Ternary carbides and nitrides

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. 

Materials for Extreme Environments Ultrahigh Temperamre Ceramics (UHTCs) and Nanolaminated Ternary Carbides and Nitrides (MAX Phases)... 

Hoi] Holleck, H., Binary and Ternary Carbides and Nitrides of Transition Metals and Their Phase Relationships (in German), Report KfK 3087B, Kemforschungszentrum, Karlsruhe, 181-183 (1981) (Phase Diagram, Review, 41)... 

Today, it has been fairly well established that the layered ternary carbides and nitrides with the general formula +iAX,j, and where n = 1,2 or 3, M is an early transition metal, A is an A-group element (mostly group IIIA or IVA), and X is either C or N, represent a new class of solids [1, 2]. These phases are layered, with M +iX layers interleaved with pure A-group element layers. 

Many ternary carbides and nitrides are known and some of these compounds have excellent properties. For instance, the hardness of ternary-carbide systems of the same group (Group IV or Group V) is considerably higher than the hardness of the binary constituents.1 1 A hardness of approximately 43.1 GPa is reported for the compound TIq 4C... 

The existence of ternary carbides and nitrides was discussed in Ch. 4, Sec. 5.0. As shown in Fig. 4.7 (Ch. 4), VC, NbC, and TaC have complete mutual solubility and variable solubility with the carbides of Group IV. With the partial exception of VC, they are also mutually soluble with the nitrides of Groups IV and V (see Fig. 4.8).O i... 

Energy states and chemical bonding in ternary carbides and nitrides formed in Ti-(AI, Ge)-(C, N) systems... 

Electronic structure of ternary carbide and nitride alloys... 

Because of the evident structmal similarities between transition metal carbides and transition metal nitrides the carbon atoms in group 4 and 5 carbides can be replaced completely by nitrogen without changing the structme of the binary phases. So far only one distinct ternary phase Cr2 (C,N)2 has been reported. Intersolubihty between the binary nitrides and carbides in the group 6 carbonitride systems Cr-C-N and Mo-C-N is not complete because of the differences in the crystal structmes of the carbide and nitride phases. 

Upon additional alloying ternary carbonitrides quaternary carbonitrides are obtained. The group 4 and 5 transition metal carbides and nitrides are completely miscible except TiN-VC and ZrN-VC. Thus, modified material properties can be obtained (see also Section 9.2). Information on the properties of these carbides are still scarce," a few data are given in Figure 13 and Table 4. 

A variety of other ternary and quaternary carbides and carhonitrides is especially interesting for use in metal cutting tools in the form of layers, and powder particles have been investigated recently for their specific heat, temperature and thermal conductivity [66]. The behavior of the heat conductivity of most of these compounds is similar to that of the group IVB carhonitrides for (near) stoichiometric composition showing a positive curvature of heat conductivity as a function of temperature. Interestingly, however, Nb- and Mo-containing ternary titanium carbides and nitrides and quaternary titanium carhonitrides show a hnear behavior in the same temperature interval. 

Holleck, H., Ternary Carbide Systems of Actinoids wifli Transition Metals of Other Groups (in German), in Binary and Ternary Transition Metal Carbide and Nitride Systems , Petzow, G. (Ed.) Gebraeder Bomtraeger Berlin, Stuttgart, 92-111 (1984) (Crys. Structure, Phase Diagram, Phase Relations, Review, 91)... 

While most of the binary carbides and nitrides considered above form unlimited homogeneous solid solutions, some other 5 and p elements (B, Be, Al, Mg, etc.) have only a low solubility in these phases. As their content in carbides and nitrides increases, ternary compounds with very specific crystal structures are formed which were reviewed by Alyamovsky et al (1981) and Goldschmidt (1967). It is well known (see Samsonov, Serebryakov and Neronov (1975)) that B or transition metal borides do not form unlimited solid solutions, when interacting with MX phases (X = C, N) and single-phase TiNjBj, compounds exist over a narrow composition range for example, when z + y = 0.62-0.94, y < 0.03 (see Alyamovsky, Zainulin and Shveikin (1976)). As the B/N ratio increases. 

The effects on the properties of transition metal carbides and nitrides produced by metal sublattice doping have been studied for quite an extended period. So far, large groups of ternary (and more complex) carbide and nitride alloys of the M M i (C,N) type, where M, M are metals, have been synthesised (see Goldschmidt (1967) or Samsonov, Upadkhaya and Neshpor (1974)). In this chapter we review the results of researches on the electronic structure and interatomic bonding in such solid solutions. 

The problems outlined above determined the structure of the book we start with the simplest compounds - binary carbides and nitrides (Chapters 2, 3) and proceed gradually to more complicated systems (Chapters 3-8), demonstrating some capabilities (and at the same time limitations) of the computational methods used. The book therefore acquires a certain reference character, which is somewhat unusual for publications on quantum chemistry of solid-phase materials. Apart from the properties of the particular substances, the authors have tried to discuss the methods used in the calculation of some experimental characteristics (primarily the thermomechanical characteristics, which are most interesting for this series of compounds) which have not been adequately addressed until recently (Chapter 1). The last statement can be applied as well to Chapters 4-8, where we make an attempt to develop a unified approach to the available data on the electronic energy spectra of ternary... 

M.W. Barsoum, T. El-Raghy, The MAX phases unique new carbide and nitride materials — ternary ceramics turn out to be surprisingly soft and machinable, yet also heat-tolerant, strong and hghtweight. Am. Sci. 89 (2001) 334—343. 

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

Metallic nitrides, sometimes termed interstitial compounds, are formed from combinations of N with transition metals of groups IVA, VA, and VIA. As the name implies, they exhibit electrical conductivity and most of the general characteristics associated with standard metals. They are also refractory and hard, and usually depart from the ideal stoichiometry ratios displayed above (see 17.3.9, Table 1). They readily form solid solutions with carbides and oxides, which gives rise to problems when it is necessary to obtain nitrides in pure form. Included in this category are numerous ternary nitrides of a transition metal with a group B metal. 

G.16 W. B. Pearson. A Handbook of Lattice Spacings and Structures of Metals and Alloys (New York Pergamon Press, 1958). A most useful source of information. Gives the crystal structures of intermediate phases, and the variation of lattice parameter with composition in solid solutions, of binary and ternary alloys. Also gives the crystal structures of metal borides, carbides, hydrides, nitrides, and binary oxides. 

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