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Effects of heat on compressed silicates

  1. Jun 14, 2016 #1
    Hi, I'm hoping to make small batches of synthetic minerals by compressing & heating small liquid or semi-liquid samples of sodium silicate w/ variable amounts of other salts dissolved within. As I understand it, many of these will require high pressure & temperature to form. So my strategy is to make some forced air, charcoal fired clay pot crucibles with room for sealed metal pipe sections with an internally threaded cap at one end that I can torque down prior to firing. (The liquid silicate solution goes in the pipe) That's the idea. Now my question, or series of related questions, begins with: Is there a specific law or shortcut I can use to calculate my initial pressure & consequent rise in fluid pressure as the temperature rises? I know there is a formula for computing pressure & density of gases at a specific pressure but as far as I know, it doesn't apply to compressed fluids. I admit I'm an amateur so if you see a flaw in the reasoning feel free to point it out. Also, my math skills are limited to linear algebra & trig.
  2. jcsd
  3. Jun 14, 2016 #2

    Paul Colby

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    I don't think the pressures will get anywhere near what's required to make gems. From the ideal gas law ##P_1/P_2 = T_1/T_2## where ##T_i## are the starting and ending temperatures. I would not even try what you're suggesting because what you describe is like a pipe bomb. Elevated temperatures will soften the metal making it even less capable of withstanding pressure.
  4. Jun 14, 2016 #3
    Hm, that's a good point. Maybe I'll stay at room temperature & devise a piston with Bridgman seal. I'll bury it outside inside a cinder block so if it bursts it doesn't break anything important.
  5. Jun 15, 2016 #4


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    Even if you do as planned, you must design a vessel that will is strong enough to contain the your required consolidating pressure for your mixture without exceeding its elastic stress limit or you will simply continue to expand the vessel as the pressure increases until it ruptures without ever reaching the consolidating pressure pressure you need.
    A further risk assuming you design a strong enough solid wall vessel, then the elastic expansion of the vessel due to the consolidation pressure will result in a sustained contained pressure on your sample and you will be required to carefully cut away the vessel; or, if you use a split bolted cylinder then carefully unbolt it; and in either case unless you perform this action in a vacuum your risk having entrained air in your sample that can cause the sample to shatter, split or even explode as you relieve the piston load or open the vessel.
  6. Jun 15, 2016 #5
    Could I minimize the latter danger by drying the samples prior to compression? I have an ultrasonic agitator available although the frequency range is fixed. I am thinking I can vibrate bubbles out while the mixture is still liquid, then dry the mixture solid, then cut it into discs. I am not too concerned with splits or cracks in the samples, though explosion would be problematic for a number of reasons.
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