ASTM C829-81(1995)e1
(Practice)Standard Practices for Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method
Standard Practices for Measurement of Liquidus Temperature of Glass by the Gradient Furnace Method
SCOPE
1.1 These practices cover procedures for determining the liquidus temperature (Note 1) of a glass (Note 1) by establishing the boundary temperature for the first crystalline compound, when the glass specimen is held at a specified temperature gradient over its entire length for a period of time necessary to obtain thermal equilibrium between the crystalline and glassy phases.
Note 1--These terms are defined in Definitions C162.
1.2 Two methods are included, differing in the type of sample, apparatus, procedure for positioning the sample, and measurement of temperature gradient in the furnace. Both methods have comparable precision. Method B is preferred for very fluid glasses because it minimizes thermal and mechanical mixing effects.
1.2.1 Method A employs a trough-type platinum container (tray) in which finely screened glass particles are fused into a thin lath configuration defined by the trough.
1.2.2 Method B employs a perforated platinum tray on which larger screened particles are positioned one per hole on the plate and are therefore melted separately from each other.
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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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e1
Designation: C 829 – 81 (Reapproved 1995)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practices for
Measurement of Liquidus Temperature of Glass by the
Gradient Furnace Method
This standard is issued under the fixed designation C 829; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Section 10 was added editorially in April 1995.
1. Scope 2.2 Other Document:
NIST Certificate for Liquidus Temperature, SRM 773
1.1 These practices cover procedures for determining the
liquidus temperature (Note 1) of a glass (Note 1) by establish-
3. Significance and Use
ing the boundary temperature for the first crystalline com-
3.1 These practices are useful for determining the maximum
pound, when the glass specimen is held at a specified tempera-
temperature at which crystallization will form in a glass, and a
ture gradient over its entire length for a period of time
minimum temperature at which a glass can be held, for
necessary to obtain thermal equilibrium between the crystalline
extended periods of time, without crystal formation and
and glassy phases.
growth.
NOTE 1—These terms are defined in Definitions C 162.
4. Apparatus
1.2 Two methods are included, differing in the type of
4.1 The apparatus for determining the liquidus temperature
sample, apparatus, procedure for positioning the sample, and
shall consist essentially of an electrically heated gradient
measurement of temperature gradient in the furnace. Both
furnace, a device for controlling the furnace temperature,
methods have comparable precision. Method B is preferred for
temperature measuring equipment, and other items listed.
very fluid glasses because it minimizes thermal and mechanical
4.1.1 Furnace:
mixing effects.
4.1.1.1 Method A—Horizontal temperature gradient, electri-
1.2.1 Method A employs a trough-type platinum container
cally heated furnace, tube type, as illustrated in Fig. 1, Fig. 2,
(tray) in which finely screened glass particles are fused into a
and Fig. 3 and described in A1.1.
thin lath configuration defined by the trough.
4.1.1.2 Method B—An alternative furnace detail employing
1.2.2 Method B employs a perforated platinum tray on
pregrooved Al O cores and dual windings, as illustrated in
which larger screened particles are positioned one per hole on
2 3
Fig. 4 and Fig. 5, and described in A1.2.
the plate and are therefore melted separately from each other.
4.1.1.3 Equivalent temperature gradient conditions may also
1.3 This standard does not purport to address all of the
be obtained with furnaces having multiple windings equipped
safety concerns, if any, associated with its use. It is the
with separate power and control, or a tapped winding shunted
responsibility of the user of this standard to establish appro-
with suitable resistances. For high precision, temperature
priate safety and health practices and determine the applica-
gradients in excess of 10°C/cm should be avoided.
bility of regulatory limitations prior to use.
4.1.2 Furnace Temperature Control:
2. Referenced Documents
4.1.2.1 Method A—A suitable temperature controller shall
2.1 ASTM Standards: be provided to maintain a fixed axial temperature distribution
over the length of the furnace.
C 162 Terminology of Glass and Glass Products
E 220 Method for Calibration of Thermocouples by Com- 4.1.2.2 Method B—A rheostat shall be used to supply power
to the outer winding. A separate rheostat and controller shall be
parison Techniques
used for the inner core winding. The basic furnace temperature
level is achieved by controlling power to both inner and outer
These practices are under the jurisdiction of ASTM Committee C-14 on Glass
core windings. The slope of the gradient is achieved by
and Glass Productsand are the direct responsibility of Subcommittee C14.04 on
adjusting power input to the outer core winding only. The
Physical and Mechanical Properties.
established temperature gradient is then maintained by control-
Current edition approved Dec. 28, 1981. Published March 1982. Originally
published as C 829-76. Last previous edition C 829-76.
ling power to the inner core winding only.
From NBS Research Paper RP2096, Vol 44, May 1950, by O. H. Grauer and
E. H. Hamilton, with modification and improvement by K. J. Gajewski, Ford Motor
Co., Glass Research and Development Office (work unpublished).
3 5
Annual Book of ASTM Standards, Vol 15.02. National Institute of Standards and Technology, Office of Standard Reference
Annual Book of ASTM Standards, Vol 14.03. Materials, Room B311, Chemical Building, Gaithersburg, MD 20899.
C 829
NOTE 1—See A1.1 for further description.
1. Outer shell (stainless steel) 7. Outer protection tube
4 5
2. End plate (Transite) 8. Sil-O-Cel insulation
3. End plate (quartz) 9. Control thermocouple (platinum/rhodium)
4. Stand 10. Heating element wire
5. Inner protection tube 11. Specimen tray
6. Heating element tube
FIG. 1 Liquidus Furnace (Method A)
Material: 26-gage stainless steel
FIG. 2 Liquidus Furnace Shell (Method A)
Millimetres
No. of Turns
A: 6 turns—4.8-mm spacing
B: 13 turns—9.5-mm spacing
C: 5 turns—6.4-mm spacing
D: 24 turns—4.8-mm spacing
FIG. 3 Recommended Liquidus Furnace Winding (Method A)
4.1.3 Temperature-Measuring Equipment— Furnace tem- the measurement accuracy specified may be used for tempera-
peratures shall be measured with calibrated Type R or S ture measurement.
thermocouples in conjunction with a calibrated potentiometer,
4.1.4 Microscope—A microscope capable of resolution of at
or other comparable instrumentation, capable of measurements
least 5 μm at 1003 is required. A petrographic microscope is
within 0.5°C. In addition to control thermocouples, Method A
preferred for ease of crystal identification under polarized light.
requires an unshielded supported thermocouple for insertion
4.1.5 Additional Equipment for Method A:
into the furnace chamber to determine temperature gradients,
4.1.5.1 Laboratory stand to support thermocouple horizon-
and Method B requires five thermocouples mounted in the
tally (see Fig. 7).
specimen support fixture as shown in Fig. 6. An alternative
4.1.5.2 Trough-type platinum boats (see Fig. 8 and Annex
method is to attach (spot weld) the thermocouples to a fixed
A2).
platinum or platinum alloy plate which supports the tray or
perforated plate. A solid-state digital thermometer capable of 4.1.5.3 Reshaping die for trough-type boats (see Fig. 8).
C 829
NOTE 1—See A1.2 for further description.
1. Stainless steel shell 7. Inner heating element tube
2. End plates (Transite ) 8. Perforated platinum tray
3. End seals (Fiberfrax ) 9. Mullite tube of riding device
4. Insulating cover (Fiberfrax ) 10. Alumina spacers
5. Refractory or Sil-O-Cel insulation 11. Controlling thermocouple
6. Outer heating element tube
FIG. 4 Liquidus Furnace (Method B)
FIG. 5 Liquidus Furnace Heating Cores (Method B)
NOTE 1—Hottest thermocouple positioned at forward edge of cut-away section of mullite tube.
FIG. 6 Specimen Support Fixture (Method B)
4.1.5.4 Stainless steel mortar and pestle. (The stainless steel 4.1.5.10 Other minor items as described in the text.
must be magnetic.) 4.1.6 Additional Equipment for Method B:
4.1.5.5 Sieve, U.S. Standard, No. 20 (850-μm) with receiver 4.1.6.1 Riding device for simultaneously holding and posi-
pan. tioning multiple thermocouples and a perforated platinum tray.
4.1.5.6 Small horseshoe magnet. This device is provided with leveling screws, a means for
4.1.5.7 Glass vials with covers. lateral adjustment, and a positive stop for precisely locating the
4.1.5.8 Graduated measuring rod. boat and thermocouples within the furnace. The device shown
4.1.5.9 Stainless steel tongs. in Fig. 9 meets these requirements.
C 829
single- or the double-core furnace may be used. Modify the
double-core furnace design to accommodate two samples by
providing two riding devices and means for insertion from both
ends of the furnace.
6.2 Method B—Use one or two perforated specimen trays
that are free of cracks, pits, or adhering glass. Using the
pointed stainless steel tongs or tweezers, select chips of the
sample from the No. 12 (1.70-mm) sieve and place one in each
of the drilled holes in each tray. Position a tray in the cut-away
section of the mullite tube on the riding device with the double
FIG. 7 Thermocouple and Support (Method A)
row of holes forward (toward the hot end), and the forward end
of the tray indexed precisely over the most forward of the five
thermocouples against the forward edge of the cut-away
4.1.6.2 Perforated platinum trays (see Fig. 10 and Annex
section, as shown in Fig. 4. An alternative method is to move
A2).
4.1.6.3 Stainless steel mortar and pestle. the furnace into position around a fixed tray. One sample in one
tray supported by one riding device may be tested in the
4.1.6.4 Sieves, U.S. Standard, No. 8 (2.36-mm) and No. 12
double-core furnace. Two samples may be tested simulta-
(1.70-mm) with receiver pan.
neously by modifying the furnace design to provide for
4.1.6.5 Glass vials with covers.
insertion from both ends. Carefully feed the riding device
4.1.6.6 Stainless steel pointed tongs.
containing the tray into the furnace until the prepositioned stop
4.1.6.7 Other minor items as shown in illustrations and
plate is contacted. Close the end opening of the furnace around
described in the text.
the riding device with suitable insulation.
5. Preparation of Test Specimens
6.3 Treatment Time—Leave the specimens in the furnace
5.1 Select a mass of glass of approximately 70 g. Break the until equilibrium between the crystal and glassy phases is
sample into pieces of a size that will fit into the mortar. Clean
established. The time required is a function of the glass
the sample with acetone, rinse with distilled water, and dry. composition. Twenty-four hours is sufficient for many glasses,
Clean the mortar and pestle, sieve, and magnet in the same
but some glasses may take days to reach equilibrium. Complete
manner (Note 2). Crush the sample, using the mortar and crystallization of the specimen indicates insufficient tempera-
pestle, by using a hammer or other suitable means.
ture in heat treatment. Total lack of crystallization indicates
insufficient time or excess temperature.
NOTE 2—From this point on, contact with bare hands or other source of
6.4 Temperature Gradient—Determine the temperature gra-
contamination must be avoided.
dients over the lengths of the specimens at the end of the
5.2 Method A—Pour the crushed sample onto a No. 20
heating period just prior to removal from the furnace.
(850-μm) sieve. Retain the material not passing the sieve and
6.4.1 Single-Core Furnace—Establish a temperature profile
repeat the crushing procedure until all the glass has been
over the length of each tray by using a traveling unshielded
reduced to a size to pass through the sieve into the receiver pan.
Type R or S thermocouple supported horizontally as near the
With the test specimen still in the pan, move the magnet
top of the trays as practical and centered over their widths.
throughout the specimen to remove magnetic fragments that
Start the probe at the hotter end of each tray, toward the center
may have been introduced during crushing. If not to be tested
of the furnace, and make successive temperature readings
immediately, place the specimen in a covered glass vial or
along the tray length at ⁄2-in. (12.7-mm) intervals. Allow the
other suitable container.
thermocouple temperature to stabilize in each position as
5.3 Method B—Pour the crushed sample onto a No. 8
indicated by constancy of temperature over a period of time.
(2.36-mm) sieve fitted over a No. 12 (1.70-mm) sieve and
Record the temperature of each thermocouple position to the
receiver pan. Retain only that part of the sample not passing
nearest 1°C as related to tray position, and plot as in Fig. 11.
through the No. 12 sieve. That glass retained on the No. 8 sieve
6.4.2 Double-Core Furnace—Obtain the temperature pro-
may be recrushed if necessary to increase the No. 12 sieve
file as related to tray position from readings of the five Type R
sample size. Discard the fines passing through to the receiver
or S thermocouples mounted in fixed positions in the riding
pan. If not to be tested immediately, place the specimen in a
device.
covered glass vial or other suitable container.
6.5 Method A:
6. Procedure
6.5.1 Remove the specimens from the furnace, free from the
6.1 Method A—Fill to one-half to three-quarters full two trays, cool, and examine under a microscope for evidence of
specimen trays that are free of cracks, pits, or adhering glass crystallization. If the single-core furnace has been used for the
with the crushed glass specimen. Distribute evenly over the heat treatment, grasp the trays with smooth-faced forceps and
length of each tray. Place the filled trays in the furnace, one on drag outside the furnace onto a heat-resistant flat surface. If the
either side of the maximum temperature point, and locate so double-core furnace has been used, retract the riding device
that their centers are at the predetermined gradient temperature from the furnace, remove the tray, and place it on the
level corresponding to the liquidus temperature, if known. heat-resistant flat surface. Immediately upon removal and
Record the location of the trays in the furnace. Either the before the glass specimen hardens, bend the sidewalls of the
C 829
FIG. 8 Platinum Tray and Reforming Die (Method A)
NOTE 1—See A1.2 and Fig. 4 for legend.
FIG. 9 Riding Device (Method B)
tray slightly inward at 1-in. (25.4-mm) intervals along its remove the specimen. Tapping the top of the tray on a hard, flat
length. After the specimen has solidified, but is still quite hot, surface is usually required to remove the specimen. Immedi-
bend the sidewalls outward to separate the specimen from the ately return the hot specimen to its original position in the tray
tray. Repeat the inward and outward bending as needed to to avoid thermal shock breakage and to preserve orientation.
separate the specimen from the tray. Finally, bend the sides of Cool the specimen to room temperature and mark to identify
the tray to nearly their original shape, and invert the tray to either the end that was hotter or cooler when in the f
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