Ceramics polyphase

Experimental studies of the polyphase ceramics noted above demonstrate that hollandite is one of the most durable titanate phases in aqueous solutions. Pham et al. (1994) carried out experimental work on synthetic Ba-hollandite doped with Cs and containing Al on the B-site for charge balance. These authors suggested that, following the initial release of Cs and Ba from reactive surface sites the first few monolayers of the structure rapidly dissolved due to the release of Al and consequent precipitation of Al-OH species, driving solution pH to lower values. However, the alteration process was mediated via the formation of a continuous Al- and Ti-rich surface layer. Further evidence for selective removal of Ba and enrichment of Al and Ti on the surface of hollandite tested at 250-300 °C was presented by Myhra et al. (19886). These conclusions were largely based on the different release rates of Ba (10 g/m2/d), Al (7 x 10 3 g/m2/d), and Ti (<8 x 10 4 g/ m2/d) after 14 days of dissolution testing, combined with XPS analyses of the altered surfaces. 

Microstresses arise inside the material as a result of the unequal thermal expansion coefficients of the glass and of the crystals. This phenomenon is characteristic of polyphase ceramics. In porcelains, the stresses arise in particular at the boundary between large quartz crystals and glass. Their formation is also contributed to by the modification inversion of quartz. The stresses sometimes bring about formation of microscopically visible cracks inside the quartz grains or around them. The structure of porcelain thus contains weak points which enhance the development of fracture on loading. 

The given material is characterized not only by chemical, but also by phase heterogeneity. The various phases have unequal reaction ability, i. e., during the synthesis of ceramics the preservation of the unreacted free phases of plutonium is rather probable. To increase the reaction ability of the precursor, it was offered to use an additive of surplus quantity of metal zirconium powder with a subsequent synthesis of polyphase ceramics on the basis of zircon/zirconium dioxide (Zr,Pu)Si04/(Zr,Pu)02, as well as other phases of non-radioactive elements -impurities. 

DR Clarke, F Adar. Raman microprobe spectroscopy of polyphase ceramics. In DR Rossington, RA Condrate, RL Synder, eds. Advances in Materials Characterization. Materials Science Research Volume 15. New York Plenum Press, 1983, pp. 199-214. 

FECAP (Ferric-Calcium-Phosphorous-Oxide polyphasic) ceramics,... 

In a polyphasic ceramic, the total rate of dissolution (R ot) is the sum total of the rates of individual phases. The rates of individual phases are also a function of fheir areas exposed to the corrosive medium. Thus, we have to consider their weighted surface areas. The weighfed surface area of fhe i-fh phase is given by ifs surface area (SJ divided by fhe fofal surface area of fhe ceramic body (S) under consideration. Therefore, is given by ... 

Polyphase ceramics are more common than single-phase ones. They contain mixtures of one or more phases and pores. The conductivity of such ceramics depends on ... 

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