Niobium carbides preparation

Niobium pentaoxide is used for preparing many niobium salts, including niobium carbide (Balke process). It also is used in the aluminothermic process in the production of niobium metal. 

Electrodeposition is one of a few techniques used to crystallize high-melting materials at convenient temperatures [e.g., tantalum carbide, TaC (mp 3900°C) and niobium carbide, NbC (mp 3500°C) are crystallized at 750°C]. The preparation involves electrolysis of melts containing Ta20s (or Nb205), Na2B407, Na2C03, NaF, and KF. 

Niobium carbide is used as a protective coating for niobium metal.[10] It can be prepared by the reaction of elemental niobium metal with methane or by reacting NbCIs with CCI4 and H2. It also has been obtained from the arene complex Nb(CH3-C(,H,[Pg.385]

Tantalum carbide is very similar structurally and chemically to niobium carbide and is used as a protective coating for tantalum metal. It can be prepared by the CVD of a mixture of elemental Ta metal and methane or a mixture of tantalum pentachloride, methylchloride and hydrogen [10]. 

Kim H S, Bugli G, Djega-Mariadassou G (1999) Preparation and characterization of niobium carbide and carbonitride. J Solid-State Chem 142 100-107... 

This process works as a galvanic ceU where the anodic metal (Nb) dissolves in the bath. Nb ions react with the cathodic metal (Ni) to give a defined compound NbNis (Fig. 1). Likewise, tantalum and niobium carbides are also prepared by coelectrodeposition of Ta and C [20] or metalliding [21]. 

Niobium carbide with a composition near NbCj o was first prepared by Joly (1877) from the reaction of KjO 3Nb205 with carbon. NbjOj has been used as a starting material by most early workers and is presently used in the industrial preparation of the carbide. 

Sihca is reduced to siUcon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous siUcon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum haUdes, siUca can be converted to silane in high yields by reaction with hydrogen (15). SiUcon itself is not hydrogenated under these conditions. The formation of siUcon by reduction of siUca with carbon is important in the technical preparation of the element and its alloys and in the preparation of siUcon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and siUcate. At 800—900°C, siUca is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce siUca to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

Niobium and rhodium cluster anions have been prepared by laser vaporization and the reactions with benzene studied by FT-ICR/MS (58). The reactions of the anions and similar cations have been compared. With few exceptions the predominant reaction of the niobium cluster anions and cations was the total dehydrogenation of benzene to form the metal carbide cluster, [Nb C6]-. The Nb19 species, both anion and cation, reacted with benzene to form the coordinated species Nb 9C6I I6p as the predominant product ion. The Nb22 ions also formed some of the addition complex but the Nb2o Nb2i, and all the other higher clusters, formed the carbide ions, Nb C6. ... 

It can be prepared by heating metallic niobium or any of the lower oxides, or the sulphide, carbide, or nitride of niobium, in air or oxygen. Ammonium niobium oxyfluoride, (NH4)jNbOFs, also yields the pentoxide on being heated in air. Solutions of the alkali niobates yield a white gel of the hydrated pentoxide when treated with mineral adds, sulphuric acid bring usually preferred. Insoluble niobates on fusion... 

The metaniobates of the alkali metals, MNb03, the orthoniobates MjNbOj and the pyroniobates, M+NbeOy, where M is an alkali metal, can be prepared by various alkali carbonate or hydroxide fusion processes. Niobium fonns a nitride, NbN, and a carbide, NbC. 

Use Cemented carbide tipped tools, special steels, preparation of niobium metal, coating graphite for nuclear reactors. 

Table 2 shows the initial results for the catalytic dry reforming of methane using bulk carbides of niobium, tantalum, molybdenum and tungsten, prepared by CH4 TPR. The conversions and yields obtained over P-M02C and a-WC are very similar to those predicted by thermodynamic considerations, and thus these materials are efficient catalysts for methane dry reforming. At atmospheric pressure, deactivation was observed over both catalysts after about 8 hours on stream. Examination of the post-catalytic samples by powder XRD (Figure 2) revealed that as the reaction proceeded the active P-M02C was oxidised and converted to... 

Green and co-workers (68) prepared 5-NbC with surface areas as high as 113 m /g from the TPRe of niobium oxide with C2H6/8.6 H2 as a reactive gas. They also synthesized 5-NbC with a surface area of 76 m /g from the carburization of niobium nitride using CH4/4H2 mixture gas. They did not report the elemental analysis data for these materials, which would give information on the carbon contamination. In most cases, the use of the nitride as a precursor or ethane as a reactant increases the surface area of the products, as well as lowers the required synthesis temperature. Nitrides can be converted readily to carbides while maintaining both the high surface area and structure. 

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