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Kinetics of thermal decomposition of copper basic carbonate: Part I. The analysis of thermogravimetric data

The bubbles have been widely applied in industrial processing, including steelmaking. Recently, industrial trials of natively generated bubbles via decomposition reactions have been successfully adopted in steel refining and inclusion removal. The refining efficiency was proved to be outstanding due to the small bubble sizes and the subsequent satisfying dynamic conditions. However, the bubble behaviors, including growth and detachment, are still not thoroughly clarified due to the strict requirements for observation conditions. Therefore, the growth and detachment behavior of the bubbles generated by decomposition reactions were carefully observed with physical modeling and shadow imaging method. The detachment sizes of the bubbles were extracted accordingly. Based on the statistical data on the detachment bubble sizes, a traditional nozzle flow model was modified for the prediction of the bubble detachment size in decomposition reactions. This work provides the foundation for further studies on the interaction mechanism between the natively generated bubbles and the impurities in liquid steel in terms of inclusion removal.

The spectral emissivity of basic copper carbonate (Cu₂(OH)₂CO₃) was measured by a Fourier Transform Infrared (FTIR) spectrometer in the wavelength range of 5–20 μm during the heating process, and the integral emissivity was calculated to study the effect of decomposition on emissivity. The surface composition of the samples was investigated by X-ray diffraction. Based on the spectral emissivity data and the measurement of X-ray diffraction, it can be concluded that Cu₂(OH)₂CO₃ starts breaking down at 513 K and exists a critical state at 453–493 K. This state would cause a drop in spectral emissivity value, and enhance the oscillation intensity of spectral emissivity in 5–8 μm and spectral absorption at 14.95 μm. Above 513 K, heating time and temperature have great influences on emissivity. The emissivity changes more obvious as the increasing temperature. The emissivity of Cu₂(OH)₂CO₃ gradually tends to be stable with heating time when the decomposition process is completed.

The influence of self-generated gaseous products on the kinetics and mechanism of the thermal decomposition of synthetic malachite, Cu₂CO₃(OH)₂, was investigated by means of conventional TG–DTA under various atmospheric conditions, TG–MS and CRTA under a reduced atmospheric condition, and powder X-ray diffractometry of the partially decomposed sample. It was found that the sample decomposes at a lower temperature under a higher partial pressure of self-generated gases. This interesting behavior, in contrast to the general consideration of chemical equilibrium, results from catalytic action of evolved H₂O on the crystallization of the product CuO, and from an interaction of evolved CO₂ with poorly crystallized CuO under reduced pressure.

The thermal decomposition of copper hydroxy carbonate was examined using conventional rising temperature thermogravimetry and constant rate thermal analysis (CRTA). The low-pressure CRTA results showed that the two product gases, water and carbon dioxide, are evolved at different rates throughout the decomposition. A CRTA apparatus using infrared gas detectors was able to measure and control the evolution of these two gases independently and established that more water is evolved at the start of the reaction and more carbon dioxide near the end. The kinetics of the reaction were investigated using both rising temperature and CRTA results and reasonable agreement was found for the activation energy. However, the results for the reaction mechanism proved inconclusive. The development of the surface area as a function of the extent of reaction was investigated and found to be markedly non-linear. This fact is discussed in relation to the evolved gas results and a previously proposed mechanism for solid state decomposition reactions.

The thermal decomposition of basic copper carbonate, CuCO₃ · Cu(OH)₂ · H₂O, was studied by high-pressure DTA under high-pressure carbon dioxide (0–50 atm).

The DTA-TG measurement in air showed that the peak temperature was influenced more by heating rate than by sample weight.

Decomposition via dehydration and decarbonation was rapidly finished in a single step, and no intermediate was found. The decomposition temperature was strongly influenced by the partial pressure of carbon dioxide. The decomposition temperature increased in the range 0 atm < _Pco2 < 7 atm, but was nearly constant above P_co2 = 7 atm. Explaining these phenomena was approached by various considerations.