In this study, the effects of atmosphere firing and pre-heating treatment on the characteristics of sodium titanates were investigated. The materials were successfully prepared from titanium tetraisopropoxide-sodium chloride (TTIP-NaCl) precursors assisted by organic templates (ethylene glycol and citric acid) via facile templating and hydrothermal methods. Sodium titanates were initially prepared by mixing a sodium precursor solution with a titanium precursor solution at a stoichiometric mole ratio of 1.6:1 under vigorous stirring. This was followed by pre-heating treatment via a hydrothermal method at 150°C for 6 h and then calcination at 800°C for 1 h in two different atmospheres including reduction and oxidation conditions. The same process was carried out in the synthesis of the other samples without the preheating treatment. The thermal behaviors of all the as-synthesized samples were evaluated. Meanwhile, the mineralogy and microstructures of all calcined samples were investigated. Both atmosphere firing and pre-heating treatment influenced the thermal behaviors of the assynthesized sodium titanates, resulting in various sodium titanate types with different microstructures. To prepare the sodium titanates from TTIP-NaCl precursors, the pre-heating treatment and the reduction firing seemed to be the optimum conditions for the formation of sodium titanate, in order to produce Na 2 Ti 6 O 13 -type sodium titanates with rod-like particles in nanometer sizes.
Sodium manganese oxide plays an important role in the cathode application of sodium ion batteries. In this study, sodium manganese oxide Na 2 Mn 3 O 7 (NMO) with a triclinic structure was successfully synthesized via a low-cost, simple conventional mixing method. NaMnO materials were synthesized by mixing Na 2 CO 3 precursors and the two different types of Mn precursors, namely MnO 2 by a solid method (the sample C) and MnCl 2 by a solgel method (the Sample D). The calcination of both samples was carried out at 800°C for 3 h. The results shown that the thermal behavior and crystal characteristics of the Sample D are slightly better than another one. Nevertheless, the Sample C exhibits a better microstructure, showing rod-like particles more dominant than particular particles. In addition, the Sample C reveals a little bit larger surface area than the Sample D.
This current study successfully synthesized Na2Mn3O7 in two steps. Firstly, the synthesis of MnO from NaCl and MnCl2.4H2O precursors. NaCl was mixed with citric acid as a chelating agent, while MnCl2.4H2O was mixed with two types of chelating agents (citric acid and 1% chitosan). The solutions of [NaCl-a chelating agent] and [MnCl2.4H2O-a chelating agent] were stirred for ±2 hours. The solutions were hydrothermally heated at 150°C for 6 hours and then calcined at 800°C for 1 hour in a nitrogen condition. The MnO presence was then analyzed using an XRD method. As a comparison, another sample was water leached. Then, it was examined by an XRD method. Secondly, the synthesis of Na2Mn3O7 from MnO and Na2CO3 powder was carried out through a solid method. The calcination was carried out at 800°C for ±3 hours in an oxidizing atmosphere. The XRD results showed the presence of Na2Mn3O7 in the final products of both samples. Based on these experimental results, the sample [NaCl-citric acid; MnCl2.4H2O-1%chitosan] showed higher purity than the sample [NaCl-citric acid; MnCl2.4H2O-citric acid], so that it had a higher intensity of the Na2Mn3O7 phase than the sample [NaCl-citric acid; MnCl2.4H2O-citric acid]. Besides, the Cl- ions removal after calcination greatly affected the intensity of the MnO and Na2Mn3O7 formed.
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