IEC 61006-2004 pdf – Electrical insulating materials – Methods of test for the determination of the glass transition temperature.
1 Scope This International Standard specifies procedures for test methods for the determination of the glass transition temperature of solid electrical insulating materials. They are applicable to amorphous materials or to partially crystalline materials containing amorphous regions which are stable and do not undergo decomposition or sublimation in the glass transition region. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 glass transition physical change in an amorphous material or in amorphous regions of a partially crystalline material from (or to) a viscous or rubbery condition to (or from) a hard one NOTE The glass transition generally occurs over a relatively narrow temperature region and is similar to the solidification of a liquid to a glass state; it is not a first order transition. Not only do hardness and brittleness undergo rapid changes in this temperature region, but other properties such as thermal expansion and heat capacity also change rapidly. This phenomenon is also referred to as a second order transition, rubber transition or rubbery transition. Where more than one amorphous transition occurs in a material, the one associated with changes in the segmental motions of the molecular backbone or accompanied by the largest change in properties is usually considered to be the glass transition. Blends of amorphous materials may have more than one glass transition, each associated with a separate component of the blend. 2.2 glass transition temperature T g midpoint of a temperature range over which the glass transition takes place NOTE 1 The glass transition temperature can be determined readily only by observing the temperature range in which a significant change takes place in some specific electrical, mechanical, thermal, or other physical property. Moreover, the observed temperature can vary significantly depending on the property chosen for observation and on details of the experimental technique
2.4 differential thermal analysis DTA technique in which the temperature difference between a tested material and a reference material is measured as a function of temperature while the common environment of the tested material and the reference material is subjected to a controlled temperature programme NOTE 1 The record is the differential thermal analysis or DTA curve. NOTE 2 There are four characteristic transition points associated with a glass transition (see Figure 1 ). − Extrapolated onset temperature (T f ) in °C – The point of intersection of the tangent drawn at the point of greatest slope on the transition curve with the extrapolated baseline prior to the transition. − Extrapolated endset temperature (T e ) in °C – The point of intersection of the tangent drawn at the point of greatest slope on the transition curve with the extrapolated baseline following the transition. − Midpoint temperature (T m ) in °C – The point on the thermal curve corresponding to half the heat flow difference between the extrapolated onset and extrapolated endset. − Inflection temperature (T i ) in °C – The point on the thermal curve corresponding to the peak of the first derivative (with respect to temperature) of the parent thermal curve. This point corresponds to the inflection point of the parent thermal curve. Two additional transition points are sometimes identified and are defined. − Temperature of first deviation (T o ) in °C – The point of first detectable deviation from the extrapolated baseline prior to the transition. − Temperature of return-to-baseline (T r ) in °C – The point of last deviation from the extrapolated baseline beyond transition. For the purpose of this standard T m will be taken as the glass transition temperature T g which usually corresponds more closely to the transition determined by the dilatometric and other methods. NOTE 3 Other temperatures than those previously defined can be used for specification purposes as established by individual contract.