Navegando por Palavras-chave "Synthetic Graphite"

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    Estudo Das Propriedades Termomecânicas E Características Morfológicas De Grafites Sintéticos De Uso Aeroespacial
    (Universidade Federal de São Paulo (UNIFESP), 2017-07-31) Motta, Jose Andre Da [UNIFESP]; Rezende, Mirabel Cerqueira [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    In a rocket motor with solid propulsion, the energy of the combustion reaction of chemical propellant at high pressure results in the generation of gases at temperatures in the order of 2700 °C. These extreme operating conditions lead to the search for materials with adequate mechanical characteristics around 2500 °C, good heat conductors and which are little affected by severe thermal shock. In compliance with these strict requirements, one of the materials used is the synthetic graphite. Considering that there is no available direct correlation in the literature among morphological, thermal and mechanical characteristics of synthetic graphites for space use, the present work has the objective of characterizing three types of synthetic graphites by means of mechanical tests (tensile and compression strength), physical (porosity, density and of thermal expansion coefficients and thermal diffusivity measurements) and morphological (optical microscopy) analyses. The results obtained in morphological analyses show that the studied samples are anisotropic carbon materials with very different optical textures. The analysis of the surface porosity shows values between ~2.3 and 30%, depending on the type of graphite and the radial or longitudinal position of withdrawal of the specimen in the graphite billet. The apparent density varied between 1.72 and 1.79 g/cm3. The density values obtained by helium pycnometry ranged from 2.05 to 2.14 g/cm3. These results indicate that the samples present different volumes of open pores. BET and BJH analyses confirm that the samples present a micropores distribution with different shapes. Measurements of coefficient of thermal expansion (3.58-4.64x10-6 oC-1, in the range 25-500 oC) and thermal diffusivity (~ 14-26x10-6 m2/s at 850 oC) show the influence of grain direction and also indicate that one of the samples of graphite was probably obtained by uniaxial pressing and not by extrusion. The correlation of tensile (~10 to 26 MPa) and compression (~30 to 76 MPa) strength results as a function of surface porosity shows that these properties are affected by the porosity level in a non-linear manner. The results show that the evaluation of the optical textures and the distribution of surface pores and also the tensile and compression strength are priority requirements in the selection of synthetic graphite of space use.