Accession Number:

AD0894806

Title:

The Modeling of Thermochemical Ablation of Pyrolyzed Plastics and Graphites. Part 1. Applications of Oxidative Thermogravimetry to Evaluating Arrhenius Constants and Defining Mechanisms

Descriptive Note:

Technical rept.

Corporate Author:

AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OH

Personal Author(s):

Report Date:

1972-02-01

Pagination or Media Count:

102.0

Abstract:

Future reentry vehicles will use pyrolyzed plastics and monolithic graphites for shape stable, and thermal protection systems. Oxidation kinetic models and kinetic constants for these models will be necessary to predict linear and mass losses, altered heat and mass transport features of the ablation contaminated flow field, the effects of ablative and contaminant species on opticalradar observables, and related phenomena. Constant heating rate thermogravimetry was used to study the fundamental kinetics and mechanisms of surface oxidation at temperatures to 1000 deg C. The materials included an ablative pyrolyzed plastic, an ammonium chloride-filled version of this material, three graphites, graphite fabric, and a carbon. The thermograms of powder samples of the pyrolyzed plastic and most of the other materials were similar. Oxidative resistance was reduced by an increase in airflow rate, heating rate, oxygen concentration, pressure, or surface area. These sample and environmental responses were consistent with an Arrhenius-type kinetic model. There was evidence of diffusive effects, of the type normally found at temperatures above 1000 deg C, in some of the heating rate, oxygen concentration, and surface area experiments. This unexpected result was tentatively explained in terms of a phase boundary control theory of surface oxidation.

Subject Categories:

  • Polymer Chemistry
  • Refractory Fibers
  • Guided Missile Reentry Vehicles

Distribution Statement:

APPROVED FOR PUBLIC RELEASE