Compósitos cerâmicos porosos de alumina - zircônia para aplicação em sistemas de controle térmico para satélites: obtenção e caracterização / Alumina-zirconia porous ceramic composites for application in satellite thermal control systems: obtaining and characterization

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

To control the temperature of satellites are used various thermal control heat systems. The Loop Heat pipe (LHP) are being developed at the DEM (Space Mechanic and Control Division) of the INPE (National Institute for Space Research) an apparatus for passive heat control of the satellites components. The main components of the LHP system are: capillary evaporator, liquid transport condenser lines and heat compensation chamber. The capillar evaporator requires a inteconected pores to be placed in its interior where the capillary forces used to move the working fluid which is contained in the pipe are generated. Heat pipe is transferred from a high temperature region to the capillary evaporator and dissipated in the cold environment of space. This procedure is carry out in a completely passive way without the need of any active control in this operation following the principles of evaporation and condensation. This work proposes the study of porous ceramics. The requirements for the use of these ceramics are: i) to have an interconnected porous structure; ii) to be chemically inert to the working fluids which are more appropriate for use in space; iii) to keep its structure integrity during assembly and take off; iv) to have a low density and low thermal conductivity but a high surface area; and v) to allow the production of parts with controlled surface groovings. Metal oxide ceramics, specially alumina and zirconia present potential for this application. To meet the requirements alumina-zirconia composites sub-microstructured and micro porous were developed and characterized at LAS (Associated Laboratory of Sensors and Materials) at INPE. In this work two different techniques were used to obtain the porous ceramic composites: i) burning of the organic particles and ii) foam incorporation. The first method (burning of organic particles) was used to process the Al2O3 e ZrO2 (3Y-TZP) composites, with the use of carboximethylcelulose (CMC) as pore generating agent. The samples were prepared by uniaxial pressing (65 MPa) and later sintered at 1400 and 1500 oC. The other method used was the foam incorporated to obtain porous ceramics in which an independently produced aquous foam was added to Al2O3 e ZrO2 (3Y-TZP) powder slurry. The Al2O3-ZrO2 samples were sintered at 1400 and 1500 oC. The microstuctures and crystalline phases of the initial powder and ceramic compounds were characterized by DRX (X-Ray diffraction) and by SEM (scanning electronic microscopy). The DTP curve (distribution of inter-connected pore size) in these samples was obtained by nitrogen and mercury porosimetry technique. The mechanical properties were obtained by the of diametral compression test. The results showed that the ceramics obtained by methods aqueous foam incorporations presented the best results since it promotes the adequate microstructural homogeneity, interconnected pores of 5 to 20 µm diameter and higher porous amount. The thermal conductivity data as a temperature function were obtained for the alumina-zirconia ceramic composites in an apparatus construted at DEM/INPE laboratory. These data showed low thermal conductivity values for the alumina-zirconia ceramic composite obtained from foam incorporation method.

ASSUNTO(S)

loop heat pipe zircônia tubos de calor circuitados evaporador alumina zirconia cerâmica porosa porous ceramic alumina evaporator

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