ISO 7884-8:1987
(Main)Glass — Viscosity and viscometric fixed points — Part 8: Determination of (dilatometric) transformation temperature
Glass — Viscosity and viscometric fixed points — Part 8: Determination of (dilatometric) transformation temperature
The temperature characterizes a certain glass transition range from the elastic brittle (low temperature) state to the viscous (high temperature) state of glass. It is used for specifying cooling programmes. The transformation temperature is determined by measuring the change in length, related to the length at intial temperature, of a rod made from the glass under test with temperature. The relative change in length is plotted against the temperature (dilatometer curve). From this dilatometer curve the transformation temperature is determined by a graphic procedure as shown in a diagramm.
Verre — Viscosité et points viscosimétriques fixes — Partie 8: Détermination de la température de transformation (dilatométrique)
General Information
Standards Content (Sample)
DARD
INTERNATIONAL ST 7884
First edition
1987-12-15
INTERNATIONAL ORGANKATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXflYHAPO,4HAfl OPrAHM3A~MR I-IO CTAH~APTM3A~MM
Vkcosity and viscometric fixed Points -
Glass -
Part 8 :
Determination of (dilatometric) transformation temperature
Reference number
ISO 7884-8: 1987 (E)
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bodies). The work of preparing International
Standards is normally carried out through ISO technical committees. Esch member
body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, govern-
mental and non-governmental, in liaison with ISO, also take patt in the work.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.
International Standard ISO 7884-8 was prepared by Technical Committee ISO/TC 48,
Laboratory glassware and related apparatus.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
0 International Organkation for Standardization, 1987
Printed in Switzerland
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ISO 7884-8 : 1987 (E)
INTERNATIONAL STANDARD
- Viscosity and viscometric fixed Points -
Glass
Part 8 :
Determination of (dilatometric) transformation temperature
2 Field of application
0 lntroduction
This method is applicable to all glasses of normal bulk-
International Standard ISO 7884, Glass - Viscosity and
production compositions. Generally, the transformation
viscometric fixed Points, consists of the following separate
Parts : temperature t, falls in the range from 350 to 800 OC, depending
on the type of glass.
Part 7 : Principles for determining viscosity and viscometric
flited poin ts.
Part 2 : Determination of viscosity b y ro tation viscometers.
3 References
Part 3 : Determination of viscosity b y fibre elongation
viscometer.
ISO 7991, Glass - Determination of coefficien t of mean linear
thermal expansion.
Part 4 : Determination of viscosity by beam bending.
Part 5 : Determination of working Point by sinking bar
IEC Publication 584-1, Thermocouples - Part 7 : Reference
viscometer.
tables.
Part 6 : Determination of softening Point.
Part 7 : Determination of annealing Point and strain Point by
beam bending.
4 Definition
o f f dila tometricl trans forma tion
Part 8 : Determination
tempera ture. For the purposes of this part of ISO 7884, the following defini-
tion applies.
transformation temperature t, of glass : The temperature
1 Scope
corresponding to the Point of intersection of two tangents,
drawn from the low-temperature branch and the high-
This part of ISO 7884 specifies a method of determining the
(dilatometric) transformation temperature t, of a glass by means temperature branch of the dilatometer curve (sec clause 5 and
figure 1).
of the thermal expansion method. This temperature character-
izes a certain glass transition range from the elastic brittle (low
NOTE - The transformation temperature tg corresponds to a dynamic
temperature) state to the viscous (high temperature) state of
viscosity of the Order of 1013!3 dPa.s*. No exact relation exists be-
glass. The transformation temperature has been found useful
tween tg and the fixed Points $3 and $4 according to ISO 7884-7.
for specifying cooling Programmes and estimating the upper
temperature limit of applicability of the respective glassware.
For usual silicate glasses, r9f3 is 5 to 10 OC higher than tg. For some
special cases (e.g. borosilicate glasses with high Si02 content) r9f3 is up
However, rYf3 tan be up to 20 OC lower than ~g
NOTE - The more direct viscometric method of annealing Point and to 30 OC higher than tg.
(e.g. in the case of crown glasses having an La203 content). In these
strain Point determination (sec ISO 7884-7) serves similar purposes.
extreme cases the annealing Point 8f3 is the more appropriate informa-
The determination of the transformation temperature tg might be con-
venient if a suitable device for determining the coefficient of thermal tion about cooling Programmes required and the temperature limit of
applicability of the respective glassware.
expansion is available in the Iaboratory.
dNs
* 1 dPa.s = 17 = 1 P
(P is the Symbol for Poise)
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ISO 7884-8 : 1987 (E)
5 Principle
The transformation temperature is determined by measuring ‘The test specimen shall be annealed before the test by heating
it to about 30 OC above the estimated transformation
the Change in length, related to the length at initial
temperature and then cooling it to about 150 OC below the
temperature, of a rod made from the glass under test with
estimated transformation temperature at a cooling rate of
temperature. The relative Change in length is plotted against
(2 + 0,2) O
...
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