Ternary carbides

A survey of preparation methods of binary and ternary carbides of alkali and alkaline earth metals has been reported by Ruschewitz (2003) where a variety of techniques has been presented and discussed. 

Here again certain trends were observed, and the most influential factor was the crystal structure which the superconducting material adopted. The most fruitful system was the NaCl-type structure (also referred to as the B1 structure by metallurgists). Many of the important superconductors in this ceramic class are based on this common structure, or one derived from it. Other crystal structures of importance for these ceramic materials include the Pu2C3 and MoB2 (or ThSi2) prototypes. A plot of transition temperature versus the number of valence electrons for binary and ternary carbides shows a broad maximum at 5 electrons per atom, with a Tc maximum at 13 K. 

Other methides are the cubic ternary carbides of the type A3MC31 where A is mostly a rare earth or transition element (e.g., Sc, Y, La—Na, Gd—Lu) and M is a metallic or semimetallic main group element (e.g., Al, Ge, In, Tl, Sn, Pb). These perovskite carbides are typically hydrolyzed by dilute HC1 to give —84-97 (wt-%) methane and 3-16% saturated and unsaturated higher hydrocarbons. 

Normally, dislocation-based plastic deformation is irreversible, that is, it is not possible to return the material to its original microstructural state. Remarkably, fully reversible dislocation-based compressive deformation was recently observed at room temperature in the layered ternary carbide Ti3SiC2 (Barsoum and El-Raghy, 1996). This compound has a hexagonal stmcture with a large cja ratio and it is believed that the dominant deformation mechanism involves dislocation movement in the basal plane. 

There are several families of ternary carbide phases with transition metals and main gronp elements. Several of them are of structnral interest snch as the H-phases, the filled /3-manganese type carbides and the /c-carbides. The rj-phases are formed in carbon-deficient hardmetals and canse embrittlement. 

Mi) Actinide-Metal Group. Alloys of U-Pu-C and U-Zr-C can be used as a nuclear fuel. Both systems are characterized by extensive mutual solubility and no ternary compounds. However, U forms ternary carbides with several transition metals to give the compound UMCj, where M = Mo, W, Re, Rh, Ir, Mn, Cr, Ni, Co, Fe or Tc. 

There are few methods designed for the formation of multicomponent carbides. The methods adopted to produce binary or ternary carbides are applicable. 

The reaction of ternary carbides with nitrogen has attracted interest because of a novel type of phase separation occurring in double pseudobinary solid solutions of transition-metal multicomponent carbonitrides. Rudy has investigated the system Ti-Mo-C-N and has found that the homogeneous solid solution (Ti, Mo) (C, N), formed at high temperatures, disproportionates into two phases, both of which are isostructural and have nearly the same lattice parameters. One of the two phases is a Ti carbonitride rich in N and poor in Mo, the other is a Ti-Mo carbide rich in Mo hut poor in N. This type of disproportionating is bound to occur in most of the double-pseudobinary carbonitride systems... 

Another material of this kind is tungsten disulphide, originally developed by NASA for aerospace applications, now also applicable to specialty industries [58]. Ti3SiC2 is a thermodynamically stable, nano-layered, ternary carbide and part of a family of over 50 ternary carbides and nitrides, the MAX phases [62]. These phases are a new class of solids possessing unique combinations of properties they are readily machinable, relatively soft for ceramics, but elastically stiff, and electrically and thermally conductive. They combine the good properties of both metals and ceramics that could lead to this technology contributing to future lubricant developments. 

Dr. Barsoum is currently a Distinguished Professor at Drexel University. He and his research group were the first to fabricate and fully characterize an important new class of machinable ternary carbides and nitrides, the M v+iAXv (so-called MAX) phases. Since 1996, Dr. Barsoum and his collaborators have published over 60 refereed papers on these ternary carbides and nitrides, including ones in Nature and Science. Dr. Barsoum has authored or co-authored over 100 refereed publications, 6 US patents awarded and 4 pending. In 2000 he was awarded a Humboldt-Max Planck Research award for Senior US Research Scientists. He spent his 2000-2001 sabbatical year at the Max Planck Research Institute in Stuttgart. Germany. 

Ternary rare-earth-X-carbon phase diagrams and ternary carbides 115... 

Phase diagrams and formation of ternary carbides in R-B-C systems 115... 

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. 

The plots of the cell volume of the ternary carbides against the atomic number of the lanthanides showed that only small deviations from the smooth curves occur for... 

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