ASTM D2149-13(R2021) pdf free download

ASTM D2149-13(R2021) pdf free download.Standard Test Method for Permittivity (Dielectric Constant) and Dissipation Factor of Solid Dielectrics at Frequencies to 10 MHz and Temperatures to 500 °C
3. Terminology
3.1 Definitions: 3.1.1 Permittivity and dissipation factor are fully defined in Terminology D1711. Briefly, the permittivity of an insulating material is the ratio of the capacitance between two conductors when embedded in the material to the capacitance between the same configuration of conductors in a vacuum (or air). The dissipation factor is the ratio of the resistive to capacitive currents in the dielectric. The product of the permittivity and dissipation factor is the loss index.
4. Significance and Use
4.1 Permittivity and dissipation factor are sensitive to changes in chemical composition, impurities, and homogene- ity. Measurement of these properties is, therefore, useful for quality control and for determining the effect of environments such as moisture, heat, or radiation.
5. Apparatus
5.1 Measuring Circuits—Suitable measuring circuits are described in Test Methods D150. For measurements from 50 Hz to 100 kHz a substitution method using a low-voltage capacitance bridge is recommended. For measurements at 1 MHz and above, a resonant-circuit susceptance variation method is recommended. The Q of the circuit has to be at least 200 except for very low loss materials, for which a Q of 500 or higher is desirable. 5.2 Test Enclosure—Unless testing only at room temperature, it is necessary to adapt a Hartshorn-Ward type specimen holder to a temperature-controlled test enclosure. Where applicable, use the requirements for a grade A enclosure as in Specification E197. A suggested arrangement is shown in Fig. 1. This arrangement provides terminal connections away from the temperature zone.5.3 Specimen Holder—The suggested arrangement shown in Fig. 1 incorporates the following requirements: 5.3.1 The selection of the metals is of utmost importance. The metal has to be ofgood thermal and electrical conductivity and yet be oxidation resistant and have sufficient strength to maintain its mechanical dimensions after repeated heating. AISI Stainless No. 316 fulfills these requirements except for the thermal conductivity. The time required for a specimen to reach equilibrium in a holder made from this material is quite long. Precious metal alloys such as type B silver-magnesium- nickel have better overall properties but require special heat treating. 5.3.2 The preferable insulator materials are aluminum oxide, beryllium oxide, or polytetrafluoroethylene. 5.3.3 Use electrodes 50 mm in diameter and at least 5 mm thick, with sharp corners. Maintain electrode parallellism to within 0.01 mm. 5.3.4 Select a length and cross-section for the lower tube so that the temperature of each insulator does not exceed 100 °C when the oven is at 500 °C. Select a length and cross-section for the upper tube so that the drive nut can be touched with the operator’s fingers (keep the drive nut less than 60 °C) when the oven is at 500 °C. 5.3.5 Use a micrometer or dial gage with a precision of 0.005 mm to determine electrode separation and to monitor specimen expansion.
10. Temperature Control
10.1 Take measurements at frequent temperature intervals (not to exceed 20 °C), until the required temperature range has been traversed. Reduce the temperature to the lowest required test temperature and leave until equilibrium has been achieved. Determine equilibrium by clamping a specimen between the holder electrodes and balancing or peaking the measuring circuit until no change takes place between balances made 2 min apart. After the required measurements have been made at the lowest test temperature increase the temperature at the rate of 2 6 0.5 °C/min to the next test temperature. Follow this procedure for achieving the test temperature until the required temperature range has been traversed. Take measurements at approximately the same test temperatures as the temperature is increasing and as the temperature is decreasing. Measurements as temperature is being increased and decreased are necessary to guard against possible hysteresis in electrical properties due to such factors as moisture and chemical change.