Structural, microstructural and thermal characterization of layer-structured CaSi2 produced by clean combustion synthesis method

Layer-structured calcium silicide (CaSi 2 ) is prepared using a fast and clean combustion synthesis (CS) method, employing silica as the silicon source. The CS process was characterized by the occurrence of an ignition reaction at 510 °C, leading to the formation of CaO, CaSi 2 , Ca 14 Si 19 , and Ca 3 SiO 5 which is converted into CaSi 2 with minor amounts of Si after an acid treatment. The mechanism involved in the CS process is discussed. The structure and microstructure of the CS-CaSi 2 is characterized and compared with the commercial CaSi 2 , and the outcomes are discussed based on the Ca-Si binary phase diagram. In comparison with the latter, the CS-CaSi 2 has a considerably greater purity, with loosely stacked structure, providing a surface area of around 43 m 2 g −1 . The thermal analysis of the CS-CaSi 2 is conducted under high purity argon and air flow of 100 mL min −1 , comprising differential scanning calorimetry (DSC) and thermal gravimetric (TG) analysis. The analysis conducted under argon provides evidence for the occurrence of the melting event at 1037 °C. Under air, the material is almost stable below 800 °C, while the oxidation is detected at higher temperatures. The oxidation peak of the material is realized from the corresponding DSC thermogram to take place at 1028 °C. The oxidation event is suggested to occur through two stages. At the first stage (T < 1030 °C), the event can be explained by the oxidation of calcium content of CaSi 2 . The second oxidation stage taking place at higher temperatures can be related to the oxidation of Si, with a lower rate. The Li-storage performances of the commercial CaSi 2 and CS-CaSi 2 are evaluated.