No abstract

Fracture toughness enhancement of ceramic materials through multilayered ceramic composites has been developed since 1990. Toughening mechanisms are based mainly on delamination, deflection, bifurcation or crack arrest effect. Delamination and crack deflection occur by means of weak interfaces. Bifurcation (and deflection as well) and crack arrest effects are result of residual stresses arising from the thermal expansion coefficient mismatch or phase transformation on alternating layers. The main manufacturing methods of these composites are slip casting of two ceramic materials, and stacking and pressing of ceramic tapes obtained by tape casting or rolling technics, followed by suitable sintering process. This review aims to present general aspects of research performed around the theme so far. It is verified that occurs the enhancement of ceramic toughness and reliability with this technic, so it is possible to enlarge its range of application in engineering.

The main objective of this work was to study the crystallization kinetics of glass-ceramic obtained from steel waste. Two compositions were melted at about 1350 °C. The obtained frits were dried and re-melted. Each composition was then wet ground, dried, and chemically characterized (X-ray fluorescence and atomic absorption spectrometry), structurally (X-ray diffraction), and thermally (thermal differential analysis). Then the powders were compacted and the samples were dried and heat treated in a kiln between 690 and 890 °C. After, the crystallized bodies were ground and the crystalline phases were identified by X-ray diffraction. Results showed that the main formed crystalline phases were magnetite, hematite, Fe2.95Si0.05O4, and CaAl2Fe4O10. The activation energies obtained by the Kissinger method were between 348 and 423 kJ.mol-1, whereas the Avrami parameter was obtained between 0.76 and 1.1 indicating surface crystallization.

Coal extraction produces large amounts of wastewater containing coal powders, which could be used to produce coke. In this case, binder materials should be used to allow compression capacity to the mixture. This work aims to study the effect of binder addition in mixtures of coals containing different contents of coal powders to obtain coke. Compositions containing different amounts of coal powders were prepared by varying the nature and the contents of the binders to allow the pressing of powders. Study of the thermal behavior of these compositions was performed. The composition that showed the best results was then homogenized, pressed and heat treated. The final composition showed FSI about 4.5 and compressive strength of 5 MPa, demonstrating high potential for coke production from coal powder.

The coal extraction generates large amounts of coal waste. Powders of this waste can be pressed with the addition of binder in order to obtain ceramics, such as ceramic membranes. In this case, polymeric fibers can be used to increase permeability. This work aims to study the permeability of ceramic structures composed by coal waste and different amounts of polymeric fibers. The compositions were homogenized, pressed and thermally treated at 1050 °C. Samples were characterized in relation to porosity determination, permeability and microstructural features. The results showed that the permeability increased with the increase of the fiber content. However, the composition containing 0.5 vol% of polypropylene fibers showed the best results for using in aerosol filtration permeability.