ASTM E1952-11 Standard Test Method for Thermal Conductivity and Thermal Diffusivity by Modulated Temperature Difference Scanning Calorimetry

The standard "ASTM E1952-11 Standard Test Method for Thermal Conductivity and Thermal Diffusivity by Modulated Temperature Differential Scanning Calorimetry" developed by the American Society for Testing and Materials (ASTM) describes a procedure for determining the thermal conductivity of homogeneous, non-porous solid materials in the range 0,10 to 1,0 W ⁄ (K m) by modulated temperature differential scanning calorimetry. This range includes many polymeric, glass, and ceramic materials. Thermal diffusivity, which is related to thermal conductivity through specific heat capacity and density, can also be derived. Thermal conductivity and diffusivity can be determined at one or more temperatures in the range 0 to 90 degrees.

For the purposes of this standard, certain technical terms used in this standard, including calibration, differential scanning calorimetry, heat capacity, modulated temperature, precision, reference material, relative standard deviation, repeatability, reproducibility, specific heat capacity, standard deviation, thermal analysis, thermal conductivity, and thermal conductivity, are defined in ASTM E473-21, ASTM E1142-23, and ASTM E2161-23.

Specifically for this standard, modulated temperature differential scanning calorimetry refers to a version of the differential scanning calorimeter that provides a sinusoidally varying temperature program to the test sample in addition to conventional isothermal or temperature ramp programs. Analysis results include apparent and specific heat capacity.

In performing tests, the heat capacity of a test specimen can be determined using the modulated temperature approach, where an oscillatory or periodically recurring temperature program (around a mean temperature) is applied to a test specimen, producing an oscillatory (periodic) heat flow into or out of the specimen. The heat capacity of a test specimen can be obtained by dividing the amplitude of the resulting heat flow by the amplitude of the oscillatory (periodic) temperature that produced it. The specific heat capacity is obtained by normalizing the heat capacity to the mass of the specimen.

The accuracy of the heat capacity obtained in this way depends on the experimental conditions. When a thin test sample encapsulated in a sample pan with high thermal conductivity is treated with long-term (low-frequency) temperature oscillations, it is assumed that the test sample has reached a uniform temperature distribution and the resulting heat capacity information is comparable to that of other non-oscillatory test methods.

When one end of a thick test specimen is subjected to short-term (high-frequency) temperature oscillations, the test specimen acquires a temperature distribution along its length, depending on its thermal diffusivity. The apparent heat capacity information thus obtained is lower than in the case of a uniform temperature distribution described above and is proportional to the square root of the thermal conductivity of the test specimens.

The thermal conductivity of the test specimen can be derived from the apparent heat capacity of a thick specimen, the true heat capacity of a thin specimen, and a number of geometric and empirical constants.

If the thermal conductivity of the test specimen is low, approaching that of the surrounding purge gas, a correction to the measured thermal conductivity is required to compensate for heat losses due to the thick test specimen.

Thermal diffusivity is derived from the determined thermal conductivity, specific heat capacity, and density of the test specimen.

Thermal conductivity is a useful design parameter for the rate of heat transfer through a material. The results of this test method can be used for design purposes, service evaluation, production control, research and development, and hazard assessment.

Since the sample size used in thermal analysis is on the order of 10 to 100 mg, care must be taken to ensure that it is homogeneous or representative of the material, or both. Calculation of thermal conductivity requires knowledge of this sample geometry. This test method requires a specific sample size and shape. Other geometries can be used by making appropriate changes to the calculation equations.

Two right circular cylinders, both nominally 6,3 mm in diameter, are selected for sampling. The first of these test specimens is nominally 0,4 mm thick and the second is nominally 3,5 mm thick. These test specimens are most conveniently obtained by cutting them from 6,35 mm diameter bar, a common form of material. Other fabrication techniques such as cutting from sheet stock using cork borers, machining from stock, or molding may also be used. The circular end surfaces of the test specimens are polished smooth and parallel to plus/minus 600 µm with 30 grit sandpaper.

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