Pyrex tolerance with magnetic stirrer

Discussion in 'Top Tips' started by JHRoss, Jan 14, 2020.

  1. Greetings,

    This is the second time I see a huge crack in a big (1L) Pyrex beaker when I expose it to 300°C (-192°C to +500°C is the range you can use it safely) using the magnetic stirring bars at the same time.

    What is happening?

    Regards
     
  2. Did you put the cold beaker on a 300-degree hotplate or did you put it on a cold hotplate and heat it up?
    Was the beaker empty?

    I suspect thermal shock.

    Also, this is not really a top tip.
     
  3. No no, I put it on before I turned on the heater, and I am 99% sure the first time this happened had done the same
     
    Alice likes this.
  4. silly question:
    It is a pyrex container and not a cheaper version? sometimes a cheaper one isn't as resilient as a pyrex one
     
  5. In that case ??? (possibly with a side of ****!)

    Sometimes glassware has had a knock which weakens it but it only shows up on heating. I'm clutching at straws though..
     
  6. JFKtech

    JFKtech and then there were two - now JFK Techs :)

    I've had this happen a few times in the past; most recently the bottom fell out of my heavy duty 2L pyrex beaker, pouring boiling water all over the bench and the floor :(:eek:

    I put it down to a combination of invisible flaws from previous knocks, thermal stress, and the beaker vibrating against the hot plate with the motion of the bubbles and the stirrer bar. It's really annoying !
     
  7. What's the heater? I'm wondering if the stir bar, being metal cored becomes a "hot spot" and creates thermal stress. My unexpected deluge was hot copper sulphate..
     
  8. I have heard it happen before with hotplate and Pyrex glass, one tip is to always make sure the hotplate diameter is bigger than the vessel being heated
     
  9. I've had it happen once in 14 years. Big batch of agar and the bottom came off and it went everywhere! Not happened since so I have put it down to an invisible flaw of some sort although I did replace it with a thicker walled one.