Papers by Keyword: Hafnium

Abstract: Nanostructured smart coatings (NSC) based on the TiAlSi-CN composite structure elements were deposited using advanced reactive physical vapor deposition (PVD) method. The novel NSC on steel substrates demonstrated enhanced wear and corrosion resistance required for multifunctional high-tech applications. The deposited NSC containing TiAlSi-CN nanoparticles strengthened by Cr, Nb and Hf additives exhibited a coefficient of friction (CoF) less than 0.2 and wear rate as low as 10E^-8 mm³/Nm. In addition, some self-healing properties were observed preventing denitrification of the core carbon-nitride (CN) layer due to specific tribochemical reactions of Al and Si constituents. Thus, the chemical composition and tentative nano-structure of the NSC can be described by a stoichiometric formula TiAlSi-CN:Me/a-C_xN_y:Si₃N₄, where Me=Cr, Nb or Hf.

Abstract: The crystal structures of the binary compounds ZrAl₃ and HfAl₃ at 600°C belong to the structure type ZrAl₃ (Pearson symbol tI16, space group I4/mmm, a = 4.00930(11), c = 17.2718(7) Å for ZrAl₃ and a = 3.9849(3), c = 17.1443(15) Å for HfAl₃). Substitution of Ge atoms for Al atoms in ZrAl₃ and HfAl₃ led to the formation of the ternary compounds ZrAl_2.52(1)Ge_0.48(1) and HfAl_2.40(1)Ge_0.60(1), respectively, where the latter is probably part of a solid solution extending from the high-temperature modification of HfAl₃. The crystal structures belong to the tetragonal structure type ht-TiAl₃ (tI8, I4/mmm, a = 3.92395(11), c = 9.0476(4) Å for ZrAl_2.52Ge_0.48 and a = 3.9021(2), c = 8.9549(8) Å for HfAl_2.40Ge_0.60). The structure types ZrAl₃ and ht-TiAl₃ are both members of the family of close-packed structures.

Abstract: The effects of the selective addition of Hafnium (Hf) on the grain boundary, phase, carbides and creep properties of experimented nickel superalloy after standard heat treatment and long-term exposure were investigated. Predicted by the Bayesian neural network, the creep life is prolonged with Hf content of 0-0.6 mass%, which is more effective at low stresses. The decrease of creep life of Hf free alloy after long term exposure was pronounced. Comparative study showed that the mainly small, coherent, blocky and closely spaced MC₍₂₎ and M₂₃C₆ carbides precipitated on the grain boundaries in the 0.4wt% Hf contained alloy, and that relatively larger, incoherent MC₍₁₎ carbides precipitated on the grain boundaries in the Hf free alloy. During long term thermal exposure, fine discrete M₂₃C₆ carbides decomposed from primary carbide, inducing a layer along the grain boundary, and the coarsening of grain boundary in Hf free alloy is more pronounced. At high stresses, the Hf-free alloy exhibited a stronger tendency of rafting than the 0.4Hf alloy, while the tendency of appearance of rafting was very similar at low stresses. However, Hf can render the alloy prone to the formation of σ phase, according to D-electrons method. Thus, the Hf content needs to be controlled to a suitable level.

Abstract: An important step of a new process being developed for the beneficiation of the mineral zircon (Zr (Hf)SiO₄) to produce nuclear grade zirconium (Zr) metal, is the separation of the Zr from the hafnium (Hf). Zr ores typically contain between 1 and 3% Hf , whereas the use of Zr metal in the nuclear industry requires a Hf content <100 ppm, owing to its high neutron-capture cross section. The separation step is therefore key in the preparation of nuclear grade Zr, which is considered to be very difficult due to the various similarities in their chemical properties. The preparation of hafnium free zirconium relies on the traditional wet separation systems, for example solvent extraction systems. In contrast to the traditional aqueous chloride systems, Necsa focusses on dry fluoride-based processes. Dry processes have the advantage of producing much less hazardous chemical waste. In the work reported her, separation is achieved by sublimation/de-sublimation in the tetrafluoride form. The tetrafluoride is prepared by fluorination of plasma dissociated zircon (PDZ or Zr (Hf)O₂•SiO₂) with ammonium bifluoride (ABF). The separation involves the selective sublimation of the two tetrafluorides in an inert atmosphere under controlled conditions, and subsequent similarly selective desublimation. An accurate estimation of the sublimation rates the zirconium tetrafluoride (ZrF₄) and hafnium tetrafluoride (HfF₄) as a function of temperature is required since this forms the basis of the development of a sublimation model to determine whether the concept under consideration is theoretically possible. The sublimation kinetics of ZrF₄ is reported in this paper.

Abstract: HfN is a transition metal nitride that shows interesting mechanical and chemical properties for using electronic, mechanical, corrosion, wear areas. In this work HfN thin films were fabricated by D.C. sputtering varying nitrogen flux. The Ar/N₂ ratio used inside in the deposition chamber was 10, 6.66, 5, 4 and 3.33. The obtained films were analyzed by X-ray diffraction, Vickers microhardness, high resistivity measurement package and tested by D.C. electrochemical techniques in order to know their crystalline structure, hardness, resistivity and corrosion resistance. We found that a straight relationship of resistivity and crystalline structure with Ar/N₂ flux ratio, because of decreasing that ratio resistivity increases meanwhile hardness decreased, this behavior due to amorphous phase of HfN. Electrochemical tests showed that sample at Ar/N₂ ratio = 5 showed the maximum polarization resistance while the sample at Ar/N₂ ratio = 4 showed less polarization resistance value. All results establish that HfN is a good material in corrosion and electronic areas.

Abstract: Crystal bar hafnium prepared by the iodide process was studied. The influences of three important factors (filament temperature, retort materials and feed types) on the removal of iron from hafnium crystal bar under iodide process were investigated. Results show that the impurity contents of iron in the hafnium crystal bar decreased with the rising K value. Both the retort materials and feed types have obvious influence on the iron impurity contents of hafnium crystal bar. It is proposed that the optimal condition was attained when hafnium turnings was used as feed, stainless steel with molybdenum cylinder liner as retort materials, and K value was at a relatively high level.

Abstract: The NaCl-KCl-K₂HfCl₆ electrolyte successfully prepared by the reaction of HfCl₄ with equimolar NaCl-KCl. Microstructure, surface morphology and components of the electrolyte were analyzed by XRD, SEM, and EDS. The results show that HfCl₄ preferentially reacts with KCl when KCl and NaCl coexist or conversion relationship exist between Na₂HfCl₆ and K₂HfCl₆. The removal rates of oxygen reached 96.98%in electrorefining of hafnium attributed to high stability and low volatility of the electrolyte.

Abstract: Metal hafnium has research significance as a rare metal. Metal hafnium, hafnium alloy and hafnium compounds are made a simple introduction, the distribution of hafnium resource is summarized at home and abroad, and the processing method of hafnium resource and the development prospect of comprehensive performance of hafnium resource are discussed.

Abstract: High-k gate dielectrics and metal gate electrodes have become essential for emerging device technologies because they enable the continuous scaling down of devices while maintaining a high performance [. However, since they are composed of novel metallic elements that have never before been used in conventional processes, special care must be taken when handling these materials in the production line. In particular, cross-contamination that occurs due to transporting contamination via processed wafers can cause serious problems such as deterioration of device properties and yield loss [. The process of cleaning the backside and bevel of a wafer is now increasingly important for avoiding these problems. To date, there has been no detailed evaluation of contamination removal on various films performed for elements such as hafnium, which is one of the key elements in high-k/metal gate technologies. In this study, we evaluated hafnium contamination on three types of wafer surface after the cleaning process and investigated the cause of different residual amounts of hafnium contamination on the different wafers.

Abstract: The structure of the new ternary compound Hf₂GaSb₃ was determined by means of X-ray powder diffraction. It crystallizes with the structure type Zr₂CuSb₃ which represents a ternary ordered derivative of the UAs₂ type (Pearson symbol tP6, space group P-4m2, a = 3.89841(8), c = 8.62650(19) Å). The ternary compound can be regarded as an ordered, Ga-stabilized derivative of the high-temperature modification of the binary antimonide HfSb₂ (structure type UAs₂).