SCHOTT Technical Glasses

10
2.2.1 Hydrolytic resistance (water resistance)
Grain-titration method A
(after leaching at 98 °C, according to DIN ISO 719; testing
of glass as a material)
An amount of 2 g of powdered glass with 300 – 500 µm
(ISO) grain size is heated with 50 ml water for one hour in
a boiling water bath. The extracted alkali is then titrated
with hydrochloric acid, c(HCI) = 0.01 mol/l*, using methyl
red sodium as an indicator. On the basis of the acid consumption
(or its alkali equiva lent), the glass is assigned to one
of the five hydrolytic class es listed in Table 1. The hydrolytic
classes shown in Table 20 (on page 68ff) were determined
using the above method.
Grain-titration method B
(after leaching at 121 °C, according to DIN ISO 720; testing
of glass as a material)
In this method, which originated in the USA and is particularly
suitable for highly resistant glasses, 10 g of powdered
glass (grain size 300 – 425 µm) is leached with 50 ml of water
in an autoclave for 30 min at 121 °C. The extracted alkali is
then titrated with hydrochloric acid, c(HCI) = 0.02 mol/l,
using methyl red sodium as an indicator. Here, too, the acid
consumption is a measure of the hydrolytic resistance. Presently,
no allocation into classes exists for DIN ISO 720.
Class 1
Consumption of hydrochloric
acid solution
[c(HCl) = 0.02 mol/l] (4.2)
per gram of glass grains
ml/g
Equivalent of alkali
expressed as mass of
sodium oxide (Na 2 O)
per gram of glass grains
µg/g
HGA 1 up to and including 0.10 up to and including 62
HGA 2
HGA 3
from 0.10 up to and
including 0.85
from 0.85 up to and
including 1.50
from 62 up to and
including 527
from 527 up to and
including 930
1
“HGA” stands for the hydrolytic resistance of glass grains according
to the autoclave test method.
Table 2. Limit values in the hydrolytic resistance grain test (autoclave test)
Surface test method A
(at 121 °C, according to ISO 4802-1 (2010) and current
Ph. Eur. and USP)
Grain-titration methods are always carried out on crushed
glass samples and the glass is tested as a material. With the
surface test method, in contrast, the water resistance of
the surface can be determined in its “as delivered” state. In
this method, new, undamaged vessels (e.g. flasks, test tubes,
vials, ampoules) are filled with water and heated for 60 min
at 121 °C in an autoclave. The leaching solution is then
titrated with hydrochloric acid, c(HCI) = 0.01 mol/l, using
methyl red sodium as an indicator. Distinguished according
to volume, the containers are classified on the basis of the
amount of acid required for neutralization.
The values gained by this method indicate not only the
behavior of the glass material as such, but also reflect possible
modifications induced in the glass surface during hot
forming. Therefore, these values are not quoted in the tables
included in this publication.
DURAN ® borosilicate glass in the laboratory
* The old term for concentration in “normal solutions N” has been replaced by “mol/l” in the SI system.