Oxide ceramics applications

Beryllium is used in satellite structures in the form of both sheet and extruded tubing and is a very important material for all types of space optics. Beryllium oxide ceramic applications take advantage of high room temperature thermal conductivity, very low electrical conductivity, and high transparency to microwaves in microelectronic substrate applications. 

It is used in gyroscopes, computer parts, and instruments where lightness, stiffness, and dimensional stability are required. The oxide has a very high melting point and is also used in nuclear work and ceramic applications. 

Chemical analysis of niobium oxide indicated that the purity of the final product depends strongly on the purity of the initial solution. Account should be taken of about 0.02-0.03% wt. cationic impurities, introduced due to interactions with metal parts of the equipment. The main added impurities are Fe, Ni, Cr, which originate mostly from the stainless steel filter. The purity of the final product can be significantly increased by using a filter made of niobium or other appropriate material. Nevertheless, the material obtained using a stainless steel filter is sufficient for use in ceramic applications or as an initial material for carbide manufacture. 

A sodium-sulfur cell is one of the more startling batteries (Fig. 12.23). It has liquid reactants (sodium and sulfur) and a solid electrolyte (a porous aluminum oxide ceramic) it must operate at a temperature of about 320°C and it is highly dangerous in case of breakage. Because sodium has a low density, these cells have a very high specific energy. Their most common application is to power electric... 

Non-oxide ceramics such as silicon carbide (SiC), silicon nitride (SijN ), and boron nitride (BN) offer a wide variety of unique physical properties such as high hardness and high structural stability under environmental extremes, as well as varied electronic and optical properties. These advantageous properties provide the driving force for intense research efforts directed toward developing new practical applications for these materials. These efforts occur despite the considerable expense often associated with their initial preparation and subsequent transformation into finished products. 

Beryllium oxide, BeO, is used in place of Si02 or A1203 in performance-sensitive ceramic applications. It is distinguished by having the highest melting point (2507°C) combined with excellent thermal conductivity and poor electrical conductivity. 

Lodestone, also known as magnetite, was one of the first known magnetic materials. Its ability to attract iron was known as far back as 600 B.C., and it was used in compasses beginning in the thirteenth century. It was studies by I. L. Snoeck at the Philips Laboratories in Holland in the 1940s, however, that led to the first application of oxide ceramics with strong magnetic properties. 

Beryllium sulfate, [CAS 13510-49-1], BeSO 4H2O, is an important salt of beryllium used as an intermediate of high purity for calcination to beryllium oxide powder for ceramic applications. A saturated aqueous solution of beryllium sulfate contains 30.5% BeSC>4 by weight at 303C and 65.2% at 111"C. 

We have studied the proton and oxide anion transport, conduction, and permeation in metals, dense oxide ceramics and, also briefly, in polymers (see also Chapters 2,5, and 8). This section describes the application of proton and oxide permeation in these materials in hydrogen and oxygen separations. 

Gaseous corrosion in combustion applications involving condensed phased deposits is important and sodium sulfate and vanadate deposits are most corrosive. These deposits are particularly injurious to non-oxide ceramic materials. The data on corrosion resistance of ceramic materials to hot gaseous environments are presented in Table 4.94. It is clear from the data that non-oxide ceramics show lesser corrosion resistance than oxide-based ceramics. 

Solid—solid reactions proceed by two different mechanisms. One mechanism is solid interdiflusion, where the two solid state reactants interdiffuse at the points of powder particle contact. This mechanism is applicable for the first six reactions given earlier and many others that form mixed oxide ceramic powders. The second mechanism is not truly a solid-solid reaction. It entails the vaporization of one of the reactants (by one of several mechanisms) and then reaction of this vapor with the other solid. 

There are presently four families of high-temperature superconductors under investigation for practical magnet applications. Table 11-25 shows that all HTS are copper oxide ceramics even though the oxygen content may vary. However, this variation generally has little effect on the physical properties of importance to superconductivity. 

Non-oxide ceramic nanomaterials, such as carbides, nitrides, borides, phosphides and silicides, have received considerable attention due to their potential applications in electronics, optics, catalysis, and magnetic storage. In contrast with the traditional processes, such as solid state reactions, CVD, MOCVD and PVD, which involve using high temperatures, toxic organometallic precursors, or complicated reactions and posttreatments, solvothermal method is a low temperature route to these materials with controlled shapes and sizes. 

Non-oxide ceramic materials such as silicon carbide has been used commercially as a membrane support material and studied as a potential membrane material. Silicon nitride has also the potential of being a ceramic membrane material. In fact, both materials have been used in other high-temperature structural ceramic applications. Oxidation resistance of these non-oxide ceramics as membrane materials for membrane reactor applications is obviously very important. The oxidation rate is related to the reactive surface area thus oxidation of porous non-oxide ceramics depends on their open porosity. The generally accepted oxidation mechanism of porous silicon nitride materials consists of two... 

Oxides. Determinations of the enthalpy and derived functions by the method of mixtures have also been made for purposes of metallurgical and ceramic applications on most of the lanthanide (III) oxides usually to temperatures of about 2000°K. 100, 152,153, 154). The results of these determinations have been summarized in Table VIII. 

---