Hafnium Carbide HfC

Hafnium Carbide. Hafnium carbide, HfC, is a dark gray brittle soHd. This carbide can be prepared by heating an intimate mixture of the elements or by the reaction of hafnium tetrachloride with methane at 2100°C, but is commonly produced by the reaction of hafnium oxide with lampblack... 

Hafnium carbide (HfC) is an interstitial carbide which, with tantalum carbide, is the most refractory compound known. Its characteristics and properties are summarized in Table 9.4. 

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 ). 

Hafnium carbide (HfC) This alloy has one of the highest melting points of any binary compound (3.890°C). It is extremely hard and resists corrosion while absorbing slow neutrons. Therefore, it is an ideal metal in the manufacture of control rods for nuclear reactors. 

Reaction with carbon at 1,500°C produces hafnium carbide, HfC. 

Zirconium carbide, ZrC, and hafnium carbide, HfC, can be manufactured in a similar way to titanium carbide. They are not very important in cemented carbide technology. The recent strong reduction in the price of HfC has enabled its application as a substitute for the dearer tantalum carbide. 

Graphite can thus be considered the most refractory of cill the elements, tungsten being second-best with a melting point of 3680 K. However hafnium carbide (HfC) and tantalum carbide (TaC) are reported to have higher melting points (approximately 4220 K and 4270 K respectively) and are the most refractory of all materials.f ... 

Nitrides are used for wear-resistant applications, most notably surface engineering of cemented carbide cutting tools and tool steels. Titanium nitride (TiN) is the most frequently employed coating, but titanium car-bonitride (TiCN), hafnium carbide (HfC), titanium aluminum nitride (TiAlN), titanium zirconium nitride (TiZrN), and chromium nitride (CrN) have also been used commercially. These coatings are applied by vapor deposition techniques (Fig. 2). 

The first carbonitride alloys based on Ti(C,N)—Ni—Mo were iatroduced ia 1970 foUowed by (Ti, Mo)(C,N)-based compositions having fine microstmctures that provided a balance of wear resistance and toughness (4). Continued research on the titanium carbonitride alloys, often called TiC—TiN cermets, ia the 1980s led to the developmeat of complex cermets having a variety of additives such as molybdeaum carbide(2 l) [12069-89-5] M02C, TaC, NbC, zirconium carbide [12020-14-3], ZrC, hafnium carbide [12069-85-1], HfC, WC, vanadium carbide [12070-10-9], VC, chromium carbide (3 2)... 

Hafnium Carbide. The need of pure zirconium [7440-67-7] for nuclear reactors prompted the large-scale separation of hafnium [7440-58-6] from zirconium. This in turn made sufficient quantities of hafnium dioxide [12055-23-17, Hf02, or Hf metal sponge available for production of HfC for use in cemented carbides (see Hafniumand hafnium compounds). 

Other compounds have been deposited by fluidized-bed CVD including zirconium carbide (from ZrCl4 and a hydrocarbon), hafnium carbide (from HfC and methane or propylene), and titanium carbide (from TiCl3 and propylene). 

The most simple methods for preparation of hafnium carbide and its composites are the follows. The powder of HfO was thermally treated with Mg in molar ratio 5 4 under a CH flow ranging from 800 to 950 °C [4]. The effective high temperature coating for carbon fiber reinforced carbon and carbon fibre reinforced silicon carbide was prepared with use of HfC [5]. For this purpose hafnium carbide layers were obtained in a thermally simulated chemical vapor deposition (CVD) reactor on nonporous substrates by reaction of hafnium tetrachloride, methane and addition of hydrogen (Eq. 10.1) ... 

Carbides Hafnium Monocarbide (HfC) 0.05 at room temp. 15 0.15at925"C 16 + 0.16atl525"C... 

Hafnium Monocarbide (HfC) Silicon Carbide (SiC) 0.053 at room temp. 0.15 + 1.20x10 T watts cm K from 1000-2000K... 

Hafnium carbide and hafiiium nitride whiskers from HfC, ... 

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