Home>ASTM Standards>ASTM C408-88(R2020) pdf free download

ASTM C408-88(R2020) pdf free download

ASTM C408-88(R2020) pdf free download.Standard Test Method for Thermal Conductivity of Whiteware Ceramics
1. Scope
1.1 This test method covers a general procedure 2 for deter- mining the thermal conductivity of whiteware ceramics over the temperature range from 100 to 300 °F (40 to 150 °C). 1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Apparatus
3.1 Essentially, the apparatus 3 shall consist ofa heating unit, upper and lower copper “thermodes” (bars that serve to introduce heat) to which the ceramic test specimen is soldered, and a cooling jacket. The foregoing set of parts shall be enclosed by a 5-in. (127 mm) diameter brass cylinder, 12 in. (305 mm) long, which is sealed to the base with a rubber gasket. With the exception of the copper thermodes and the copper cooling jackets, the instrument shall be made entirely of brass with all joints silver soldered. During operation, the system shall be evacuated to a pressure of approximately 1 µm ofmercury with an oil-diffusion pump which is backed up with a mechanical vacuum pump. 3.1.1 Heating Unit—The heating unit, shown in detail in Fig. 1, shall consist of a 500-W nichrome element helically supported by ceramic insulators inside a 2-in. (50.8 mm) diameter brass cylinder. This brass cylinder shall be highly polished to serve also as a reflector, since heat transmission to the upper thermode is primarily by radiation. Line voltage to the heater circuit shall be held constant to within 60.1 % by means of an electronic voltage regulator, and power input to the heater shall be controlled by a variable transformer. 3.1.2 Thermodes—The thermodes to which the ceramic test specimen is soldered shall be machined from electrolytically deposited pure copper to tolerances of 60.001 in. (0.03 mm) on diameters. Thermodes of diameters from 0.250 to 0.500 in. (6.50 to 12.70 mm) may be used, but in all cases the diameters of the specimen, and that portion of the upper and lower thermodes incorporating the thermocouple shall be equal in diameter to within 60.001 in. (0.03 mm). The section of the upper thermode above the upper cooling jacket shall be coated with carbon black to increase its emissivity.3.1.3 Cooling Jackets—Details of the lower cooling jacket are shown in Fig. 1. The lower thermode makes contact with the lower cooling jacket by means of a tapered fit. The upper 1 ⁄ 8 -in. (3.2 mm) brass plate which supports the heating unit shall also be water-cooled for the purpose of eliminating radiation from the heating unit to the thermodes and test specimen below. In addition, the upper thermode shall be fitted with a copper reflecting shield to prohibit any direct radiation from striking the thermodes and specimen in the chamber below. A water-circulating system shall be provided for sup- plying the cooling jackets with water at constant pressure and temperature. The water temperatures shall not vary at a rate greater than 1 °F (0.5 °C) ⁄h. 3.1.4 Thermocouples—Calibrated glass-asbestos insulated iron-constantan thermocouples shall be permanently attached to the thermodes in positions 1.75 in. (44.4 mm) apart as noted in Fig. 2. The diameter of the thermocouple wires used shall not exceed the diameter of No. 28 AWG (0.321 mm). The thermocouple wires shall be permanently attached to the thermode by silver-soldering each wire of the thermocouple into No. 70 (0.028-in. diameter) (0.71 mm) holes drilled in the thermode to a depth of 1 ⁄ 32 in. (0.8 mm) on opposite ends of a diameter. All thermocouple wires shall be taken through the base plate without any break in the continuity of the wire. An ice-water bath shall be used for cold junction reference. The instrument for measuring emf shall not have an instrument error greater than 60.001 mV.

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