Glass types can be confusing to understand, however, the variation in chemical composition provides the glass with different properties. Two types of glass commonly used for laboratory glassware are Soda-Lime and Borosilicate glass.
Glass Chemical Composition
The chemical composition of each glass type varies to give rise to unique properties:
- Expansion borosilicate glass – This 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 cause significant corrosion.
- Neutral borosilicate glass – Has excellent chemical resistance properties which make it ideal for the storing or packaging of acidic, neutral and alkaline products and for injectable solutions.
- Soda-lime glass – This type of glass is less chemically resistant than borosilicate glass and is typically suitable for storing dry powders and for containers for general sample storage applications. This glass type has only moderate hydrolytic resistance.
Typical Chemical Composition (approx. % by weight):
|Chemical||3.3 Expansion Borosilicate Glass||4.9 Expansion Borosilicate Glass (Clear)||5.4 Expansion Borosilicate Glass (Amber)||7.8 Expansion Soda-Lime Glass (Amber)||9.1 Expansion Soda-Lime Glass (Clear)|
There are a number of international standards used to define different glass types. Below is a list of key standards and the different types used to identify the variation in Soda-Lime and Borosilicate glassware. These types will be commonly displayed on product information and product datasheets, understanding the categorization will assist in identifying the best glassware of use for your application.
|Standard||3.3 Expansion Borosilicate Glass||4.9 Expansion Borosilicate Glass (Clear)||5.4 Expansion Borosilicate Glass (Amber)||7.8 Expansion Soda-Lime Glass (Amber)||9.1 Expansion Soda-Lime Glass (Clear)|
|ASTM E-438||Type 1 Class A||Type 1 Class B||Type 1 Class B||Type 2||Type 2|
|US Pharmacopoeia (USP)||Type 1||Type 1||Type 1||Type 3||Type 3|
|European Pharmacopoeia (EP)||Type 1||Type 1||Type 1||Type 3||Type 3|
Due to the demanding conditions that laboratory glassware is subjected to, maximum chemical toughness, minimum thermal expansion and high resistance to thermal shock are key properties making 3.3 expansion borosilicate glass the ideal material for use in laboratories.
- Hydrolytic Resistance
One application where this is important is during steam sterilisation procedures, where repeated exposure to water vapour at high temperature can leach out alkali (Na+) ions. Borosilicate glass has a relatively low alkali metal oxide content and consequently possess a high resistance to attack from water.
- Acid Resistance
Glass with a high percentage weight of silica are less likely to be attacked by acids. 3.3 Expansion borosilicate glass is over 80% silica and therefore are resistant to acids (with the exception of hot concentrated phosphoric acid and hydrofluoric acid). Glass is separated into 4 acid resistance classes and borosilicate glass corresponds to Class S1 in accordance with DIN 12116 and meets the requirements of ISO 1776.
- Alkali Resistance
Alkaline solutions attack all glass types and borosilicate glass can be classified as moderately resistant. The alkali resistance of borosilicate glass meets Class A2 requirements as defined by ISO 695 and DIN 52322.
- Temperature Resistance
3.3 Expansion borosilicate glass, such as Pyrex, has excellent thermal properties at both high and low temperatures. The maximum recommended working temperature for laboratory glassware 3.3 expansion borosilicate glass is 500°C (for short periods of time only). Special care should be taken when heating or cooling to avoid sudden changes in temperature which can damage the glassware.
Below are the physical properties of different glass types most commonly encountered in the laboratory:
|Physical Properties||3.3 Expansion Borosilicate Glass||4.9 Expansion Borosilicate Glass (Clear)||5.4 Expansion Borosilicate Glass (Amber)||7.8 Expansion Soda-Lime Glass (Amber)||9.1 Expansion Soda-Lime Glass (Clear)|
|Coefficient of Expansion (20-300° C) x10-6K-1||3.3||4.9||5.4||7.8||9.1|
|Working Point ° C||1252||1160||1165||1050||1040|
|Softening Point° C||821||785||770||720||720|
|Annealing Point ° C||565||565||560||540||530|
|Transformation Temperature° C||525||565||550||535||525|
|Density at 25° Cg/cm-3||2.23||2.34||2.42||2.5||2.5|
|Acc. to ISO 719||Class HGB 1||Class HGB 1||Class HGB 1||Class HGB 2||Class HGB 3|
|Acc. to EP||Type 1||Type 1||Type 1||Type 111||Type 111|
|Acc. to USP||Type 1||Type 1||Type 1||Type 111||Type 111|
|Acid Resistance (DIN 12116)||Class S1||Class S1||Class S1||Class S2||Class S1|
|Alkali Resistance (ISO 695)||Class A2||Class A2||Class A2||Class A2||Class A2|
A large selection of these products also conform to other standards set out for laboratory glassware; for example, glass beakers comply to ISO 3819 and volumetric flasks comply to ISO 1042 and DIN 12664. Typically these standards will specify not only glass type but also the dimensional detail, volumetric accuracy and tolerances.
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