Niobium carbides properties

The menstmum niobium—carbide process (7) utilizes either columbite [1310-23-2] mineral concentrates or ferroniobium as starting materials. A low level of TaC in soHd solution with NbC commonly occurs, as Ta and Nb occur together in ores. The properties of NbC are given in Table 1. The grayish brown NbC powder is used in cemented carbides to replace TaC. TaC—NbC soHd solutions that have 3 1, 2 1, 1 1, and 1 2 ratios and the corresponding ternary and quaternary soHd solutions with TiC and WC are common. 

Niobium carbide, also known as columbium carbide, is a important refractory material with a high melting point. It is used as a CVD coating mostly on an experimental basis. Niobium carbide has two phases Nb2C and the monocarbide NbC. The latter is the only phase of industrial importance and the only one reviewed here. Its characteristics and properties are summarized in Table 9.5. 

Carbides, Silicides, and Related Compounds. Niobium carbide has been obtained by deposition from a NbCl4-H2-CH4 mixture. There has been a review of the electrical, thermoelectrical, and magnetic properties of MC-TaC systems (M = Hf or... 

CY Allison, FA Modine, RH French. Optical and electrical properties of niobium carbide. Phys... 

Alternate materials as the basic core element structural material are under investigation as a backup to the graphite development. These include KT silicon carbide, molybdenum, molybdenum carbide, niobium, niobium carbide, zirconium carbide, tantalum, and tantalum carbide, all of which have properties indicating promi.se for LMF-GCR application. 

Nevertheless, little data on the tribological profile on binderless or metal bonded niobium carbide are available. The tribological properties of NbC are unexplored, although NbC is a property-determining constituent in many steels and hard metals as well as in cast irons [1,2]. 

Recent studies [3] on hot-pressed (binderless) NbC indicated, that pure niobium carbide has an intrinsic wear resistance, when bench marked against different ceramics, cermets, hard metals and thomally sprayed coatings. In consequence, because HP-NbC is still brittle, 8% of cobalt binder improved properties like toughness and strength as w ell as S PS reduced the sintering temperatures to 1,280°C and the dwell time to 4 minutes, as shown in the present paper. 

Tantalum and niobium are added, in the form of carbides, to cemented carbide compositions used in the production of cutting tools. Pure oxides are widely used in the optical industiy as additives and deposits, and in organic synthesis processes as catalysts and promoters [12, 13]. Binary and more complex oxide compounds based on tantalum and niobium form a huge family of ferroelectric materials that have high Curie temperatures, high dielectric permittivity, and piezoelectric, pyroelectric and non-linear optical properties [14-17]. Compounds of this class are used in the production of energy transformers, quantum electronics, piezoelectrics, acoustics, and so on. Two of... 

In this paper we review the results of our systematic work on the catalytic and adsorptive properties of transition metal carbides (titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and iron). We focus our attention on the oxidation of hydrogen, carbon monoxide, ammonia, and the oxidative coupling of methane. The first two reactions are examples of complete (non-selective) oxidation, while the oxidation of ammonia simulates a selective oxidation process. The reaction of oxidative coupling of methane is being intensively explored at present as a means to produce higher hydrocarbons.5 10... 

The presence of carbide and nitride precipitates in alloy steels can have a beneficial effect on the mechanical properties of the steels concerned. How-ever, the amounts, morphology and distribution of the precipitated phases must be carefully controlled in order to achieve the properties required. Because the presence of hard precipitates in a steel during hot-rolling operations can result in damage both to the rollers and to the steel, it is important that information be available on the ranges of temperature and composition in which precipitated phases are stable. For this reason, and also to achieve desired precipitation characteristics using the minimum amounts of expensive precipitating elements such as niobium, titanium, vanadium, etc., it is helpful to cany out prior calculations of the stability of precipitates in steels of different compositions. 

Most of these are carbon-manganese-molybdenum alloys with small additions of chromium and/or nickel plus vanadium or niobium. Vanadium or niobium acts as a carbide stabilizer and grain refiner, improving both elevated temperature strength and notch ductility. An exception is Fortiweld (MOBO 45 is the same steel), which is a boron-treated 1/2% molybdenum steel. This alloy is the cheapest of the group, but has hardly been used for reactors in the U.K., possible because its impact properties in thick sections are not so attractive as alternative steels. 

Carbon dissolving in the metal substrate can also modify the surface properties of the alloy by changing the heat treatment characteristics or causing the carbides of elements such as chromium, titanium, or niobium, etc., to be precipitated. This removes these elements from solution and, in the case of chromium, impairs the oxidation resistance of the alloy. The penetration of oxide scales by CO2 is an important consideration in these systems. 

Corrosion of the plates not only detracts from their mechanical properties but also gives rise to undesirable corrosion products, namely, heavy-metal ions, which, when depositing on the catalysts, strongly depress their activity. The corrosion processes also give rise to superficial oxide films on the metal parts, and these cause contact resistance of the surfaces. For a lower contact resistance, metallic bipolar plates sometimes have a surface layer of a more stable metal. Thus, in the first polymer electrolyte membrane fuel cell, developed by General Electric for the Gemini spacecraft, the bipolar plates consisted of niobium and tantalum coated with a thin layer of gold. A bipolar plate could also be coated with a layer of carbide or nitride. 

This chapter is a review of the characteristics and properties of the interstitial carbides formed by the metals of Group V vanadium, niobium, and tantalum. These three carbides have similar atomic bonding, composition, and crystallography as shown in Ch. 3. These common points can be summarized as follows ... 

The tantalum carbides and silicides and tungsten carbides cited above are used for their hardness, corrosion resistance in hot environment and their semiconducting properties, while niobium alloys (niobium-germanium, niobium-aluminium...) receive much attention for their properties of superconductivity. 

World consumption of tantalum was about 2000 tonnes in 2001. Tantalum, like niobium, is used in superalloys based on nickel and cobalt, intended for aircraft engines and other high-temperature applications. Tantalum carbide TaC is, to a limited extent, used as a hard component in cemented carbide. The oxide is used to make special glass with a high refractive index for camera lenses Two tantalum properties have, however, given the metal its special importance in modern industry. 

---