[Jewelry making - Article 01501] - Re: [Orchid] Why Hydrofluoric acid is so dangerous

[nick]

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>     Washing soda is a brilliant neutraliser of HF, though at work we
>     use sodium hydroxide as it takes less volume of chemical to do the
>     job. we tend to clean our platinum with nitric acid rather than HF
>     though nitric is not very good at dissolving enamel unless the
>     enamel has a high borax content which is the case with some of the
>     enamels used in jewellery and ceramic overglaze enamels. The German
>     made enamels I use on silver will dissolve in nitric but the very
>     vitreous English and US made ones dont. 

    Fluoride is added to water and toothpaste in very small quantities
    in a non reactive salt. The reason is that tooth enamel is made up of
    calicium phospahte in the form of hydroxyapatite. most marine
    creatures like sharks and crocodiles have chlorapatite teeth, which
    are stronger, but mammals cannot absorb the chlorine ion into their
    teeth so the more reactive fluorine ion is used instead. get it
    right and tooth decay is much reduced, too much and the tooth is
    destroyed and the person poisoned. 

    There is an inert gas called sulphur hexafluoride that is used as an
    electrical insulator in high voltage transformers instead of oil or
    PCB's (polychlorinated biphenols which destroy the ozone layer) that
    is so dense you can float aluminium on it. I helped with a chemistry
    department demo floating a metal boat in a fish tank of SF6 to the
    amazement of the children watching and then the demonstrator did a
    demo of breathing the gas in and talking which had the opposite
    effect of breathing helium- he talked really slow with a very deep
    voice. We then had to turn him upside down to pour the gas out of his
    lungs as he couldnt breathe it out naturally so dont try that one for
    yourself. 

Nick
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