Thermal stabilization of tin- and cobalt-doped manganese dioxide

Abstract

International audienceWe study the thermal stability, local structure, and electrical properties of the alpha-MnO2 phase doped with Sn and Co. It is found that doping prevents the transformation from alpha-MnO2 to alpha-Mn2O3 that occurred in the temperature range of 500-600 degrees C. Samples have been synthesized in an acidic medium using the reduction of potassium permanganate by fumaric acid. X-ray diffraction patterns (XRD) of pure and doped alpha-MnO2 prepared at 450 degrees C do not show new peaks related to dopant species. Thermogravimetric analysis (TGA) of the Sn and Co doped MnO2 reveals that transformation from MnO2 to alpha-Mn2O3 starts above 700 degrees C. The increase in the thermal stability is attributed to the presence of Sn or Co ions incorporated inside the large 2 x 2 tunnels as revealed by Fourier transform infrared (FTIR) spectra measurements. An increase in the electrical conductivity with the presence of Sn or Co ions is observed. Electrochemical features of the doped MnO2 samples in alkaline cells are reported and compared with that of the pristine alpha-MnO2 phase

Table sugar as preparation and carbon coating reagent for facile synthesis and coating of rod-shaped MnO2

“…(7) for the carbon coated MnO 2 . These values are in good agreement with those reported in our previous work [12]. Slight reduction in peak intensities was observed after coating process.…”

“…K ion plays a role as a stabilizing cation and increases the thermal stability of carbon free and carbon coated MnO 2 . It is well known that thermal decomposition reactions of MnO 2 of very low content of K occurred in two steps according to the phenomena given by [13,14] and our previous work [12]. The first decomposition of MnO 2 to Mn 2 O 3 occurs at the range of 500-600 • C. The structural change from MnO 2 phase to Mn 2 O 3 was also observed at 540 • C by Muraoka et al [14].…”

Magnetic Properties of Mn-Doped Amorphous SiO2Matrix

“…Tetragonal α phase and orthorhombic γ phase of MnO 2 obey the classical Curie-Weiss law above 150 K with the Curie-Weiss temperature of about -300 K and -180 K respectively [12,13] Magnetic characteristics of the sample with 3 at.% Mn observed at high-temperatures resemble the properties of λ-MnO 2 . There is no magnetic phase transition above 50 K, as can be seen in Fig.…”

Manganese Oxide Octahedral Molecular Sieves (OMS-2) Multiple Framework Substitutions: A New Route to OMS-2 Particle Size and Morphology Control

“…For example, partial exchange of K + ions in the K-OMS-2 tunnels with H + ions (protons) has yielded excellent acid catalysts for selective oxidation reactions, [ 18 ] whereas doping of single-type, low-, or high-valent metal cations, such as Co 2 + , Zr 2 + , Cu 2 + , Cr 3 + , Fe 3 + , In + 3 , V 5 + , W 6 + , and Mo 6 + into the framework, [19][20][21][22][23][24][25] via a subtle balance of the redox properties and depending on the extent of substitution, has produced cryptomelane with novel morphologies [ 26 ] and catalytic properties. [ 27 ] In terms of morphology, doping Cr 3 + into the K-OMS-2 structure produced well-ordered dendritic structures, which are unusual compared to the regular K-OMS-2 morphology.…”