Red Fuming Nitric Acid - Experiments

Experiments

  • Hydrofluoric Acid Content of RFNA
When RFNA is used as an oxidizer for rocket fuels, it usually has a HF content of about .6%. The purpose of the HF is to act as a corrosion inhibitor. RFNA was tested for HF with a standard solution containing 12% of NO2 and a density of 1.57. These experiments were performed using an electrometric method. It was determined that the hydrofluoric acid content was about .5% by weight. This is very close to the usually .6% in rocket fuels.
  • Water content of RFNA
To test the water content, a sample of 80% HNO3, 8-20% NO2, and the rest H2O depending on the varied amount of NO2 in the sample. When the RFNA contained HF, there was an average H2O% between 2.4% and 4.2%. When the RFNA did not contain HF, there was an average H2O% between .1% and 5.0%. When the metal impurities from corrosion were taken into account, the H2O% increased, and the H2O% was between 2.2% and 8.8%
  • Corrosion of metals in RFNA
Stainless steel, aluminum alloys, iron alloys, chrome plates, tin, gold and tantalum were tested to see how RFNA affected the corrosion rates of each. This is important to understand because the containers that RFNA is kept in will affect the RFNA. Experiments were performed using 16% and 6.5% RFNA samples and the different substances listed above. Many different stainless steels showed resistance to corrosion. Aluminum alloys did not hold up as well as stainless steels especially in high temperatures but the corrosion rates were not high enough to prohibit the use of this with RFNA. Tin, gold and tantalum showed high resistance such like that of stainless steel. These are better though because at high temperatures, the corrosion rates were still kept low. It is important to note that at higher temperatures and the presence of phosphoric acid, the corrosion rates increase while sulfuric acid helped the corrosion rates and kept the substances from corrosion.

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