Borosilicate glass vs Soda Lime glass vs Pyrex – what is the difference?
A: Different types of glass have different chemical compositions, meaning Borosilicate glass and Pyrex are better suited to heating.
Borosilicate glass has a higher proportion of silicone dioxide than Soda Lime glass, as shown on the table below;
|Compound||Borosilicate Glass – % content||Soda Lime Glass – % content|
|Silicon Dioxide SiO2||80.6||69|
|Boron Trioxide B2O3||13||1|
|Sodium Oxide Na2O||4||13|
|Aluminium Oxide Al2O3||2.4||4|
This difference means that Borosilicate glass does not expand as much on heating, so it is less likely to break when heated.
Pyrex is one particular blend of Borosilicate glass, with a particularly high heating tolerance.
Soda Lime glass is sometimes used for glassware which is not likely to be directly and strongly heated, for example, Petri dishes or TLC chromatography tanks.
Borosilicate glass or Pyrex is usually used for glassware that may be directly heated, such as beakers or boiling flasks.
Pyrex glassware and its advantages
Pyrex® is borosilicate glass which differs from other glass types as it possesses unique properties of high resistance to chemical exposure, thermal expansion and thermal shock. This has advantages in laboratory uses, a key one being where glassware is directly heated, in beakers, test tubes or flasks.
Let’s look at some of these properties in more detail and see what advantages they bring.
Glass is an inorganic mixture of metal oxides fused together at high temperatures, which upon cooling, solidifies into the clear, rigid, non-crystalline, versatile material. So what is different with Pyrex® glass?
The typical composition of Pyrex® is (% by weight):
SiO2 = 80.6%
B2O>3 = 13.0%
Na2O = 4.0%
Al2O3 = 2.3%
Pyrex® has a very high resistance to attack from water, acids, salt solutions, halogens and organic solvents. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkaline solutions can corrode; making it ideally suitable for laboratory experiments.
For many applications, it is important that laboratory glassware has excellent hydrolytic resistance. One example of this is during steam sterilisation procedures, where repeated exposure to water vapour at a high temperature can leach out alkali (Na+) ions. Pyrex® has a relatively low alkali metal oxide content and consequently a high resistance to attack from water.
Glasses with a high percentage weight of silica (SiO2) are less likely to be attacked by acids. Pyrex® is over 80% silica and therefore it has a remarkably resistant to acids (with some exceptions). It is resistant to chemical corrosion, making it perfectly suitable for laboratory experiments.
Alkaline solutions attack all glasses and Pyrex® can be classified as moderately resistant to such attacks.
Pyrex’s excellent thermal properties at both high and low temperatures is one of its key features. This is due to lower levels of expansion and contraction as a result of temperature change when compared to other glass types. Naturally, precautions to prevent sudden temperature changes should always be avoided to prevent cracking.
What are the temperature limits for Pyrex glassware?
A: Pyrex is suitable for use from -192°C to +500°C
This makes it an ideal choice for lab glassware which will be directly heated. Soda-Lime glass is less suitable for direct heating, so choose Pyrex where possible if you will be applying heat.
Beakers, test tubes and flasks that are made from Pyrex glass are suitable for direct heating by hotplate, heating mantle or bunsen burner.
Remember that heating and cooling should always be slow and steady – Pyrex can withstand huge temperature changes, but if they are too sudden it may still crack due to thermal shock.
Pyrex is available from Camlab through SciLabware it meets the following standard:
- ISO 3585, DIN 12217- Type 3.3 borosilicate glass
- ASTM E-438Type 1 - Class A borosilicate glass
- US Pharmacopoeia - Type 1 borosilicate glass
- European Pharmacopoeia - Type 1 glass
Due to the demanding conditions that borosilicate glass is subjected to, maximum chemical toughness, minimum thermal expansion and high resistance to thermal shock make Pyrex the ideal material for use in the laboratory.
SciLabware Ltd products conform to other standards set out for laboratory glassware; for example, beakers comply with ISO 3819 and volumetric flasks comply with ISO 1042 and DIN 12664. Typically these standards will specify not only glass type but also dimensional detail, volumetric accuracy and tolerances.