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Modified HDA Characterization Study

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Final technical rept. May 1977-Apr 1978

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Two techniques were employed to determine the density of Modified HDA High Density Acid, a blend of nitric acid and nitrogen dioxide, containing phosphorous pentafluoride as a corrosion inhibitor. Reliable data were obtained by use of pycnometers. Errors found by use of hydrometers were of a magnitude sufficient to affect subsequent rocket engine performance calculations. A two-cube factorial experiment was performed to determine which components of Modified HDA control vapor pressure. Nitrogen dioxide was found to be the principal controlling variable. The experiment also provided accurate data for total equilibrium pressure as a function of temperature, and demonstrated a decrease in total pressure with an increase in ullage. Such data are applicable to propellant tank and pump designs. The solubility of corrosion products in Modified HDA was studied using acids from previous corrosion tests. Solubility was found to be relatively independent of temperature and initial nitrogen dioxide or water content, but highly dependent on the specific species present in the acids, from competing corrosion reactions. Metal couples typical of those in propellant containment devices were exposed to relatively small volumes of Modified HDA to obtain further corrosion product solubility data, and to test for passivation of the metals with time. No passivation was noted within one month. Corrosion took place at a relatively constant rate. A limited number of solubility tests were performed with Standard HDA, a blend of nitric acid and nitrogen dioxide, containing hydrogen fluoride as a corrosion inhibitor. Trends were similar to those found for the less corrosive Modified HDA.

Subject Categories:

  • Test Facilities, Equipment and Methods
  • Liquid Rocket Propellants

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