High chemical resistance

When materials such as metals and plastics have reached their limits under chemically aggressive liquids or gases, glass tubing and profile glass tubing still easily hold up. The chemical resistance of glass includes water resistance, acid resistance and alkali resistance.

Water resistance as per ISO 719

The degree of water resistance of glass is determined by how resistant glass is to water.

About one-third of SCHOTT Tubing glass types meet the requirements of water-resistance class 1 as per ISO 719. In this standard, glass is divided into 5 classes, where 1 is the best and 5 is the worst water resistance. This division is based on the so-called glass-grain test. Two grams of glass is reduced to a grit size of 300 to 500μm and heated in a beaker with 50 ml water at 98°C for one hour. The number of ions (Na₂O equivalent) released from the glass within this time through the water is measured with titration. The released ions are analyzed in hydrochloric acid (0.01mol/l ) as standard solution per g glass grit ml/g. Methyl red solution is used as an indicator. If only up to 31 μg is released, the glass type is classified as Water-resistance class 1. This means that the more ions are released, the worse the water-resistance class.

Hydrolytic classes	Acid consumption of 0.01 mol/l hydrocholric acid per g glass grains ml/g	Base equivalent as Na₂O per g glass grains μg/g	Possible designation
1	up to 0.10	up to 31	very highly resistant glass
2	above 0.10 up to 0.20	above 31 up to 62	highly resistant glass
3	above 0.20 up to 0.85	above 62 up to 264	medium resistant glass
4	above 0.85 up to 2.0	above 264 up to 620	low resistant glas
5	above 2.0 up to 3.5	above 620 up to 1085	very low resistant glass

Hydrolytic classes of DIN ISO 719

Water-resistance in accordance with European and US Pharmacopoeia

Water-resistance is especially important for the manufacture of glass pharmaceutical primary packaging, since most medicines are preserved in a watery solution. In the international Pharmacopoeias PhEur and USP (Ph Eur = Pharmacopoea Europaea and USP = United States Pharmacopeia) the glass types used in manufacturing are split into water-resistance class Type I (highest resistance) to Type III. The glass-grain test described above is modified so that the container is reduced to a grain size of 425-300 μm and 10g of it are heated in purified water at a temperature of 121°C for 30 min (as per updated Ph Eur and USP). According to this glass-grain test, the neutral glass FIOLAX^® clear is a 'Type 1 glass'.

The right glass types for technical applications are chosen depending on other necessary material properties such as fusing with other glass or material or temperature resistance.

You will find a summary of glass types with hydrolytic resistance in our Glass Tubing Explorer.

If you are not sure which type of glass is right for your application or whether what you want to do can be realized with glass, Ask our glass specialists!

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Acid resistance as per DIN 12 116

Standard DIN 12116 divides glass types into Classes S1, S2 and S3, measured as per the weight loss caused by the attack of the acid on the glass. Moreover, the glass surface to be tested is boiled for 6 hours in hydrochloric acid. If half the weight loss of the surface removal comes to less than 0.7 mg per 100 cm2, the glass type is classified as Class S1 acid resistance. The more that is removed from the glass, the worse the acid-resistance class.

Depending on composition, borosilicate glass such as DUROBAX^® and DURAN^®, and soda-lime glass such as AR Glass^® are highly resistant to acid and are thus classified as S1 glass.

Find more information on acid-resistant glass types in our Glass Tubing Explorer.

Still haven't found what you are looking for? Ask our glass specialists!

Acid class	Designation	Half loss in weight after 6 h mg/100 cm²
1	highly acid resistant	up to 0.7
2	acid resistant	above 0.7 up to 1.5
3	slight acid attack	above 1.5 up to 15
4	high acid attack	above 15

Acid classes

Alkali resistance as per ISO 695

The glass surface is boiled for 3 hours to determine alkali resistance. The aqueous solution used must consist of equal parts caustic soda c(NaOH)=1 mol/l and sodium carbonate c(Na₂CO₃)=0,5 mol/l. If the weight loss of the glass after 3 hours of boiling comes to 75 mg/100cm², the glass is Alkali-resistance class 1. The higher the weight loss, the worse the classification for alkali resistance.

Alkali class	Designation	Loss in weight after 3 h mg/100 cm²
1	low alkali attack	up to 75
2	slight alkali attack	above 75 up to 175
3	high alkali attack	above 175

Alkali classes

When considering the overall results of the analyses of water resistance, acid resistance and alkali resistance, the glass types DURAN^® , FIOLAX^® clear, FIOLAX^® amber, DUROBAX^® clear and DUROBAX^® amber provide very high chemical durability.

Would you like to search for specific features in our range of glass types? Then use our Glass Tubing Explorer.

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