오톤콘 
TDA (Dilatometer)
DTA                        TGA                         STA (DTA/TGA)
SP-2A-DAS              SP-4A                     SP-5A -DAS    

TDA (Thermal Dilatometric Analysis) 열팽창계 

Thermal Dilatometric Analysis (TDA), often called "dilatometry", measures the dimensional change of a material (ceramics, glasses, metals, composites, carbon/graphite, minerals, polymers, and others) as a function of temperature. This test determines both reversible and irreversible changes in length (expansion and shrinkage) during heating and cooling, and pinpoints where reactions occur that cause expansion or contraction. Samples are quickly and easily measured for determining firing ranges and firing schedules, measuring thermal expansion ranges for glaze fits, and measuring thermal expansion ranges for R&D, QC or product certification. Orton dilatometers are used for ASTM E-228 testing.

A. Characteristics or Properties Measured
Coefficient of Thermal Expansion (CTE), softening point, glass transition temperature, curie point, crystalline transformation, phase transition, shrinkage, warping, bloating, sintering rate, isothermal creep, stress relaxation.

The test results are a graph of the TDA signal (converted to percent length change) on the Y-axis plotted versus the sample temperature in °C on the X-axis. Sample graphs of enhanced output are shown below.

Examples of Applications
Ceramics - ASTM E-228	Metals MIL I-23011C Class 7

B. Standard Dilatometers

Standard, Single Sample, Horizontal Dilatometers
	DIL 2010 B	DIL 2010 C	DIL 2010 STD	DIL 2012 STD	DIL 2016 STD
Temperature Range	RT to 1,000°C	RT to 1,000°C or -170°C to +300°C	RT to 1,000°C	RT to 1,200°C	RT to 1,600°C
Furnace	Kanthal - Tube	Nichrome - Split Shell Cryogenic Chamber	Kanthal - Tube	Kanthal - Tube	Silicon Carbide - Tube
Thermocouple	Type "N"	Type "N"	Type "S"	Type "S"	Type "S"
Sample Holder and Probe Rod	Fused Quartz	Fused Quartz	Fused Quartz	High Alumina	High Alumina
Sample Size (max)	50 mm long by 20 mm diameter	100 mm long by 10 mm diameter	100 mm long by 20 mm diameter	50 mm long by 20 mm diameter	50 mm long by 20 mm diameter
Contact Load	113 grams	Adjustable 4 grams min.	Adjustable 4 grams min.	Adjustable 4 grams min.	Adjustable 4 grams min.
Temperature Control	Orton Multi-segment Controller
Data Acquisition	Orton On-board Computer
Data Analysis	Orton Analysis Software (Windows 95/98/2000 Based)
Computer Interface	RS232 Cable
Controlled Atmosphere Option	Not Available	Yes	Yes	Yes	Yes
Power Requirements	120 VAC, 15 amp, 50/60 Hz	120 VAC, 15 amp, 50/60 Hz	120 VAC, 15 amp, 50/60 Hz	120 VAC, 15 amp, 50/60 Hz	240 VAC, 205 amp, 50/60 Hz

Other Orton Dilatometers • Vertical • 2 Sample • Multiple Sample • Non-contact Laser • Rapid turnaround • Quench (metallurgical)

Contact Orton for more details.

C. Computer Analysis
Every Orton dilatometer is supplied with the software to add to the user's PC in order to acquire, save and analyze the data generated by the dilatometer. The Orton Dilatometer Software is a Visual Basic executable routine written for Windows 95/98/2000 based personal computers. It can be used to monitor the dilatometer test in real time, or can be used to examine the test data after the run. The software imports the data through the RS232 interface, and stores it on the hard drive for immediate or post-testing analysis. The software enables the user to:

View the dilatometer data in a variety of presentations

• percent linear change (PLC) vs. temperature
• percent linear change (PLC) vs. time
• first derivative of the percent linear change (DCE) vs. temperature
• first derivative of the percent linear change (DCE) vs. time
• percent linear change (PLC) and first derivative of the percent linear change (DCE) vs. temperature
• percent linear change (PLC) and first derivative of the percent linear change (DCE) vs. time

Perform a variety of analyses

• calculate the coefficient of thermal expansion (CTE) between specified temperatures, or a series of specified temperatures
• calculate the average coefficient of thermal expansion from room temperature to a specified temperature at a specified temperature increment
• determine transition temperature
• determine softening temperature
• locate alpha-beta quartz transition Export the data in a text file format for independent analysis or archiving purposes

D. Additional Information on TDA

All materials expand and contract as a function of temperature. For two materials to adhere to each other, such as glass to metal seals, metalizations to substrates, and glazes to bodies, their respective thermal expansion characteristics must be known, matched, and controlled. Thermal Dilatometric Analysis (TDA), often called Dilatometry, measures the amount of dimensional change of a material (ceramics, glasses, metals, composites, carbon/graphite, minerals, plastics, and others) during a controlled thermal cycle. Dilatometry measures the normal expansion and contraction of a material, including its reversible phase changes. This procedure also measures the irreversible changes in length that are the result of decompositions, phase transformations, and other chemical reactions, and helps identify the temperature ranges of those events and reactions. Such testing is helpful when trying to control the thermal expansion characteristics of various lots of materials, and in determining drying and firing schedules.

Principle of Operation

The sketch above shows the concepts of a dilatometer. A sample specimen is placed between the end of the sample holder and the end of the movable probe rod, and the furnace is heated according to a pre-programmed thermal cycle. As the sample temperature changes (as recorded by the sample thermocouple), the sample expands (pushing against the probe rod) or shrinks (pulling away from the probe rod). The probe rod transmits the amount of sample movement to an electronic displacement sensor located outside of the heated chamber. The displacement sensor generates an electronic signal corresponding to the positive or negative change in sample length and continuously sends the signal to the computer. The computer converts the signal to the percent of length change (%DL) and saves it along with the elapsed time and the sample temperature. The basic TDA curve is generated by plotting the percent of length change (%DL) on the Y-axis against the sample temperature.

Horizontal Dilatometer

The photos above are a horizontal dilatometer with the furnace moved away to expose the sample holder, and a close-up view of the sample holder. The photo on the right shows how the sample is positioned between the end of the sample holder and the probe rod. After positioning the sample in the sample holder, the furnace is moved horizontally to surround the sample and sample holder.

The probe rod extends from the end of the sample, throught the sample holder tube, and connects to the displacement sensor assembly outside the furnace. The probe rod is spring loaded outside the furnace to keep it in constant contact with the sample, even when shrinking.

The main advantage of the horizontal system is the uniform temperature zone for the sample. Most dilatometer tests are performed with a horizontal unit.

Vertical Dilatometer

For larger samples, such as structural clay bodies, a vertical dilatometer is used. The sample is placed into the furnace and the vertical probe rod is lowered to contact the sample (as shown in the photo at the right). The furnace is heated according to the pre-programmed thermal cycle. As the sample temperature changes, the sample expands, pushing up on the probe rod, or shrinks, pulling away from the probe rod. The probe rod is vertically suspended and counterweighted so that gravity keeps it in constant contact with the sample. The probe rod transmits the amount of sample movement to the electronic displacement sensor located overhead and outside the furnace.

E. Frequently Asked Questions:

Percent Length Change (PLC) and Coefficient of Thermal Expansion (CTE): Percent Linear Change (PLC) is the amount of expansion or shrinkage expresses in percentage of an initial length. A standard TDA curve is usually the PLC on the Y-axis and the temperature on the X-axis. The thick, black line in the graph below is a typical TDA curve of glass.
Temperature: The temperature range for a dilatometer is determined by the type of heating element or heating system used. The standard Orton dilatometers are made for one of the following temperature ranges:

• -170°C to +300°C (Cryogenic cooling chamber and Ni-chrome Heating Element with Fused Quartz Sample Holder and Probe Rod)
• Room Temperature to 1,000°C (Kanthal Heating Element with Fused Quartz Sample Holder and Probe Rod)
• Room Temperature to 1,200°C (Kanthal Heating Element with High Alumina Sample Holder and Probe Rod)
• Room Temperature to 1,600°C (Silicon Carbide or Platinum Heating Element with High Alumina Sample Holder and Probe Rod)
• Room Temperature to 1,700°C (Molybdenum Disilicide Heating Element with High Alumina Sample Holder and Probe Rod)

Thermal Cycle: The most commonly used thermal cycle for dilatometry is a simple, controlled heat-up rate of 3°C per minute from ambient temperature to the maximum temperature, then the test is terminated. For testing materials that experience irreversible reactions or when quartz transitions are critical, the thermal cycle can be extended to include a cool down segment. For developing firing schedules or examining what happens during a certain firing schedule, the dilatometer can be programmed to follow an actual production schedule that contains multiple ramps and soaks. The Orton dilatometer can be programmed for simple cycles, or up to a 20 segment thermal cycle.
Heat-up Rate: A sample does not absorb heat instantaneously, so it does not expand or shrink instantaneously. Since a finite amount of time is required for a sample to come to an equilibrium temperature and expansion/shrinkage condition, some thermal expansion measurements are made by holding the furnace temperature constant until the sample reaches an equilibrium temperature and length. These static condition (isothermal) tests take a lot of time, and are generally performed at only a few temperatures. · To save time and generate more information over a broader range of temperatures, most thermal expansion measurements are taken while the sample is being heated during a dynamic heat up. The thermal conductivity, size, and geometry of the sample will influence how quickly the sample can absorb heat and change length. With fast heat up rates, there is a tendency for the sample temperature to lag behind the furnace temperature, and the corresponding change in length to lag as well. With slow heat up rates, the amount of thermal lag and length change lag are much less, but the tests can be very long. Over the years the common industrial practice has evolved to a compromise rate of 3°C per minute. This keeps the amount of lag to a minimum and the testing time practical. · The important factor is to be consistent in the heat up rate used, and to be consistent with the sample size and geometry.
Sample Size: The maximum sample size for the horizontal dilatometer is 2" long by 3/8" diameter or square. Samples longer than 2" will extend beyond the isothermal zone, and larger diameter samples will not fit into the sample holder. The ends of samples must be flat, parallel, and perpendicular to the length axis. · The ultimate sample length depends upon the total amount of expansion or the total amount of shrinkage expected. The displacement sensor on the standard Orton dilatometer has a total linear movement of 5.0 millimeters (0.200 inches). Orton prefers to use only the center half of this range, so total sample movement (expansion or shrinkage) is 2.5 millimeters (0.100 inches). Consequently, low expansion/shrinkage samples should be long, and high expansion/shrinkage samples can be shorter. The following table shows the maximum percent expansion / shrinkage of different length samples.

Sensitivity: (To be added later)
Atmospheres: Tests are normally performed in ambient air. By adding the controlled atmosphere option to the Orton dilatometer, inert and reducing atmospheres, as well as vacuums are possible. There are several concerns when running tests in controlled atmospheres:

• The atmosphere tube surrounding the sample is a thermal barrier, and creates a larger thermal lag between the heating elements and the sample. Faster heating rates create an even larger thermal lag. Slower heating rates may be desirable.
• Flowing a gas over the sample will cool the sample, and create an even greater thermal lag between the sample and the heating elements. Flow rates should be a low as possible to minimize this affect.
• Reducing atmospheres, such as hydrogen, will significantly degrade platinum thermocouples at elevated temperatures. Small amounts of moisture with the hydrogen will increase the rate of platinum degradation. Using "dry" hydrogen will reduce the moisture attack. Using a surrogate gas, such as dry helium, may be reducing enough, and will retard platinum deterioration. A last alternative is to use a shielded thermocouple to totally avoid platinum degradation. However, a shielded thermocouple introduces another thermal lag into the test.
• A vacuum is an excellent thermal barrier to heat transfer. There is no gas for conduction and convection. Radiation does not become an effective heat transfer mechanism until elevated temperatures.

Copyright 2001 Red Corona  All rights reserved