China
Africa
Explore chapters and articles related to this topic
Characteristics of the Metal–Metal Oxide Reaction Matrix
Published in Anthony Peter Gordon Shaw, Thermitic Thermodynamics, 2020
Titanium metal is produced by the reaction of gaseous TiCl4 with molten magnesium in a sealed reactor. The reactor walls are typically made of stainless steel, and the process must be carried out in the absence of oxygen [13]. Similar processes have been used to prepare zirconium and hafnium. Overall, the most common oxidation state of these metals is +4 although the +3 and +2 states are not uncommon for titanium. Rutile is the most common form of TiO2 and is one practical source of the metal. Another useful ore is ilmenite, FeTiO3. The compound Ti3O5 contains titanium in oxidation states +4 and +3. The compounds Ti2O3 and TiO contain the metal in the +3 and +2 oxidation states, respectively. Cubic zirconia (cubic ZrO2) has been used as a diamond simulant in inexpensive jewelry because of its high refractive index and acceptable hardness. Rutile actually has a greater refractive index, but it is softer and would not be as durable. Hafnium is found as an impurity in zirconium-bearing minerals such as zircon, ZrSiO4.
Hf, 72]
Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
Hafnium is used mainly in filaments and electrodes, and in nuclear industries, especially in power plants. Hf and Zr are used interchangeably in certain superalloys, but in others, only Hf may be used. The alloys with Nb, Ti, and W have a special application in nuclear processes, mainly for reactor-control rods and coatings of cutting tools. Also, alloys of Hf with Pd and Pt are relatively common. Some amounts of Hf are applied in photographic flashes. Biometallic materials may contain Hf, as it has a good biocompatibility and osteoconductivity (Szilagyi 2004).
Control and Shielding Materials
Published in C. K. Gupta, Materials in Nuclear Energy Applications, 1989
The combination of unique neutron absorption, good mechanical strength, and corrosion-resistant properties make hafnium ideal as a control rod material or as a poison material for increasing the stacking density of spent fuel storage or a container for corrosive media in spent fuel reprocessing plants. Hafnium, hafnium alloys (Ti, 12 wt% Hf; Zr, 15 wt% Hf), and sheathed hafnium oxide are prime candidates for these specific fields of application. Many U.S. naval reactors have made extensive use of hafnium. The Shipping Port PWR has also employed this material. The metal has been established as qualified for BWR control application where unclad solid hafnium rods alloyed with a small amount of zirconium have been projected. It may be added that alternative alloyed materials with hafnium, such as pyrohafnates (alloyed with one or more rare earth), Hf-In-Ag, and Ag-Hf, have received attention for application as control rods. The binaries or the ternaries are basically intended to provide the best attributes of the constituents with which they are formed.
Fukushima Daiichi fuel debris retrieval: results of aerosol characterization during laser cutting of non-radioactive corium simulants
Published in Journal of Nuclear Science and Technology, 2021
Emmanuel Porcheron, Claire Dazon, Thomas Gelain, Christophe Chagnot, Ioana Doyen, Christophe Journeau, Emmanuel Excoffier, Damien Roulet
The ex-vessel fuel debris simulant composition has been determined by CEA [9] based on calculations by Japanese and international experts of ex-vessel corium undergoing an MCCI scenario in Fukushima Daiichi Unit 1 pedestal sump (the configuration maximizing the fraction of concrete decomposition products) including the fission products inventory 10 years after the accident [10,11]. The in-vessel fuel debris simulant composition has been determined [9] from the average of the Fukushima Daiichi unit 2 lower head debris composition calculated within the OECD/BSAF project [12] in which the fission products inventory estimated 10 years after the accident has been considered. As proposed and justified by [9] based on a previous study [13], uranium and plutonium are simulated by hafnium and cerium, respectively, due to their similar thermophysical characteristics, such as melting points, while fission products are simulated by their natural isotopic compositions. Hafnium has been identified for its thermal properties close to Uranium Oxide, such as melting point, thermal conductivity in solid state, heat of fusion and specific densities at room temperature.
Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system
Published in Science and Technology of Advanced Materials, 2018
Andrei Ionut Mardare, Cezarina Cela Mardare, Jan Philipp Kollender, Silvia Huber, Achim Walter Hassel
Hafnium, niobium and tantalum have similar electrochemical characteristics in that they are all valve metals. This classification and its name are based on their current rectification upon electric field reversal (hence, the name ‘valve’) during metals anodisation under high field conditions. The final anodic oxide thickness is proportional to the applied potential and oxide formation factors of 2.3, 2.6 and 1.8 nm V−1 were measured for Hf, Nb and Ta, respectively [11]. The oxides of the aforementioned pure metals have applications in various fields. Due to its high dielectric constant and excellent thermal stability, hafnium oxide is investigated mainly as a gate material for field effect transistors and supercapacitors, while hafnium oxynitride is studied as a catalyst for oxygen reduction reactions [12,13]. Additionally, Hf1−xTaxO2 based memristors with excellent bipolar resistive switching characteristics were recently demonstrated, which promote the use of mixed Hf and Ta oxides in modern electronics [14]. The spectrum of niobium oxide applications is broad, ranging from use in capacitors to applications in electrochromic devices, gas sensors and solar cells [15–18]. Applications of Ta2O5 are found in the same major areas. Tantalum oxides, usually applied in high power resistors and capacitors, started recently to be investigated for cathodes in fuel cells, lithiation support in batteries and counter electrodes in solar cells [19–22].
Evaluation of nanocrystalline hafnium nitride coating exposed to molten uranium
Published in Surface Engineering, 2018
A. Ravi Shankar, Vipin Chawla, P. Venkatesh, B. Prabhakara Reddy, Ramesh Chandra, U. Kamachi Mudali
Hafnium nitride exhibits high melting point, high hardness, high thermal conductivity and chemical inertness. These properties make hafnium nitride suitable material for application as diffusion barriers at high temperatures. HfN is reported to be more stable and exhibit higher hot hardness above 1073 K, compared to TiC or TiN [11]. Therefore, HfN coatings were considered for containing molten uranium at high temperatures. Optimisation of parameters was carried out to deposit nanocrystalline hafnium nitride coating on high-density graphite and niobium samples by the magnetron sputtering technique, the details of which are reported elsewhere [12]. The present work focuses on the degradation behaviour of HfN coating in contact with molten uranium. Figure 2 shows the photograph of HfN coated on Nb and HD graphite discs after the uranium melting experiment. As shown in the figure, uranium sample got fused to the HfN-coated niobium disc. On the other hand, the uranium sample on HfN-coated HD graphite disc was unaffected and easily released as shown in Figure 2. Discolouration of coating was observed on HfN-coated Nb disc, while discolouration was insignificant on HD graphite disc. The discolouration observed on HfN-coated niobium disc could be attributed to the surface oxidation.