1、Designation: C372 94 (Reapproved 2012)Standard Test Method forLinear Thermal Expansion of Porcelain Enamel and GlazeFrits and Fired Ceramic Whiteware Products by theDilatometer Method1This standard is issued under the fixed designation C372; the number immediately following the designation indicates
2、 the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of th
3、e linearthermal expansion of premelted frit (porcelain enamel andglaze) and ceramic whiteware products by the thermal dilatom-eter method. This test method is applicable to apparatusmeeting the reproducibility and accuracy requirements of thistest method, which are to produce percent linear expansio
4、naccuracy of 63 % or better and coefficient of linear expansionaccuracy of 65 % or better.1.2 This standard does 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 practic
5、es and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E220 Test Method for Calibration of Thermocouples ByComparison TechniquesE228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod DilatometerE230 Specification
6、 and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 mean coeffcient of linear thermal expansionfromtemperature T1to temperature T2(T1 T2):a,
7、mm/mmC or in./in.C 50.01 PT22 T1where:a = mean coefficient of linear thermal expansion fromtemperature T1to T2, andP = percent linear thermal expansion as defined in 3.1.2.3.1.2 percent linear thermal expansionfrom temperatureT1to temperature T2(T1 T2):P 5L22 L1L03 100 1 A5DLL03 100 1 Awhere:P = per
8、cent linear thermal expansion from temperatureT1to T2,L0= sample length at T0(T0between 20 and 30C),L1= sample length at T1,L2= sample length at T2, andA = instrument correction.4. Significance and Use4.1 Measurement of thermal expansion is useful for predict-ing stress within joined materials or si
9、ngle materials underconditions of changing or nonuniform temperature. It can alsoserve as an indicator of phase composition or changes instructure.5. Apparatus5.1 Thermal Dilatometer:5.1.1 General DescriptionA thermal dilatometer is anapparatus that provides means for varying the temperature of ates
10、t specimen in a controlled manner, measuring the specimenlength, and measuring the temperature of the specimen for eachreading of specimen length. There are several different types asfollows:5.1.1.1 ManualA manual dilatometer is one in which anyor all of the above are done by manual means and the co
11、rrectedpercent linear thermal expansion curve is plotted by hand.1This 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 appr
12、oved April 1, 2012. Published April 2012. Originallyapproved in 1955. Last previous edition approved in 2007 as C372 94(2007). DOI:10.1520/C0372-94R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStan
13、dards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.1.1.2 RecordingA recording dilatometer is an apparatusby which the above are recorded by inst
14、rumental means but thefinal corrected percent linear thermal expansion curve isplotted by hand.5.1.1.3 Automatic RecordingAn automatic recordingdilatometer is a recording dilatometer with provision forautomatically plotting the corrected percent linear thermalexpansion curve.5.1.2 Any generally acce
15、pted apparatus that is capable ofmeasuring the length changes produced by thermal expansionmay be used in this method. The accuracy of the expansion-measuring apparatus including transducer, electronic, mechani-cal or optical amplification and readout device must be60.0001 in. (60.003 mm) and should
16、 be reproducible to60.00005 in. (60.0013 mm). A dilatometer may use a directmethod of sighting on either of the two ends of the testspecimen or suitable markings at the ends, by means of twotelescopes mounted on a measuring bank. Another methodtransmits the change in length of the specimen to a sens
17、itivedial gage or transducer by means of members that are chemi-cally inert and free of phase transformations, having groundand polished surfaces at points of contact with the testspecimens.5.2 Scale or Caliper, capable of measuring the length of thespecimen with an accuracy of 60.0005 in. (60.010 m
18、m) mustbe used.5.3 Furnace that is electrically heated and designed so thatthe thermal gradient over the length of the test specimen shallbe less than 3C. This may be accomplished by electricalshuntings, individually controlled zones, or other methods.5.4 Temperature-Measuring DeviceTemperature mea-
19、surements shall be made by means of a thermocouple placed incontact with the test specimen approximately at its mid-length.The thermocouple shall have the accuracy specified in Table 15of Standard E230. Type S or Type K thermocouples arerecommended for this method.5.5 Temperature-Indicating DeviceTh
20、e temperature-indicating device may be a millivolt potentiometer, a calibratedmeter or recorder, or other apparatus with a precision of 65Cand an accuracy specification equivalent to the precision.6. Test Specimens6.1 For frit or dried slip samples, specimens shall beprepared as follows:6.1.1 Frit s
21、hould be crushed and screened through a 10-mesh sieve to remove large lumps. Then, a refractory boatcrucible shall be filled with the sample material. If it is desiredto reuse the crucible, it should be first lined with powderedalumina as a parting agent. The crucible can be of any suitablerefractor
22、y material such as porcelain or alumina, but shall beunglazed. For frits that will be fired at less than 800C, a metalmold may be used, if desired.6.1.2 The test specimen shall be subjected to the same firingcycle used commercially in order to give a smooth surface ona bulk sample.NOTE 1The sample m
23、ust be cooled slowly over several hours topreserve structural integrity.6.2 For all samples, test specimens may be of any conve-nient length, provided the uniformity of the furnace has beendetermined over that length. The minimum thickness of thespecimen shall be 0.2 in. (5.1 mm) and the maximum cro
24、ss-sectional area shall be 0.45 in.2(2.9 cm2). The ends of thespecimen shall be ground flat and perpendicular to the axis ofthe specimen.6.3 Test specimens shall be conditioned in accordance withthe history of the specimen. Conditioning shall include drying,annealing, or protection against moisture
25、expansion, as may benecessary.6.4 The length of the specimen shall be measured to withinan accuracy of 0.1 %.7. Calibration7.1 Periodic calibration of the thermal dilatometer is recom-mended to assure the accuracy required by this method.Procedures for calibrating the component parts of the dilatom-
26、eter are given below. A less time-consuming method forstandardizing a complete apparatus, especially the recordingtype, is also given. A calibration check of the components ofthe apparatus should be done on an annual basis and calibrationof the complete instrument using a standard sample should bedo
27、ne within 90 days preceding a report prepared under thismethod. The date of last calibration by either method should beincluded on the report.7.2 Calibration Procedures:7.2.1 Dilatometer:7.2.1.1 If a direct sighting method is used, the dilatometercan be calibrated with a standard sample with a known
28、 lengththat has been measured by a micrometer with an accuracy of60.0001 in. (0.003 mm).The reference sample should be madefrom a material that has a very low thermal expansion, such asfused silica or invar. The dilatometer system can be calibratedby measuring the length of the sample using a movabl
29、etelescope and comparing it with the known value.7.2.1.2 If a dial gage transducer system is used, the dilatom-eter can be calibrated with a micrometer or thickness gage. Fixthe dial gage transducer and micrometer in position on theinstrument itself or in a special fixture during calibration. Thesys
30、tem can be calibrated by displacing the probe of thetransducer a known amount with the micrometer or thicknessgage and adjusting the instrument to give that value. Which-ever technique is used, the micrometer or thickness gage shallbe accurate to 60.0001 in. (0.003 mm).7.2.2 FurnaceThe thermal gradi
31、ent that occurs over thesample length within the furnace should be determined bysimultaneously measuring the temperature at the center, and atthe ends of an alumina sample38 to12 in. (10 to 13 mm) indiameter and equal in length to the standard size sample forwhich the apparatus is intended. The ther
32、mocouples shall beType S or Type K. Thermocouple wire of 0.010-in. (0.25-mm)diameter or less should be used. The thermocouple beadsshould be in contact with the test sample surface. Bringthermocouple wires out of the furnace for termination. Acommon negative wire may be used for all three thermocoup
33、lesto reduce the number of leads brought from the furnace.Reference the center thermocouple to 0C and use for theC372 94 (2012)2temperature reading in degrees Celsius. Connect the thermo-couples in differential as shown in Fig. 1 so as to indicate thetemperature difference between the center and eac
34、h end. Withthe specimen, sample tubes, and readout thermocouple in theirnormal measuring configuration mounted in the furnace, thefurnace should be heated as specified in 8.2. The temperaturedifferentials can be measured with a microvoltmeter at inter-vals of 50C or less during heating. The microvol
35、tmeter shouldhave an accuracy of 61 V. The maximum thermal gradientshall be 3C.7.2.3 Temperature-Measuring DeviceAny one of thetechniques described in Method E220 may be used to calibratethe thermocouple to the accuracy given in Table 15 of StandardE230. The temperature readout device can be calibra
36、ted with apotentiometer or other source of known millivoltage that has anaccuracy of 60.01 mV. This testing device shall have anaccuracy of 60.5 % and shall be capable of being read to60.25 % of full scale.7.2.4 Determination of Instrument CorrectionA correc-tion, A, must be added algebraically to t
37、he measured values ofpercent expansion to compensate for the percent linear thermalexpansion of the material comprising the supporting membersof the dilatometer and other parameters of the apparatus thatcause a reproducible deviation from the correct values. Whileline-of-sight apparatus have no devi
38、ation caused by the sup-porting members, there will be reproducible deviations intro-duced by other parts of the apparatus for which correctionsmust be made. Determine the correction by the followingmethod:7.2.4.1 Prepare a sample of chemically pure (99.9 %) plati-num in accordance with the requirem
39、ents of this method. Areference standard as described in 7.2.6 may also be used.7.2.4.2 Measure by the method given in Section 8 theexpansion of the selected standard over the complete tempera-ture range for which the apparatus is intended. Plot the percentlinear thermal expansion measured. In autom
40、atic recordingdilatometers the automatic correction should not be connected.Plot on the same graph the curve for the accepted values of thestandard material or reference standard (see Test Method E228,Table A2).7.2.4.3 The difference between the two curves is the correc-tion for the apparatus. This
41、amount must be added algebra-ically to all observed percent expansion measurements toproduce the corrected percent expansion curve required for thismethod. The addition can be done either manually or byautomatic recording means.7.2.5 Calibration Using Platinum or Reference StandardPeriodic calibrati
42、on of the complete apparatus can be accom-plished as follows. The reference standard must meet therequirements of 7.2.6.7.2.5.1 Run the platinum or reference standard in accor-dance with the requirements of this method.7.2.5.2 Plot the percent expansion obtained for the platinumor reference standard
43、 with the correction factor added as shownin 9.1.7.2.5.3 Plot the accepted values of the platinum or referencestandard on the same graph plotted in 7.2.5.2 at no more than100C intervals. The results plotted in 7.2.5.2 must agree withthe accepted values for the platinum or reference standardwithin 61
44、% of the expansion value of platinum over thefull-scale temperature range. If the values do not agree withinthat amount, the values of the correction at those points shouldbe adjusted to produce results within tolerance. These newvalues of correction, either manual or automatic, should beused until
45、the next calibration. If corrected measured valuesdiffer from the accepted values by more than 62.5 % of fullscale at any reading, it is recommended that the completecalibration of the component parts of the apparatus as requiredby this method be done. In dilatometers using fused silicasupport membe
46、rs it is recommended that the tubes be checkedvisually for devitrification effects before complete calibrationis undertaken. Devitrification becomes evident as haze in thetube. Tube devitrification will result in the formation ofrecrystallized quartz and produce additive or subtractive effectsdepend
47、ing upon which member is devitrified. Moreover, whendevitrification occurs, breakage can be expected shortly.7.2.6 Reference StandardA reference standard of rela-tively stable nature can be used. The reference standard shouldbe of size and shape consistent with the requirements of thismethod. For th
48、is method a reference standard should be similarin composition to a typical whiteware body with quartz as amajor component. Prepare and treat the reference standard insuch a manner that it is stable up to 1200C. Determine thecorrected (accepted values) percentage expansion of the refer-ence standard
49、 in a thermal dilatometer that has been calibratedagainst platinum to within 60.5 % of full scale at every 100Cinterval in the temperature range. The calibration againstplatinum must immediately precede the determination of thevalues for the reference standard with a time lapse of no morethan one day.8. Procedure8.1 Insert the test specimen into the furnace at roomtemperature. Allow it to stand until specimen temperature andfurnace temperature are equal. At this time, record the readingof the dial indicator or other device that indicates the expansion
