Adamczak, Andrea Diane (2010-05). High Temperature Materials for Aerospace Applications. Doctoral Dissertation. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • May 2010