Niobium system, iron

The ternary iron oxides, as exemplified by the iron-niobium system, offer an opportunity to obtain single-phase, conducting n-type iron oxides in which the conductivity can be controlled by means of chemical substitution. At first glance, FeNbO and FeNb Og might appear to be very different materials. Yet as MM O and MM Og they merely represent superstructures of the basic a-PbO. structure obtained under the conditions of preparation (7 ). Consequently, they form a solid solution in which the two valence states of iron are uniformly distributed throughout a single homogeneous phase (j3). 

Pau] Paul, E., Swartzendraber, L.J., The Fe-Nb (Iron-Niobium) System , Bull. Alloy Phase Diagrams, 7(3), 248-254 (1986) (Crys. Stractine, Phase Diagram, Thermodyn., Assessment, Review, Magn. Prop., 83)... 

Das] Das, R.C., Jha, R., Mukherjee, X, The Carbon-Iron-Niobium System , J. Alloy Phase Diagrams, 2(2), 131-140 (1986) (Phase Diagram, Thermodyn.)... 

Experimental investigations of the thermodynamic properties Cr-Fe-Nb alloys have not been reported. Thermodynamic data for liquid, ferrite and austenite of some iron-based systems were optimized by [1998Mie] in order to give a more accurate representation of phase equilibria between these phases in multieomponent steels. But for the Cr-Fe-Nb system, the auflior has noted fliat a eareM examination of the system is necessary in order to get a reliable prediction of die partitioning tendency of niobium. 

Impressed current systems are normally based upon anodes of silicon iron, platinised titanium or platinised niobium. The method of anode installation is usually by suspension. The anode configuration and number must be such as to ensure uniform current distribution. Considerable use is made of wire-type platinised-titanium, and niobium anodes which offer minimal weight and relative ease of mounting/suspension. 

Small ey(Ib) that cobalt and niobium clusters react in a very selective fashion with deuterium was rapidly followed by similar studies on a variety of other metal systems. Three groups simultaneously reported similar dramatic behavior for iron c usters( 2b, 3b). Di hydrogen or di deuteri urn addition reactions have been reported for vanadium( 3e), i ron(lc,2a-d,3b), cobalt(lb),... 

COLUMBITE. A mineral oxide of iron, manganese, niobium (colum bium). and tantalum (Fe.MnjfNb.TaJsOf,. Crystallizes in the orthorhombic system. Hardness 6 sp gr 5.20 color, red to brown. 

However, many ternary systems incorporate a second photoactive center in addition to the [FeO ] octahedra in the present case, [NbO ] octahedra. The interaction between such multiple centers has not previously been investigated. In the present work, interband transitions are observed which appear characteristic of niobium centers, together with other transitions characteristic of the iron centers. Since these are homogeneous, singlephase materials, this result suggests that caution should be exercised when applying the conventional band model to such oxide semiconductors. 

The corrosion resistance of various metals and alloys in high-temperature liquid lithium is shown in Figure 11. Unfortunately, lithium is much more corrosive than sodium. Consequently, it will be impossible to take full advantage of its many attractive heat-transfer properties until a satisfactory container material is found. The most corrosion-resistant pure metals in a static isothermal system are molybdenum, niobium, tantalum, tungsten, and iron. Of the commercially available structural materials, no alloys tested to date have had satisfacto corrosion resistance at a temperature above 1400 F. for extended time periods in systems where temperature differentials exist. Even though iron has good resistance in static isothermal lithium, iron and iron-base alloys suffer from mass trans-... 

Design of cathodic protection for marine structures in both fresh and salt water require special techniques. Galvanic systems usually employ zinc or aluminum alloy anodes. Impressed current systems frequently use high silicon, chromium bearing iron, platinized niobium, or mixed-metal oxide/titanium anodes. The structure being protected affects the design. Stationary facihties such as bulkheads and support piles require different techniques from ship hulls [55]. 

Further thermochemical work on low-melting-temperature alloys need not be encouraged. Data for high-melting-temperature alloys, on the other hand, are still in short supply. Iron alloys, it is true, have attracted much attention from thermochemists, for obvious reasons, but in view of the large number of elements found in alloyed steels more results are still required. Thermochemists should make sure, however, that the ferrous system they intend to study has not already been adequately investigated. More thermochemical data are needed for alloys of transition metals of technical interest, such as titanium, zirconium, niobium, tantalum, chromium, molybdenum, and tungsten. 

Silicon, niobium, hafnium, and tantalum were beneficial additions to the Tl-Mo system, as well as palladitun, aluminum, and iron. 

Since the number of slip systems is not usually a function of temperature, the ductility of face-centered cubic metals is relatively insensitive to a decrease in temperature. Metals of other crystal lattice types tend to become brittle at low temperatures. Crystal structure and ductility are related because the face-centered cubic lattice has more slip systems than the other crystal structures. In addition, the slip planes of body-centered cubic and hexagonal close-packed crystals tend to change at low temperature, which is not the case for face-centered cubic metals. Therefore, copper, nickel, all of the copper-nickel alloys, aluminum and its alloys, and the austenitic stainless steels that contain more than approximately 7% nickel, all face-centered cubic, remain ductile down to the low temperatures, if they are ductile at room temperature. Iron, carbon and low-alloy steels, molybdenum, and niobium, all body-centered cubic, become brittle at low temperatures. The hexagonal close-packed metals occupy an intermediate place between fee and bcc behavior. Zinc undergoes a transition to brittle behavior in tension, zirconium and pure titanium remain ductile. 

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