FEELING THE HEAT? 

by Chris Price, Glass Product Manager

Did you know that glass can get stressed when feeling the heat?

When you heat laboratory glassware, you can add to the internal stresses in the glass that can cause it to break.

Welcome to the second instalment of blogs on the safe and sustainable use of lab glassware.  In this edititon we provide a guide on the safe heating of glassware and how to minimise the possibility of breakages occurring.

  • Expansion and contraction – The low co-efficient of expansion of Pyrex® borosilicate glass (3.3x10-6K-1) means that the glass expands or contracts very little when heated or cooled, making it safe to use over a very wide temperature range. Pyrex® borosilicate glass can be safely cooled down to -192oC and heated to a maximum recommended working temperature of 500oC (for short periods only). However, once the temperature exceeds 150oC extra care must be taken to ensure that the heating and then cooling of the glassware is achieved in a slow and uniform manner.
  • Thermal shock – Always heat glassware gently and gradually to avoid sudden temperature changes which may cause the glass to break due to thermal shock. Similarly, allow hot glassware to cool gradually and in a location away from cold draughts.
  • Even distribution of heat – If you are using a hotplate, ensure that the top plate is larger than the base of the vessel to be heated. This will ensure the even distribution of heat through the base of the glassware, reducing the possibility of the glass breaking due to hotspots. Hotspots can occur when localised areas of the glass heat up and expand at different rate causing the base of the vessel to break. Also, never put cold glassware onto a pre-heated hotplate. Always warm up the glassware from ambient temperature.
  • Avoiding hotspots – If you are using a Bunsen burner, employ a soft flame and use a wire gauze with a ceramic centre to diffuse the flame. Never apply direct localised heat to a piece of glassware as this can cause a hotspot to develop. 
  • Microwave-safePyrex® borosilicate glass is microwave safe. However, as with any microwave vessel, ensure that it holds microwave absorbing material, before placing it in the oven. Many Pyrex® and Quickfit® products utilise plastics screwcaps and connectors. These components are typically manufactured from polypropylene or PTFE, both of which are also microwave safe.
  • Autoclaving – When autoclaving Pyrex® containers e.g. bottles with screwcaps, always loosen off the caps. Autoclaving glassware with a tightly screwed cap can result in pressure differences which will cause the container to break.  

Pyrex® is a registered trade mark of Corning Inc. SciLabware is a registered user.

This technical information is provided in good faith by SciLabware Limited for the safety of its customers.

Please note that the advice given is for general laboratory applications and may not necessarily apply to all tests and procedures.

If you are in doubt, or require more technical information on SciLabware glass products, please contact SciLabware for specific advice via our contact us page and select 'Technical enquiries' in the drop down. 

We hope you found this interesting. Please stay tuned for the next instalment which will be available on our website later this month.

ABOUT THE AUTHOR

Chris Price is the Glass Product Manager at SciLabware. Chris has over 30 years' experience in laboratory glassware with extensive experience in product development, innovation management and product marketing.