Columbium oxide

Berzelius went on to explain the differences between Ekeberg s tantalum oxide and the columbium oxide prepared by Hatchett ... 

The extent of oxidation of columbium after 20 hours in air, for several temperatures, was reported by the Fansteel Metallurgical Corporation (33). Columbium starts to oxidize in air at about 200°C. The oxide is said to be adherent and to prevent further oxidation unless the temperature is raised. Columbium is reported not to become brittle on heating in air for short periods, as tantalum does, because the oxide film prevents further reaction. The columbium oxides dissolve into the metal when heated in a vacuum at temperatures between red heat and 1200°C. Above 1200°C. the oxides are reported to evaporate. Columbium, in the oxide free state, is an active getter in vacuum tubes. 

The plot of Fig. 14 shows a straight line relationship from which an energy of activation of 27,400 cal./mol is calculated for the oxidation of tantalum. The temperature independent factors e s /B are evaluated from Equation (5) mentioned above. A similar analysis of the data on columbium oxidation yields an activation energy of 22,800 cal./mol. 

Rose analysed columbites and tantalites from different deposits. And every time he found that, along with tantalum, they contained another element whose properties were close to those of tantalum. Rose named the stranger niobium (Niobe was Tantalus daughter). In the summer of 1845, the scientist studied the same mineral in which Hatchett once detected columbium and isolated niobium oxide from it, which proved to be similar to columbium oxide. 

In the same year that del Rio found his erythronium, C. Hatchett examined a mineral which had been sent to England from Massachusetts and had lain in the British Museum since 1753. From it he isolated the oxide of a new element which he named columbium, and the mineral columbite, in honour of its country of origin. Meanwhile in Sweden A. G. Ekeberg was studying some Finnish minerals and in 1802 claimed to have identified a new element which he named tantalum because of the difficulty he had had in dissolving the mineral in acids. It was subsequently thought that the two elements were one and the same, and this view persisted until at least 1844 when H. Rose examined a columbite sample and showed that two distinct elements were involved. 

Synonyms niobium(V) oxide diniobium pentaoxide columbium pentaoxide... 

Berzelius warmly defended Ekeberg s claim to the discovery of this element. In the autumn of 1814 he wrote to Thomas Thomson objecting to an alteration which had been made in an English translation of one of his memoirs. Berzelius had used the word tantalum., and Thomson had evidently substituted the word columbium, whereupon Berzelius wrote, Without wishing to depreciate the merits of the celebrated Hatchett, it is nevertheless necessary to observe that tantalum and its properties in the metallic as well as in its oxidized condition were not known at all before Mr. Ekeberg. ... 

Hatchett named the new metal columbium and stated that its olive green prussiate and the orange-coloured gallate. . . may probably be employed with advantage as pigments. He also described his unsuccessful attempts to reduce the oxide to the metaL From his careful use of Lavoisier s new nomenclature, it is evident that Hatchett was not a phlogistonist. 

Tantalum is found in a number of oxide minerals, which almost invariably also contain niobium (columbium). The most important tantalum-bearing minerals are tantalite and columbite. which are variations of the same natural compound (Fe, Mn)(Ta, Nb Og. Much of the tantalum concentrates has been obtained as a byproduct from tin mining in recent years, tin slags, which are a byproduct of the smelting of cassiierite ores, such as those found in the Republic of Congo. Nigeria, Portugal. Malaya, and Thailand have been an important raw material source for tantalum. 

To illustrate the application of the method to the study of the oxidation of metals, some of our recent results on the oxidation of columbium and tantalum (30) will be described here. Their high melting points and their other valuable physical and chemical properties have made these metals useful to both science and industry. Chemically columbium and tantalum are resistant to corrosion by gases and liquids at room temperature. However, at temperatures of 250°C. and higher the metals react readily with oxygen and hydrogen. 

A number of publications deal with the gas phase reactions of columbium and tantalum with 02, N2, and H2, but only fragmentary data are available on the kinetics of these reactions. Although the free energy of formation of the oxide Ta2Os (31) at 25° C. has been determined and some thermodynamic work has been reported on columbium and its oxides, the data are not sufficient to permit equilibria calculations for elevated temperatures. The rate of oxidation of columbium and tantalum has been studied by McAdam and Geil (32) using the interference color method. Tantalum is reported to oxidize more slowly than columbium, zirconium, and iron. 

Fig. 12. Comparison oxidation of tantalum with columbium, titanium, and zirconium.

Colored oxide films were observed to have formed on columbium after... 

The effect of temperature on the rates of oxidation of columbium metal is also shown in Fig. 10. The temperature effect is very marked and the rate appears to follow an exponential law. A film of 290 A. thickness is formed after 2 hours of reaction at 200°C. and a film of 8250 A. thickness at 375°C. 

Figure 12 shows a comparison of the behavior toward oxygen of columbium and tantalum as compared to titanium and zirconium. Although the reaction temperatures differ, it is evident that tantalum oxidizes more rapidly than titanium but slower than columbium and zirconium. 

Table VII lists the rate constants K as evaluated by Equation (1), the activation energies E, entropies AS, and free energies AF involved in the oxidation of columbium and tantalum.

Table VIII lists the same quantities for the parabolic rate law for columbium, tantalum, titanium, zirconium, and iron. The K values show that the resistance to oxidation increases in the series columbium, tantalum, zirconium, titanium, iron. This is borne out by a comparison of the AF values for these oxidations. Although the oxidation of tantalum needs the highest energy of activation E, it is actually not as resistant to oxidation as, for example, iron, since the entropy difference for the tantalum oxidation is not sufficiently negative to make the overall potential barrier as high as that existing for the oxidation of iron. These...

The atoms of the vanadium group metals have five valence electrons. In vanadium (Z — 23) and niobium (columbium, Z = 41), these valence electrons lie beyond ra re-gas cores, whereas in tantalum (Z = 73), they lie beyond the xenon core which has been augmented by fourteen 4/ electrons. The +5 oxidation state is characteristic of this family for niobium and tantalum it is the only oxidation state of importance. Oxidation is often regarded as removal of five valence electrons, followed by coordination of the pentapositive ion (which cannot exist for appreciable time in chemical systems) to basic groups which are present (H2O, OH, Cl, etc.). Although such a description almost certainly has very little resemblance to the actual path of oxidation of these metals, it is clerically convenient and may be used if not taken literally. In the same way, the lower oxidation states of vanadium may be considered vanadium atoms with the two 4s electrons removed, and with additional removal of one or two 3d electrons. 

Niobium (columbium) High melting point nonvolatile oxide ductile moderate density Oxidizing rapidly... 

Niobium (formerly called columbium) and tantalum are Transition Metals having a considerable affinity for oxygen donor groups they are thus called oxophilic see Oxophilic Character). They occur as mixed-metal oxides such as columbites (Fe/Mn)(Nb/Ta)206 and pyrochlore NaCaNb206p. Their discovery in minerals extends back to the beginning of the nineteenth century, when they were believed to be identical and called tantalum. Rose showed that at least two different elements were involved in the minerals, and named the second one niobium. Their separation was resolved around 1866, especially by Marignac. These metals often display similar chemical behavior as a result of nearly identical atomic radii (1.47 A) due to the lanthanide contraction see Periodic Table Trends in the Properties of the Elements)... 

Carlson and Nielsen (C3) described the pilot and full-scale plant separation of an ore containing more than 30% combined columbium and tantalum oxide using a sulfuric-hydrofluoric acid leach and methyl isobutyl ketone (MIBK) as solvent in pulsed columns. The —200 mesh columbite-tantalite ore was digested with 70% HF until the combined (Ca + Ta)20s in the leach liquid reached 3 Ib/gal at which time it was diluted to 15N free acid and clarified by filtration. This solution was contacted countercurrently in the pulsed column where Ta and Cb were extracted by MIBK. Columbium was stripped from the organic with demineralized water which diluted the free acid in the solvent, making possible the transfer of all the Cb the Ta-loaded solvent was then stripped with demineralized water causing the transfer of Ta to the aqueous phase. The oxides were then precipitated with 28% ammonium hydroxide solution. Conversion to the respective oxides was by calcination of the precipitates. 

Preparation of Pure Tungsten Trioxlde.—The oxide prepared by any of the above processes is alwaj s impure, the nature of the imj urities depending on the composition of the ore and on the materials employed in the process. If alkali has been used, the presence of sodium, potassium, or calcium tends to give the product a greenish appearance. Iron, manganese, silica, phosphorus, tin, molybdenum, vanadium, and columbium may all be present, and since tungsten is prone to form complex compounds with many of these, the purification of the oxide is not easily accomplished. 

Pitchblende is one of the most fertile sources of radioactive material. Its composition varies widely, but it always contains an oxide of uranium, associated with oxides of other metals, especially copper, silver, and bismuth the Austrian mineral contains cobalt and nickel the American, samples contain no cobalt or nickel but are largely associated with iron pyrites and arsenic zinc, manganese, and the rare earths are frequently present, while occasionally calcium, barium, aluminium, zirconium, thorium, columbium, and tantalum are reported. Dissolved gases, especially nitrogen and helium, are present in small proportions. 

In contrast to these characteristics the three members of Division A are extremely difficult to reduce from their oxides and have high melting and boiling points. They are all typically metallic in appearance and general behavior. Vanadium is less basic than columbium and tantalum, as is to be expected,... 

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