CaO, P2O5 systems

On the basis of the compositions shown in Table 2-14, however, it must be noted that although the Si02—AI2O3—CaO glass system represents the base system, the amounts of the different additives such as P2O5, Fc203, or MgO are considerable. The large number of main components clearly shows... 

Figure 11 Experimentally determined phase relationships for pyrolite H—5 wt.% H2O hy Khodyrev et al. (1990). Their bulk composition (in wt.%) was Si02 45.15, TiOz 0.64, AI2O3 3.7, FeO 7.8, MnO 0.13, MgO 37.88, CaO 3.25, Na20 0.66, K2O 0.14, P2O5 0.05, Cr203 0.4, NiO 0.2. For comparison, this composition is projected into the Mg0-Si02-H20 system in Figure 6. For comparison, the breakdown reaction for clinohumite with Xp . = 0.19, Xpi = 0.46, and Xp = 0 (Figure 9) from Weiss (1997) is shown by the dashed line labeled W. The solidus and clinohumite-out curves for serpentinite from Stalder and Ulmer (2001) (Figure 10) are shown for comparison as well.

Less intensive opaline opacity can be brought about by the introduction of phosphates (3 — 8% P2O5 in glass) in the presence of CaO an emulsion of calcium phosphate is precipitated in the glass and then partially crystallized. The systems P2O5 —RO (where RO = BaO, SrO, CaO, MgO, ZnO, CdO, PbO) are glass-forming up to 56—65 mole % RO. The opacity of phosphate opals is promoted by the addition of fluorides. 

There are few experimental data for the density of phosphate slags but xV(P205) values were derived from data for the systems CaO + FeO + P2O5 and Na20 + P205 A constant value of V = 65.7 cm3 mol was obtained from the selected linear relationship. 

Steineke, R.A. (1991) Development of chemically bonded ceramics in the CaO-Si02-P2O5-H2O system. Cement and Concrete Research 21,66-72. 

The above glass-ceramic system was selected with the intention of producing biomaterials to replace bone in human medicine. It was particularly important to achieve a high content of apatite in the glass-ceramic as well as a Ca reservoir to assure the subsequent ion release of the implant by adding CaO and P2O5 to the glass-ceramic. 

In Figure 5.4 the corners of this diagram are chosen such that P2O5 is on top while mixtures Na20 and CaO are represented by the bottom line. The first line above the base is all of the possible anhydrous sodium-calcium-orthophosphates. Above this line is the smallest sodium-calcium-po/yphosphates, sodium-calcium-pyrophosphates. There are known crystalline tri-, penta-, and hexaphosphates in the sodium-calcium-polyphosphate system. The author could find no reliable evidence that a tetraphosphate of sodium, calcium, or mixtures of these two had been crystallized. A sodium tetraphosphate has been claimed from time to time, but has never been reliably demonstrated. 

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