1、Designation: C 829 81 (Reapproved 2005)Standard Practices forMeasurement of Liquidus Temperature of Glass by theGradient Furnace Method1This standard is issued under the fixed designation C 829; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These practices cover procedures for determining theliquidus temperature (Note 1) of a glass
3、(Note 1) by establish-ing the boundary temperature for the first crystalline com-pound, when the glass specimen is held at a specified tempera-ture gradient over its entire length for a period of timenecessary to obtain thermal equilibrium between the crystallineand glassy phases.NOTE 1These terms a
4、re defined in Definitions C 162.1.2 Two methods are included, differing in the type ofsample, apparatus, procedure for positioning the sample, andmeasurement of temperature gradient in the furnace. Bothmethods have comparable precision. Method B is preferred forvery fluid glasses because it minimize
5、s thermal and mechanicalmixing effects.1.2.1 Method A employs a trough-type platinum container(tray) in which finely screened glass particles are fused into athin lath configuration defined by the trough.1.2.2 Method B employs a perforated platinum tray onwhich larger screened particles are position
6、ed one per hole onthe plate and are therefore melted separately from each other.21.3 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 practices and de
7、termine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C 162 Terminology of Glass and Glass Products2.2 Other Document:NIST Certificate for Liquidus Temperature, SRM 77343. Significance and Use3.1 These practices are useful for determining the ma
8、ximumtemperature at which crystallization will form in a glass, and aminimum temperature at which a glass can be held, forextended periods of time, without crystal formation andgrowth.4. Apparatus4.1 The apparatus for determining the liquidus temperatureshall consist essentially of an electrically h
9、eated gradientfurnace, a device for controlling the furnace temperature,temperature measuring equipment, and other items listed.4.1.1 Furnace:4.1.1.1 Method AHorizontal temperature gradient, electri-cally heated furnace, tube type, as illustrated in Fig. 1, Fig. 2,and Fig. 3 and described in A1.1.4.
10、1.1.2 Method BAn alternative furnace detail employingpregrooved Al2O3cores and dual windings, as illustrated inFig. 4 and Fig. 5, and described in A1.2.4.1.1.3 Equivalent temperature gradient conditions may alsobe obtained with furnaces having multiple windings equippedwith separate power and contro
11、l, or a tapped winding shuntedwith suitable resistances. For high precision, temperaturegradients in excess of 10C/cm should be avoided.4.1.2 Furnace Temperature Control:4.1.2.1 Method AA suitable temperature controller shallbe provided to maintain a fixed axial temperature distributionover the leng
12、th of the furnace.4.1.2.2 Method BArheostat shall be used to supply powerto the outer winding.Aseparate rheostat and controller shall beused for the inner core winding. The basic furnace temperaturelevel is achieved by controlling power to both inner and outercore windings. The slope of the gradient
13、 is achieved byadjusting power input to the outer core winding only. Theestablished temperature gradient is then maintained by control-ling power to the inner core winding only.4.1.3 Temperature-Measuring Equipment Furnace tem-peratures shall be measured with calibrated Type R or S1These practices a
14、re under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and are the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved Sept. 1, 2005. Published November 2005. Originallyapproved in 1976. Last previous edition approved in 2000
15、 as C 829-81(2000).2From NBS Research Paper RP2096, Vol 44, May 1950, by O. H. Grauer andE. H. Hamilton, with modification and improvement by K. J. Gajewski, Ford MotorCo., Glass Research and Development Office (work unpublished).3For referenced ASTM standards, visit the ASTM website, www.astm.org,
16、orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 3460, Gaithersburg, MD 20899-34601Copyri
17、ght ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.thermocouples in conjunction with a calibrated potentiometer,or other comparable instrumentation, capable of measurementswithin 0.5C. In addition to control thermocouples, Method Arequires an
18、unshielded supported thermocouple for insertioninto the furnace chamber to determine temperature gradients,and Method B requires five thermocouples mounted in thespecimen support fixture as shown in Fig. 6. An alternativemethod is to attach (spot weld) the thermocouples to a fixedplatinum or platinu
19、m alloy plate which supports the tray orperforated plate. A solid-state digital thermometer capable ofthe measurement accuracy specified may be used for tempera-ture measurement.4.1.4 MicroscopeAmicroscope capable of resolution of atleast 5 m at 1003 is required. A petrographic microscope ispreferre
20、d for ease of crystal identification under polarized light.4.1.5 Additional Equipment for Method A:4.1.5.1 Laboratory stand to support thermocouple horizon-tally (see Fig. 7).4.1.5.2 Trough-type platinum boats (see Fig. 8 and AnnexA2).4.1.5.3 Reshaping die for trough-type boats (see Fig. 8).4.1.5.4
21、Stainless steel mortar and pestle. ( The stainless steelmust be magnetic.)NOTE 1See A1.1 for further description.1. Outer shell (stainless steel) 7. Outer protection tube2. End plate (Transite)48. Sil-O-Cel5insulation3. End plate (quartz) 9. Control thermocouple (platinum/rhodium)4. Stand 10. Heatin
22、g element wire5. Inner protection tube 11. Specimen tray6. Heating element tubeFIG. 1 Liquidus Furnace (Method A)Material: 26-gage stainless steelFIG. 2 Liquidus Furnace Shell (Method A)MillimetresNo. of TurnsA: 6 turns4.8-mm spacingB: 13 turns9.5-mm spacingC: 5 turns6.4-mm spacingD: 24 turns4.8-mm
23、spacingFIG. 3 Recommended Liquidus Furnace Winding (Method A)C 829 81 (2005)24.1.5.5 Sieve, U.S. Standard, No. 20 (850-m) with receiverpan.4.1.5.6 Small horseshoe magnet.4.1.5.7 Glass vials with covers.4.1.5.8 Graduated measuring rod.4.1.5.9 Stainless steel tongs.4.1.5.10 Other minor items as descri
24、bed in the text.4.1.6 Additional Equipment for Method B:4.1.6.1 Riding device for simultaneously holding and posi-tioning multiple thermocouples and a perforated platinum tray.This device is provided with leveling screws, a means forlateral adjustment, and a positive stop for precisely locating theb
25、oat and thermocouples within the furnace. The device shownin Fig. 9 meets these requirements.NOTE 1See A1.2 for further description.1. Stainless steel shell 7. Inner heating element tube2. End plates (Transite4) 8. Perforated platinum tray3. End seals (Fiberfrax6) 9. Mullite tube of riding device4.
26、Insulating cover (Fiberfrax6) 10. Alumina spacers5. Refractory or Sil-O-Cel insulation 11. Controlling thermocouple6. Outer heating element tubeFIG. 4 Liquidus Furnace (Method B)FIG. 5 Liquidus Furnace Heating Cores (Method B)NOTE 1Hottest thermocouple positioned at forward edge of cut-away section
27、of mullite tube.FIG. 6 Specimen Support Fixture (Method B)C 829 81 (2005)34.1.6.2 Perforated platinum trays (see Fig. 10 and AnnexA2).4.1.6.3 Stainless steel mortar and pestle.4.1.6.4 Sieves, U.S. Standard, No. 8 (2.36-mm) and No. 12(1.70-mm) with receiver pan.4.1.6.5 Glass vials with covers.4.1.6.6
28、 Stainless steel pointed tongs.4.1.6.7 Other minor items as shown in illustrations anddescribed in the text.5. Preparation of Test Specimens5.1 Select a mass of glass of approximately 70 g. Break thesample into pieces of a size that will fit into the mortar. Cleanthe sample with acetone, rinse with
29、distilled water, and dry.Clean the mortar and pestle, sieve, and magnet in the samemanner (Note 2). Crush the sample, using the mortar andpestle, by using a hammer or other suitable means.NOTE 2From this point on, contact with bare hands or other source ofcontamination must be avoided.5.2 Method APo
30、ur the crushed sample onto a No. 20(850-m) sieve. Retain the material not passing the sieve andrepeat the crushing procedure until all the glass has beenreduced to a size to pass through the sieve into the receiver pan.With the test specimen still in the pan, move the magnetthroughout the specimen t
31、o remove magnetic fragments thatmay have been introduced during crushing. If not to be testedimmediately, place the specimen in a covered glass vial orother suitable container.5.3 Method BPour the crushed sample onto a No. 8(2.36-mm) sieve fitted over a No. 12 (1.70-mm) sieve andreceiver pan. Retain
32、 only that part of the sample not passingthrough the No. 12 sieve. That glass retained on the No. 8 sievemay be recrushed if necessary to increase the No. 12 sievesample size. Discard the fines passing through to the receiverpan. If not to be tested immediately, place the specimen in acovered glass
33、vial or other suitable container.6. Procedure6.1 Method AFill to one-half to three-quarters full twospecimen trays that are free of cracks, pits, or adhering glasswith the crushed glass specimen. Distribute evenly over thelength of each tray. Place the filled trays in the furnace, one oneither side
34、of the maximum temperature point, and locate sothat their centers are at the predetermined gradient temperaturelevel corresponding to the liquidus temperature, if known.Record the location of the trays in the furnace. Either thesingle- or the double-core furnace may be used. Modify thedouble-core fu
35、rnace design to accommodate two samples byproviding two riding devices and means for insertion from bothends of the furnace.6.2 Method BUse one or two perforated specimen traysthat are free of cracks, pits, or adhering glass. Using thepointed stainless steel tongs or tweezers, select chips of thesam
36、ple from the No. 12 (1.70-mm) sieve and place one in eachof the drilled holes in each tray. Position a tray in the cut-awaysection of the mullite tube on the riding device with the doublerow of holes forward (toward the hot end), and the forward endof the tray indexed precisely over the most forward
37、 of the fivethermocouples against the forward edge of the cut-awaysection, as shown in Fig. 4. An alternative method is to movethe furnace into position around a fixed tray. One sample in onetray supported by one riding device may be tested in thedouble-core furnace. Two samples may be tested simult
38、a-neously by modifying the furnace design to provide forinsertion from both ends. Carefully feed the riding devicecontaining the tray into the furnace until the prepositioned stopplate is contacted. Close the end opening of the furnace aroundthe riding device with suitable insulation.6.3 Treatment T
39、imeLeave the specimens in the furnaceuntil equilibrium between the crystal and glassy phases isestablished. The time required is a function of the glasscomposition. Twenty-four hours is sufficient for many glasses,but some glasses may take days to reach equilibrium. Completecrystallization of the sp
40、ecimen indicates insufficient tempera-ture in heat treatment. Total lack of crystallization indicatesinsufficient time or excess temperature.6.4 Temperature GradientDetermine the temperature gra-dients over the lengths of the specimens at the end of theheating period just prior to removal from the f
41、urnace.6.4.1 Single-Core FurnaceEstablish a temperature profileover the length of each tray by using a traveling unshieldedType R or S thermocouple supported horizontally as near thetop of the trays as practical and centered over their widths.Start the probe at the hotter end of each tray, toward th
42、e centerof the furnace, and make successive temperature readingsalong the tray length at12-in. (12.7-mm) intervals. Allow thethermocouple temperature to stabilize in each position asindicated by constancy of temperature over a period of time.Record the temperature of each thermocouple position to th
43、enearest 1C as related to tray position, and plot as in Fig. 11.6.4.2 Double-Core FurnaceObtain the temperature pro-file as related to tray position from readings of the five Type Ror S thermocouples mounted in fixed positions in the ridingdevice.6.5 Method A:6.5.1 Remove the specimens from the furn
44、ace, free from thetrays, cool, and examine under a microscope for evidence ofcrystallization. If the single-core furnace has been used for theheat treatment, grasp the trays with smooth-faced forceps anddrag outside the furnace onto a heat-resistant flat surface. If thedouble-core furnace has been u
45、sed, retract the riding devicefrom the furnace, remove the tray, and place it on theheat-resistant flat surface. Immediately upon removal andbefore the glass specimen hardens, bend the sidewalls of theFIG. 7 Thermocouple and Support (Method A)C 829 81 (2005)4tray slightly inward at 1-in. (25.4-mm) i
46、ntervals along itslength. After the specimen has solidified, but is still quite hot,bend the sidewalls outward to separate the specimen from thetray. Repeat the inward and outward bending as needed toseparate the specimen from the tray. Finally, bend the sides ofthe tray to nearly their original sha
47、pe, and invert the tray toremove the specimen. Tapping the top of the tray on a hard, flatsurface is usually required to remove the specimen. Immedi-ately return the hot specimen to its original position in the trayto avoid thermal shock breakage and to preserve orientation.Cool the specimen to room
48、 temperature and mark to identifyeither the end that was hotter or cooler when in the furnace.FIG. 8 Platinum Tray and Reforming Die (Method A)NOTE 1See A1.2 and Fig. 4 for legend.FIG. 9 Riding Device (Method B)C 829 81 (2005)56.5.2 Remove the cooled specimen from the tray and placeit on the stage o
49、f a microscope with the bottom surface upward.Apply a refractive index matching fluid to this surface. Theserequirements permit clearer observation of the specimen inte-rior, avoiding interference due to devitrification or composi-tional changes or both at the top surface. Use of crossed Nicolprisms with a full-wave tint plate aids in the observation of anycrystals. Scan the bottom surface region of the specimen fromthe cold toward the hot end. Observe beneath the surface, butnot deeper than18 in. (3 mm), and in the middle three fourthsof the width
