Preparation of tricobalt tetroxide by thermal decomposition of basic cobalt carbonate and its characterization_Industrial additives

Cobalt tetraoxide (Co3O4) is widely used in lithium-ion batteries [1-3], gas sensors [3], catalysts [4], magnetic materials [5] and other fields. Methods for preparing Co3O4 include thermal decomposition method [6-8], sol-gel method [9], hydrothermal method [10-11], solvothermal method [12-13], etc. At present, the thermal decomposition of cobalt salts is widely used in industry to prepare Co3O4. This method is simple and easy to operate. In the early days, cobalt nitrate, cobalt oxalate, cobalt acetate, etc. were used for thermal decomposition. In recent years, carbonate precipitation is used to prepare the precursor, and then oxidation and calcination are used to prepare Co3O4. Using this method can reduce production costs.

Co3O4 produced by a separate thermal decomposition method has poor activity, low purity, easy agglomeration, large particle size, and wide particle size distribution. The hydrothermal-pyrolysis method uses hydrothermal reaction to prepare precursors and then roasts them in air. It is an effective method to prepare nano-oxides with different morphologies [14-15]. It has the advantages of mild hydrothermal method conditions, high product purity, complete grain development, small particle size and uniform distribution, no agglomeration, good dispersion, and controllable shape. Since the morphology and particle size of Co3O4 have a significant impact on its physical and electrochemical properties [3], the author of this article used a hydrothermal method to prepare the basic cobalt carbonate precursor, and then thermally decomposed the precursor. Globular chain and quasi-spherical Co3O4 were prepared, and the structure and morphology of the precursor and Co3O4 product were characterized.

Preparation of cobalt tetraoxide by thermal decomposition of basic cobalt carbonate and its characterization 1 experiment

1.1 Sample preparation

Dissolve 10 mmol Co (CH3COO) 2·4H2O in 10 mL deionized water, add 15 mL 50 g/L polyethylene glycol (relative molecular mass approximately 20000) and 15 mL n-butanol to prepare a solution A; Dissolve 10 mmol (NH4) 2CO3 in 30 mL deionized water to prepare solution B. At 30°C and under magnetic stirring, slowly drop solution B into solution A. After the dropwise addition is completed, transfer the mixed solution into a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene. The filling degree is 75%, after sealing, heat it to 160°C and keep it for 10 hours, and then cool it naturally to room temperature. Centrifuge the purple-red precipitate in the reaction kettle, wash it with deionized water and absolute ethanol three times each, and dry it at 80°C for 6 h to obtain the Co2 (OH) 2CO3 precursor. The precursor is calcined at 450°C for 3 hours. h and adopt a two-stage thermal decomposition method, that is, calcining at ℃ for 1 h and then calcining at 800℃ for 2 h to obtain the Co3O4 product.

1.2 Characterization of samples

The American Mettler TGA/SDTA 851e simultaneous thermal analyzer was used to conduct thermogravimetric analysis of the precursor. An air atmosphere was used during the test, the heating rate was 5°C/min, and the temperature analysis range was room temperature to 800°C; Avatar from Nicolet, the United States was used The 360 ​​infrared spectrometer was used to test the infrared spectra of the precursor and the calcined product; a Rigaku D/Max2500 model 18 k W rotating target X-ray diffractometer (Cu Kα ray, wavelength λ=0.154 056 nm, tube voltage of 40 kV, Rigaku, Japan) was used. The current is 250 mA, the step width is 0.02°, and the diffraction angle (2θ) range is 10o~70o). Analyze the phase composition of the praseodymium carbonate precursor at 25~500℃; use the JEM-1230 transmission electron microscope of JEOL, Japan. The morphology and particle size of the precursors and calcined products were analyzed.

2 Results and discussion

2.1 Thermogravimetric curve of precursor

Figure 1 shows the thermogravimetric (TG) and derivative thermogravimetric (DTG) curves of the precursor. It can be seen from the TG curve that the mass loss of the precursor is divided into two processes: the first process is
The precursor loses adsorbed water, and its mass loss rate is about 4%; the second process is the decomposition of Co2 (OH) 2CO3, and its mass loss rate is about 28%. It can be seen from the DTG curve that the precursor has a peak at around 275°C, which corresponds to the decomposition of Co2 (OH) 2CO3 to generate Co3O4. When the temperature is ~800°C, its mass remains basically unchanged, indicating that Co3O4 formed by thermal decomposition has good thermal stability in this temperature range.

The decomposition process of the precursor can be expressed by the following reaction equation:

2.2 Infrared spectrum analysis

Figure 2 shows the infrared (IR) spectrum of the basic cobalt carbonate precursor and the Co3O4 product obtained by calcining the precursor at 450°C for 3 h. It can be seen that the O—H bond stretching vibration absorption peaks in the precursor are located at 3 500.81 and 3 380.02 cm-1, and the characteristic absorption peaks of CO32- are located at 1 548.20, 1 348.26 and 836.15 cm-1. There is no Co— in Co3O4. The absorption peak of O bond indicates that the precursor after hydrothermal treatment is basic cobalt carbonate. The product of the precursor calcined at 450°C for 3 h has stretching vibration absorption peaks of the Co—O bond in Co3O4 at 660.81 and 562.47cm-1, indicating that the product at this time is Co3O4.

2.3 X-ray diffraction analysis

Figure 3 shows the X-ray diffraction (XRD) spectrum of the precursor at 25~500°C. It can be seen that the X-ray diffraction peak of the precursor at 25~250℃ is consistent with the characteristic peak of Co2 (OH) 2CO3, indicating that after using (NH4) 2CO3 as the precipitant and hydrothermal treatment, the obtained precursor is Co2 (OH) 2CO3 . The X-ray diffraction results of the product when the precursor is at 270~500°C are consistent with the cubic phase Co3O4 results of the X-ray diffractometer’s built-in software. It does not contain any impurity peaks, indicating that the obtained product is cubic phase Co3O4, and with temperature As the value increases, the diffraction peaks of the product become sharper, indicating that the Co3O4 grains gradually grow and its crystal structure becomes more complete. Table 1 shows the lattice constants (a, b and c), unit cell volume and density of Co3O4 products at 290~500℃. It can be seen that as the temperature increases, the lattice constant and unit cell volume of Co3O4 increase slightly, but the density of Co3O4 decreases slightly.

Preparation of cobalt tetraoxide by thermal decomposition of basic cobalt carbonate and its characterization 3 Conclusion

a. Using cobalt acetate as the cobalt source, ammonium carbonate as the precipitant, polyethyleneAlcohol (relative molecular mass is about 20 000) is used as surfactant. In a water-n-butanol solvent system, after hydrothermal treatment, a flaky basic cobalt carbonate precursor with a length of about 2µm and a width of about 1µm is obtained. Thermal decomposition of the precursor can produce cubic phase Co3O4.

b. Different thermal decomposition methods are used to process the basic cobalt carbonate precursor to obtain different morphologies of Co3O4. The precursor was calcined at 450°C for 3 h to obtain spherical chain Co3O4 with a diameter of about 40 nm and a length of about 100 nm; and a two-stage heat treatment method was used to calcine the precursor calcium bicarbonate body at °C for 1 hour and then calcined at 800°C for 2 h, spherical Co3O4 was obtained. As the calcination temperature increases, the morphology of Co3O4 changes, and the obtained Co3O4 shows a spheroidization trend.