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Significance and Use
5.1 Thermogravimetric analyzers are used to characterize a broad range of materials. In most cases, one of the desired values to be assigned in thermogravimetric measurements is the temperature at which significant changes in specimen mass occur. Therefore, the temperature axis (abscissa) of all apparent-mass-change curves must be calibrated accurately, either by direct reading of a temperature sensor, or by adjusting the programmer temperature to match the actual temperature over the temperature range of interest. In the latter case, this is accomplished by the use of either melting point or magnetic transition standards.
1.1 This practice describe the temperature calibration of thermogravimetric analyzers over the temperature range from 25 to 1500 °C and is applicable to commercial and custom-built apparatus. This calibration may be accomplished by the use of either melting point standards or magnetic transition standards.
1.2 The mass change curve in thermogravimetry results from a number of influences, some of which are characteristic of the specimen holder assembly and atmosphere rather than the specimen. The variations from instrument to instrument occur in the point of measurement of the temperature, the nature of the material, its size and packing, the geometry and composition of the specimen container, the geometry and design of the furnace, and the accuracy and sensitivity of the temperature sensor and displaying scales. These all contribute to differences in measured temperatures, which may exceed 20 °C. In addition, some sample holder assemblies will show variations of measured temperature with sample size or heating/cooling rate, or both. Since it is neither practical nor advisable to standardize sample holders or thermobalance geometries, instruments may be calibrated by measurement of the deviation of a melting or magnetic (Curie Point) transition temperature from the standard reference temperature. This deviation can be applied as a correction term to subsequent measurements.
1.3 This practice assumes that the indicated temperature of the instrument is linear over the range defined by a two-point calibration and that this linearity has been verified. These two calibration temperatures should be as close to the experimental measurements to be made as possible.
1.4 This practice describes three procedures for temperature calibration of thermogravimetric analyzers using any type balance. Procedures A and B use melting point standards with vertical and horizontal balances. Procedure C uses magnetic transition standards for calibration. Procedure A is designed specifically for use with horizontal-type balances. Procedure B is designed specifically for use with vertical hang-down balances.
1.6 The data generated by these procedures can be used to correct the temperature scale of the instrument by either a positive or negative amount using either a two-point temperature calibration procedure or a multi-point temperature calibration with best line fit for the generated data.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E473 Terminology Relating to Thermal Analysis and Rheology
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E967 Test Method for Temperature Calibration of Differential Scanning Calorimeters and Differential Thermal Analyzers
E1142 Terminology Relating to Thermophysical Properties
Other StandardsISO11358 Plastics -- Part 4: Thermogravimetry (TG) of Polymers -- General Principles Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
ICS Number Code 17.200.20 (Temperature-measuring instruments)