CeraMat

The oxidation resistances of different kinds of SiC-based laminates are compared. The materials under investigation are produced by tape casting of green ceramic sheets, followed by stacking of the sheets in a multilayer structure and laminate consolidation by de-binding and sintering. Three kinds of specimens are tested: multilayer SiC with fully dense layers, multilayer SiC integrating porous layers and multilayer composites made by stacking SiC/Cf composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) are used for the manufacture of the composite sheets.

Tape casting combined with layer stacking, debinding and sintering proved to be a suitable technique for processing SiC-based multilayers to be used as thermal protection system for space vehicles. In this paper two methods have been evaluated in order to decrease the thermal conductivity through the thickness of the material: the insertion of layers containing a pore forming agent able to leave residual porosity; the deposition of an external insulating coating made of yttria-partially stabilized zirconia (YPSZ). Both techniques contribute to the reduction of thermal conductivity.

Co-continuous metal/ceramic composites were obtained by the Reactive Metal Penetration (RMP) method. With the aim of components cost reduction, commercial cordierite preforms and standard aluminium infiltrating alloys (1050, 2011 and 7075) were used in the process. Kinetics of the infiltration reaction, microstructure and mechanical properties of the composites were found to be influenced by both quantity and type of alloying elements.

Presently, one of the most interesting approaches to the generation of H2 is based on sulphur-based cycles, that however require structural components able to work in a corrosive environment at high temperature. Silicon carbide (SiC) is one of the most promising materials for this application, and to increase its limited toughness multilayered structures can be envisaged, since crack deviation and delamination increase energy adsorption during fracture.

In present work, SiC multilayer samples for thermal conductivity test in X (along tape casting direction), Y (perpendicular to tape casting direction and thickness direction) and Z (through thickness direction) directions were successively prepared by tape casting and pressureless sintering. Effect of oxidation treatment on the thermal diffusivity and conductivity was investigated. Elongated SiC grains were observed in three directions, especially in Y direction. The specific heat capacity of SiC multilayer increased with temperature, which could be well fitted.

In view of possible application of multilayer SiC as oxidation resistant and self-passivating component of re-usable thermal protection systems for space re-entry vehicles, this material was tested in a re-entry simulation chamber. A multilayer SiC laminate was processed by tape casting and pressure less sintering. Both the as-processed multilayer SiC and a similar passivated material, with a surface silica layer obtained by high temperature oxidation, were investigated. The microstructure and the mechanical features of these two materials were compared before and after the re-entry test.

Silicon carbide multilayer composites containing short carbon fibres (Csf/SiC) were prepared by tape casting and pressureless sintering. The C fibres were dispersed in solvents with dispersant (Triton X-100) firstly and then mixed with the SiC slurry to make green Csf/SiC tapes. Fibres were homogeneously distributed in the tape and tended to align fairly well along the tape casting direction. The addition of short C fibre hindered the shrinkage in the plane containing the fibres as well as the grain growth of SiC during sintering.

In this work, thermal degradation of commercial polymer mixtures was evaluated as a promising approach to the production of ceramic brake components. Currently, there is a wide interest for the production of cost effective ceramic pads, and carbon based materials are good candidates both in monolithic form and as porous networks to be reinfiltrated with a convenient polymer. The process parameters for obtaining porous glassy carbon, starting from mixtures of commercial polymers, have been evaluated in this work with the goal of producing samples with optimized mechanical properties.

In view of the possible application of SiC-based ceramic laminates as critical components of hydrogen generation plants based on sulfur-iodine or hybrid-sulfur thermochemical cycles, the effect of corrosion on this kind of ceramics has been investigated.

A processing method common to composite ceramics with very different ZrB2/SiC ratios was developed in order to exploit ZrB2–SiC laminates comprising alternate layers with different compositions for thermal protection systems of re-entry vehicles. Ceramic laminates were made using SiC, ZrB2 and composites with a SiC/ZrB2 ratio ranging from 100 vol.-%SiC to 100 vol.-%ZrB2. The preparation was performed by tape casting of a slurry, layer stacking, debinding and pressureless sintering.