ASTM D7739-11(R2020) pdf free download

ASTM D7739-11(R2020) pdf free download.Standard Practice for Thermal Oxidative Stability Measurement via Quartz Crystal Microbalance
1. Scope
1.1 This laboratory practice covers the quantitative determi- nation of surface deposits produced during the thermal oxida- tion of gas turbine fuels by monitoring the oscillation fre- quency of a quartz crystal during thermal exposure. In this practice, “thermal oxidative stability” refers to the tendency of a fuel to resist surface deposit formation during heating. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 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.
2. Summary of Practice
2.1 A quartz crystal, fitted with gold electrodes, is fully immersed in test fuel contained within a reactor. An oscillator circuit, connected to the crystal, supplies energy to excite the quartz crystal and monitors its resonant frequency (nominally 5 MHz) over time via a computer interface. The reactor is equipped with a magnetic stir bar, pressure gauge/transducer, oxygen sensor (not recommended for certain test conditions, see 4.11), and thermocouple to monitor and control test conditions. Prior to testing, the fuel is bubbled with the test gas for 30 min to equilibrate. After equilibration, the reactor vessel is isolated and raised to test temperature and pressure. As deposits accumulate on the crystal surface during the run, the crystal frequency decreases.
3. Significance and Use
3.1 The tendency of a jet fuel to resist the formation of deposits at elevated temperature is indicative of its oxidative thermal stability. This practice provides a technique for the simultaneous determination of deposit formation and oxygen consumption during the thermal oxidation ofjet fuels and other hydrocarbon liquids. The practice can be used to evaluate the thermal stability of fuels and to determine the efficacy of additives in inhibiting deposition or slowing oxidation, or both. Atest temperature of140 °C and run length up to 16 h has been found to be effective for the relative evaluation of fuels and fuel additives. This practice has also been employed for other hydrocarbon liquids, such as gasoline and diesel fuels, but additional safety issues may need to be addressed by the user.
4. Apparatus
4.1 All dimensions without tolerance limits are nominal values. 4.2 Reactor—A T316, 100 mL stainless steel reactor cylin- der with an internal diameter of 5.23 cm (2.06 in.) and a depth of 4.93 cm (1.94 in.). 3,4 A T316 stainless steel reactor head with several openings (for example, gas inlet via dip tube, gas release fitted with a dial gauge or pressure transducer, thermocouple, safety rupture disk, frequency signal connection, sleeve for oxygen concentration probe). A 0.952 cm ( 3 ⁄ 8 in.) hole is drilled in the center ofthe reactor head to accommodate the frequency signal connectors. This hole shall have a 0.952 cm ( 3 ⁄ 8 in.) clearance from any adjacent opening.4.3 SMA Coaxial Connector Assembly—This assembly pro- vides the electronic connection through the reactor head to the quartz crystal and consists ofseveral key parts (see Fig. 1). The cable from the oscillator (see 4.6) connects to a subminiature version A (SMA) adapter plug. 5,4 The SMA adapter plug connects to two male SMA connectors. 6,4 The male SMA connectors are first welded together, and then laser welded in place on both sides ofthe reactor head. 7,4 A mating set ofSMA connectors (male and female) was not used since these were not available in 0.952 cm ( 3 ⁄ 8 in.) diameter. The threaded end of the SMA connector on the bottom of the reactor head connects to the Quartz Crystal Adapter (see 4.5). 4.4 ReactorHeater—Open bottom band heater used to bring test fuel to temperature. 8,4 4.5 Heater Controller—Proportional-integral-derivative (PID) controller for regulating the open bottom reactor band heater. 9,4 A second heater controller may be used as a high temperature safety cut-off should the outside skin temperature of the reactor exceed a preset limit.