1,721,132 research outputs found
Mechanical Activation of calcium titanate formation from CaCO3-TiO2 mixtures
No full textComplete CaTiO3 formation has been found to occur in CaCO3-TiO2 (anatase or rutile) mixtures subjected to mechanical activation by high energy milling. Such formation has been demonstrated to occur by rapid heating (20 K/min) up to 1250degreesC. The first stage of the reaction takes place as CaO forms, the reaction, then, proceeds at higher temperatures reaching its maximum rate at about 1000degreesC. Alternatively CaTiO3 formation can be effected by 12-h annealing of the activated mixtures at temperatures between 750 and 850degreesC. Partial CaTiO3 formation was realized when starting from physical mixtures neither by rapid heating to 1250degreesC nor by 12-h annealing at temperatures as high as 1000degreesC
Oxidation Behaviour of Mechanically Activated Mn3O4 by TGA/DSC/XRPD
No full textThe 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 lithiated manganese oxides from mechanically activated Li2CO3-Mn3O4 mixtures
No full textThe solid state formation of lithium manganese oxides has been studied from the thermal decomposition of mixtures Li2CO3/Mn3O4 with XLi (lithium cationic fraction) = 0.33
(LiMn2O4), 0.50 (LiMnO2) and 0.66 (Li2MnO3). The analysis of the reactivity has been performed mainly by thermoanalytical (TG/DSC) and diffractometric (XRPD) techniques either on physical mixtures and on mixtures subjected to mechanical activation by high energy
milling. At XLi/0.33, the cubic lithium manganese spinel oxide (LiMn2O4) forms in air. TG measurements showed that the reaction starts at a considerably lower temperature in the
activated mixture. By variable temperature X-ray diffraction it has been assessed that, upon mechanical activation, LiMn2O4 forms directly and its formation is completed within 700 °C
whereas, starting from a physical mixture, the formation goes through Mn2O3 and is complete only at 800 8C. At T>820 °C LiMn2O4 reversibly decomposes to LiMnO2 and Mn3O4 with
an enthalpy of 30.05 kJ mol-1 of LiMn2O4. At XLi=0.50, by annealing under nitrogen flow for 6 h at 650 °C the activated mixture, the orthorhombic LiMnO2 is formed. Such a
formation goes through a mixture of LiMnO2 and LiMn2O4. The enthalpy of LiMnO2 solid state formation from the activated mixture has been determined to be 57.4 kJ mol-1 of
LiMnO2. At XLi=0.66 in air the mechanical activation considerably lowers the temperature within the monoclinic phase Li2MnO3 forms. Besides the reaction enthalpy could be
determined as 40.13 kJ mol-1 of Li2MnO3. The reaction, when performed under nitrogen flow, goes through the formation of LiMnO2. Such a first stage of the reaction is affected by the temperature of reaction rather than by mechanical activation. The activation greatly enhances the second stage of the reaction leading from LiMnO2 to Li2MnO3
Synthesis of SrxBa(1-x)O3 Solid Solutions from the Mechanically Activated System BaCO3-SrCO3-TiO2
No full textMixtures xSrCO3 (1 – x)BaCO3 TiO2 (0 < x < 1) have been mechanically activated by high energy milling in order to promote the formation of mixed (Sr,Ba) carbonate that decomposes, in a single stage, at temperatures generally lower than for the corresponding physical mixtures.
By annealing such milled mixtures at high temperatures (about 1000 °C), cubic solid solutions SrxBa(1-x)TiO3 are obtained (except at x = 0.1 where a tetragonal solid solution forms) whose lattice parameters decrease linearly with x. The enthalpy of solid solution formation changes with composition showing higher values in the x range between x = 0.2 and 0.5, where the reaction has been demonstrated to occur via the formation of Ba2TiO4. By contrast, the enthalpy values
decrease for x > 0.5
Thermogravimetry and X-ray diffraction study of the thermal decomposition processes in Li2CO3-MnCO3 mixtures
Full text linkThe 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
Thermoanalytical (TGA-DSC) and High Temperature X-Ray Diffraction (HT-XRD) Study of the Thermal Decomposition Processes in Li2CO3 – MnO Mixtures
Full text linkThe thermal decomposition processes taking place in solid state mixtures Li2CO3–MnO (XLi=0.10–0.50, XLi=lithium cathionic fraction) have been studied (in air) by High
Resolution Thermogravimetric Analysis (HRes-TGA), Heat Flux Differential Scanning Calorimetry (Heat Flux-DSC) and temperature variable X-ray Powder Diffractometry
(HT-XRPD), in order to get a better understanding of the intermediate reaction stages and to assess the equilibrium compounds as well. As concerns the measurements performed on mixtures with XLi0.333, LiMn2O4 and excess Mn2O3 are the obtained equilibrium products.
By 0.33XLi0.50 a mixture of LiMn2O4 and Li2MnO3 is obtained whose proportions depend on the reaction path followed. A stoichiometric model, where both lithium
manganese oxides form simultaneously, holds for XLi=0.45 and 0.50 mixtures. A two stage model, where Li2MnO3 forms first, followed by reaction with excess Mn2O3 to yield
LiMn2O4, is the reaction path for the XLi=0.35 mixture
Solid State Synthesis of Strontium Oxoferrates from the Mechanically Activated System SrCO3-Fe2O3
No full textThe 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
The Role of Dislocations in the Thermal Dehydration of Lithium Formiate Monohydrate
No full textThe kinetics of lithium formate monohydrate dehdration (single crystal sample) has been investigated at constant temperature, from 317 K to 353 K, under dynamic vacuum both optically and thermogravimetrically
Effect of Mechanical Milling on Solid State Formation of BaTiO3 from BaCO3 – TiO2 (Rutile) Mixtures
No full textThe present work reports the results obtained in the set-up of the preparation method of BaTiO3 by milling and annealing mixtures of BaCO3 and TiO2
Kinetic Parameters from Thermogravimetric Data
No full textThe differential method of Achar, Brindley and Sharp and the integral one of Coats and Redfern are applied to the dehydration of BaB2 * H2O and HCOOLi*H2O and the kinetic parameters so obtained are compared with those deduced isothermally
- …
