Thermogravimetric analysis solid-state 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. 

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. 

Pyrolysis of ammonia-borane is a complex process, and the products of the decomposition reaction markedly depend on the conditions employed. Furthermore, the initial process is a solid-state reaction for which the onset of decomposition is a function of heating rate of the substrate (P). In thermogravimetric analyzer-Fourier transform infrared (TGA-FTIR) and thermogravimetric analyzer-differential scanning (TGA-DSC) analysis, heating a borazane sample to 90°C at a rate of 0.5°C/ min and then holding it at that temperature for 200 min resulted in a loss of about 10.2% of initial... 

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. ... 

One of the main tasks in the studies of solid-state reactions is the determination of the kinetics of the corresponding reactions. The technology of TA is often used to reveal the thermal behavior and thermal character of solid-state reactions, the primary aim is to establish the values of the apparent activation energy E and pre-exponential factor A in the Arrhenius equation, and to choose the most probable mechanism function f(a) of the reaction. The used mathematical apparatus and calculation procedures are quite varied, but they all are related to the mathematical analysis of thermogravimetric curves [6-8]. The analysis of these curves allows determining the mechanism of rate-controlled stage of the conversion, and the values of the kinetic parameters that characterizing it. 

On thermal decomposition of 1, l,2,2,3,3,4,6,7,8,9-undecachloro-l, 2-dihydro-3i/-phenothiazine (25) the free radical octachloropheno-thiazinyl (26) has been obtained in the solid state by Bodea and Silberg. ° Thermogravimetric and elemental analysis data confirm the following reaction ... 

The presence of the co-ordinated hydroxy-groups was confirmed from i.r. and thermogravimetric data. Oxidative addition of iodine to [Pt(acac)2], either in the solid state or in carbon tetrachloride solution, has yielded the black complex [Pt(acac)2l2]- U.v.-visible and mass spectral measurements show the reaction to be reversible in solution or in the gas phase, and a singlecrystal X-ray analysis (Table 8) indicates trans octahedral geometry for the product. 

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

Similarly, the reactions between solid 1-3 dimethylbarbituric acid (dmb) with vapours of NH3 and of the volatile amines NH2(CH3), and NH(CH3)2 have been investigated [69]. The barbiturate salts [NH4]dmb, [NH3(CH3)]dmb and [NH2(CH3)2]dmb have been characterized by X-ray powder diffraction (XRPD), differential scanning calorimetry and thermogravimetric analysis. The solid-gas reactions were monitored by UV-Vis spectroscopy in the solid state. In the case of [NH2(CH3)2]dmb, recrystallization from methanol yields the salt... 

Thermogravimetry (TG) is the most widely used technique of thermal analysis, in which the mass of a substance is measured as a function of the temperature while it is subjected to a controlled temperature program. The record on the thermogravimetric, or TG, curve is the mass plotted against the temperature (T) or time (f) if the variation of temperature with time can be indicated as well on the same graph. In solid-state decomposition reactions, the reactant material degrades, often to be replaced by the solid product. An example of this is the decomposition of limestone to quicklime. 

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