Gd-Fe-C system

The ternary R-Fe Co, Ni)-C phase diagrams Phase diagrams of the Ce-Fe-C, Gd-Fe-C, Sm-Co C and Y-Ni-C systems have been reported. The Ce-Fe-C and Gd-Fe-C systems are, respectively, representative of the light and heavy lanthanide systems (Park et al. 1982, Stadelmaier and Park 1981), forming two and six ternary compounds, respectively. 

The Gd-Fe C system. In the iron gadolinium-carbon system, the liquidus projection and the 900°C isothermal section (fig. 21) were determined (Stadelmaier and Park 1981). Six ternary carbides were found in this system. Unlike the binary gadolinium carbides, they do not decompose readily in water. Two ternary carbides are metal-rich and the structures are derivatives of binary Fe-Gd structures. The crystal structures of the six ternary compounds are listed in table 16. 

Fig. 21. The isothermal section of the ternary Gd-Fe-C system at 900°C (Stadelmaier and Park 1981).

Only one compound forms in the Gd-Fe-Sn system. Its composition is GdFegSiig. Phase equilibria at 870 K and 670 K (up to 55 a/c and more than 55 a/c Sn, respectively) were ascertained by Skolozdra (1993). 

Bodak et al. (1978) investigated the phase equilibria in the system Gd-Fe-Si at 800 °C by means by X-ray powder and metallographic analysis of 250 alloys which were prepared by arc melting and subsequent annealing in evacuated silica tubes (800 °C, 720 h). 

The structure of the Y-B-C phase (Bauer and Nowotny 1971) consists of the B-B zigzag chains with C-branches and trigonal metal prisms, which is similar to that of the phases U-B-C (Toth et al. 1961) and MojBC (Jeitschko et al. 1963). Later work by Bauer and Debuigne (1972, 1975) also found phases with this type of structure in the R-B-C (R = Dy, Gd, Tb) systems. The Dy-B-C phase has lattice parameters a = 3.384 A, fe = 13.727 A and c = 3.647 A. The positions of atoms in the Djh-Cmmm space groups are four dysprosium atoms at 4i sites, y = 0.135 four boron atoms at 4j sites, y = 0.711 and four carbon atoms at 4j sites, y = 0.591. 

Markova et al. (1967) constructed a phase diagram for the dysprosium-yttrium system utilizing thermal analyses, X-ray diffraction, metallography, hardness and electrical resistance measurements. Their starting materials were distilled yttrium and dysprosium of 99.6 to 99.7(wt )% purity. Both metals contained gaseous impurities as well as the metals Ca, Fe, Cu, Y, Gd, Dy and Ta. Alloys were prepared at approximately 10 at% intervals, arc-melted under purified helium and annealed at 850°C for 70 hr. The structure of all specimens was single phase with the hep lattice. A continuous series of solid solutions between isomorphic modifications was observed. 

The final cluster obtained from stoichiometric control resulted from variation in the reaction conditions used to form cluster 15, and has a general formula of [Mn 4Ln 4(bis-C[4])2(p3-OH)4(p-C03)2(dmf)8(H20)4] (17, Ln = Gd, Tb or Dy, Fig. 25.5h) [41]. The metallic skeleton is a distorted square of Ln ions that is doubly-capped on distal edges by [Mn 2(bis-C[4])]" moieties (Fig. 25.6h), a structiwal feature observed in the Fe 5Ln 4 cluster described above (14, Fig. 25.5e). Each half of the assembly can be considered a distorted Mn 2Ln 2 butterfly-Uke cluster, with these being connected by p-carbonates that arise from atmospheric CO2 fixation, a relatively commMi phenomenon in Ln coordinatimi cluster chemistiy and one that we have also seen with C[4]-supported systems. 

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