Preparation and Thermal Decomposition of Basic Magnesium Chloride Whiskers

doi:10.15541/jim20180508

Abstract

Abstract:

Basic magnesium chloride (BMC) whiskers were prepared by hydrothermal method using magnesium chloride and calcium hydroxide as raw materials. Subsequently, nano-MgO was obtained by pyrolysis of the resulting whisker. Transmission electron microscopy (TEM) images showed that the diameter of nano-MgO was between 20 and 40 nm. The corresponding selected-area electron diffraction (SAED) pattern demonstrated the single-crystalline nature with the exposed plane of {111} and {110}. TG-DTG, SEM, XRD, and FT-IR analysis confirmed the four-step pyrolysis processes of BMC whisker. Results showed two molecules of crystal water lost during the first and second steps, respectively. Subsequently, two hydrogen chloride molecules were released in the third step. Finally, hydroxy water was dehydrated. The thermal decomposition kinetics of BMC whisker was studied by means of Satava and differential method. It indicates that the first step of the thermal decomposition of BMC whiskers is random nucleation and subsequent growth mechanism. The second step is two-dimensional diffusion. The third and the final steps are phase boundary reaction and one-dimensional phase boundary reaction mechanism, respectively.

Key words: basic magnesium chloride, nano magnesium oxide, thermal decomposition, whiskers, hydrothermal method

CLC Number:

TQ132

GOU Sheng-Lian, NAI Xue-Ying, XIAO Jian-Fei, YE Jun-Wei, DONG Ya-Ping, LI Wu. Preparation and Thermal Decomposition of Basic Magnesium Chloride Whiskers[J]. Journal of Inorganic Materials, 2019, 34(7): 781-785.

Figures/Tables 9

Fig. 1 XRD patten (a) and SEM image (b) of the sample

Fig. 2 TG-DTA curves of the sample

Fig. 3 XRD patterns of the products burned at different temperatures

Fig. 4 SEM images of the products burned at different temperatures (a) 220 ℃; (b) 300 ℃; (c) 340 ℃; (d) 500 ℃

Fig. 5 TEM images and SAED patterns of the product burned at 500 ℃

Fig. 6 FT-IR spectra of the products burned at different temperatures (a) BMC; (b) 220 ℃; (c) 300 ℃; (d) 340 ℃; (e) 500 ℃

Table 1 Algebraic expressions of G(α) and the correlation coefficients for the four decomposition steps

Function name	Mechanism	G(α)	R²
Function name	Mechanism	G(α)	Ⅰ	Ⅱ	Ⅲ	Ⅳ
Avrami-Erofeev equation	Random nucleation and its subsequent growth	[-ln(1-α)]^3/4	0.9991	0.9521	0.9129	0.9829
Jander equation	Two-dimensional diffusion	[1-(1-α)^1/2]^1/2	0.9716	0.9978	0.9919	0.9957
Mampel power low	Phase boundary reaction	α^1/2	0.9598	0.9929	0.9970	0.9817
Mampel power low	Phase boundary reaction(One-dimensional)	α	0.9988	0.9932	0.9916	0.9996

Fig. 7 Diagram of a and b

Table 2 Dynamic calculation results of the thermal decomposition of BMC whiskers

Parameter	Ⅰ	Ⅱ	Ⅲ	Ⅳ
n	0.6	0.6	0.5	1.1
E/(kJ?mol^-1)	38.16	152.35	125.38	85.52
A/min^-1	1.01×10⁵	4.87×10¹⁴	3.65×10¹⁰	1.90×10⁶

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