The solubility of carbon in sodium

Evaluation of Microstructural, Mechanical Properties and Corrosion Behavior of AISI Type 316LN Stainless Steel and Modified 9Cr-1Mo Steel Exposed in a Dynamic Bimetallic Sodium Loop at 798 K (525 °C) for 16,000 Hours

“…The diffusion coefficient of carbon in the ferritic steel is similar to that of austenitic stainless steel. [37] Under such conditions where carbon activity is higher in sodium, it is only expected that carburization took place in both 316LN stainless steel and modified 9Cr-1Mo steel. It has been reported that in modified 9Cr-1Mo steel, the carbon concentration at the surface was 0.56 wt pct compared with the initial concentration of 0.10 wt pct, in sodium containing 0.10 wppm of carbon, after 200,000 hours of operation.…”

Carbon Transfer in Sodium System Under Thermal Cycling-Possibility of “Metal Dusting”

“…When the carbon content is 0.0153 ppm, the solubility limit of disodium acetylide will be attained at 525.6 K and its precipitation is initiated. Thus, in a system with a maximum temperature of 823 K, deposition of sodium acetylide is likely to occur in the down-stream region which is maintained at temperatures lower than 525.6 K. The existence of sodium acetylide in sodium systems have been reported in the literature ( Ref 16,18,20,[24][25][26][27][28]. This would not cause any serious problem in the cold leg as the diffusion coefficient of carbon is very low at this temperature.…”

“…When the temperature of the sodium containing 0.0153 ppm carbon is lowered to 632 K saturation occurs (limit of dissolution of graphite). At this solubility limit of graphite a solution of disodium acetylide exists in sodium ( Ref 16,18,20). The solubility of disodium acetylide is given by (quoted in Ref 20) …”

“…Realizing this situation, the other investigators employed an indirect method to dissolve carbon. They have employed carbon dissolved in nickel ( Ref 17,18) where wppm in the bracket indicates the solubility, which is expressed in weight ppm. Employing this equation, the solubility at 723 K is calculated to be 0.222.…”

Liquid metals for nuclear applications

“…To evaluate the metallurgical risk linked to the decarburizing/carburizing potential of sodium, accurate measurements of the carbon solubility were required. By using an equilibration method between nickel foils (one decarburized and the other unsaturated in carbon), a reliable expression of the solubility of carbon in sodium (wt ppm), presumably in the form of dicarbide ion, has been determined between 490°C (0.6 wt ppm) and 832°C (160 wt ppm) [50,51]: log 10 ðx sat CðNaÞ Þ ¼ 7:646 À 5970=T ðKÞ :…”