Thermogravimetry and X-ray diffraction study of the thermal decomposition processes in Li2CO3-MnCO3 mixtures

The thermal decomposition processes taking place in solid state mixtures Li2CO3–MnCO3 (xLi=0.10–0.50, xLi=lithium cathionic fraction) have been studied (both in air and nitrogen flow) by thermogravimetric analysis (TGA), in order to get a better understanding of the different possible by-products, and by X-ray powder diffractometry (XRD) to assess the equilibrium compounds. As concerns the measurements performed in air, LiMn2O4 and excess Mn2O3 are the equilibrium products obtained for xLi up to 0.33. By 0.33xLi0.50 a mixture of LiMn2O4 and Li2MnO3 is obtained. In this case the TGA data show that an excess lithiated spinel phase (Li1+xMn2O4) is obtained as an intermediate phase. The measurements performed in nitrogen (xLi up to 0.33) show, when examined by TGA, the formation reaction of LiMn2O4 and Mn3O4 which is completed within about 720°C. At higher temperatures a rather complex reaction takes place between LiMn2O4 and the excess Li2O present at 720°C, leading to the formation of the compounds Li2Mn2O4 and LiMnO2 again with excess of Mn3O4. At higher mixture lithium content (0.33xLi0.50) LiMn2O4, Li2MnO3 and Mn3O4 form up to about 720°C. At higher temperatures LiMnO2 is by far the majority phase present which is formed by solid state reactions occurring between LiMn2O4 and Li2MnO3 and between Li2MnO3 and Mn3O4

TG/FT-IR: An Analysis of the Conditions Affecting the Combined TG/Spectral Response

The results of TG/FT-IR measurements performed on hydrated beta-cyclodextrin at different heating rates and with different carrier gas fluxes are reported. It is shown that the shape of the spectral curve and the its degree of matching with the DTG curves depend on both the TG heating rate and the carrier gas flow rate

Effect of extended ball milling on graphite

Graphite has been milled for up to 1000 h in a laboratory scale tumbling ball mill under vacuum. Raman spectroscopy of the powders indicated the increasing dominance of D-type graphitic sp bonding over G-type bonding with increasing milling time. Diamond-like sp bonding and possibly fullerene-like bonding also became evident after milling. TEM of the 100 h sample showed the presence of ribbons which were composed of sheets showing defects, delamination, translation, warping and curvature. Interplanar spacings of 0.40–0.50 nm were measured with the spacing increasing towards the edge of the ribbons where delamination was evident. Thermogravimetric analysis in argon of the powder after exposure to air showed an increasing mass loss with milling time indicating the presence of chemisorbed gas. Using TG–FTIR the gas was found to be a mixture of CO and an unidentified gas (probably oxygen). BET surface area measurements showed a maximum in the surface area; however, this was shown to be massively in error for the longer milling times due to the presence of the chemisorbed gas

Mechanothermal Solid-state Synthesis of Cobalt(II) Ferrite and Determination of its Heat Capacity by MTDSC

Cobalt ferrite (CoFe2O4) has been synthesized by a solid-state mechanothermal process, and its molar heat capacity has been determined. A stoichiometric mixture of CoC2O4 ・ 2H2O and FeC2O4 ・ 2H2O was subjected to a combination of mechanical activation (by high-energy milling) and thermal activation (by annealing at temperatures between 300 and 700 °C). The process was followed by thermogravimetric analysis and high-temperature X-ray powder diffraction. It has been shown that CoFe2O4 forms at all temperatures, though with different degrees of crystallization, while Co3O4 and Fe2O3 are the only products formed when starting from unmilled mixtures. The molar heat capacity of CoFe2O4 has been determined in the temperature range 60 - 400 °C by MTDSC. It has been shown that the molar CP values of CoFe2O4 samples produced at T ≥ 500 °C are close to each other while those of the samples produced at 300 and 400 °C are lower. Furthermore the CoFe2O4 samples prepared at T ≥ 500 °C show very similar microstructures

Solid State Synthesis of CaMnO3 from CaCO3-MnCO3 Mixtures by Mechanical Energy

Abstract A solid state synthesis of calcium manganite (CaMnO3) is described where equimolecular mixtures CaCO3:MnCO3 have been subjected to mechanical stress (high energy milling) so yielding CaCO3-MnCO3 solid solutions of nanometric particle size. TG measurements have shown that a link exists between milling time, the extent of non-stoichiometry and the milling-induced decomposition of MnCO3 to Mn3O4. A short (2 h) annealing at 850 °C performed on a sample mixture milled for 25 h leads to non-stoichiometric CaMnO3−x. No sure conclusion could be drawn for the stoichiometry of CaMnO3 obtained, under the same annealing conditions, from a mixture milled for longer time (150 h). No synthesis of CaMnO3 could be effected by long (48 h) annealing at 1200 °C of mixtures that had not been subjected to mechanical stress

Oxidation Behaviour of Mechanically Activated Mn3O4 by TGA/DSC/XRPD

The effect of high energy milling on the solid-state reactions taking place in Mn3O4 has been studied. Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) have been employed to study the solid-state reaction occurring under air in the temperature range between room temperature (rt) and 1100 °C. X-ray Powder Diffractometry (XRPD) has been used to ascertain the chemical nature of the transformations brought into evidence by thermo-analysis

Solid State Synthesis of Strontium Oxoferrates from the Mechanically Activated System SrCO3-Fe2O3

The solid state reactions occurring in the SrCO3 - Fe2O3 system have been studied by DSC, TGA and XRPD techniques. The enthalpies of reactions have been determined

Kinetics of BaBr2·2H2O Dehydration: Comparison Between Isothermal and non-Isothermal Methods

For the reaction of dehydration of BaBr2 with a different content of water molecules, a comparison was made between the experimental non-isothermal alpha vs time curves and those calculated on the basis of a isothermal study. For low heating rates, the two data sets are in good agreement

Effect of mechanical activation on the preparation of SrTiO3 and Sr2TiO4 ceramics from the solid state system SrCO3-TiO2

By thermoanalysis (TGA and DSC) and X-ray powder diffraction it has been shown that the compounds SrTiO and Sr2TiO4 can be prepared by mechanical activation of, respectively, 1:1 and 2:1 SrCO –TiO (rutile) mixtures followed by annealing for 12 h at 800–8508C. These compounds could not be obtained by heating the physical mixtures to temperatures as high as 1000 °C. Moreover, the enthalpies of the reactions leading from Sr carbonate and rutile to the formation of these compounds have been determined. By combining these data with the enthalpy of SrCO decomposition, also obtained in this work, the enthalpies of formation of SrTiO and Sr2TiO4 have been calculated. On the contrary, no Sr3Ti2O7 was shown to form, by the same annealing procedure, when starting from a mechanically activated mixture. DSC and XRD results agree in indicating that a mixture of Sr TiO and SrTiO forms instead

Synthesis of LaCoO3 powder by a combined mechanical/thermal process

Lanthanum cobaltite, LaCoO3, finds applications as an oxidation and reduction catalyst in gas-sensing materials and in electrode materials for high-temperature fuel cells. The compound has been synthesized through several routes aimed at obtaining LaCoO3 at lower temperatures. We propose a synthetic procedure based on the combined use of mechanical and thermal energy on mixtures of Co(II) oxalate dehydrate and La acetate sesquihydrate. We studied the reactions taking place by increasing the temperature. The study has been performed either on mixtures prepared by a simple physical mixing of the reactants or on the same mixtures after having been subjected to mechanical activation by high-energy milling. The products formed in the mixtures by annealing at different temperatures have been characterized by means of different experimental techniques