Ceramic oxide layers

Gorges et al. [155] introduced anodic spark deposition (ASD), a modification of anodic oxidation, for the formation of polycrystalline ceramic oxide layers on passivating metals (Figure 2.99). The method is therefore limited to Ti, Al and Zr... 

A major advance was the Ucarsep UF membrane patented by Union Carbide in 1973 and made from a nonsintered ceramic oxide layer (usually Zr02 ) deposited on to a carbon porous tubular support (6 mm inner diameter). The worldwide license of these membranes was sold to SPEC, who added die sintering of the Zr02 layer to obtain a permanent attachment to the support. With die Carbosep trademark, these membranes were marketed by SPEC from 1980, and later, die company was sold to Rhone-Poulenc, which created a subsidiary. Tech Sep, still having die Zr02 UF membrane as its main inorganic product... 

Metal to ceramic (oxide) adhesion is very important to the microelectronics industry. An electron transfer model by Burlitch and co-workers [75] shows the importance of electron donating capability in enhancing adhesion. Their calculations are able to explain the enhancement in adhesion when a NiPt layer is added to a Pt-NiO interface. 

Another approach is to use the LB film as a template to limit the size of growing colloids such as the Q-state semiconductors that have applications in nonlinear optical devices. Furlong and co-workers have successfully synthesized CdSe [186] and CdS [187] nanoparticles (<5 nm in radius) in Cd arachidate LB films. Finally, as a low-temperature ceramic process, LB films can be converted to oxide layers by UV and ozone treatment examples are polydimethylsiloxane films to make SiO [188] and Cd arachidate to make CdOjt [189]. 

Ceramic oxide superconductors have distinct atomic layers. The Cu-containing superconductors contain planes of copper and oxygen atoms, as the molecular view shows. These planes alternate with layers containing oxygen and the other metals that make up the superconductor. Superconductivity takes place in the Cu—O planes. 

For Eurodif and for Pierrelatte, the supports were made by private industrial companies, the final separating layer by SPEC and the CEA developed the process and had the overall technical responsibility. A handful of companies were competing to manufacture the membrane support structure. Finally, two companies proposing ceramic oxide based supports, Ceraver (the new name of CGEC) and Euroceral (a 50/50 joint venture between Norton and Desmarquest) each won 50% of the market. This happened in 1975. Within a matter of 6 years, each company had to deliver more than 2,000,000 m of supports which SPEC would convert into more than 4,000,000 m of membranes (Charpin and Rigny 1990). Special plants were built at a very rapid pace. These were close to Tarbes for Ceraver, close to Montpellier for Euroceral and close to the Eurodif site for SPEC. 

This concept later evolved into the Ucarsep membrane made of a layer of nonsintered ceramic oxide (including Zr02) deposited on a porous carbon or ceramic support, which was patented by Union Carbide in 1973 (Trulson and Litz 1973). Apparently, the prospects for a significant industrial development of these membranes were at the time rather limited. In 1978, Union Carbide sold to SPEC the worldwide licence for these membranes, except for a number of applications in the textile industry in the U.S. At that time, SPEC recognized the potential of inorganic membranes, but declassification of the inorganic membrane technology it had itself developed for uranium enrichment was not possible. 

The exceptional properties of the alloy are due in no small way to the yttrium component which together with the aluminium forms a stable and firmly bound oxide layer that exhibits excellent resistance to exhaust gas emissions at high temperatures over prolonged periods.( ) At the same time, it provides an ideal surface to receive another coating of metal or metal oxide which, in the context of catalyst applications, is most essential. At the present time most catalytic convertors utilise ceramic substrates which are prone to damage by both mechanical and thermal shock. 

If local stresses exceed the forces of cohesion between atoms or lattice molecules, the crystal cracks. Micro- and macrocracks have a pronounced influence on the course of chemical reactions. We mention three different examples of technical importance for illustration. 1) The spallation of metal oxide layers during the high temperature corrosion of metals, 2) hydrogen embrittlement of steel, and 3) transformation hardening of ceramic materials based on energy consuming phase transformations in the dilated zone of an advancing crack tip. 

Fig. 34a-d. Oxide layers on Si3N4 ceramics oxidised at 1500 °C. a HIP-SN (no additives 2500 h), b SSN (Y2O3/AI2O3 additives 1000 h), c SSN (Y203 additive 5000 h), d Si3N4/MoSi2 composite (Y203 additive 5000 h)... 

Figure 22 Bipolar cell for aluminum electrolysis due to Alusuisse [236], The vertical bipolar electrodes consist of 3, an anode layer, a ceramic oxide 4, an intermediate conducting layer 5, a cathode layer, e.g., TiB2. 

Although some of the concepts established for metal/ oxide systems are also valid for non-oxide ceramics, there are other concepts which are specific to these kinds of ceramics, owing to their predominantly covalent (SiC, BN, AIN) or metallic (TiC, TiN, WC) character. These materials seldom can be obtained as the high-purity monocrystalline specimens desirable for fundamental wetting studies. Usually, they are sintered materials with impurity contents higher than 0.1% and they often contain open porosity. Further difficulties arise from the high oxidization tendency of many of them, the presence of an oxide layer dramatically changing their wettability by liquid metals. 

Mobius H and Roland B, 1968, Method of Producing Fuel Cells with Solid Electrolytes and Ceramic Oxide Electrode Layers. US Patent 3,377,203. 

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