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  • zinc oxide?

    Posted by natiyo123 on November 5, 2020 at 1:56 am

    So I know zinc oxide is an amphoteric oxide and most importantly not soluble in water, so therefore no pH… SO that means it is compatible with any pH, (having the function of a filler and antibacterial) ?? in an oil based formulation

    pharma replied 3 years, 3 months ago 2 Members · 4 Replies
  • 4 Replies
  • pharma

    Member
    November 5, 2020 at 7:56 pm
    Amphoteric? How so?
    It’s nearly insoluble in water but not entirely insoluble (especially with qualities which contain traces of carbonate and hydroxide). So, zinc oxides often react alkaline. Given that it’s a metal oxide, it will react with acids and is therefore incompatible with these. Without water, i.e. in pure oil formulations, there is by definition no pH, no matter what you add (unless it’s a protic solvent or the like).
  • natiyo123

    Member
    November 6, 2020 at 12:38 am

    Pharma said:

    Amphoteric? How so?
    It’s nearly insoluble in water but not entirely insoluble (especially with qualities which contain traces of carbonate and hydroxide). So, zinc oxides often react alkaline. Given that it’s a metal oxide, it will react with acids and is therefore incompatible with these. Without water, i.e. in pure oil formulations, there is by definition no pH, no matter what you add (unless it’s a protic solvent or the like).

    I read it can react with both bases and acids, I suppose strong ones?

    I meant the pH once its on the skin, supposing it gets wet with sweat… I read it does react with acids?? I want to use it in an anhydrous deo stick with , triethyl citrate, basically thats the point of my question. I know triethyl citrate hydrolyzes into citric acid

  • natiyo123

    Member
    November 6, 2020 at 12:49 am

    I just found an article that suggests ZnO + CA are compatible and antibacterial. I guess I answered my own Q. 

    Evaluation of anti-microbial activities of ZnO, citric acid and a mixture of both against Propionibacterium acnes

  • pharma

    Member
    November 6, 2020 at 5:57 am
    Given slow reaction times, triethyl citrate should work fine.
    Can’t access that link at the moment… citric acid does react with zinc oxide to form zinc citrates and obviously, that one is more effective against microbes ;) . A publication doesn’t mean the two chemicals are ‘cosmetically’ compatible. I’ve read enough rubbish papers to know that just because people see an effect in the lab doesn’t make it true and just because people publish something doesn’t mean that they’re intelligent beings.

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