Hydrolytic class
The hydrolytic class or hydrolytic resistance of a glass quantifies the extent to which basic compounds can be extracted from the glass by attack by water at 98 ° C. The hydrolytic class is also the basis for the classification of types of glass for pharmaceutical use according to the European Pharmacopoeia. The standardized test ISO 719 ( DIN 12111) is used to determine the hydrolytic class . The types of glass are divided into five classes according to the following procedure: 2 g glass, grain size 300-500 μm, is boiled for 60 min in 50 ml deionized water of quality 2 at 98 ° C. 25 ml of the solution obtained is titrated against 0.01 mol / l HCl until neutralization . The volume of HCl used is noted and the glass classified according to the information in the following table:
| Consumed 0.01M HCl to neutralize extracted basic oxides, ml |
Extracted Na 2 O - equivalent, ug |
Hydrolytic class |
|---|---|---|
| up to 0.1 | up to 31 | 1 |
| more than 0.1 up to 0.2 | more than 31 up to 62 | 2 |
| more than 0.2 up to 0.85 | more than 62 up to 264 | 3 |
| more than 0.85 up to 2.0 | more than 264 up to 620 | 4th |
| more than 2.0 up to 3.5 | more than 620 up to 1085 | 5 |
| more than 3.5 | more than 1085 | > 5 |
The standardized test ISO 719 is therefore not suitable for glasses that contain little or no extractable basic constituents but are nevertheless attacked by water, for example quartz glass , B 2 O 3 glass, or P 2 O 5 glass.
Common glasses are divided into the following classes:
- Hydrolytic class 1 (type I)
- This class, also known as neutral glass , includes borosilicate glasses (for example Duran , Pyrex , Fiolax and others). Glass in this class contains substantial amounts of boron , aluminum or alkaline earth oxides . Due to its composition, neutral glass has both a high level of resistance to temperature shock and the highest hydrolytic resistance. It has a very good chemical resistance to acidic and neutral solutions, and also to alkaline solutions due to its low alkali content.
- Hydrolytic class 2 (type II)
- This is usually soda-lime silicate glass with a very high hydrolytic resistance thanks to surface refinement . Soda-lime silicate glass is a silicate glass that contains alkali and alkaline earth oxides, mainly sodium and calcium oxide .
- Hydrolytic class 3 (type III)
- Glass of the 3rd hydrolytic class usually consists of soda-lime silicate glass and has an average hydrolytic resistance, which is at least ten times lower than glass of the 1st class.
The hydrolytic class according to DIN 12111 (ISO 719) must be distinguished from the acid class according to DIN 12116 and the alkali class according to DIN 52322 (ISO 695).
See also
Individual evidence
- ↑ Ph. Eur. 5.0, 2005, 3.2.1 Glass containers for pharmaceutical use
- ↑ International Organization for Standardization, Procedure 719 (1985)