Oxide substrates spinel

It is also vital that a constant supply of aluminum is guaranteed through the diffusion from the substrate in order to ensure the surface is totally covered with alumina. Otherwise Cr203 and Fe-Cr spinel would be obtained mainly. The addition of the already mentioned RE in contents of less than 0.1% increase the resistance to oxidation of the Fe-Cr-Al alloys. Moreover the alumina grains are reduced in size. 

Chemical vapor deposition (CVD) was applied to produce homogeneous thin films of pure and doped spinel cobalt oxide with similar morphology on the surface of planar and monolithic supports. The planar substrates were used to investigate the thermal stability and the redox properties of the spinel using temperature-programmed methods monitored by emission-FTIR spectroscopy, while the monolithic substrates were used to test the catalytic performance of the deposited films toward the deep oxidation of methane and to evaluate its durability. The high performance of cobalt oxide to oxidize methane in diluted streams was demonstrated at 500 °C. Furthermore, controlled doping of cobalt oxide layers with suitable cations was demonstrated for nickel as an example, which resulted in substantial increase of electric conductivity. 

Despite the linear relation between the composition of the feedstock and that of the deposited flhns, it can be noted that the concentration of nickel doping in the deposited films was lower than that of the liquid feedstock. This effect might be justified either by a selective depletion of the nickel precursor during the transport or by its lower sticking coefficient on the surface of the substrate at the deposition temperature. The IR analyses of the deposited NixCo3.x04 (0 < x < 1) films, not shown, revealed their spinel structure, and a shift of the characteristic vibration bands indicated the incorporation of nickel into the spinel lattice. Further evidence about the controlled incorporation of nickel into the lattice of cobalt oxide can be drawn from conductivity measurements. Fig. 5b shows a substantial increase in conductivity as a function of the concentration of nickel incorporated into the film. The formation of a secondary phase should be expressed by a discontinuity, which is clearly absent in the investigated range of conditions. 

Reactive bonding. A small amount (0.1-1%) of CuO or CdO is added to the paste formulation. During firing the oxides react with the alumina substrate to form a copper or cadmium spinel, CUAI2O4 or CdAl204, respectively. 

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