Metal-nitride

Metallic nitrides have similar properties to the corresponding carbides. They are of minor industrial impoitance 

The metal nitrides of the transition metals of the subgroups of the IVth, Vth and Vlth groups are very similar to the corresponding carbides in their. structures (interstitial compounds of the MN type) and their properties such as hardness, melting point and electrical conductivity (see Table 5.6-3). Tungsten and molybdenum nitrides are exceptions with different structures and decompose with nitrogen loss above 800°C. 

The following processes are used in the manufacture of metal nitrides  

By comparison with the metal carbides, the industrial demand for the nitrides is very small. This is in part due to the poor wettability of the nitrides by ferrous metals, which makes the manufacture of hard metal alloys more difficult. 

TiN-coatings are industrially important, increasing the abrasion resistance of cemented carbides and producing a decorative golden yellow coloration on articles of jewelry. 

Many metal nitrides exhibit interesting properties such as extreme hardness, high melting points and resistance towards organic solvents and inorganic acids (Table 7-1). Several non-metallic nitrides also are of great interest. Among them, boron nitride and silicon nitride are of particular interest. The properties and preparation of these two compounds by CVD are described elsewhere (see Chapter 6). Most nitrides can be prepared by solid state reactions [142]. However, for the preparation of thin films, CVD is the method of choice. This section focuses on nitrides which have not been described in previous chapters. 

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Wallace C H 1998 The rapid solid-state synthesis of group III and transition metal nitrides at ambient and high pressures PhD Dissertation University of California, Los Angeles... 

Hafnium has been successfully alloyed with iron, titanium, niobium, tantalum, and other metals. Hafnium carbide is the most refractory binary composition known, and the nitride is the most refractory of all known metal nitrides (m.p. 3310C). At 700 degrees C hafnium rapidly absorbs hydrogen to form the composition HfHl.86. 

Although there are several hundred biaary nitrides, only a relative few ternary bimetallic metal nitrides are known (6). A group of ternaries of the composition where M is an alkah, alkaline-earth, or a rare-earth metal and M is a transition or post-transition metal, have been synthesized (6). 

Small amounts of TiN, HfN, and other metallic nitrides are produced on a pilot-plant scale. Titanium nitride is sold for 40—100/kg, depending on purity and grain si2e. Prices for HfN are ca 400 /kg. 

Molybdenum compounds Hydrodesulphurization and hydrotreating of petroleum Oxidation of methanol to formaldehdye Epoxidation of olefins Decomposition of alkali metal nitrides Irritation of eyes and respiratory tract Pneumoconiosis... 

The conversion of coordinated NSCI into a nitrido ligand provides a useful synthesis of transition-metal nitrides. For example, treatment of ReCl4(NSCl)(POCl3) with triphenylphosphine generates the nitrido complex ReNClaCPPhsla. "... 

Metal nitrides have also been prepared by adding KNH2 to liquid-ammonia solutions of the appropriate metal salts in order to precipitate the nitride, e.g. CU3N, Hg3N2, AIN, TI3N and BiN. 

The most extensive group of nitrides are the metallic nitrides of general formulae MN, M2N, and M4N in which N atoms occupy some or all of the interstices in cubic or hep metal lattices (examples are in Table 11.1, p. 413). These compounds are usually opaque, very hard, chemically inert, refractory materials with metallic lustre and conductivity and sometimes having variable composition. Similarities with borides (p. 145) and carbides (p. 297) are notable. Typical mps (°C) are ... 

Hardness on the Mohs scale is often above 8 and sometimes approaches 10 (diamond). These properties commend nitrides for use as crucibles, high-temperature reaction vessels, thermocouple sheaths and related applications. Several metal nitrides are also used as heterogeneous catalysts, notably the iron nitrides in the Fischer-Tropsch hydriding of carbonyls. Few chemical reactions of metal nitrides have been studied the most characteristic (often extremely slow but occasionally rapid) is hydrolysis to give ammonia or nitrogen ... 

The crystal chemistry of metal nitrides has been reviewed and there have recently been some intriguing developments in our understanding of the stoichiometries and structures of ternary and quaternary metal nitrides. 

Titan-kaliumfluorid, n. potassium fluotitanate, -karbid, n, titanium carbide, -metall, n. titanium metal, -nitrid, n, titanium nitride, TitanofluorwasserstoffsMure, /. fluotitanous acid, fluotitanic(III) acid,... 

The values of f (l) given in the table for electronegative atoms are their normal covalent single-bond radii28 (except for boron, discussed below). The possibility that the radius 0.74 A. of Schomaker and Stevenson29 should be used for nitrogen in the metallic nitrides should be borne in mind. 

Gordon,R. G., Recent Advances in the CVD of Metal Nitrides and Oxides, Proc. of the Conf on MOCVD of Electronic Ceramics, Material Research Soc., Pittsburgh, PA (1994)... 

Metathetical reactions between NbCl4(THF)2, NbCls, TaCls, [(Et2N)2TaCl3]2, or (R2N)3Ta(=NBu (R = Me, Et) with various amounts of lithium amidinates have been employed to synthesize the corresponding heteroleptic niobium and tantalum amidinate complexes. The products were investigated as potential precursors to metal nitrides (cf. Section VI) Carbodiimide insertion routes... 

As a result of their reactivity, particular attention must be given to preparation and purification of the metals, the conditions under which the metals, alloys and compounds are handled and the choice of material for the containment vessel. Ultrapure group-IIB metals may be used without further purification, but it is advisable to purify the group-IIA metals by a multidistillation process, the final distillation preferably being carried out in situ. The reactants and products are best handled in an atmosphere of a purified inert gas, usually He or Ar (N2 cannot be used because of the ready formation of group-IIA metal nitrides) alternatively, they can be handled under vacuum or, in rare cases, under halide fluxes. The containment vessel is normally fabricated from a refractory. 

Fig. 9. The MoFe protein cycle of molybdenum nitrogenase. This cycle depicts a plausible sequence of events in the reduction of N2 to 2NH3 + H2. The scheme is based on well-characterized model chemistry (15, 105) and on the pre-steady-state kinetics of product formation by nitrogenase (102). The enzymic process has not been chsiracter-ized beyond M5 because the chemicals used to quench the reactions hydrolyze metal nitrides. As in Fig. 8, M represents an aji half of the MoFe protein. Subscripts 0-7 indicate the number of electrons trsmsferred to M from the Fe protein via the cycle of Fig. 8.

As nitridoborates are known as A3(BN2) for alkaline elements (A = Li, Na) and as AE3(BN2)2 for alkaline-earth elements (AE = Ca, Sr, Ba) it would be interesting to find methods for the synthesis of nitridoborates of transition or lanthanide elements. Can they be made straightforward Hke Ii3(BN2) and AE3(BN2)2 from metal nitrides and layer-like a-BN, or do they require new preparative strategies - if they can be made at all ... 

Li3(BN2) have already demonstrated the decomposition of (BN2) ions into boron nitride. The remaining nitride can lead to the formation of a binary metal nitride or reduce the transition metal ion under the formation of N2. Both mechanisms have been obtained experimentally, depending on the stability of the metal nitride. For instance niobium pentachloride forms NbN, titanium trichloride forms TiN, and nickel dichloride forms Ni, plus BN and nitrogen, respectively, in reactions with Li3(BN)2 (at 300-600°C) [24]. 

We note that the valence orbitals of metal atoms order in energy as AE>Ln>M. The d-levels of transition elements (M) range the lowest, and are therefore most sensitive for reduction, or to form a stable binary metal nitride. This may also explain the virtual absence of d-element compounds with 16 (valence) electron species, such as [N=N=N] , [N=C=N] , [N=B=N] T [C=C=CfT or [C=B=C] T at least through high-temperature syntheses. 

Nitridoborates of lanthanum and the lanthanides were obtained from reactions of lanthanide metal or lanthanide metal nitride with layer-like (a-)BN at elevated temperatures (3>1200°C). These reactions require elaborated techniques in the inert gas sample-handling and the use of efficient heating sources, such as induction heating. Only some compounds remain stable in this high-temperature segment, and the yields of such reactions are often limited due to the competing stability of binary phases, allowing only the most (thermodynamically) stable compounds to exist. 

Metal-rich compounds are readily obtained when a metallothermic reduction is included into the metathesis reaction by using an electropositive metal (10). In addition, metal-rich and nitrogen-rich compounds are obtained when a metal and a metal nitride are employed in reactions (11, 12) ... 

Structures of the lanthanide nitridoborates appear as layered structures with approximate hexagonal arrangements of metal atoms, and typical coordination preferences of anions. As in many metal nitrides, the nitride ion prefers an octahedral environment such as in lanthanum nitride (LaN). As a terminal constituent of a BNx anion, the nitrogen atom prefers a six-fold environment, such as B-N Lns, where Ln atoms form a square pyramid around N. Boron is typically surrounded by a trigonal prismatic arrangement of lanthanide atoms, as in many metal borides (Fig. 8.10). All known structures of lanthanide nitridoborates compromise these coordination patterns. 

Compounds with nitrogen-metal (nitride) bonds... 

Metal oxides, metal sulfides, metal nitrides, metal carbides, metal borides, metal alloys, metallic glasses, molecular sieves, salts, acids... 

The extension of this approach to artificial leaves based on titanates, niobates, tantalates, metal nitrides and phosphides, metal sulfides, and other transition metal oxides appears possible and useful in order to enhance the photocatalytic efficiency. In addition, the construction of multicomponent systems such as Ti02-CdS or MoS2-CdSe for overall water splitting could also lead to further improvements. This... 

Potassium nitride Mellor, 1940, Vol. 8, 99 Potassium and other alkali-metal nitrides react on heating with phosphorus to give a highly flammable mixture which evolves ammonia and phosphine with water. 

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