Study on the changes of emissivity of basic copper carbonate in the decomposition process

https://doi.org/10.1016/j.ijheatmasstransfer.2019.05.047Get rights and content

Highlights

  • Emissivity of Cu2(OH)2CO3 in the thermal decomposition is studied.

  • The Cu2(OH)2CO3 exists a critical state prior to its decomposition (453–493 K).

  • Microscopic discussion on the decomposition process of Cu2(OH)2CO3 by surface emissivity.

Abstract

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.

Introduction

Basic copper carbonate is usually used in catalysts, pyrotechnics, pesticides, pigments, fungicides, electroplating, antisepsis, and manufacture of copper compounds [1], [2], [3], [4], [5], [6], [7], [8]. And a systematical study on the thermal decomposition of basic copper carbonate has great significance in industry, agriculture, and scientific research, etc. [9], [10], [11], [12]. In the previous research, the thermogravimetric analysis (TGA) and the differential thermal analysis (DTA) were generally used to determine the kinetic parameters, the activation energy and the reaction order of thermal decomposition of basic copper carbonate. The effects of different atmospheric environments and different pressures on the decomposition of Cu2(OH)2CO3 were studied by DTA-TG, DTGA and high-pressure DTA, and the relation between different concentration products and the decomposition rate were reported [13], [14], [15], [16]. In order to describe the properties of Cu2(OH)2CO3 more detail, the FTIR spectra and the Raman spectra of Cu2(OH)2CO3 were studied at room temperature, and the spectral absorption caused by chemical bonds of basic copper salts (malachite, Cu2(OH)2CO3) have been reported systematically [16], [17], [18], [19].

In the thermal decomposition process, Cu2(OH)2CO3 would decompose into CuO, H2O and CO2. These changes in composition and surface structure would lead to a huge variation in infrared spectra. Several literatures have studied the decomposition temperature of Cu2(OH)2CO3 by the methods of DTA and TG. For instance, ZD Z¯ivković et al. have reported that the thermal decomposition reaction of Cu2(OH)2CO3 begins at 493 K [14]. And Ivan M. Uzunov et al. have reported that the quasi-isothermal decomposition of Cu2(OH)2CO3 occurs at 513–553 K [15]. However, few spectral data in the decomposition process has been reported in detail.

The spectral emissivity is an important thermophysical parameter of solid surface. The spectral emissivity of Cu2(OH)2CO3 can not only provide the key parameter for radiation temperature measurement of the surface in the decomposition process, but can help to monitor the composition changes on-line [20], [21]. In this paper, the infrared spectral emissivity of basic copper carbonate was measured by a FTIR spectrometer in the wavelength range from 5 to 20 μm and temperature between 373 and 573 K. And the integral emissivity was calculated to study the effect of decomposition on emissivity. The effect of heating temperature and heating time on emissivity was investigated systematically. Additionally, the components of the surface were investigated by X-ray diffraction to verify the degree of decomposition of the samples heated at different temperatures for 60 min.

Section snippets

Definition of emissivity

The normal spectral emissivity given by ελ(T) is the ratio of spectral radiance intensity of a real surface to that of the ideal blackbody [22], [23], [24].ελ(T)=Ls(λ,T)Lbb(λ,T)where, Ls(λ,T) and Lbb(λ,T) respectively represent the spectral radiance intensity from the sample and blackbody at the same wavelength and temperature. And the normal spectral radiance L is measured in terms of [W/(m2⋅sr⋅μm)] units (per spatial angle). Based on the definition, the integral radiant emissivity can be

Spectral emissivity of Cu2(OH)2CO3 in the decomposition process

The data of spectral emissivity of Cu2(OH)2CO3 were obtained under different temperature conditions in the decomposition process. As shown in Fig. 2(a), the spectral emissivity at 373, 393, 413 and 433 K shows a similar trend. The curves decrease with wavelength and oscillate obviously in 5–8 μm. One possible reason cause this oscillation could be the absorption of H2O considering that the infrared radiation is transmitted in atmospheric environment. Another possibility is that the apparatus

Conclusion

In this paper, the spectral emissivity of Cu2(OH)2CO3 was measured by a FTIR spectrometer from 5 to 20 μm in the heating process, and the effect of heating temperature and heating time on emissivity was investigated systematically.

In the temperature range from 373 to 433 K, the emissivity of Cu2(OH)2CO3 increases with temperature, and the spectral emissivity at different temperature shows a similar trend: the curves decrease with wavelength and oscillate obviously in 5–8 μm; a strong peak can

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 61675065, 61627818 and 61475043).

References (31)

Cited by (0)

View full text