Thermogravimetric analysis solids, reactions

When solids react, we would like to know at what temperature the solid state reaction takes place. If the solid decomposes to a different composition, or phase, we would like to have this knowledge so that we can predict and use that knowledge In preparation of desired materials. Sometimes, intermediate compounds form before the final phase. In this chapter, we will detail some of the measurements used to characterize the solid state and methods used to foUow solid state reactions. This will consist of various types of thermal analysis (TA), including differentlEd thermal analysis (DTA), thermogravimetric analysis (TGA) and measurements of optical properties. 

When heated, many solids evolve a gas. For example, most carbonates lose carbon dioxide when heated. Because there is a mass loss, it is possible to determine the extent of the reaction by following the mass of the sample. The technique of thermogravimetric analysis involves heating the sample in a pan surrounded by a furnace. The sample pan is suspended from a microbalance so its mass can be monitored continuously as the temperature is raised (usually as a linear function of time). A recorder provides a graph showing the mass as a function of temperature. From the mass loss, it is often possible to establish the stoichiometry of the reaction. Because the extent of the reaction can be followed, kinetic analysis of the data can be performed. Because mass is the property measured, TGA is useful for... 

When a solid is capable of decomposing by means of several discrete, sequential reactions, the magnitude of each step can be separately evaluated. Thermogravimetric analysis of compound decomposition can also be used to compare the stability of similar compounds. The higher the decomposition temperature of a given compound, the more positive would be the DG value and the greater would be its stability. 

The Powder Diffraction File search was unsuccessful and therefore, further analysis and a structure solution were undertaken. Thermogravimetric analysis in an oxygen atmosphere reveals sharp 7.3 wt. % weight loss at 300°C and the powder diffraction pattern, collected from a solid residue after the TGA, confirms the formation of molybdenum oxide, M0O3. Assuming the following decomposition reaction ... 

In this paper we have measured the resistance dependence and oxygen content of Er Ba2Cu 0Q and Y.Ba Cu OQ - samples above room temperature under the conditions or a simulated sintering and annealing process. The results provide insight into the importance of specific sample preparation procedures. We will start with a detailed discussion of the two most common preparation procedures for copper oxide superconductors at this moment the solid state reaction method and the coprecipitation method. A discussion of the resistance and thermogravimetric analysis (TGA) data and how it correlates to the sample formation will follow. 

We will also examine methods of characterizing such solid state reactions, including DTA (Differential Thermal Analysis) and Thermogravimetric Analysis, i.e,-TGA). We will reserve the discussion of how size of particles and a particle size distribution is determined until the next chapter. 

When SiO (Patinal) was heated in pure O2, thermogravimetric analysis showed a slow weight increase above 1000 °C, but even at 1500 °C oxidation was not exhaustive. When a sample was kept at 1300 °C in air for 48 h, crystalline Si and Si02 (cristobalite) were observed by XRD. Thus, disproportionation into Si and Si02 is much faster than oxidation at this temperature. The conclusion from these experiments is that solid-state reactions of SiO must be carried out at temperatures below 1000 °C to exclude the possibility that the observed products originate from initial oxidation and/or disproportionation reactions. ... 

Shen Xing, Differential Thermal Analysis, Thermogravimetric Analysis and Kinetics of Isothermal Reaction in the Solid State. Beijing, Metallurgical Industry Press, 1995 (in Chinese). 

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