نتایج جستجو برای: hfb2
تعداد نتایج: 67 فیلتر نتایج به سال:
Abstract: The refractory diborides (HfB2 and ZrB2) are considered as promising ultra-high temperature ceramic (UHTCs) where low damage tolerance limits their application for the thermal protection system in re-entry vehicles. In this regard, SiC and CNT have been synergistically added as the sintering aids and toughening agents in the spark plasma sintered (SPS) HfB2-ZrB2 system. Herein, a nove...
Hard, dense and conformal hafnium diboride (HfB2) thin films were obtained by CVD from the precursor Hf[BH4]4 at deposition temperatures ≤350 °C. As-deposited films were X-ray amorphous but transformed to a nanocrystalline structure after being annealed at 700 °C. Amorphous HfB2 films exhibited a respectable hardness of 20 GPa; the hardness increased in the nanocrystalline state to 40 GPa. Tern...
Transformants of the Trichoderma reesei strains QM9414 and Rut-C30 were constructed in which the genes for the two major hydrophobin proteins, hydrophobins I (HFBI) and II (HFBII), were deleted or amplified by molecular biological techniques. Growth parameters and foam production of the transformant strains were compared with the corresponding properties of the parent strains by cultivation in ...
HfBx coatings were deposited on cemented carbide substrates by direct current magnetron sputtering (DCMS) and high-power impulse (HiPIMS). The effect of the deposition conditions, i.e., temperature, bias voltage gas pressure, crystal structure mechanical properties analyzed systematically. results show that DCMS-deposited has random orientations HfB2(001), (100), (101) (102), whereas HiPIMS-dep...
Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB2 and HfB2 for a range of temperatures. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations which can be identified with mixed metal-Boron optical phonon modes. A...
In this research, solid state carbothermal synthesis of HfB2 Nano powders was investigated. For this purpose, HfO2,H3BO3, carbon active or phenolic resin were used as raw materials for carbothermal reaction. After 2-4 hours of milling the raw materials by a planetary ball in an ethanol media, the mixture was heat dried and pressed in to disks under pressure of 20-30 bar. The disks were then pla...
In this study, ZrB2-HfB2 composite was produced by pressureless sintering method. MoSi2 B4C and SiC particles were used as reinforcement. ZrB2 powder was milled in planetary ball mill apparatus and then reinforcement particles were added to the milled powder. The composite powders were then CIPed and sintered at 2100oC and 2150oC. Scanning electron microscopy (SEM) with an energy dispersive X-r...
Transition metal diborides in hexagonal AlB2 type structure typically form stable MB2 phases for group IV elements (M = Ti, Zr, Hf). For group V (M = V, Nb, Ta) and group VI (M = Cr, Mo, W) the stability is reduced and an alternative hexagonal rhombohedral MB2 structure becomes more stable. In this work we investigate the effect of vacancies on the B-site in hexagonal MB2 and its influenc...
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