Pyrex tolerance with magnetic stirrer

Discussion in 'Top Tips' started by JHRoss, Jan 14, 2020 at 9:38 AM.

  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?

  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