Sodium silicate, a new type of CO2 sorbent, has a relatively low cost, but its sorption reactivity is not yet good enough. Alkali carbonate doping is commonly used as an effective means to improve the CO2 uptake reactivity of solid sorbents. In this study, sodium orthosilicate, Na4SiO4, was synthesized and mixed with 5, 10, and 20 mol% of Li2CO3–Na2CO3 or Li2CO3–Na2CO3–K2CO3 as CO2 sorbents. The promotion of alkali carbonates on Na4SiO4 in CO2 capture was characterized using thermal analyses in an 80 vol% CO2–20 vol% N2 atmosphere. The phase evolution and structural transformations during CO2 capture were characterized by in situ XRD and Raman, and the results showed that the intermediate pyrocarbonate, C2O52−, which emerged from alkali carbonates, enhanced the CO2 capture of Na4SiO4 to form Na2CO3 and Na2SiO3 from 100 °C. Isothermal analyses showed that 10 mol% of Li2CO3–Na2CO3 was the optimal additive for Na4SiO4 to attain better CO2 uptake performance. The alkali carbonates were effective in reducing the activation energy for both chemisorption and bulk diffusion, improving the cycle stability of Na4SiO4.
The anodic dissolution of hypoeutectic cast iron consisting of pearlite and ledeburite was studied in a sulfuric acid solution by electrochemical methods. The oxidation activities of ferrite and cementite, which are two phases in cast iron, are evaluated by their structural and electronic properties according to the first-principles calculations. The results show that the anodic dissolution of ferrite occurs at the more negative potential compared with cementite. With comparison of ledeburite, the microstructure of pearlite is more easily crumbled during anodic dissolution because more of the ferrite dissolves from the framework of pearlite. The first principle calculations demonstrate that the Fe 3d-band center of iron is closer to Fermi level than that of cementite, indicating that Fe atoms in ferrite are more active and prone to suffering electrophilic attack. This is the intrinsic reason that cementite is more stable than ferrite under anodic polarization in the sulfuric acid solution.
The electrochemical behaviors of Li + and Nd 3+ were investigated on W, liquid Sn pool and Sn film electrodes in LiCl-KCl-NdCl 3 melt at 673 K. Various electrochemical techniques, such as cyclic voltammogram, square wave voltammogram, and open circuit chronopotentiometry, were conducted to evaluate the electrochemical behaviors of Li + and Nd 3+ . The reduction of Nd 3+ was found to be a two-step process in the W electrode and a one-step process in the liquid Sn electrode. During the formation of the Nd-Sn intermetallic compounds, only the NdSn 3 would be formed without the reduction of the Li + in the liquid Sn electrode. When the reduction potential moves over −2.77 V vs Cl 2 /Cl − , the Li + in the electrolyte would inevitable be reduced into the liquid Sn electrode. The Nd-Sn intermetallic compounds were deposited on the liquid Sn pool electrode at −2.74 V vs Cl 2 /Cl − in the LiCl-KCl-NdCl 3 melts for 5 h. The products were characterized by SEM-EDS and XRD. The loose product on the surface of the deposition displayed the existence of NdSn 3 in Nd-Sn intermetallic compounds. The high content of Nd inclusion formed by segregation was detected in the solidified Sn electrode.
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