Metal-oxide ceramic materials

In the following periodic table, the underlined elements are those of which mixed metal-oxide ceramic materials have been prepared," whilst the encircled ones indicate the elements whose heterometallic alkoxide chemistry has been investigated ... 

In spite of considerable initial scepticism, the synthesis of an increasing number of well-characterized heterometallic alkoxides is now well established and attempts are being directed towards the synthesis of single-source precursors for preparation of mixed metal-oxide ceramic materials by the sol-gel or MOCVD processes. " " Before proceeding to a brief account of some novel types of heterometal glycolate and aminoalkoxide derivatives, it is appropriate to mention four review articles" summarizing the state of knowledge about the conventional heterometallic alkoxide systems at the end of the twentieth century. 

The chemical properties of heterometallic alkoxides are in general similar to their homometal counterparts (i) hydrolysis, (ii) alcoholysis, (iii) trans-esterification reactions, (iv) reactivity with carboxylic acids and enolic forms of chelating ligands such as /3-diketones/j6-ketoesters. The hydrolytic reactions are now widely employed for the preparation of homogeneous mixed metal-oxide ceramic materials and the rest have found wide applications for the synthesis of a variety of novel metallo-organic derivatives (sometimes unique), which are not often available through any other synthetic route. ... 

Electroceramic a group of metal oxide (ceramic) materials that are of interest due to their electrical properties, such as computer memories, high dielectric materials, and capacitors. 

Crucibles must be suitable for the required experimental conditions with respect to their material, capacity and shape. As in the techniques of the chemical laboratory, crucible materials are selected to avoid the possibility of reaction between crucible and sample material. The main materials used are the precious metals, oxide ceramics, quartz and graphite. The size of the crucible is determined by the volume to be weighed. 

The loss of the catalytically active surface of Raney nickel due to recrystallization is a continuously progressing process that can be retarded to some extent in Raney-nickel anodes by dispersing oxide ceramic materials like Zr02 and Ti03 in the nickel matrix. More serious is anodic oxidation for some metals additionally accompanied by dissolution of the catalyst to which even platinum is subject but which is an even more serious hazard for the less noble catalysts as silver and Raney nickel. 

In the following sections some examples are given of the ways in which these principles have been utilized. The first example is the use of these techniques for the low temperature preparation of oxide ceramics such as silica. This process can also be used to produce alumina, titanium oxide, or other metal oxides. The second example describes the conversion of organic polymers to carbon fiber, a process that was probably the inspiration for the later development of routes to a range of non-oxide ceramics. Following this are brief reviews of processes that lead to the formation of silicon carbide, silicon nitride, boron nitride, and aluminum nitride, plus an introduction to the synthesis of other ceramics such as phosphorus nitride, nitrogen-phosphorus-boron materials, and an example of a transition metal-containing ceramic material. 

The main purpose of synthesizing metal derivatives of special ligands (e.g., fluoro-, alkoxy-, amino-, sterically demanding-, and during the last 10-15 years, alcohols) was to enhance solubility (in organic solvents), volatility, and to reduce the oligomeric nature of the resulting product. These properties make them suitable precursors for oxide-ceramic materials by MOCVD/sol-gel processes (6, 23, 24, 27, 31, 38, 39, 72). 

The inadvertent isolation of a large number and variety of oxo-alkoxide derivatives (42) during the last decade has added a fascinating dimension to metal alkoxide chemistry as a whole. This dimension will direct it into a new phase of unprecedented novelty in the chemistry of these compounds and reveal their possible role(s) between the metal alkoxides and oxide-ceramic materials (243). 

The synthesis of nanophase ceramics is one of these concepts, it allows micro-porous ceramic materials with ceramic grains in the nanometer range to be obtained. Research in the field of nanophase materials is very active. A number of results on the control of microstructure and temperature stability of metal oxide ceramics can be applied to membrane preparation. Works carried out on non-oxide ceramics such as silicon carbide, silicon oxinitride or aluminum nitride should be regarded in order to extend the domain of available membrane materials. 

The term nanoparticles usually refers to particles with a size up to 100 nm [1]. Nanoparticles exhibit completely new or improved properties based on specific characteristics such as size, distribution, and morphology if compared with larger particles of their bulk material. Nanoparticles can be made of a wide range of materials, the most common being metal oxide ceramics, metals, silicates, and nonoxide ceramics. Even though other materials (e.g., polymer nanoparticles) exist, the former count for those used in most current applications [1]. 

Fig. 8.3 Perovskite crystal structure of oxide ceramic materials used to fabricate composite membranes. A very large fraction of the metals in the periodic table can be substituted into the A and B lattice sites. A-sites contain larger cations such as alkaline earth and rare earths, including Ca, Sr and La, whereas the B-sites contain smaller transition metal cations such as H, Nb, V, Fe, Cr, Cu and Co. A near infinite variety of materials can be synthesized...

The interconnect material s function is to connect the single cells to provide higher output. They are in contact with both the anode and the cathode. Therefore, they must be stable with both electrode materials and in oxidizing and reducing environments. To reduce the ohmic losses and increase efficiency, the interconnect material must also maintain a low electrical resistance. Basically, two materials are used as interconnect materials metallic and ceramic materials, in which chromium are present, such as CoCr204, YCrOj, and LaCrOj. Glass composite interconnects have also been considered. 

Lukasz J, Jozef U, Slawonir S, Jerzykiewiez BL, Leszek K, Piotr S. Synthesis and characterization of mixed-metal aryloxo-organometaUic precursors for oxide-ceramic materials. J Chem Mater 2008 20 4231-9. 

J.L. Utko, S. Szafert, L.B. Jerzykiewicz, L. Kepinski, and P. Sobota, Synthesis and characterization of mixed-metal aryloxo-organometallic precursor for oxide-ceramic materials, Chem. Mater., vol. 20, no. 13, pp. 4231-4239,2008. 

Honeycomb monoliths are obtained by extruding a paste made by catalytic material, whereas plate catalysts are made by depositing the catalytic material onto a stainless steel net or a perforated metal plate. Composite ceramic monolith catalysts, consisting of a monolith matrix made of cordierite coated with metal oxide SCR material, are also offered. However, they may suffer adhesion problems in the presence of dust and their use may be preferably limited to clean environment. Coated metal monoliths are constructed of thin metal foil and are characterized by large cell densities. In view of this, they are used exclusively in dust-free applications. 

Sensor surfaces can consist of most materials. Metals, oxide ceramics and carbon in its different modifications including diamond, silicates and organic... 

Deteriorative mechanisms are different for the three material types. In metals, there is actual material loss either by dissolution (corrosion) or by the formation of nonmetallic scale or film (oxidation). Ceramic materials are relatively resistant to deterioration, which usually occurs at elevated temperatures or in rather extreme environments the process is frequently also called corrosion. For polymers, mechanisms and consequences differ from those for metals and ceramics, and the term degradation is most frequently used. Polymers may dissolve when exposed to a liquid solvent, or they may absorb the solvent and swell also, electromagnetic radiation (primarily ultraviolet) and heat may cause alterations in their molecular structures. 

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