ASTM E928-2019 pdf free download

ASTM E928-2019 pdf free download.Standard Test Method for Purity by Differential Scanning Calorimetry
1. Scope
1.1 This test method describes the determination ofpurity of materials greater than 98.5 mole percent purity using differen- tial scanning calorimetry and the van’t Hoff equation. 1.2 This test method is applicable to thermally stable compounds with well-defined melting temperatures. 1.3 Determination of purity by this test method is only applicable when the impurity dissolves in the melt and is insoluble in the crystal. 1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.5 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.6 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
6. Interferences
6.1 This test method is nonspecific. Many impurities may cause the melting temperature broadening. Thus, it is not useful in identifying the nature of the impurity or impurities but only the total mol percent of impurity present. 6.2 The van’t Hoff theory assumes the following: 6.2.1 The impurities dissolve in the melt of the major constituent forming a solution approximately described by ideal solution theory; 6.2.2 The solubility of the impurity in the solid of the major constituent is negligible; and 6.2.3 The major constituent displays a single well-defined melting endotherm in the temperature range of interest. Micro- scopic investigations of the melt and the solid may help to establish whether or not solid or liquid solutions have been formed. 6.2.4 The solute and solvent are close in molecular size. 6.3 In some cases the sample may react with air during the temperature cycle, causing an incorrect transition to be mea- sured. Where it has been shown that this effect is present, provision shall be made for sealing the specimen and running the test under an inert gas blanket. Since some materials degrade near the melting region, carefully distinguish between degradation and transition. See Appendix X1. 6.4 Since milligram quantities of sample are used, ensure that samples are homogeneous and representative. 6.5 Sublimation or decomposition will lead to a different heat consumption and, perhaps, a change in composition of the specimen. The specimen holder should be examined after the measurement for crystals not part of the resolidified melt.
7. Apparatus
7.1 The essential equipment required to provide the mini- mum instrument capability for this test method includes: 7.1.1 Differential Scanning Calorimeter (DSC), consisting of: 7.1.1.1 DSC Test Chamber, composed of a furnace(s) to provide uniform controlled heating of a specimen and refer- ence to a constant temperature or at a constant rate within the applicable temperature range ofthis test method; a temperature sensor to provide an indication of the specimen temperature readable to 60.1 K; a differential sensor to detect a heat flow difference between the specimen and reference equivalent to 10 µW; and a means of sustaining a test chamber environment of N 2 at a purge rate of 15 mL/min to 50 mL/min 6 5 mL/min. 7.1.1.2 Temperature Controller, capable of executing a spe- cific temperature program by operating the furnace(s) between selected temperature limits at a rate of temperature change of 0.3 K/min to 0.7 K/min constant to 60.01 K/min. 7.1.1.3 Data Collection Device, to provide a means of acquiring, storing, and displaying measured or calculated signals, or both. The minimum output signals required for DSC are heat flow, temperature, and time. 7.1.2 Containers, that are inert to the specimen, and that are ofsuitable structural shape and integrity for use in the DSC test chamber, made of materials of high thermal conductivity, such as aluminum.