Niobium melting point

A somewhat similar phenomenon is knife-line attack which may be observed after welding titanium or niobium stabilised austenitic stainless steels. In this case there is a very narrow band of severe intergranular attack along the interface between the parent metal and the fusion zone. During welding, the parent metal immediately adjacent to the fusion zone is heated to just below the melting point and both chromium carbides and niobium or titanium carbides dissolve completely. On cooling rapidly, the conditions are such that when relatively thin sections are welded, neither chromium carbide nor niobium or titanium carbide have time to precipitate. If the weld is now... 

Another anhydrous solvent that is frequently used for the synthesis of tantalum and niobium fluoride compounds is bromine trifluoride, BrF3. At ambient temperature, bromine trifluoride is light yellow liquid characterized by a boiling point of 126°C, a melting point of 9°C and a density of 2.84 g/cm3 at melting temperature. 

Table 49 lists the melting points of some niobium-containing fluoride compounds. 

The method based on a net melt-holder is used successfully for materials with relatively low melting points and is less promising for the investigation of fluoride melts containing tantalum and niobium. 

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. 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

The melting points of chromium (1857 °C) and of manganese (1244 °C) are considerably lower than that of alumina. The heat requirement in respect of the reactions leading to the formation of these metals was calculated by considering alumina melting as the objective. The objective changes when aluminothermy is applied to the production of the refractory metals niobium and tantalum. Niobium melts at 2468 °C and tantalum at 3020 °C. Thus, when these metals are the products, the heat requirements for reaching temperatures in excess of 2500 °C and 3050 °C have to be calculated. 

The excess aluminum in the charge compensates for the loss of aluminum due to nonreductive air oxidation, and also provides aluminum for alloying with the niobium metal produced in the reduction. As mentioned earlier, the liquidus temperatures of niobium-aluminum alloys are lower than the melting point of niobium. The melting of this alloy and the alumina slag is achieved even with the reduced amount of heat available from the reaction implemented without preheating in the open reactor. 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

Anhydrous tantalum pentoxide, as usually prepared, is a white, nonvolatile,8 tasteless, odourless, amorphous powder, which remains white at high temperatures. When heated to dull redness it glows and assumes a crystalline form (rhombic prisms), isomorphous with niobium pentoxide 10 the same change takes place when the amorphous substance is fused with boric acid or microcosmie salt.11 Its melting-point... 

In contrast, the combustion temperatures recorded for the tantalum-nitrogen and niobium-nitrogen systems were much lower than the melting points of the respective metals. Photographs of the cross-sections of undiluted samples do not indicate any macroscopic effect of melting, and neither do SEM photographs of the products. 

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

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