| China has fairly rich reserves of magnesium, most of which exists in the water of sea and salt lake, as the form of MgCl2 or MgSO4. However, we only used the sodium and potassium of the salt lake, with large amounts of magnesium wasted. So, full advantage of magnesium in salt lake and industrial waste has become a problem to be solved urgently.Magnesium hydroxide (Mg(OH)2) whisker is a good flame retardant with good reinforcing properties. It has been widely used as flame retardant in polymers and has tremendous market potentials. So far, the indirect hydrothermal method has been the main method to product Mg(OH)2 whiskers. However, the indirect- hydrothermal method was characterized by problems such as high energy consumption, low yields and complex process and economically unacceptable. As a result, it is significant to prepare Mg(OH)2 whiskers using a simple direct precipitation method, investigate the influence factors of the phase and morphology and exploring the growth mechanism.In this work, Mg(OH)2 particles were prepared by a simple wet precipitation method, and characterized by X-ray diffraction(XRD),scanning electron microscope (SEM), transmission electron microscope(TEM) and Fourier transform spectroscopy (FT-IR). The influence factors of the phase and morphology of Mg(OH)2 whiskers were investigated, such as precipitators, molar ratio of Mg2+ to OH-, concentration of reactants, reaction temperatures, aging temperatures and impurities and so on. It was found that:(1)Ammonium was an appropriate precipitator to prepare Mg(OH)2 whiskers.(2)The molar ratio of Mg2+ and OH- was a critical affecting factor to obtain the matter phase of Mg(OH)2.(3)The concentration of reactants and aging temperatures affected the dispersibility and particle size of Mg(OH)2.(4)At different reaction temperatures, needle-like and lamer-like Mg(OH)2 particles were obtained.(5)Different impurities had complex influences on the crystal phase and morphology.(6)The appropriate processing conditions were: 50 ml MgCl2 solution with concentration 0.5 mol/L, ammonium 15%, n (Mg2+)/n (OH-) 1:2.2, with 0.1g PEG12000 as dispersant and template, reaction temperature 40℃and ageing temperature 60℃. The Mg(OH)2 sample obtained under the above conditions was nanowhisker with diameter about 25-30 nm, and long about 650 nm.The calcium magnesium sludge was acidulated and refined to obtain MgCl2 solution, which was used as the source of magnesium to prepare Mg(OH)2 whiskers, under the processing conditions obtained from single factor test. The Mg(OH)2 sample was nanowhisker with a diameter about 25-30 nm, and long about 650 nm. Basically, its quality was in accordance with the quality indicators of Mg(OH)2 nanoparticles (HG/T 3607-2006).The crystal growth habits of Mg(OH)2 and its affecting factors were analyzed, using the chemical bonding theory. Based on the experimental results, the growth mechanism of Mg(OH)2 nonowhiskers was speculated: It is PEG12000 that played an important role as the dispersant and template, and its work ways were influenced by temperature. At low temperature, PEG12000 was adsorbed on the crystal faces except (001) and (001 ), and then Mg(OH)2 grew along the c axis and formed needle shape. At high temperature, PEG was adsorbed on the crystal faces (001) and (001 ), and then the crystal grew to form lamer shape. |
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