Glass - Determination of coefficient of mean linear thermal expansion
1 Scope
This standard specifies a method for determining the coefficient of mean linear thermal expansion of glass in the elastic solid-like state.
This standard is applicable to the determination of coefficient of mean linear thermal expansion of glass made of various materials.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1216 External micrometer
GB/T 21389 Vernier, dial and digital display calipers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
coefficient of mean linear thermal expansion
α(t0;t)
the ratio of the change in length of a specimen within a temperature interval to that temperature interval, related to the initial specimen length. It is given by Equation (1):
(1)
where,
t0——the initial or reference temperature, ℃;
t——the actual specimen temperature after heating, ℃;
L0——the length at temperature t0 of the specimen of glass under test, mm;
L——the specimen length at temperature t, mm.
For the purposes of this standard, the nominal reference temperature, t0, is 20℃; therefore the coefficient of mean linear thermal expansion is denoted by α(20℃;t).
3.2
transformation point
tg
the temperature corresponding to the point of intersection of two tangents, drawn from the high-temperature branch and the low-temperature branch of the dilatometer curve, at which the glass undergoes a transition from a brittle state to a viscous state. The transformation point corresponds to a dynamic viscosity of the order of 1012.4Pa·s
Foreword II
1 Scope
2 Normative references
3 Terms and definitions
4 Apparatus
5 Test specimen
6 Procedure
7 Expression of results
8 Performance test
9 Test report
Annex A (Informative) Devices for self-adjusting alignment of specimen and push-rod axis
