Artículos SCI

Self-joining of St. Gobain Si₃N₄ (NT-154) using a ductile Cu–Al–Si–Ti active braze (Cu-ABA) was demonstrated. A reaction zone (∼2.5–3.5 μm thick) developed at the interface after 30 min brazing at 1317 K. The interface was enriched in Ti and Si. The room temperature compressive shear strengths of Si₃N₄/Si₃N₄ and Inconel/Inconel joints (the latter created to access baseline data for use with the proposed Si₃N₄/Inconel joints) were 140 ± 49 MPa and 207 ± 12 MPa, respectively. High-temperature shear tests were performed at 1023 K and 1073 K, and the strength of the Si₃N₄/Si₃N₄ and Inconel/Inconel joints were determined. The joints were metallurgically well-bonded for temperatures above 2/3 of the braze solidus. Scanning and transmission electron microscopy studies revealed a fine grain microstructure in the reaction layer, and large grains in the inner part of the joint with interfaces being crack-free. The observed formation of Ti₅Si₃ and AlN at the joint interface during brazing is discussed.

Biomorphic SiC (bioSiC) is a low cost SiC/Si composite obtained by melt infiltration of carbon preforms obtained from the pyrolysis of cellulose precursors. The porosity and pore size distribution of bioSiC can be tailored for specific applications by adequate selection of the wood precursor. Natural and artificial industrial woods were explored as possible bioSiC precursors. Silicon was removed by chemical etching. Relevant microstructural parameters such as pore size distribution, total porosity, and permeability were characterized. Since the filtration process involves large pressure gradients along the material at high temperatures, mechanical properties of porous bioSiC from the different precursors were evaluated at room temperature and 800 °C. The feasibility of porous bioSiC as a filtration material for high temperature gasification processes is discussed in terms of these properties. MDF-bioSiC is shown to be a promising material for such applications because of its good mechanical properties, interconnected porosity, pore sizes, and permeability.