High-purity ceramics

Reaction Formed Ceramics. A variety of specialty ceramics are produced by a combination of a chemical reaction and growth, or by simultaneous chemical reaction and consoHdation using relatively novel ceramic reaction forming and thermal consoHdation processes. Reaction forming processes provide the potential of producing unique ceramics and ceramic composites and high purity ceramics for specialty appHcations. 

Laser ion source in laser plasma by e impact Wa 1°4-nx1°5K ne 1 016-1 O20 crrr3 M+ high < 1 4 Pa double-focusing SFMS (Mattauch-Herzog) traces, high-purity ceramics... 

On the other hand, improvements in ceramic powder processing technology, the routine preparation of high-purity ceramics of nanometre scale, and the new techniques for the processing of these powders such as HIP, SPS, microwave furnace, etc., will be the driving forces for a very active study on nanoceramics in the near future, probably opening up new phenomena and new applications. 

At present, americium is separated and purified in Kg/yr quantities at the new plutonium facility at Los Alamos (Figure 1). The feed for the americium production comes from a line which produces high purity ceramic grade Pu02 for the Fast Flux Test Facility (FFTF) at Richland, Washington. The feed for this FFTF PuO is aged plutonium metal which contains sizable amounts of 24 Am... 

Solution preparation of ceramic powders is often thought to be a speciality technique for small lots of high purity ceramic materials. High quality powders can be (obtained, and solution technique are chosen to produce many of the powders used in the ceramic industry in large quantities. A major example is AI2O3, most of which is produced when the mineral bauxite is dissolved in an alkaline solution and hydrated oxides are precipitated from the solution ... 

Until recently, mostly ceramic manufacturers have commercially exploited isostatic pressing, but only to a limited extent and mainly in the United States. Isostatic pressing is particularly suitable for the production of high purity ceramics and long ceramic tubes for which there is an increasing demand. 

When firing dirty fuels, always specify a blanket lining of high purity ceramic. If a back-up blanket conteiining iron is used, it will fail very quickly from chemical attack. 

The reaction is facile at room temperature and in the absence of catalysts only for alkali metals (M = Li, Na, K) and barium [59]. To obtain the derivatives of alkaline earth metals with aliphatic alcohols, it is necessary to apply heat (reflux) and add a catalyst, usually elementary iodine, to clean the surface of the metal applied [110]. The same is true for aluminum alkoxides that can be produced in high yields by reaction of aluminum metal with dry alcohols on addition of l2(s) [2]. For drying the alcohols, one can apply aluminum alkoxides produced even from household aluminum foil, but it is necessary to remember that the latter is doped by some few percent of iron and is not a suitable material for the synthesis of aluminum alkoxides for preparation of high-purity ceramics. 

In the field of composite materials, inorganic-organic hybrid polymers offer great promise as precursors to ceramic matrix materials. In these applications, high purity ceramics are often not necessary and preceramic polymers allow the introduction of inorganic elements such as silicon and boron in quantities which can be directed by polymer structure and stoichiometry. 

Relatively smaller amounts of very high purity A1F. are used ia ultra low loss optical fiber—duotide glass compositions, the most common of which is ZBLAN containing tirconium, barium, lanthanum, aluminum, and sodium (see Fiber optics). High purity A1F. is also used ia the manufacture of aluminum siUcate fiber and ia ceramics for electrical resistors (see Ceramics AS electrical materials Refractory fibers). 

T. J. Carbone, "Production Processes, Properties, and Apphcations for Calcined in High-Purity Aluminas," in L. D. Hart, ed., Jilumina Chemicals Science and Technology Handbook, The American Ceramic Society, Columbus, Ohio, 1990. 

Precipitation of a hydrated titanium oxide by mixing aqueous solutions of titanium chloride with alkaU forms the precipitation seeds, which are used to initiate precipitation in the Mecklenburg (50) variant of the sulfate process for the production of pigmentary titanium dioxide. Hydrolysis of aqueous solutions of titanium chloride is also used for the preparation of high purity (>99.999%) titanium dioxide for electroceramic appHcations (see Ceramics). In addition, hydrated titanium dioxide is used as a pure starting material for the manufacture of other titanium compounds. 

Ceramic-grade beryllium oxide has also been manufactured by a process wherein organic chelating agents (qv) were added to the filtered beryllium sulfate solution. Beryllium hydroxide is then precipitated using ammonium hydroxide, filtered, and carefully calcined to obtain a high purity beryllium oxide powder. 

Table 2. Properties of High Purity Beryllium Oxide Ceramics...

Vapor-Phase Techniques. Vapor-phase powder synthesis teclmiques, including vapor condensation, vapor decomposition, and vapor—vapor, vapor—Hquid, and vapor—soHd reactions, employ reactive vapors or gases to produce high purity, ultrafine, reactive ceramic powders. Many nonoxide powders, eg, nitrides and carbides, for advanced ceramics are prepared by vapor-phase synthesis. 

---