Replacement nano dry drying method
    Drying method is the so-called displacement liquid phase resulting precipitate was dried in a solvent before use water displacer ( including organic solvents, liquid carbon dioxide , supercritical carbon dioxide, etc. ) for the replacement process , and then using an appropriate drying method to obtain nano-materials product method of operation .
    In the wet chemical method nanopowders , you need pretreatment before drying filtering process, washed several times with deionized water . Remaining in the liquid phase as various impurity ions removed , but after washing drying process , will inevitably lead to agglomeration of the powder particles . A surface tension lower than water, an organic solvent instead of water remaining in the particles , less agglomeration of the powder can be obtained . The amount of the solvent for the gel , is often required for subsequent drying process . Replacement method used mainly in the following four kinds .
    An organic solvent washing . Precipitate with an organic solvent ( or gel ) for repeated soaking, washing, filtration ( coagulation effect for the preparation of bulk and generally do not filter this step ) , the maximum extent possible to remove moisture , so the drying process powder particles caused ask reunion. Common organic solvents are : methanol , ethanol , butanol , tert-butanol , acetone , hexane , and silicone oil .
    2 azeotropic distillation . The suspension is made of nano- powders , washed with water , after which the secrets of impurities , and then added to the water partially miscible with ( or immiscible ) and a boiling point higher than water, an organic solvent in the azeotropic distillation with stirring , the water and an organic solvent to form a minimum azeotrope is removed to maximize . Azeotropic distillation of the solvent : n- butanol, isoamyl alcohol , isopropyl drunk , propanol , ethylene glycol , ethanol, benzene , toluene , etc. The most commonly used is n-butanol .
    3 . Liquid carbon dioxide replacement . Because liquid carbon dioxide solubility in water is very small , so during supercritical carbon dioxide prior to drying the gel to substitution with an organic solvent to obtain an organic solvent in the aqueous gel , liquid carbon dioxide and then the organic solvent replacement sentence .
    4 supercritical carbon dioxide extraction replacement . Small holes in the gel , the gel liquid carbon dioxide diffuses into the holes takes a long time , therefore , the liquid carbon dioxide replacement operation takes a long time . If the solvent exchange process used liquid carbon dioxide into a supercritical carbon dioxide fluid is supercritical carbon dioxide extraction replacement .