Niobium carbides melting temperatures

Electrodeposition is one of a few techniques used to crystallize high-melting materials at convenient temperatures [e.g., tantalum carbide, TaC (mp 3900°C) and niobium carbide, NbC (mp 3500°C) are crystallized at 750°C]. The preparation involves electrolysis of melts containing Ta20s (or Nb205), Na2B407, Na2C03, NaF, and KF. 

The scanning electron photograph of the surface of the St.3 substrate after holding in NaCl-KCl-K2Nbp7 melt (10 w/o) for 3 h at a temperature of 1073 K shows spheroidal crystals of niobium carbide NbC on the substrate surface according to the X-ray data. The rate of formation of niobium carbide is low in the case of currentless transfer, but it increases with both increase in the temperature of the melt, and in the concentration of potassium fluoroniobate, and when metallic niobium powder is used as the metal. The experiments showed that for a 30 w/o concentration of K2Nbp7, the use of metallic... 

CERAMICS. Tliese are brittle and corrosion resistant compounds made out of metallic and nornnetaUic elements. Some examples of ceramics are A/2O3 (alumina), SiC (silicon carbide), MgO (magnesia), Fe O (magnetite), and ZrO (zirconia). Other ceramics are made of basic ceramics and are known as bricks, clay, concrete, porcelain and the like. On the other hand, refractories are ceramics that withstand very high temperatures prior to melting, such as NhC (niobium carbide) 3615°C and MgO 2852°C In addition, ceramics are immune to corrosion by almost all environments. Those which are not dissolve by chemical oxidation. 

Nickel-based alloys, which form the bulk of alloys produced, are basically nickel-chrome alloys with a face-centered cubic solid-solution matrix containing carbides and the coherent intermetallic precipitate y-NijlAfTi). This latter precipitate provides most of the alloy strengthening and results in useful operating temperatures up to 90% of the start of melting. Further additions of aluminum, titanium, niobium, and tantalum are made to combine with nickel in the y phase, and additions of molybdenum, tungsten, and chromium strengthen the solid solution matrix. 

---