1、Designation: C408 88 (Reapproved 2016)Standard Test Method forThermal Conductivity of Whiteware Ceramics1This standard is issued under the fixed designation C408; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers a general proced
3、ure2for deter-mining the thermal conductivity of whiteware ceramics overthe temperature range from 100 to 300F (40 to 150C).1.2 The values stated in inch-pound units are to be regardedas the standard. The SI (metric) units given in parentheses arefor information purposes only.1.3 This standard does
4、not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Significance and Use2.1 This test m
5、ethod provides information useful in under-standing and quantifying such parameters as thermal shockresistance and ability to conduct or dissipate heat.3. Apparatus3.1 Essentially, the apparatus3shall consist of a heating unit,upper and lower copper “thermodes” (bars that serve tointroduce heat) to
6、which the ceramic test specimen is soldered,and a cooling jacket. The foregoing set of parts shall beenclosed by a 5-in. (127-mm) diameter brass cylinder, 12 in.(305 mm) long, which is sealed to the base with a rubbergasket. With the exception of the copper thermodes and thecopper cooling jackets, t
7、he instrument shall be made entirely ofbrass with all joints silver soldered. During operation, thesystem shall be evacuated to a pressure of approximately 1 mof mercury with an oil-diffusion pump which is backed up witha mechanical vacuum pump.3.1.1 Heating UnitThe heating unit, shown in detail inF
8、ig. 1, shall consist of a 500-W Nichrome element helicallysupported by ceramic insulators inside a 2-in. (50.8-mm)diameter brass cylinder. This brass cylinder shall be highlypolished to serve also as a reflector, since heat transmission tothe upper thermode is primarily by radiation. Line voltage to
9、the heater circuit shall be held constant to within 60.1 % bymeans of an electronic voltage regulator, and power input tothe heater shall be controlled by a variable transformer.3.1.2 ThermodesThe thermodes to which the ceramic testspecimen is soldered shall be machined from electrolyticallydeposite
10、d 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 diametersof the specimen, and that portion of the upper and lowerthermodes incorporating the thermocouple shall be equal indiameter to w
11、ithin 60.001 in. (0.03 mm). The section of theupper thermode above the upper cooling jacket shall be coatedwith carbon black to increase its emissivity.3.1.3 Cooling JacketsDetails of the lower cooling jacketare shown in Fig. 1. The lower thermode makes contact withthe lower cooling jacket by means
12、of a tapered fit. The upper18-in. (3.2-mm) brass plate which supports the heating unitshall also be water-cooled for the purpose of eliminatingradiation from the heating unit to the thermodes and testspecimen below. In addition, the upper thermode shall be fittedwith a copper reflecting shield to pr
13、ohibit any direct radiationfrom striking the thermodes and specimen in the chamberbelow. A water-circulating system shall be provided for sup-plying the cooling jackets with water at constant pressure andtemperature. The water temperatures shall not vary at a rategreater than 1F (0.5C)/h.3.1.4 Therm
14、ocouplesCalibrated glass-asbestos insulatediron-constantan thermocouples shall be permanently attachedto the thermodes in positions 1.75 in. (44.4 mm) apart as notedin Fig. 2. The diameter of the thermocouple wires used shallnot exceed the diameter of No. 28 AWG (0.321 mm). Thethermocouple wires sha
15、ll be permanently attached to thethermode by silver-soldering each wire of the thermocoupleinto No. 70 (0.028-in. diameter) (0.71-mm) holes drilled in thethermode to a depth of132 in. (0.8 mm) on opposite ends of adiameter. All thermocouple wires shall be taken through thebase plate without any brea
16、k in the continuity of the wire. An1This test method is under the jurisdiction ofASTM Committee C21 on CeramicWhitewares and Related Products and is the direct responsibility of SubcommitteeC21.03 on Methods for Whitewares and Environmental Concerns.Current edition approved July 1, 2016. Published J
17、uly 2016. Originally approvedin 1957. Last previous edition approved in 2011 as C408 88 (2011). DOI:10.1520/C0408-88R16.2This work was done under the sponsorship of the U.S. Signal Corps., SquierSignal Laboratory, Ft. Monmouth, NJ, and the U.S. Air Force, Wright-Patterson AirDevelopment Center, OH.3
18、A suitable type of apparatus is described by Edwin Ruh in “Improved Methodof Measuring Thermal Conductivity of Dense Ceramics,” Journal, Am. CeramicSociety, Vol 37, 1954, No. 5, pp. 224229.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United Stat
19、es1ice-water bath shall be used for cold junction reference. Theinstrument for measuring emf shall not have an instrumenterror greater than 60.001 mV.4. Test Specimens4.1 The ceramic test specimens used in the thermal conduc-tivity instrument shall be accurately ground cylinders. Thespecimens may be
20、 formed using normal ceramic procedures ofslip-casting, dry-pressing, or extrusion. After firing to maturity,the specimens shall be ground to within 60.001 in. (0.03 mm)of the diameter of the thermodes being used. The bases shall beperpendicular to the axis of the cylinder within 615 min. Thelength
21、of the cylinder shall be equal to its diameter within61%.5. Preparation of Test Specimens5.1 Metallize the plane faces of the specimen to be evalu-ated with a fired-on platinum alloy, silver, or other metallicglaze that may be readily soft soldered. Then soft solder themetallized specimen into posit
22、ion between the upper and lowerthermodes by placing solder preforms between the specimenand thermode and applying heat to the thermode. UponFIG. 1 Thermal Conductivity ApparatusC408 88 (2016)2completion of this soldering operation, polish the thermodes toreduce their emissivity.6. Procedure6.1 After
23、 the test specimen has been satisfactorily solderedto the thermodes, and positioned in the apparatus, close off thesystem and evacuate it to approximately 1 m of mercury. Thenapply heat to the upper thermode by means of the heaterelement and establish a temperature gradient along the copperand along
24、 the specimen. When the heat input equals the heatflowing down the thermode, steady-state conditions have beenattained. For practical purposes, when the temperature of thethermocouple nearest the heater element changes at some ratesmaller than 0.05F (0.03C)/min, steady-state is consideredattained. A
25、fter steady-state conditions have been reached, readthe emf of the four thermocouples in the following order: 1, 2,3, 4, 3, 2, and 1, No. 1 thermocouple being the one nearest theheater element. Then convert the average emf for each ther-mocouple to temperature for use in the calculations. Take three
26、such sets of readings at each steady-state point. The threecalculated thermal conductivity values must agree with eachother within 1 % to be acceptable.7. Recording Test Data7.1 Record the following test:7.1.1 Linear dimensions of the test specimen,7.1.2 Weight of the dry specimen before metallizing
27、,7.1.3 Diameter of the thermodes,7.1.4 Distance between thermocouples Nos. 1 and 2,7.1.5 Three sets of temperature readings, measured by thethermocouples as described in Section 4 for each set ofsteady-state conditions,7.1.6 Mean temperature of the upper thermode, as calcu-lated from temperatures me
28、asured with the thermocouples Nos.1 and 2, and7.1.7 Mean temperature of the samples as calculated fromtemperatures measured with thermocouples Nos. 2 and 3.8. Calculation8.1 Calculate the thermal conductivity as follows:Ks5 KCuACutCuXs!/AstsXCu(1)where:Ks= thermal conductivity of the test specimen e
29、xpressed inBtuin./hft2F (or gcal/scm2C),KCu= thermal conductivity of the copper thermode at themean temperature calculated in 7.1.6, expressed inBtuin./hft2F (or gcalcm/scm2C (Table 1),ACu= cross-sectional area of the thermode, taken perpen-dicular to the direction of the heat flow,As= cross-section
30、al area of the specimen, taken perpen-dicular to the direction of the heat flow,tCu= temperature difference in F (or C) between thermo-couple Nos. 1 and 2,ts= temperature difference in F (or C) between thermo-couple Nos. 2 and 3,Xs= length of the specimen, andXCu= distance (or centimetres) between t
31、hermocouple Nos.1 and 2.NOTE 1In taking measurements and making calculations, care shouldbe taken not to mix inch-pound and metric units. For purposes ofconversion the following factor may be used:1 Btuin./hft2 F = 0.000 345 gcalcm/scm2 C.9. Report9.1 Report the following information:9.1.1 General d
32、escription of the material being tested,9.1.2 Thermal conductivity data reported at the mean speci-men temperature calculated in 7.1.7, and9.1.3 A curve showing the actual thermal conductivityvalues plotted as a function of mean temperature.10. Precision and Bias10.1 Based on repeated tests made ove
33、r the thermal conduc-tivity range normally associated with ceramic material usingNOTE 11 in. = 25.4 mm.FIG. 2 Detail of Thermodes for 0.410-in. (10.41-mm) DiameterSpecimenTABLE 1 Thermal Conductivity of Electrolytically Deposited PureCopper Used for ThermodesMean temperature,F (C)Thermal Conductivit
34、y (KCu)Inch-PoundUnitsAMetricUnitsB32 (0) 2693 0.927212 (100) 2623 0.903392 (200) 2590 0.891ABtuin./hft2F.Bgcalcm/scm2C.C408 88 (2016)3the same sample and on samples having the same composition,the precision of the apparatus is of the order of 62.5 %.10.2 Based on thermal conductivity determinations
35、 made onvitreous silica, on high purity freezing-point lead, and on highpurity freezing-point tin standards, the bias of the apparatus is63%.11. Keywords11.1 thermal conductivity; whiteware ceramicsASTM International takes no position respecting the validity of any patent rights asserted in connecti
36、on with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible
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38、deration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Ba
39、rr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 88 (2016)4
