Vanadium and Niobium

Figure 3. Logarithm of the reactivities of niobium and vanadium clusters. The Exxon data (circles) are scaled relative to the Argonne Fe o reactivity, and the Rice data (crosses) are normalized to Nbg.

Tantalum has properties similar to niobium and vanadium above it in group 5. It is a very hard and heavy metal with a bluish color when in its rough state, but if polished, it has a silvery shine. It is ductile, meaning it can be drawn into fine wires, and also malleable, meaning it can be hammered and worked into shapes. Thin strips and wires of tantalum will ignite in air if exposed to a flame. 

As in the case of hydrated niobium and vanadium pentoxides, it is a difficult matter to remove traces of mineral acids from the precipitate. Treatment with water gives rise to a cloudy hydrosol which passes through an ordinary filter. This can be prevented by addition to the wash-water of a small quantity of ammonia or acetic acid.4 In the preparation of anhydrous tantalum pentoxide, traces of adds can be removed by igniting the gel in admixture with a small quantity of ammonium carbonate. 

Group r In order of increasing atomic number, ihese are vanadium, niobium Isomelimes culled columbiunti. and tantalum. Vanadium and tanlalum have two electrons in an ouler shell niobium has one electron in ils ouler shell. Although niobium and vanadium also have other valences, all of ihe elements in this group have a 5+ valence in common... 

Beyond providing bulk structural information about 3-D metal oxide phases, Raman spectroscopy can also provide information about the terminating (and thus 2-D) surface layers of bulk metal oxides. For example, surface Nb=O, V = O, and Mo=O functionalities were detected by Raman spectroscopy for bulk Nb2Os, and for vanadium-niobium, molybdenum-vanadium, molybdenum-niobium, and vanadium-antimony mixed oxide phases (Guerrero-Perez and Banares, 2004 Jehng and Wachs, 1991 Zhao et al., 2003). 

Hence, the challenge remains to fully analyze the surface layers of bulk oxide catalysts. Recently, Zhao et al. succeeded for the first time in detecting surface MoO and VOv species on molybdenum-niobium and vanadium-niobium mixed metal oxides by Raman spectroscopy (Zhao et al., 2003). 

Other catalysts effective in the conversion of isocyanates into carbodiimides include the naphthenates of Mn, Fe, Co, Cu and Pb, derivatives of metallic acetylacetonates, the alkoxides of titanium, zirconium and niobium and vanadium oxides or chlorides. Sterically hindered isocyanates are readily converted into carbodiimides upon heating in the presence of a catalytic amount of a strong base. For example, heating of... 

Membrane surface contamination. Although not as hydrogen selective as Pd and its alloys, other metals such as niobium and vanadium in dense form also have moderate to high hydrogen permselectivity and potentially can be considered as membrane materials. Inevitably the membrane surface is contaminated with non-metal impurities prior to or during separation or membrane reactor applications. 

Cionzalez, G., Saraiva, S.M.. and Aliaga. W., Experimental and predicted isoelectric points for niobium and vanadium pentoxide. South. Braz. J. Chem.. 2. 5, 1994. 

In this work, the activity and selectivity of catalysts based on niobium and vanadium oxides supported on high surface area anatase Ti02 in ethane ODH have been investigated. Specifically, the influence of the cooperation of vanadium and niobium oxides supported phases as components inducing respectively redox and acid properties, together with the effect of the preparation conditions on the catal3dic performances have been studied. 

Then we would jump to element 104, which should come after the actinide group and be a member of the family of elements including hafnium, zirconium, and titanium. Similarly, element 105 should be chemically related to tantalum, niobium, and vanadium. Heavier elements, through 118, should then fill in the rest of the same horizontal row on the Periodic Table. 

Fig. 7 Niobium and vanadium complexes bearing both ditbiocarboxylato and rf-S2 ligands...

Hydrogen reduction of chlorides in thermal plasma can be apphed not only to produce powder of individual metals but also to produce different intermetalhc compounds. The composition of the generated crystals copies the composition of the chloride mixture in the gas phase. This effect permits the production of the intermetallic compounds with the required composition. Refractory intermetallic compounds based on niobium and vanadium were synthesized from their chlorides (conversion close to 100%) in a hydrogen plasma jet generated by RF-ICP discharge (Bashkirov Medvedev, 1968). The reaction products were crystallized on a substrate sustained at a temperature of about 1000°C. The plasma-metallurgical technology is proven to be effective in the synthesis of vanadium-Hsilicon... 

Ponzoni A., Comini E., Sberveglieri G., Alessandri I., Bontempi E., and Depero L. E., Tin, niobium and vanadium mixed oxide thin films based gas sensors for chemical warfare agent attacks prevention, in IEEE Sensors Conference, pp. 1322-1325, 2007. 

Elements, which usually originate from alloyed steel scrap and non-ferrous metals in the steel charge, of the type which can be added to steels as alloying elements. They include nickel, chromium, molybdenum, copper, niobium and vanadium. Residual elements... 

In one embodiment patented by Makrides et al., tantalum foils were electrolyti-cally etched in hydrofluoric acid, washed with acetone and, while still wet with acetone, placed in vacuum and dried by evacuation. Using an argon plasma at a pressure of about 1 mm Hg (133.3 Pa), palladium was deposited onto both sides of the membranes to recommended thicknesses between 10 and 100 nm. Membranes of niobium and vanadium were prepared in the same manner, except that, in addition, vanadium was degassed in vacuum at 1273 K (1000 °C) to remove oxygen. Unalloyed palladium as well as Pd-Ag, Pd-Au and Pd-B, were also patented as hydrogen dissociation catalysts and as protective layers for the highly reactive niobium, tantalum and vanadium. 

All elements that form isochains can also form heterochains with other elements. In addition, simple heterochains can sometimes be formed by the next higher row of the periods III, IVB, and VB, namely aluminum, iron, and bismuth. Compounds with multicenter bonds are also formed by beryllium and a few elements from higher rows, e.g., niobium and vanadium. In these compounds, as well as the OH and H groups, the elements of period VIIB can also occur as the central atoms in multicenter bridge bonding, that is, in borohydrides, niobium iodide, etc. These elements, however, do not represent true chain atoms. 

A variety of other nanoparticles have been formed by such in situ sol-gel reactions. Examples are the oxides of titanium, aluminum, - tanta-lum, zirconium, niobium, and vanadium. Some nanocomposites of this type have also included barium titanate, calcium oxide, calcium salts, borates, HTiNbOg, and Eu dopants. ... 

Ta(CO)6] is obtained in a manner analogous to that of niobium and vanadium hexacarbonyl anions ... 

The results of Fig. 1 show the following remarkable features. At all temperatures only one resonance line with a width of the order of Avj/2 = 10 Hz has been observed, the experimental chemical shift resolution thus being Av/Vq 10 ppm. A strong temperature dependence is observed both for the relaxation rate T2 and the chemical shift. The decrease in Avi/2(T) with increasing temperature apparently is connected with an increase in the chemical shift 8. The latter behaviour is a well known fact for niobium and vanadium complexes. In the following discussion we focus on the behaviour of the Nb line width and thus of the relzucation rate. 

The history of element discoveries shows notable similarities for niobium and vanadium as shown in Table 22.1. 

Kolpachev, A. B. Nikiforov, I. Ya. (1988). Electronic Energy Structure of Substoichiometric Niobium and Vanadium Carbides. Moscow, All-Union Institute of Scientific and Technical Information (VINITI) deposited materials. No 2522-B88. 

Perovskites containing a transition metal are of particular interest because of the availability of multiple oxidation states, which facilitate electrocatalytic processes and provide mechanisms for electronic conductivity. For example, under reducing atmospheres the transition metal ions change to lower oxidation states, effectively freeing up electrons to pass current. Typical examples of such species are titanium, niobium, and vanadium. SrNbOs has an electronic conductivity of 10" Scm under reducing conditions [14], and Petrie reported a conductivity of 10 cm for SrVOs under similar conditions [15]. Unfortunately, it was also found that these compounds could not be fabricated in air. 

A. Sanmcci, S. Tosti, A. Basile, Alternatives to paUadium in membranes for hydrogen separation Nickel, niobium and vanadium alloys, ceramic supports for metal alloys and porous glass membranes, in Handbook of Membrane Reactors, volume 1, A. Basile, ed., ComwaU Woodhead Publishing Series in Energy, 2013, pp. 183-217. 

---