Abstract
Magnesium hydroxide and hydromagnesite nano and microstructures have been prepared by using microwave-assisted technique. Magnesium chloride, magnesium acetate and magnesium metal have been used as a magnesium source. Urea has been added to the solution with controlled pH=10 while the temperature was 220°C. The hydrolysis of urea under these hydrothermal conditions leads to the production of hydromagnesite instead of magnesium hydroxide. The as-prepared samples were investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), thermographmetric analysis (TGA) and differential scanning calorimetry (DSC). SEM shows a wide distribution of pseudo-hexagonal nanodisk up to microdisk. Spherical rosette morphology has been noticed in the samples in which the urea has been used. XRD reveals the existence of Mg(OH)2 with some impurities which can be attributed to the high concentrations of the initial materials and absorption of carbon dioxide from the air when urea is not employed and hydromagnesite when urea is present in the synthesis. TGA showed a weight loss within the temperature range of 360–450°C with a total percentage of weight loss 29% which can be attributed to the (Mg(OH)2). However in the case of synthesis with urea the weight loss was 57% which is the expected value for hydromagnesite. The production of pure hydromagnesite utilizing hydrothermal methods has been reported; the synthesis reported here is much simpler and faster.
A microvave assisted synthesis of hydrous magnesium compounds demonstrates the ability to rapidly synthesize nanocrystalline Mg(OH)2 and hydromagnesite in high purity. The hydromagnesite exhibits a rosette morphology that results in high surface areas and is mediated by urea. [Display omitted]
► Synthesis of hydrous magnesium compounds is dominated by the urea hydrolysis reaction. ► High purity crystalline hydromagnesite is only produced when urea is present. ► Microwave method gives a very highly crystalline hydromagnesite in a very short time.