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Metal Borides, Carbides and Nitrides

Metal borides are generally prepared by the direct reaction of the elanents at high temperatures or by the reduction of metal oxides or halides. Thus, reduction of mixtures of BjOj and metal oxides by carbothermic reaction yields metal borides. Reaction of metal oxides with boron or with a mixture of carbon and boron carbide is another route. Some metal borides are prepared by fused salt electrolysis (e.g. TaBj). Borides of IVA-VIIA elements as well as ternary borides have been reviewed by Nowomy [1], The method employed to prepare TiB starting with TiCl is interesting [2], TiCl and BCI3 react with sodium in a nonpolar solvent (e.g. heptane) to produce an amorphous precursor powder along with NaCl. NaCl is distilled off and the precursor crystallized at relatively low temperatures (-970 K). [Pg.151]

The reaction probably proceeds through the formation of the CI3B-T1CI3 intermediate. Solid-state metathesis reactions between transition-metal chlorides and magnesium [Pg.151]

Essentials of Inorganic Materials Synthesis, First Edition. C.N.R. Rao and Kanishka Biswas. 2015 John Wiley Sons, Inc. Published 2015 by John Wiley Sons, Inc. [Pg.151]

Metal carbides are generally prepared by the direct reaction of the elements at high temperatures (-2470 K). Reaction of metal oxides with carbon is another important route. Reaction of metal vapour with hydrocarbons also yields metal carbides. Phase relations in carbides of IVA, VA and VIA group elements as well as actinides have been reviewed by Storms [5], SiC has been prepared by the reaction of SiCl and CCl with Na, a similar reaction of CCl and BClj with Na gives B C [2]. SiC is formed by the decomposition of CH3S1H3 or (CHj)jSiClj. Pyrolysis of organosilicon polymer precursors has been employed to prepare SiC [6]. Some of the precursor reactions are discussed in Chapter 4 of this book. Various metal carbides have also been synthesized by sol-gel chemistry [7]. [Pg.152]

Metal nitrides are generally prepared by the direct reaction of the elements. Ionic nitrides are also prepared by the decomposition of metal amides as illustrated by the following reaction  [Pg.152]


The small atoms at the center of the first row of the Periodic Table (B, C, N, O, and to a lesser extent Al, Si, and P) can fit into the interstices of aggregates of larger transition metal atoms to form boride, carbide, and nitride compounds. These compounds are both hard and moderately good electronic conductors. Therefore, they are commonly known as hard metals (Schwarzkopf and Kieffer, 1953). [Pg.131]

The structures of the prototype borides, carbides, and nitrides yield high values for the valence electron densities of these compounds. This accounts for their high elastic stiffnesses, and hardnesses. As a first approximation, they may be considered to be metals with extra valence electrons (from the metalloids) that increase their average valence electron densities. The evidence for this is that their bulk modili fall on the same correlation line (B versus VED) as the simple metals. This correlation line is given in Gilman (2003). [Pg.131]

Hydrogen reacts with metal borides, carbides, silicides, nitrides, phosphides, oxides, sulfides, and halides to form a solid solution of hydrogen in the compound with... [Pg.466]

The hydrid( S, borides, carbides and nitrides of the transitional elements have metallic properties. Only atoms with small covalent radii are capable of occupying the interstices in relatively close-packed arrangements ... [Pg.147]

A. .. A etc. contacts between the layers (see later). The reason for the great importance of the most closely packed structures is that in many halides, oxides, and sulphides the anions are appreciably larger than the metal atoms (ions) and are arranged in one of the types of closest packing. The smaller metal ions occupy the interstices between the c.p. anions. In another large group of compounds, the interstitial borides, carbides, and nitrides, the non-metal atoms occupy Interstices between c.p. metal atoms. [Pg.127]

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. [Pg.530]

The interstitial structures comprise the compounds of certain metallic elements, notably the transition metals and those of the lanthanide and actinide series, with the four non-metallic elements hydrogen, boron, carbon and nitrogen. In chapter 8 we discussed the structures of a number of hydrides, borides, carbides and nitrides of the most electropositive metals, and these we found to be typical salt-like compounds with a definite composition and with physical properties entirely different from those of the constituent elements they are generally transparent to light and poor conductors of electricity. The systems now to be considered are strikingly different. They resemble... [Pg.343]

By referring to relevant sections earlier in the book, write a brief account of the formation of hydrides, borides, carbides and nitrides of the [Pg.553]

F. Richter, R. Pintaske, J. Hahn, and Th. Welzel, in Hard Coatings Based on Borides, Carbides and Nitrides Synthesis Characterization and Applications, A. Kumar, Y.-W. Chang, and R. W. J. Chia (Eds), The Minerals, Metals and Materials Society, Warrendale, PA, 1998, pp. 153-168. [Pg.444]

Following the previous description of the atomic structure of boride, carbide and nitride ceramics, Table 2 lists physical crystalline stmctural differences of a variety of UHTCs along with respective density and melting point. Note that density increases with increasing mass of the metal atom. Note also the differences in melting points between materials whereby the carbides typically have the highest melting points, above borides or nitrides of the same metal constituent. [Pg.203]

Use the Miedema parameters to derive the existence of borides, carbides, and nitrides of transition metals. [Pg.84]

The rare earth borides, carbides, and nitrides aU have compounds that manifest superconductivity, fundamental magnetic transitions, and other interesting phenomena such as strongly correlated heavy fermion behavior. Some of the rare earth transition metal borocarbides such as RTr2B2C have shown fascinating properties where magnetism and superconductivity phenomena coexist. [Pg.276]

Borides, in contrast to carbides and nitrides, are characterized by an unusual structural complexity for both metal-rich and B-rich compositions. This complexity has its origin in the tendency of B atoms to form one- two-, or three-dimensional covalent arrangements and to show uncommon coordination numbers because of their large size (rg = 0.88 10 pm) and their electronic structure (deficiency in valence electrons). The structures of the transition-element borides are well established " . [Pg.123]

In contrast to the carbides and nitrides, there are a large variety of formulas and structure types for borides (from M4B to MB 5). Although it is possible to establish a comparison between metal-rich borides and carbides, B-rich borides have no counterpart in the carbides. [Pg.123]

Compounds isotypic with the k phases arc found among intcrmetallics, borides, carbides and oxides and also with silicides, germanides, arsenides, sulfides and sclcnides no nitrides, however, are found. The mode of filling the various voids in the metal host lattice of the k phases follows the schemein Ref. 4 and is presented in Table 1 for all those compounds for which the atom distribution is well known from x-ray or neutron diffraction. Accordingly, B atoms in tc-borides, Zr, Mo, W, Re)4B and Hfy(Mo, W, Re, Os)4B , occupy the trigonal prismatic interstices within the parent metal framework of a Mn, Aln,-type structure (see Table 1 see also ref. 48). Extended solid solutions are found for (Hf, Al)[Pg.140]

When discussing metal alloys (Section 4.3), we saw that atoms of non-metallic elements such as H, B, C, and N can be inserted into the interstices (tetrahedral and octahedral holes) of a lattice of metal atoms to form metal-like compounds that are usually nonstoichiometric and have considerable technological importance. These interstitial compounds are commonly referred to as metal hydrides, borides, carbides, or nitrides, but the implication that they contain the anions H, B3, C4, or N3- is misleading. To clarify this point, we consider first the properties of truly ionic hydrides, carbides, and nitrides. [Pg.108]

Other metal-like compounds, nitrides, borides and silicides of transition metals, can also be used as catalysts for the oxidative coupling of methane.17 Typically, the activity of carbides and nitrides is superior to those of borides and silicides, whereas the latter catalyst s selectivity is... [Pg.174]

In earlier work, it was found for borides, silicides and nitrides that specific activity, expressed as total rate of methane consumption per unit surface area, plummeted with increasing surface area of the catalyst samples.1718 The same relationship was also found for transition metals carbides (Figure 16.4). It should be noted the dependence of specific activity on surface area rather than catalyst composition is unusual for heterogeneous catalytic reactions. In addition, it can be found that the reaction order in the oxidant is perceptibly in excess of 1 (Tables 16.8 and 16.9). Such an order is hard to explain in terms of common mechanism schemes for heterogeneous catalytic oxidative reactions. [Pg.175]


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Borides

Carbide nitrides

Metal borides

Metal carbides

Metal nitrides

Metallic carbides

Metallic carbides metals

Nitrides and Borides

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