Preparation And Microstructure And Properties Of Cu₂O-Cu Cermets

A new Cu₂O-Cu cermet material with different Cu shape and size was prepared as candidate inert anode material for Al production. The microstructure of the cermet and the products after corrosion tests were observed and analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM). Mechanical properties, thermal expansion coefficient, thermal conductivity and electrical conductivity of the cermets were tested. The corrosion rate of the cermets in electrolyte (Na3AlF6) was measured as well. The relationship between the properties of the cermet and the Cu content, shape and size was investigated, and the mechanisms of these relationships were demonstrated.The results show that the Cu₂O-Cu cermet with branched Cu (ZR) and spherical Cu (QR) could be obtained with processing parameter controlling, and the real Cu content was well agree with the calculated Cu content. The Cu structure in Cu₂O-Cu cermet prepared with branched Cu is worm like, and the one prepared with spherical Cu (QR200, QR300, QR400) is basically spherical shape. In all Cu₂O-Cu cermet, the crystals of the Cu₂O matrix are isometric, and the size of them is affected by the Cu content and size.The elastic modulus, strength and toughness of the Cu₂O-Cu cermet increase with increasing Cu content. With same Cu content, the elastic modulus and toughness increase with increasing shape factor and decreasing size of the Cu phase. The thermal shock resistance property of the Cu₂O-Cu cermet has a fluctuation phenomenon with increasing of thermal shock temperature difference. The thermal shock resistance property increases with increasing of Cu content. The remaining flexural strength after thermal shock increases with increasing aspect ratio and decreasing size of the Cu phase.The results of the electrical conductivity tests show the typical percolation phenomenon, and the regularity of it can be described by using GEM (General Effective Method) equation. After the percolation, the electrical conductivity was about 10⁴¹0⁶Ω^-1·m^-1. The percolation threshold is largely influenced by the shape factor of the conductors. The Cu₂O-Cu cermet prepared with branched Cu has a lower percolation threshold than the one prepared with spherical Cu. The conductive mechanism of the Cu₂O-Cu cermet is different with different Cu content.The thermal expansion coefficient of the Cu₂O-Cu cermet increases with increasing temperature. The variation process is largely influenced by the internal thermal stress state and release mechanisms. Under the same temperature, the thermal expansion coefficient increases with increasing Cu content and aspect ratio of Cu phase. The size effect is affected by the Cu content.The thermal conductivity of the Cu₂O-Cu cermet is largely influenced by Cu content and Cu shape. The thermal conductivity increases with increasing of Cu content and aspect ratio of Cu phase. The size effect is affected by the Cu content. The size effect with lower Cu content is smaller than the one with higher Cu content.During the corrosion tests, there is a CuAlO₂ layer formed and protected the Cu₂O-Cu cermet. This protective layer decreases the corrosion rate. The corrosion rate increases with increasing content, aspect ratio, and decreasing size of the Cu phase. The corrosion mechanism of Cu₂O-Cu cermet in the electrolyte is mainly resulted from the dissolve of the cermet, the chemical reaction of Cu₂O and Al₂O₃, and the physical migration of Cu.