Refractory metals hafnium

Hafnium has been successfully alloyed with iron, titanium, niobium, tantalum, and other metals. Hafnium carbide is the most refractory binary composition known, and the nitride is the most refractory of all known metal nitrides (m.p. 3310C). At 700 degrees C hafnium rapidly absorbs hydrogen to form the composition HfHl.86. 

Nitrogen and carbon are the most potent solutes to obtain high strength in refractory metals (55). Particulady effective ate carbides and carbonitrides of hafnium in tungsten, niobium, and tantalum alloys, and carbides of titanium and zirconium in molybdenum alloys. 

The manufacture of refractory metals such as titanium, zirconium, and hafnium by sodium reduction of their haHdes is a growing appHcation, except for titanium, which is produced principally via magnesium reduction (109—114). Typical overall haHde reactions are... 

Refractory metals Zirconium Hafnium Titanium Kroll process, chlorination, and magnesium reduction Chlorine, chlorides, SiCli Wet scrubbers... 

Hafnium is used in control rods for nuclear reactors. It has high resistance to radiation and also very high corrosion resistance. Another major application is in alloys with other refractory metals, such as, tungsten, niobium and tantalum. 

The hot-wire process was developed by Van Arkel and de Boer [V2], who used it to produce the first pure, massive specimens of many refractory metals, notably titanium, zirconium, hafnium, and thorium. An interesting account of early uses of this process is given in... 

Hafnium has also been tested in a variety of medical techniques, and has recently been shown as a good refractory metal with good biocompatibility and osteocon-ductivity (Matsuno et al. 2001). 

Matsuno H, Yokoyama A, Watari F, Uo M and Kawasaki T (2001) Biocompatibility and osteogenesis of refractory metal implants, titanium, hafnium, niobium, tantalum and rhenium. Biomaterials 22 1253-1262. 

The addition of fluorides in the melt is also considered beneficial to the coating process, due to the complexing properties of fluoride ions, leading to a higher stability of high valencies of refractory metals. As an example, we consider this effect on the reduction of hafnium tetrachloride in molten NaCl-KCl in the square wave voltammogram of Fig 2a and 2-b presented by Serrano et al [12] in pure chloride melts (Fig. 2a), the reduction path includes two 2 electrons steps from Hf to Hf metal. In the presence of fluoride ions (Fig.2b), the decomposition potential of Hf is shifted cathodically, so that its reduction takes place in one step with 4 exchanged electrons. 

Even when fluorides are present in the electrolyte, the refractory metals coatings in chloride media are dendritic or powdery and these media are only used for metals electro winning in pilot plants, such as for hafnium [13]. 

Lamaze A.P. and Charquet D., Development of hafnium tetrachloride electrolysis, in Refractory Metals Extraction, Processing and Applications, The Minerals, Metals Materials Society, 1990. 

Hafnium is a refractory metal (melting temperature 2233°C). Regarding the compatibility with potential cladding materials, it forms a solid solution with Zr and shows a eutectic at 1300°C with iron. The crystal structure is hexagonal (hep) below 1760°C and cubic (bcc) above. The yield strength is about 250 MPa and ultimate strength 350 MPa at 300°C. 

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