Metaphosphates glass-ceramic

Calcium metaphosphate is the most significant of the metaphosphate glass-ceramics with regard to its applications. The structure of calcium metaphosphate, which has been studied in detail by Rothammel et al. 

Metaphosphate glasses are of particular interest in the development of glass-ceramics and glass-ceramic fibers (Griffith 1995) by the controlled crystallization of phosphate base glasses. These glasses are composed of (PO ) tetrahedra chains. In chemical terms, these structural units must be called condensed phosphates. 

R. Majumdar, D. Lahiri, Redox equilibrium and spectral absorption of some colouring oxides in sodium metaphosphate glass. Trans. Ind. Ceram. Soc. XXXI(5) (1972)... 

The latter reaction can form long chain phosphates, where n is theoretically infinite. Being formed by heat treatments, these phosphates are excellent candidates for high-temperature ceramics and glasses. Because the subject of this volume is low-temperature ceramics, we will not discuss the condensed phosphates in detail, except in one case in Chapter 15, where cements for geothermal wells are discussed with sodium metaphosphate. However, bear in mind that CBPCs can be precursors to high temperature phosphates and glasses. For this reason, as we have seen in the literamre survey presented in Chapter 3, early interest in CBPCs was the formation of refractory shapes at room temperature, which were then fired to produce the final refractory components. 

Heating alkali metal or alkaline earth metal dihydrogen phosphates produces polymeric salts (cyclic metaphosphates and linear polyphosphates) and cross-linked polyphosphates (ultraphosphates), depending on temperature and the presence of other ingredients (11,12). This complex group of polymers includes materials with crystalline, glass-like, fibrous, or ceramic properties as well as some with thermoplastic and thermoset characteristics some are useful as binders for metals, ceramics, and dental restorations. Reviews are available on glasses (12,13), crystalline compounds (14), and polyphosphate fibers (15). 

For elucidation of the role of substituents in adhesion of ceramic materials, these monomers have, thus, been evaluated in terms of adhesion strength toward calcium metaphosphate ceramic (CMP) as a new type of castable ceramic. CMP, like tooth enamel, is a calcium phosphate material derived from the glass with a basic composition of 49Ca052P205. As shown by a cross-section microscopic photograph of CMP in Fig. 1, CMP consists of both crystalline and glass phases, and the crystalline rods are oriented toward the surface. The structure is quite similar to that of tooth enamel, in which the enamel crystalline rods also grow toward the tooth surface. 

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