1、Designation: C829 81 (Reapproved 2015)Standard Practices forMeasurement of Liquidus Temperature of Glass by theGradient Furnace Method1This standard is issued under the fixed designation C829; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、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 These practices cover procedures for determining theliquidus temperature (Note 1) of a glass (No
3、te 1) by establish-ing the boundary temperature for the first crystallinecompound, when the glass specimen is held at a specifiedtemperature gradient over its entire length for a period of timenecessary to obtain thermal equilibrium between the crystallineand glassy phases.NOTE 1These terms are defi
4、ned in Terminology C162.1.2 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 minimizes therma
5、l 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 positioned one p
6、er 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 determine
7、the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C162 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 maximumtemp
8、erature 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 heated gra
9、dientfurnace, 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 Figs. 1-3 anddescribed in A1.1.4.1.1.2 Method BAn alternati
10、ve furnace detail employingpregrooved Al2O3cores and dual windings, as illustrated inFigs. 4 and 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 control, or a tapped winding shunted
11、with 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 length of the furnace.4.1.2.2 Meth
12、od 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 is achieved byadjusting power
13、 input to the outer core winding only. Theestablished temperature gradient is then maintained by control-ling power to the inner core winding only.1These practices are under the jurisdiction of ASTM Committee C14 on Glassand Glass Productsand are the direct responsibility of Subcommittee C14.04 onPh
14、ysical and Mechanical Properties.Current edition approved May 1, 2015. Published May 2015. Originallyapproved in 1976. Last previous edition approved in 2010 as C829 81 (2010).DOI: 10.1520/C0829-81R15.2From NBS Research Paper RP2096, Vol 44, May 1950, by O. H. Grauer and E.H. Hamilton, with modifica
15、tion 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, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the
16、standards Document Summary page onthe ASTM website.4Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Unit
17、ed States14.1.3 Temperature-Measuring Equipment Furnace tem-peratures shall be measured with calibrated Type R or Sthermocouples in conjunction with a calibrated potentiometer,or other comparable instrumentation, capable of measurementswithin 0.5C. In addition to control thermocouples, Method Arequi
18、res an 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
19、platinum 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 100 is required. A petrographic microscope ispr
20、eferred 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).NOTE 1See A1.1 for further description.1. Outer shell (stainless steel) 7. Outer protection tube2. End plate (Transite)
21、48. Sil-O-Cel5insulation3. End plate (quartz) 9. Control thermocouple (platinum/rhodium)4. Stand 10. Heating element wire5. Inner protection tube 11. Specimen tray6. Heating element tubeFIG. 1 Liquidus Furnace (Method A)Material: 26-gauge stainless steelFIG. 2 Liquidus Furnace Shell (Method A)Millim
22、etresNo. of TurnsA: 6 turns4.8 mm spacingB: 13 turns9.5 mm spacingC: 5 turns6.4 mm spacingD: 24 turns4.8 mm spacingFIG. 3 Recommended Liquidus Furnace Winding (Method A)C829 81 (2015)24.1.5.2 Trough-type platinum boats (see Fig. 8 and AnnexA2).4.1.5.3 Reshaping die for trough-type boats (see Fig. 8)
23、.4.1.5.4 Stainless steel mortar and pestle. (The stainless steelmust be magnetic.)4.1.5.5 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 d
24、escribed 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 forNOTE 1See A1.2 for further description.1. Stainless steel shel
25、l 7. Inner heating element tube2. End plates (Transite4) 8. Perforated platinum tray3. End seals (Fiberfrax6) 9. Mullite tube of riding device4. Insulating cover (Fiberfrax6) 10. Alumina spacers5. Refractory or Sil-O-Cel insulation 11. Controlling thermocouple6. Outer heating element tubeFIG. 4 Liqu
26、idus Furnace (Method B)FIG. 5 Liquidus Furnace Heating Cores (Method B)NOTE 1Hottest thermocouple positioned at forward edge of cut-away section of mullite tube.FIG. 6 Specimen Support Fixture (Method B)C829 81 (2015)3lateral adjustment, and a positive stop for precisely locating theboat and thermoc
27、ouples within the furnace. The device shownin Fig. 9 meets these requirements.4.1.6.2 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
28、.6.6 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 w
29、ith 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
30、 APour 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 specim
31、en to 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 (2.36mm) sieve fitted over a No. 12 (1.70 mm) sieve and receiverpan. Re
32、tain only that part of the sample not passing through theNo. 12 sieve. That glass retained on the No. 8 sieve may berecrushed if necessary to increase the No. 12 sieve sample size.Discard the fines passing through to the receiver pan. If not tobe tested immediately, place the specimen in a covered g
33、lassvial 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 s
34、ide 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-cor
35、e furnace 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 th
36、esample 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 for
37、ward 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 si
38、multane-ously by modifying the furnace design to provide for insertionfrom both ends. Carefully feed the riding device containing thetray into the furnace until the prepositioned stop plate iscontacted. Close the end opening of the furnace around theriding device with suitable insulation.6.3 Treatme
39、nt TimeLeave 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 th
40、e specimen 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 t
41、he furnace.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, towar
42、d the 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 t
43、o thenearest 1C as related to tray position, and plot as in Fig. 11.6.4.2 Double-Core FurnaceObtain the temperature profileas related to tray position from readings of the five Type R orS thermocouples mounted in fixed positions in the ridingdevice.6.5 Method A:6.5.1 Remove the specimens from the fu
44、rnace, 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 andFIG. 7 Thermocouple and Support (Method A)C829 81 (2015)4drag outside the furnace onto a heat-r
45、esistant flat surface. If thedouble-core furnace has been used, 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 thetray slightly inward at 1-in. (25.4 mm)
46、intervals 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 sh
47、ape, and invert the tray toremove the specimen. Tapping the top of the tray on a hard, flatFIG. 8 Platinum Tray and Reforming Die (Method A)NOTE 1See A1.2 and Fig. 4 for legend.FIG. 9 Riding Device (Method B)C829 81 (2015)5surface is usually required to remove the specimen. Immedi-ately return the h
48、ot specimen to its original position in the trayto avoid thermal shock breakage and to preserve orientation.Cool the specimen to room temperature and mark to identifyeither the end that was hotter or cooler when in the furnace.6.5.2 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 specimeninterior, avoiding interference due to devitrification or compo-sitional 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 wi
