Date

2022-12-2

Author

Saç, Kaan

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The stability of propellant grade white fuming nitric acid (WFNA) during storage was investigated experimentally. A custom method was developed to monitor the propellant storage up to 600 hours at elevated temperatures. Two sets of test matrices were designed: a control test matrix was conducted for safety and test system qualification, and the master test matrix was carried out to assess the WFNA storage. The test parameters were selected as follows: two different ullage space values – 13.0% & 19% –, five different storage container material types – PTFE, AISI316L, AISI904L, Al5083-H111 & Al6061-T6 –, three different pressurizing gases – helium, nitrogen & air. Furthermore, whether the surface of the container is passivated by citric acid surface treatment was also an experimental parameter. The temperature was kept at 50 C for all tests. To carry out the tests, a pressure vessel body and a test tube were designed, qualified and manufactured. Commercial connections, measurement and safety equipment were combined with the manufactured parts to assemble the MPV (Mini Pressure Vessel) fixture. The effect of each of the four variables were analyzed individually, by keeping the others at a fixed value. Time-dependent pressure data was collected and recorded at 1 Hertz. This time-dependent pressure data was used to monitor the effects of control variables on pressure. Moreover, samples of stored white fuming nitric acid were analyzed for their elemental and chemical compositions by inductively coupled plasma optical emission spectroscopy, and ultraviolet-visible spectroscopy. The effect of dissolved metals and composition shifts were further analyzed by performing ignition delay tests with a fresh amine based fuel. In addition, mass losses of test tubes after storage was measured and the corrosion rate of each tube was determined based upon ASTM G31 – 72 standard. The experiments and subsequent analyses revealed that stainless steel containers were not suitable for WFNA storage: stainless steel containers deteriorated very rapidly while corroding the container tubes. This was independent of the storage conditions and whether the tube was passivated with citric acid. In contrast, Aluminum based containers performed better compared to stainless steel in terms of the WFNA deterioration, but they corroded by forming 𝐴𝑙(𝑁𝑂3)2, 𝑀𝑔(𝑁𝑂3)2 and 𝑀𝑛(𝑁𝑂3)2 which precipitated extensively. Furthermore, Al6061 provided the best performance in terms of corrosion rate with an average of 0.11 mm per year. According to the ignition delay results, which are specific to the test conditions, the shortest times were generally obtained from the acid in the Al6061 material, at the order of 10 ms.

Subject Keywords

Storage Conditions of White Fuming Nitric Acid, Corrosion Rate, Ignition Delay, Pressure Rise Rate, Elemental Analysis

URI

https://hdl.handle.net/11511/101235

Collections

Graduate School of Natural and Applied Sciences, Thesis