Advanced Materials Research
ISSN: 1662-8985, Vol. 624, pp 313-316
doi:10.4028/www.scientific.net/AMR.624.313
© 2013 Trans Tech Publications, Switzerland
Online: 2012-12-27
Preparation of Fibrous Basic Magnesium Chloride Single Crystal
Qingli Ren1,a and Qiang Luo2,b
1
School of Technical Physics, Xidian University, Xi’an 710071, China
2
The Second Artillery Institute of Engineering, Xi’an 710025, China
a
b
[email protected], [email protected]
Keywords: basic magnesium chloride, fibrous, preparation
Abstract: The preparation of fibrous basic magnesium chloride single crystal was investigated. And
the fibrous basic magnesium chloride single crystal samples were prepared by liquid reaction method
at the atmospheric pressure. Based on the test results of SEM, TEM diffraction and XRD, the effects
of the mole rate of calcium hydroxide to magnesium chloride, reaction temperature, mixing time and
ripening time on the preparation of the fibrous basic magnesium chloride single crystal are discussed.
And based on the output and the length of the fibrous, the best technological conditions for preparing
the fibrous basic magnesium chloride are as follows: (1) the mole rate of calcium hydroxide to
magnesium chloride is between 0.35 and 0.4; (2) the reaction temperature is 45 centigrade
temperature degree; (3) the mixing time is between 2 hours and 5 hours; (4) the ripening time is
between 24 hours and 36 hours. The fibrous basic magnesium chloride single crystal, whose length is
about between 30µm and 100µm and whose diameter is about between 0.2µm and 1µm, is obtained.
Introduction
Flame-retardant materials are extensively used for safety in cable industry. Their practical use
requires the following properties: avoiding short-circuits between neighboring wires, producing a
minimum of toxic gases and dark smoke during pyrolysis, and keeping good mechanical properties.
Such fire behavior can be achieved by developing polymer compounds whose formulations contain a
variable loading of inorganic fillers.
Fibrous basic magnesium chloride is a new kind of such inorganic fillers [1,2]. However, known
deposits of natural fibrous basic magnesium chloride are very little on the earth [1]. And previous
attempts to synthesize this kind of fibrous are not much practical for industrial scale production of
synthetic basic magnesium chloride by reason of high pressures and the need of rinse process with the
use of ethanol [3]. The purpose of the present work is to study the preparation of fibrous basic
magnesium chloride single crystal by liquid reaction method at the atmospheric pressure and without
using ethanol for the sample’s rinse.
Experiment
The reagents MgCl2 and Ca(OH)2 were weighted in a proper mol ratio according to the nominal
composition Mg2(OH)3Cl·4H2O and mixed in water by stirring for n hours at about 45-90 centigrade
temperature degree at atmospheric pressure. The slurry was then ripened at 40 centigrade temperature
degree for m hours.
X-ray diffraction data were obtained with a Rigaku D/MAX-2400 X-ray diffractometer with CuKα
radiation. And the microstructures of the samples were observed by the JXA-840 scanning electron
microscope (SEM) and the JEM-200CX transmission electron microscope (TEM).
Results
Scanning Electron Microscopy. Fig.1, Fig.2, Fig.3 and Fig.4 show the SEM photos for fibrous basic
magnesium chloride samples made in different technology process, where the mole rate of Ca(OH)2
to MgCl2 is between 0.35 and 0.55 and the reaction temperature is about 45-90 centigrade temperature
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degree and the mixing time is between 2 hours and 10 hours and the ripening time is 5-72 hours. It is
clear that both the length and the output of the fibrous basic magnesium chloride decrease with
increasing the the mole rate of Ca(OH)2 to MgCl2 from 0.35 to 0.55. Moreover, compared with the
ripening time of 35 hours, either for that of 5 hours or 72 hours, the length and the output of the
fibrous are decreased. But the length and the output of the fibrous are affected little either by the
mixing time or by the reaction temperature.
Transmission Electron Microscopy. Fig.5 shows the electron diffraction spot for the fibrous
whose SEM photos is Fig. 3(b), which indicates that the fibrous is a kind of single crystal.
(a) 0.35
(b) 0.45
(c) 0.55
Fig.1 SEM photos of the fibrous with different the mole rate of Ca(OH)2 to MgCl2.
(a) 45 centigrade temperature degree
(b) 90 centigrade temperature degree
Fig.2 SEM photos of the fibrous with different reaction temperature
(a) 5 hours
(b) 35 hours
(c) 72 hours
Fig.3 SEM photos of the fibrous with different ripening time.
(a) 2 hours
(b) 10 hours
Fig.4 SEM photos of the fibrous with different mixing time
Advanced Materials Research Vol. 624
Fig.5 The electron diffraction of TEM for the
fibrous shown in Fig. 3(b)
315
Fig.6 The XRD pattern for the fibrous shown in
Fig.1(a)
Phase Composition. Fig.6 shows the XRD pattern for the fibrous sample whose mole rate of
Ca(OH)2 to MgCl2 is 0.35 (see Fig.1(a))， which shows that the highly pure fibrous basic magnesium
chloride Mg2(OH)3Cl·4H2O single crystal is obtained.
Discussion
According to the modern liquid theory [4,5], both the positive ion and negative ion do not serve alone
as an isolated ion shape in the electrolyte liquid. In the non-concluded electrolyte liquid, each ion is
surrounded by oppositely charged ions in a spherical microscopic region. And in a concluded
electrolyte liquid, the new gathering body can be formed if the distance between the positive and
negative ions is of about a certain critical value and the Coulomb attraction energy between the ions is
greater than their thermal moving energy. These ion-gathering bodies have so much stable enough
energy that the solvent molecule can not separate them by collision. If these ions gathering bodies can
translate to a more stable phase through the chemical reaction, there are growth units of the more
stable phase.
The complex ions, which are composed of center cation and hydroxyl (OH-), are found in the
liquid. They are especially in the nearby region of the crystal interface according to the test results of
the Raman spectrum, IR spectrum and the low-angle diffraction of the X-ray. Moreover, the stability
of the cation which complexes the hydroxyl (OH-) and forms the complex ions is higher than that of
the single cation based on the calculation of the complex ion combined energy [6].
Based on the above theory and the above experimental results, the reagents MgCl2 and Ca(OH)2
offer Mg2+, Cl-, OH- for fibrous basic magnesium chloride Mg2(OH)3Cl·4H2O. So, the mole rate of
Ca(OH)2 to MgCl2 determines the number of the positive ion Mg2+ and negative ion Cl-, OH-, which
affects the ion-gathering bodies related with the formation of Mg2(OH)3Cl·4H2O. And with a more
reasonable ripening time, the complex ions, which are composed of center cation Mg2+ and hydroxyl
(OH-), can translate to a more stable phase Mg2(OH)3Cl·4H2O by combining with Cl- and H2O.
Otherwise, when the ripening time is bigger than 35 hours or when the mole rate of Ca(OH)2 to MgCl2
is bigger than 0.45, there are many positive ion Ca2+ in the reaction liquid, which tend to move into the
nearby region of containing OH- or Cl- and greatly impede the formation of the complex ions of OH-,
Cl- and Mg2+, where these ions Cl-, OH- and Mg2+ tend to combine together and translate to a more
stable phase Mg2(OH)3Cl·4H2O by crystal growth. So, the complex ions of the center cation Mg2+ and
hydroxyl OH- or Cl- can be separated by collision of the Ca2+ ions.
Summary
The highly pure fibrous basic magnesium chloride Mg2(OH)3Cl·4H2O was synthesized. The fibrous
is indexed as a kind of single crystal, whose length is about 30-100µm and whose diameter is about
0.2-1µm. The mole rate of Ca(OH)2 to MgCl2 and the more reasonable ripening time determine
ion-gathering bodies and their translating to a more stable phase through the chemical reaction, which
affect the crystal growth of the highly pure fibrous basic magnesium chloride Mg2(OH)3Cl·4H2O
finally.
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Acknowledgement
The project supported by “the Fundamental Research Funds for the Central Universities”.
References
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system, J of Inorganic Materials. 25 (2010) 129-134.
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