment at temperatures between 773 and 973 K. Carbon concentration-distance profiles were obtained as a function of sodium-exposure time, temperature, and carbon in sodium and the carburization/ decarburization rate constants were evaluated. The results show that the Fe-9 Cr-Mo steels are more resistant to carbon transfer than the low-alloy Fe- 2 1 4 Cr-1 Mo steel. The conditions of temperature and carbon concentration in sodium for carburization or decarburization of Fe—9 Cr—Mo steels are quite similar to those for stainless steels. However, the extent of carbon transfer in Fe-9 Cr—Mo steels is lower than that of the stainless steels. The composition and carbide structure of the steel had a significant effect on the carburization/decarburization behavior. Fe-9 Cr-Mo steels that decarburize to very low carbon concentrations either contain M 2X phase or have M 6C as the only stable carbide.

Application of bremsstrahlung activation analysis for the determination of carbon and nitrogen in sodium

Carbon and nitrogen are determined by means of the photonuclear reactions:12C(γ n)11C and14N(γ, n)13N. This article presents a simultaneous chemical separation method for the isolation of11C and13N. It is based mainly on combustion of the sample, after irradiation and etching, in a mixture of oxidising acid fused salts (B2O3 and Pb3 O4) containing a dispersing agent (NaCl and KCl) and the respective carriers. Each analysis takes about 40 min altogether. Minimum carbon and nitrogen contents of a few 10−2 μg·g−1 can be measured. The influence of the main competitive nuclear reactions on neighbouring elements, including the sodium itself, is examined.

The solubility of carbon in sodium

The solubility of carbon in sodium has been determined over the temperature range 490 to 832°C and can be expressed by the relation log 10S( wt ppm) = 7.646 − 5970/T( K) . The carbon is present probably as the dicarbide ion, except if oxygen or nitrogen is added, when the amount of dissolved carbon is enhanced by the formation of carbonate and cyanide respectively. When the sodium is cooled below freezing, the dissolved carbon readily plates out or absorbs on to surfaces in a way which is not easily reversed.

Monitoring and Measurement of Carbon Activity in Sodium Systems

An equilibration method has been developed to measure accurately the activity of carbon in liquid sodium. Foils of Fe – 8 wt% Ni, Fe – 16 wt% Ni, and Fe – 18 wt% Cr – 8 wt% Ni alloys can be exposed...

Irreversible behaviour of an electrochemical device for the monitoring of carbon in liquid sodium

The use of a fused salt solution of calcium carbide as the electrolyte in an electrochemical cell for the monitoring of carbon in metal solutions is shown to be unsatisfactory due to partial electronic conductivity in the electrolyte. The experimental results of Salzano et al. [1] using such a device with liquid sodium-carbon solutions are shown to correspond to a steady state situation in which a carbon flux, equivalent to the electron flux in the electrolyte, is established from the graphite electrode to the steel barrier separating the electrolyte from the liquid sodium. The cell e.m.f., calculated by assuming this carbon flux to be equal to the carbon flux by diffusion through the steel barrier to the liquid sodium, agrees within the uncertainty limits of the calculation, to the measured e.m.f.

Electrochemical Measurement of the Solubility of Carbon in Sodium

Electrochemical Measurement of the Solubility of Carbon in Sodium

An Electrochemical Carbon Meter for Use in Sodium

The feasibility of an electrochemical carbon meter which measures the chemical activity of carbon in sodium at temperatures from 600 to 700°C has been demonstrated. The meter is based on the cell a...

Solubility of carbon in sodium

AbstractThe solubility of carbon in sodium over the range 600‐950° may be expressed by the equation: log sol. = 7.20‐5465/T where solubility is in ppm and T in °K.From plots of carbon activity versus concentration, and from observations that oxygen does not affect carbon solubility, it is proposed that carbon dissolves in sodium as single atoms.

Thermodynamic and kinetic aspects of carbon transport in sodium-steel systems

The thermodynamic activity and solubility of carbon in Fe-Cr-Ni alloys were calculated in the temperature range of 500–800 °C by extrapolation of higher temperature data in the Fe-Cr-C and Fe-Ni-C systems. These results were used with phase-equilibria information and data for the solubility of carbon in sodium to obtain an equilibrium relationship between the total carbon concentration in the alloys and that in sodium. The calculations showed that the Fe-Cr-Ni alloys with nominal initial carbon concentrations may undergo carburization or decarburization depending upon the carbon concentration in sodium in the temperature range of 500–800 °C. Computed carbon concentrations in sodium for incipient carbide formation in an 18-8 stainless steel were significantly lower (< 1 ppm) than those commonly reported (15–30 ppm) for stainless steel-sodium systems operating at temperatures below 700 °C. The phaseequilibria and activity data were used to explain the observed phenomenon of transfer of carbon from austenitic steel to sodium when chromium depletion, due to mass transfer, occurs. In addition, the driving force for carbon transfer from ferritic to austenitic steel under isothermal conditions was calculated.

Evaluation of vanadium and vanadium-base alloys in hot-trapped sodium

Corrosion tests were conducted with vanadium-base alloys in zirconium-purified sodium from 450° to 750°C for 500 to 4000 hr. The materials tested were vanadium, binary vanadium alloys containing from 10 to 40 wt pct Ti, and two ternary alloys: V-5Ti-15Cr and V-15Ti-7.5Cr. The sodium was analyzed to contain from 1.7 to 8.7 ppm O by the vacuum-distillation technique. The behavior of these materials was determined from weight change data, and from chemical, metallographic, and electron-microprobe analyses of the test specimens. At temperatures up to 650°C, the maximum weight-change varied from a weight loss of 0.45 for vanadium to a weight gain of 0.46 mg per sq dm-day for the V-40Ti alloy. Chemical analyses of the corrosion test specimens indicated that vanadium-base materials were sensitive to the activity of oxygen, carbon, and/or nitrogen in sodium. Alloys containing >10 wt pct Ti increased in oxygen, carbon, and in some tests, nitrogen content, indicating that alloys of this titanium content are not compatible with sodium of the present purity. Complex titanium carbide precipitates were observed near the surface. V-5Ti-15Cr alloy was more resistant to liquid sodium than the other vanadium materials investigated.