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How to change Zinc Oxide surface area/particle size?

  1. Oct 19, 2012 #1
    Hello,

    I need some help with my research on zinc oxide. It is produced through melting of zinc and vapourization process. Now the question is how the surface area can be manipulated as per requirements or if possible can particle size also be manipulated ?

    thanks...
     
  2. jcsd
  3. Oct 19, 2012 #2
    Zinc oxide is produced in nanoscale particles for use in some cosmetic products and/or sunscreens. Whether details of particle size control are available in the open literature rather than as commercial secrets I do not know -- you would have to research that for yourself.

    The secret of making very small particles of any substance is to arrange conditions so that plenty of seed crystallites will nucleate, but larger crystals will have no opportunity to grow. This often implies some sort of "shock treatment" -- for example quenching a melt by immersion of small drops in a much colder liquid, or arranging for sudden disappearance of a solvent. A simple example is preparation of small particles of sulfur by dissolving the sulfur in acetone, and then adding the solution dropwise to near-boiling water.

    Zinc is a very volatile metal, boiling around 900°C. At about the same temperature it will spontaneously react with atmospheric oxygen, producing "white clouds of zinc oxide". Obviously there is no real opportunity for particle size control if zinc oxide is formed in this way.

    However, I can think of another possible approach. If you react solutions of zinc chloride and sodium hydroxide in stoichiometric proportions, you will get a gelatinous precipitatie of zinc hydroxide. This can be filtered off, and the gel washed with very pure water -- probably needs to be carbon-dioxide free to avoid carbonate formation -- the gel will contain only zinc hydroxide and water.

    There is a large thermal window of opportunity between about 200°C, where all of the water will be lost from the gel, and the hydroxide converted to the oxide, and 1100°C where zinc oxide might start to sublime and/or anneal. So spreading the gel as a thin paste and introduction into a furnace at a variety of temperatures in this range might prove a useful avenue for research into particle size control. (Or it might not -- I am just thinking of possibilities; no practical knowledge in the area)
     
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