12034-80-9Relevant articles and documents
Simultaneous synthesis and consolidation of nanostructured NbSi2-Si3N4 composite from mechanically activated powders by high-frequency induction-heated combustion
Park, Hyun-Kuk,Shon, In-Jin,Yoon, Jin-Kook,Doh, Jung-Mann,Ko, In-Yong,Munir
, p. 560 - 564 (2008)
Dense nanostructured 4NbSi2-Si3N4 composite was synthesized by high-frequency induction-heated combustion synthesis (HFIHCS) method within 1 min in one step from mechanically activated powders of NbN and Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense 4NbSi2-Si3N4 composite with relative density of up to 98% was produced under simultaneous application of a 60 MPa pressure and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.
Determination of standard free energy of formation for niobium silicides by EMF measurements
Fujiwara, Hiroyasu,Ueda, Yukitomi,Awasthi, Alok,Krishnamurthy, Nagaiyar,Parkash Garg, Sheo
, p. J43-J48 (2003)
EMF measurements were carried out at temperatures ranging from 1280 to 1490 K in the following cells: Mo, Si + NbSi2 + SiO2/SiO2-sat. Li2O-SiO2/NbSi2 + Nb5Si3 + SiO2, Mo ⊕, Mo, Si + NbSi2 + SiO2/SiO2-sat. Li2O-SiO2/Nb5Si3 + NbO + SiO2, Mo⊕, and Mo, NbSi2 + Nb5Si3 + SiO2/SiO2-sat. Li2O-SiO2/Nb5Si3 + NbO + SiO2, Mo⊕, using SiO2-saturated lithium silicate liquid electrolyte. Each of the cells showed a reliable electromotive force (emf) corresponding to the difference in silicon potential between the electrodes. Based on these emf values measured, the molar standard free energy of formation for NbSi2 and Nb5Si3 were determined to be ΔG°NbSi2/kJ = -165 + 0.008 (T/K) ± 13 and ΔG°Nb5Si3/kJ = -526 + 0.009 (T/K) ± 63, respectively.
A comparative study on combustion synthesis of Nb-Si compounds
Yeh,Chen
, p. 216 - 222 (2006)
A comparative study on the preparation of niobium silicides (such as Nb3Si, Nb5Si3, and NbSi2) in the Nb-Si system was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts of different stoichiometries. Effects of the sample green density, preheating temperature, and starting stoichiometry on combustion characteristics, as well as on product composition were studied. Test specimens with five different compositions including Nb:Si = 3:1, 5:3, 3:2, 1:1, and 1:2 were employed in this study. Experimental observations indicated that except for the sample of Nb:Si = 3:1, upon ignition self-sustained combustion was well established and proceeded throughout the entire sample. Measured results showed that the reactant compact of Nb:Si = 5:3 had the highest flame-front propagation velocity, followed sequentially by the powder compacts with Nb:Si = 3:2, 1:1, and 1:2. Variation of the combustion temperature with sample initial stoichiometry is in a manner consistent with that of the flame-front velocity. On account of the close atomic ratios, the test specimens made up of either Nb:Si = 5:3 or 3:2 yielded a single-phase silicide Nb5Si3 in both α and β forms. As identified by the XRD analysis, it was found that α-Nb5Si3 was dominant in the final product from the Nb:Si = 5:3 compact, but β-Nb5Si3 was the major composition formed by the Nb:Si = 3:2 compact. Because of the nonexistence of a silicide phase with the atomic ratio Nb/Si = 1, a multiphase product consisting of α-Nb5Si3 and NbSi2 was synthesized from the reactant compact of Nb:Si = 1:1. For the samples with Nb:Si = 1:2, the disilicide NbSi2 was monolithically produced along with trivial amounts of unreacted Nb and Si. Based upon the temperature dependence of combustion wave velocity, the activation energies associated with combustion synthesis of Nb5Si3 and NbSi2 were determined to be 259.2 and 160.9 kJ/mol, respectively.
Thermodynamic calculation and an experimental study of the combustion synthesis of (Mo1-xNbx)Si2 (0 ≤ χ ≤ 1)
Wang, Xiaohong,Lu, Qiong,Wu, Guangzhi,Shi, Jialing,Sun, Zhi
, p. 181 - 187 (2015)
The theoretical adiabatic temperature of (Mo1-xNbx)Si2 (0 ≤ x ≤ 1) is calculated. The results indicate that the theoretical adiabatic temperature of (Mo1-xNbx)Si2 increases with an increasing Nb content when (Mo1-xNbx)Si2 is of a single-phase structure, but decreases with an increasing Nb content when (Mo1-xNbx)Si2 is of a double-phase structure. All of the temperatures are higher than 1800 K, indicating that (Mo1-xNbx)Si2 (0 ≤ x ≤ 1) can be prepared by the combustion synthesis method. In this work, (Mo1-xNbx)Si2 (0 ≤ x ≤ 1) alloys are successfully synthesized by the combustion synthesis process from elemental powders of Mo, Nb, and Si. The highest combustion temperature and combustion product structure are studied. The results confirm that the variation of the experimental maximum combustion temperature of (Mo1-xNbx)Si2 is consistent with that of the theoretical adiabatic temperature. The combustion products are non-equilibrium species, and a supersaturated solid solution of C11b type (Mo1-xNbx)Si2 forms during combustion synthesis.
Silicide coating on refractory metals in molten salt
Tatemoto,Ono,Suzuki
, p. 526 - 529 (2005)
For better oxidation resistance of refractory metals in air, the electroless coating of silicide in the molten salt was developed in open air at 973-1173 K. The molten salt consists of NaCl, KCl, Na2SiF6 and Si powder, where the prop
Preparation of Nb-25Si, Nb-37.5Si, Nb-66.6Si powders by high-energy ball milling and subsequent heat treatment
Fernandes, Bruno Bacci,Ramos, Erika Coaglia Trindade,Silva, Gilbert,Ramos, Alfeu Saraiva
, p. 509 - 513 (2007)
The present paper reports on the syntheses of the Nb3Si, α-Nb5Si3 and NbSi2 compounds by mechanical alloying and subsequent heat treatment. The milling process was carried out in a planetary Fritsch P-5 ball mill under argon atmosphere using stainless steel balls and vials, rotary speed of 200 rpm and a ball-to-powder weight ratio of 10:1. Following, the milled powders were heat-treated at 1600 °C for 1 h in order to obtain the equilibrium microstructures. The milled and heat-treated powders were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), microanalysis via energy dispersive spectrometry (EDS). Results indicated that the silicon atoms were dissolved into the Nb lattice during milling to form supersaturated solid solutions. The Nb3Si compound was formed after heat treatment at 1600 °C for 1 h only, while the Nb5Si3 and NbSi2 compounds were successfully formed during ball milling. Results have indicated that a significant iron contamination close to 5 at% was found in mechanically alloyed Nb-25Si, Nb-37.5Si and Nb-66Si powders. Consequently, the nominal compositions of Nb-Si powders were altered and other phases were also formed after heat treatment at 1600 °C for 1 h.
Solid state metathesis synthesis of metal silicides; reactions of calcium and magnesium silicide with metal oxides
Nartowski, Artur M.,Parkin, Ivan P.
, p. 187 - 191 (2002)
Reactions of transition metal oxides (V2O3, V2O5, Nb2O5, LiNbO3, Ta2O5, LiTaO3, MoO3 and Li2MoO4) with lithium silicide (Li2Si) and calcium silicide-magnesium silicide mix (CaSi2, Mg2Si) could be initiated by grinding, flame, filament or bulk thermal methods to produce a range of single phase transition metal silicides (VSi2, NbSi2 and TaSi2) in good yields (approximately 90%). The silicides were characterised by X-ray powder diffraction, scanning electron microscopy (SEM), energy dispersive analysis by X-rays (EDAX), electron probe, FTIR and microelemental analysis.
Effects of Nb substitution on thermoelectric properties of CrSi2
Nagai, Hiroki,Takamatsu, Tomohisa,Iijima, Yoshihiko,Hayashi, Kei,Miyazaki, Yuzuru
, p. 37 - 41 (2016)
The effects of Nb substitution on the solubility range, lattice parameters, and thermoelectric properties of CrSi2with a C40-type structure have been investigated. Polycrystalline samples of Nb-substituted Cr1-xNbxSi2(0 ≤ x ≤ 0.15) have been prepared by a two-step arc-melting process, followed by spark plasma sintering. XRD patterns confirm that single-phase Cr1-xNbxSi2is obtained in the composition range 0 ≤ x ≤ 0.10. As x increases from 0 to 0.10, the a- and c-axis lengths increase linearly. For x > 0.10, the a- and c-axis lengths do not obey Vegard's rule. The electrical conductivity of Cr1-xNbxSi2(0 ≤ x ≤ 0.10) increases with increasing x, although the Seebeck coefficient gradually decreases with increasing x over the entire temperature range. In addition, the total thermal conductivity decreases with increasing x, owing to the reduction in lattice thermal conductivity. As a consequence, the dimensionless figure-of-merit ZTmaxincreases from 0.16 (x = 0) at 600 K to 0.20 (x = 0.05) at 700 K.
NbSi2 coating on niobium using molten salt
Suzuki, Ryosuke O.,Ishikawa, Masayori,Ono, Katsutoshi
, p. 280 - 285 (2002)
For obtaining better oxidation resistance of niobium in air, a niobium silicide was non-electrolytically deposited onto niobium from the molten salt, where a disproportional reaction occurs between Na2SiF6, SiO2, and Si. A single phase of NbSi2 was formed with a homogeneous thickness of about 10 μm above 1073 K. The oxidation resistance of pure niobium with this coating layer was improved. During the oxidation at the high temperatures, Nb5Si3 was formed at the interface between the Nb substrate and the NbSi2 layer. Due to this intermediate layer formation, the oxidation resistance became better than for pure NbSi2.
Microstructural effect on oxidation kinetics of NbSi2 at 1023 K
Zhang,Zhang,Shan,Wu
, p. 308 - 312 (2006)
Poly- and single crystalline NbSi2 specimens with different microstructures were prepared by arc-melting, spark plasma sintering (SPS) and optical-heating floating zone melting for oxidation experiments at 1023 K. The effects of cracks, pores and grain boundary in the microstructure on the oxidation behavior of NbSi2 were investigated. For arc-melted poly-crystalline specimens containing micro-cracks, NbSi2 fully turned into powders after 3 h exposure at 1023 K, which is known as the pesting phenomenon. As a comparison, no pesting was found in the dense SPS poly-crystalline specimens and single crystals after 89 h. The oxide scale consists of Nb2O5 and SiO2. The oxidation kinetics of all specimens follows a linear law. The oxidation rate was higher in the poly-crystalline specimen in comparison to single crystalline. The mechanism of oxidation has been analysed using a kinetic model.
