Nano magnesium oxide (MgO) is a new type of high-functional fine inorganic material, which has some optical, thermal, electrical, magnetic, mechanical and chemical properties different from those of the body due to the special effects of the surface effect, volume effect, quantum size effect and macroscopic quantum tunneling effect of nanomaterials. In recent years, it has important applications in the fields of antimicrobial agents, catalysts, adsorbents, advanced ceramics, optoelectronic materials, refractory materials, fillers, medicine and so on. Nano magnesium oxide usually has different morphological features, and different morphological features lead to different properties, and its main forms are powder, film, sheet, rod, tube, filament, etc., as well as some special morphology.
The currently reported methods for the preparation of magnesium oxide nanoparticles are mainly divided into gas-phase, solid-phase and liquid-phase methods, of which solid-phase and liquid-phase methods are the most common, and the solid-phase methods mainly include mineral calcination, mechanical pulverization, and solid-phase chemical reaction. Liquid-phase methods mainly include precipitation method, sol-gel method, electrochemical method, metal-alcohol salt hydrolysis method, hydrothermal method, dolomite carbonization method, microwave method, microemulsion method and so on. Among them, mineral calcination method is one of the commonly used methods for large-scale preparation of magnesium oxide due to abundant raw materials and low cost, but the commonly used minerals are usually magnesite, which usually requires complex pretreatment process before calcination, and most of the produced magnesium oxide is low-end. And although the quality of magnesium oxide produced in the liquid-phase method is high, the method requires a large number of chemical reagents, and even the introduction of organic impurities causing pollution, and the equipment requirements, high cost, and industrialized production is facing challenges. Therefore, it is an important task at present to find a method with low cost, no pollution and suitable for industrial production of high quality magnesium oxide products.
Hydromagnesite is a kind of natural alkali carbonate minerals with abundant reserves. in the late 1950s, the mineral was first discovered in Tibet, such as Bango Lake and other areas. China has now proved the Hydromagnesite resource content of more than 100 million tons, is a rare large-scale deposits, mainly distributed in the northern Tibet salt lake area and some salt lake zone in Qinghai. Hydromagnesite pure texture, white color, “snow-white” or “white-flower” called, its chemical formula is 4MgCO·Mg(OH)·4H2O, in which the content of CaO and other impurities is low, the impact on the general application is very small, is the preparation of flame retardant, active magnesium oxide, heavy magnesium alkali carbonate, nano-magnesium hydroxide and other magnesium products such as high-quality raw materials of minerals. However, due to geographical, transportation and other factors, it has not been better developed and utilized, and the research on the preparation of different characteristics of nano-magnesium oxide from hydromagnesite has not been reported.
Preparation method
Hebei Messi Biology Co., Ltd. adopts the process route of “calcination-hydration-calcination” to prepare magnesium oxide nanoparticles. The specific steps are as follows:
Calcination: Hydromagnesite at high temperature to get magnesium oxide. The calcination temperature and time have a significant effect on the morphology, crystallinity, grain size and specific surface area of magnesium oxide. For example, calcining at 650°C for 1 hour can obtain mesoporous reticulated magnesium oxide with a specific surface area as high as 188.3 m²/g, while calcining at 850°C for 4 hours can obtain rod-like and dumbbell-like magnesium oxide nanoparticles.
Hydration: The calcined magnesium oxide was hydrated to form magnesium hydroxide. The hydration step can further improve the crystallinity and grain growth of magnesium hydroxide.
Re-calcination: the hydrated magnesium hydroxide is calcined again to obtain magnesium oxide nanoparticles with different morphologies. For example, calcination after the second hydration can obtain magnesium hydroxide nanoparticles with hexagonal flakes, and further calcination can obtain flaky magnesium oxide nanoparticles.
Factors affecting the properties of nanoparticles in the preparation process
Temperature: the increase of temperature or the extension of calcination time can help to improve the crystallinity of magnesium oxide and promote the growth of crystals, but it will reduce the specific surface area.
Time: The length of calcination time also affects the morphology and crystallinity of magnesium oxide. For example, calcining at 650°C for 1 hour can obtain mesoporous reticulated magnesium oxide with high specific surface area, while calcining at 850°C for 4 hours can obtain rod-like and dumbbell-like magnesium oxide nanoparticles.
Hydration conditions: the hydration step can change the crystallinity and grain growth of magnesium hydroxide, further affecting the morphology and properties of the final magnesium oxide nanoparticles.
Equipment and techniques used in the preparation process
During the preparation process, a variety of testing instruments were used to characterize the products, including thermogravimetric analysis (TG-DTG), specific surface area test (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
By controlling the above steps and conditions, magnesium oxide nanoparticles with different morphologies and properties can be successfully prepared, which are widely used in the fields of antimicrobial agents, catalysts, adsorbents, advanced ceramics, photovoltaic materials, refractories, fillers, and pharmaceuticals.