Papers by Keyword: Hafnium

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Authors: Jia You Wang, C.H. He, J.Z Huang, J. Chen, C.F. Fang
Abstract: The present work proposes an ultrasonic-frequency pulsed arc approach to improve effectively the service life of oxidative plasma cutting electrode, and introduces the implementation and principle of the pulsed arc system. A number of electrode arcing experiments were then carried out to demonstrate effectiveness of this novel way. Experimental results show that this ultrasonic frequency pulsed process can contract the cathode zone of the arc while speeding up the movement of the cathode spots, and thus reduced the scope and depth of erosion pit on the hafnium electrode. The life of the electrode was finally increased by 47.8% at the pulse frequency of 40 kHz.
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Authors: Ayesha Courrech Arias, Leandro García-González, Julian Hernandez Torres, Teresa Hernandez Quiroz, Gonzalo Galicia Aguilar
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.
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Authors: Guillaume Vérité, F. Willaime, Chu Chun Fu
Abstract: The vacancy properties in group-IV hexagonal close-packed metals (Ti, Zr and Hf) have been investigated by Density Functional Theory (DFT) calculations performed with the SIESTA code. The migration energies are found to be systematically lower by »0.15 eV within the basal plane than out of the basal plane. The electronic origin of this significant contribution to diffusion anisotropy is evidenced by the analysis of the local electronic densities of states and by a comparison with and empirical potential. The average value of the migra- tion energy is in very good agreement with available experimental data in Zr. The activation energies for self-diffusion obtained assuming a vacancy mechanism are in good agreement with experiments in Zr and Hf, although slightly too small, but a significant discrepancy is observed in Ti.
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Authors: Iryna Tokaychuk, Yaroslav Tokaychuk, Roman E. Gladyshevskii
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).
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Authors: Håkon Hallem, Børge Forbord, Knut Marthinsen
Abstract: In the present work the precipitation behaviour and recrystallisation resistance of Alalloys containing Hf, Sc and Zr in different concentrations and combinations have been investigated. Special focus has been put on the Hf-containing alloys, as one of the objectives of this work was to find out if Hf can be used as a replacement for Sc. Additions of Sc, either alone or in combination with Zr, leads to the formation of coherent and homogeneously distributed dispersoids, which very efficiently inhibit recrystallisation. Despite these attractive properties, the high price of Sc has limited its use as an alloying element in aluminium. The present investigation has revealed that Hf cannot fully replace Sc, as only heterogeneous dispersoid distributions are obtained in the absence of Sc, i.e. in regions where the number density is low the alloys would still be prone to recrystallisation. However, as an extra addition to the already remarkably stable Sc+Zr-containing alloys, Hf can lead to further improvements and consequently open for the use of aluminium alloys at very high temperatures. Al3(Sc,Zr,Hf)-dispersoids were present at the largest f/r-ratios and also displayed lower coarsening rates than Al3(Sc,Zr)-dispersoids. Very promising results were obtained for an Al-Hf-Sc-Zr alloy, which maintained mainly an unrecrystallised structure after extrusion and large degrees of cold rolling.
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Authors: Yu Bo, Xiao Liu, Yun Gang Li, Zong Ying Cai
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.
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Authors: Jie Shan Hou, Jian Ting Guo, Chao Yuan, Yong An Guo, Gu Song Li, Lan Zhang Zhou
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.
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Authors: Wei Cai, Chun Lin Fu, Jia Cheng Gao, Xiao Ling Deng, Wei Hai Jiang, Ze Bin Lin
Abstract: Pure and Hf-doped BaZr0.2Ti0.8O3 (short for BZT) ceramics are prepared by a conventional solid state reaction method. The crystal structure and dielectric properties of Hf-doped BZT ceramics have been investigated. The results indicate that Hf4+ ions have entered the unit cell maintaining the perovskite structure of solid solution and the pure and Hf-doped BZT ceramics are cubic phase. Addition of hafnium leads to the fall of the phase transition temperature and can decrease the dielectric loss of BZT ceramics at room temperature. When Hf content is more than 0.5 wt.%, the diffuseness of the phase transition enhances with the increasing of Hf content and when Hf content is 3 wt.%, the diffuseness of Hf-doped BZT ceramics is more than that of the pure BZT ceramics.
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Authors: Suguru Saito, Yoshiya Hagimoto, Hayato Iwamoto
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.
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Authors: Dai Shou, Ding Shan Ruan, Feng Hou
Abstract: In this paper, Hf element was introduced into the Si-O-C network by the sol-gel method using the dimethyldiethoxysiloxane (DMDES, (CH3)2Si(OC2H5)2) and hafnium tetra(n-butoxide) (HfOR, Hf(OC4H9)4) as raw materials. The SiOC/HfO2 ceramic composite was obtained by pyrolyzing Si-Hf-O-C gel at 1000 °C in argon. FT-IR spectra revealed the presence of Si-O-Hf peaks at 932 cm-1. The weight loss of the as-prepared SiOC/HfO2 was about 0.2 wt.% under argon atmorsphere up to 1550 °C, which was much lower than the hafnia-free SiOC composites and exhibited a remarkable improved thermal stability.
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