Thermal behaviour of natrite Na₂CO₃ in the 303–1013 K thermal range

Abstract

This study reports a structural investigation, at a fine temperature scale, of natrite Na 2 CO 3 from 303 to 1013 K by laboratory parallel-beam X-ray powder diffraction. Within the investigated thermal range, Na 2 CO 3 undergoes the C2/m(0)0s ! C2/m ! P6 3 /mmc phase transitions. Results indicate that all modulation amplitudes tend to decrease to zero, approaching the ! transition temperature. However, a high-amplitude anti-phase modulation of the two symmetry-equivalent C-O1 distances starts at ca 520 K and reaches a maximum value of ca 0.7 valence units at the ! transition. Therefore, it seems that O1 instability represents the driving force of the ! transition. The -polymorph is characterized by a disordered structure showing multiple site splitting and a strong anisotropic microstrain, starting immediately after the ! transition. The structure of -Na 2 CO 3 was also refined and found to differ from reference data. Similarly, for -K 2 CO 3 and -Rb 2 CO 3 a considerable disorder at the O site was observed.

Use of Nanoporous FeOOH as a Catalytic Support for NaHCO3 Decomposition Aimed at Reduction of Energy Requirement of Na2CO3/NaHCO3 Based CO2 Separation Technology

“…Because of the nearly amorphous nature of the material, it cannot be determined which polytype of FeOOH is present from XRD data. Figure c,d shows XRD patterns of NaHCO 3 and Na 2 CO 3 derived from the decomposition of NaHCO 3 at 180 °C and matches well with data reported in the literature. , Consistent with FTIR spectra, the XRD patterns of 20 wt % NHF in Figure a before CO 2 desorption and Figure b after CO 2 desorption do not show the characteristic peaks of NaHCO 3 or Na 2 CO 3 . Neither do these peaks appear for the 50 wt % NHF before and after decomposition in Figure c,d; the peak due to FeOOH at 62° is not easily discernible for the 50 wt % NHF.…”

Dehydration dynamics and thermal stability of erionite-K: Experimental evidence of the “internal ionic exchange” mechanism

“…This instrumental set up has been recently proven to provide temperature-resolved data of excellent quality [20][21][22][23][24]. More in detail, the paper is aimed at: a) Defining the thermal stability of erionite-K, including the structure breakdown temperature and its classification on the basis of the categories indicated by Alberti and Vezzalini [17]; b) Detecting and monitoring the eventual occurrence of the socalled ''internal ion exchange'' mechanism; c) Correlating the framework modifications occurring as a function of temperature with both the dehydration and cations migration processes; d) Monitoring the mobility of the various cation species.…”

Thermal behaviour of alum-(K) KAl(SO4)2·12H2O fromin situlaboratory high-temperature powder X-ray diffraction data: thermal expansion and modelling of the sulfate orientational disorder

“…Diffraction patterns were measured in transmission mode on a sample prepared as a capillary mount. The experimental set-up used in this investigation was chosen for its capability to produce high-quality diffraction data, at the same level as synchrotron radiation beamlines (Ballirano, 2011). Diffraction patterns are virtually texture-free and measured under conditions of excellent thermal stability and limited thermal gradient onto the capillary.…”