Crystallization To Improve Powder Flow And Preparation Of High Mobility Highly Activity Magnesium Oxide

Powders are the most common form of solids and have the advantage of being easy to measure,transfer and process.In many industries such as pharmaceuticals,food,construction,agriculture,energy,environmental protection and others,products,raw materials or intermediates are generally in powder form.Powder flow has an important influence on production,safety and product quality and is a key property of powders that needs to be controlled.Granulation,coating and spray drying are generally used to improve powder flowability.Crystallisation,as a common method for powder production,has its own unique advantages in improving powder flowability.In this study,the application of crystallisation in improving powder flowability was investigated which activated magnesium oxide and mannitol were used.Activated magnesium oxide has a high activity and is widely used in environmental protection,electronic materials and pharmaceuticals.Magnesium oxide particles are generally small and poorly flowable.During the development of a laxative,it was found to be difficult to mix uniformly with the excipients.In order to prepare a highly active and fluid magnesium oxide,various precursors have been investigated and finally ammonium magnesium carbonate chosed.Magnesium ammonium carbonate crystals are nearly spherical and have good powder flowability.The crystal structure of magnesium ammonium carbonate was solved for the first time by incubating single crystals,and the mechanism of thermal decomposition of magnesium ammonium carbonate was analysed by its structure.Ammonium magnesium carbonate decomposes at room temperature to release ammonia gas,which can be converted to magnesium oxide at about 400°C.The whole decomposition process gives off significantly more gas than other carbonates,thus facilitating to obtain highlyactive magnesium oxide.By controlling the decomposition temperature and rate,the particle shape can be kept unchanged,which is beneficial to obtain high fluidity powder.By controlling the particle size distribution and morphology of ammonium magnesium carbonate,eventually highly active and highly mobile magnesium oxide has been obtained with a near spherical shape and a D₅₀ of up to 60μm.In crystallisation,mannitol tends to form needle-like crystals with low powder stack density and poor flowability.We investigated the method of spherical agglomeration and ended up with a mannitol product with good flowability and high stack density.Mannitol crystals were prepared by solvatochromic crystallisation with water as the solvent and acetone as the counter-solvent,then gradually added ethyl acetate to the solution until the solvent began to appear in a liquid-liquid phase.The small amount of liquid phase that separated out stuck the mannitol crystals together and slowly agglomerated under stirring,resulting in agglomerated spherical mannitol particles with adjustable particle sizes from 100μm to 3 mm and an increased stack density from 0.15 g/cm³ to 0.8 g/cm³.In conclusion,both inorganic and organic small molecule crystals have found ways to improve their powder flowability,significantly increasing the product’s stack density and powder flowability.These methods are generalisable and are expected to be extended to other powder products to improve their powder properties.