Further crosslinking of the fluorinated polyimide was examined to separate the
cure reactions from degradation and to determine the optimum post curing conditions.
Glass transition/melting temperatures were ascertained using DSC, while weight loss
during curing and Td were determined using TGA. Furthermore, the mechanical
properties were measured using an Instron to relate to the thermal properties to find the
optimum curing conditions. The polyimide resin exhibited the best post-curing
conditions for further crosslinking for 8 hours at 410 degress C based on Tg, thermal stability,
and mechanical properties.
Blister temperatures, resulting from rapid heating, were obtained by monitoring
changes in transverse thickness expansion using two different techniques. Both
techniques employed showed similar blister temperatures in relation to the amount of
absorbed moisture, regardless of sample size. The polyimide resin exhibited blister
temperatures ranging from 225 - 362 degrees C, with 1.7 - 3.0 wt% absorbed moisture, and the
polyimide composite had blister temperatures from 246 - 294 degrees C with 0.5 - 1.5 wt%
moisture.
Weight loss of the fluorinated polyimide and its corresponding polyimide carbon
fiber composite under elevated temperature was examined. Weight loss as a function of
exposure temperature and time was measured using TGA and by pre- and post-weighing
of specimens treated in an oven. Both techniques showed similar weight loss trends as a
function of time and temperature, but TGA showed much greater weight loss due to
greater surface area to volume (i.e., small sample size). The neat polyimide resin and
carbon fiber composite exhibited negligible weight loss at temperatures below 430 degrees C
for exposure times up to 20 minutes.
Transition-metal carbides were initially synthesized by carbothermal reduction of
transition-metal halides and polymer precursor mixtures, at temperatures that range from
900 to 1500 degrees C in an argon atmosphere. TaC was synthesized from TaBr5, as a model
carbide for this process. Significant (> 40 vol%) amounts of TaC were formed at
reaction temperatures as low as 900 degrees C for one hour, with greater times and temperatures
leading to > 90 vol% yield. Universality of method was also proven by using other
various transition-metal halide salts (NbBr5, WCl4, and WCl6) with the polyimide.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-7828 |
| Date | 2010 May 1900 |
| Creators | Adamczak, Andrea Diane |
| Contributors | Grunlan, Jaime C. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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